Cardio - Physiology Part 2 Flashcards
What type of murmur occurs in late systole after a midsystolic click and is loudest at S2?
Mitral prolapse
In tricuspid stenosis, the murmur gets louder with _____ (inspiration/expiration) due to increased blood flow into the right atrium.
Inspiration
Which murmur is often due to age-related calcification?
Aortic stenosis
What happens during phase 3 of the cardiac myocyte action potential?
Rapid repolarization due to increased permeability to potassium
During phase 4 of the action potential in a ventricular myocyte, to which ion is the membrane highly permeable?
Potassium; as a result, the resting potential of the cell is close to that of potassium
What happens during phase 0 of the cardiac myocyte action potential?
Rapid depolarization due to increased sodium permeability
What happens during phase 1 of the cardiac myocyte action potential?
Initial repolarization due to increased potassium permeability
What happens during phase 2 of the cardiac myocyte action potential?
Electrical plateau due to equivalent calcium influx and potassium efflux
What happens during phase 3 of the cardiac myocyte action potential?
Rapid repolarization due to potassium efflux that returns the cell to a more negative potential
What is the voltage value of the resting potential of a ventricular myocyte?
- 85 mV; the value is maintained by the sodium/potassium pump and high permeability to potassium
How long does the effective refractory period of the cardiac myocyte last?
For the duration of the action potential until the cell returns to resting potential
Cardiac myocytes in which locations have pacemaker action potentials?
The sinoatrial and the atrioventricular nodes
What happens in phase 0 of the pacemaker action potential?
Voltage-gated calcium channels open
The lack of voltage-gated sodium channels in pacemaker cells results in what effect on cardiac conduction?
A slowed conduction velocity through the atrioventricular node to prolong transmission from the atria to the ventricles
As compared with the myocardial action potential, which phases are absent from the pacemaker potential?
Phases 1 and 2
What happens in phase 4 of the cardiac pacemaker action potential?
Slow diastolic depolarization due to increased permeability to sodium ion
During the pacemaker action potential, the slope of which phase determines the heart rate?
Phase 4
How does acetylcholine affect the rate of diastolic depolarization and heart rate?
It decreases the rate of diastolic depolarization (the slope of phase 4 of the action potential) and thus decreases heart rate
What happens in phase 3 of the cardiac pacemaker action potential?
Inactivation of the calcium channels and activation of the potassium channels
Sympathetic stimulation _____ (decreases/increases)the possibility that Ifchannels are open.
Increases; as a result, the pacemaker cell depolarizes more frequently and the heart beats faster
Which ion channels in a pacemaker cell are permeable to sodium?
If channels
On an electrocardiogram, what does the P wave represent?
Atrial depolarization
On an electrocardiogram, what does the PR segment represent? How long is a normal PR interval?
Conduction delay through the atrioventricular node; normally less than 200 msec
On an electrocardiogram, what does the QRS complex represent? What is considered a normal QRS duration?
Ventricular depolarization; normally less than 120 msec
What segment of the electrocardiogram corresponds with the mechanical contraction of the ventricles?
The QT interval
On an electrocardiogram, ventricular repolarization is represented by what?
The T wave
In what part of the electrocardiogram is atrial repolarization?
Atrial repolarization is masked within the QRS complex
On an electrocardiogram, what does the ST segment represent?
The isoelectric state after the ventricles have been depolarized and before repolarization
What do U waves on an electrocardiogram represent?
Hypokalemia or bradycardia
What is the physiologic benefit of the atrioventricular delay?
It allows time for ventricular filling
Define torsades des pointes.
A ventricular tachycardia that is characterized by shifting sinusoidal waves on an electrocardiogram; a literal translation is, “twisting of the points”
What are the most dangerous sequelae of torsades des pointes?
Ventricular fibrillation and death
What is the main risk factor for torsades des pointes?
Prolongation of the QT interval, usually due to drug adverse effects or genetic syndromes
What is the etiology of congenital long QT syndromes?
Most often they are due to defects in sodium or potassium channels
Congenital long QT syndromes can be associated with what other pathology?
Severe congenital sensorineural hearing deficit (Jervell and Lange-Nielsen syndrome)
What is the electrocardiogram finding pathognomonic for Wolff-Parkinson-White syndrome and what does it signify?
