Viva Cardiovascular Flashcards
What structural characteristics of
cardiac muscle enable its continuous
rhythmic contractions?
These are: Presence of pacemaker cell that
initiates autorhythmicity, presence of special
conductive tissue and presence of free
branchings between the muscle fibres
(syncytium) ensure the quick passage of
impulse from pacemaker cell to all parts of
heart to initiate continuous rhythmic
contractions.
Name the special conducting tissues
of heart.
SA node, AV node, bundle of His and Purkinje fibers (Fig. 15.1
What is cardiac pacemaker?
SA node is called as the cardiac pacemaker
because it is made up of ‘P’cells which can
generate the impulse more rapidly than any
of the pacemaker tissue of heart and
thereby determine the rate at which the
heart beats
What is law of heart muscle?
It states that the size of muscle fibers,
glycogen content and rate of conduction
increases from nodal to Purkinje’s fiber
whereas length of systole, duration of
refractory period and rhythmicity increases
in the reverse direction.
What is intercalated disc and what is
its importance?
At the point of contact of two cardiac muscle
fibers, extensive folding of cell membrane
occurs which is known as intercalated discs.
They provide a strong union between fibers
so that the pull of one contractile unit can be
transmitted to the next, thereby helps in
increasing force of contraction.
What is the role of gap junction in
cardiac muscle?
Gap junction is present in the intercalated
disc of cardiac muscle fibers and helps in
rapid transferring of electrical currents, ions,
etc. from one cell to another without coming
in contact with ECF. Thus they provide low
resistance bridge for the rapid spread out
of electrical impulse, thereby helps the
cardiac muscle to act as syncytium
(functional)
Name the valves and their location
There are 4 valves—two in between the atria
and ventricles known as atrioventricular
valves (A-V valves) and two are at the
opening of the blood vessels arising from
the ventricles (semilunar valves).
• A-V valves: These are present in between
the atria and ventricles. The valve present
in between right atria and right ventricle
is known as Tricuspid valve and the
valve present in between left atria and
left ventricle is known as Bicuspid valve.
• Semilunar valves: There are two semilunar
valves namely Pulmonary valve and
Aortic valve. The pulmonary valve is
present at pulmonary orifice which leads
from RV to pulmonary artery and the
aortic valve is present at aortic orifice
which leads from LV to the aorta
Name the special junctional tissues
and their conduction rate.
The special junctional tissues and their rate of impulse generating capacity are: Special junctional tissues Impulse generating capacity S A Node 75 ± 5 times/min A V Node 60 times/min Bundle of His 40 times/min Purkinje’s fiber 20 times/min
What do you mean by pacemaker
potential or diastolic depolarization?
The pacemaker tissue is characterized by
unstable RMP due to slow depolarization
resulting from leakage of Na+ from outside
to inside through Na
+ leak channels. This
show leakage of Na+ inside the cell causes
increase in electropositively inside the
cell which ultimately enables to induce
another action potential easily. This slow
polarization in between action potential is
known as prepotential or pacemaker
potential or diastolic depolarization.
Why SA node is called as cardiac
pacemaker?
A node acts as a pacemaker of heart
because the rate of impulse generation in
normal heart is determined by this node
because of its highest rate of impulse
generating capacity (75 ± 5 times/min) than
other junctional tissues. This is why it is
known as cardiac pacemaker.
What is ectopic pacemaker?
When the pacemaker is other than SA Node
(e.g. AV node, etc.) it is called as ectopic
pacemaker.
What is the duration of refractory
period in cardiac muscle?
Refractory period is very long in cardiac
muscles. It is about 0.53 seconds. In this, the
absolute refractory period is 0.27 seconds
and relative refractory period is 0.26
seconds
What is the significance of long
refractory period in cardiac muscles?
Due to the long refractory period, the
complete summation of contractions,
fatigue and tetanus do not occur in cardiac
muscle.
What do you mean by nodal and
idioventricular rhythm?
The AV node takes the charge of generating
impulse rhythmically when SA node does
not work. In this condition atria and
ventricles beat almost simultaneously at the
rate of 60 times per min. This rhythm of
heart is known as Nodal rhythm. Whereas
2nd Stannius ligature applied over the A-V
groove makes the atria to continue beating
with it’s own rhythm whereas the ventricle
stops beating due to blockade of impulse
from atria to ventricles. After sometime
ventricle generates it’s own impulse and
starts beating at much slower rate. This
rhythm of heart beat in which atria and
ventricular beating do not follow any specific
pattern is known as idioventricular
rhythm.
What is AV delay? What is its
significance?
When the impulse reaches to AV node, there
is a delay of about 0.1 sec to pass the impulse
to bundle of His. This time gap is known as
AV delay. It allows the atria to contract just
ahead of ventricular contraction thereby
atria is emptied before ventricular ejection.
What is Frank-Starling’s law
Within the physiological limit the larger the
initial length of muscle fiber (end diastolic
fiber length), the greater will be the force of
contraction of the heart which is known as
Frank-Starling’s law of heart.
What is the ionic basis of plateau
phase of cardiac action potential?
Immediately after depolarization voltage
gated Na+ channel‘s used to close resulting
stoppage of entry of Na+ ions and voltage
gated K+ channel start opening resulting exit
of K+. These results in rapid fall of
electropositivity initially known as rapid
repolarization. Afterwards, the rate of
repolarization becomes slower due to
prolonged opening of voltage gated Ca+2
channel through which Ca+2 enters inside.
Thus the exit of K+ is almost counterbalanced by entry of Ca+2 resulting sustained
depolarization known as plateau phase in
(Fig. 15.2).
Enumerate the properties of cardiac
muscle.
• Excitability • Rhythmicity • Conductivity • Contractility Contractility includes: – All or none law – Staircase phenomenon – Summation of subliminal stimuli – Refractory period.
all or none law applicable in heart?
