Background Interstitial lung involvement limits the quality of life of systemic sclerosis patients (SSc). Our belief that its early diagnosis would allow early treatment and limit the consequences led us to search for a parameter of early alveolar/capillary damage that could be used as a test in routine clinical practice.
Objectives The aim is to study the behaviour of the respiratory system under stress on the basis of the lung carbon monoxide diffusing (DLCO) measured during effort in attempt to identify possible sub-clinical impairment.
Methods Were enrolled 20 SSc patients with limited forms (SScl) with normal pulmonary HRCT and 20 healthy controls. At baseline lung volume and dynamic spirometric parameters were assessed by means of plethysmography, DLCO was measured using the single breath technique. The Kco was derived form DLCO/alveolar volume. The effective pulmonary blood flow (Qc) was calculated using the rebreathing CO2 method, using Fick's formula.The skin involvement was rated using the mRSS. Durig exercise by cycle ergometer, perfomed in accordance with a standardized cardiopulmonary exercise test procedure, DLCO, Kco and Qc were calculated at 25% and 50% of predicted maximum workload (25%pmw and 50%pmw).
Results The disease duration was 4±6 years t: 99% had ANA, 75% anti-centromere antibodies, and 81% abnormal nail fold capillary microscopy.There were no differences between the patients and controls in terms of age (50±5 vs 51±4 years), BMI (25±3 vs 24±4 kg/m2), socioeconomic status, or lung function and Qc at rest. DLCO, Kco, and DLCO/Qc at the three time points were significantly greater in the controls than in the SScl patients (p<0.001), but there were no statistically significant differences in Qc (Qc25% pmw 7.5±0.6 vs. 7.3±0.4 L/min, ns; Qc50% pmw 11±0.6 vs 10.8±0.5 L/min, ns). In the SScl patients, there was only a small increase in DLCO and Kco at 50% of predicted maximum workload (respectively 90±13% vs 100±13%, p<0.05, and 92±12% vs 101±13%, p<0.05), and no statistically significant changes in DLCO/Qc throughout the test. On the basis of their responses to effort, the SScl patients were divided into two groups: nine responders in whom DLCO25% pmw and DLCO50% pmw increased by at least 5% and 10% respectively; and 11 non-responders in whom the increases were less than 5% and 10% respectively. At rest, the non-responders showed significantly reduced DLCO (86±9% vs 94±8%, p<0.05), Kco (87±7% vs 94±8%, p<0.05) and DLCO/Qc values (4.3±0.4 vs 4.9±0.5 mL/L mmHg, p<0.001) and greater skin involvement (mRSS 6.1±5.6 vs 1.3±1, p<0.0001). The percentage increase from baseline in DLCO, Kco and DLCO/Qc at 25% and 50% of predicted maximum workload negatively correlated with mRSS (r -0.60, p<0.01, r -0.5, p<0.05, and r -0.65, p<0.005); there were no significant correlations between DLCO, Kco e DLCO/Qc measured at 25% and 50% of predicted maximum workload and age, duration of disease or the presence of autoantibodies.
Conclusions Moderate effort in SScl patients may reveal a latent impairment in gas diffusion trough the alveolar/capillary membrane, thus confirmig that exertional DLCO can identify lung damage at an early stage than DLCO at rest. DLCO measuremt during exertion could be used for early diagnosis of pulmonary involvement in SScl patients
Disclosure of Interest None declared