Chapter 10 - Cardiovascular Responses to Physiological Stresses

Question 1

Explain the respiratory pump:

Answer 1

• Normal inspiration: intrathoracic pressure decreases (from negative 2 mm Hg to negative 7 mm Hg)as diaphragm contracts/chest wall expands.
• Unidirectional venous valves: venous return is increased more by inspiration than it is decreased by expiration
  => venous return from the periphery is facilitated by the periodic fluctuations caused by respiration

Question 2

• What is the Valsalva maneuver ?

Answer 2

• Forced expiration against a closed glottis during defecation
• Arterial pressure is abruptly elevated for several beats due to the intrathoracic pressure transmitted to the thoracic aorta
• Sustained elevation in intrathoracic pressure
  => fall in venous return and a fall in blood pressure
  => induces a compensatory reflex with increase in the heart rate and peripheral vasoconstriction
• cessation of the maneuver:
  => abrupt fall in pressure for a couple of beats due to the reduction of intrathoracic pressure.
  => venous blood then moves rapidly into the central venous pool;
  => stroke volume, cardiac output, and arterial pressure increase rapidly;
  => a reflex bradycardia occurs

=» Particularly dangerous for people who are candidates for cerebral vascular accidents

Question 3

How does a positive pressure ventilator influence the cardiovascular system?

Answer 3

-lungs are inflated artificially: intrathoracic pressure
goes up rather than down, as occurs during normal inspiration
=> no more respiratory pump increasing venous return during inspiration
=> positive-pressure ventilator decreases venous return during lung inflation
+ compresses the pulmonary microcirculation
=> increases right ventricular afterload