Sternomastoid muscle size and strength in patients with severe chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) imposes a major strain on the respiratory muscle pump, and it is conventionally thought that the inspiratory muscles of the neck adapt to this chronic overload by developing hypertrophy. Yet previous anthropometric studies have shown atrophy of the sternomastoid muscles. To solve this discrepancy, we have measured the cross-sectional area of these muscles by computed tomography. Ten stable patients with severe airflow obstruction (FEV(1) = 0.76 +/- 0.12 L) and hyperinflation (FRC = 210 +/- 29% of predicted) and 10 control subjects matched for age, sex, and height were studied. The sternomastoid cross-sectional area in the patients averaged (mean +/- SD) 4.29 +/- 1.48 cm(2), and that in the control subjects was 3.96 +/- 0.82 cm(2). This small difference could be entirely accounted for by hyperinflation, and it was not statistically significant. Sternomastoid muscle torque in patients was also similar to that in the control subjects. In patients with severe COPD, therefore, the sternomastoid muscles are essentially normal. As a corollary, their frequent prominence on clinical examination is only apparent.