Physiologic appraisal of a new rescue respirator with positive pressure

Abstract

Four healthy firemen worked on the bicycle ergometer during four steps: (1) without a mask; (2) with a mean mask pressure equal to atmospheric pressure; (3) with a slight positive mean pressure of + 3.1 cm H₂O inside the mask; (4) with a higher positive mean pressure of + 6.3 cm H₂O inside the mask and a minimal mask pressure of + 2.2 cm H₂O. Intraesophageal mean pressure increased only half as much as mask pressure. Only a slight tachycardia and a slight arterial hypotension was seen in step 4 compared to the control steps. Accordingly, a moderate increase of the preejection period (PEP) and a decrease of the left ventricular ejection time (LVET) was recorded, leading to a rise of the PEP/LVET ratio (left ventricular dysfunction). In contrast, no trace of arterial hypoxemia was seen. Opening of closed airways may explain this unexpected result.

The new positive pressure respirator used in this study seems to be suitable for rescue work in smoke and toxic gases. The following preconditions have to be remembered: (1) The mean pressure in the mask should never exceed + 6.5 cm H₂O; (2) a fireman's physical performance seems to be reduced to 2000–2500 ml/min O₂ uptake; (3) the upright body position may increase positive pressure-induced tachycardia and arterial hypotension.