Abstract
Hypoxemia occurs after walking in patients with chronic obstructive pulmonary disease （COPD）, but the recovery of blood oxygen saturation （SpO2） after walking has not been studied, and its underlying mechanism remains unclear. This study evaluated changes over time in hypoxemia occurring after walking and examined SpO2 recovery–related factors in patients with COPD after the incremental shuttle walking test （ISWT） and six-minute walking distance test （6MWT）. Forty-four patients with COPD were included. They underwent a pulmonary function test and performed the ISWT and 6MWT. SpO2 was recorded every second and ⊿SpO2 （extent of the change in this value of resting SpO2 and during or after walking SpO2） was used in Simpson’s formula for calculating decrease in SpO2 （expressed in terms of area） every minute during and after walking. Decrease in SpO2 after walking was inversely correlated with percent diffusing capacity for carbon monoxide （％DLco） and peak expiratory flow （PEF, expressed as a percentage of the predicted peak flow: ％PEF）. Classification based on ％DLco＝70％ showed that those with ％DLco ＜70％ had significantly greater decrease in SpO2 after walking than did those with ％DLco≧70％. SpO2 recovery was not noted 1 minute after walking but significantly improved at 2 minutes. These results suggest that SpO2 recovery after walking is related to ％DLco. Continuous walking led to exercise-induced dynamic lung hyperinflation in the 6MWT, indicating that SpO2 recovery may be related to both ％DLco and ％PEF. The results suggest that hypoxemia continues for up to 2 minutes after walking, indicating that patients with COPD need a 2-minute rest period （rough standard） after walking.
