Effect of temperature on pressure-volume hysteresis of excised lungs

Dexamethasone-induced changes in lung function are not prevented by concomitant treatment with retinoic acid

Alveolarization is impaired in rats treated with dexamethasone (Dex) on postnatal days 4-13, but concomitant treatment with all-trans retinoic acid (RA) increases alveolar number. To determine whether morphological changes induced by Dex and/or RA predict changes in lung function at 1 mo, we assessed resting breathing parameters, dynamic compliance, ventilation required to maintain O(2) saturation at > or = 90%, and pressure-volume curves of air-filled lungs. During resting breathing, mean tidal volume per gram was greater in Dex + RA-treated rats than in controls (P < 0.05). Dynamic compliance was also greater in Dex- and Dex + RA-treated rats than in controls or RA-treated rats (P < 0.02). In Dex- and Dex + RA-treated rats, we observed increased hysteresis ratios (P < or = 0.006), air trapping (P < 0.05), and lung volumes at 5 and 13.5 cmH(2)O pressure (P < 0.001) and decreased elastic recoil (P < 0.007). The effect of Dex on elastic recoil was greater in female than in male rats (P = 0.006). Despite impaired septation, O(2) saturation was not compromised in Dex- or Dex + RA-treated rats. Thus lung function changes induced by Dex treatment during alveolarization were not prevented by concomitant treatment with RA.

Ventilatory responses to changes in temperature in mammals and other vertebrates

This article reviews the relationship between pulmonary ventilation (VE) and metabolic rate (oxygen consumption) during changes in ambient temperature. The main focus is on mammals, although for comparative purposes the VE responses of ectothermic vertebrates are also discussed. First, the effects of temperature on pulmonary mechanics, chemoreceptors, and airway receptors are summarized. Then we review the main VE responses to cold and warm stimuli and their interaction with exercise, hypoxia, or hypercapnia. In these cases, mammals attempt to maintain both oxygenation and body temperature, although conflicts can arise because of the respiratory heat loss associated with the increase in ventilation. Finally, we consider the VE responses of mammals when body temperature changes, as during torpor, fever, sleep, and hypothermia. In ectotherms, during changes in temperature, VE control becomes part of a general strategy to maintain constant relative alkalinity and ensure a constancy of pH-dependent protein functions (alphastat regulation). In mammals on the other hand, VE control is aimed to balance metabolic needs with homeothermy. Therefore, alphastat regulation in mammals seems to have a low priority, and it may be adopted only in exceptional cases.