Journal of applied physiology
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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.