Beat-to-Beat Tracking of Pulse Pressure and Its Respiratory Variation Using Heart Sound Signal in Patients Undergoing Liver Transplantation

Abstract

Purpose: To investigate the possibility of esophageal phonocardiography as a monitor for invasively measured pulse pressure (PP) and its respiratory variation (PPV) in patients undergoing liver transplantation. Methods: In 24 liver transplantation recipients, all hemodynamic parameters, including PP and PPV, were measured during five predetermined surgical phases. Simultaneously, signals of esophageal heart sounds (S1, S2) were identified, and S1–S2 interval (phonocardiographic systolic time, PST) and its respiratory variation (PSV) within a 20-s window were calculated. Beat-to-beat correlation between PP and its corresponding PST was assessed during each time window, according to the surgical phases. To compare PPV and PSV along with 5 phases (a total of 120 data pairs), Pearson correlation was conducted. Results: Beat-to-beat PST values were closely correlated with their corresponding 3360 pairs of PP values (median r = 0.568 [IQR 0.246–0.803]). Compared with the initial phase of surgery, correlation coefficients were significantly lower during the reperfusion period (median r = 0.717 [IQR 0.532–0.886] vs. median r = 0.346 [IQR 0.037–0.677]; p = 0.002). The correlation between PSV and PPV showed similar variation according to the surgical phases (r = 0.576 to 0.689, p < 0.05, for pre-reperfusion; 0.290 to 0.429 for the post-reperfusion period). Conclusions: Continuous monitoring of intraoperative PST with an esophageal stethoscope has the potential to act as an indirect estimator of beat-to-beat arterial PP. Moreover, PSV appears to exhibit a trend similar to that of PPV with moderate accuracy. However, variation according to the surgical phase limits the merit of the current results, thereby necessitating cautious interpretation.

Non-contact thermography-based respiratory rate monitoring in a post-anesthetic care unit

“…Surely to be dismissed as inferior and niche, thermography shares several features of other “disruptive” technologies that have eventually come to replace their predecessors [ 19 ]. In the field of anesthesiology and critical care medicine, there have been many trials to estimate various kinds of vital signs using non-invasive measurement techniques, such as electrocardiography [ 20 ], pulse transit time [ 21 ], and phonocardiography [ 22 – 25 ]. Although we acknowledged that these techniques are still under development, we believe that all of these studies, including the present study, will improve patient safety and well-being in the near future.…”

Correlations between heart sound components and hemodynamic variables

“…In the two studies, we analyzed the time-domain and frequency-domain characteristics of heart sound signals obtained from digitalized recordings of ESS in patients under general anesthesia. The two studies demonstrated that 1) heart sounds varied differently depending on the mechanism of hemodynamic variations, and 2) the variation trend of the heart sound interval index was similar to that of the pulse pressure (PP) 8 .…”

Heart and Lung Sound Measurement Using an Esophageal Stethoscope with Adaptive Noise Cancellation

“…In previous studies, it has been shown that digital esophageal stethoscope systems can help to detect the intratracheal accumulation of secretion [3], to measure cardiovascular function [4,5], and predict fluid responsiveness during surgery [6]. However, when using a digital esophageal stethoscope in an operating room, there is a lot of noise coming from outside of the patient, which corrupts the main heart and lung sound signals.…”