Chapter 14 Dr. D. Washington

Cardiac Output I. Definition: C.O. (L/min)= heart rate X stroke volume or(ml/min) (beats/min)(ml/beat) II. Cardiac Index (C.O./m 2 body surface) III. Regulation of cardiac output A. Rate of Venous return (limiting factor) 1. Peripheral resistance 2. Mean systemic pressure (filling) 3. Right atrial pressure therefore V.R. = mean systemic pressure - Rt. atrial. P total peripheral resistance

Cardiac Output B B. Pumping Effectiveness (permissive regulator) 1. Starling’s Law 2. Starling’s Curve 3. Sympathetic & Drug Actions a. Chronotropic Affects (heart rate) b. Inotropic Affects (strength of contraction) positive inotropic ‘’ ‘’ ‘’ negative inotropic ‘’ ‘’ ‘’ 4. Relative terms a. End diastolic vol (pres) 120 ml/ventricle b. End systolic vol ‘’ 40 ‘’ ‘’ c. Stroke volume 80 ml/beat

systole diastole Filling pressure (myocardial fiber length) intensity of contraction Starling’s Curve

Control of Cardiac Output

End-diastolic volume Venous return Negative Intrathoracic pressure Blood Volume Venous pressure Breathing Urine Tissue-fluid Venoconstriction Skeletal volume volume muscle pump Sympathetic Nerve stimulation

Measurement of Cardiac Output I. Direct or Invasive a. Fick method B. Indicator Dilution method II. Indirect or Non-invasive a. Echocardiography b. Computed Tomography c. Radionuclide Imaging

Cardiac Output A. Fick Method C.O. = O 2 consumption = 250 ml/min Arterial Blood= 190 ml/L Venous Blood= 140 ml/L C.O. = 250 ml/min = 5 L/min O 2 consumption (ml/min) [AO 2 ] - [VO 2 ] ml/min

Cardiac Output Fick Method Lungs O 2 consumption = 250 ml/min Cardiac Output = 5,000 ml/min O 2 = 140 ml/L Rt heart O 2 = 190 ml/L Lt heart

Other Techniques Currently Used to Measure Cardiac Output Radionuclide (gamma camera) Echocardiography Computed Tomography