Physiology Flashcards
(45 cards)
According to the Fick principle, CO =
Rate of O2 consumption / (arterial O2 content - venous O2 content)
Mean arterial pressure (MAP) =
CO x total peripheral resistance (TPR)
OR
(2/3 diastolic pressure) + (1/3 systolic pressure)
Pulse pressure =
Systolic pressure - diastolic pressure
Relationship between pulse pressure and stroke volume
Pulse pressure is proportional to stroke volume
Relationship between pulse pressure and arterial compliance
Pulse pressure is inversely proportional arterial compliance.
Stroke volume (SV) =
[End-diastolic volume (EDV)] - [end-systolic volume (ESV)]
During the early stages of exercise, CO is maintained by…
Increased heart rate and increased stroke volume.
During the late stages of exercise, CO is maintained by…
Increased heart rate only (stroke volume plateaus)
…is preferentially shortened with increased heart rate.
Diastole – less filling time leads to decreased cardiac output (e.g., ventricular tachycardia)
Conditions associated with increased pulse pressure
- Hyperthyroidism
- Aortic regurgitation
- Aortic stiffening (isolated systolic hypertension in elderly)
- Obstructive sleep apnea (increased sympathetic tone)
- Exercise (transient)
Conditions associated with decreased pulse pressure
- Aortic stenosis
- Cardiogenic shock
- Cardiac tamponade
- Advanced heart failure
Increased stroke volume is seen with:
- Increased contractility (e.g., anxiety, exercise, pregnancy)
- Increased preload
- Decreased afterload
A failing heart is associated with…
Decreased stroke volume.
Contractility and stroke volume increase with:
- Catecholamines – increase activity of Ca2+ pump in sarcoplasmic reticulum
- Increased intracellular Ca2+
- Decreased extracellular Na+ – due to decreased activity of Na+/Ca2+ exchanger
- Digitalis – blocks Na+/K+ pump –> increases intracellular Na+ –> decreases Na+/Ca2+ exchanger activity –> increases intracellular Ca2+
Contractility and stroke volume decrease with:
- Beta1-blockade – decreases intracellular cAMP
- HF with systolic dysfunction
- Acidosis
- Hypoxia/hypercapnia (decreased PO2/increased PCO2)
- Non-dihydropyridine Ca2+ channel blockers
Myocardial O2 demand is increased by:
- Increased contractility
- Increased afterload (proportional to arterial pressure)
- Increased heart rate
- Increased diameter of ventricle (due to increased wall tension)
Wall tension follows Laplace’s law:
Wall tension = (pressure x radius) / (2 x wall thickness)
Preload may be approximated by…
Ventricular end-diastolic volume.
Preload depends on…
Venous tone and circulating blood volume.
Venodilators such as nitroglycerin…
Decrease preload.
Afterload may be approximated by…
The mean arterial pressure.
The left ventricle compensates for increased afterload by…in order to decrease…
Thickening (hypertrophy); wall tension
Vasodilators such as hydralazine…
Decrease afterload.
ACE inhibitors and ARBs decrease…
Both preload and afterload.
