Respiratory Muscle Strength, Lung Function, and Dyspnea in Patients with Sarcoidosis

Background: Sarcoidosis is a systemic granulomatous disorder that is estimated to involve the skeletal muscles in up to 50% of patients. There is little information on the relationship among respiratory muscle strength, lung volumes, and the degree of dyspnea in patients with sarcoidosis.

Design And Patients: Lung function and maximal respiratory muscle force generation were measured in 36 patients with sarcoidosis (24 patients with pulmonary parenchymal infiltration) and 25 control subjects free of cardiorespiratory disease. Dyspnea in the sarcoidosis patients was quantitated by a score based on an activity tolerance assessment scale (ranging from rest to climbing hills or stairs).

Setting: Outpatient clinics of two teaching hospitals.

Results: Mean FVC, maximal voluntary ventilation, total lung capacity (TLC), functional residual capacity, residual volume (RV), and diffusing capacity of the lung for carbon monoxide (DLCO) were all at least 16% less than corresponding control values (in all cases, p < 0.001), while maximal inspiratory mouth pressure (PImax) and maximal expiratory mouth pressure (PEmax) were 37% and 39% less, respectively, than control values (both at p < 0.0001). PImax and PEmax declined with increasing dyspnea in a more graded, steady manner than did spirometric and DLCO values. For all measurements, however, the lowest mean values were found in patients with the most severe level of dyspnea. Strong inverse relationships were observed between PEmax and PImax with dyspnea level (p < 0.0001 and p < 0.01, respectively). Both PImax and PEmax correlated best with absolute values of FVC, while only PEmax correlated with RV (absolute and percent predicted) and percent predicted values of TLC.

Conclusions: Maximal respiratory pressures correlate more closely with dyspnea level than lung volumes and DLCO. Since dyspnea is the most common presentation in early to moderately advanced sarcoidosis, respiratory pressures may be a more reliable index of functional work capacity and reflection of activities of daily living than standard tests of lung function.