Performance comparison of ventricular and arterial dP/dtmax for assessing left ventricular systolic function during different experimental loading and contractile conditions

Abstract Background Maximal left ventricular (LV) pressure rise (LV dP/dtmax), a classical marker of LV systolic function, requires LV catheterization, thus surrogate arterial pressure waveform measures have been proposed. We compared LV and arterial (femoral and radial) dP/dtmax to the slope of the LV end-systolic pressure-volume relationship (Ees), a load-independent measure of LV contractility, to determine the interactions between dP/dtmax and Ees as loading and LV contractility varied. Methods We measured LV pressure-volume data using a conductance catheter and femoral and radial arterial pressures using a fluid-filled catheter in 10 anesthetized pigs. Ees was calculated as the slope of the end-systolic pressure-volume relationship during a transient inferior vena cava occlusion. Afterload was assessed by the effective arterial elastance. The experimental protocol consisted of sequentially changing afterload (phenylephrine/nitroprusside), preload (bleeding/fluid bolus), and contractility (esmolol/dobutamine). A linear-mixed analysis was used to assess the contribution of cardiac (Ees, end-diastolic volume, effective arterial elastance, heart rate, preload-dependency) and arterial factors (total vascular resistance and arterial compliance) to LV and arterial dP/dtmax. Results Both LV and arterial dP/dtmax allowed the tracking of Ees changes, especially during afterload and contractility changes, although arterial dP/dtmax was lower compared to LV dP/dtmax (bias 732 ± 539 mmHg⋅s− 1 for femoral dP/dtmax, and 625 ± 501 mmHg⋅s− 1 for radial dP/dtmax). Changes in cardiac contractility (Ees) were the main determinant of LV and arterial dP/dtmax changes. Conclusion Although arterial dP/dtmax is a complex function of central and peripheral arterial factors, radial and particularly femoral dP/dtmax allowed reasonably good tracking of LV contractility changes as loading and inotropic conditions varied

Validity and variability of xBRS: Instantaneous cardiac baroreflex sensitivity

Spontaneous oscillations of blood pressure (BP) and interbeat interval (IBI) may reveal important information on the underlying baroreflex control and regulation of BP. We evaluated the method of continuously measured instantaneous baroreflex sensitivity by cross correlation (xBRS) validating its mean value against the gold standard of phenylephrine (Phe) and nitroprusside (SNP) bolus injections, and focusing on its spontaneous changes quantified as variability around the mean. For this purpose, we analyzed data from an earlier study of eight healthy males (aged 25–46 years) who had received Phe and SNP in conditions of baseline and autonomic blocking agents: atropine, propranolol, and clonidine. Average xBRS corresponds well to Phe/SNP-BRS, with xBRS levels ranging from 1.2 (atropine) to 102 msec/mmHg (subject asleep under clonidine). Time shifts from BP- to IBI-signal increased from ≤1 sec (maximum correlations within the current heartbeat) to 3–5 sec (under atropine). Plotted on a logarithmic vertical scale, xBRS values show 40% variability (defined as SD/mean) over the whole range in the various conditions, except twice when the subjects had fallen asleep and it dropped to 20%. The xBRS oscillates at frequencies of 0.1 Hz and lower, dominant between 0.02–0.05 Hz. Although xBRS is the result of IBI/BP-changes, no linear coherence was found in the cross-spectra of the xBRS-signal and IBI or BP. We speculate that the level of variability in the xBRS-signal may act as a probe into the central nervous condition, as evidenced in the two subjects who fell asleep with high xBRS and only 20% of relative variation

Feasibility of Noninvasive continuous finger arterial blood pressure measurements in very young children, aged 0-4 years

Our goal was to study the feasibility of continuous noninvasive finger blood pressure (BP) monitoring in very young children, aged 0-4 y. To achieve this, we designed a set of small-sized finger cuffs based on the assessment of finger circumference. Finger arterial BP measured by a volume clamp device (Finapres technology) was compared with simultaneously measured intra-arterial BP in 15 very young children (median age, 5 mo; range, 0-48), admitted to the intensive care unit for vital monitoring. The finger cuff-derived BP waveforms showed good resemblance with the invasive arterial waveforms (mean root-mean-square error, 3 mm Hg). The correlation coefficient between both methods was 0.79 +/- 0.19 systolic and 0.74 +/- 0.24 diastolic. The correlation coefficient of beat-to-beat changes between both methods was 0.82 +/- 0.18 and 0.75 +/- 0.21, respectively. Three measurements were related to measurement errors (loose cuff application; wrong set-point). Excluding these erroneous measurements resulted in clinically acceptable measurement bias (-3.8 mm Hg) and 95% limits of agreement (-10.4 to + 2.8 mm Hg) of mean BP values. We conclude that continuous finger BP measurement is feasible in very young children. However, cuff application is critical, and the current set-point algorithm needs to be revised in very young childre

Bridging cardiovascular physics, physiology, and clinical practice: Karel H. Wesseling, pioneer of continuous noninvasive hemodynamic monitoring

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Comparison of differences in cohort (forwards) and case control (backwards) methodological approaches for validation of the Hypotension Prediction Index.

