VENTILATORY EFFECTS OF MEDICAL ANTISHOCK TROUSERS IN HEALTHY-VOLUNTEERS

The ventilatory effects of medical antishock trousers (MAST) were investigated using 10 healthy volunteers. Use of the MAST (60-80 mm Hg) decreased forced expiratory volume (-8% +/- 4%, p < 0.01), vital capacity (-8% +/- 5%, p < 0.01), and functional residual capacity (-12% +/- 6%, p < 0.01) and induced a significant decrease in tidal volume (-30% +/- 17%, p < 0.05), but minute ventilation was unmodified because of a concomitant increase in respiratory rate (+17% +/- 8%, p < 0.001). The MAST modified the breathing pattern: the abdominal contribution to ventilation was markedly decreased (-57% +/- 22%, p < 0.001), suggesting a decrease in the diaphragmatic contribution to ventilation. The MAST increased both the end-expiratory (+131% +/- 115%, p < 0.01) and inspiratory variation (DELTA-Pgas: +42% +/- 40%, p < 0.05) of gastric pressure, whereas the end-expiratory and inspiratory variation of esophageal pressure remained unchanged. Because of a higher DELTA-Pgas, the dynamic compliance of the abdominal compartment markedly fell (-77% +/- 10%, p < 0.001). Transdiaphragmatic pressure (Pdi: +28% +/- 30%, p < 0.05) significantly increased and the pressure-time index of the diaphragm significantly increased (+32% +/- 32%, p < 0.05) after inflation of the MAST, suggesting an increase in the diaphragmatic cost of breathing. Inspiratory activity of the parasternal intercostal muscles significantly increased after the MAST was inflated. Computerized tomography showed that the MAST induced a cephalad shift of the diaphragm, which reduced pulmonary height. In contrast, the transverse and sagittal diameters of the thorax increased. The thoracic transverse area significantly increased, but this increase was associated with an increase in the mediastinal area but not the lung area. In conclusion, the ventilatory effects of MAST in healthy volunteers are moderate but might be deleterious or enhanced in shocked trauma patients.