Cardiac Output

Other factors that influence heart rate

Age, Gender, Exercise, Body temperature

Regulation of stroke volume; preload, Frank-starling law

At rest, cardiac muscle cells are shorter than optimal length- the more they are stretched, the more forcefully they contract.

Cardiac Output Equation

CO = HR x SV. Where HR refers to the number of beats per minute (Heart Rate). SV refers to the volume of blood pumped out by a ventricle with each beat (Stroke volume).

Congestive Heart failure; causes

Coronary atherosclerosis, persistent High blood pressure. Multiple myocardial infarcts, Dilated Cardiomyopathy.

Regulation of stroke volume; contractility, Negative inotropic agents

Decrease contractility. Such as acidosis, increased extracellular K+ and calcium channel blockers.

Chemical regulation of Heart rate; Hormones

Epinephrine form adrenal medulla enhances heart rate and contractility. Thyroxine increases heart rate and enhances the effects of norepinephrine and epinephrine.

Regulation of stroke volume; contractility, positive inotropic agents

Increase contractility. Such as increased Ca++ influx due to sympathetic stimulation. Stimulation due to Hormones.

Regulation of stroke volume; preload, Frank-starling law, venous return

Increased return of blood to the rt atrium ( venous return) stretches the ventricles and increases contraction force. Increased venous return = increased EDV = increased preload.

Venous return; stroke volume

Increased venous return = increased EDV = increased SV. Decreased venous return = decreased EDV = decreased SV.

Chemical regulation of Heart rate; Intra/Extracellular ion concentrations

Ions such as Ca++ and K+ must be maintained for normal heart function.

Autonomic Nervous System regulation; sympathetic Nervous system

Is activated by emotional or physical stressors. leads to Atrial reflex which is a sympatheic reflex initiated by increased venous return. Stretch of the atrial walls sends signals to the medulla oblongata which the stimulates the SA node throught sym. fibers, HR increases.

Venous return; muscular activity and filling time

Muscular activity refers to activation of muscles and respiratory pumps. Filling time refers to the duration of ventricular diastole, longer filling time means more blood in ventricles.

Congestive Heart Failure

Refers to a progressive condition where the CO is so low that blood circulation is inadequate to meet tissue needs.

Regulation of stroke volume; contractility

Refers to the contractile strength at a given muscle length, independent of muscle stretch and EDV.

Regulation of stroke volume; Afterload

Refers to the pressure that must be overcome for ventricles to eject blood (i.e. pressure in the aorta). Hypertension increases afterload. Increased afterload = increased ESV = Decreased SV

Cardiac Output

Refers to the volume of blood pumped by each ventricle in one minute. Heart must maintain appropriate levels of CO to meet the body's oxygen demands

stroke volume

Three main factors affect SV. Preload (EDV), contractility (affects ESV), and Afterload (affects ESV)

Venous return

is the main factor affecting preload (EDV). It influenced by blood volume, muscular activity, filling time

Autonomic Nervous System regulation; parasympathetic Nervous system

opposes the sympathetic effects to decrease HR

Regulation of stroke volume; preload

refers to the degree of stretch of cardiac muscle cells before they contract. Describe by the Frank-starling law of the heart