STRUCTURE OF THE LATISSIMUS-DORSI MUSCLE AND RESPIRATORY-FUNCTION

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.