Physiological measurement
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Physiological measurement · Jan 2008
Robust heart rate estimation from multiple asynchronous noisy sources using signal quality indices and a Kalman filter.
Physiological signals such as the electrocardiogram (ECG) and arterial blood pressure (ABP) in the intensive care unit (ICU) are often severely corrupted by noise, artifact and missing data, which lead to large errors in the estimation of the heart rate (HR) and ABP. A robust HR estimation method is described that compensates for these problems. The method is based upon the concept of fusing multiple signal quality indices (SQIs) and HR estimates derived from multiple electrocardiogram (ECG) leads and an invasive ABP waveform recorded from ICU patients. ⋯ Data fusion of each HR estimate was then performed by weighting each estimate by the Kalman filters' SQI-modified innovations. This method was evaluated on over 6000 h of simultaneously acquired ECG and ABP from a 437 patient subset of ICU data by adding real ECG and realistic artificial ABP noise. The method provides an accurate HR estimate even in the presence of high levels of persistent noise and artifact, and during episodes of extreme bradycardia and tachycardia.
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Physiological measurement · Jan 2008
Assessment of volume and leak measurements during CPAP using a neonatal lung model.
Although several commercial devices are available which allow tidal volume and air leak monitoring during continuous positive airway pressure (CPAP) in neonates, little is known about their measurement accuracy and about the influence of air leaks on volume measurement. The aim of this in vitro study was the validation of volume and leak measurement under CPAP using a commercial ventilatory device, taking into consideration the clinical conditions in neonatology. The measurement accuracy of the Leoni ventilator (Heinen & Löwenstein, Germany) was investigated both in a leak-free system and with leaks simulated using calibration syringes (2-10 ml, 20-100 ml) and a mechanical lung model. ⋯ In conclusion, the present in vitro study showed that the Leoni allowed accurate volume monitoring under CPAP conditions similar to neonates. Air leaks of up to 90% of patient flow were reliably detected. For an F(i)O(2) > 0.4 and for leaks > 19%, a numerical correction of the displayed volume should be performed.
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Physiological measurement · Dec 2007
The vulvalgesiometer as a device to measure genital pressure-pain threshold.
The construction and application of the vulvalgesiometer are described. This manually-applied device allows for the quantifiable measurement of pressure-pain thresholds in the external female genital region. A set of five vulvalgesiometers exerting pressures from 3 to 950 g was used in two studies. ⋯ Results demonstrated high levels of inter-rater reliability, indicating that the vulvalgesiometers can be consistently used by different investigators. Further, results indicated significant negative correlations between pressure-pain thresholds and pain intensity ratings recorded during the cotton-swab test, suggesting that the lower the threshold, the higher the pain ratings during vestibular palpation. The vulvalgesiometers can be utilized for several purposes, including treatment outcome studies and measuring the degree of PVD severity.
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Physiological measurement · Nov 2007
Noise analysis and MR pulse sequence optimization in MREIT using an injected current nonlinear encoding (ICNE) method.
Magnetic resonance current density imaging (MRCDI) and magnetic resonance electrical impedance tomography (MREIT) visualize an internal distribution of current density and/or conductivity by injecting current into an electrically conductive object such as the human body using an MRI scanner. MREIT measures the induced magnetic flux density which appears in the phase part of the acquired MR image data. Recently, the injected current nonlinear encoding (ICNE) method in MREIT extended the duration of the current injection until the end of a reading gradient to maximize the signal intensity of the magnetic flux density. ⋯ On the other hand, practically, the prolonged T(s)* may result in undesirable artifacts including blurring, chemical shift and phase error along the phase encoding direction. We observe that the noise level is a function of the data acquisition time T(s) and the rate of change in the noise level is slow near T(s)=T(s)*. Numerical phantom experiments show that a compromised T(s) between the ordinary data acquisition time and the optimal T(s)* reduces a relatively large amount of undesirable artifacts and almost maintains the optimized noise level of the measured magnetic flux density.
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Physiological measurement · Oct 2007
Research on the relationship between brain anoxia at different regional oxygen saturations and brain damage using near-infrared spectroscopy.
The objective of this paper is to investigate the difference in physiological parameters, EEG and morphology of brain tissues in newborn pigs with different regional oxygen saturations of brain (rSO(2)) and provide a basis for the determination of brain injury and degree of injury with the rSO(2) in clinical practice. A noninvasive near-infrared spectroscopy (NIRS) technique was used to monitor the rSO(2) of 27 newborn pigs. After mechanical ventilation and inhalation of 3-11% oxygen for 30 min by the newborn pigs, the pigs were grouped according to the rSO(2) in the brain caused by inhalation of different concentrations of oxygen. ⋯ When the rSO(2) was less than 30%, circulatory failure occurred, the level of blood lactic acid increased, there was serious metabolic acidosis, the amplitudes of the EEG significantly decreased, there were vacuolization and broken fragments of cells under the light microscope and the mitochondria in the neurons in the CA1 zone of hippocampi were seriously injured. Under varying degrees of hypoxia, when the rSO(2) is between 30% and 40%, brain injury occurs and the functional zones of mitochondria are injured in newborn pigs. When the rSO(2) is less than 30%, the brain functions are seriously abnormal, and the serious morphological impairment in the functional zones of mitochondria is the basis for the disturbance of energy metabolism in brain neurocytes after hypoxia and the sequelae of the nervous system.