A delta wave, which signifies partial early depolarization of the ventricles via an accessory pathway
What is the Bundle of Kent?
An accessory conduction pathway from atria to ventricles, which bypasses the atrioventricular node; occurring in Wolff-Parkinson-White syndrome
In patients with Wolff-Parkinson-White syndrome, what does the delta wave on electrocardiogram represent?
Early depolarization of the ventricle due to the accessory conduction pathway (bundle of Kent), which bypasses the atrioventricular node
Patients with Wolff-Parkinson-White syndrome are at higher risk for which type of arrhythmia?
Supraventricular tachycardia
Which rhythm on electrocardiogram is classically described as having an irregularly irregular pattern with no discrete P waves?
Atrial fibrillation
Which rhythm on electrocardiogram is described as having a “sawtooth” baseline?
Atrial flutter
What is the characteristic electrocardiogram finding of first-degree atrioventricular block?
Prolonged PR interval (> 200 msec) with no lengthening of the interval and no dropped beats
Is first-degree atrioventricular block symptomatic or asymptomatic?
Asymptomatic
What is the dangerous sequela of atrial fibrillation?
Atrial stasis leading to thrombosis, which can embolize and cause stroke
A 67-year-old male presents with an irregularly irregular electrocardiogram tracing at a routine doctor’s visit. Which drug can decrease his risk of stroke? Which drug can control his heart rate?
Warfarin (Coumadin) to prevent thromboembolism and -blockers or calcium channel blockers to control heart rate
A 73-year-old female presents with an electrocardiogram tracing with a “sawtooth” pattern. Which three classes of drugs can be given to treat this condition?
Class IA, IC, or III antiarrhythmics
Which form of second-degree atrioventricular block is more likely to progress to a third-degree block?
Mobitz type II
Does progressive lengthening of the PR interval take place in Mobitz type I, Mobitz type II, or both?
Type I involves progressive lengthening followed by a dropped beat; in type II there are dropped beats without progressive lengthening
Given an electrocardiogram showing second-degree Mobitz type II heart block, how can the arrhythmia be further classified?
By the ratio of P waves to QRS complexes (eg, 2:1 or 3:1)
In what type of heart block do the atria and ventricles beat independently of each other?
Third-degree heart block
An electrocardiogram shows dropped beats that are not preceded by a change in the length of the PR interval. What is the most likely diagnosis?
Second degree atrioventricular block, Mobitz type II
An electrocardiogram shows P waves and QRS complexes that have no temporal relation to each other. The atrial rate is faster than the ventricular rate. What is the most likely diagnosis?
Third degree (complete) atrioventricular block
An electrocardiogram shows no identifiable waves. What is the most likely diagnosis?
Ventricular fibrillation
In third-degree heart block, the atrial rate is _____ (slower/faster) than the ventricular rate.
Faster
A 65-year-old male presents with an electrocardiogram tracing that displays P waves and QRS complexes that occur independently of each other. Which therapeutic intervention would be most appropriate?
Treatment with an implantable pacemaker
An electrocardiogram has an increasing PR interval with each successive beat until a QRS complex does not appear after a P wave. The next beat has a normal PR interval. What is the most likely diagnosis?
Second-degree atrioventricular block, Mobitz type I (Wenckebach)
Which infectious disease can cause third-degree heart block?
Lyme disease
By what two mechanisms is a decrease in mean arterial pressure sensed?
The medullary vasomotor center detects decreased baroreceptor firing; the juxtaglomerular apparatus in the kidney detects decreased renal perfusion
What are the two main regulators that increase mean arterial pressure when it is low?
Increased sympathetic tone and activation of the renin-angiotensin system
By what mechanism does aldosterone increase cardiac output and mean arterial pressure?
Aldosterone works in the kidneys to increase blood volume (and thus cardiac output)
By what mechanism does angiotensin II increase blood pressure?
Angiotensin II causes vasoconstriction
What is atrial natriuretic peptide?
It is released from the atria in response to elevated pressure and causes vascular relaxation and diuresis in the kidneys
Atrial natriuretic peptide _____ (constricts/dilates) efferent renal arterioles, and _____ (constricts/dilates) afferent arterioles.
Constricts; dilates; as a result, glomerular filtration rate is increased
By what mechanism does activation of the renin-angiotensin system cause an increase in mean arterial pressure?
