Cardiac Output

1. Cardiac Output (CO) - blood amount pumped per minute
2. Stroke Volume (SV) - ventricle blood pumped per min.
3. Heart Rate (HR) - cardiac cycles per minute

• CO (ml/min) = HR (beats/min) X SV (ml/beat)
• Normal CO = 75 beats/min X 70 ml/beat = 5.25 L/min

1. End Diastolic Volume (EDV) - total blood collected in ventricle at end of diastole; determined by length of diastole and venous pressure (~120 ml)
2. End Systolic Volume (ESV) - blood left over in ventricle at end of contraction (not pumped out); determined by force of ventricle contraction and arterial blood pressure (~50 ml)
• SV (ml/beat) = EDV (ml/beat) - ESV (ml/beat)
• Normal SV = 120 ml/beat - 50 ml/beat = 70 ml/beat
3. Frank-Starling Law of the Heart - critical factor for stroke volume is "degree of stretch of cardiac muscle cells"; more stretch = more contraction force

• Increased EDV = more contraction force

• slow heart rate = more time to fill
• exercise = more venous blood return

1. Autonomic Regulation of Heart Rate (HR)
1. Sympathetic - NOREPINEPHRINE (NE) increases heart rate (maintains Stroke Volume)
2. Parasympathetic - ACETYLCHOLINE (ACh) decreases heart rate
3. Vagal tone - parasympathetic inhibition of inherent rate of SA node, allowing normal HR
4. Baroreceptors, Pressoreceptors - monitor changes in blood pressure and allow reflex activity with the autonomic nervous system
2. Hormonal and Chemical Regulation of Heart Rate (HR)
1. Epinephrine - hormone released by adrenal medulla during stress; increases heart rate
2. Thyroxine - hormone released by thryroid; increases heart rate in large quantities; amplifies effect of epinephrine
3. Ca++, K+, and Na+ levels very important;
• Hyperkalemia - increased K+ level; KCl used to stop heart on lethal injection
• Hypokalemia - lower K+ levels; leads to abnormal heart rate rhythms
• Hypocalcemia - depresses heart function
• Hypercalcemia - increases contraction phase
• Hypernatremia - HIGH Na+ concentration; can block Na+ transport & muscle contraction
3. Other Factors Effecting Heart Rate (HR)
1. Normal heart rate - fetus 140-160 beats/minute
• female 72- 80 beats/minute
• male 64- 72 beats/minute
  
2. Exercise - lowers resting heart rate (40-60)
3. Heat - increases heart rate significantly
4. Cold - decreases heart rate significantly
   
5. Tachycardia - HIGHER than normal resting heart rate (over 100); may lead to fibrillation
6. Bradycardia - LOWER than normal resting heart rate (below 60); parasympathetic drug side effects; physical conditioning; sign of pathology in non-healthy patient

Category: Physiology Notes