Cardiac output and gas exchange during heavy exercise with a positive pressure respiratory protective apparatus.

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Abstract
Continuous positive pressure breathing effectively prevents inward leakage of noxious agents into a breathing apparatus but may interfere with venous return and cardiorespiratory performance during heavy work. Cardiac output was therefore recorded with a dye dilution method, and ventilatory variables were measured from expired air, for 7 well-trained firemen at a work load of 150 W. All the variables except the invasive ones were also measured during the maximal work load that each subject could sustain for 10 min. At random the subjects worked with a mouthpiece and a face mask with and without a positive pressure of 0.4 kPa. No variable deteriorated during positive pressure breathing, although the central venous O2 pressure increased, an occurrence indicating higher cardiac output in relation to O2 demand. Dead space ventilation decreased, an indication of increased ventilatory efficiency. Positive pressure breathing (0.4 kPa) thus does not deteriorate cardiopulmonary function during intermediate or maximal work loads.