Rationale:

Pulse oximetry is commonly used to monitor arterial oxygen saturation (SpO₂) during exercise in individuals with COPD. However, many patients exhibit poor exercise tolerance despite normal SpO₂. Thus, near-infrared spectroscopy (NIRS), which estimates skeletal muscle oxygen saturation (StO₂), may be more advantageous than pulse oximetry for monitoring patients with COPD during exercise.

Objectives:

To examine how an incremental treadmill walking test (TMT) effects SpO₂, StO₂, and calf blood flow (BF) in individuals with COPD (n = 6; 70 +/- 4 yr) and healthy controls (CON; n = 20; 58 +/- 6 yr).

Methodology:

SpO₂ and StO₂ were assessed at rest, during, and after TMT. The TMT consisted of seven stages with a constant speed of 2.0 mph and 3.5% increases in grade every three minutes. Calf BF was assessed with venous occlusion plethysmography before and after TMT. Independent t-tests and ANOVA with repeated measures were utilized to analyze the data. Significance was set at P <=.05.

Results:

There were no significant group differences at rest for StO₂ or BF, but SpO₂ was significantly higher in CON (97.3 +/- 1.4 vs. 95.5 +/- 1.9 %; P <.05). Although SpO₂ stayed above 90% during TMT for both groups, there were greater reductions in SpO₂ during the TMT for COPD as compared to CON (all P <.05). Similarly, there was consistently lower StO₂ during TMT for COPD compared to CON (all P <=.05). On the contrary, there were similar, significant increases in BF following TMT for both CON and COPD (122% and 114%, respectively; P <.001). Finally, COPD exhibited significantly shorter walking times than CON (11.8 vs. 20.1 min, respectively; P <.05).

Conclusions:

Although both groups had similar BF responses to TMT and SpO₂ remained within acceptable ranges, COPD had lower StO₂ and walking times, indicating that skeletal muscle dysfunction limits exercise capacity in COPD. Thus, NIRS may be an effective device for monitoring those with COPD during aerobic exercise.