Respiratory pump contributes to increased physiological reserve for compensation during reductions in central blood volume (707.4)

The impedance threshold device (ITD) represents a therapy for increasing systemic circulation through creation of negative intrathoracic pressure. PURPOSE: To evaluate the respiratory pump effect on the diminution of compensatory responses during progressive reductions in central blood volume. METHODS: The Compensatory Reserve Index (CRI) algorithm measured compensation capacity to reduced central blood volume. Continuous analog recordings of arterial waveforms were extracted from data files of 7 volunteers. Subjects had previously participated in experiments designed to induce hemodynamic decompensation by application of graded lower body negative pressure (LBNP). The LBNP protocol was completed while spontaneously breathing through a standard medical facemask without (sham ITD) and with (active ITD) a resistance (~-7cmH2O). RESULTS: At the onset of pre-syncope in the sham ITD, CRI (0.08±0.02) was smaller (P=0.05) than CRI at the same time point in the active ITD (0.09±0.01). CRI at pre-syncope in the ac...