Unobtrusive continuous hemodynamic monitoring method using processed heart sound signals in patients undergoing surgery: a proof of concept study.

Abstract

Heart sounds provide essential information about cardiac function; however, their clinical meaning and potential for minimally invasive hemodynamic monitoring in real world clinical settings remain underexplored. This study assessed relationships between heart sound indices and hemodynamic parameters during liver transplant surgery. Data from 80 liver transplant recipients were analyzed across five procedural phases (approximately 1,680k cardiac beats). The heart sound indices (S1 amplitude, S2 amplitude, systolic time interval, systolic time variation (STV)) were compared with hemodynamic parameters (mean blood pressure, peak arterial pressure gradient, stroke volume, systemic vascular resistance (SVR), stroke volume variation (SVV)). Relationships were assessed using Pearson's correlation, Bland-Altman analysis, and concordance correlation coefficient (CCC). The heart sound indices showed significant correlations with hemodynamic parameters during liver transplantation. S1 amplitude had positive correlations with dP/dt_max (r = 0.467-0.548), while S2 amplitude was correlated with SVR (r = 0.364-0.406). The STV showed the strongest and most consistent correlations with SVV across surgical phases (r = 0.687-0.721). Agreement metrics between STV and SVV showed mean biases ranging from - 0.34 to 0.28 with limits of agreement ranging from - 6.20 to 6.10, and the CCC ranged from 0.55 to 0.69. The amplitudes of S1 and S2 and their interval variation may reflect changes in dP/dt_max, SVR and SVV, respectively. These results suggest that heart sound parameters can serve as valuable minimally invasive indicators of hemodynamic changes during complex surgical procedures such as liver transplantation.