PROBLEM SESSION ANSWERS: Problem 4

Answer: Yes, call the lifeguard!

If use large tube (vacuum cleaner hose), very high dead space reduces alveolar ventilation.

If use small tube to reduce dead space, high resistance makes it impossible to move air fast, reducing total ventilation.

Suppose use large hose, breath in through mouth and out through nose (why does this solve the dead space and resistance problems?). Still notify the life guard because 300 cmH2O pressure on chest will prevent any inspiration (maximum inspiratory effort can only generate about 100 cmH2O water pressure).

How to go deep than 20-30 cm? (1) Hold breath. (2) Scuba (Self-Contained Underwater Breathing Apparatus) - tank of compressed air and valve; valve adjusts pressure at mouth to be the same as pressure on chest permitting normal breathing.

Problem of "bends" (decompression sickness) in scuba diving. High air pressure necessary to balance high water pressure causes nitrogen to dissolve in body tissues, especially fat tissue. If ascend slowly, nitrogen diffuses out of fat and is lost from lungs. But if ascend rapidly, nitrogen becomes a supersaturated solution in the blood and forms small bubbles (nitrogen emboli) particular at sites of mechanical vibration (e.g. joints). The emboli block tissue blood flow, causing pain and, if severe, tissue necrosis. Note use of hyperbaric chamber to recompress (to redissolve nitrogen) and then decompress slowly.