By production of angiotensin II and aldosterone, which cause increased total peripheral resistance and increased blood volume, respectively
By what mechanism does activation of the sympathetic nervous system cause an increase in mean arterial pressure?
By activation of -1 and α-1 receptors, which cause an increase in cardiac output and total peripheral resistance, respectively
By what mechanism does activation of -1 receptors cause an increase in cardiac output?
Activation of -1 receptors causes an increase in heart rate and contractility
By what mechanism does activation of α-1 receptors cause an increase in mean arterial pressure?
α-1 Receptor activation causes venoconstriction, which increases venous return and thus cardiac output; and arterial vasoconstriction, which causes an increase in total peripheral resistance
An 80-year-old woman is in shock in the intensive care unit. The attending physician orders the determination of a pulmonary capillary wedge pressure. What instrument is used to perform this study?
A Swan-Ganz catheter
Pulmonary capillary wedge pressure is a good approximation of the pressure of which chamber?
The left atrium
What is the normal pressure for the right atrium?
<5 mmHg
What is the normal pressure for the right ventricle during systole and diastole?
<25 / <5 mmHg
What is the normal pressure for the pulmonary artery during systole and diastole?
<25 / 10 mmHg
What is the normal pressure for the left atrium?
<12 mmHg
What is the normal pressure for the left ventricle during systole and diastole?
<130 / 10 mmHg
What is the normal pressure for the aorta during systole and diastole?
<130 / 90 mmHg
What is the normal pulmonary capillary wedge pressure?
<12 mmHg
A 75-year-old male with congestive heart failure presents with worsening shortness of breath. On physical exam he has a 3/6 diastolic murmur best heard in the fifth intercostal space in the midclavicular line and crackles in the bases of the lungs. What murmur does he have and what would be the dominant pressure?
This patient has mitral stenosis and one would expect the pulmonary capillary wedge pressure to be greater than the left ventricular diastolic pressure
The pulmonary vasculature is unique in that _____ causes vasoconstriction whereas in other organs it causes vasodilation.
Hypoxia
Which local metabolite(s) govern autoregulation of perfusion of the heart?
Oxygen, adenosine, and nitric oxide
Which local metabolite(s) determine autoregulation of perfusion of the brain?
Carbon dioxide (or pH)
Which factors govern autoregulation of perfusion of the kidneys?
Myogenic and tubuloglomerular feedback
Which local metabolites govern autoregulation of perfusion of the skeletal muscles?
Lactate, adenosine, and potassium
Which factor governs autoregulation of perfusion of the skin?
Sympathetic stimulation
Sympathetic stimulation alters perfusion of the skin to control which aspect of homeostasis?
Temperature control
What is meant by autoregulation of blood flow?
The method by which blood flow to an organ remains constant over a wide range of blood pressures
In the lungs, what is the physiologic advantage of vasoconstriction in response to hypoxia?
The mechanism allows for only well-ventilated areas to remain perfused, optimizing gas exchange
What is the equation for net filtration pressure?
Net filtration pressure = [(capillary pressure - interstitial fluid pressure) - (plasma colloid osmotic pressure - interstitial fluid colloid osmotic pressure)]
The filtration constant for capillary permeability is denoted by what symbol?
Kf
How is net fluid flow calculated?
Net fluid flow = (net filtration pressure) × (filtration constant for capillary permeability)
What would a patient with excess fluid outflow into the interstitium present with?
Swelling (oedema)
Which pressures, when increased, have a tendency to cause fluid to move out of the capillaries and into tissue?
Capillary fluid pressure and interstitial fluid colloid osmotic pressure
Which pressures, when increased, have a tendency to cause fluid to move into the capillaries and out of tissue?
Interstitial fluid pressure and plasma colloid osmotic pressure
An 80-year-old male with a history of right-sided heart failure presents with bilateral ankle oedema. In terms of capillary fluid exchange, what is the mechanism by which he developed his oedema?
Heart failure results in increased capillary pressure, which causes fluid to move out of the capillaries and into the interstitial space
A 55-year-old male with long-standing alcoholic cirrhosis presents with bilateral pedal oedema and ascites. In terms of capillary fluid exchange, what is the mechanism by which he developed his oedema?
