Hemodynamics

Question 1

Edematous fluid in pitting edema typically arises from. . .

Answer 1

. . . the arterial system via changes in Starling forces.

Question 2

The balance of oncotic and osmotic pressures that work to keep fluid in the venous system

Answer 2

Interstitial space may pull some fluid out of the veins due to osmotic pressure differentials (higher osmotic pressure in the veins). When this happens, not only is the hydrostatic pressure of the vein reduced, but the albumin in the venous blood becomes more concentrated, along with all of its other solutes. This increases the oncotic pressure of the vein, forcing fluid back in.

This constant tug-of-war on fluid results in an equilibrium where most of the fluid is in the vein at any given moment.

Question 3

What are some common causes of edema?

Answer 3

Increased hydrostatic pressure in the venous system, resulting from obstruction or heart defects.

Decreased oncotic force from reduced blood solute concentration. Albumin deficiencies may be caused by malnutrition, blood loss, or catabolic processes in the body taking up albumin as a resource.

Question 4

Intravascular volume depletion

Answer 4

There is not enough volume in the circulatory system to maintain adequate blood pressure for optimal organ function.

Question 5

Pressure cutoff for hypertension

Answer 5

a diastolic pressure consistently ≥90 mm Hg or a systolic pressure ≥140 mm Hg establishes the diagnosis of hypertension

Question 6

Recent evidence suggests that ___ more accurately predicts cardiovascular complications

Answer 6

Recent evidence suggests that systolic pressure more accurately predicts cardiovascular complications

Question 7

Blood pressure vs age (stratified by anatomical sex)

Answer 7

Question 8

Mechanisms for regulating systemic blood pressure (diagram)

Answer 8

Question 9

No matter how high the CO or TPR, ___ has the capacity to completely return blood pressure to normal by ___

Answer 9

No matter how high the CO or TPR, renal excretion has the capacity to completely return blood pressure to normal by reducing intravascular volume

Question 10

pressure natriuresis

Answer 10

In the presence of normally functioning kidneys, an increase in blood pressure leads to augmented urine volume and sodium excretion, which then returns the blood pressure back to normal.

Question 11

baroreceptor reflex

Answer 11

Mediated by receptors in the walls of the aortic arch and the carotid sinuses. If the arterial pressure rises, the baroreceptors are stimulated, relaying the signal to the medulla. Negative feedback signals are then sent back to the circulation, inhibiting sympathetic nervous system outflowandexciting parasympathetic effects.

The net result is (1) vasodilation and (2) reduction in CO

Question 12

Baroreceptor signals from the carotid sinus receptors are carried by . . .

Answer 12

the glossopharyngeal nerve (cranial nerve IX)

Question 13

Baroreceptor signals from the aortic arch receptors are carried by . . .

Answer 13

the vagus nerve (cranial nerve X)

Question 14

Short-term blood pressure adaptation is mediated by ____. Long-term blood pressure adaptation is mediated by ____.

Answer 14

Short-term blood pressure adaptation is mediated by the baroreceptor reflex. Long-term blood pressure adaptation is mediated by kidney regulation and cardiomyocyte proliferation.

Question 15

Why aren’t baroreceptors good for long-term blood pressure adaptation?

Answer 15

The reason for this is that the baroreceptors constantly reset themselves. After a day or two of exposure to higher-than-baseline pressures, the baroreceptor-firing rate slows back to its control value.

Question 16

essential hypertension

Answer 16

Approximately 90% of hypertensive patients have blood pressures that are elevated for no readily definable reason. This is the diagnosis they receive.

The diagnosis of EH is one of exclusion. Heredity appears to play an important role, but good genetic markers have not been identified.

Question 17

Negative chronotropic effect

Answer 17

Effect of decreasing the heart rate

Question 18

The lusitropic effect

Answer 18

Downstream of beta-1 signaling and cAMP, PKA phosphorylates and inactivates phospholamban, increasing the activity of the SERCA pump.

This, in turn, speeds up the rate of calcium re-uptake, reducing the time of systole and increasing compliance of the ventricle.

