Journal of applied physiology
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Gravity-dependent changes of regional lung function were studied during normogravity, hypergravity, and microgravity induced by parabolic flights. Seven healthy subjects were followed in the right lateral and supine postures during tidal breathing, forced vital capacity, and slow expiratory vital capacity maneuvers. Regional 1) lung ventilation, 2) lung volumes, and 3) lung emptying behavior were studied in a transverse thoracic plane by functional electrical impedance tomography (EIT). ⋯ During tidal breathing, the differences in ventilation magnitudes between the right and left lung regions were not significant in either posture or gravity phase. A significant nonlinearity of lung emptying was determined at normogravity and hypergravity. The pattern of lung emptying was homogeneous during microgravity.
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Ventilation-perfusion (VA/Q) inhomogeneity was modeled to measure its effect on arterial oxygenation during maintenance-phase anesthesia involving an inspired mixture of 30% O(2) and either N(2)O or N(2). A multialveolar compartment computer model was constructed based on a log normal distribution of VA/Q inhomogeneity. Increasing the log SD of the distribution of blood flow from 0 to 1.75 produced a progressive fall in arterial PO(2) (Pa(O(2))). ⋯ The improvement in Pa(O(2)) when N(2)O was present instead of N(2) was greatest when the degree of VA/Q inhomogeneity was in the range typically seen in anesthetized patients. Models based on distributions of expired and inspired alveolar ventilation give quantitatively different results for Pa(O(2)). In the presence of VA/Q inhomogeneity, second-gas and concentrating effects may have clinically significant effects on arterial oxygenation even at "steady-state" levels of N(2)O uptake.
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Volatile anesthetics have multiple actions on intracellular Ca(2+) homeostasis, including activation of the ryanodine channel (RyR) and sensitization of this channel to agonists such as caffeine and ryanodine. Recently it has been described that the nucleotide cADP-ribose (cADPR) is the endogenous regulator of the RyR in many mammalian cells, and cADPR has been proposed to be a second messenger in many signaling pathways. I investigated the effect of volatile anesthetics on the cADPR signaling system, using sea urchin egg homogenates as a model of intracellular Ca(2+) stores. ⋯ The reverse was also true: addition of subthreshold concentrations of cADPR sensitized the homogenates to halothane. In contrast, all the volatile anesthetics used had no effect on the activity of the enzyme that synthesizes cADPR. I propose that the complex effect of volatile anesthetics on intracellular Ca(2+) homeostasis may involve modulation of the cADPR signaling system.
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Positive-pressure ventilation (PPV) may affect left ventricular (LV) performance by altering both LV diastolic compliance and pericardial pressure (Ppc). We measured the effect of PPV on LV intraluminal pressure, Ppc, LV volume, and LV cross-sectional area in 17 acute anesthetized dogs. To account for changes in lung volume independent of changes in Ppc and differences in contractility, measures were made during both open- and closed-chest conditions, during closed chest with and without chest wall binding, and after propranolol-induced acute ventricular failure (AVF). ⋯ The decrease in EDV was greater in control than in AVF conditions, whereas the shift of the ESV to the left of the ESPVR was greater with AVF than in control conditions. We conclude that the hemodynamic effects of PPV inspiration are due primarily to changes in intrathoracic pressure and that the inspiration-induced decreases of LV EDV reflect direct effects of intrathoracic pressure on LV filling. The decreases in LV ESV exceed the amount explained solely by a reduction in LV ejection pressure.