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Physiology - Cardiovascular > Cardiovascular physiology > Flashcards

Cardiovascular physiology Flashcards

1
Q

How is cardiac output calculated?

A

Stroke volume – approximately 70 mL. This is multiplied by the heart rate to calculate the cardiac output

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2
Q

What is required to create flow of a fluid?

A

A difference in pressure (pressure gradient)

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3
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4
Q

Why does the pressure in the LV change so much between systole and diastole?

A

For the LV to fill during diastole, the pressure must be slightly lower than that in the LA. To empty during systole, it must be greater than aortic pressure.

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5
Q

Why is the systolic pressure in the RV so much lower than the LV?

A

The pulmonary circulation has a much lower resistance than the systemic circulation, and so the pressure needed to perfuse it is smaller.

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6
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7
Q

Why is the biggest pressure drop in the arterioles?

A

“Their small radius produces a high resistance. Resistance is inversely proportional to the fourth power of the radius.

The pressure in the veins is low, but they hold a large proportion of the circulating blood volume: the capacitance vessels.

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8
Q

When is the volume of blood in the veins reduced?

A

In hypovolaemia, when the body’s responses lead to vasoconstriction, particularly in the skin/gut with most of the blood kept in the central circulation to perfuse the vital organs.

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9
Q

In which phase of the cardiac cycle does most of the coronary blood flow to the LV occur?

A

Diastole, when the LV is relaxed.

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10
Q

What change lowers the proportion of time spent in diastole, thus reducing the time for LV perfusion?

A

An increase in heart rate.

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11
Q

How does the anatomy of the coronary arteries help maintain perfusion?

A

They run on the outside of the heart initially, and are not compressed by LV contraction during this part of their course.

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12
Q

What activates the carotid sinus baroreceptors?

A

Stretch produced by a rise in blood pressure.

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13
Q

Where is angiotensin I converted to angiotension II?

A

The lung.

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14
Q

What measurements might be useful to identify hypovolaemia?

A

“Blood pressure, heart rate, capillaryrefill

Urine output, respiratory rate, central venous pressure (CVP).”

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15
Q

Why would tetanic contraction be so harmful in heart muscle?

A

The heart would be unable to relax to allow filling.

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16
Q

How much longer is the cardiac action potential than that of a nerve cell?

A

200 times (300 ms vs 1-2 ms)

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17
Q

What is the natural firing rate of the SA node?

A

100-120/min. The heart rate is normally slower because of dominant vagal parasympathetic activity.

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18
Q

What are the advantages of delayed conduction at the AV node?

A

“It allows time for atrial emptying and protects the ventricles from atrial tachyarrhythmias.

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19
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23
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24
Q

What is the normal cardiac output at rest?

A

Around 5 L/min (stroke volume 70 mL x rate 70/min)

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25
Q

How is an increase in cardiac output brought about?

A

By an increase in both heart rate and stroke volume, driven mainly by the sympathetic nervous system.

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44
Q

Can you think of any pathological conditions where EDPVR curve shifts up and to the left?

A

Pathological conditions which cause ventricular diastolic dysfunction such as ischaemia and ventricular hypertrophy shift the EDPVR curve up and to the left.

45
Q

an you think of any pathological conditions where the ESPVR curve shifts upwards and to the left?

A

Sympathetic stimulation and use of positive inotropic drugs will shift the ESPVR curve upwards and to the left.

46
Q

Can you think of any pathological conditions where the ESPVR curve shifts downwards and to the right?

A

Negative inotropic drugs (β blockers) and inhalational anaesthetic agents will shift the ESPVR curve downwards and to the right.

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49
Q

“Which drug is commonly used in septic patients to correct excessive vasodilatation i.e. decreased afterload?

”

A

Noradrenaline. In septic patients excessive systemic vasodilatation (decreased SVR) lowers the blood pressure despite normal or even high CO. The lower blood pressure means lower perfusion pressure and inadequate supply of oxygen and nutrients to the peripheral tissue. When used in appropriate doses noradrenaline will raise the SVR and hence the BP.

50
Q

Can you think how atropine changes the heart rate?

A

Atropine is an parasympatholytic (anticholinergic) drug which inhibit the effect of parasympathetic tone on heart while sympathetic effect remains intact (in other words it is chemical denervation of parasympathetic nerve supply only). A completely denervated heart beats at a rate of more than 100/min, parasympathetic block with atropine would produce a much higher rate in an otherwise normal heart due to unopposed sympathetic activity.

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55
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What is the somatosympathetic reflex?

A

The somatosympathetic reflex is the pressor response to stimulation of somatic afferents.

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57
Q

Does orthostasis, the adoption of an upright position, present any challenge to the circulation?

A

Yes, orthostasis presents a serious challenge to the circulation.
After standing up abruptly, the initial blood pressure drop is quickly restored by neuroendocrine reflexes.

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Physiology - Cardiovascular (8 decks)

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