Abstract
Rationale: Predictors of exercise desaturation are emphysema scores and severity on pathology and CT imaging with FEV1and resting SpO2 showing variable results. However, nocturnal hypoxemia predictors are less studied; hence we evaluated 6MWT with continuous pulse oximetry and spirometry indices for it. Methods: 28 patients of COPD with nocturnal hypoxemia were prospectively evaluated at Metro Centre for Respiratory Diseases, between May to July 2011 Parameters measured1) Spirometry: Pre and Post-bronchodilator 2) Six Minute Walk test (6MWT) using continuous oximetry: baseline SpO2(SpO2base),minimum SpO2 (SpO2min.),End SpO2 (SpO2end),maximum heart rate (HR max),minimum HR (HRmin)and 6 minute walk distance (6MWD) and 3) Nocturnal Oximetry: baseline, minimum & mean SpO2,% time SpO2 < 90%,. All parameters were statistically analyzed using SPSS Results: Of 28 patients with COPD (mean age 61.42±12.04 Yrs) 20 were males. Mean SpO2 baseline at start of 6MWT was 94.3±3.23%. SpO2min during nocturnal oximetry was significantly correlated with SpO2min during 6MWT (r = 0.878; p value <0.001),SpO2end (r = 0.552; p value =0.002)and post-bronchodilator FEV1(r = 0.461;p = 0.013). Time of sleep with SpO2<90% in nocturnal oximetry was also significantly correlated with SpO2min.on 6MWT (r = -0.427; p value 0.024) and SpO2base(r= -0.543;p value=0.003) but not with SpO2end (r= -0.269; p value = 0.166) and 6MWD (r =-0.073; p-value =0.713). Conclusion: Baseline SpO2 and maximum desaturation during exercise on 6MWT and post- bronchodilator FEV1 are good predictors of degree and duration of nocturnal hypoxemia in COPD. Hence such patients should be evaluated for nocturnal hypoxia.