All or none law which states that if a
stimulus is applied, whatever may be the
strength of stimulus, the cardiac muscle
responds maximally or it does not give any
response at all (Fig. 15.2). Of course, it is
applicable only in whole atrial muscle (i.e.
atrial syncytium) or in whole ventricular
muscle (i.e. ventricular syncytium) not to a
single cardiac muscle fiber.
Define staircase phenomenon. Why
does it occur?
If stimuli are applied repeatedly, with an
interval of 2 seconds to the cardiac muscles,
the force of contraction increases gradually
for the first few contractions. Later the force
remains the same. The gradual increase in
the force of contraction is known as staircase
phenomenon or treppe response. It occurs
because of the short interval of 2 seconds in
between the stimuli. During this period, the
beneficial effect is produced and this
facilitates the force of successive contraction
Why left ventricular subendocardial
region is more prone to myocardial
infarction?
The blood supply to the cardiac muscle in
different areas of heart is not same. On the
surface of the cardiac muscle there are large
epicardial arteries supplying more blood to
those areas whereas in the subendocardial
region blood supply is less because it is
supplied by smaller intramuscular arteries
and plexus of subendocardial artery the
diameter of which are less. This blood supply
to the subendocardial plexus is further
reduced during systole. Therefore the
subendocardial region is more prone to
myocardial infarction. Again as the left
ventricular thickness is much more than that
of right ventricle the occlusion is more
severe in left ventricle. For this region LV
subendocardial region is more prone to MI.
What are the importance of anastomotic channels in heart muscle?
In the normal heart there are some
collaterals among the smaller arteries which
become active under abnormal conditions
like myocardial ischemia. They open up
within a few seconds after the sudden
occlusion of larger artery and become
double in number by the end of 2nd or 3rd
day and reach to normal by one month.
When atherosclerosis causes constriction of
coronary arteries slowly over a period of
many years, collateral vessels develop
restoring normal blood and thus the patient
never experiences acute episode of cardiac
dysfunction.
What is the importance of autoregulation in blood supply in heart muscle?
Like some other organs the heart has the
capacity to regulate it’s own blood flow up
to a certain limit in order to maintain an
almost constant blood flow to the cardiac musculature in spite of any alteration of
systemic blood flow. This is known as
autoregulation of coronary blood supply
What is the importance of autoregulation in blood supply in heart muscle?
Like some other organs the heart has the
capacity to regulate it’s own blood flow up
to a certain limit in order to maintain an
almost constant blood flow to the cardiac
musculature in spite of any alteration of
systemic blood flow. This is known as
autoregulation of coronary blood supply.
Angina pectoris
Due to myocardial ischemia there is
stimulation of nociceptors present in heart
muscle resulting in pain sensation which is
normally referred to upper sternum, left
forearm, left shoulder, neck and side of the
face. This clinical condition is known as
angina pectoris.
Why cardiac muscle cannot be
tetanized?
It is because of it’s long absolute refractory
period and thus summation of contractile
response is not possible which is essential
for tetanization of heart muscle.
Cardiogram
The record of the mechanical activity of the
heart is known as cardiogram
Define and give normal values of
end diastolic volume, stroke volume and
end systolic volume.
During ventricular diastole the intraventricular volume is increased which results
filling of the ventricles. At the end of diastole
the amount of blood filled by the ventricle
is known as end diastole volume (EDV). It
is about 120-130 ml.
During ventricular systole intraventricular
volume decreases which results increase in
pressure thus ejection of blood out of
ventricles. During each systole the amount
of blood pumped out by each ventricle is
known as stroke volume (SV). Normal
value:70 ml/beat.
At the end of systole however some
amount of blood is remained in each
ventricle which is known end systolic
volume (ESV). The normal volume: 50-60
ml/ beat.
What do you mean by vagal escape?
What is its cause?
If strong vagal stimulation to heart is
continued then after a pause the ventricles resume to beat at a slow rhythm which is
called as vagal escape represented by
Figure 15.3.
During prolonged vagal stimulation right
auricle stops beating and distends due
to blood overflow which leads to fall of
BP → afferent impulse from carotid sinus to
cardiac centers → stimulate ventricles to start
its beat.
Q.30 What is the action of sympathetic
nerves on heart?
Sympathetic nerves increase the rate and
force of contraction of heart by secreting
noradrenaline
What is sympathetic tone?
Continuous stream of accelerator impulses
that arises from cardio accelerator center
and reaches the heart via sympathetic
nerves is known as sympathetic tone or
cardio accelerator tone. However, under
resting conditions, the vagal tone is more
dominant over the sympathetic tone.
Define apex beat
Apex beat is the impulse or throb which is
felt and seen on the chest wall normally in
the left 5th intercostal space just medial to
left nipple.
What is protodiastole? Is it part of
systole or diastole?
Protodiastole is the very brief phase before
diastole in which ventricular systole has
ceased but relaxation yet to start.
It can not be well defined whether the
protodiastole is a part of systole or diastole
as some workers include it in diastole as
muscle contraction is stopped at this phase
whereas some others believe that it is a part
of systole as muscle relaxation has not yet
started
Define cardiac cycle.
he sequence of events (mechanical,
electrical, etc.) associated with consecutive
heart beat
is repeated cyclically which is
known as cardiac cycle (Fig. 15.4). Normal
dura
tion is 0.8 sec if heart rate is 75 beats/
min.
What are the causes of 1st heart
sound?
These are: • Closure and vibrations of AV valves at the beginning of ventricular systole. • Vibrations of blood surrounding the AV valves. • Vibrations of major blood vessels around the heart. • Vibrations of walls of heart.
What are the characteristics of 1st
heart sound? (Fig. 15.4)
It is: • Soft, prolonged with low pitch. • Duration is 0.12 sec and occurs in peak or downstroke of R wave in ECG and just before onset of ‘c’ wave in jugular pulse tracing. • Best heard at apex beat area and is associated with onset of ventricular systole.
What is the significance of 1st heart
sound?
It indicates force of contraction, condition
of myocardium and competence of AV
valves.
What are the causes of 2nd heart
sound?
