CONTROL OF BREATHING IN A SUBSET OF PATIENTS WITH SYSTEMIC LUPUS-ERYTHEMATOSUS

Background: Inspiratory muscle weakness and abnormalities in breathing pattern and in respiratory drive have been reported in patients with multisystem disorders. In patients with systemic lupus erythematosus ( SLE), data on respiratory muscle strength and control of breathing are scarce. Methods: We studied a subset of nine female patients with SLE with no major findings of cardiovascular, renal, or neurologic involv ement, and with a normal routine chest radiograph. An age- and sex-mat ched normal group was also studied as a control. We evaluated lung vol umes, diffusing lung properties (TLco, TLco/VA), maximal inspiratory ( MIP) and expiratory (MEP) pressures, end-tidal carbon dioxide tension (Pco(2)), and breathing pattern: ventilation (VE), tidal volume (VT), inspiratory time (TI), and respiratory frequency (Rf). Neural respirat ory drive, assessed in terms of mean inspiratory flow (VT/TI), mouth o cclusion pressure (P0.1), and surface electromyographic activity of th e diaphragm (Edi) and intercostal (Eps) muscles was also evaluated. Re sults: As a whole, patients exhibited mild decrease in MIP; vital capa city was slightly reduced in two patients and TLco/VA was moderately r educed in three. During a hypercapnic rebreathing test, Delta VT/Delta Pco(2) was lower, Delta P0.1/Delta Pco(2) was normal, while Delta Edi /Delta Pco(2) and Delta hEps/Delta Pco(2) were higher in patients comp ared with normal control subjects. Delta VT/Delta Pco(2) significantly related to MIP. At 60 mm Hg of Pco(2) patients maintained the rapid a nd shallow pattern of breathing (RSB) exhibited during room-air breath ing: lower VT, shorter TI, and greater Rf, with VE, VT/TI, and Edi bei ng greater compared with the normal control subjects. Conclusions: The se data seem to indicate that in this SLE subset, mild decrease in res piratory muscle strength may accompany an increased respiratory drive, and contribute to a qualitatively abnormal ventilatory response (RSB) to carbon dioxide stimulation.