Static volume-pressure relationship in normal rats at various stages of growth.

Static deflation air volume-pressure (V-P) curves were studied in 136 open-chested normal male rats ranging from 103 to 604 g in weight. The lungs accepted a greater volume of air as rats grew in size, but beyond 8 weeks of age, the volume expressed per g of lung weight progressively decreased. In older rats, V-P curves in precent maximum lung air volume (%MLV) were shifted upward and to the left compared to younger rats. We believe that these differences reflect various phases in the postnatal growth of rat lungs and loss of tiss elasticity due to the aging process, respectively. Lung air volume at 30 cm H2O Ptp (MLV30) showed a significantly higher linear relationship with body weight (r = 0.93) than with lung-heart weight (r = 0.80) as the independent variable. We present V-P nomograms and discuss two techniques of measuring V-P relationships with their specific applications.