A comparative study of the effects of dry vs. humidified ventilation on canine lungs.

To compare the effects on canine ciliary and bronchial mucosal function of varying periods of ventilation with dry vs. humidified gas mixtures, 29 anesthetized dogs underwent 2, 4, and 6 hours of ventilation through a Carlen's double-lumen tube. Six dogs were evaluated by clearance studies, nine by differential bronchospirometry, six by surfactant studies, six by electron microscopy, and two by ventilation scanning. By means of two separate respiratory systems, dry gas (DG) was used to ventilate the right lung, and humidified gas (HG) ventilated the left lung in each dog. Serial chest roentgenograms showed more rapid clearance of inspired tantalum dust from the HG-ventilated lung in each of the six dogs, the disparity in clearance between the two lungs being more pronounced after longer periods of ventilation. The surface tension in DG-ventilated lungs increased fourfold, whereas in HG-ventilated lungs it increased only twofold as compared to preoperative values. Longer periods of ventilation did not change the surface tension appreciably in either DG- or HG-ventilated lungs. Scanning electron micrographs of bronchial mucosa from DG-ventilated lungs showed tangling and matting of cilia with a granular and stringy material attached to most cilia; these changes were much less pronounced in HG-ventilated lungs. Bronchospirometric studies showed an increase in ventilatory function in each of the lungs ventilated with the HG mixture (percent Vo2 on 100 percent oxygen increased 27.7 percent) to compensate for the decreased gas exchange provided by the contralateral DG-ventilated lung. Function in each of the lungs returned to normal within 24 hours. Ventilation scans with Xenon133 showed no apparent change in isotope uptake in the HG-ventilated lungs as compared to the DG lungs during the first 24 hours after ventilation. The observations from the present study suggest that ventilation of canine lungs with DG for 4 or more hours dries mucus and transiently retards mucociliary clearance and gas exchange. These changes may be minimized by ventilation with a humidified gas mixture. Application of these findings to patients undergoing prolonged general anesthesia and to lung preservation studies is suggested.

Evaluation of pulmonary function in the ischemic expanded canine lung.

Twenty-four dogs underwent in vivo left pulmonary hilar occlusion with the lung continuously expanded at 10 centimeters or 25 centimeters of water pressure to determine the period of pulmonary ischemia that may be tolerated before consistent pulmonary edema and congestion develop after lung revascularization. Consistent and prolonged pulmonary edema and congestion that caused death of the dog occurred in at least one-half of the dogs when the period of hilar occlusion was extended beyond six hours. Elevation of the left pulmonary artery pressure was only a rough measurement of the severity of the anoxic pulmonary injury. Expansion of the lung at 10 centimeters of water continuous pressure was more beneficial than was expansion at 25 centimeters of pressure. Cyclic ventilation with slight negative-expiratory pressure provided less support to the lung than did continuous expansion at either pressure tested. Intial decreases in both ventilation and perfusion isotope uptake and the percentage of the total volume of oxygen uptake per minute by the ischemic lung returned to near normal levels in three weeks in dogs that survived. Lung expansion during periods of ischemia appears to prevent alveolar collapse and to facilitate oxygenation.