Question 19

Concentric hypertrophy

Answer 19

The type of cardiac wall thickening you see as a result of increased pressure in the ventricles. Results from the adding of additional muscle fibres to the ventricular wall, which aid in doing pressure work (high pressure with low or normal volume).

Question 20

Eccentric hypertrophy

Answer 20

Type of hypertrophy in which, rather than thickening of the ventricular wall, the ventricular radius increases. This type of hypertrophy is a response to mitral regurgitation, and aids in doing volume work (high stroke volume with low or normal pressure).

Question 21

Hypertrophy becomes maladaptive when. . .

Answer 21

. . . cellular structural changes of hypertrophy result in mismanaging calcium. In short, an over-hypertrophied heart eventually becomes energy inefficient. Other pathological changes include:

• Diastolic filling is impaired
• Capillarity is decreased
• Shift towards apoptosis
• Increase in arrhythmia frequency (partially related to the above, manifestation of interference in conduction system)
• Increased susceptibility to ischemia-reperfusion injury

Question 22

Heart failure on a Starling plot

Answer 22

Question 23

Capillarity

Answer 23

of blood vessels / # of cardiomyocytes

If muscle is proliferating and hypertrophying faster than the endothelium can grow to supply it, risk of ischemia greatly increases.

Question 24

Both ___ and ___ increase cardiac contractility.

Answer 24

Both epinephrine and norepinephrine increase cardiac contractility.

Question 25

If you wanted to increase the cardiac contractility of a patient under general anestesia for an operation, what are you probably going to use?

Answer 25

digoxin (a classical positive inotrope)

Question 26

Consequences of increased contractility

Answer 26

1. Increased ejection fraction
2. Increased stroke volume

Question 27

Indicator dilution method of measuring cardiac output

Answer 27

Put a catheter in and deliver indicator in the right atrium, then remeasure in the pulmonary artery. Typically cooled saline is used for this, and temperature is measured via IR light to visualize (thermodilution).

Question 28

Fick method for measuring cardiac output

Answer 28

Measure 1) the pulmonary arterial ppO2, 2) the venous ppO2, and 3) the oxygen consumed by the individual over the period of time.

Question 29

Normal ejection fraction range

Answer 29

55-70%

Question 30

Ejection fraction may be measured by. . .

Answer 30

• echocardiography
• radionucleotide ventriculography

Question 31

Blood pressure ‘set point’

Answer 31

Point to which blood pressure will return from minute-to-minute variations. Mediated by baroreceptor reflex.

Question 32

Which baroreceptors are functionally more important in humans?

Answer 32

The carotid

Question 33

Outputs via which the CNS responds to baroreceptor signals

Answer 33

1. Heart rate
2. Stroke volume
3. Systemic vascular resistance

Question 34

Arginine vasopressin (aka antidiuretic hormone / ADH)

Answer 34

Brain hormone synthesized in the supraoptic and paraventricular neurons in the hypothalamus. Travels down the hypothalamic-pituitary axis and is released from the posterior pituitary.

Major regulator of vascular tone, maintaining it at a certain level (positive effect). Also regulates kidneys via vasopressin receptors (V2R) in the kidney collecting ducts, resulting in AQP2 insertion and water re-uptake.

Question 35

Baroreceptors and vasopressin

Answer 35

Under normal conditions, the cardiovascular control center inhibits production and release of vasopressin in the hypothalamus, keeping levels low.

An acute fall in blood pressure results in interruption of this inhibition, increasing vasopressin levels. It then increases blood pressure by 1) increasing SVR and 2) increasing intravascular volume.

Question 36

Renin-angiotensin-aldosterone system

Answer 36

Renin is released by the kidney, and converts angiotensinogen to angiotensin I. Angiotensin I is converted to angiotensin II by angiotensin converting enzyme (ACE). Angiotensin II is a powerful vasoconstrictor, and also promotes aldosterone synthesis by adrenal cortex. Aldosterone acts on mineralocorticoid receptors in kidney tubules, increasing Na and water reuptake (raising intravascular volume).

