It has been suggested that low body weight may be associated with decreased respiratory
muscle function in COPD, but the precise mechanism is not known. Since body compositional
change inevitably accompanies body weight change, we decided to study the possible
relationship between respiratory muscle strength and body composition in patients
with COPD. We studied respiratory muscle strength, pulmonary function, and body composition
in 24 Japanese male patients with COPD. Patients were divided into two groups according
to their body weight (group A, body weight lower than 80% of ideal body weight vs
group B, 80% or more) and a comparison was made together with age-matched controls
(group C). Maximal inspiratory mouth pressure (PImax) and maximal expiratory mouth
pressure (PEmax) were measured by a previously reported method. Body compositional
analysis was performed using dual energy x-ray absorptiometry (DXA; Norland XR26).
It showed significantly lower fat body mass (FAT), FAT/body weight%, and lean body
mass (LEAN) in group A than those in group B. The PImax in group A was significantly
lower than that in group B and C (44.2 +/- 13.8, 76.4 +/- 29.9, and 88.6 +/- 18.1
cm H2O, respectively). PEmax in group A was also significantly lower than that in
group B and group C (61.9 +/- 20.1, 86.7 +/- 26.8, and 90.4 +/- 17.6 cm H2O, respectively).
Both PImax and PEmax were significantly correlated with LEAN (r = 0.656, r = 0.591,
p < 0.01, respectively) in patients with COPD. These results show that respiratory
muscle strength is closely associated with body weight and lean body mass in patients
with COPD. The present approach to compare respiratory muscle strength with lean body
mass should be useful for studying the mechanism of respiratory muscle weakness in
patients with COPD.