CV Review, Essentials, Develop. Physiol., Dr. D. Penney

Misconception Index - Module 20:

Heart Misconceptions:

  1. Cardiac and skeletal muscle are both striated, and identical in their functional characteristics.

  2. Cardiac contractions occur only by virtue of central nervous system connections to the heart.

  3. Ventricular filling occurs as a purely passive process and is completely dependent upon atrial contraction.

  4. The major reason the mitral valve closes at the beginning of ventricular contraction is because of increasing pressure in the ventricle.

  5. The aortic valve closes at the end of systolic ejection because ventricular pressure falls below aortic pressure.

  6. The right an left heart pump exactly the same amount of blood per beat in every cardiac cycle.

  7. The right and left ventricles begin and end contractions at exactly the same time.

  8. Coronary blood flow (i.e. blood flow in general) is always maximal when arterial pressure is maximum.

  9. Blood flow in the up-raised arm declines sharply with resulting pain and/or numbness because the heart must pump blood up to the fingers against gravity.

  10. The heart increases its oxygen uptake by increasing both oxygen extraction from the blood and blood flow.

    Blood Vessel Misconceptions:

  11. Pressure is the only form of energy determining blood flow.

  12. Pressure in veins is always low (i.e. above 50 mm Hg); lower than that in an artery.

  13. Pressure in arteries is always high (i.e. above 50 mm Hg); higher than that in any vein.

  14. Flow velocity in veins is always low (sluggish).

  15. One milliliter of blood would require less than 1 hour to flow through a single capillary.

  16. The total surface area of all capillaries in an adult human is approximately 6.3 square meters.

  17. Change in vascular resistance to blood flow can be determined by assessing the change in arterial pressure alone.

  18. A Reynolds number (using radius) above 1000 always indicates the presence of turbulence; below 1000, laminar flow.

  19. Blood flows like water (i.e. constant viscosity regardless of velocity or tube dimensions).

  20. The stretchibility (compliance) of most venous walls is far greater than that of most arterial walls at the same wall thickness.

  21. Arterial blood always contains a higher oxygen content than venous blood.

  22. The sounds heard through the stethoscope when taking blood pressure by the auscultatory method are made by heart valves opening and closing.

  23. Systolic arterial blood pressure steadily declines from the root of the aorta to the smaller distal arteries.

  24. Blood flow falls to zero only when perfusion pressure reaches zero (i.e. there is a linear relationship).

  25. A shift to the right of the hemoglobin-oxygen dissociation curve and increasing P50 value indicate an increased affinity for oxygen.

    Overall Mechanisms:

  26. Hyperventilation produces dizziness because too much oxygen reaches the brain

  27. Cardiovascular changes during diving are responses to increased hydrostatic (i.e. water) pressure

  28. Blood volume is primarily affected by drinking

  29. Gravity has no influence on the cardiovascular system

  30. The Valsalva maneuver is a military exercise

.......Last changed 10/10/00

Cardiac Cycle

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