Abstract
This paper develops a means of more easily and less invasively estimating ventricular dead space volume (Vd), an important, but difficult to measure physiological parameter. Vd represents a subject and condition dependent portion of measured ventricular volume that is not actively participating in ventricular function. It is employed in models based on the time varying elastance concept, which see widespread use in haemodynamic studies, and may have direct diagnostic use. The proposed method involves linear extrapolation of a Frank-Starling curve (stroke volume vs end-diastolic volume) and its end-systolic equivalent (stroke volume vs end-systolic volume), developed across normal clinical procedures such as recruitment manoeuvres, to their point of intersection with the y-axis (where stroke volume is 0) to determine Vd. To demonstrate the broad applicability of the method, it was validated across a cohort of six sedated and anaesthetised male Pietrain pigs, encompassing a variety of cardiac states from healthy baseline behaviour to circulatory failure due to septic shock induced by endotoxin infusion. Linear extrapolation of the curves was supported by strong linear correlation coefficients of R = 0.78 and R = 0.80 average for pre- and post- endotoxin infusion respectively, as well as good agreement between the two linearly extrapolated y-intercepts (Vd) for each subject (no more than 7.8% variation). Method validity was further supported by the physiologically reasonable Vd values produced, equivalent to 44.3–53.1% and 49.3–82.6% of baseline end-systolic volume before and after endotoxin infusion respectively. This method has the potential to allow Vd to be estimated without a particularly demanding, specialised protocol in an experimental environment. Further, due to the common use of both mechanical ventilation and recruitment manoeuvres in intensive care, this method, subject to the availability of multi-beat echocardiography, has the potential to allow for estimation of Vd in a clinical environment.
Highlights
Ventricular dead space volume (Vd) and the related ventricular volume at zero pressure (V0) are important subject-specific parameters for normalising inter- and intra- subject variation in cardiovascular models, including the widely used end-systolic pressure-volume relation (ESPVR) and time varying elastance (TVE) models [1,2,3,4,5,6]
In cardiac models based on the TVE concept, which are widely used in haemodynamic studies [1,2,3,4,5,6], Vd and V0 are used to account for variations in heart size, shape and efficiency between individuals and as an individual’s condition changes
This paper presents a novel method for deriving Vd as physiologically defined in [7]: the volume at which ‘the ventricle cannot develop any systolic pressure’
Summary
Ventricular dead space volume (Vd) and the related ventricular volume at zero pressure (V0) are important subject-specific parameters for normalising inter- and intra- subject variation in cardiovascular models, including the widely used end-systolic pressure-volume relation (ESPVR) and time varying elastance (TVE) models [1,2,3,4,5,6]. Vd has been defined as the volume at which ‘the ventricle cannot develop any systolic pressure’, which occurs at ‘a volume coordinate only mildly less than V0 [1, 7]’ (referred to as Vd ). As such, being able to estimate and account for Vd and V0 on a subject and condition specific basis improves the physiological accuracy and the ability to accurate compare results from these models, where such models offer significant potential clinical benefits [4, 5, 8, 9].
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