Association of the time to return to initial saturation after the six minute walk test with prognostic markers in patients with idiopathic pulmonary fibrosis

Background: Six minute walk test (6MWT) is commonly used to assess functional exercise capacity and prognosis in patients with idiopathic pulmonary fibrosis (IPF). However, there is not enough studies about changes in oxygen saturation during and after 6MWT. In our study, we investigated the relationship between the time to return to initial saturation after the, 6MWT prognostic markers and pulmonary hypertension (PH). Method: In our cross-sectional study, IPF cases who were followed up in the followed up ITF Interstitial Lung Disease Outpatient Clinic between 2021 and 2022, who were diagnosed according to current guidelines, were included. Demographic data of the cases were recorded. Spirometry, diffusion capacity measurement, arterial blood gas analysis, transthoracic echocardiography and a device that continuously measures and records peripheral oxygen saturation and heart rate were performed with 6 MWT. Time to return to initial saturation after test, distance-saturation product (DSP), gender-age-physiology (GAP) index and composite physiologic index (CPI) scores were calculated. In addition to the sociodemographic and clinic characteristics of the cases, dsypne severity were assessed by modified Medical Research Council (mMRC) and Dyspne-12 (D-12) Scale, fatigue severity by Multidimensional Fatigue Inventory (MFI-20) and quality of life by St. George's Respiratory Questionnaire (SGRQ). (EthicNo: 2021/227450) Results:Fifty IPF cases (35 men, 15 women, age: 66.8±7.3) were included in the study. Pulmonary hypertension (PH) was detected in twenty patients (40%). Mean values were; FVC: 77.8±19.3%, DLCO: 52.9±17.1%, 6MWM: 385.7±90.6m, GAP index score: 3.5±1.5 (28 stage 1, 18 stage 2, 4 stage 3). Oxygen saturations after 6MWT had reached pre-test values in an average of 135.6 ± 73.5 seconds. Oxygen saturation recovery time was longer in patients with higher the GAP index score (Rs=0.870, p<0.001), GAP stage (Rs=0.826, p<0.001), CPI score (Rs=0.906, p<0.001), desaturation in 6MWT (Rs=0.817, p<0.001), FVC%/DLCO% (Rs=0.418, p=0.002), sPAP (Rs=0.492, p=0.001), TRV (Rs=0.504, p=0.001), mMRC (Rs=0.913, p<0.001) , MFI-20 (Rs=0.944, p<0.001), D-12 scale (Rs=0.915, p<0.001) and SGRQ score (Rs=0.927, p<0.001); with lower FVC (%) (Rs=-0.627, p<0.001), DLCO (%) (Rs=-0.892, p<0.001), PaO2 measured on the room air (Rs= -0.779, p<0.001), DSP (Rs=-0.835, p<0.001), 6MWM (Rs=-0.763, p<0.001). In multiple regression analysis, oxygen saturation recovery time was independently associated with 6MWM (p=0.030) and GAP index score (p<0.001). CONCLUSION: In our study, it was indicated oxygen saturation recovery time was a relationship between PH and prognostic markers. We were recommended the continuous measurement of oxygen saturations after 6MWT had reached pre-test values. Oxygen saturation recovery time was prolonged in patients should be further investigated for hypoxia and pulmonary hypertension.