4. During \"strained\" defecation it is not uncommon to hold the breath and comp

Question

4. During "strained" defecation it is not uncommon to hold the breath and compress the thoracic and abdominal muscles. This is called the Valsalva maneuver. It can cause fainting and is believed to be the can cause and is believed to be the reason why more falls and even deaths occur in the bathroom than any other part of the home. Explain why by answering the following questions. a. The increased pressure in the thoracic cavity compresses the venae cavae. What would happen to venous blood pressure, venous return, stroke volume and cardiac output? b. Why might a person faint? c. What compensatory mechanisms are activated to correct the effects described above? d. The increased pressure in the thoracic cavity also compresses the aortic arch. What compensatory mechanisms might be activated due to this compression?

Explanation / Answer

Valsalva maneuver is a forceful attempted exhalation against a closed pathway.It can use to clear the ears,during bowel movement,or unintentionally during coughing.The increase in intrathoracic activity causes a sequence of changes in the preload and after load stress.During strain,return of the heart is decreased and peripheral venous pressure is increased.There are 4 phses in valvasa manuever,

1.becuse of straining and increased intrathoracic pressure,the heart rate does not change but the blood pressure increases.

2.because of decreased venous return there is increase in stoke volume and pulse pressure.

3.Then because of the release in straining,there is decrease in intrathoracic pressure and blood flow is normalised.

4.blood pressure overshoots with return of heart rate to baseline.

The vasovagal response is bit different where there is increase in the sympathetic tone followedd by stressful incident followed by decrease in tone once stress is sudden drop in the sympathetic stim causes the heart rate and blood pressure to fall which leads to fainting.

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