Cardio-respiratory interactions in response to lower-body negative pressure.

OBJECTIVE: The goal of this study is to investigate the potential of the physiological interaction between heart rate and blood pressure, and cardiorespiratory coupling to track the progression of simulated hemorrhage, as well as differentiate individuals with low tolerance (LT) from the ones with high tolerance (HT) to hypovolemia.

APPROACH: Wavelet transform coherence and convergent cross-mapping techniques were employed to study the physiological interdependence and the causal relationship between heart rate, blood pressure, and respiration in nineteen subjects who underwent a progressive lower body negative pressure (LBNP) protocol.

MAIN RESULTS: The interaction between blood pressure and heart rate to maintain homeostasis was higher in the LT group during baseline, and LBNP simulated mild, moderate, and severe hemorrhage. The significant time of interaction between blood pressure, and respiration, and the causal effect of blood pressure on respiration were higher in the HT group during baseline compared to the LT group. HT participants also had a higher causal effect of respiration on blood pressure compared to LT. The calculated metrics to distinguish LT from HT subjects achieved a sensitivity of 58-83%, accuracy of 63-84%, and an area under the ROC curve of 74-86%, while the overlap of LT individual responses with HT was 0-33%.

SIGNIFICANCE: The outcomes of this study indicate the potential of cardiorespiratory coupling, and heart rate and blood pressure interaction toward tracking the progression of hemorrhage and distinguishing individuals with low tolerance to hypovolemia from those with high tolerance. Measurements of such interactions could improve clinical outcomes for patients with low tolerance to hypovolemia and therefore reduce morbidity and mortality through early implementation of life-saving interventions.