These are: Closure and vibration of semilunar valves at the end of ventricular systole. Vibrations of blood surrounding these valves. Vibrations of walls of aorta and pulmonary artery. Vibrations of the wall of ventricles to a little extent.
What are the characteristics of 2nd
heart sound
It is:
• Sharp, short and high pitched.
• Duration is 0.08 sec and follows T wave in
ECG and coincides with ‘v’ wave in
jugular venous pulse tracing.
• Best heard at 2nd right costal cartilage for
aortic component and 2nd intercostal
space at left sternal border for pulmonary
component.
• Associated with onset of ventricular
diastole.
1 What is the significance of 2nd heart
sound?
It indicates the competence of semilunar
valves
When and how 3rd heart sound is
produced?
3rd heart sound is produced during the first
1/3 of ventricular diastole. It occurs due to
the vibrations set up by the rushing of the
blood during the rapid filling phase of
ventricular diastole.
What is murmur
It is the sound produced by turbulence produced in the blood by a forward flow through a stenosed (narrowed) valve or back flow (regurgitation) through a deformed or incompetent valve
How do you classify murmur?
It will be classified on the basis of their
relationship with main heart sounds like
presystolic, systolic, diastolic and also to and
fro murmurs
What are the maximum and
minimum pressure in heart?
• Maximum pressure in left ventricle is
above 120 mm Hg.
• Max pressure in right ventricle is above
25 mm Hg
• Minimum pressure in left ventricle is 80
mm Hg.
• Minimum pressure in right ventricle is
few mm Hg
What is the normal heart rate? What
are the factors affecting heart rate (HR)?
Normal value of HR is 72 beat/min with
the normal range 60-90 beat/min.
The factors are: age, sex, body temperature, hypoxia, emotion, exercise, etc. and
drugs like epinephrine and norepinephrine.
Why HR is slightly higher in
females than males?
It is because of two reasons:
• Lower systemic BP
• More resting sympathetic tone
What is Cushing reflex?
It is represented by following sequential events: Increased intracranial pressure → decreases blood supply to medullary hypoxia and hypercapnia → stimulation of medullary vasomotor center → increase of systemic BP → stimulation of baroreceptors → stimulation of vagus nerve → decrease of HR and respiration. This reflex mechanism by which increased intracranial pressure results bradycardia is known as Cushing reflex.
What do you mean by sinus
arrhythmia?
Heart rate increases with inspiration and
decreases during expiration. This phenomenon is known as sinus arrhythmia.
State Marey’s law
If the other conditions remain constant then
the HR is inversely related with systemic
BP (Fig. 15.5
Define cardiac output, stroke volume
and cardiac index.
Cardiac output: The amount of blood pumped out by each ventricle per min is called as cardiac output. The normal value is 5 lit/min/ventricle. Stroke volume: The amount of blood pumped out by each ventricle in each beat is known as stroke volume. Normal value is 70 ml/beat/ventricle. Cardiac index: It is the cardiac output per square meter of body surface area. The normal value is 3.2 L/m2 /min.
What do you mean by extrinsic
and intrinsic autoregulation of cardiac
output?
If cardiac output is controlled by controlling
only heart rate (as CO = HR × SV) it
is known as extrinsic autoregulation of
cardiac output whereas if it is regulated by
regulating only stroke volume, it is known
as intrinsic autoregulation.
What is the difference between
heterometric and homometric regulation
of cardiac output?
To control cardiac output when ventricular
contraction is regulated by controlling initial
length of the muscle fiber, i.e. EDFL, then it
is called as heterometric regulation which is
independent of cardiac nerves. Whereas
when cardiac nerves regulate the myocardial
contractility to control the cardiac output, it
is known as homometric regulation of
cardiac output.
What is Frank-Starling’s law of heart?
What is its relation with venous return?
It states that within the physiological limit,
the force of ventricular contraction is
directly proportional to the initial length of
muscle fibers (EDFL).
If venous return is increased the EDFL of
the ventricular muscle is also increased
resulting in more force of ventricular
contraction thereby more cardiac output.
What do you mean by Vis A Tergo
and Vis A Fronte in relation to cardiac
pump?
Vis A Tergo is the force which drives the
blood forward from behind, e.g. the
contraction of the heart drives the blood in
forward direction, whereas Vis A Fronte is
the force acting from front that attracts
blood in the veins towards the heart, e.g.
ventricular systolic and diastolic suction
pressure.
Enumerate the factors affecting
venous return.
The factors are: Thoracic or respiratory
pump, cardiac pump, muscle pump, total
blood volume and increased sympathetic
activities on veins
Two methods cardiac output is measured
Direct Fick method and
• Indirect dye dilution method
Ficks principle
It states that the amount of a substance
taken up by an organ or by whole body
per unit time is equal to the arterial level of
that substances minus the venous level
(i.e. A-V difference) times the blood flow,
i.e. amount of substance taken/min = A-V
difference of the substance × blood flow/
min
What are the disadvantages of Fick’s
method?
These are:
• As it is the invasive method the subject is
exposed to all risk of hemorrhage,
infection, etc.
• As the subject is conscious of the whole
technique cardiac output may be higher
than normal.
Bundle of kent
n the individuals with WPW syndrome,
there is one additional nodal connecting
tissue in between atria and ventricles besides
AV node which conducts the impulse more
rapidly than AV node. This additional
conducting pathway is known as Bundle of
KENT.
Define blood pressure (BP)
It is the lateral pressure exerted by the
moving column of blood on the wall of
blood vessels during its flow.
Define systolic, diastolic, mean and
pulse pressure with each of their normal
average values
Systolic pressure (SP): It is the maximum
pressure exerted during systole of the heart.
Normal value = 120 mm Hg (Normal
range:110-140 mm Hg).
Diastolic pressure (DP): It is the minimum
pressure during diastole of the heart.
Normal value = 80 mm Hg (Normal range:
60-90 mm Hg).
Pulse pressure (PP): Pulse pressure is the
difference between systolic and diastolic
pressure. Normal value = 40 mm Hg.
