The aim of this study was to evaluate whether respiratory function inf
luences the structure of the latissimus dorsi muscle (LD). Twelve pati
ents (58 +/- 10 yr) undergoing thoracotomy were studied. Lung and resp
iratory muscle function were evaluated before surgery. Patients showed
a forced expired volume in 1 s (FEV(1)) of 67 +/- 16% of the referenc
e value, an FEV(1)-forced vital capacity ratio of 69 +/- 9%, a maximal
inspiratory pressure of 101 +/- 21% of the reference value, and a ten
sion-time index of the diaphragm (TTdi) of 0.04 +/- 0.02. When patient
s were exposed to 8% CO2 breathing, TTdi increased to 0.06 +/- 0.03 (P
< 0.05). The structural analysis of LD showed that 51 +/- 5% of the f
ibers were type I. The diameter was 56 +/- 9 mu m for type I fibers an
d 61 +/- 9 mu m for type II fibers, whereas the hypertrophy factor was
87 +/- 94 and 172 +/- 208 for type I and II fibers, respectively. Int
erestingly, the histogram distribution of the LD fibers was unimodal i
n two of the three individuals with normal lung function and bimodal (
additional mode of hypertrophic fibers) in seven of the nine patients
with chronic obstructive pulmonary disease. An inverse relationship wa
s found between the %FEV(1)-forced vital capacity ratio and both the d
iameter of the fibers (type I: r = -0.773, P < 0.005; type II: r = -0.
590, P < 0.05) and the hypertrophy factors (type I: r = -0.647, P < 0.
05; type II: r = -0.575, P = 0.05). The increase in TTdi when the subj
ects breathed CO2 directly correlated with the diameter of all the LD
fibers (r = 0.636, P = 0.05). These results strongly suggest that the
structure of the LD can be influenced by changes in respiratory functi
on. Thus, it does not appear to be the most appropriate control. for s
tructural studies of the respiratory muscles.