Respiratory physiology & neurobiology
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Respir Physiol Neurobiol · Jun 2007
Clinical TrialEstimation of arterial PCO2 from a lung model during ramp exercise in healthy young subjects.
The aim of this study is to propose a new approach to estimate non-invasively arterial carbon dioxide partial pressure (P(a)CO2) approach was based on the reconstruction of alveolar gas composition over each breath from a tidally ventilated lung model (P(M)(CO2)). Eight healthy young subjects were studied during a ramp exercise test on a cycle ergometer. Arterial samples were drawn at rest and every minute during the exercise test for determination of P(a)CO2. ⋯ The difference between estimated and measured P(a)CO2 on the whole ramp exercise was -0.3+/-1.9mmHg for P(M)(CO2), 1.0+/-2.2mmHg for P(ET)(CO2) and -1.7+/-1.7mmHg for P(J)(CO2). P(ET)(CO2) and P(J)(CO2) were significantly different from actual P(a)CO2 (P<0.001). It is concluded that, on the basis of the bias, the breathing lung model gave better estimates of P(a)CO2 than the two other indirect methods during ramp exercise.
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Respir Physiol Neurobiol · Mar 2007
Review Meta AnalysisArterial versus capillary blood gases: a meta-analysis.
A meta-analysis determined whether capillary blood gases accurately reflect arterial blood samples. A mixed effects model was used on 29 relevant studies obtained from a PubMed/Medline search. From 664 and 222 paired samples obtained from the earlobe and fingertip, respectively, earlobe compared to fingertip sampling shows that the standard deviation of the difference is about 2.5x less (or the precision is 2.5x better) in resembling arterial PO(2) over a wide range of arterial PO(2)'s (21-155 mm Hg ). ⋯ No real difference between sampling from the earlobe or fingertip were found for pH as both sites accurately reflect arterial pH over a wide range of pH (587 total paired samples, range 6.77-7.74, adjusted r(2)=0.90-0.94, mean bias=0.02). In conclusion, sampling blood from the fingertip or earlobe (preferably) accurately reflects arterial PCO(2) and pH over a wide range of values. Sampling blood, too, from earlobe (but never the fingertip) may be appropriate as a replacement for arterial PO(2), unless precision is required as the residual standard error is 6 mm Hg when predicting arterial PO(2) from an earlobe capillary sample.
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Respir Physiol Neurobiol · Mar 2007
Detection of partial endotracheal tube obstruction by forced pressure oscillations.
Rapid airway occlusions during mechanical ventilation are followed immediately by high-frequency pressure oscillations. To answer the question if the frequency of forced pressure oscillations is an indicator for partial obstruction of the endotracheal tube (ETT) we performed mathematical simulations and studies in a ventilated physical lung model. Model-derived predictions were evaluated in seven healthy volunteers. ⋯ According to the predictions derived from mathematical simulations, narrowing of the ETT's ID from 9.0 to 7.0mm decreased the frequency of the pressure oscillations by 11% while changes of the respiratory system's compliance had no effect. In volunteers, a similar reduction (10.9%) was found when 5 ml fluid were applied. We conclude that analysis of pressure oscillations after flow interruption offers a tool for non-invasive detection of partial ETT obstruction.
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Respir Physiol Neurobiol · Feb 2007
Oxidative stress time course in the rat diaphragm after freezing-thawing cycles.
Hyperthermia was shown to induce oxidative stress by uncoupling mitochondrial respiratory chain and to reduce superoxide dismutase (SOD) activity in muscles. Reactive carbonyl groups, malondialdehyde (MDA)-protein adducts, 3-nitrotyrosine immunoreactivity, Mn-SOD, and catalase were detected using immunoblotting in rat diaphragm specimens and homogenates thawed at room temperature (after previous storage at -80 degrees C) for 5, 15, 30, and 60 min, and 3, 6, and 24h to be subsequently and immediately stored at -80 degrees C. ⋯ Mn-SOD expression and activity were significantly reduced over time, while catalase expression showed no significant variation. Protein oxidation was significantly increased in the rat diaphragms exposed to freezing-thawing cycles of different time lengths, while Mn-SOD was substantially reduced in all muscles.
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Respir Physiol Neurobiol · Jan 2007
Clinical TrialAn additive interaction between different qualities of dyspnea produced in normal human subjects.
We evaluated the sensation of dyspnea induced by hypercapnia alone and a combination of hypercapnia and flow-resistive loading by the use of visual analogue scale (VAS) and the use of 13 listed descriptors in 23 healthy subjects. Hypercapnia alone caused a modest degree of dyspnea characterized by both air hunger and work/effort sensations. An addition of inspiratory flow-resistive loading (IRL) caused an increase in inspiratory difficulty and some attenuation of 'work/effort.' The addition of expiratory flow-resistive loading (ERL) caused an increase in expiratory difficulty and attenuation of 'air hunger.' The addition of both IRL and ERL caused a marked increase in dyspnea, the amount of which was close to the sum of the increases obtained individually by IRL and by ERL, while the quality of dyspnea was characterized predominantly by work/effort. These results suggest that despite the difference in quality of sensations, the intensity of dyspnea would sum linearly when the two kinds of loads are presented at the same time.