Concomitant ventilatory and circulatory functions of the diaphragm and abdominal muscles

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Expulsive maneuvers (EMs) caused by simultaneous contraction of diaphragm and abdominal muscles shift substantial quantities of blood from the splanchnic circulation to the extremities. This suggests that the diaphragm assisted by abdominal muscles might accomplish ventilation and circulation simultaneously by repeated EMs. We tested this hypothesis in normal subjects by measuring changes (Δ) in body volume (Vb) by whole body plethysmography simultaneously with changes in trunk volume (Vtr) by optoelectronic plethysmography, which measures the same parameters as whole body plethysmography plus the volume of blood shifts (Vbs) between trunk and extremities: Vbs = ΔVtr-ΔVb. We also measured abdominal pressure, pleural pressure, the arterial pressure wave, and cardiac output (Qc). EMs with abdominal pressure ~100 cmH(2)O for 1 s, followed by 2-s relaxations, repeated over 90 s, produced a "stroke volume" from the splanchnic bed of 0.35 ± 0.07 (SD) liter, an output of 6.84 ± 0.75 l/min compared with a resting Qc of 5.59 ± 1.14 l/min. Refilling during relaxation was complete, and the splanchnic bed did not progressively empty. Diastolic pressure increased by 25 mmHg during each EM. Between EMs, Qc increased to 7.09 ± 1.14 l/min due to increased stroke volume and heart rate. The circulatory function of the diaphragm assisted by simultaneous contractions of abdominal muscles with appropriate pressure and duration at 20 min(-1) can produce a circulatory output as great as resting Qc, as well as ventilation. These combined functions of the diaphragm have potential for cardiopulmonary resuscitation. The abdominal circulatory pump can act as an auxiliary heart.