Summarveither by denaturation of intracellular enzymes andlor nucleoNeonatal rats (4-7 days old) and adult rats (approximately 8 0 days old) were continuously exposed to either 96-98% oxygen or air. Examination of the lungs of neonatal rats, who survived 5 days of oxygen exposure with no evidence of respiratory distress, showed significant increases in the pulmonary superoxide dismutase (SOD) activity (peak value: 144% of airexposed controls), glutathione peroxidase (GP) activity (126%), glutathione reductase (GR) activity (122%), reduced glutathione (GSH) level (176%), and glucose-6-phosphate dehydrogenase activity (151%). Adult rats, most of whom succumbed within 3 days of oxygen exposure, did not show any significant increase in the activities of pulmonary SOD, GP, GR, and the level of GSH as compared to the air-exposed adult animals. Glucose-6-phosphate dehydrogenase was significantly elevated in the 72-hr oxygen-exposed adult rats. It. is concluded that increases in the lung complement of SOD, GR, GP, and GSH in the neonatal rat during oxygen challenge may provide the mechanism(s) for their increased tolerance to hyperoxia-induced lung injury as compared to the adults. SpeculationFurther knowledge about the role of the antioxidant defense mechanism(s) of the neonatal lung may have important implications in the pursuit of the etiology of neonatal respiratory disease and in the identification of agent@) that may minimize pulmonary toxicity associated with oxygen therapy.

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Chest physiotherapy is a frequently practiced but poorly documented form of therapy. Twenty neonates (mean age43 hr) were studied with a variety of respiratory disorders to assess the effect of complete chest physiotherapy on arterial blood cases. This was compared to the alteration of blood gases following suctioning of the airway. Nine were receivin~ added oxygen alone, six were receiving continuous distending pressure and five were intubated receiving mechanical ventilation. Complete chest physie therapy treatment consisted of postural drainage with percussions and vibrations in each drainage position followed by suctioning of the airway. The treatment was performed for a specific area of lung involvement if present. For generalized lung disorders, drainage was performed with an emphasis on the basal segments of the lower lobes. Each infant had arterial blood gases performed five minutes prior to and twenty minutes fdllowing suctioning, and similarly before and after physiotherapy (average interval between the two pairs=1.8 hr) There was a mean increase of 20.8 mm Hg in the pO following physiotherapy. (p(0.01) with no sipificant change zbserved following suctioning. There was no significant change in the pH or pCO with either procedure. Analysis of covariance revealed no signihcant correlations between p02 and sex, age, body weight, gestation, inspired oxygen concentration, or the order of receiving the procedures. In neonates with respiratory distress, oxygenation is improved following physiotherapy. VT were unchanged. Two hour followup values f o r a l l parameters studied were s i m i l a r t o control values except f o r a trend toward increased compl lance. There were no s i g n i f i c a n t d i f f e rences a t any stage o f the study f o r PaC02, pH, base excess. VT. o r minute ventilation. This studv indicates t h a t there i s a j i g n i f i c a n t de rease i n Pa02 a f t e s t v b t i o n nd suc toning n rease i n pa82 a f t e r hy erventPFa€!on but Feiese ceianges f o not appear t o be related t o ayterations i n lung volume. 190 E"%N,EBfvTef F k E E S~~a X F f l % e f R P T~i t i t u t eFACTORS AFFECTING LUNG VOLUME IN POST EXTUBATED NEONATES. William W. Fox, Jacob G. Schwartz. Thomas The Hospital for Sick Children, Toronto, Canada. It has been well established that slowly adapting vagal The failure to elicit a deflation reflex in all infants, and the absence of response to mucosal stimulation in sane infants suggasta that vagal irritant reflexes are weak or absent in human newborns. This may be one reason why aspiration is common in this age group. s~e c i a l 06biems. since neonatal CT tdbes are'uniuffed they Perm i t leakege o f gas around the tube during respiration and, therefore, introduce errors i n FRC determination. The present study evaluates a new 60 second closed c i r c u i t helium (He) d i l u t i o n technique f o r determination o f FRC independent o f small ga: leaks. By a n a l y t i c a l l y r e l a t i n q the f a l l i n lie concentration due LO mixi n g w i t h that due ...