A data-driven model to estimate breathing-induced intra-trunk blood shifts during exercise.

The pressure swings generated by the respiratory muscles induce blood shifts (Vbs) between the trunk and the extremities. Vbs varies with swing amplitude and breathing pattern and can reach sizable volumes. Although Vbs was successfully explored using double-body plethysmography, the extent of intra-trunk blood shifting (between abdomen and thorax, VbsIT) remains to be quantified. We here present an electrical model of the cardiovascular system that allows to derive quantitative estimates of breath-by-breath VbsIT. We first validated the model with experimental data collected from healthy participants performing exercise with various breathing patterns, including spontaneous (CTRL), abdominal (AB), and rib cage breathing (RC), and with external expiratory flow limitation (EFLe). We then fed the model with other experimental data to derive VbsIT in a proof-of-concept fashion. Breath-by-breath fluctuations in Vbs derived from the model matched experimental data. Computations of VbsIT were in line with expectations, showing small fluctuations with spontaneous breathing and substantial increases during AB, RC, and EFLe. Intra-breath VbsIT showed a close relationship with intra-breath transdiaphragmatic pressure during inspiration in all conditions and during expiration in AB and RC, reflecting the net effect of hydraulic pressure fluctuations on blood displacement between the two compartments. This model may benefit further work investigating (patho)physiological mechanisms of various conditions affecting cardiorespiratory function, both at rest and during exercise.NEW & NOTEWORTHY This study presents an electrical model of the cardiovascular system, capable of estimating breath-by-breath intra-trunk blood shifting (VbsIT) between the abdomen and thorax. The model was validated using data from healthy participants performing various breathing patterns during exercise. It allowed quantifying VbsIT fluctuations, with significant increases during abdominal and rib cage breathing and expiratory flow limitation. This model offers a valuable tool for exploring cardiorespiratory function in health and disease, including COPD and heart failure.