Mean pressure: It is average pressure
during each cardiac cycle. Normal value
= 93.3 mm Hg.
Q.66
Enumerate the significance of SP,
DP, PP and MP.
• Systolic pressure indicates the extent of
work done by the heart and also the force
with which the heart is working. It also
indicates the degree of pressure the
arterial wall have to withstand.
• Diastolic pressure is the measure of the
total peripheral resistance and it indicates
the constant load against which heart has
to work.
• Pulse pressure determines the pulse
volume. Whereas mean pressure indicates
the perfusion pressure head which causes
the flow of blood through the arteries,
arterioles, capillaries, veins and venules.
Why does systolic pressure increase
after meal?
After meal pressure over heart increases due
to distended abdomen which in turn
increases heart rate and also there is a
release of epinephrine which also increases
systolic blood pressure.
What do you mean by baroreceptors?
Where are they located
Baroreceptors are the pressure receptors
stimulated in response to change of pressure
around them.
These are located in the wall of blood
vessels (e.g. arterial baroreceptor–present in carotid sinus, aortic arch, root of right
subclavian artery, junction of thyroid artery
with common carotid artery, also
pulmonary trunk) and also in the walls of
the heart (e.g. atriocaval receptors, atrial
receptors)
What do you mean by buffer nerves?
Why they are so called?
Carotid sinus nerve originated from carotid
sinus and aortic nerve arised from arch of
aorta are collectively known as buffer
nerves as they prevent any change in
systemic BP and thus help the BP to keep
normal.
What is Bain-bridge reflex?
Rapid injection of blood or saline in
anesthetized animals produces a rise in
heart rate if the initial heart rate is low. This
is called as Bain-bridge reflex (Fig. 15.6). This
is due to the stimulation of stretch receptors
in the wall of right atrium.
Name different chemoreceptors
responsible for BP regulation. What are
their stimulants?
These are carotid bodies and aortic
bodies. They get stimulated by hypoxia,
hypercapnia, asphyxia and also acidemia.
What is the effect of chemoreceptors
on heart rate?
In conditions like hypoxia, hypercapnia and
increased hydrogen ion concentration, the
chemoreceptors send inhibitory impulses to
vasodilator area (cardioinhibitory center).
Now, the vagal tone is reduced and heart
rate is increased.
Sudden standing increases diastolic
BP—explain how?
On standing there is peripheral pooling of
blood in lower parts of body → lowering of
venous return to the heart → decrease
cardiac output → thereby decrease systolic
BP → leads to decrease baroreceptor
discharge → thereby increases sympathetic
activity → results increase of the total
peripheral resistance due to vasoconstriction → ultimately leads to increase
of diastolic pressure.
4 If mean BP is decreased to 60 mm
Hg then what compensatory mechanism
will operate to bring it to normal?
Both baroreceptor mechanism (which operates in between 60-200 mm Hg mean blood pressure) and chemoreceptor mechanism which operates between 40-100 mm Hg of mean BP.
f BP is decreased to 40 mm Hg then
which compensatory mechanism will start
into action?
Both chemoreceptor mechanism and CNS
ischemic response.
If mean BP is increased to 140 mm
Hg then what compensatory mechanism
will be operated?
Only baroreceptor mechanism
What do you mean by stress
relaxation and reverse stress relaxation
mechanism in relation to BP regulation?
Rise in arterial BP due to intravenous transfusion of blood increases perfusion pressure in blood storage organs that causes relaxation of blood vessels, thereby decreases venous return and thereby decreases cardiac output. This leads to decrease BP to normal level. This mechanism is known as stress relaxation. The opposite phenomenon is known as reverse stress relaxation mechanism which is as follows: Prolonged bleeding causes decrease of BP → thereby decreases perfusion pressure → leads to vasoconstriction of blood storage organs → results in increase of venous return and thus increases cardiac output → which in turn increases BP to normal level.
What is hypertension? What do you
mean by systolic hypertension and white
coat hypertension?
Chronic elevation of blood pressure beyond
140/90 is generally labelled as hypertension.
In advanced age, due to loss of elasticity of
blood vessels, stretching of the wall of blood
vessels decreases which results in increment
of pressure during systole with normal
diastolic pressure. This condition is
known as systolic hypertension which is
characterized by high pulse pressure.
Some hypertensive patients because of
nervousness, have higher BP in the clinician’s
chamber than during their normal day time
activity. This condition is known as white
coat hypertension
. What do you mean by malignant
hypertension?
In some patients the blood pressure especially the diastolic pressure is increased to very high level (>120 mm Hg) within a short period. This condition is known as malignant hypertension.
Which pressure is considered better
to judge the hypertension–SP or DP?
Justify your answer
Clinically diastolic pressure is more useful
to characterize the state of hypertension
because diastolic pressure is comparatively
constant and does not fluctuate like SP in
response to day-to-day activity.
What do you mean by labile
hypertension?
In early stages of essential hypertension,
systolic BP fluctuates. This is why it is
referred to as labile hypertension.
What is hypotenision
Chronic low BP specially the diastolic
pressure below 60 mm Hg is called as
hypotension.
What do you mean by postural
hypotension?
In some hypotensive patients, sudden
standing causes further fall of systemic BP
that may result in dizziness, dimness of
vision and even fainting. This is known as
postural hypotension.
What is the difference between pulse
pressure and pressure pulse?
Pulse pressure is the difference of systolic
and diastolic pressure whereas the pressure
pulse or pulse is the wave transmitted to
the arteries like radial arteries due to
stretching and relaxation of wall of aorta in
response to ventricular ejection of blood and
ventricular filling respectively during cardiac
cycle.
What is the purpose of doing exercise
tolerance test?
It is for determining the efficiency of the
heart as a pumping organ.
What is isometric (isovolumetric)
contraction of the heart?
The period during which the ventricles of
the heart contract as closed cavities (because
all the valves are closed) without any change
in the volume of ventricular chambers or in
the length of muscle fibers is known as
isometric (isovolumetric) contraction.
