Some short essay questions on CVS physiology with their answers by Dr Khaled A Abulfadle

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Define: Bainbridge effect and reflex

Bainbridge effect: increased HR secondary to distension of right atrium by increased VR which stimulates directly SA node to increase its rate of discharge i.e. it is a local effect not reflex

Bainbridge reflex: reflex increased HR (tachycardia) secondary to increase in right atrial pressure

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Admin عدد المساهمات : 9680 تاريخ التسجيل : 06/08/2009

Define Frank-Starling's law

Frank-Starling's law
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within certain limits, increased VR (preload or EDV) increases initial cardiac muscle length with resulting increased cardiac contractility

Smile

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Define Stroke volume and mention factors affecting it

Stroke volume (SV):

Definition: volume of blood pumped by each ventricle per beat.
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Factors controlling stroke volume:
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1-Preload (VR, EDV): direct relation with stroke volume (Frank-Starling's law).

2-Contractility of cardiac muscle (load): direct relation with stroke volume.

3-Afterload (systemic pressure): inverse relation with stroke volume i.e. increasing systemic pressure (as in the case of high blood pressure), increases the strain on the heart muscle and decreases stroke volume.

4-Chronic exercise training will increase an individual's stroke volume both at rest and during exercise. By slowing down the heart rate, the ventricles have more time to fill with blood, thereby increasing preload and leading to greater stroke volume.

5-Sympathetic stimulation increases cardiac contractility and stroke volume.

6-Blood volume: its increase will increase VR with increased stroke volume.

7-End systolic volume (ESV): inverse relation with stroke volume (as SV= EDV-ESV).

8-HR: marked increase in HR decreases ventricular filling and SV.

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Outline cardiac events occurring in the cardiac cycle?

Answer

[ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذه الصورة]

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Question

In mitral stenosis, the murmur occur corresponding which phase in cardiac cycle

Answer

During rapid and reduced ventricular filling phases and also can occur during atrial systole phase of the cardiac cycle

Explanation: as blood during these phases should pass through mitral valve from left atrium to left ventricle and as the mitral valve in this condition is stenosed, thus, turbid blood flow occurs causing a diastoled cardiac murmur

..

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Question:

What is the effect of diurnal variations on blood pressure

Answer:

Blood pressure varies across the day being highest in the morning and lower towards evening and this is called the "diurnal variation." Some decrease should occur during sleep

the cause of being increased in the morning:

1-on standing from lying down, there release of some catecholamines which increase ABP
2-thinking of what should be done after awaking up causes sympathetic stimulation which increases ABP

pale

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Question:

What is the cause of murmur in acute rheumatic fever

Answer:

:

At 1st functional murmurs due to hyperdynamic circulation 2ry to fever

THEN, organic murmurs, 2ry to acute rheumatic carditis and the most common murmurs of which are those due to mitral and aortic regurgitation caused by valvular inflammation

flower

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Question

Calculate the duration of cardiac cycle when heart rate is 60 beat per minute

Answer

sixty beat per sixty sec (1min), so, each beat (cycle) duration will be 60/60= 1sec

flower

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Q: Outline
1-Baroreceptor mechanism in regulation of blood pressure
2-Chemoreceptor mechanism in regulation of respiration
====
A:

homeostatic system is formed of stimulus, receptor, center and response, thus:

1-Baroreceptor mechanism in regulation of blood pressure:
Stimulus: increased arterial blood pressure.
Receptor: baroreceptors ( receptors in carotid sinus and aortic arch respond to change in arterial blood pressure).
Center: cardiovascular centers in brainstem.
Response: decreased heart rate and vasodilatation to decrease arterial blood pressure towards normal.

2-Chemoreceptor mechanism in regulation of respiration:
Stimulus: decreased arterial O2 and increased arterial CO2.
Receptor: chemoreceptors ( receptors in carotid and aortic bodies respond to change in arterial O2 and CO2 concentrations).
Center: respiratory centers in brainstem.
Response: increased respiratory rate to increase O2 and decrease CO2 towards normal.

