REPRODUCIBILITY OF TWITCH MOUTH PRESSURE, SNIFF NASAL INSPIRATORY PRESSURE, AND MAXIMAL INSPIRATORY PRESSURE

Twitch mouth pressure (P-mo,P-tw) during magnetic phrenic nerve stimul ation and sniff nasal inspiratory pressure (SNIP) were recently propos ed as alternative noninvasive methods for assessing inspiratory muscle strength. This study aimed to compare their reproducibility with maxi mal inspiratory pressure (MIP) in normal subjects. Ten healthy subject s were studied at functional residual capacity in semirecumbent positi on. Cervical magnetic phrenic nerve stimulation was performed during g entle expiration against an occlusion incorporating a small leak. Cons tancy of stimulation was controlled by recording diaphragmatic electro myogram. Within and between-session reproducibility of pressure were s tudied for P-mo,P-tw, SNIP, and MIP. The subjects were studied during a session of 10 manoeuvres repeated after 1 day and 1 month. The mean values were 16 cmH(2)O for P-mo,P-tw, 118 cmH(2)O for SNIP, and 115 cm H(2)O for MIP. For the three tests, the within subject variation was s mall in relation to between-subject variation, with the intraclass cor relation coefficient ranging 0.79-0.90 for P-mo,P-tw, 0.85-0.92 for SN IP, and 0.88-0.92 for MIP. At 1 day interval, the coefficient of repea tability (2 SD of differences) was 3.6 cmH(2)O for P-mo,P-tw, 32 cmH(2 )O for SNIP and 28 cmH(2)O for MIP. At 1 month interval, the coefficie nt of repeatability was 5.8 cmH(2)O for P-mo,P-tw, 23 cmH(2)O for SNIP and 21 cmH(2)O for MIP. We conclude that the within session reproduci bility of the new tests twitch mouth pressure and sniff nasal inspirat ory pressure is sufficient to be clinically useful, For sniff nasal in spiratory pressure, the between session reproducibility established af ter 1 day was maintained after 1 month. For twitch mouth pressure, the between session reproducibility declined slightly after 1 month. Thes e characteristics should be considered when using these methods to fol low an individual patient over time.