BackgroundThe Hypotension Prediction Index (the index) software is a machine learning algorithm that detects physiological changes that may lead to hypotension. The original validation used a case control (backwards) analysis that has been suggested to be biased. We therefore conducted a cohort (forwards) analysis and compared this to the original validation technique.MethodsWe conducted a retrospective analysis of data from previously reported studies. All data were analysed identically with 2 different methodologies and receiver operating characteristic curves (ROC) constructed. Both backwards and forwards analyses were performed to examine differences in area under the ROC for HPI and other haemodynamic variables to predict a MAP < 65mmHg for at least 1 minute 5, 10 and 15 minutes in advance.ResultsTwo thousand and twenty-two patients were included in the analysis, yielding 4,152,124 measurements taken at 20 second intervals. The area-under-the-curve for the index predicting hypotension analysed by backward and forward methodologies respectively was 0.957 (95% CI, 0.947-0.964) vs 0.923 (95% CI, 0.912-0.933) 5 minutes in advance, 0.933 (95% CI, 0.924-0.942) vs 0.923 (95% CI, 0.911-0.933) 10 minutes in advance , and 0.929 (95% CI, 0.918-0.938) vs. 0.926 (95% CI, 0.914-0.937) 15 minutes in advance. No other variable had an area-under-the-curve > 0.7 except for MAP. Area-under-the-curve using forward analysis for MAP predicting hypotension 5, 10, and 15 minutes in advance was 0.932 (95% CI, 0.920-0.940), 0.929 (95% CI, 0.918-0.938), and 0.932 (95% CI, 0.921-0.940). The R 2 for the variation in the index due to MAP was 0.77.ConclusionUsing an updated methodology, we found the utility of the HPI index to predict future hypotensive events is high, with an area under the receiver-operating-characteristics curve similar to that of the original validation method

The reliability of continuous noninvasive finger blood pressure measurement in critically ill children.

Contains fulltext : 81204.pdf (publisher's version ) (Closed access)INTRODUCTION: Continuous noninvasive arterial blood pressure can be measured in finger arteries using an inflatable finger cuff (FINAP) with a special device and has proven to be feasible and reliable in adults. We studied prototype pediatric finger cuffs and pediatric software to compare this blood pressure measurement with intraarterially measured blood pressure (IAP) in critically ill children. METHODS: We included sedated and mechanically ventilated children admitted to our pediatric intensive care unit. We performed simultaneous arterial blood pressure measurements during a relatively stable hemodynamic period and compared FINAP, IAP, and the noninvasive blood pressure oscillometric technique. We also compared IAP to a reconstruction of brachial pressure from finger pressure. RESULTS: Thirty-five children between 2 and 22 kg body weight were included. In total, 152 attempts to record a FINAP pressure were performed of which 4.6% were unsuccessful. When comparing FINAP to IAP, bias was -16.2, -7.7, and -10.2 mm Hg for systolic arterial blood pressure, diastolic arterial blood pressure, and mean arterial blood pressure. Limits of agreement (LOA) were respectively 26.1%, 30.1%, and 22.6%. When reconstruction of brachial pressure from finger pressure was compared to IAP, these results were -11.8, 0.6, and -0.9 mm Hg for bias and 21.7%, 8.9%, and 8.9% for LOA. When noninvasive blood pressure oscillometric technique was compared to IAP, the results were: -6.8, -0.9, and -3.8 mm Hg for bias and 18.2%, 38.6%, and 22.1% for LOA. CONCLUSION: Beta type continuous noninvasive arterial blood pressure monitoring using a finger cuff with brachial arterial waveform reconstruction seems reliable in hemodynamically stable critically ill children

Feasibility of noninvasive continuous finger arterial blood pressure measurements in very young children, aged 0-4 years

Our goal was to study the feasibility of continuous noninvasive finger blood pressure (BP) monitoring in very young children, aged 0-4 y. To achieve this, we dedigned a set of smallsized finger cuffs based on the assessment of finger circumference. Finger arterial BP measured by a volume clamp device (Finapress technology) was compared with simultaneously measured intra-arterial BP in 15 very young children (median age, 5 mo; range, 0-48), admitted to the intensive care unit for vital monitoring. The finger cuff-derived BP waveforms showed good resemblance with the invasive arterial waveforms (mean root-mean-square error, 3 mm Hg). The correlation coefficient between both methods was 0.79 ± 0.19 systolic and 0.74 ± 0.24 diastolic. The correlation coefficient of beat-to-beat changes between both methods was 0.82 ± 0.18 and 0.75 ± 0.21, respectively. Three measurements were related to measurement errors (loose cuff application; wrong set-point). Excluding these erroneous measurements resulted in clinically acceptable measurement bias (-3.8 mm Hg) and 95% limits of agreement (-10.4 to + 2.8 mm Hg) of mean BP values. We conclude that continuous finger BP measurement is feasable in very young children. However, cuff application is critical, and the current set-point algorithm needs to be revised in very young children. (Pediatr Res 63: 691-696, 2008