heart pt.6 Flashcards
equation for calculating cardiac output
heart rate (HR) times (*) stroke volume (SV). HR * SV = cardiac output
volume of blood pumped out of ventricle per contraction
stroke volume
amount of blood in the ventricles before heart contracts
end diastolic volume (EDV)
the volume of blood in a ventricle at the end of contraction, or systole
end systolic volume (ESV)
EDV - ESV =
stroke volume
Amount of venous blood delivered to right atrium each minute. Reduces when blood volume goes down. Increases when skeletal muscles contract and compress adjacent veins, peripheral tissues increase activity. Factors: blood volume, muscular activity and rate of blood flow through peripheral capillaries.
venous return
The duration of ventricular diastole; The longer it is, the more filing occurs.
Slows HR if venous return remains constant, increasing EDV. Increasing heart rate decreases EDV.
filling time
The amount of myocardial stretching.
Increases with greater the EDV. If EDV is very small, the sarcomeres are too short to develop much power. As EDV increases, then sarcomeres reach optimum length leading to more powerful and efficient contractions.
Greater EDV = greater stroke volume (Frank-Starling law of the heart)
preload
The amount of force during a contraction at a given amount of preload. Increases with sympathetic stimulation (epinephrine, thyroid hormones, glucagon). Reduced by beta blockers and calcium channel blockers.
contractility
The amount of tension the contracting ventricle must produce to force open the semilunar valve and eject blood. Stroke volume decreases as this increases. Greater afterload means longer period of isovolumetric contraction, the shorter the period of ventricular ejection, and thus the larger the ESV. Is increased by any factor that restricts blood flow through arterial system (i.e. vasoconstriction).
afterload
the greater the ______, the larger the ESV
afterload
