test 2 Flashcards
what is slow conduction in the heart mainly caused by
diminished numbers of gap junctions along pathway resulting in an increase in the resistance to conduction
what is the threshold for the SA node
-40 mV
what is the parasympathetic system mostly distributed to in the heart
SA and AV nodes
what is the sympathetic system mostly innervation in the heart
distributed to all parts of the heart, but mainly the ventricles
what is depolarization represented by in an ECG
P and QRS waves:
P=atrial depolarization
QRS= ventricular depolarization
what is depolarization represented by in ECG
T wave (ventricular repolarization)
what does an ECG measure
extracellular potential
what are the normal time durations for the P-Q (P-R) interval and the Q-T interval
P-Q = 0.16 sec
Q-T: 0.35 sec
what does the limb lead 1 connect
neg terminal end connected to right arm
positive term end is connected to left arm
*looks at the heart from left to right
what does the limb lead 2 connect
neg term is connected to right arm
pos term connected to left leg
*looks at heart from upper right to lower left
what does the limb lead 2 connect
neg term connected to left arm
positive term connected to left leg
*looks at heart from upper left to lower left
what is eithoven’s law
if the electrical potentials of any 2 of the 3 bipolar limb ECG leads are known at any given instant, the 3rd can be determined by summing the first 2
how does current typically flow in the ventricles (ECG)
negative to positive primarily in the direction from the base of the heart toward the apex for most of the heart cycle until the very end
define vector
arrow that points in the direction of the electrical potential generated by the current flow, with the arrowhead in the positive direction
what is the direct of the lead for lead 1-3
1: 0
2: 60
3: 120
what is the degree for the QRS vector in relation to the zero reference point
+59 degrees
where does atrial depolarization begin
Sinus node
what is the first part to become depolarized in the atrial T-wave
sinus node area
what are the main leads used for ECG
3 conventional bipolar limb leads
six standard leads (V1-V6)
Three augmented leads (aVR, aVL, aVF)
what are some abnormal ventricular conditions that cause axis deviation
change in position of heart in the chest hypertrophy of one ventricle bundle branch block fluid in pericardium pulmonary emphysema
what is the most common cause of increased voltage in the standard bipolar leads
hypertrophy of the ventricle
what is decreased voltage of the QRS complex typically caused by
cardiac myopathies
conditions around the heart
what are abnormalities that cause current of injury
mechanical trauma
infectious processes
ischemia (most common cause)
what is the effect of current of injury on QRS complex
abnormal negative current flows from infarcted area and spreads toward the rest of the ventricles
what is the J point
reference point for analyzing current of injury
define tachycardia
fast heart rate (>100 beats/min)
what are the causes of tachycardia
increased body temperature
stimulation of the heart by sympathetic nerves
toxic conditions of the heart
what occurs during endogenously mediated tachycardia (i.e. exercise)
heart rate increases, cardiac output increases, filling time is reduced by SV does not fall
what occurs during pathologically mediated tachycardia
heart rate increases
cardiac output decreases
occurs because atrial pressure decreases and activates the sympathetic nervous system, which occurs after the fact and is unable to compensate
define bradycardia
slow heart rate (
what are the causes of bradycardia
athletic heart
vagal stimulate
extremely sensitive carotid baroreceptors in carotid sinus syndrome
what does spillover signals do (respiratory type of sinus arrhythmia)
alternately increase and decrease number of impulses transmitted through sympathetic and vagus nerves to the heart
what are characteristics of sinoatrial block
sudden cessation of P waves
resultant standstill of atria
ventricles pick up a new rhythm, usually originating in the AV node
Rate of QRS is slowed but not otherwise altered
what conditions cause atrioventricular block
ischemia of AV node or AV bundle fibers through coronary insufficiency
compression of AV bundle by scar tissue or calcified portions of the heart
inflammation of the AV node or bundle
Extreme stimulation of the heart by the vagus nerves
when does a first degree incomplete atrioventricular block occur
when the P-R interval increases to greater than 0.20 sec, the P-R interval is prolonged
when does a 2nd degree incomplete atrioventricular block occur
P-R time interval increases to 0.25 to 0.45 sec
atria P wave is present by QRS-T wave may be missing, resulting in dropped beats of the ventricle,
2:1 rhythm or other variations may develop
what usually occurs as a result from a complete atrioventricular block
person will faint due to lack of blood to the brain until the ventricles escape
typically these fainting spells are referred to as Stokes-Adams syndrome
define partial intraventricular block
referred to as electrical alternans
refers to an alternation in the amplitude of P waves, QRS complexes, or T waves
what do most premature contraction result from
ectopic foci: local ischemic areas, calcified plaques, irritation of the conduction system or nodes
what occurs during paroxysmal tachycardia
heart becomes rapid in paroxysms:
paroxysm begins suddenly and lasts for a few seconds, minutes or longer
paroxysm ends suddenly
