Maximum static inspiratory and expiratory pressures with different lung volumes

BACKGROUND: Maximum pressures developed by the respiratory muscles can indicate the health of the respiratory system, help to determine maximum respiratory flow rates, and contribute to respiratory power development. Past measurements of maximum pressures have been found to be inadequate for inclusion in some exercise models involving respiration. METHODS: Maximum inspiratory and expiratory airway pressures were measured over a range of lung volumes in 29 female and 19 male adults. A commercial bell spirometry system was programmed to occlude airflow at nine target lung volumes ranging from 10% to 90% of vital capacity. RESULTS: In women, maximum expiratory pressure increased with volume from 39 to 61 cmH(2)O and maximum inspiratory pressure decreased with volume from 66 to 28 cmH(2)O. In men, maximum expiratory pressure increased with volume from 63 to 97 cmH(2)O and maximum inspiratory pressure decreased with volume from 97 to 39 cmH(2)O. Equations describing pressures for both sexes are: P(e)/P(max )= 0.1426 Ln( %VC) + 0.3402 R(2 )= 0.95 P(i)/P(max )= 0.234 Ln(100 - %VC) - 0.0828 R(2 = )0.96 CONCLUSION: These results were found to be consistent with values and trends obtained by other authors. Regression equations may be suitable for respiratory mechanics models.