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
How do anxiety, exercise, and pregnancy affect stroke volume?
Increase SV
Myocardial oxygen demand is increased by what four variables?
Myocardial = Contractility, Afterload (proportional to arterial pressure), heart Rate, Diameter of ventricle (increased wall tension)
A patient has decreased afterload. The myocardium responds by increasing its thickness. Explain this compensatory response
Thicker myocardium decreases wall tension (which is ↑ with elevated afterload) (wall tension = [pressure × radius]/[2 × wall thickness])
____ (Preload/afterload) = ventricular end-diastolic volume. ____ (Preload/afterload) = mean arterial pressure.
Preload (depends on venous tone and circulating blood volume); afterload
Would you expect nitroglycerin to decrease preload or afterload? By what mechanism? What about these questions for hydralazine?
Preload via venodilation; Afterload via vasodilation (hydralazine)
A 60-year-old man mistakenly receives triple the maintenance level of IV fluids for 24 hours. Will his preload increase or decrease?
Increase because of increased blood volume
A patient has chronic hypertension. How will his left ventricle compensate?
LV will hypertrophy to ↓wall tension (pressure × radius/2 × wall thickness) (↑MAP will ↑afterload, thereby ↑pressure & wall tension)
ACE inhibitors and ARBs cause ____ preload and ____ afterload (choices are increased/decreased).
Decreased, decreased
What vital sign may be used to approximate afterload?
Mean arterial pressure
What are the two ways for measuring ejection fraction? What is the normal value?
EF = stroke volume/end-diastolic volume & (end-diastolic volume - end-systolic volume)/end-diastolic volume; normal ≥ 55%
How is ejection fraction affected in systolic heart failure and diastolic heart failure?
EF decreases in systolic heart failure, whereas it remains normal in diastolic heart failure
Ejection fraction is used as an indication of which cardiac parameter?
Contractility
Do β-blockers increase or decrease contractility?
Decrease
Does sympathetic stimulation (e.g., catecholamines) increase or decrease contractility of the heart?
Increase
Does digoxin increase or decrease contractile strength?
Increase, similar to catecholamines
A patient has an MI and develops dilated cardiomyopathy years later. How does all of this affect contractility of the heart?
Both MIs and dilated cardiomyopathies decrease cardiac contractility
A patient has heart failure and severe hypertension. Do you treat the hypertension with a non-dihydropyridine calcium channel blocker?
No, as this will further reduce contractility and likely worsen the symptoms of heart failure
A man w/heart failure enters atrial fibrillation. He is treated with digoxin instead of a non-dihydropyridine calcium channel blocker. Why?
Digoxin is a positive inotrope that will help to increase cardiac contractility & that will treat the arrhythmia via AV node inhibition
What is the relationship between net changes in pressure, resistance, and flow?
Driving pressure (ΔP) = flow (Q) × resistance (R), which is similar to Ohm’s law (ΔV = I × R)
• What is the equation for blood vessel resistance that incorporates variables of viscosity, length, and radius?
Resistance = (8 × viscosity × length)/(π × r4)
In cardiology, by what factor does resistance increase in a vessel whose size is reduced by half?
16 times (resistance is inversely proportional to the radius to the fourth power)
What is the equation for the total resistance of blood vessels in series?
TR = R1 + R2 + R3 and so on
What is the equation for the total resistance of blood vessels in parallel?
1/TR = 1/R1 + 1/R2 + 1/R3 and so on
What parameter does the viscosity of blood mostly depend on? What disease states increase the viscosity of blood?
Primarily hematocrit; polycythemia, multiple myeloma, or other hypoproteinemic states (by this logic, viscosity ↓ anemia)
Pressure gradient drives flow from ____ (high/low) pressure to ____ (high/low) pressure.
High, low
You study blood flow in a rat’s capillaries. You find that arteriolar dilators change the TPR and thus capillary blood flow. Why is this?
Arterioles regulate capillary flow and account for most of TPR
How is volumetric flow rate (Q) related to flow velocity (v) and cross-sectional area (A)?
Q = v × A, as capillaries have the highest total cross-sectional area in the body, hence lowest flow velocity
A patient undergoes nephrectomy. How will the patient’s cardiac output be affected?
Cardiac output will ↓ as organ removal results in increased in TPR, thereby causing a decrease in cardiac output
____ (Arteries/veins) provide most of the blood storage capacity.
Veins
A patient is running on a treadmill. How does her cardiac output change? Why?
CO increases; this is due to increased heart rate and decreased total peripheral resistance
Narcotic overdose causes ____ (increased/decreased) cardiac output for a particular end-diastolic volume.
Decreased, as inotropy (and therefore contractility) decreases
Sympathetic activity causes ____ (increased/decreased) right atrial pressure for a given cardiac output.
Increased
How do catecholamines or digoxin cause increased cardiac output?
They increase contractility, so CO increases for a given right atrial pressure
