CVS Physiology

         Because the extraction of oxygen is almost maximal under resting conditions, increased oxygen delivery to the tissue can be accomplished only by an increased blood flow.

·         (A-V) difference is degree of O2 extraction.

·         Ki channels are open at rest in ventricle. They close when depolarization starts. Also remember ungated K+ channels are always open.

·         In SA node, Although the concept is still somewhat controversial, it is generally held that phase 4 is associated with a decreasing potassium conductance, which increases excitability.

Phase 0 is mainly a slow channel or calcium spike rather than a fast channel or sodium spike.

Effectof Sympathetics on SAN

The slope of the prepotential increases, threshold is reached sooner, and the intrinsic firing rate increases (via increased calcium conductance of nodal fibers).

Effect of Parasympathetics on SAN

Hyperpolarize the cell via increasing potassium conductance. Thus, it takes longer to reach threshold, and the intrinsic firing rate decreases.

There may also be a decrease in the slope of the prepotential.

·         Contactility affects SYSTOLIC interval, HR affects DIASTOLIC interval.

·         Cardiac Function Curve:

A cardiac function curve is generated by keeping contractility constant and following ventricular performance as preload increases. Thus:

1. All points on a ventricular function curve have the same contractility.
2. All curves will have an ascending limb, a peak point, and possibly a descending limb.
3. The pericardium normally prevents the large increases in preload necessary to reach the peak of a cardiac function curve.

·         EDV = Preload

ESV = 1/ contractility

·         Preload has little effect on EF. Contractility has major role to change EF.

·          

·         Left side of the heart is higher pressure and higher resistance

o   Will always close first

o   Always open second

§  Mitral Valve/AorticValve

·         Right side of the heart is under lower pressure

o   Will always close 2^nd

o   Open 1^st

·         Heart sounds are never made by valve OPENING → Sounds are primarily made by valves CLOSING

Ejection Click is a sound made by the “tight valve” at systole → High Pressure

o   Aortic Stenosis

o   Pulmonary Stenosis

Opening snap – when the valve is forced open during DIASTOLE

o   Mitral stenosis

o   Tricuspis stenosis

Mid-systolic click è Mital valve regurgitation (prolapse)

·         Raise BP by ­SV, ­HR, ­ TPR and viceversa

§  HTN in blacks and hispanics is SV probelm

·         treat with diuretics

§  HTN in white male is caused by ­HR (stressed)

·         Treatment è b-blocker

§  HTN in white female is caused by ­TPR

·         stress, smokes and drinks to vasocontric

·         Treatment è vasodialation

·         The work required to eject the blood is called the stroke work.

The stroke work is the product of mean left ventricular systolic pressure and stroke volume:

Stroke work = MLVSP  x SV

·         Preload is defined as the  sarcomere length at the end of diastole. The parameter most directly related  to sarcomere length during this time period is left ventricular end-diastolic volume. Although blood volume, central venous pressure, pulmonary capillary wedge pressure, and left ventricular end-diastolic pressure can all  influence preload, they all exert their influence through changes in enddiastolic volume. Each of these parameters could change without altering  preload.

·         The afterload is the force  that the sarcomeres must overcome in order to shorten during systole.  According to the law of Laplace, this force is proportional to the pressure (P) and radius (r) of the ventricle during ejection (force ∝ P × r). The mean left  ventricular systolic pressure would therefore be the best index of afterload.  Although total peripheral resistance can influence afterload by causing changes in mean arterial blood pressure, these factors can only influence  afterload by causing a change in ventricular pressure. Pulmonary capillary  wedge pressure and left ventricular end-diastolic pressure are estimates of the volume of blood in the ventricle during diastole and are indices of preload.

·         Blood flow through the coronary vessels of the left ventricle is determined by the ratio of perfusion pressure to vascular resistance. The perfusion pressure is directly related to the aortic pressure at the ostia of the coronaries. Myocardial vascular resistance is significantly influenced by the contractile activity of the ventricle. During systole, when the ventricle is contracting, vascular resistance increases substantially. Flow is highest just at the beginning of diastole because, during this phase of the cardiac cycle, aortic pressure is still relatively high and vascular resistance is low due to the fact that the coronary vessels are no longer being squeezed by the contracting myocardium.

·   The segments of the circulation are in series with each other.

