Unit 1: Pt 3 Physiology III Flashcards
What are some extrinsic influences on the heart?
- Autonomic NS
- Hormonal influences
- Ionic influences
- Temperature influences
What will sympathetic innervation have on the heart?
- Increase HR
- Increase strength of contraction
- Increase conduction velocity
What will parasympathetic innervation have on the heart?
- Decrease heart rate
- Decrease strength of contraction
- Decrease conduction velocity
How are SNS effects on the heart blocked?
Using propranolol (beta blocker), Which blocks beta receptors (which bind NE and Epi)
How are parasympathetic effects on the heart blocked?
Using atropine, which block muscarinic receptors (which bind Ach)
- HR will increase
- Strength of contraction decreases
Describe the interaction of the ANA under resting conditions. (What is dominant at rest?)
Parasympathetic NS exerts a dominant inhibitory influence on HR (rate of contraction)
Sympathetic NS exerts a dominate stimulatory influence on strength of contraction
If we were to block BOTH sympathetic and parasympathetic autonomic systems, what would occur?
HR will go up and strength of contraction will go down
What neurotransmitter does the postganglionic neurons of the SNS and the Parasympathetic neurons release?
SNS— NE
Parasymp— ACh
How does the interaction of the SNS and paraysmp. Systems work?
They inhibit each other (think about brake and gas pedal, do not want to push on both at same time)
What is the intrinsic rate of the SA when there is no neural influence?
100-110 bpm
T/F. Indirect effect of cardiac cells accounts for most of the SNS effect.
False. Direct innervation of cardiac cells accounts for most of the SNS effect
Which system is NE acting on beta-1 receptors an example of?
Sympathetic nervous system
What would indirect effects of SNS on the heart be?
Due to circulating catecholamines (Epi and NE) released primarily from the adrenal medulla (blood borne), which would find their way to cardiac beta-1 receptors
SNS influence on the heart comes from ______ percent Direct innervation, and _____ percent Indirect effects.
85% direct
15% indirect
If a heart is de-innervated, can there still be SNS effect on the heart?
YES, due to the circulating catecholamines (80% epi and 20% NE)
What percent of the circulating catecholamines released primarily from the adrenal medulla is Epinephrine and NE?
Epi = 80% NE = 20%
When the SNS stimulates the left stellate ganglion, what occurs?
- Decreased ventricular fibrillation threshold
- Prolongation of QT interval
(worry about LV in D-Fib)
When the SNS stimulates the right stellate ganglion, what occurs?
- Increased ventricular fibrillation threshold
puts you in more protective position
Is it better to have SNS stimulation of the left or right stellate ganglion?
The right stellate ganglion b/c that will increase ventricular fibrillation threshold, and therefore put you in more protective position
Recall: What nerve controls about 75% of the parasympathetic nervous system?
Vagus Nerve
Left cardiac sympathetic denervation can increase what activity?
Vagus nerve activity —incrase vagal activity has a lot of benefits, like preventing life threatening arrhythmias like D-Fib
(chiro adjustments are shown to help Vagal activity)
What is the Cardioaccelerator reflex?
AKA Brainbridge reflex; stretch on the right atrial wall will stimulate stretch receptors which send signals to medulla oblongata and stimulate SNS outflow of heart
What does the Brainbridge/ Cardioaccelerator reflex prevent?
It prevents damning of blood in the heart and central veins
What is the Benzold-Jarisch reflex? What nerve(s) are involved?
Are baroreceptors in ventricles (stretch receptors detecting pressure)
- Reflex via CN X, to CNS
Where is the site of the majority of the baroreceptors involved in the Benzold-Jarisch reflex?
Inferoposterior wall of LV (supplied by circumflex artery)
*What two things does the Benzold-Jarisch reflex result in? (as in when the baroreceptors are detecting too much pressure)
Reflex effects result in:
- Hypotension
- Bradycardia
What is the Benzold-Jarisch reflex stimulated by?
- occlusion of circumflex artery (inf. wall infarct
- increase in LVP and LV volume (i.e. aortic stenosis)
How do Thyroid hormones influence the heart?
- positive inotropic (increase strength of contraction)
- positive chronotropic (increase HR)
- increase in CO by increase in BMR (basal metabolic rate)
How is the heart affected in hypothyroidism?
BMR decreases; and therefore heart pumps less blood
also get cold, and decrease weight loss
How is the heart affected in hyperthyroidism?
BMR increase; and therefore heart pumps more blood (also get hot, and increases weight loss)
What is the effect on cardiac cells of elevated concn. of K+ in extracellular fluid (ECF)?
