PULMONARY-FUNCTION ALTERATIONS AFTER 3 WK OF EXPOSURE TO HYPOBARIA AND OR HYPOXIA IN GROWING RATS/

We studied lung growth in rats between 4 and 7 wk of age under differe nt conditions. There were five groups, seven animals in each: 1) gener al controls (ambient pressure and room air, food ad libitum); 2) hypob aric normoxic [barometric pressure (PB) 410 mmHg, PO2 153 Torr]; 3) no rmobaric hypoxic (ambient pressure, PO2 80 Torr); 4) hypobaric hypoxic (PB 410 mmHg, PO2 80 Torr); and 5) weight-matched controls to hypobar ic hypoxic. Residual volume, functional residual capacity, vital capac ity, and total lung capacity grew 10-20% more in both hypoxic groups t han in weight-matched and general controls. Expiratory flow rates corr ected for forced vital capacity decreased, and specific airway resista nce increased significantly. In addition, the ratio of forced expirato ry volume in 0.1 s to %forced vital capacity, peak expiratory flow rat e, and forced maximal midexpiratory flow were also lower in normobaric hypoxic animals compared with weight-matched controls. Above a transp ulmonary pressure of 6 cmH(2)O, flows were reduced in both hypoxic gro ups. No differences were observed between hypobaric normoxic and gener al control groups for lung volume and lung function. In weight-matched animals, total lung capacity decreased but lung function remained unc hanged. We conclude that accelerated lung growth in hypobaric hypoxia and normobaric hypoxia is dysanaptic. Lung growth in hypobaric hypoxia is primarily induced by low oxygen, but differences between hypobaric hypoxia and normobaric hypoxia suggest a beneficial effect of low pre ssure.