Expiratory muscle conditioning in hypotonic children with low vocal intensity levels

The purpose of this study was to determine if expiratory muscle conditioning in children with low muscle tone and reduced vocal intensity would effect improvements in muscle strength and endurance which would be reflected in increased sound pressure level. Ten subjects (ages 8-14 yr) with speech impairment were tested for expiratory muscle strength (RMS) and endurance (RME), subglottal pressure (P_S), and sound pressure level (SPL) during a standard syllable task. Expiratory muscle strength was measured as maximum expiratory pressure (Pe max), RME as the decrease in Pe max performed for 5 seconds every 10 seconds for 2 min. Sound pressure level (SPL) was measured using a sound level meter. Subglottal pressure was estimated from intraoral air pres-sure as subjects repeated /pa/ seven times continuously at "comfortable" and "high" SPLs. Tests were performed prior to, at 2-week intervals during, at the end of, and 3 weeks following a 6-week conditioning period. Subjects wore a face mask fitted with a resistor (2.5-7.5 cm H₂O) 15 min a day, 5 days a week for 6 weeks. Expiratory muscle strength increased significantly (30%) within 2 weeks and continued to increase (69%) by 6 weeks. The improvement was still evident (44%) by 3 weeks postconditioning. There was no change in RME. Subglottal pressure increased by 40% and 38%, compared to baseline, during comfortable and high SPL voice, respectively, after 6 weeks of conditioning. Sound pressure level improved at 2 weeks (8% comfortable, 7% high SPL) and continued to improve (18% comfortable, 19% high SPL) by 6 weeks. This improvement was evident 3 weeks postconditioning (11% comfortable, 9% high SPL). Conditioning of the expiratory muscles with a face mask can improve respiratory muscle function and vocal performance in children with voice impairments related to low muscle tone.