- dilation of flaccidity of cardiac muscle at concs. 2-3x normal
- decreases resting membrane potential
The effect that elevated conc. of K+ is associated with what way of death?
ass. with drowning in fresh water
- b/c increase RBC lysis and the RBC’s release K+
What is the effect on cardiac cells of elevated conc. of Ca++ ECF?
spastic contraction
Ca++ binds troponin
What does the effect of an elevated body temp have on our Heart Rate?
HR increases about 10 beats for every degree F elevation in body temp.
What does the effect of elevated body temp have on the heart’s contractile strength?
Contractile strength will increase TEMPORARILY, but prolonged fever can decrease contractile strength due to exhaustion of metabolic systems
What effect does decreased body temp have on the heart?
will decreased HR and strength
What is the preferred energy substrate for the heart?
fatty acids – 70% preferred
can also use: Glucose, glycerol, lactate, pyruvate, amino acids
Most of the energy the heart utilizes is converted into what? What is the remaining percentage utilized as?
heat; 75%
remaining 25% used for Work
How is the 25% of energy utilized for work by the heart broken down?
Pressurization of blood >99%
Acceleration of blood <1%
What is most of the Work of the heart used as?
Pressurization >99%
potential energy
Pressurization of the blood = _________, where as Acceleration of blood to its ejection velocity = ________.
= potential energy
= kinetic energy
What does pressurization of the blood involve?
moving blood from low pressure to high pressure
(volume pressure work or external work)
–is the majority of the work component, at >99%
What does the acceleration of blood to its ejection velocity involve?
out the aortic and pulmonary valves; accounts fro less than 1% of work component
can increase to 50% with valvular stenosis
What does an EKG measure?
measures potential difference across the surface of the myocardium with respect to time
For an EKG, what is the definition of a lead?
= pair of electrodes (one + and one -)
For an EKG, what is the line connecting the electrodes called??
axis of lead
For an EKG, what is the line perpendicular to axis of lead called?
transition line (this is the weak spot for bipolar limb leads–therefore need the unipolar limb leads)
What is the normal rate of the heart?
60-80 bpm
What is it called when the HR is greater than 100 bmp?
tachycardia
What is it called when the HR is less than 50bpm?
bradycardia
What does the PR interval include?
includes the AV node delay
should be ~ .16 sec
If the PR interval is greater than .20 seconds what does it equal?*
= 1st degree AV block (longer than normal)
If the PR interval is less than .10 seconds, what does this mean?
inadequate delay–> possible accessory conduction pathway from atria to ventricle
What does the P wave represent?
atrial depolarization
What does the QRS complex represent?
ventricular depolarization
What does the T wave represent?
ventricular repolarizaiton
What is normally buried in the QRS complex and doesn’t show up on an EKG?
Atrial repolarization
What does the U wave represent?
repolarization of purkinje system (not always seen)
What is the difference between intervals and segments on an EKG?
intervals = include wave form
segments = on baseline; have no wave form
What it comes to the Leads for an EKG, what does the pair of recording electrodes consist of?
+ electrode = active
- electrode = a reference
What is the direction of the deflection based on for an EKG?
it can be + or -; and it is based on what the active electrode (+) sees relative to the reference electrode (-)
How many leads does a routine EKG consists of?
12 leads:
- 6 frontal plane leads
- 6 chest leads (horizontal/transverse plane)
What type of deflection is it when a wave of depolarization is moving toward the + electrode?
a positive deflection (R wave)
What type of deflection is it when a wave of repolarization is moving toward the + electrode?
negative deflection
What type of deflection is it when a wave of depolarization is moving toward the - electrode?
negative deflection (S wave)
What type of deflection is it when a wave of repolarization is moving toward the - electrode?
positive deflection (T wave)
What plane are the limb leads in for an EKG?
frontal plane
What lane are the chest (V) leads in for an EKG?
view heart in horizontal/transverse plane
What are all the bipolar limb leads and where do they go? (may want to draw the triangle)
Lead I (+LA -RA)
Lead II (+LL -RA)
Lead III (+LL -LA)
What are all the unipolar limb leads (Augmented)?–may want to draw triangle
(assist with/helps/adds to)
AvR (+RA -LA and LL)
AvL (+LA -RA and LL)
AvF (+LL -RA and LA)
Which Unipolar limb lead is perpendicular to Lead I?
Lead II?
Lead III?
Lead I –> AvF (F for foot)
Lead II –> AvL
Lead III –> AvR
If the wave is perpendicular to the axis of the bipolar limb lead, will there be a deflection?
no
Where are the positive electrodes for the Chest leads? Where are the negative electrodes?
Positive electrodes– all on chest wall
Negative electrodes– all limb electrodes hooked together
What does and EKG NOT give us information about?
about the mechanical activity of the heart
- could take a valve out and the EKG would be normal
The analysis of an EKG can tell us what 5 things?
- rate
- rhythm and intervals
- axis
- hypertrophy
- infarction/ischemia
What are the sequence of numbers one can use to count the big boxes b/w R waves to get the estimated HR?