pacemaker of the heart instantly shifts back to the sinus node
define fibrillation
twitching (usually slow) of individual muscle fibers in the atria or ventricles and also in recently denervated skeletal muscle fibers
occurs as a result of circus movements
what are 3 different conditions that cause circus movement
pathway around the circle is too long’
length of the pathway remains constant but the velocity of the conduction slows down
refractory period of the muscle might become greatly shortened
what causes the length of the pathway to remain normal. but the conduction velocity of the impulse to slow down (circus movement)
because of blockage of the purkinje system, ischemia or high potassium levels
what causes the refractory period of the muscle to shorten (circus movement)
may occur in response to drugs such as epinephrine
may occur after repetitive electrical stimulation
how are the atrial muscle fibers separated from the ventricular muscle fibers
cardiac fibrous skeleton
what are causes of atrial fibrillation
enlargement of atria
inadequate emptying of the ventricles causing blood to back up into the atria
what are the values for arterial pressure
120 mm Hg (systolic)
80 mm Hg (diastolic)
what is the arterial pressure at the vena cava
0 mm Hg
what is the systolic pulmonary artery pressure value
25 mm Hg
what is the pulmonary diastolic pressure value
8 mm Hg
what are the functional parts of circulation
arteries (transport under high pressure)
arterioles (control conduits)
capillaries (exchange between blood and extra cell fluid)
venules (collect blood from the capillaries and gradually coalesce into progressively larger veins)
veins (function as conduits for transport of blood from the venules back to the heart & serve as a major reservoir of extra blood )
what is the distribution of blood (percentages)
84% in systemic circulation (64% in veins, 13% in arteries, 7% in systemic arterioles and capillaries)
16% in heart and lungs
what is the equation for velocity of blood flow
V=F/A (F=volume of blood flow)
what are the 3 functional principles of the circulatory system
- rate of blood flow to each tissue of the body is almost always precisely controlled in relation to the tissue need
- cardiac output is controlled mainly by the sum of all the local tissue flows
- arterial pressure regulation is generally independent of either local blood flow control or cardiac output control
what monitors tissue needs in each tissue
microvessels
what happens if arterial pressure falls below 100 mm Hg, nervous reflexes:
- increase force of heart pumping
- constrict large venous reservoirs
- generally constrict most of the arterioles throughout the body (increases arterial pressure)
- kidneys may later play important role in pressure control
define pressure gradient
pressure difference between the 2 ends of a vessel
define resistance
impediment to blood flow through the vessels
define poiseuille equation
F= (P1-P2)/R
what are the typical units for blood flow
ml/min or liters/min
what are characteristics of laminar blood flow
- streamline flow
- blood flows at a steady rate
- blood vessel is long and smooth
- blood flows in streamlines (layers)
- each layer maintains same distance from vessel wall
- central-most portion of the blood stays in the center
- each layer slips easily past surrounding layers
- velocity of fluid flowing in center is greater than that of fluid flowing towards the outer edges
what are characteristics of turbulent flow
*nonlayered flow
creases murmurs
produces more resistance than laminar flow
occurs when: flow is too great, blood passes an obstruction within the vessel, blood has to make a sharp turn, blood passes over a rough surface
*blood flows with greater resistance when eddy currents flow
when does the tendency for turbulent flow increases
- in direct proportion to velocity of blood flow
- in direct proportion to the diameter of the vessel
- in direct proportion to the density of the blood
- inversely to the viscosity of the blood
what is laminar flow directly proportional and inversely proportional with
- directly: mean velocity of blood flow in cm/sec, vessel diameter in cm, density
- indirectly: viscosity (in poise)
define blood pressure
force exerted by the blood against any unit area of the vessel wall
how is pressure measured
with a mercury manometer or with electronic transducers
what is the impediment to blood flow in a vessel
resistance
how is resistance calculated
it must be indirectly calculated from measurements of blood flow and pressure
what are the 3 main variables that determine resistance
vessel radius
blood viscosity
vessel length
what is resistance proportional to and inversely proportional to
proportional: blood viscosity and vessel length
inversely: radius (radius of blood vessel is to the fourth power)
what is the lowest arterial pressure
diastolic
what is the rate of blood flow through the entire circulatory system
=cardiac output
=100ml/sec
what is the pressure difference from systemic arteries to systemic veins
100 mmHg
resistance of entire systemic circulation
100/100=1 PRU
what is the mean pulmonary arterial pressure
avg 16 mm Hg
Mean left arterial pressure
avg 2 mm Hg
what is the total pulmonary vascular resistance when cardiac output is normal at 100 ml/sec
14/100=0.14 PRU
define conductance
measure of blood flow through a vessel for a given pressure difference (usually expressed in ml/sec per ml Hg
how are arterioles, capillaries, venues, and veins arranged?
