Physiology

Question 1

Cardiac Output

Calculation

Answer 1

• CO = stroke volume (SV) * heart rate (HR)

- CO = rate of O2 consumption / (arterial O2 content - venous O2 content)

Question 2

Mean Arterial Pressure

Calculation

Answer 2

• MAP = CO * total peripheral resistance (TPR)

- MAP = 2/3 diastolic pressure + 1/3 systolic pressure

Question 3

Pulse pressure

Calculation, Relations

Answer 3

• Pulse pressure = systolic pressure - diastolic pressure

- It is directly related to SV and inversely related to arterial compliance

Question 4

Stroke Volume (SV)
(Calculation)

Answer 4

• SV = end-diastolic volume (EDV) - end-systolic volume (ESV)

Question 5

Increased Pulse Pressure

Causes

Answer 5

• Hyperthyroidism
• Aortic regurgitation
• Aortic stiffening (isolated systolic hypertension in elderly)
• Obstructive sleep apnea (increased sympathetic tone)
• Exercise (transient)

Question 6

Decreased Pulse Pressure

Causes

Answer 6

• Aortic stenosis
• Cardiogenic shock
• Cardiac tamponade
• Advanced heart failure

Question 7

Stroke Volume (SV)
(Relations)

Answer 7

• Contractility (directly)
• Preload (directly)
• Afterload (inversely)

Question 8

Increased Contractility

Causes

Answer 8

• Catecholamines (inhibition of phospholamban —> increased Ca++ entry into sarcoplasmic reticulum —> increased Ca++-induced Ca++ release)
• Increased intracellular Ca++
• Decreased extracellular Na+ (decreased activity of Na+/Ca++ exchanger)
• Digiltalis (blocks Na+/K+ pump —> decrease Na+/Ca++ exchanger activity —> increased intracellular Ca++)

Question 9

Decreased Contractility

Causes

Answer 9

• Beta-1 blockade (decreased cAMP)
• HF with systolic dysfunction
• Acidosis
• Hypoxia/hypercapnia (decreased Po2/increased Pco2)
• Non-dihydropyridine Ca++ channel blockers

Question 10

Increased Myocardial Oxygen demand

Causes

Answer 10

• Increased contractility
• Increased afterload (proportional to arterial pressure)
• Increased heart rate
• Increased diameter of ventricles (increased wall tension)

Question 11

Wall Tension (Law of Laplace)
(Calculation)

Answer 11

Wall tension = pressure * radius / 2 * wall thickness

Question 12

Preload (EDV)

Relations

Answer 12

• Venous tone (directly)

- Circulating blood volume (directly)

Question 13

Ejection Fraction

Calculation, Normal value

Answer 13

• EF = SV / EDV = (EDV - ESV) / EDV

- It is equal or more than 55%