300-150-100-75-60-50
1 1/2 1/3 1/4 1/5 1/6
What on the EKG is the time from SA node to entering the ventricle?
PR interval
What on the EKG includes the AV nodal delay?
PR interval
If a PR interval is greater than .2 seconds, what is that called?
1st degree AV block
If someone has a prolonged QT interval, what are two increased risks they may experience?
- increased incidence of sudden cardiac death
- high propensity to develop ventricular fibrillation
What is a sinus arrhythmia?
an irregular heartbeat that is either too slow or too fast
- longest and shortest RR vary by greater than .16 seconds
Do we want a heart rate that has increased variability or no?
- less the heart is varying = more at risk you are to die
- increase heart rate variability = the better off you are
What is AV block?
Atrioventricular block is a type of heart block where conduction b/w the atria and ventricles of heart is impaired
What is 1st degree AV block?
depolarization wave from atria to ventricle is delayed excessively
- PR interval is greater than .2 seconds
An occasional P wave with no associated QRS complex (a dropped heart beat) describes what?
2nd Degree AV block
- some depolarization wave pass, others blocked
What is a 3rd degree AV block?
ALL depolarization waves from atria to ventricles are blocked
- no relationship b/w P waves and QRS complexes
What is the normal duration of QRS complex?
duration .06-.08 seconds
A QRS complex that is prolonged, greater than .12 seconds is associated with what?
with ventricular hypertrophy or conduction block in purkinje system
What is the Mean Electrical Axis (MEA)?
average direction of ventricular depolarization
How does the ventricle depolarize?
A.D.I.O
- from base (above) to apex (down)
- from endocardium (inside) to epicardium (out)
What is the axis range for a normal heart beat?
between -30 and +105 degrees
What must the QRS of lead I and the AvF must be to be a MEA that is normal?
both are positive
What way will the axis shift if there is a problem such as conduction block or hypertrophy?
axis will shift to the side of the problem
If there is left bundle branch block, how will the axis shift/ what will the deviation be?
a left axis deviation
Hypertrophy may results if the QRS complex is shortened or prolonged?
if it is prolonged to greater than .12 seconds
What can be associated with anything that creates an abnormally high work load on the ventricle chamber?
hypertrophy
What is an example of something that may increase work load on the left ventricle? What can it cause?
Systemic hypertension; will cause hypertrophy of that left ventricle
What supplies the myocardium?
- the coronary arteries and their branches
Cells near the endocardium may be able to receive some oxygen from where?
some oxygen from chamber blood
When is myocardial blood flow limited? Esp. where in the heart?
during cardiac muscle contraction; esp. limits the LV
When does left coronary artery flow peak? When does right coronary artery flow peak?
Left– at onset of diastole
Right– as mid systole
– due to more compression of small blood vessels in wall of LV during systole
At resting HR the myocardium will take maximum oxygen out of the perfusing coronary flow, which is what percentage?
70% extraction rate
How is any increase demand on the heart met?
by increase coronary flow
Normally the ____ cells to depolarize are the ____ cells to repolarize.
first; last
T/F. Depolarization and repolarization waves are in the same directions.
False; they are in opposite directions
The ___ and the ___ wave point in the same direction.
QRS and T wave
What does ischemia prolong? Therefore, what is it delaying?
prolongs depolarization, therefore delays repolarizaiton
What does ischemia cause the depolarization and repolarization waves to do?
What will this cause on an EKG?
go in same direction
will cause an inversion in T wave
If there is an inversion in T wave (opposite deflection compared to QRS), what do we think is occurring to the heart?
ischemia
When an infarction occurs, what do damaged cells lose the ability to do?
repolarize
When does most of the frank damage occur when an infarction occurs?
upon reperfusion and is associated with free radical damage
The damaged area from an infarction is in an abnormal what?
in an abnormal state of depolarizaiton
What occurs when normal myocardium is in a resting polarized state, but there is damage from an infarction on part of the heart?
there is a “current of injury” b/w damaged and normal myocardium
What is created on an EKG when there is a “Current of injury” b/w damaged and normal myocardium?
creates a depressed baseline which appears as an elevated ST segment
When we see a depressed baseline, which is appearing as an elevated ST segment on an EKG, what do we think occurred?
an infarciton, and therefore why there is a “current of injury” b/w damaged and normal myocardium when normal myocardium is in a resting polarized state
What are preferred blood markers to tell if there has been an infarction?
cardiac troponins T and I are preferred markers for myocardial injury
What have the highest sensitivities and specificities for the diagnosis of acute myocardial infarction?
cardiac troponins T and I
Why is troponin used as an elevated marker in a myocardial infarction?
b/c troponin is a contractile protein NOT normally found in serum
- is released ONLY when myocardial necrosis occurs
