Physiological measurement
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Physiological measurement · Dec 2005
Clinical TrialAnalysis of intracranial pressure during and after the infusion test in patients with communicating hydrocephalus.
The cerebrospinal fluid (CSF) infusion test is used to evaluate the dynamics of CSF circulation in patients with communicating hydrocephalus and is based on constant-rate infusion of the normal saline into cerebrospinal fluid space. The aim of the study was to refine methods of the analysis of intracranial pressure (ICP) recorded during and after the infusion test. The mathematical model of cerebrospinal fluid circulation was extended by the equation describing ICP decrease after the infusion. ⋯ In 20 tests the differences between post- and pre-infusion resting ICP (DeltaICP) was higher than 1 mmHg, which was considered as significant. The mean value of DeltaICP for 20 infusion tests was 3.0 +/- 0.7 mmHg. The cerebral elasticity evaluated during the infusion was greater than the elasticity estimated from the decreasing phase after the infusion (0.24 +/- 0.07 ml(-1) versus 0.14 +/- 0.03 ml(-1); p < 0.01).
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Although the ventricular P-V loop has become a popular tool to characterize aspects of the performance of the heart, an arterial system P-V loop has not yet been described. In principle, the volume stored in the arterial system (V) could be calculated by integrating the difference between inflow and outflow. In practice, however, flow out of the innumerable arterioles cannot be measured directly. ⋯ Recently, the classical Windkessel model was generalized with the concept of apparent arterial compliance (C(app)), the transfer function relating pressure and volume expressed in the frequency domain. The arterial system P-V loop serves as a time-domain representation of C(app). This simple technique provides the first known characterization of an arterial system P-V loop.
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Physiological measurement · Dec 2005
Comparative Study Clinical TrialHeart rate variability: comparison among devices with different temporal resolutions.
Several devices based on ECG can acquire beat-to-beat intervals, and some of these devices may be used for heart rate variability (HRV) analysis. Most of these devices and their methods to acquire the beat-to-beat intervals need to be validated for HRV analysis by comparing them against traditional methods. Some of these methods have low temporal resolution, which may be sufficient for certain studies. ⋯ The HRV measures were further analyzed using the one-way repeated-measures analysis of variance (ANOVA) and statistically significant differences were observed in some of the HRV parameters obtained from the low-resolution method, especially the mean RR (p < 0.001) and the mean heart rate (p < 0.001). Since the same software was used for HRV analysis of the three methods, any differences were due to the temporal resolution of the RR intervals measured by the methods. Overall, both the methods correlated very well with the referent method among healthy volunteers in resting conditions and may be used by researchers for HRV studies.
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Physiological measurement · Dec 2005
Controlled Clinical TrialNoninvasive measurement of blood pressure variability: accuracy of the Finometer monitor and comparison with the Finapres device.
To assess the accuracy of spectral indices of arterial pressure variability and baroreflex sensitivity obtained from beat-by-beat noninvasive blood pressure recordings by the Finometer device, we compared these measures with those obtained from intra-arterial recordings. The performance of the Finometer was also compared to the traditional Finapres device. In 19 cardiac disease patients, including myocardial infarction, heart failure and cardiac transplant, we estimated the power of systolic and diastolic pressures in the VLF (0.01-0.04 Hz), LF (0.04-0.15 Hz) and HF (0.15-0.45 Hz) bands and computed absolute and percentage errors relative to intra-arterial brachial pressure. ⋯ The results for diastolic pressure were similar, but the Finapres errors in the VLF and LF bands were lower. Baroreflex sensitivity was significantly underestimated by both devices (Finometer: -31%, Finapres: -24%). Despite previous studies having shown that brachial artery waveform reconstruction performed by the Finometer has improved the accuracy of blood pressure measurement compared to the Finapres device, measurement of blood pressure variability in cardiac disease patients provides worse results in most spectral parameters and a better accuracy only in the HF band of systolic pressure.
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Physiological measurement · Dec 2005
Clinical TrialEstimation of breathing interval from the photoplethysmographic signals in children.
Two important parameters that are generally under continual observation during clinical monitoring are heart rate (HR) variability and breathing interval (BI) of patients. Current HR monitoring during night-long childhood respiratory sleep studies is well tolerated but BI monitoring requires instrumentation, like nasal cannula, that can be less accommodating for children. In this study, BI was extracted from the photoplethysmographic (PPG) signals using a two-stage signal processing technique termed zero-phase digital filtering. ⋯ Statistical analysis revealed that mean BI attained from the PPG signals were significantly related during tidal breathing (r(2) = 0.76; range 0.61-0.83; p < 0.05) and with the IRL (r(2) = 0.79; range 0.68-0.85; p < 0.05) in the absence of motion artefacts. Preliminary findings herein suggest that besides having the capability to monitor HR and arterial blood oxygen saturation measurements, the PPG signals can be used to derive BI for children. This can be an attractive alternative for children who are more disturbed by intrusive techniques in prolonged clinical monitoring.