During this period, the pressure increases
very much.
What is the significance of isometric
contraction of the heart?
During isometric contraction, the pressure
in the ventricles is greatly increased. When
the ventricular pressure increases more than
the pressure in aorta and pulmonary artery
the semilunar valves open. Thus, the high
pressure developed during isometric
contraction is responsible for the opening
of semilunar valves leading to ejection of
blood from the ventricles.
What is isometric or isovolumetric
relaxation of the heart?
The period during which the ventricles of
the heart relax as closed cavities (because all
the valves are closed) without any change
in the volume of ventricular chambers or in
the length of muscle fibers is known as
isometric or isovolumetric relaxation. The
pressure decreases very much during this
period
By observing HR can you predict
the intensity of exercise or work done by a
person?
Yes,- If HR is <100 ; it will be light exercise.
- If HR is 100-125 ; it will be moderate exercise.
- If HR is 126-150 ; it will be heavy exercise.
- If HR is >150 ; it will be severe exercise
What is cardiac reserve?
It is the difference between the basal cardiac
output of an individual and the maximum
cardiac output that can be achieved in that
person. It is also expressed as cardiac reserve
percent.
Where do you find physiological
bradycardia?
It is seen in athletes, during sleep and
meditation.
Wgat is apex pulse deficit
Normally the pulse rate and heart rate are
identical but in some cases like extrasystoles
and atrial fibrillations, some of the heart
beats are too weak to be felt at the radial
artery resulting in missing of that particular
pulse. This causes higher heart rate than
pulse rate. This condition is known as apexpulse deficit or pulse deficit
What is isometric (isovolumetric)
contraction of the heart?
The period during which the ventricles of
the heart contract as closed cavities (because
all the valves are closed) without any change
in the volume of ventricular chambers or in
the length of muscle fibers is known as
isometric (isovolumetric) contraction.
During this period, the pressure increases
very much.
What is the significance of isometric
contraction of the heart
in the ventricles is greatly increased. When
the ventricular pressure increases more than
the pressure in aorta and pulmonary artery
the semilunar valves open. Thus, the high
pressure developed during isometric
contraction is responsible for the opening
of semilunar valves leading to ejection of
blood from the ventricles.
8 What is isometric or isovolumetric
relaxation of the heart?
The period during which the ventricles of
the heart relax as closed cavities (because all
the valves are closed) without any change
in the volume of ventricular chambers or in
the length of muscle fibers is known as
isometric or isovolumetric relaxation. The
pressure decreases very much during this
period
What is cardiac reserve
It is the difference between the basal cardiac
output of an individual and the maximum
cardiac output that can be achieved in that
person. It is also expressed as cardiac reserve
percent.
Name the waves of normal arterial
pulse tracing. What are their physiological
basis?
n the normal arterial pulse recording, there
are one steep upstroke called anacrotic limb
and one rather slow down stroke called
catacrotic limb. The end of anacrotic limb
and beginning of catacrotic limb is
designated as percussion wave (p). In the
catacrotic limb there is also a negative wave
called dicrotic notch (n) followed by a
positive wave called dicrotic wave. Besides
this, sometimes after the peak of the tracing
there is another small wave called tidal wave
(t). The waves are represented by Figure 15.7.
• Percussion wave: It is due to expansion of
the artery for ventricular ejection during
ventricular systole.
• Catacrotic limb: It is due to normalization
of artery due to slow passing of blood
towards periphery.
• Dicrotic notch:
It is due to backflow of the
blood from aorta towards heart due to
pressure difference during ventricular
diastole.
• Dicrotic wave: It is due to increase pressure
again in the aorta due to prevention of
back flow of blood towards heart by
closure of aortic valve.
Can you indicate the systolic and
diastolic phases of the ventricle on the
arterial pulse tracing?
Yes, the maximum ejection phase lasts from
the start of the upstroke to peak of ‘p’ wave
while the reduced ejection phase lasts from
peak of ‘p’ wave to peak of dicrotic notch.
The rest time period represents diastole.
What is dicrotic pulse
There are two palpable waves—one in
systole and another in diastole in congestive
cardiomyopathy patients where stroke
volume is low. This type of pulse is known
as dicrotic pulse
What is plateu phase
During some pathological conditions like
aortic stenosis the pulse wave rises slowly,
followed by delayed and sustained peak and
then the pulse faded slowly. Such type of
pulse is known as plateau pulse as
represented by Figure 15.8.
Anacrotic pulse
Slow rising and slow fall of pulse wave due
to prolonged ventricular ejection as occurs
in aortic stenosis is known as anacrotic pulse
What do you mean by pulsus alterans
and paradoxus
Pulsus alterans is alternative weak and strong beating of pulse whereas the phenomenon when pulse disappears or becomes feeble during inspiration and becomes maximum during expiration is known as pulsus paradoxus
What is hammer pulse
In some conditions like aortic regurgitation
there is sharp and steep rise followed by
sleep fall of pulse which is known as water
hammer pulse.
How does jugular venous pulse
record give the idea about right atrial
pressure?
Jugular vein is connected directly with right
atrium and as there is no valve at the junction
of superior vena cava and right atrium, any
change of right atrial pressure is directly
transmitted to the jugular vein. That is why jugular venous pressure record gives the
idea about right atrial pressure.
Name the waves of jugular venous
pulse and the causes of their onset.
The waves and their causes are as follows:
• ‘a’ wave – It is due to increase in pressure
within atrium due to atrial systole.
• ‘c’ wave – It is due to increased pressure
within atrium due to bulging of the
tricuspid valve into the right atrium during
isovolumic ventricular contractile phase.
• ‘v’ wave – It is due to the rise in atrial
pressure due to atrial filling before the
tricuspid valve opens during diastole.
• X descends-It is due to fall of intra-atrial
pressure due to descend of the tricuspid
valves.
