Cardiac output

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Cardiac output

  1. 1. Cardiac Output When the heart contracts
  2. 2. Cardiac Vocabulary <ul><li>Contractility :  Contractility is the intrinsic ability of cardiac muscle to develop force for a given muscle length. </li></ul>
  3. 3. Cardiac Vocabulary <ul><li>Preload :  Preload is the muscle length prior to contractility, and it is dependent of ventricular filling (or end diastolic volume …EDV)  </li></ul><ul><li>This value is related to right atrial pressure. </li></ul><ul><li>  </li></ul><ul><li>The most important determining factor for preload is venous return . </li></ul>
  4. 4. Cardiac Vocabulary <ul><li>Afterload :  Afterload is the tension (or the arterial pressure ) against which the ventricle must contract.  </li></ul><ul><li>If arterial pressure increases, afterload also increases. </li></ul><ul><li>Afterload for the left ventricle is determined by aortic pressure </li></ul><ul><li>Afterload for the right ventricle is determined by pulmonary artery pressure. </li></ul>
  5. 5. Cardiac Output <ul><li>Cardiac Output is the volume of blood pumped each minute, and is expressed by the following equation: </li></ul><ul><li>CO = SV x HR </li></ul><ul><li>Where: </li></ul><ul><li>CO  is cardiac output expressed in L/min (normal ~5 L/min) </li></ul><ul><li>SV  is stroke volume per beat </li></ul><ul><li>HR  is the number of beats per minute </li></ul>
  6. 7. Heart Rate (HR) <ul><li>Heart rate is directly proportional to cardiac output </li></ul><ul><li>Adult HR is normally 80-100 beats per minute (bpm.)  </li></ul><ul><li>Heart rate is modified by autonomic, immune, and local factors.  For example : </li></ul><ul><li>An increase in parasympathetic activity via M 2 cholinergic receptors in the heart will decrease the heart rate. </li></ul><ul><li>An increase in sympathetic activity via B 1 and B 2 adrenergic receptors throughout the heart will increase the heart rate. </li></ul>
  7. 8. Stroke Volume (SV) SV = EDV - ESV <ul><li>Is determined by three factors: preload , afterload , and contractility .  </li></ul><ul><li>Preload gives the volume of blood that the ventricle has available to pump </li></ul><ul><li>Contractility is the force that the muscle can create at the given length </li></ul><ul><li>Afterload is the arterial pressure against which the muscle will contract. </li></ul><ul><li>  </li></ul><ul><li>These factors establish the volume of blood pumped with each heart beat.  </li></ul>
  8. 9. Preload
  9. 10. afterload
  10. 11. Cardiac Volumes <ul><li>SV = end diastolic volume (EDV) - end systolic volume (ESV) </li></ul><ul><li>EDV = amount of blood collected in a ventricle during diastole </li></ul><ul><li>ESV = amount of blood remaining in a ventricle after contraction </li></ul>
  11. 13. Cardiac Reserve <ul><li>Cardiac reserve is the difference between resting and maximal CO </li></ul><ul><li>Cardiac Output: Example </li></ul><ul><li>CO (ml/min) = HR (75 beats/min) x SV (70 ml/beat) </li></ul><ul><li>CO = 5250 ml/min (5.25 L/min) </li></ul>
  12. 14. Frank – Starling Principle <ul><li>This principle illustrates the relationship between cardiac output and left ventricular end diastolic volume (or the relationship between stroke volume and right atrial pressure.) </li></ul>
  13. 16. Frank – Starling Principle <ul><li>The Frank Starling principle is based on the length-tension relationship within the ventricle. </li></ul><ul><li>If ventricular end diastolic volume ( preload ) is increased, it follows that the ventricular fiber length is also increased, resulting in an increased ‘tension’ of the muscle. </li></ul><ul><li>Cardiac output is directly related to venous return, the most important determining factor is preload.  </li></ul><ul><li>The contraction and therefore stroke volume in response to changes in venous return is called the Frank-Starling mechanism (or Starling's Law of the heart). </li></ul>
  14. 19. How (TPR)Total Peripheral Resistance effects CO
  15. 21. Regulation of Heart Rate: Autonomic Nervous System <ul><li>Sympathetic nervous system (SNS) stimulation is activated by stress, anxiety, excitement, or exercise </li></ul><ul><li>Parasympathetic nervous system (PNS) stimulation is mediated by acetylcholine and opposes the SNS </li></ul><ul><li>slowing heart rate </li></ul><ul><li>Baroreceptors          a. carotid sinus reflex - maintains BP in brain </li></ul><ul><li>b. Bainbridge reflex – maintains BP in heart </li></ul><ul><li>c. Aortic sinus reflex – maintains BP in aorta </li></ul>
  16. 23. Bainbridge Reflex <ul><li>Bainbridge (atrial) reflex – a sympathetic reflex initiated by increased blood in the atria </li></ul><ul><li>Causes stimulation of the SA node </li></ul><ul><li>Stimulates baroreceptors in the atria, causing increased SNS stimulation </li></ul>
  17. 24. Cardiac Neurotransmitters & Receptors
  18. 25. Chemical Regulation of the Heart <ul><li>The hormones epinephrine and thyroxine (T 4 ) increase heart rate </li></ul><ul><li>Hormonal Regulation of Blood Pressure       1. Renin       2. ADH </li></ul><ul><li>3. Aldosterone </li></ul><ul><li>Intra- & extracellular ion concentrations must be maintained for normal heart function </li></ul>
  19. 26. Homeostatic Imbalances <ul><li>Hypocalcemia – reduced ionic calcium depresses the heart </li></ul><ul><li>Hypercalcemia – dramatically increases heart irritability and leads to spastic contractions </li></ul><ul><li>Hypernatremia – blocks heart contraction by inhibiting ionic calcium transport </li></ul><ul><li>Hyperkalemia – leads to heart block and cardiac arrest </li></ul>
  20. 29. Congestive Heart Failure (CHF) <ul><li>caused by: </li></ul><ul><li>Coronary atherosclerosis </li></ul><ul><li>Increased blood pressure in aorta </li></ul><ul><li>Successive myocardial infarcts </li></ul><ul><li>Dilated cardiomyopathy (DCM) </li></ul>
  21. 30. Coronary Artery Bypass Surgery
  22. 31. Heart Auscultation Normal Heart Beat Mid Systolic Click Diastolic Murmur Aortic Stenosis

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