in series
what are some circulations arranged in parallel
brain, kidney, muscle, GI, skin, coronary circulation
what can occur if there is amputation of a limb or kidney that removes a parallel circuit
- reduces total vascular conductance
- reduces total blood flow
- increases total peripheral vascular resistance
what is viscosity
measure of the fluid’s internal resistance
how does the viscosity of normal blood compare to that of water
viscosity of normal blood is about 3X as great as that of water
what occurs to viscosity in anemia and polycythemia
anemia: decreases viscosity
polycythemia: increases viscosity
define vascular distensibility
increase in volume/ (increase in pressure X original volume)
are arteries or veins more distensible
veins
define vascular compliance
increase in volume/increase in pressure
what does vascular compliance tell us
tells us the total quantity of blood that can be stored in a given portion of the circulation for each mm Hg rise in pressure
how is capacitance related to elastance
inversely proportional
what happens to the elastance as the amount of elastic tissue increases in a blood vessel
elastance increases
compliance decreases
define compliance
measure of the ease with which a hollow viscus may be distended: volume change resulting from the application of a unit pressure differential between the inside and outside of the viscus
define vascular compliance
total quantity of blood that can be stored in a given portion of the circulatory system
define elastance
measure of the tendency of a hollow viscus to recoil toward its original dimensions upon removal of a distending or collapsing force
what are the 2 major factors that effect pulse pressure
stroke volume output of the heart
compliance of the arterial tree
what is the most important determinant of pulse pressure
stroke volume output of the heart
what happens to the diastolic pressure during ventricular systole
it remains unchanged
what happens during aortic valve stenosis
diameter of the aortic valve opening is reduced significantly, and the aortic pressure pulse is decreased significantly
blood flow through the aortic valve is diminished
what happens during patent ductus arteriosus
half or more of the cardiac output flows back into the pulmonary artery and lung blood vessels
diastolic pressure falls very low before next heartbeat
what happens during aortic regurgitation
the aortic valve is absent or will not close properly
aortic pressure may fall all the way to zero between heartbeats
what is the progressive reductio of the pulsations in the periphery
damping of the pressure pulses
what is the calculation for mean arterial pressure
diastolic pressure + (1/3) pulse pressure
what are factors that regulate right atrial pressure
ability of the heart to pump blood out of the right atrium/ventricle
tendency of blood to flow into the right atrium
what are factors that increase venous return
increased blood volume
increased peripheral venous pressures due to increased large vessel tone
dilation of arterioles
describe arterioles
small arteries that control blood flow to each tissue
local conditions in tissues control diameter of arterioles
arterioles are highly muscular
describe capillaries
smooth muscle fiber encircles capillary at point where it originates from a met arteriole (referred to as pre capillary sphincter)
what do slit pores do
located in capillaries
allow for rapid diffusion of water, water-soluble ions, and small solutes
what do plasmalemmal vesicles do
formed from cave-ins
play a role in endocytosis and transcytosis
what is the most important factor regulating vasomotion
concentration of oxygen in the tissues
what type of substances can diffuse readily through the capillary cell membranes
lipid soluble substances such as oxygen and CO2
why is the passage of substances through the interstitial mostly via diffusion rather than flow
because of the large number of proteoglycan filaments found in the interstitial
rivulets that allow fluid flow through the interstitial do sometimes form
what are the outward starling forces
capillary pressure and interstitial fluid colloid pressure
what are the inward starling forces
interstitial fluid pressure and capillary plasma colloid osmotic pressure
what are some factors that increase lymph flow
elevated capillary hydrostatic pressure
decreased plasma colloid osmotic pressure
increased interstitial fluid colloid pressure
increased permeability of capillaries
what is the equation for determining rate of lymph flow
interstitial fluid pressure and activity of lymphatic pump
