Background Systemic Sclerosis (SSc) patients with lung involvement have impaired DLCO and pulmonary arterial hypertension, and a DLCO of ≤50% of the predicted value is a predictor of death. It has also been shown that oxygen desaturation measured by means of pulse oximetry (SpO2 reduction ≥4%) during the 6 minutes walk test (6MWT) correlates with age, the dyspnea index, positive anti-Scl70 autoantibodies, forced vital capacity and DLCO.
Objectives The aim of this study was to evaluate the development of 6MWT performance over time in a group of patients with diffuse SSc with interstitial lung disease, and identify factors indicating exercise-induced oxygen desaturation.
Methods One hundred and twenty-one consecutive adults with diffuse SSc and interstitial lung disease diagnosed by means of high-resolution computed tomography and/or open lung biopsy were enrolled by the physicians. Twenty-eight were excluded from the study because of articular disabilities. The remaining 93 patients were followed up for five years.
The follow-up included clinical and functional lung tests, DLCO measurements (VMax 227 Autobox, Sensormedics, Yorba Linda, CA, USA), the 6MWT using a fingertip sensor for pulse oximetry (Nonin 2500, Nonin Medical INC, Plymouth, MN, USA), a dyspnea evaluation based on the Borg scale before and after the 6MWT, and transthoracic echocardiography (IE33 Echocardiography System, Philips, Amsterdam, The Netherlands). Oxygen saturation was recorded by means of pulse oximetry after a 5-minute rest before the test, throughout the test itself, and immediately afterwards. A decrease in SpO2 of ≥4% or SpO2 ≤88% was used as the criterion defining a desaturator.
Results During the follow-up, 32 patients (35%) became desaturators during the 6MWT: 20 (63%) because of a decrease in SpO2 of ≥4% and 12 (37%) because of a reduction in SpO2 to ≤88%. There was no statistically significant difference in any of the considered characteristics of the two groups at baseline but, in comparison with baseline, the desaturators had a longer disease duration (p<0.0001), reduced minimum SpO2% levels during the 6MWT (p<0.0001), DLCO (p<0.0001), and DLCO/alveolar volume (DLCO/AV) (p=0.05) at the time of desaturation.Comparison of the desaturators defined on the basis of a reduction in SpO2 to <88% and those defined on the basis of a decrease in SpO2 of ≥4% showed that the former had lower minimum SpO2% levels during 6MWT (p<0.001), DLCO (p=0.01) and DLCO/AV (p=0.05), a higher breath rate and Borg scale at the end of 6MWT (p=0.05), and higher RVsystP (p=0.01). At the time of desaturation, the desaturators' minimum SpO2 level during 6MWT correlated with their DLCO (r =0.78; p<0.001), DLCO/AV (r =0.64; p<0.01) and RVsystP (r = -0.53; p<0.05).
Conclusions DLCO and DLCO/AV seemed to be the parameters affecting our patients' ability to exercise because those who became desaturators had reduced DLCO and DLCO/AV values. The same parameters were also the determinants of greater desaturation, which is likely to cause an increase in pulmonary artery pressure. Our data seem to confirm the close interdependence between pulmonary diffusion capacity and oxygen desaturation during exercise, and between the latter and the risk of pulmonary hypertension.
Disclosure of Interest None declared