Effects of muscle group recruitment on sniff transdiaphragmatic pressure and its components

Measuring maximal sniff pressures is an easy way of assessing inspiratory m uscle strength. During a static manoeuvre, the pattern of inspiratory muscl e recruitment during a sniff can vary from one individual to another. We th erefore assessed how voluntarily changing muscle recruitment would affect s niff oesophageal, gastric and transdiaphragmatic pressures (Pes,sn, Pga,sn and Pdi,sn, respectively). Ten normal subjects (age 27-39 years) performed natural sniff manoeuvres ("nat"), and preferentially diaphragmatic ("dia") or extra-diaphragmatic ("extradia") sniff manoeuvres, after having learnt t o dissociate between the inspiratory muscle groups. Abdominal displacements were monitored using a belt-mounted strain gauge. Natural patterns of musc le recruitment varied among subjects. On average, Pes,sn,nat was [median (r ange)] 81 (21-105) cmH(2)O. All of the subjects were able to modify inspira tory muscle recruitment voluntarily. Pes,sn was not significantly affected by the type of manoeuvre performed, as opposed to Pdi,sn, which, as expecte d, increased with both the diaphragmatic and extradiaphragmatic manoeuvres [Pdi,sn,dia 132 (99-157) cmH(2)O, Pdi,sn,extradia 96 (50-146) cmH(2)O, P < 0.05]. Whatever the manoeuvre, there was no correlation between Pes and Pdi , but Pga and Pdi were correlated during both the diaphragmatic (r=0.82, P <0.05) and the extradiaphragmatic manoeuvre (r = 0.70, P < 0.05). Pes,sn ma y have limitations as an index of diaphragm function, but by showing its in dependence from inspiratory muscle recruitment, this study contributes to i ts validation as a robust index of global inspiratory muscle strength that is particularly well suited for follow-up studies. This should extend to Pe s,sn substitutes measured at the airway opening.