MCAT cardiovascular pressure and flow cheat sheet

Blood flow depends on what key principle?

Blood flow (Q) is driven by the pressure gradient (ΔP) and is inversely related to resistance (R): $\displaystyle Q = \\frac{\Delta P}{R}$.

True or False: Blood flow is equal in all vessels.

False. Blood flow varies according to vessel diameter and resistance, especially between arteries and veins.

Fill in the blank: Blood flow increases with __________.

increased pressure and decreased resistance.

What does compliance refer to in blood vessels?

Compliance is the ability of a vessel to expand and contract with pressure changes: $\displaystyle C = \\frac{\Delta V}{\Delta P}$.

Compare arteries and veins regarding pressure.

Arteries have higher pressure (80-120 mmHg) and lower compliance; veins have lower pressure (5-10 mmHg) and higher compliance.

The formula for resistance in a vessel is?

$\displaystyle R = \\frac{8\mu L}{\pi r^4}$, where \displaystyle  is viscosity, $\displaystyle L$ is length, and $\displaystyle r$ is radius.

True or False: Viscosity affects blood flow.

True. Increased viscosity raises resistance, decreasing blood flow.

What drives venous return?

Venous return is driven by pressure gradient, skeletal muscle pump, and respiratory pump.

Cardiac output (CO) formula is?

$\displaystyle CO = HR \times SV$, where HR is heart rate and SV is stroke volume.

List factors affecting stroke volume.

- Preload - Afterload - Contractility

True or False: Increasing afterload decreases cardiac output.

True. Increased afterload makes it harder for the heart to eject blood, reducing stroke volume.

What is the effect of vasodilation on blood flow?

Vasodilation decreases vascular resistance, leading to increased blood flow to tissues.

How does exercise affect cardiac output?

Exercise increases heart rate and stroke volume, significantly boosting cardiac output.

The relationship between flow and pressure in a rigid vessel?

In a rigid vessel, increased pressure results in reduced flow due to fixed volume and resistance.

What does the term 'mean arterial pressure' (MAP) represent?

MAP is the average pressure in a person's arteries during one cardiac cycle: $\displaystyle MAP = DBP + \\frac{1}{3}(SBP - DBP)$.

Cause → Effect: Increased blood viscosity.

Increased viscosity leads to increased resistance and decreased blood flow.

Pressure gradient's role in blood flow?

Blood flows from high pressure to low pressure areas, driven by the pressure gradient.

True or False: Increased resistance decreases blood flow.

True. Increased resistance (e.g., narrowed vessels) leads to reduced flow according to Ohm's law.

What does compliance refer to?

Compliance is the ability of a blood vessel to expand with increasing pressure, affecting volume capacity.

Fill in the blank: Ohm's Law is expressed as _____.

Q = ΔP/R, where Q is flow, ΔP is pressure difference, and R is resistance.

Compare arteries and veins in terms of compliance.

- Arteries: Low compliance, maintain pressure - Veins: High compliance, accommodate volume changes

How does vessel diameter affect flow?

Flow is inversely proportional to resistance; smaller diameters increase resistance, decreasing flow.

Cause → Effect: Increased blood volume.

Increased blood volume leads to increased venous return and elevated stroke volume.

What is vascular resistance dependent on?

Vascular resistance depends on vessel length, diameter, and blood viscosity.

Relationship between blood flow and pressure difference?

Blood flow increases with greater pressure differences, demonstrating direct proportionality.

True or False: Compliance decreases with age.

True. Vascular compliance generally decreases with age, increasing cardiovascular risk.

Formula for total resistance in parallel vessels?

For parallel resistance: $$\\frac{1}{R_{total}} = \\frac{1}{R_1} + \\frac{1}{R_2} + ... + \\frac{1}{R_n}$$

How does autoregulation affect blood flow?

Autoregulation adjusts vascular resistance to maintain consistent blood flow despite pressure changes.

What are the phases of the cardiac cycle?

1. Atrial Systole 2. Ventricular Systole 3. Isovolumetric Relaxation 4. Ventricular Filling

During ventricular systole, what happens to pressure?

Pressure in the ventricles rises significantly, exceeding atrial pressure, causing AV valves to close.

True or False: Atrial pressure is always higher than ventricular pressure during diastole.

False - During ventricular filling, atrial pressure is higher, allowing blood flow into the ventricles.

What occurs during isovolumetric contraction?

All valves are closed; ventricles contract, pressure rises without volume change, preparing for ejection.

The pressure in the right ventricle during systole is approximately _____ mmHg.

25 mmHg, whereas the left ventricle reaches around 120 mmHg.

Cause → Effect: Increased venous return leads to _____ during diastole.

Increased preload, enhancing stroke volume via the Frank-Starling mechanism.

Fill in the blank: The period of rapid ventricular filling occurs during _____ phase.

Early diastole, when AV valves open and blood rushes into ventricles.

Comparison: Atrial vs. Ventricular pressure during systole.

Ventricular pressure > Atrial pressure; this differential ensures blood ejection.

What pressure is required to open the aortic valve?

Aortic valve opens when left ventricular pressure exceeds aortic pressure, approximately 80 mmHg.

During diastole, how is the coronary blood flow affected?

Increases due to lower ventricular pressure, allowing perfusion of the myocardium.

What happens to the heart rate during increased sympathetic stimulation?

Heart rate increases (positive chronotropic effect), speeding up the cardiac cycle.

Formula: Cardiac Output (CO) is calculated as _____?

$\displaystyle CO = SV imes HR$ (Stroke Volume x Heart Rate)

Hypertension effect on the heart?

Increases workload, leading to left ventricular hypertrophy and heart failure.

True or False: Atherosclerosis reduces blood flow due to plaque buildup.

True. Plaque narrows arteries, increasing resistance and decreasing flow.

Compensatory mechanism in heart failure?

- Increased heart rate - Ventricular dilation - Activation of the renin-angiotensin-aldosterone system (RAAS)

What is cardiogenic shock?

A condition where the heart fails to pump sufficiently, leading to inadequate blood flow and tissue perfusion.

Coronary artery disease impact?

Reduces oxygen delivery to heart muscle, causing ischemia and possible myocardial infarction.

Fill in the blank: In heart failure, __________ can lead to fluid accumulation and edema.

Increased venous pressure

Difference between systolic and diastolic heart failure?

Systolic: Reduced ejection fraction; Diastolic: Impaired filling with preserved ejection fraction.

What is the effect of anemia on cardiovascular pressure?

Decreased oxygen-carrying capacity leads to compensatory increase in heart rate and potential heart failure.

Symptoms of pulmonary hypertension?

- Shortness of breath - Fatigue - Chest pain - Syncope

True or False: Valvular stenosis decreases pressure upstream from the valve.

False. It increases pressure upstream due to obstruction.

What causes atrial fibrillation?

Dysfunctional electrical conduction in the atria leads to irregular heartbeats and possible thrombus formation.

Compensatory response in shock states?

- Increased heart rate - Vasoconstriction - Activation of sympathetic nervous system