MAXIMAL VALUES OF SNIFF NASAL INSPIRATORY PRESSURE IN HEALTHY-SUBJECTS

Background- Inspiratory muscle strength is often better reflected by o esophageal pressure during a maximal sniff (sniff FOES) than by maxima l inspiratory pressure (PImax). Sniff FOES can be estimated non-invasi vely by measuring the sniff nasal inspiratory pressure (SNIP). The aim was to establish maximal normal values for the SNIP and to compare th em with PImax. Methods - One hundred and sixty healthy subjects (80 me n) aged 20-80 years were recruited. Ah subjects had a forced vital cap acity (FVC) of >80%, a forced expiratory volume in one second (FEV(1)) /FVC of >85% predicted value, and a body mass index of 18-31 kg/m(2). Because PImax is known to be reduced in the supine posture, the SNIP w as measured in both the sitting and the supine positions. PImax sustai ned over one second was measured from functional residual capacity (FR C) in the sitting position with a standard flanged mouthpiece during f our manoeuvres. SNIP was measured from FRC in the sitting and supine p ositions using a catheter through a plug occluding one nostril during 10 maximal sniffs through the contralateral nostril. For each test the largest pressure measured in cm H2O was taken into account. Results - For both men and women maximal SNIP was negatively correlated with ag e, and was similar in the sitting and the supine positions. In the sit ting position maximal SNIP was greater or equal to PImax in 107 of 160 subjects. The mean (SD) ratio SNIP/PImax was 1.08 (0.22) in men and 1 .17 (0.29) in women. Conclusions - Normal values of maximal SNIP can b e predicted from age and sex. Maximal SNIP is similar in the sitting a nd the supine position and is significantly higher than PImax in healt hy subjects. The low level of agreement between maximal SNIP and PImax indicates that the two manoeuvres are not interchangeable but complem entary.