History of Cardiovascular Physiology, Dr. D. Penney

Misconceptions about Blood Vessels:

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

  • Pressure in veins is always low (i.e. below 50 mmHg); lower than that in any artery.

  • Pressure in arteries is always high (i.e. above 50 mmHg): higher than that in any vein.

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

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

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

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

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

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

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

  • Arterial blood always contain a higher oxygen content than venous blood.

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

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

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

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

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