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Q:

During measurement of BP:

1. Why do we tie the BP cuff at the level of the heart?

2. Palpatory method is used only to measure systolic BP, why not diastolic BP?

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A:

Regarding blood pressure examination:

1-We tie the BP cuff at the level of the heart to reflect the exact arterial blood pressure at the heart level as If the arm (or cuff) is lower than the heart, an erroneously high pressure will be recorded and if higher than the heart, the pressure will be erroneously low (refer to effect of gravity on BP).

2-Palpatory method is used as a rough preliminary estimation of systolic blood pressure to be confirmed by the auscultatory method to avoid the auscultatory gap, although some studies recently done to evaluate effect of palpatory method on measuring diastolic blood pressure which has some limitations as shivering, tremor, severe obesity, and moderate to severe hypotension. Shivering and tremor causes mechanical interference in measurement. In severe obese thick subcutaneous fat probably prevent thrill to transmit to surface. Elderly patient have very thin subcutaneous fat, which leads to continuous palpation of pulse throughout measurement and pose difficulty to identify thrill in pulse. Also, palpatory method need more experience and clinical sense. The final result is that in some conditions we may be obligated to estimate diastolic blood pressure using palpatory method as if stethoscope is not present, but, still estimation of systolic blood pressure by palpation (absence of pulse while increasing pressure in cuff and its reappearance with deflation) is more easy and standard than for diastolic blood pressure (absence or weakening of pulse during deflation).

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Why there is bradycardia with typhoid fever?

Answer

Typhoid fever is caused by a bacteria that produce a powerful endotoxin responsible for the clinical manifestations.the endotoxin produce myocarditis as a clinical feature.when the cardiac muscle is inflamed by the toxin, autorythmic cells cannot escape inflammation.because SA node and other related structures determine the pace of the heart, the cause of relative bradycardia is inflammation of the myocardium with the autorythmic cells .

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Q: Why in AV nodal rhythm p wave is inverted
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A: When AV node is the pacemaker of the heart, the direction of atrial depolarization wave will be away from the recording electrode at V5, and according to dipole law, a negative P wave will be recorded

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Question
Fetal hearts use glucose as their primary metabolic substrate. Adult hearts use free fatty acids, which are less efficient (require more O2 to synthesize the same amount of ATP); however, during cardiac failure, the heart can switch to glucose utilization. Why doesn't it just use glucose all the time?
========
Answer
Lipids require more oxygen to burn, but also they are cheaper to store (since they have great calorific power than carbohydrates and they're hydrophobic, thus not requiring water for their storage). The body can store so much lipids that it becomes an almost everlasting energy source (A normal adult have enough energy stored as fat to allow basal metabolism for weeks to months), which cannot apply to glucose. If fat is not present, glucose would have vanished from the body long time ago. Glucose levels must be maintained at a certain level, because it's the main energy source for the brain (which cannot use lipids).

For all the previous reasons, the heart (and many other organs, like the liver) uses fat while possible. If possible just means when not starving to death and with sufficient oxygen supply. This second condition doesn't apply to heart failure. In this case, oxygen supply fails and the tissue switch to glucose just because they can use it without oxygen (glycolysis and lactic fermentation).

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Q: Mean systemic filling pressure

Answer
Mean systemic pressure (mean systemic filling pressure (MSFP), or mean circulatory filling pressure, MCFP
================================
=is defined as the mean pressure that exists in the circulatory system when the blood has had a chance to redistribute evenly to all vessels and organs.
=MSFP is approximately 7 mm of Hg.
=It is an indicator of how full the circulatory system is
=It is influenced by the volume of circulating blood and the smooth muscle tone in the walls of the venous system (which determines the capacity of the system).
=MSFP is measured after clamping the aortic root and the great veins at point of entry to right atrium.
=It increases if there is an increase in blood volume or if there is a decrease in venous compliance (where blood is shifted from the veins to the arteries).

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Q: Ventricular escape beat

A: -A ventricular escape beat is a self-generated electrical discharge initiated by, and causing contraction of, the ventricles of the heart.
-Normally the heart rhythm is begun in the atria of the heart and is subsequently transmitted to the ventricles.
-The ventricular escape beat follows a long pause in ventricular rhythm and acts to prevent cardiac arrest.
-It indicates a failure of the electrical conduction system of the heart to stimulate the ventricles (which would lead to the absence of heartbeats, unless ventricular escape beats occur).

