Journal of clinical monitoring and computing
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A new application of photoplethysmography (PPG) has emerged recently to provide the possibility of heart rate monitoring without a telemetric chest strap. The aim of this study was to determine if a new device could detect pulsation over a broad range of skin types, and what light wavelength would be most suitable for detecting the signals. A light emitting diode-based PPG system was used to detect changes in pulsatile blood flow on 23 apparently healthy individuals (11 male and 12 female, 20-59 years old) of varying skin types classified according to a questionnaire in combination with digital photographs with a skin type chart. Four different light wavelengths (470, 520, 630, and 880 nm) were tested. Normalized modulation level is calculated as the AC/DC component ratio and represents the change in flow over the underlying constant state of flow or perfusion. ⋯ We concluded that a PPG-based device can detect pulsation across all skin types and that a greater resolution was obtained using a green light wavelength at rest and a green or blue light wavelength during exercise.
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J Clin Monit Comput · Jun 2013
Randomized Controlled TrialStO₂ guided early resuscitation in subjects with severe sepsis or septic shock: a pilot randomised trial.
The scientific community has agreed upon developing accurate monitoring of tissue perfusion and oxygenation to improve the management of subjects with sepsis. This pilot study aimed to investigate the feasibility of targeting tissue oxygen saturation (StO₂) in addition to the currently recommended resuscitation goals, central venous pressure, mean arterial pressure and central venous oxygen saturation, in patients with severe sepsis or septic shock. A pilot, single-centre, randomised, non-blinded trial recruited 30 subjects with severe sepsis upon intensive care unit admission at an academic medical centre in France. ⋯ At study day 7, there were 5/15 (33.3 %) subjects who died or had a DSOFA > 0 in the experimental arm and 4/15 (26.6 %) who died or had a DSOFA > 0 in the control arm (p = 1.00). This pilot study was the first randomised controlled trial using an algorithm derived from the SSC recommendations, which included StO₂ as a treatment goal. However, the protocol showed no clear trend for or against targeting StO₂.
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J Clin Monit Comput · Jun 2013
A system for portable sleep apnea diagnosis using an embedded data capturing module.
Sleep apnea (SA) is a very common disease with serious health consequences, yet is very under-diagnosed, partially because of the high cost and limited accessibility of in-laboratory polysomnography (PSG). The purpose of this work is to introduce a newly developed portable system for the diagnosis of SA at home that is both reliable and easy to use. The system includes personal devices for recording breath sounds and airflow during sleep and diagnostic algorithms to process the recorded data. The data capturing device consists of a wearable face frame with an embedded electronic module featuring a unidirectional microphone, a differential microphone preamplifier, a microcontroller with an onboard differential analogue to digital converter, and a microSD memory card. The device provides continuous data capturing for 8 h. Upon completion of the recording session, the memory card is returned to a location for acoustic analysis. We recruited 49 subjects who used the device independently at home, after which each subject answered a usability questionnaire. Random data samples were selected to measure the signal-to-noise ratio (SNR) as a gauge of hardware functionality. A subset of 11 subjects used the device on 2 different nights and their results were compared to examine diagnostic reproducibility. Independent of those, system's performance was evaluated against PSG in the lab environment in 32 subject. The overall success rate of applying the device in un-attended settings was 94 % and the overall rating for ease-of-use was 'excellent'. Signal examination showed excellent capturing of breath sounds with an average SNR of 31.7 dB. Nine of the 11 (82 %) subjects had equivalent results on both nights, which is consistent with reported inter-night variability. The system showed 96 % correlation with simultaneously performed in-lab PSG. ⋯ Our results suggest excellent usability and performance of this system and provide a strong rationale to further improve it and test its robustness in a larger study.
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J Clin Monit Comput · Jun 2013
Usefulness of perfusion index to detect the effect of brachial plexus block.
The traditional method to evaluate adequacy of the block for surgery is based on loss of sensory response to stimuli, which requires patient cooperation. Several methods have been described for objective assessment of the nerve block. The aim of the study was to investigate whether perfusion index (PI), a measure of peripheral perfusion from a pulse oximetry finger sensor, is a reliable and objective method for assessing the adequacy of infraclavicular blockade and to describe the time course of PI changes once peripheral nerve block has been achieved during surgery. ⋯ The perfusion index is a predictor of infraclavicular block success. The largest changes in PI occur 30 min after the block administration but significant changes in PI were detected 10 min after administration. Perfusion index monitoring may provide a highly valuable tool to quickly evaluate the success of regional anesthesia of the upper extremity in clinical practice.
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J Clin Monit Comput · Jun 2013
Reference values for volumetric capnography-derived non-invasive parameters in healthy individuals.
The aim of this study was to determine typical values for non-invasive volumetric capnography (VCap) parameters for healthy volunteers and anesthetized individuals. VCap was obtained by a capnograph connected to the airway opening. We prospectively studied 33 healthy volunteers 32 ± 6 years of age weighing 70 ± 13 kg at a height of 171 ± 11 cm in the supine position. ⋯ Volunteers showed better clearance of CO₂ compared to anesthetized patients as indicated by (median and interquartile range): (1) an increased elimination of CO₂ per mL of VT of 0.028 (0.005) in volunteers versus 0.023 (0.003) in anesthetized patients, p < 0.05; (2) a lower normalized slope of phase III of 0.26 (0.17) in volunteers versus 0.39 (0.38) in anesthetized patients, p < 0.05; and (3) a lower Bohr dead space ratio of 0.23 (0.05) in volunteers versus 0.28 (0.05) in anesthetized patients, p < 0.05. This study presents reference values for non-invasive volumetric capnography-derived parameters in healthy individuals. Mechanical ventilation and anesthesia altered these values significantly.