Liver failure results in decreased plasma proteins, which decreases plasma colloid oncotic pressure, and in turn causes fluid to move out of the capillaries and into the interstitial space
A 43-year-old female presents with bilateral pitting leg oedema and lab results remarkable for high low-density lipoprotein, low albumin, and proteinuria (likely nephrotic syndrome). In terms of capillary fluid exchange, what is the mechanism by which she developed her oedema?
Nephrotic syndrome results in proteinuria and subsequent hypoalbuminemia, which decreases plasma colloid oncotic pressure, and in turn causes fluid to move out of the capillaries and into the interstitial space
What is the mechanism by which toxins, infections, and burns can cause edema?
Any insults (eg, toxins, infections, or burns) that cause increased capillary permeability can cause an increase in the filtration constant (Kf) and subsequently cause fluid to move out of the capillaries and into the interstitial space
A 50-year-old Ethiopian male presents with severe bilateral leg and scrotal oedema due to Elephantiasis (lymphatic obstruction caused by filarial nematodes). In terms of capillary fluid exchange, what is the mechanism by which he developed his oedema?
Lymphatic obstruction causes increased interstitial fluid colloid osmotic pressure, which causes fluid to move out of the capillaries and into the interstitial space
During what phase of the cardiac myocyte action potential does extracellular calcium enter the cell?
The plateau phase
What is the effect of extracellular calcium entering the cardiac myocyte?
Calcium release from the cardiac muscle sarcoplasmic reticulum (calcium-induced calcium release); and the resulting muscle contraction
The plateau in cardiac muscle action potential is caused by what?
Calcium influx
Which ion channels cause the automaticity of cardiac nodal cells?
If channels cause the cells to spontaneously depolarize
How is cardiac muscle different from skeletal muscle?
Cardiac muscle action potential has a plateau due to calcium ion influx; cardiac nodal cells display automaticity by spontaneously depolarizing; and cardiac mycytes are electrically coupled via gap junctions
The aortic arch receptors transmit impulses to the medulla via which nerve? In response to which stimulus?
Aortic receptor afferents travel via the vagus in response to only high blood pressure
The carotid sinus receptors transmit impulses to the medulla via which nerve? In response to which stimuli?
Carotid sinus receptor afferents travel via the glossopharyngeal nerve in response to both high and low blood pressure
Changes in which two parameters of brain interstitial fluid affect the response of central chemoreceptors?
pH and the partial pressure of carbon dioxide
Central chemoreceptors respond to changes in the pH and the partial pressure of carbon dioxide of the brain interstitial fluid, which in turn are influenced by what?
Arterial carbon dioxide
Are peripheral or central chemoreceptors responsible for the Cushing reaction?
Central chemoreceptors
What is Cushing’s triad?
Cushing’s triad is the triad of hypertension, bradycardia, and respiratory depression in response to ischemia in the brain
Which type of receptors are most important in causing the bodys response to severe haemorrhage?
Baroreceptors
Why does carotid massage cause bradycardia?
Carotid massage causes increased pressure/stretch on the carotid artery, which causes the afferent baroreceptors to fire, which results in a decrease in heart rate
Describe the bodys response after baroreceptors sense hypotension.
Hypotension causes decreased arterial pressure/stretch, which decreases afferent baroreceptor firing, increases efferent sympathetic firing, and decreases efferent parasympathetic stimulation, all of which cause vasoconstriction, increased heart rate, contractility, and blood pressure
What chemical changes of blood elicit a response from peripheral chemoreceptors? How do central chemoreceptors differ?
Low PO2, (< 60 mmHg), high PCO2, and low pH of blood; central chemoreceptors are not sensitive to oxygen
What is Cushings reaction?
The chain reaction that occurs in response to increased intracranial pressure. Increased intracranial pressure leads to arteriolar vasoconstriction, which causes cerebral ischemia, leading to a sympathetic response of hypertension, and ultimately resulting in reflex bradycardia
Which internal organ gets the largest share of the systemic cardiac output?
The liver
Which organ has the highest blood flow per gram of tissue?
The kidney
A 25-year-old athlete begins training for the Olympics. As she runs her standard 3 miles, is the increased oxygen demand of the heart met by increased coronary blood flow or increased extraction of oxygen?
Increased coronary blood flow; the heart always operates with maximal oxygen extraction
Which organ has the greatest arteriovenous oxygen concentration difference and why?
The heart, because oxygen extraction is always approximately 100%
