Respiratory responses to chest compression in human subjects.

To test the hypothesis that respiratory compensation for chest compression in the conscious state is different from that in the unconscious state, a range of chest compression was applied to eight conscious and eight anesthetized subjects. Chest compression was carried out by inflating a pneumatic cuff inserted under a chest corset and placed over the anterior chest wall for 5 min. Cuff inflation pressures were 25, 50, and 100 mm Hg: light, moderate, and heavy chest compression, respectively. In both conscious and anesthetized subjects, chest compression immediately caused a decrease in tidal volume (VT) and a concomitant increase in respiratory frequency (f). These changes stabilized within 2 min and remained nearly steady for the rest of the sustained chest compression. The decrease in VT was more prominent the greater the loads, and the change in f was in reverse proportion to the change in VT. In conscious subjects the increase in f was due to shortening of both inspiratory time (T1) and expiratory time (TE), whereas in anesthetized subjects the increase in f was due solely to shortening of TE. In conscious subjects, the values of minute ventilation (VI) and end-tidal PCO2 (PETCO2) during light and moderate chest compression were not different from the control values, whereas VI increased and PETCO2 decreased during heavy chest compression. In anesthetized subjects, the values of VI and PETCO2 were not different from the control values at any different magnitudes of chest compression.(ABSTRACT TRUNCATED AT 250 WORDS)