Maximal inspiratory and expiratory mouth pressures in sitting and half-lying positions in normal subjects

Maximal inspiratory (Pimax) and expiratory (Pemax) mouth pressures were measured in seven normal adults in both sitting and half-lying positions on 2 days. Analysis of variance did not reveal significant differences between measurements made in the two positions for either Pimax or Pemax. Measurements were repeatable and the results obtained in both positions were pooled. The coefficient of variation of Pimax was 4·7% between-trials and 10·3% between-days, and those for Pemax were 3·4% and 4·4%, respectively. It is suggested that measurements of Pimax and Pemax made in the half-lying position after thoracic surgery can be compared to pre-operative values which are commonly obtained in sitting without any influence from a positional effect. Details of the methodology to improve the reliability of the respiratory mouth pressures technique are discussed