Cardiac Output and Venous Return Lecture Notes

Comprehensive vocabulary flashcards covering the definitions, formulas, and physiological principles of cardiac output, venous return, and associated hemodynamic measures.

Cardiac Output

The volume of blood pumped from each ventricle each minute, calculated as $Cardiac output = Heart rate \times stroke volume$. At rest, it is approximately $5 L/min$.

Cardiac Index

The amount of blood ejected by the heart per minute per square meter of body surface area ($m^2$). In a person with a $1.7 m^2$ body surface area, it is approximately $3 L/min/m^2$.

Cardiac Reserve

The maximum amount of blood that can be pumped out by the heart above the normal value, usually expressed as a percentage ($300-400\%$ in normal young adults; $500-600\%$ in athletes).

End Diastolic Volume (EDV)

The volume of blood in each ventricle at the end of diastole, typically measuring between $110-130 ml$.

End Systolic Volume (ESV)

The volume of blood that remains in each ventricle at the end of systole, typically measuring between $40-60 ml$.

Stroke Volume (SV)

The amount of blood pumped out by each ventricle in each beat, calculated as $Stroke volume = EDV - ESV$. The normal rest value is approximately $70 ml$. (Example: $120 ml - 50 ml = 70 ml$).

Ejection Fraction

The percentage of the $EDV$ that is ejected with each stroke, calculated as $\frac{SV}{EDV} \times 100$. It is normally about $60-65\%$ and is a valuable index of ventricular function.

Preload

The degree to which the myocardium is stretched before it contracts.

Afterload

The resistance against which blood is expelled during ventricular contraction.

Fick Principle

A measurement method stating that the amount of a substance taken up by an organ (or whole body) per unit time is equal to the arterial level of the substance minus the venous level times the blood flow.

Venous Return (VR)

The quantity of blood flowing from the veins into the right atrium each minute; it is the primary controller of cardiac output.

Mean Systemic Filling Pressure

The equilibrated pressure measured everywhere in the systemic circulation after blood flow has ceased, with a normal value of $7 mm Hg$.

Frank-Starling Law

States that the force of contraction of the heart is directly proportional to the initial length of the muscle fibers before the onset of contraction.

Myocardial Contractility

The ability of the muscle fiber to contract and the force developed by it to expel blood.

Respiratory Pump

Mechanism where inspiration causes the thoracic cavity to expand and intrathoracic pressure to become negative, increasing the diameter of the inferior vena cava and increasing venous return.

Muscle Pump

Muscular activity that compresses veins and uses proximal valves to propel blood toward the heart, thereby increasing venous return.

Ballistocardiography

A direct method (in animals) used for measuring cardiac output.

Peripheral Resistance

The resistance in peripheral vessels; an increase in this factor leads to decreased stroke volume and decreased cardiac output.