Journal of applied physiology
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In ten mechanically ventilated patients, six with chronic obstructive pulmonary disease (COPD) and four with pulmonary edema, we have partitioned the total respiratory system mechanics into the lung (l) and chest wall (w) mechanics using the esophageal balloon technique together with the airway occlusion technique during constant-flow inflation (J. Appl. Physiol. 58: 1840-1848, 1985). ⋯ The work performed by the ventilator to inflate the lung (WL) averaged 2.04 +/- 0.59 and 1.25 +/- 0.21 J/l in COPD and pulmonary edema patients, respectively, whereas Ww was approximately 0.4 J/l in both groups, i.e., close to normal values. We conclude that, in mechanically ventilated patients, abnormalities in total respiratory system mechanics essentially reflect alterations in lung mechanics. However, abnormalities in chest wall mechanics can be relevant in some COPD patients with a high degree of pulmonary hyperinflation.
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In comparing gas exchange responses of the methacholine- (MCh) challenged mongrel dog with leukotriene receptor blockers and placebo at different inspiratory O2 fractions (FIO2), we previously noted systematically different values of cardiac output as a function of drug administration and/or FIO2. This confounds identification of the effects of FIO2 and/or drugs on gas exchange, because shunt is well known to vary directly with cardiac output when other factors are equal. Accordingly, in six dogs we examined the dependence of combined shunt and low ventilation-perfusion (VA/Q) blood flow ("shunt") on cardiac output in the MCh-challenged mongrel dog. ⋯ With 12% O2 breathing shunt rose by only 2.2% per 1-l/min rise in blood flow. This FIO2 -dependent behavior of the shunt-cardiac output relationship was highly reproducible, both within and between animals. It suggests that the increase in shunt with cardiac output depends more on vascular tone of noninjured areas than on tone of the low VA/Q regions (which are hypoxic at all FIO2 values).
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Comparative Study
Shivering and pathological and physiological clonic oscillations of the human ankle.
Shivering and physiological and pathological clonus of the ankle were compared using power spectral and cross-correlation analysis of their respective electromyographic and acceleration waveforms. The major spectral peaks from each type of involuntary oscillation possessed similar frequencies (5-7 Hz). Soleus electromyographic activity was significantly correlated with the motion signal, whereas no correlation was observed between motion and tibialis anterior electromyographic signal. These data suggest that although shivering and physiological and pathological clonus are activated by different stimuli, these overt ankle oscillations may be an expression of a common spinal neuronal network.
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Normal subjects have a larger diffusing capacity normalized per liter alveolar volume (DL/VA) in the supine than in the sitting position. Body position changes total lung diffusing capacity (DL), DL/VA, membrane conductance (Dm), and effective pulmonary capillary blood volume (Qc) as a function of alveolar volume (VA). These functions were studied in 37 healthy volunteers. ⋯ The relationship between Qc and VA was best described by a second-order polynomial characterized by a maximum Qc at a VA greater than 60% of TLC. Qc was significantly higher in the supine position than in the sitting position, but the difference became smaller with increasing age. In observing the sitting and supine positions, we saw a decrease in maximum Qc normalized per square meter of body surface area with age.
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The role of blood rheology in the pathogenesis of acute mountain sickness and high-altitude pulmonary edema was investigated. Twenty-three volunteers, 12 with a history of high-altitude pulmonary edema, were studied at low altitude (490 m) and at 2 h and 18 h after arrival at 4,559 m. Eight subjects remained healthy, seven developed acute mountain sickness, and eight developed high-altitude pulmonary edema. ⋯ The erythrocyte aggregation was about doubled 18 h after the arrival compared with low-altitude values, which reflects the acute phase reaction. There were, however, no significant differences in any rheological parameters between healthy individuals and subjects with acute mountain sickness or high-altitude pulmonary edema, either before or during the illness. We conclude that rheological abnormalities can be excluded as an initiating event in the development of acute mountain sickness and high-altitude pulmonary edema.