Sniff nasal inspiratory pressure. A noninvasive assessment of inspiratory muscle strength.

The measurement of esophageal pressure during maximal sniffs (sniff Pes) has been shown useful to assess inspiratory muscle strength. The aim of this study was to validate a noninvasive method for estimating sniff Pes. The sniff nasal inspiratory pressure (SNIP) was measured through a plug occluding one nostril during sniffs performed through the contralateral nostril. Sniff Pes was simultaneously measured with an esophageal balloon. Ten normal subjects performed 338 sniffs of variable intensity. The correlation coefficient of SNIP and sniff Pes was 0.99 +/- 0.01 (p < 0.001). The ratio SNIP/sniff Pes was 0.91 (range, 0.82 to 0.99) and the mean difference between the two measures (SNIP - sniff Pes) was -4.56 cm H2O (-1.2 to -8.6 cm H2O). Twelve patients with neuromuscular or skeletal disorders performed 181 maximal sniffs. The correlation coefficient of SNIP and sniff Pes was 0.96 +/- 0.04 (p < 0.001). The ratio SNIP/sniff Pes was 0.93 (0.77 to 1.07) and the mean difference (SNIP - sniff Pes) was -4.66 cm H2O (+0.47 to -14.26 cm H2O). Nasal mucosal congestion was induced by nebulization of increasing doses of histamine in four normal subjects. The ratio SNIP/sniff Pes was 0.93 (0.72 to 1.02) when nasal peak flow was > 100 L/min, and 0.49 (0.36 to 0.57 L/min) when nasal peak flow fell below 100 L/min. We conclude that SNIP provides a reliable and noninvasive estimation of sniff Pes in normal subjects and in patients with neuromuscular or skeletal disorders. The validity of this method may by impaired by severe nasal congestion.