Question 37

Baroreceptors and the renin-angiotensin-aldosterone axis

Answer 37

If blood pressure falls abruptly, baroreceptors mediate increase in sympathetic tone. SNS stimulation of the kidney results in renin production, feeding into the axis. This restores blood pressure in two ways: 1) vasoconstriction from angiotensin II, and 2) increase in intravascular volume from aldosterone.

Question 38

Baroreceptor-independent renin release

Answer 38

The glomerulus also contains its own form of pressure sensor, independent of the CNS-coupled receptors. This is important for maintaining kidney function, as kidneys must adjust renal arterioles in series to regulate pressure and achieve filtration. These sensors may pick up a decreased blood pressure and increase renin production independent of the CNS.

Question 39

The vasoconstrictive properties of angiotensin II and vasopressin respond within ___ to a change in blood pressure.

Answer 39

The vasoconstrictive properties of angiotensin II and vasopressin respond within minutes to hours to a change in blood pressure.

So, not a rapid as the CNS’s system, but not chronic by any means.

Question 40

Effective arterial blood volume

Answer 40

The volume perceived by the body’s baroreceptors to be arterial. May be low even when the total vascular volume is high, as with patients with cardiac failure. If the heart isn’t working well, blood will be trapped in the venous system.

This is a problem the kidneys can’t solve, since the intravascular volume is fine, and adding more fluid will just result in increased edema (for the most part). But, the kidneys have no way of knowing this, and so they increase water retention anyway.

Question 41

Natriuretic peptides produced in the heart

Answer 41

Peptide hormones produced in the heart in response to high blood pressure (measured as chronic atrial stretching). Include atrial natriuretic peptide and B-type natriuretic peptide. Act on the kidney to increase salt and water elimination, reducing intravascular volume.

ANP also inhibits the renin-angiotensin-aldosterone axis and vasodilates.

Question 42

Endothelins

Answer 42

Synthesized by mural cells. Act at ET_AR on vascular smooth muscle to potently vasoconstrict. Can also act in the CNS to increase arterial pressure and vasopressin secretion.

Can also act at ET_BR on endothelial cell membranes, causing eNOS stimulation and NO-mediated vasodilation.

Question 43

BP in supine position

Answer 43

Body does not have to work against gravity to return blood from the legs to the heart.

Question 44

Lying/sitting down to standing BP response

Answer 44

Blood initially pools more in the legs and abdomen, causing decreased venous return and thus blood pressure drop. This is called orthostatic hypotension when it is pathologically large, clinically greater than a 10 mmHg drop in pressure.

Question 45

BP measured while standing is always ___ than BP taken supine or sitting.

Answer 45

BP measured while standing is always lower than BP taken supine or sitting.

Question 46

You’re on an airplane and a woman a few rows in front of you develops chest pressure (“this is my angina”). She tells you she has a history of CAD and high blood pressure, but she has missed all of her meds for the last few days because of her travel. You check her blood pressure and it is 190/110 mm Hg and her pulse is 98 bpm. The flight attendant gives you the airplane first aid kit; what would you give right now?

Answer 46

Nitroglycerin and metoprolol

Nitroglycerin will widen the coronary arteries, metoprolol will decrease the oxygen demand by lowering heart rate and contractility.

Question 47

As cardiac output increases, pulmonary artery pressure. . .

Answer 47

. . . doesn’t change very much. It increases a bit, but not by as much as one might expect if the tubes were rigid. This is because pulmonary vessels have a greater compliance than most, so the pulmonary vessels are expanding. Intuitively, if the work being done on the fluid is greater and the pressure isn’t changing much, we can infer that the velocity is going up much more.

Question 48

Phenylephrine

Answer 48

α1 agonist. Used clinically to constrict blood vessels in the periphery, increasing SVR / afterload. This is one way to raise blood pressure and to shift the Starling curve down.

Question 49

Agents that increase contractility

Answer 49

Catecholamines and β1 agonists

Question 50

Effects of afterload on the starling curve

Answer 50

Shifts the Starling curve down.

Question 51

During exercise, the systemic vascular resistance. . .

Answer 51

Might go up or down. If the individual is very warm, then thermoregulatory dilation will have a powerful effect on decreasing resistance. β2 activity opens up vessels to skeletal muscle, while α1 activity constricts vessels to the enteric system.