• Y descends-It is due to the fall of intraatrial pressure due to the opening of
tricuspid valves to result ventricular
filling
Define ecg
It is the record of electrical activities of heart
by electrocardiograph during different
periods of cardiac cycle (Fig. 15.9)
Clinical significance of ecg
Any abnormalities of the heart like ischemic
heart disease, myocardial infarction,
extrasystole, heart block, ventricular
fibrillation and flutter, sinus arrhythmias,
etc. are detected by the ECG record of the
person.
What does ‘P’ wave represent? What
does it signify?
P’ wave represents the atrial depolarization.
Any abnormalities of the ‘P’ wave means
abnormality in the atria like larger ‘P’ wave
denotes the atrial hypertrophy.
What do QRST and QRS represent?
What is the duration of ventricular
complex?
QRST represents ventricular complex, i.e.
ventricular depolarization and ventricular
repolarization. Normal duration is 0.48 sec.
QRS complex represents ventricular
depolarization only
What do Q and RS waves indicate?
Q’ wave indicates the ventricular septal
activity whereas ‘RS’ wave indicates the
excitation of ventricle proper with duration
of 0.08-0.1 sec
What is the significance of T wave?
It is due to repolarization of ventricles and
its normal duration is 0.27 sec. It indicates
the functional activity of base of the heart.
Clinically it signifies the myocardial damage
in case of any abnormality in T wave
What does PR interval represent?
What is its significance?
It represents atrial depolarization and conduction through bundle of His. Normal duration is 0.13-0.16 sec. It is the interval from beginning of P wave to the beginning of Q or R wave. Prolonged PR interval signifies the conduction block.
What is TP interval and what is its
significance?
It is the period from the end of T wave to
the beginning of P wave of next cardiac
cycle. It represents the diastole or polarized
state of whole heart. Normal duration is 0.2
sec at a HR of 75/min.
What is QT interval and what does
it represent?
It is the interval from the beginning of Q
wave to the end of T wave (Normal duration
0.40-0.43 sec). It represents ventricular
events.
What is ST interval? What does it
represent?
End of S wave to the end of T wave is known
as ST interval. The normal duration of
which is 0.32 sec. It represents ventricular
repolarization only
What is ST segment? What is its
significance?
Following the QRS there is a long isoelectric
period which extends from the end of S
wave to the beginning of T wave called as
ST segment. Any change of the position of
ST segment from the isoelectric line indicates
the functional abnormalities of the heart.
Deviation of ST segment more than 2 mm
up from the isoelectric line is called elevated
ST segment which is the clinical feature of
MI. Similarly deviation of the same more
than 2 mm downward from the isoelectric
line is called as depressed ST segment as
seen in angina pectoris.
Define leads
The electrocardiographic connections, i.e.
wires along with the electrodes to record
ECG is known as lead.
Classify leads
Leads are classified as unipolar and bipolar leads which are again divided as follows: • Unipolar lead • Unipolar augmented limb lead – aVR – aVL – aVF • Chest lead (V1-V6) • Bipolar lead – Standard limb lead—I – Standard limb lead—II – Standard limb lead—III
Unipolar leads
In this type of leads, one electrode becomes
inactive (indifferent electrode) whereas
other one is active (exploring electrode).
That is why it is known as unipolar lead
Rule of the thumb
It is the general observation in the ECG
record obtained from chest leads as follows:
• As we pass across the chest leads (V1- V6)
‘R’ wave increases gradually in size and
‘S’ wave becomes smaller gradually. In
lead V3 both are equal.
• R wave in V6 and S wave in V1 represent
left ventricular activity whereas R wave
in V1 and S wave in V6 represent right
ventricular activity
What is augmented limb lead? Why
is it so called?
Augmented limb leads are unipolar type
limb leads with slight modification in the
recording technique where one electrode
(active) is connected to the positive terminal
of ECG machine and other two are
connected through electrical resistant to the
negative terminal of the ECG machine.
It is so called because the magnitude of
different waves become larger by 50
percent than the same obtained from
standard limb leads without any change of
its normal pattern. These are classified as
aVR, aVL and aVF.
What do unipolar chest leads
represent?
V1 and V2 are associated with right atrial
and ventricular activity respectively whereas
V4, V5 and V6 represent left ventricular
activity. V3 is regarded as transitional zone
What do you mean by dextrocardiogram?
In case of damage of left branch of bundle
of His, the impulse travels through right
branch to the right ventricle resulting in
predominant activity of right ventricle. Such
a record is called as dextrocardiogram
What is levocardiogram?
When right branch of bundle of His is
damaged there is predominance of left
ventricular activity. This type of record is
called as levocardiogram.
What do you mean by Einthoven’s
triangle?
The equilateral triangle obtained by
connecting the right arm, left arm and right
leg, by means of electrical wires with current
source as the heart at its center is known as
Einthoven’s triangle (Fig. 15.10).
What is Einthoven’s law?
It states that if the electrical potentials of
any two of the three bipolar leads are known
at any given instant, the 3rd one can be
determined mathematically from the 1st two
by simply summing the 1st two by
What is the effect of hyperkalemia
on the heart?
Normal potassium concentration in serum
is about 3.5 to 5 mEq/L. When it increases
above 6 mEq/L (hyperkalemia) the resting
membrane potential in cardiac muscle is
decreased leading to hyperpolarization. It
reduces the excitability of the muscle. ECG
shows a tall T wave.
The increased potassium concentration
above 8 mEq/L affects the conductive
system also. And in ECG, P-R interval and
the duration of QRS complex are prolonged.
During severe hyperkalemia (above 9
mEq/L), atrial muscle becomes unexcitable.
So, in ECG, P wave is absent and QRS
complex merges with T wave.
In experimental animals, increased
potassium concentration stops the heart in
diastole immediately
What is the effect of change in the
blood sodium concentration on the heart?
Increased sodium concentration in blood decreases the rate and force of contraction. Very high sodium concentration can stop the heart in diastole. Very low level of sodium produces low voltage waves in ECG.
What is the effect of hypokalemia
on the heart?
