Physiological measurement
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Physiological measurement · Aug 2013
Clinical TrialA respiratory monitoring device based on clavicular motion.
Respiratory rate is one of the key vital signs yet unlike temperature, heart rate or blood pressure, there is no simple and low cost measurement device for medical use. Here we discuss the development of a respiratory sensor based upon clavicular motion and the findings of a pilot study comparing respiratory rate readings derived from clavicular and thoracic motion with an expiratory breath flow reference sensor. Simultaneously sampled data from resting volunteers (n = 8) was analysed to determine the location of individual breaths in the data set and from these, breath periods and frequency were calculated. ⋯ This pilot study demonstrates the viability of clavicular respiratory sensing. The sensor is unobtrusive, unaffected by bioelectrical or electrode problems and easier to determine and more consistent than thoracic motion sensing. With relatively basic signal conditioning and processing requirements, it could provide an ideal platform for a low-cost respiratory monitor.
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Physiological measurement · Aug 2013
Validation of a spectroscopic sensor for the continuous, noninvasive measurement of muscle oxygen saturation and pH.
New patient monitoring technologies can noninvasively and directly provide an assessment of the adequacy of tissue perfusion through the simultaneous determination of muscle oxygen saturation (SmO2) and muscle pH (pHm). Non-pulsatile near infrared spectroscopy is used to determine these microvascular parameters. Two separate studies were conducted using an isolated perfused swine limb preparation to widely vary venous blood oxygen saturation (SviO2) and pH (pHvi) to assess the accuracy of a noninvasive sensor with the capability to simultaneously measure both parameters. ⋯ Sensors were also evaluated on human subjects. There was no statistical difference in SmO2 by gender or location when multiple sensors were evaluated on the right and left calf, deltoid, and thigh of resting men and women (N = 33). SmO2 precision for subjects at rest was 5.6% over the six locations with four different sensors.
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Physiological measurement · Jun 2013
Uniform background assumption produces misleading lung EIT images.
Electrical impedance tomography (EIT) estimates an image of conductivity change within a body from stimulation and measurement at body surface electrodes. There is significant interest in EIT for imaging the thorax, as a monitoring tool for lung ventilation. To be useful in this application, we require an understanding of if and when EIT images can produce inaccurate images. ⋯ The conductivity gradient associated with gravitational lung collapse causes conductivity changes in non-dependent lung to be overestimated by up to 100% with respect to the dependent lung. Eliminating the mismatch by using a realistic conductivity distribution in the forward model of the reconstruction algorithm strongly reduces these undesirable effects. We conclude that subject-specific anatomically accurate forward models should be used in lung EIT and extra care is required when analysing EIT images of subjects whose background conductivity distribution in the lungs is known to be heterogeneous or exhibiting large changes.
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Physiological measurement · Feb 2013
Comparative StudyEvaluation of pulse rate variability obtained by the pulse onsets of the photoplethysmographic signal.
This work presents the evaluation of pulse rate variability (PRV) obtained from pulse onsets of photoplethysmographic (PPG) signals. Three published algorithms were used to determine the pulse onsets: diastolic point, maximum second derivative and tangent intersection. ⋯ Furthermore, the concordance correlation coefficient was used to correlate the indices. In all the cases, PRV indices obtained through the tangent intersection method showed better accuracy and precision (Bland-Altman analysis, bias ± 1.96 standard deviation: low frequency, LF(ms)(2) = -28.06 ± 72.68; high frequency, HF(ms)(2) = -68.23 ± 192.85; high frequency in normalized units, HF(nu) =-2.02 ± 7.08; LF/HF = 0.17 ± 0.71) and higher correlation (concordance correlation coefficients: low frequency, LF(ms)(2) = 0.99; high frequency, HF(ms)(2) = 0.98; high frequency in normalized units, HF(nu) = 0.97; LF/HF = 0.90) with HRV indices than other methods, and could be used as a good surrogate of HRV.
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Physiological measurement · Feb 2013
Obstructive sleep apnea screening by integrating snore feature classes.
Obstructive sleep apnea (OSA) is a serious sleep disorder with high community prevalence. More than 80% of OSA suffers remain undiagnosed. Polysomnography (PSG) is the current reference standard used for OSA diagnosis. ⋯ Clinical diagnosis supported by standard PSG was used as the reference diagnosis to compare our results against. Our proposed techniques resulted in a sensitivity of 93±9% with specificity 93±9% for females and sensitivity of 92±6% with specificity 93±7% for males at an AHI decision threshold of 15 events/h. These results indicate that our method holds the potential as a tool for population screening of OSA in an unattended environment.