Non-invasive hemodynamic monitoring during hemorrhage and blood transfusion: opportunities and challenges

Objective. We investigated (i) if blood volume decompensation status (BVDS) can be trend-tracked by hemodynamic parameters, and (ii) if hemodynamic parameters capable of trend-tracking BVDS can be trend-tracked by the physio-markers derived from the physiological signals measured using wearable sensors.Approach. In 9 pigs undergoing controlled hemorrhage and blood transfusion, we measured gold standard arterial blood pressure (BP), heart rate (HR), stroke volume (SV), and cardiac output (CO) via invasive aortic BP and flow signals. In addition, we derived non-invasive physio-markers from the electrocardiogram, photoplethysmogram (PPG), and seismocardiogram signals measured using wearable sensors. Then, we determined the best hemodynamic parameters to trend-track BVDS by comparing their correlation with BVDS. Finally, we investigated the feasibility of trend-tracking BVDS via non-invasive physio-markers in terms of their correlation with hemodynamic parameters as well as BVDS.Main results. SV and CO could trend-track BVDS more consistently and explainably than BP and HR during hemorrhage and blood transfusion. The physio-markers of SV (the ratio between left ventricular ejection time (LVET) and pre-ejection period (PEP): LVET/PEP and PPG amplitude:A_PPG) and CO (HR·LVET/PEP and HR·A_PPG) showed close and monotonic relationships to SV (LVET/PEP: Spearman correlation 0.96 (0.93-0.98) and Pearson correlation 0.96 (0.93-0.98)) and CO (HR·LVET/PEP: Spearman correlation 0.95 (0.91-0.97) and Pearson correlation 0.91 (0.89-0.97)), and they likewise showed close and monotonic relationships to BVDS. However, substantial inter-individual variability in the hemodynamic parameters and their physio-markers was also observed.Significance. These findings suggest the feasibility of wearable-enabled hemodynamic monitoring during hemorrhage and blood transfusion, as well as the challenges therein.