Diffusing Pulmonary Capacity Measured During Effort: A Possible Early Marker of Pulmonary Involvement In Systemic Sclerosis

Background: Interstitial lung involvement is common and potentially limits the quality of life in patients with systemic limited sclerosis (SScl). Objectives: To study the lung carbon monoxide diffusion (DLCO) measured during effort in order to identify a possible subclinical impairment. Methods: We enrolled 20 SScl patients without interstitial lung involement and 20 healthy controls. At enrolment all subjetcs underwent plethysmography, DLCO by single-breath technique, and evaluation of pulmonary blood flow (Qc) with the rebreathing CO2 method. Skin involvement in the SScl patients was rated using the modified Rodman skin score (mRSS). During exercise on a cycle ergometer, DLCO, DLCO/alveolar volume (Kco) and Qc were calculated at 25% and 50% of predicted maximum workload (25% pmw and 50% pmw). Results: At baseline two groups did not differ in age, body mass index, lung function or Qc. In the controls, DLCO, Kco and DLCO/Qc measured at 25% pmw and 50% pmw were significantly higher than in SScl patients, while Qc was not different. Based on response to effort, SScl patients were divided into two groups: responders, with an increase of DLCO25%pmw and DLCO50%pmw at least 5% and 10% respectively, and non-responders. The non-responders showed greater skin involvement and significantly reduced DLCO, Kco and DLCO/Qc values at rest than responders. Conclusions: Moderate effort in SScl patients may reveal a latent impairment in gas diffusion through the alveolar/capillary membrane, thus confirmig that exertional DLCO can identify lung damage at an earlier stage than DLCO at rest.