Cardiac Output
Contributing factors
Description: Volume of blood pumped by each ventricle in one minute; product of HR and SV.
Average Adult Cardiac Output: 5.25 L/min.
Has a direct relationship between stroke volume (SV) and heart rate (HR).
Heart Rate
Stroke Volume
Regulation: Parasympathetic Nervous System regulates normal HR through the vagus nerve
Sympathetic Nervous System regulates HR in times of stress, anxiety or exercise
Atrial (Bainbridge) reflex: Increased blood in atria → baroreceptors in atria are stimulated → increased stimulation of SA node
Description: Volume of blood pumped out by one ventricle each beat (70/ml per beat) Increased Stroke Volume increases Cardiac Output
Regulation:
SV = end diastolic volume (EDV) minus end systolic volume (ESV) (Normally 70 mL)
Influences:
Influences
Age: HR slows with age. Fetal HR is between 120-160 beats/min
Gender: Women tend to have a faster HR than men
Exercise increases HR; trained athletes have a lower HR, but they have a higher SV
Body Temperature: HR increases with increased body temperature
Persistant HR changes
Tachycardia: Abnormally high HR at 100 beats/min., can lead to fibrillation
Bradycardia: Unusually slow HR, Can cause inadequate blood circulation in non-athletes. May be a favorable result of endurance training.
Preload (Amount ventricles are stretched by contained blood)
Contractility (Cardiac cell contractile force)
Afterload (Back pressure exerted by blood in the large arteries leaving the heart)
Most important factor is preload stretching of cardiac muscle is venous return - amount of blood returning to heart
Slow heartbeat and exercise increase venous return to the heart, increasing SV
Blood loss and extremely rapid heartbeat decrease venous return and SV
Negative inotropic agents decrease contractility
Positive inotropic agents increase contractility:
Increased extracellular K+
Calcium channel blockers
Acidosis
Certain hormones (epinephrine, thyroxine, and glucagon)
Ca2+ (required for binding to troponin, resulting in the binding of actin and myosin)
Increased sympathetic stimuli
NOT a major determinant of SV in normal individuals, but is important in people with hypertension
Hypertension increases afterload → increased ESV, decreased SV
More blood is going to be left over in the ventricles because the ventricles are having a hard time overcoming the pressure in the aorta
Cardiac Reserve: the difference between resting CO and maximal CO (COm-COr=CR)
Description: Number of times the heart beats per minute; sinus rhythm is 75 beats per minute.
EDV = amount of blood collected in a ventricle during diastole (Normally 120 mL)
ESV = amount of blood remaining in a ventricle after contraction (Approx. 50 mL)
Affected by contractility and afterload
Affected by preload