Physiological measurement
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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.
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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 · Aug 2005
Air mattress sensor system with balancing tube for unconstrained measurement of respiration and heart beat movements.
The cardio-respiratory signal is a fundamental vital sign used for assessment of a patient's status. Additionally, the cardio-respiratory signal provides a great deal of information to healthcare providers wishing to monitor healthy individuals. The air mattress sensor system allows the measurement of the respiration and heart beat movements without the use of a harness or sensor on the subject's body, which eliminates the difficulties these pose for long term measurements. ⋯ With this balancing tube, the meaningful frequency range could be selected using a pneumatic method. A mathematical model was constructed and validation experiments were performed for step and sinusoidal input signals. This technique was applied to measurements of respiration and heart beat movements in the supine posture on the bed, which showed potential for applications in sleep analysis, unconstrained healthcare monitoring and neonate monitoring.
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Physiological measurement · Aug 2005
Randomized Controlled Trial Comparative Study Clinical TrialVariability in time delay between two models of pulse oximeters for deriving the photoplethysmographic signals.
Pulse oximetry is commonly used as an arterial blood oxygen saturation (SaO2) measure. However, its other serial output, the photoplethysmography (PPG) signal, is not as well studied. Raw PPG signals can be used to estimate cardiovascular measures like pulse transit time (PTT) and possibly heart rate (HR). ⋯ Novametrix differed from ECG by 0.71+/-0.58% (p<0.05) while Masimo differed by 4.51+/-3.66% (p>0.05). Modern oximeters can be attractive for their improved SaO2 measurement. However, using raw PPG signals obtained directly from these oximeters for timing-related measurements warrants further investigations.
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Physiological measurement · Aug 2005
Clinical Trial Controlled Clinical TrialInfluence of data resolution and interpolation method on assessment of secondary brain insults in neurocritical care.
Continuous monitoring of physiologic vital signs is routine in neurocritical care. However, this patient information is usually only recorded intermittently (most often hourly) in the medical record. It is unclear whether this is sufficient to represent the occurrence of secondary brain insults (SBIs) or whether more frequent data collection will provide more comprehensive information for patient care. ⋯ MR data tended to underestimate the number of total events. 95% limits of agreement were most narrow for trapezoidal interpolation of MR data, but even these limits were fairly broad. Assessment of secondary brain insults is highly dependent on (1) the temporal resolution of the method used to acquire patient data and on (2) the interpolation method if data are acquired intermittently. High frequency data acquisition may be necessary for more precise evaluation of secondary brain injury in neurocritical care.