PURPOSE: Distance walked during 6MWT is used to assess functional exercise capacity in COPD. Pulse oximetry is optional, recommended for detecting exercise desaturation for ambulatory oxygen therapy. However, the role of combined 6-minute walk test with pulse oximetry in functional assessment of COPD patients is unclear. Analysis of SpO2 kinetics during 6MWT by using continuous pulse oximetry was done and correlated with spirometry indices.
METHODS: 92 patients of COPD were prospectively evaluated at Metro Centre for Respiratory Diseases, India, by 6MWT performed according to ATS guidelines and continuous pulse oximetry analyzed using PulseOx 7500(with computarized data download and print). Baseline SpO2 (SpO2baseline), minimum SpO2 (SpO2min), SpO2 at the end of the test (SpO2end), 6-minute walk distance, rate of perceived exertion (RPE on Borg Scale), heart rate and systolic blood pressure at the beginning and end of the test and spirometry indices (FVC% predicted, FEV1% predicted & FEV1/FVC) were recorded. Pearson correlation coefficient was used to analyze the relation between various parameters. The significant value was taken at p ≤ 0.01.
RESULTS: All patients completed 6MWT. SpO2min was observed at 161.09 ± 85.2 sec after start of the test in 88 patients (95.65%). SpO2baseline was 95.76±2.3%, SpO2min was 85.45±7.5%, and SpO2end was 90.57±6.7%. FEV1% was significantly correlated to SpO2min (p=0.002) and SpO2end (p=0.004) though there was no significant correlation with the 6-minute walk distance (p=0.024). Significant desaturation (≥4% fall in SpO2 ) was observed in 76/92 (82.6%) patients. Desaturation was 55.3% (p< 0.001) more if SpO2min was considered instead of SpO2end for recording significant desaturation. Also, exercise desaturation in 52/92 patients (56.52%) would have been missed if SpO2end was considered for exercise hypoxemia.
CONCLUSION: Maximal desaturation occurs before the end of the 6MWT in majority of patients of COPD. Continuous pulse oximetry during 6MWT reflects accurately the exercise induced hypoxemia in patients with COPD.
CLINICAL IMPLICATIONS: Exercise induced hypoxemia is reflected truly by using continuous pulse oximetry with 6MWT. This can be further used to evaluate progression of COPD and response to interventions.
DISCLOSURE: Mir Ali, No Financial Disclosure Information; No Product/Research Disclosure Information