Minimally invasive, patient specific, beat-by-beat estimation of left ventricular time varying elastance

Abstract

BackgroundThe aim of this paper was to establish a minimally invasive method for deriving the left ventricular time varying elastance (TVE) curve beat-by-beat, the monitoring of which’s inter-beat evolution could add significant new data and insight to improve diagnosis and treatment. The method developed uses the clinically available inputs of aortic pressure, heart rate and baseline end-systolic volume (via echocardiography) to determine the outputs of left ventricular pressure, volume and dead space volume, and thus the TVE curve. This approach avoids directly assuming the shape of the TVE curve, allowing more effective capture of intra- and inter-patient variability.ResultsThe resulting TVE curve was experimentally validated against the TVE curve as derived from experimentally measured left ventricular pressure and volume in animal models, a data set encompassing 46,318 heartbeats across 5 Piétrain pigs. This simulated TVE curve was able to effectively approximate the measured TVE curve, with an overall median absolute error of 11.4% and overall median signed error of −2.5%.ConclusionsThe use of clinically available inputs means there is potential for real-time implementation of the method at the patient bedside. Thus the method could be used to provide additional, patient specific information on intra- and inter-beat variation in heart function.Electronic supplementary materialThe online version of this article (doi:10.1186/s12938-017-0338-7) contains supplementary material, which is available to authorized users.

Patient-Specific Monitoring and Trend Analysis of Model-Based Markers of Fluid Responsiveness in Sepsis: A Proof-of-Concept Animal Study

“…where E lv is the end systolic elastance of the left ventricle, V s,lv (t) is the stressed volume and e(t) is the normalised time-varying function derived following the work of Davidson et al [7] and detailed in the following section.…”

“…Time varying elastance (TVE) represents the active elastance in the cardiac chambers dictating the heart's contraction and expansion [7], [36]. TVE curves are derived using ventricular pressure and volume waveforms and contain information which can be used to drive cardiovascular models.…”

“…where V u is the unstressed volume in the left ventricle and P lv and V lv are the left ventricle pressure and volume, respectively. Previous work [7] has shown baseline V u can be approximated as a fixed percentage of the end-systolic volume (V es ), which allows an approximation of V u during an initial echocardiographic calibration, in which V es is available [7]. Thus, V u can be expressed [6]:…”

“…The method used to derive the driver function in this work is described by Davidson et al [7] and recreates pressure and volume waveforms using simple physiological assumptions combined with readily available clinical measurements. Continuous measurements of aortic pressure (P a ) and heart rate (HR), typically available in the ICU, in addition to baseline measurements of end-systolic (V es )…”

Blood pressure waveform contour analysis for assessing peripheral resistance changes in sepsis

“…One of the leading worldwide causes of intensive care unit (ICU) admission and mortality is cardiovascular disease and dysfunction (CVD), which costs an estimated $863 billion USD per annum (2010), and is the cause of roughly 31% of global deaths (2013) [ 1 ]. Thus, research into mitigating these large human and economic costs is a significant and ongoing field, ranging from work on less invasively estimating useful, but difficult to measure, clinical metrics [ 2 – 5 ], or a lumped model of the cardiovascular system [ 6 , 7 ], in an ICU environment, to work on investigating, selecting or estimating metrics of preclinical risk of cardiovascular [ 8 , 9 ] and arterial disease [ 10 , 11 ].…”