Physiological measurement
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Physiological measurement · Mar 2014
Pitfalls in microdialysis methodology: an in vitro analysis of temperature, pressure and catheter use.
Microdialysis of macromolecules within the brain provides a unique insight into physiological and pathological processes occurring within an otherwise inaccessible cranial cavity. The physically restricted nature of the intracranial compartment may present wider variations of pressure and temperature than those experienced in the rest of the body. ⋯ Our results demonstrate that the wide variation of recovery attributable to different catheter use outweighed any effects caused by temperature or pressure. Investigators performing cytokine microdialysis using the CMA 71 system should be aware of the wide inter-catheter variability and potential effects of temperature on recovery.
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Physiological measurement · Mar 2014
Efficacy of dynamic indices in predicting fluid responsiveness in patients with obstructive jaundice.
Previous studies have shown that the stroke volume variation (SVV), the pulse pressure variation (PPV) and the pleth variability index (PVI) could be successfully used for predicting fluid responsiveness (FR) in surgical patients. The aim of this study was to validate the ability of SVV, PPV and PVI to predict intraoperative FR in mechanically ventilated patients with obstructive jaundice (OJ). Thirty-two patients with OJ (mean serum total bilirubin 190.5 ± 95.3 µmol L(-1)) received intraoperative volume expansion (VE) with 250 ml colloids immediately after an exploratory laparotomy had been completed and after a 5 min period of hemodynamic stability. ⋯ Eleven (34%) patients were responders and 21 patients were nonresponders to VE. The PPV was the unique dynamic index that had the moderate ability to predict FR during surgical procedures, the area under the curve was 0.71 (95% CI, 0.523 to 0.856; P = 0.039) and the threshold (sensitivity and specificity) discriminated responders was 7.5% (63.6%/71.4%). The present study concluded that SVV and PVI were not reliable predictors of FR, but PPV has some value predicting FR in patients with OJ intraoperatively.
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Physiological measurement · Feb 2014
In vitro estimation of pressure drop across tracheal tubes during high-frequency percussive ventilation.
Tracheal tubes (TT) are used in clinical practice to connect an artificial ventilator to the patient's airways. It is important to know the pressure used to overcome tube impedance to avoid lung injury. Although high-frequency percussive ventilation (HFPV) has been increasingly used, the mechanical behavior of TT under HFPV has not yet been described. ⋯ Model 3 presented the most robust resistance-related coefficient. Estimated inertances did not vary among the models using the same tube. In conclusion, in HFPV ΔPTT can be easily calculated by the physician using model 3.
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Physiological measurement · Feb 2014
The human ear canal: investigation of its suitability for monitoring photoplethysmographs and arterial oxygen saturation.
For the last two decades, pulse oximetry has been used as a standard procedure for monitoring arterial oxygen saturation (SpO2). However, SpO2 measurements made from extremities such as the finger, ear lobe and toes become susceptible to inaccuracies when peripheral perfusion is compromised. To overcome these limitations, the external auditory canal has been proposed as an alternative monitoring site for estimating SpO2, on the hypothesis that this central site will be better perfused. ⋯ In contrast, no significant changes were seen in the red and infrared EC PPG amplitude measurements, which changed by +2.5% and -1.2% respectively. The RIF and LIF pulse oximeters have failed to estimate accurate SpO2 in seven and four volunteers respectively, while the EC pulse oximeter has only failed in one volunteer. These results suggest that the EC may be a suitable site for reliable monitoring of PPGs and SpO2s even in the presence of peripheral vasoconstriction.
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Physiological measurement · Dec 2013
Characterization of the mechanical behavior of intrapulmonary percussive ventilation.
A new device delivering intrapulmonary percussive ventilation (IPV), called Impulsator® (Percussionaire Corporation, Sandpoint, ID, USA), has recently been introduced in an effort to provide effective clearance and to promote homogeneity of ventilation in the lungs of patients with cystic fibrosis. In order to optimize the treatment based on its use, a better understanding of its functioning is still necessary. ⋯ Quantitative information was obtained about the physical variables administered by the device like percussive frequency, ratio of inspiratory to expiratory time, flow and pressure magnitudes and volume exchanged. The analysis of the data determined the relations among these variables and between them and the mechanical loads, laying the basis for an optimal clinical application of the device.