Hypokalemia (decrease in potassium
concentration) reduces the sensitivity of
heart muscle. In ECG, S-T segment is
depressed. Amplitude of T wave is reduced.
In severe hypokalemia, T wave is inverted.
U wave appears. P-R interval is prolonged
What is the effect of hypercalcemia
on human heart
Normal serum calcium level is 9 – 11
mg%. In hypercalcemia, there is reduction
in duration of S – T segment and Q – T
interval, with slight increase in excitability
and contractility
What is calcium rigor
The stoppage of the heart in systole when a
large quantity of calcium ion is infused in
experimental animals is known as calcium
rigor. It is a reversible phenomenon. When
the calcium ions are washed, the heart starts
functioning normally
What is the effect of hypocalcemia
on heart?
Hypocalcemia (reduction in serum calcium
level) reduces the excitability of the cardiac
muscle. In ECG, the duration of S – T
segment and Q – T interval is prolonged
What do you know about U wave in
ECG?
It is rarely seen as a small positive round
wave after the T wave. It is due to slow
repolarization of papillary muscles. It is
more commonly seen in children
What do you mean by left and right
axis deviation? From the ECG record how
can you assess whether any person is
having left or right axis deviation?
If the normal direction of mean QRS vector
falls in between –30° to +30°, it is called as
left axis deviation which represents the
horizontal position of heart. Similarly, if it
falls in between +75° to +110°, it is known
as right axis deviation which also represents
vertical position of heart. Clinically axis
deviations are made by finding the
amplitude of R wave in the bipolar leads as
follows:
• If R wave is the tallest in lead II, it is normal
electrical axis of heart (+59°).
• If R wave is the tallest in lead I, it is left
axis deviation.
• If R wave is the tallest in lead III it is called
as right axis deviation
What are the physiological left or
right axis deviation? What is the clinical
significance of electrical axis of heart?
Physiological left axis deviation is seen:
• During expiration
• When a person lies down
• If the person is stocky and fatty.
Physiological right axis deviation is seen:
• During inspiration
• When a person stands up
• Normally in tall and lanky people.
Clinical significance: Hypertrophy of any
ventricles and bundle branch block is
indicated from the electrical axis of heart. In
patients with hypertrophy of left ventricle
and left bundle branch block, left axis
deviation is seen whereas in hypertrophy
of right ventricles and right bundle branch
block patients, right axis deviation takes
place.
What is the extrasystole or premature
contraction?
Sometimes, any part of the heart other than
SA node can produce an impulse. This is
called an ectopic focus. The ectopic focus
produces an extra beat of the heart, which
is called extrasystole or premature
contraction.
What is compensatory pause? What
is its cause?
Extrasystole is always followed by a long
pause where the heart stops. This
temporary stoppage of heart, immediately
after extrasystole is known as a
compensatory pause. It occurs because the
heart has to wait for the arrival of next
natural impulse from the pacemaker
What is the difference between 1st
degree and 2nd degree heart block?
When all atrial impulses reach the ventricles
therefore atrial rate: ventricular rate
becomes 1:1 but PR interval becomes longer
than 0.2 sec, it is called as 1st degree
incomplete heart block.
Whereas when all atrial impulses are not
conducted to the ventricles producing atrial
and ventricular contraction at a rate of either
2:1 or 3:1 ratio with gradual lengthening of
PR interval till one ventricular beat is missed,
this type of heart block is known as 2nd
degree incomplete heart block.
What do you mean by Wenckebach
phenomenon?
In case of 2nd degree heart block, there is a
gradual increase of PR interval until one
ventricular beat is missed. This is known as
Wenckebach phenomenon
What is 3rd degree heart block? What
do you mean by idioventricular rhythm?
Complete blockade of conduction of
impulse from atria to ventricle is known as
third degree or complete heart block.
In the case of complete heart block,
ventricle starts beating at its own rate, i.e.
45 beats/min which is independent to SAN.
This rhythmic ventricular contraction is
known as idioventricular rhythm.
Difference between flutter and fibrillation
What are the clinical findings of ECG
during MI?
• Elevation of ST segments in the leads overlying the area of infarct and • Depression of ST segment in the reciprocal leads.
What do you mean by Stokes-Adams
syndrome?
In case of complete heart block, there is some
delay before ventricles start beating at their
own rate. During this period the systemic
blood pressure falls to a very low level and
blood supply to brain becomes inadequate.
If ventricles do not beat for more than few
seconds it causes dizziness and fainting called
as Stokes-Adams syndrome.
What are the ECG changes during
bundle branch block? What changes take
place in heart sound production during its
bundle branch block?
The ECG changes are as follows:
• Prolonged QRS complex (>0.12 sec)
• Abnormal ST segment and T wave.
• The second heart sound is splited
What types of ECG changes take
place in atrial flutter and atrial fibrillation?
In case of atrial flutter following changes are seen: • Shortening of all time intervals, e.g. PR, TP intervals • Merger of T wave with P wave of next cardiac cycle • 2nd degree type (2:1) of heart block. In case of atrial fibrillation following changes are seen: • Absence of P wave. • Appearance of fibrillation (f) waves • Absence of T wave • Irregular QRS complex.
How does the ECG record change
with time after MI?
• Within few hours after MI: Elevation of ST segment. • After some days of MI: Elevation of ST segment along with inversion of T wave. • After several weeks of MI: ST segments return to normal but inversion of T wave is still present along with appearance of Q wave. • After months and years of MI: T wave becomes normal and Q wave becomes deep
What do you mean by mean
circulatory filling pressure and mean
systemic filling pressure?
If the heart beat is stopped, the flow of blood
every where in the circulation ceases after
few seconds resulting in equal pressure
within the whole circulation which is known
as mean circulatory filling pressure.
Whereas the mean systemic filling
pressure is the pressure measured
everywhere in the systemic circulation after
blood flow is stopped by the clamping of
the large blood vessels at the heart.
Normally the amount of both are almost
equal.
Name different types of blood
vessels in vascular system with examples
of each.
