SIZE AND STRENGTH OF THE RESPIRATORY AND QUADRICEPS MUSCLES IN PATIENTS WITH CHRONIC ASTHMA

There have been few studies of respiratory and limb muscle size and fu nction in middle-aged patients with asthma and persistent airways obst ruction. We have compared the forces generated by the respiratory and thigh muscles with their dimensions assessed by ultrasound in nine mid dle-aged patients with chronic asthma (mean age 56 (SD 8) yrs; functio nal residual capacity/total lung capacity ratio (FRC/TLC) 60 (10) %), and in nine normal subjects (aged 53 (7) yrs; FRC/TLC 55 (5) %). Diaph ragm thickness was measured at the zone of apposition by B-mode ultras ound during relaxation (DiTrelax) and during a maximum-effort inspirat ory manoeuvre (DiTPL,max) at FRC. Cross-sectional area of the relaxed rectus femoris muscle (ARF) was determined by ultrasound at mid-thigh level. Isometric strength of the right quadriceps muscle group was mea sured during maximum voluntary contraction. Asthmatic patients had pre served quadriceps strength and ARF but moderately impaired maximum ins piratory pressure (PI,max) (-52 (18) cmH(2)O) and thicker DiTrelax (2. 2 (0.4) mm), compared to normal subjects (-73 (21) cmH(2)O and 1.7 (0. 3) mm, respectively). Middle-aged patients with chronic asthma and a s mall increase in functional residual capacity/total lung capacity rati o have preserved limb muscle force and dimensions, modestly impaired i nspiratory muscle strength, and slightly increased thickness of the co stal diaphragm. Future studies of respiratory muscle function in asthm a should be aided by measurement of diaphragm thickness and of limb mu scle strength and size. Such studies are required particularly in olde r patients with severe hyperinflation who are most likely to have impa irment of muscle function. (C)ERS Journals 1997.