Effects of Body Position on Blood Pressure Response

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Effects of Body Position on Blood Pressure
Response
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Question

• Consider a normal individual who quickly goes
  from supine posture to standing. Explain your
  predictions for the immediate changes (increase,
  decrease, or no change) that will occur in the
  following cardiovascular parameters stroke
  volume, heart rate, cardiac output, total
  peripheral resistance, arterial pressure in foot,
  venous pressure in foot, capillary pressure in
  foot, pressure in large cerebral arteries.
  Describe how activation of the baroreceptor
  reflex would help to increase mean arterial
  pressure.

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Cardiac Output

• Cardiac Output Stroke volume x Heart Rate

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Stroke Volume

• When you stand, the skeletal muscle and
  respiratory pumps return a greater volume of
  venous blood to the heart.
• Frank-Starlings Law of the heart
• within physiological limits, the heart pumps all
  the blood that returns to it without undue
  blocking of blood in the veins.

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Total Peripheral Resistance

• Standing causes vasoconstriction via venous
  pooling in lower extremities.
• Vasoconstriction is one factor which effects
  peripheral resistance.
• Stroke Volume then either decreases or does not
  change.
• Viscosity does not change
• Total length of veins also does not change

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Pressure in Foot

• Standing causes skeletal muscle contraction which
  increases venous pressure in lower extremities.
• This contraction leads to a decrease in pressure
  because it moves blood from the lower extremities
  decreasing pooling.
• Increased venous pressure increases capillary
  pressure.

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Pressure in large cerebral arteries

• Arteries carrying blood away from the heart will
  not see an initial increase in BP because cardiac
  output has not yet changed.

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Baroreceptor Reflex

• The baroreceptor reflex is the bodys rapid
  response system for dealing with changes in blood
  pressure.
• Receptors are located
• Aortic Arch
• Carotid Sinus
• The Medulla Oblongata acts as the reflex control
  center for neural integration.
• The effectors are located through-out the body
• Arterioles Veins
• SA Node

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Changes seen when standing quickly
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Analogy

• The ball float mechanism of a toilet acts like a
  baroreceptor. Standing up quickly is like
  flushing the toilet causing the water line to
  drop, simulating a drop in blood pressure. Much
  like the baroreceptor activates neural
  integration correcting the BP decrease, the
  float activates water input returning the water
  line in the tank to an adequate level.

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References

• Frank Orme. University of Pittsburgh.
  http//members.aol.com/Bio50/LecNotes/lecnot21a.ht
  ml
• Oxbridge Solutions Ltd. http//www.gpnotebook.co.u
  k/cache/-543555543.htm
• Richard E. Klabunde. Cardiovascular Physiology
  Concepts. http//www.cvphysiology.com/Blood20Pres
  sure/BP012.htm
• Silverthorn, D. Human Physiology. Pearson
  Education. 2007.