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Question
Discuss ventricular stretch reflex

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Answer

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Q: Mary's law
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A: Mary's law
In 1859, a French scientist Étienne-Jules Marey noticed that when at rest a person's pulse rate is inversely proportional to blood pressure. Or in other words, the slower the heart beats, the higher the blood pressure is..

It is important to note that the dependent variable in this equation is the blood pressure. Assuming that everything else is normal, and the person is not exercising, unhealthy, or stressed, his blood pressure will determine the rate at which hisheart beats.

This effect comes about because the body responds to lowered blood pressure, in the short term, by increasing the heart rate. Conversely, when blood pressure is too high, the heart will slow.

This 'law' does not apply in all conditions; for example, during exercise heart rate will increase (to supply oxygen to the working muscles), but diastolic blood pressure will remain approximately the same (because blood vessels in the working muscles dilate to accept more blood flow). A more technical counterexample is the Bainbridge reflex, when an increase in right atrial pressure results in an increased heart rate.

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Q: Explain why hyperkalemia decreases cardiac contractility
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Answer: Potassium and Cardiac Function
===================
The contraction of the heart involves electrical currents. The contraction of cardiac muscle fibers requires calcium. The release of calcium from internal stores is controlled by changes in the electrical charge within the cell. Because potassium plays a pivotal role in maintaining this electrical charge, fluctuations in potassium levels can disrupt calcium release within the heart, disrupting the timing and rhythm of cardiac muscle contractions needed for the heart to pump blood efficiently throughout the body.

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Question
How negative interstitial hydrostatic pressure is considered as a safety factor against edema formation
===
Answer

when the intersttial hydrostatic pressure is negative it acts as a safety factor against edema as
there will be a low compliance of interstitium decreasing the incidence of edema formation, but if it becomes positive the
compliance will increase facilitating edema formation

[ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذه الصورة]

in normal tissues with negative interstitial fluid pressure, virtually all the fluid in the interstitium is in gel form. That is, the fluid is bound in a proteoglycan meshwork so that there are virtually no "free" fluid spaces larger than a few hundredths of a micrometer in diameter. The importance of the gel is that it prevents fluid from flowing easily through the tissues because of impediment from the "brush pile" of trillions of proteoglycan filaments. Also, when the interstitial fluid pressure falls to very negative values, the gel does not contract greatly because the meshwork of proteoglycan filaments offers an elastic resistance to compression. In the negative fluid pressure range, the interstitial fluid volume does not change greatly, regardless of whether the degree of suction is only a few millimeters of mercury negative pressure or 10 to 20 mm Hg negative pressure. In other words, the compliance of the tissues is very low in the negative pressure range

in other words

low compliance of the interstitium when interstitial fluid pressure is in the negative pressure range,
-compliance of the tissues, defined as the change in volume per millimeter of mercury pressure change,
.
-it is low as long as the interstitial fluid hydrostatic pressure is in the negative pressure range
.
-normally the interstitial fluid hydrostatic pressure is -3, so it must increase by 3 mm Hg before large amounts of fluid will begin to accumulate in the tissues

in other words

in the negative pressure range, there is low compliance of the interstitium i.e. small increases in interstitial fluid volume cause relatively large increases in interstitial fluid hydrostatic pressure, opposing further filtration of fluid into the tissues i.e. prevents edema

when interstitial fluid pressure rises to the positive pressure range, there is a tremendous accumulation of free fluid in the tissues. In this pressure range, the tissues are compliant, allowing large amounts of fluid to accumulate with relatively small additional increases in interstitial fluid hydrostatic pressure.

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Q: What is the difference between left ventricular hypertrophy and enlargement?
===
A:

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Why are arterioles known as resistance vessels?

Arterioles have a larger cross-sectional area than the aorta, but they also have a higher resistance because the diameter of the arterioles (and hence the radius) is way smaller.

The cross-sectional area increase in the arterioles is not enough to make up for the increase in resistance going from aorta to arterioles.

This is different in capillaries since their total cross-sectional area is huge, and the change in resistance is smaller since the change in diameter going from arterioles to capillaries is smaller compared to going from aorta to arterioles.

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Q: Mention actions of atrial natriuretic peptide

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