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See detailMinimally invasive estimation of ventricular dead space volume through use of Frank-Starling curves.
Davidson, Shaun; Pretty, Chris; Pironet, Antoine et al

in PLoS ONE (2017), 12(4), 0176302

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 ... [more ▼]

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. [less ▲]

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See detailMinimally invasive, patient specific, beat-by-beat estimation of left ventricular time varying elastance.
Davidson, Shaun; Pretty, Chris; Pironet, Antoine et al

in BioMedical Engineering OnLine (2017), 16(1), 42

BACKGROUND: The 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 ... [more ▼]

BACKGROUND: The 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. RESULTS: The 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 Pietrain 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%. CONCLUSIONS: The 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. [less ▲]

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See detailEvaluation of a plasma insulin model for glycaemic control in intensive care.
Dickson, Jennifer; Thomas, Felicity Louise ULiege; Pretty, Chris et al

in Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference (2015), 2015

Hyperglycaemia is a common complication in the intensive care unit (ICU), and is associated with worsened outcomes. Model-based insulin therapy protocols have been shown to be safe and effective in ... [more ▼]

Hyperglycaemia is a common complication in the intensive care unit (ICU), and is associated with worsened outcomes. Model-based insulin therapy protocols have been shown to be safe and effective in intensive care. Such protocols rely on correct modeling of glucose-insulin dynamics. In particular, model-based control typically relies on insulin sensitivity (SI) metrics, which are heavily influenced by plasma insulin kinetics. Plasma insulin samples were taken as part of a sepsis study and compared to modeled plasma insulin. Samples were taken in septic patients at the onset of glycaemic control, and once the patient consistently met less than two of the SIRs criteria that help define sepsis. It was found that inter-patient insulin dynamics were more variable at the onset of insulin therapy, than in the later samples after sepsis abated. Overall, the model adequately captured crucial steady state dynamics. Transient dynamics in plasma insulin following a bolus were faster than modeled, indicating greater clearance of insulin than currently modeled. [less ▲]

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See detailAccuracy and optimization of a subcutaneous insulin model for less acute critical care patients.
Thomas, Felicity Louise ULiege; Dickson, Jennifer; Pretty, Chris et al

in Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference (2015), 2015

Extending safe, effective glycemic control to the general wards requires a simple approach using subcutaneous (SC) insulin. However, this approach can increase relative risk compared to intravenous ... [more ▼]

Extending safe, effective glycemic control to the general wards requires a simple approach using subcutaneous (SC) insulin. However, this approach can increase relative risk compared to intravenous insulin due to the increased variability of SC insulin appearance. This paper evaluates the accuracy of a SC plasma insulin model and optimizes its parameters using measured plasma insulin data from 6 less acute critical care patients treated with SC insulin. The SC plasma insulin model used captures the dynamics of regular SC insulin well. However, there appears to be a positive bias leading to an overall median [IQR] residual error of -28.3 [-37 - 19] mU/L. The optimized model reduced the RMS residual error by 20-70% for each patient. The distinct inter- and intra-patient, and cohort variation seen in this data highlights the importance to of understanding how SC insulin appearance dynamics may be affected by the subject condition. [less ▲]

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See detailValidation of a Virtual Patient and Virtual Trials Method for Accurate Prediction of TGC Protocol Performance
Suhaimi, Fatanah; Le Compte, Aaron; Penning, Sophie ULiege et al

Poster (2011, March)

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See detailEnhanced insulin sensitivity variability in the first 3 days of ICU stay: Implications for TGC
Chase, Geoffrey; Le Compte, Aaron; Penning, Sophie ULiege et al

Poster (2011, March)

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