Journal of applied physiology
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Values of the classical Haldane coefficient, i.e, the change in the concentration of total CO2 in whole blood per unit of change in the concentration of total O2 at constant PCO2, have been calculated at different combinations of plasma pH (range 7.25-7.50), erythrocyte 2,3-diphosphoglycerate (DPG) concentration (range 3.5-6.5 mM), PCO2 (range 25.0-65.0 Torr), initial hemoglobin O2 saturation (range 0.50-0.80), and erythrocyte volume fraction (range 0.25-0.55). The principle of the calculations is to utilize the so-called reciprocity relations to determine the amount of protons and CO2 released from hemoglobin on oxygenation and to estimate the resulting change in the concentration of total CO2 from published data on the interaction coefficient for the binding of O2 and protons to hemoglobin, the interaction coefficient for the binding of O2 and CO2 to hemoglobin, the distribution of protons across the erythrocyte membrane, the equilibrium constants for the reactions between CO2 and H2O, and CO2 and oxyhemoglobin, the buffer capacity of oxygenated erythrolysate, and the buffer capacity of plasma. ⋯ Furthermore, the coefficient depends on the hemoglobin O2 saturation and the erythrocyte volume fraction. The dependency of the Haldane coefficient on the O2 saturation and the PCO2 causes an increase in the O2-linked CO2 flux across the alveolar membrane by more than 30% in patients with respiratory insufficiency.
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The modulatory role of endogenous opiates on the Hering -Breuer inflation reflex was examined in 11 newborn kittens, aged 10-31 days, during active and quite sleep. The Hering -Breuer apnea duration was significantly shortened by naloxone (1 mg/kg, intraperitoneally; P less than 0.05). ⋯ Hering -Breuer apnea is a result of the inspiratory inhibition and expiratory excitation of medullary neurons in response to lung stretch; the apnea is terminated by the opposing influences of chemoreceptors, which respond to hypercapnia and hypoxia. The results suggest that opioid influences on the Hering -Breuer reflex are due to an opioid modulation of the carotid body discharge in hypoxia, or of its central integration, and that sleep state is not implicated in such modulation in kittens.
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Although esophageal pressures have been substituted for direct pleural pressure measurement in humans, we have investigated the validity of this approach under circumstances when left and right pleural pressures are not equal. Esophageal and bilateral pleural pressures in awake sheep were compared by using matched balloon catheters in close proximity. In standing sheep, both end-expiratory pressures and inspiratory pressure swings were similar in all three catheter systems. ⋯ In the lateral decubitus position, positive end-expiratory pleural pressures were consistently observed. This was believed to be due to a combination of contraction of expiratory muscles, rapid respiratory rate resulting in insufficient expiratory time to reach an equilibrium pressure, and increased airways resistance resulting from compression of the dependent lung by the abdominal viscera. A single study in a paralyzed ventilated sheep showed less positive expiratory pressures, which were further reduced to zero or less when the respiratory rate was slowed to 10 breaths/min.
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Comparative Study
Effects and mechanism of action of terbutaline on diaphragmatic contractility and fatigue.
We studied the effects of intravenously administered terbutaline on diaphragmatic force and fatigue during electrical stimulation of the diaphragm in 17 anesthetized dogs. The diaphragm was stimulated indirectly through the phrenic nerves with electrodes placed around the fifth roots and directly with electrodes surgically implanted in the abdominal side of each hemidiaphragm. Transdiaphragmatic pressure (Pdi) during direct or indirect supramaximal 2-s stimulation applied over a frequency range of 10-100 Hz was measured with balloon catheters during tracheal occlusion at functional residual capacity. ⋯ At the end of the fatigue procedure Pdi decreased by 50 +/- 5 and 30 +/- 8% of control values at 10 and 100 Hz, respectively, for either direct or indirect stimulation. The decrease in Pdi for low frequencies of stimulation (10 and 20 Hz) lasted 100 +/- 18 min, whereas it lasted only 40 +/- 10 min for the high frequencies (50 and 100 Hz). When terbutaline (0.5 mg) was administered after the fatiguing procedure, Pdi increased within 15 min by 20 +/- 4% at 10 Hz and by 12 +/- 3% at 100 Hz for either direct or indirect stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)
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Despite numerous efforts, a reliable model of chronic embolic pulmonary hypertension has not been established. To develop such a model five conscious mongrel dogs were embolized repeatedly over 16-30 wk with Sephadex microspheres 286 +/- 70 micron in diameter. Hemodynamic and respiratory measurements were obtained just prior to each embolization. ⋯ Reembolization in one of these caused further pulmonary hypertension. In two dogs acute pulmonary vasodilation by O2 breathing and administration of prostaglandin E1 reduced, but did not abolish, the increased pulmonary vascular resistance, suggesting some vascular tone was present. An embolic model of chronic pulmonary hypertension in awake dogs allows further investigation into the evolution of pulmonary hypertension.