Rapid declines in systolic blood pressure are associated with an increase in pulse transit time

PLOS ONE RESEARCH ARTICLE Rapid declines in systolic blood pressure are associated with an increase in pulse transit time Sebastian Grøvdal Schaanning1, Nils Kristian Skjaervold ID1,2* 1 Department of Circulation and Medical Imaging, Norwegian University of Science and Technology, Trondheim, Norway, 2 Department of Anaesthesia and Intensive Care Medicine, Trondheim University Hospital, Trondheim, Norway a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 * Abstract Background OPEN ACCESS Citation: Schaanning SG, Skjaervold NK (2020) Rapid declines in systolic blood pressure are associated with an increase in pulse transit time. PLoS ONE 15(10): e0240126. https://doi.org/ 10.1371/journal.pone.0240126 Editor: Kenta Matsumura, Toyama Daigaku, JAPAN Received: April 29, 2020 Accepted: September 20, 2020 Published: October 8, 2020 Peer Review History: PLOS recognizes the benefits of transparency in the peer review process; therefore, we enable the publication of all of the content of peer review and author responses alongside final, published articles. The editorial history of this article is available here: https://doi.org/10.1371/journal.pone.0240126 Copyright: © 2020 Schaanning, Skjaervold. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: The waveform data analysed during the current study is available in the MIMIC-III Waveform Database Matched Subset, found at https://archive.physionet.org/physiobank/ database/mimic3wdb/matched/. The associated clinical data is available in the MIMIC-III Clinical The correlation between pulse transit time and blood pressure has been proposed as a route to measure continuous non-invasive blood pressure. We investigated whether pulse transit time trends could model blood pressure trends during episodes of rapid declines in blood pressure. Methods From the Medical Information Mart for Intensive Care waveform database we identified substantial blood pressure reductions. Pulse transit time was calculated from the R-peak of the electrocardiogram to the peak of the arterial pulse waveform. The time-series were processed with a moving average filter before comparison. Averaged, continuous heart rate was also analysed as a control. The intra-individual association between variables was assessed per subject using linear regression. Results In the 511 patients included we found a median correlation coefficient between blood pressure and pulse transit time of -0.93 (IQR -0.98 to -0.76) with regression slopes of -1.23 mmHg/ms (IQR -1.73 to -0.81). The median correlation coefficient between blood pressure and heart rate was 0.46 (IQR -0.16 to 0.83). In supplementary analysis, results did not differ substantially when widening inclusion criteria, but the results were not always consistent within subjects across episodes of hypotension. Conclusions In a large cohort of critically ill patients experiencing episodes of rapid declines in systolic blood pressure, there was a moderate-strong intra-individual correlation between averaged systolic blood pressure and averaged pulse transit time. Our findings encourage further investigation into using the pulse transit time for non-invasive real-time detection of hypotension. PLOS ONE | https://doi.org/10.1371/journal.pone.0240126 October 8, 2020 1 / 16 PLOS ONE Database, found at https://physionet.org/content/ mimiciii/1.4/. Funding: SGS was internally funded within Trondheim University Hospital and the Norwegian University of Science and Technology. The funding body did not participate in the design, collection, analysis, interpretation or writing of the study/ manuscript. NKS receives postdoctoral funding from Central Norway Health Authority, Grant nr 46056918 Competing interests: NKS is chief medical officer and shareholder in Moon Labs, a medicaltechnology company that is prototyping a wearable biosensor; the company is currently not working with continuous blood pressure monitoring. SGS declares that he has no competing interests. This does not alter our adherence to PLOS ONE policies on sharing data and materials. Pulse transit time and blood pressure Introduction Blood Pressure (BP) is an essential vital parameter that is monitored in most if not all hospitalized patients. BP measurements guide inpatient treatment of hypertension, act as a marker of hemodynamic status and severity of illness and can be used for cardiovascular risk stratification. The detection of acute hypotension is of particular interest, as this may signify the onset of circulatory shock, a feared clinical entity that requires prompt hemodynamic support and diagnostic workup [1]. Continuous BP-monitoring, however, is currently reserved for patients in whom the invasive insertion of an arterial line can be justified. In practice, this means that for most hospitalized patients, BP is monitored using intermittent cuff-based measurements. The interval between measurements may be several hours, and a recent publication found that a substantial proportion of significant BP-perturbations may go undetected with standard monitoring [2]. This implies that continuous non-invasive BP-monitoring (cNIBP) could benefit patients who are not candidates for arterial line placement. Various techniques for cNIBP have been proposed, and some integrated systems have been developed. Perhaps most known is the vascular-unloading technique, originally proposed by Marey, and later by Shirer and Penaz [3–5], and employed by Finapres1 devices. In this method, a finger cuff is combined with a measure of finger blood volume using photoplethysmography (PPG). By varying the finger cuff pressure to keep the PPG signal constant, a pressure wave can be obtained that approximates the arterial pressure waveform [6]. Another technique for cNIBP is arterial tonometry, which aims to reproduce the arterial waveform based on the transcutaneous displacement produced by a pulsating artery. The method employs an external pressure transducer placed over a superficial artery, typically the radial artery [7]. A third technique which has been subject to much research is utilization of pulse wave velocity (PWV) and the related distance-invariant pulse transit time (PTT). This concept can be rooted in two physio-mathematical relationships, namely the Moens-Korteweg equation [8] and the relationship between elastic modulus and pressure, as empirically demonstrated by Hughes et al. [9], among others. In summary, the combination of these models entails that for an elastic tube the PWV is proportional to the elastic modulus of the tube wall, which in turn is proportional to the pressure within the tube. A further elaboration on these relationships is outside the scope of this article. PWV and PTT, have been studied extensively for their relationship to (...truncated)