Self-contained respirators: effects of negative and positive pressure-demand types on physical exercise

Ten volunteer subjects performed maximal exercise tests on a bicycle ergometer and a treadmill while under three breathing conditions: negative pressure-demand (NPD), positive pressure-demand (PPD) and normal breathing (N). No differences between breathing conditions were found in maximal work level, maximal heart rate or maximal blood lactate concentration. The experienced firemen among the subjects did show a lower respiration rate in NPD compared to PPD and N during submaximal exercise, but this was compensated for by an increased tidal volume. A remarkable finding concerned carbon dioxide pressure in arterialized blood, which was lower (0.5 to 0.8 kPa) during PPD compared to NPD or N, indicating an improvement in pulmonary gas exchange. In summary, it can be concluded that neither negative pressure-demand nor positive pressure-demand breathing affects maximal physical working capacity; therefore, their influence on the function of various organ systems during exercise apparently falls within normal physiological range.