These are as follows:
• Distensible (Windkessel) vessels—aorta, pulmonary artery and their large branches. • Resistance vessels—arterioles, metaarterioles • Exchange vessels—capillaries • Capacitance vessels—venules and venous compartments • Shunt vessels—AV anastomoses.
What is windkessel effect?
The blood flow through aorta is pulsatile in
nature, i.e. it increases during systole and
decreases during diastole of the heart.
However, the blood flow through other
blood vessels becomes uniform and
continuous. This is because, during systole,
aorta (and to some extent the other larger
blood vessels) dilates and later it recoils. This
elastic recoiling of aorta causes the
continuous blood flow through other blood
vessels. Thus, the pulsatile blood flow is
converted into continuous flow. This
recoiling effect is known as windkessel
effect and the blood vessels exerting this
effect are called the windkessel vessels
What are the components of
vasomotor system
- Vasomotor center
- Vasoconstrictor fibers
- Vasodilator fibers
Where is vasomotor center situated?
Vasomotor center is situated in the reticular
formation of medulla oblongata
What are the components of
vasomotor center?
- Vasoconstrictor or pressor area
- Vasodilator or depressor area.
- Sensory area
Name the vasoconstrictor and
vasodilator nerve fibers
Vasoconstrictor fibers are the sympathetic vasoconstrictor fibers. Vasodilator fibers are: • Parasympathetic fibers • Sympathetic cholinergic fibers • Antidromic nerve fibers
What is the mode of action of
sympathetic adrenergic fibers on blood
vessels?
Sympathetic adrenergic fibers cause constriction of blood vessels (vasoconstriction)
by secreting noradrenaline.
What is vasomotor tone?
Vasomotor tone is the continuous discharge
of impulses from vasoconstrictor center to
arterioles through vasoconstrictor nerve
fibers. Vasomotor tone maintains arterial
blood pressure by producing constant partial
constriction of blood vessels (peripheral
resistance). The arterial blood pressure is
directly proportional to vasomotor tone.
Blood flow to the different body
organs can be so effectively regulated by
only small changes in the caliber of the
arteries. How is it possible?
As resistance to blood flow is inversely
proportional to the 4th power of the radius
(r) of arterioles, the small changes of radius
can cause greater changes of resistance to
blood flow and thereby flow to the different
body organ.
What do you mean by critical closing
pressure?
Extravascular tissues exert a small but
definite pressure on vessels and when the
intraluminal pressure falls below this
extravascular pressure the vessel collapses.
The pressure at which the flow ceases is
called as critical closing pressure.
State the law of Laplace. What is its
functional significance?
It states that the distending pressure (P)
in a distensible hollow object is equal at
equilibrium to the tension in the wall (T)
divided by two principal radii of curvature
of object (R1 and R2), i.e. P = T (1/R1+1/R2).
Significance: (i) smaller the radius of the
blood vessels lesser the tension in the wall
necessary to balance the distending
pressure. This is why (i) thin and delicate
capillaries are less prone to rupture, (ii)
dilated heart has to do more work than
normal heart.
What is axon reflex
In response to a firm stroke in the skin the
afferent impulses are relayed to the endings
near cutaneous arterioles down the branches
of sensory nerve to result cutaneous
arteriolar dilatation. This neural pathway
which does not involve CNS is known as
axon reflex.
What do you mean by cold blue skin
and warm red skin?
Cold blue skin is the skin in which the
arterioles are constricted and the capillaries
are dilated whereas in warm red skin both
arterioles and capillaries are dilated
What is triple response?
A firm and strong stroke on the skin by a
blunt object evokes a series of responses
which are
• Red reaction
• Flare and
• Wheal.
These responses to the injury are
collectively known as triple response.
On what factors the peripheral
resistance does depend.
It depends on the elasticity of vessel wall,
diameter of arterioles (inversely), viscosity
and velocity of blood directly.
Define Poiseuille’s law
It states that resistances to blood flow in a
blood vessel proportionately varies with
length of blood vessels and viscosity of
blood and inversely with 4th power of radius
of lumen of vessels.
What is circulation time? Give the
value of total circulation time.
It is time taken by blood to flow from one
site to any other specific site. Normal total
circulation time is 12-16 sec
Coronary blood flow fluctuates with
each phases of cardiac cycle, explain
During systole the coronary blood flow is
reduced because of compression of
coronary vessels due to contraction of
cardiac muscle whereas during diastole as
cardiac muscle relaxes, there is distention of
coronary vessels to its original diameter and
thus blood flow through it to heart muscle
is increased.
Why does the subendocardial
portion of left ventricle is more prone for
MI?
It is for two reasons as follows:
• No blood flows to this portion during
systole because of poor blood supply in
this region and also compression of blood
vessels during systole.
• Anaerobic respiration goes on in inner
layer which increases further under stress.
What is the normal time taken for
coronary circulation?
8 sec
What are the factors on which
coronary blood flow depends?
These are mainly lumen of coronary
vessels, mean aortic pressure and also by
cardiac output, HR, body temperature, CO2
con-centration in blood and cardiac
sympathetic stimulation.
What is normal pulmonary blood
flow rate
It is about 3-5 lit/min
4 What is the normal blood flow rate
in liver?
It is about 1500 ml/min.
What is the normal coronary blood
flow?
It is about 225 ml/min
Give the normal value of cerebral
blood flow
It is approx. 750 ml/min.
Define shock
Shock is a syndrome characterized by low
cardiac output which is inadequate to
maintain normal tissue perfusion. It is of 4
types—hypovolemic, vasogenic, cardiogenic
and obstructive shock.
What do you mean by cold shock?
When the amount of fluid in the vascular
system is inadequate to fill it, resulting in
decrease in circulatory blood volume it is
known as hypovolemic or cold shock.
Warm shock
When the diameter of capacitance vessels is
increased by vasodilatation, there is a
decrease of cardiac output in spite of normal
blood volume. This type of shock is
vasogenic shock and in this type of shock as
skin becomes warm it is also called as warm
shock.
