Breathing and lung mechanics in hamsters: effect of pentobarbital anesthesia

An adaptation of the method reported by Skornik, Heimann, and Jaeger (Toxicol. Appl. Pharmacol. 59: 314-323, 1981) was used to evaluate pulmonary mechanics in intact awake hamsters. Lung volume changes were measured with a pressure plethysmograph, and pleural pressure was estimated by the use of a saline-filled esophageal catheter. We report data for normal awake hamsters studied at 18, 20, 22, 32, and 98 wk of age. Age-related differences were observed in tidal volume, dynamic compliance, and pulmonary resistance. To determine to what extent pulmonary mechanics are changed by anesthesia, hamsters were measured during spontaneous breathing while awake and while anesthetized. We found that anesthesia had a marked effect on the breathing pattern of normal hamsters. Twenty-five minutes after injection of pentobarbital sodium (70 mg/kg ip), tidal volume, dynamic compliance, pulmonary resistance, breathing frequency, and minute ventilation were 66, 40, 375, 60, and 41% of the corresponding awake values. Anesthesia always provoked a significant and dose-related decrease in tidal volume and an increase in respiratory period, together resulting in a profound decrease in minute ventilation. These significant differences from the awake values call into question the value of measurements in anesthetized animals. The methods described here yield reasonable and repeatable measurements and, because no anesthesia or surgery is required, they can be used in longitudinal studies when repeated measurements in the same animal over long periods of time can help define pathological changes or the effectiveness of various interventions.