Noninvasive tracking of right ventricular systolic pressure via multi-channel digital auscultation

Background Invasive monitoring of intracardiac pressures previously proved effective to reduce hospitalization of patients with heart failure (HF). Nevertheless, it is leveraged only in severe cases, leaving a wide population at risk for HF unmonitored. Digital phonocardiography (PCG) offers a non-invasive alternative, provided that patients can autonomously record their heart sounds at home. Multi-channel PCG could enable this by covering all potential auscultation areas, eliminating the need for precise sensor positioning by the patient. The second heart sound (S2) split, i.e., the interval between aortic and pulmonary valve closures, is related with the pulmonary artery pressure (PAP), making it a promising non-invasive surrogate for tracking intracardiac hemodynamics. Purpose We aim to show that, in an animal model, the S2 split, extracted using a custom-developed multi-channel PCG prototype, timely tracks changes in the Right Ventricular Systolic Pressure (RVSP), which equals the PAP in the systolic phase. Methods We analyzed hemodynamic data from an in vivo animal study comprising 8 pigs. A total of 16 experiments were conducted, where RVSP was transiently elevated via induced hypoxemia or hypercapnia before returning to baseline. Simultaneous recordings were taken using right heart catheterization (ground-truth RVSP) and our custom multi-channel PCG prototype, recording heart sounds from 48 points over the chest. The S2 splits were extracted from each heartbeat using an envelope-based approach. We evaluated the Pearson correlation coefficient (R) between S2 split and RVSP and performed a cross-correlation analysis to quantify the temporal delay (in heartbeats) between signal changes. Results The S2 split and RVSP showed a strong correlation (R > 0.5) in 13 out of 16 experiments, yielding an average R of 0.74. Cross-correlation showed an average delay of 12 heartbeats (range: -66 to 34) between signals. This confirms that non-invasive S2 split monitoring reliably captures invasive pressure shifts within approximately one minute. Conclusions The S2 split derived from a noninvasive multi-channel PCG prototype proved to timely track variations in RVSP. According to our results, a one-minute daily recording could be sufficient to flag significant RVSP variations. By removing the need for precise clinical placement, this multi-channel approach represents a plausible noninvasive method for daily at-home HF monitoring, enabling early detection of hemodynamic worsening in a wider population. The method will require further validation on HF patients in a real home monitoring scenario.