φυσιολογ. Flashcards
Your patient has a heart rate of 80 beats/min with a stroke volume of 62.5 mL/beat. What is her cardiac output?
5 L/min, as CO = SV × HR
State the Fick principle/equation.
CO = rate of oxygen consumption ÷ (arterial oxygen content - venous oxygen content)
What are the two ways/equations for measuring mean arterial pressure?
MAP = CO × total peripheral resistance (TPR); TPR (or MAP) = 1/3 systolic pressure + 2/3 diastolic pressure
How is pulse pressure calculated? What is it proportional to?
Systolic pressure - diastolic pressure; it is proportional to stroke volume (and inversely proportional to arterial compliance)
A marathoner has an increased stroke volume while running. What are the two parts of the equation for SV?
SV = cardiac output/heart rate = end-diastolic volume - end-systolic volume
↑ ____ and ____ maintain cardiac output (CO) in early stages of exercise. But ↑ ____ maintains CO after prolonged exercise.
Stroke volume, heart rate; HR (since SV plateaus)
During late phases of exercise, increase in cardiac output is a result of an increase in what?
Heart rate
On physical exam, a patient’s pulse pressure is found to be decreased. Name four conditions that may cause this finding in this patient.
Aortic stenosis, cardiogenic shock, tamponade, and advanced heart failure
A patient with ventricular tachycardia experiences syncope. How do the two symptoms relate to each other?
At high heart rates, the ventricles are unable to fill completely during diastole (preferentially shortened), causing ↓ CO and syncope
Name five conditions that can cause increased pulse pressure.
Hyperthyroidism, aortic regurgitation, aortic stiffening (elderly), obstructive sleep apnea (↑ sympathetic tone), and exercise (transient)
What three variables affect stroke volume?
Contractility, Afterload, and Preload (SV CAP)
Increased SV can be caused by ____ preload, ____ afterload, or ____ contractility (choices include increased/decreased).
Increased, decreased, increased
By what mechanism do catecholamines increase cardiac contractility and stroke volume?
Increased activity of the calcium pump in the sarcoplasmic reticulum, which increases contractility and SV
How does increasing intracellular calcium affect contractility (and thus stroke volume)?
It increases contractility
How does decreasing extracellular sodium affect contractility (and thus stroke volume)?
It decreases the activity of the sodium/calcium ion exchanger, thereby increasing contractility and SV
A patient on digitalis wants to know how his medicine works and how it affects his heart. Explain.
It blocks the sodium/potassium pump, increasing intracellular sodium, which increases intracellular calcium and contractility
How does β1-blockade affect contractility and stroke volume?
β1-blockade decreases cAMP, which decreases contractility and stroke volume
A patient presents with a history of congestive heart failure. How does systolic dysfunction affect contractility?
It decreases contractility
A patient with congestive heart failure has confusion and shortness of breath. Lactate levels are elevated. What is causing his symptoms?
Metabolic acidosis, which decreases contractility and causes volume overload
A woman with known COPD is admitted for pneumonia. Her O2 saturation is 81%. How is her cardiac output affected?
Hypoxia and hypercapnia cause a decrease in contractility and in stroke volume
How do calcium channel blockers affect contractility and stroke volume?
Non-dihydropyridine calcium channel blockers decrease intracellular calcium, which decreases contractility