Respiratory Pump Contributions to Hemodynamic Responses in Lower-Body Negative Pressure: Preliminary Results

The goal of this work is to investigate the cardiovascular and respiratory responses to progressive hemorrhage simulated using lower body negative pressure (LBNP). Subjects were classified based on their tolerance to LBNP, participants who showed presyncope signs before reaching −60 mmHg were classified as non-finishers while the ones who completed the experiment without any presyncope symptoms were considered finishers. Results showed that the non-finishers group has a lower mean arterial pressure at − 30mmHg, − 40mmHg, and − 50mmHg compared to the finishers. The inhale time was lower in the non-finishers group at rest, and at − 50mmHg compared to the finishers, while no difference in exhale time was observed between the two groups. In the non-finishers group, the inhale/exhale ratio was lower at − 30mmHg − 40mmHg and − 50mmHg compared to the finishers group. Our results suggest that the finishers group has the greatest compensation to the hypovolemic challenge, apparent in the increased inspiratory time resulting in a longer duration of intrathoracic pressure, and thus increasing mean arterial blood pressure via the respiratory pump mechanism. The findings of this study can help in distinguishing patients with a limited tolerance to hypovolemia who might necessitate life-saving interventions sooner than those with high tolerance.