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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