The organs in the body are in parallel with each other.

·   UPRIGHT POSTURE: Highest pressure in lowest artery.

IN SUPINE: Greatest pressure change in lowest vessel.

·         AUTOREGULATION of BF: (acc to metabolic vasodilator hypothesis) RANGE 50-150mmHg

Cerebral- PaCO2

Cardiac- Adenosine

Exercising muscle- Lactic acid

Kidney & Splanchnic circulation in normal condition.

In exercising, BP in LUNG even remains normal if lungs are normal.

And BP in systemic circulation remains normal.

BF to heart increases due to Adenosine.

·         In early HTN, heart works against increasing resistance and person may feel as AT TOP OF THE WORLD. As ADENOSINE is increased in the heart, it’s just like doing exercise 24x7.

·         Veins are regulated by the parasympathetic system.

·         Arteries are regulated by the sympathetic system.

·         Every organ has RESISTANCE in PARALLEL except…

o   Liver- to allow detoxification

o   Kidney – to allow filtration

§  Pressure in these organs is higher

§  Blood is sitting in “traffic jam”

·         The most important way to regulate flow is through changing the radius

·         The increase in sodium permeability allows sodium to flow into the cell and produces the end-plate potential.

The plateau phase of ventricular muscle action potentials and the upstroke of smooth muscle action potentials are produced by an increase in calcium conductance.

 An increase in potassium conductance is responsible for the downstroke of the action potential.

The refractory period is caused by an increase in potassium conductance and a decrease in the number of sodium channels available to produce an action potential.

·         At birth, two major events cause changes in the fetal circulation. First, loss of the placenta results in increased peripheral resistance and increased systemic arterial pressure. Second, expansion of the lungs allows marked pulmonary vasodilatation, which, by diminishing vascular resistance and promoting pulmonary blood flow, results in elevation of left atrial pressure.

·         Blood flow to the brain remains constant during exercise. To counteract the increased perfusion pressure that occurs during exercise, an autoregulatory process increases vascular resistance in cerebral circulation.

       Blood flow to the kidney is decreased in order to shunt blood to the heart and exercising muscles. Circulating blood volume decreases during exercise because of the increased capillary pressures within the exercising muscles and the accumulation of metabolites in the interstitial spaces which produces an osmotic flow of water out of the capillaries.

·         In many small vessels bloodflow is non-Newtonian and Poiseuilles law is not applicable. 

·         The Adam-Stokes syndrome is a clinical disorder caused by a partial AV-block, with a long P-Q interval and a wide QRS complex in the ECG, suddenly becoming a total bundle block. The condition results in unconsciousness and cramps caused by brain hypoxia and sometimes resulting in universal cramps (grand mal) due to violent activity in the motor cortex. Disease processes in the AV node and the bundle of His elicit the Adam-Stokes syndrome.

·         T lymphocytes in most lymphoid tissue are comprised predominantly of TCRαβ cells, but in the lung and gastrointestinal system, scattered submucosal T lymphocytes have a disproportional high number of TCRγδ cells. These TCRγδ cells appear to be a first line of defense in these environmentally exposed organs.

·         The right ventricle receives less blood than the left ventricle. This is related to the work load each ventricle performed being higher in the left than the right ventricle.

·         The factors that influence wall stress are given by the Laplace relationship (WS = [P × r] ÷ Th), where P equals the transmural pressure across the wall of the ventricle, r, the radius of the ventricle (determined by end-diastolic volume), and Th, the thickness of the ventricular wall.

·         Pulse pressure is proportional to the amount of blood entering the aorta during systole and inversely proportional to aortic compliance

·         Under normal circumstances, circulating blood volume decreases during aerobic exercise.

·         At birth, two major events cause changes in the fetal circulation. First, loss of the placenta results in increased peripheral resistance and increased systemic arterial pressure. Second, expansion of the lungs allows marked pulmonary vasodilatation, which, by diminishing vascular resistance and promoting pulmonary blood flow, results in elevation of left atrial pressure.

·         Guyton curves

A decrease in blood volume or venous tone shifts the vascular function curves to the left; an increase in blood volume or venous tone shifts the vascular function curves to the right.

The cardiac function curves are shifted up and to the left by an increase in contractility and a decrease in afterload; they are shifted down and to the right by a decrease in contractility and an increase in afterload.