Analysis of the metabolic and ventilatory response to self-paced 12-minute treadmill walking in patients with severe chronic obstructive pulmonary disease.
BACKGROUND
The 12-minute walking test is frequently used to measure exercise capacity in patients with severe chronic obstructive pulmonary disease. However, the physiological response to this test has been the subject of limited investigation.


METHODS
In this study, the metabolic and ventilatory consequences of a self-paced 12-minute treadmill walking test (WT) were measured in 17 patients with severe chronic obstructive pulmonary disease (FEV1: 40 +/- 9%) and evaluated using the physiological response to symptom-limited cycle ergometry (CE). During exercise testing, heart rate, transcutaneous oxygen saturation, and lactate concentration were measured, and oxygen consumption, carbon dioxide production, tidal volume, and breathing frequency were recorded breath by breath.


RESULTS
After 4 minutes walking, the peak oxygen consumption (VO2) was already 99 +/- 11% of last-minute walking VO2. Walking speed was chosen within 2 minutes and remained stable throughout the test. The WT and CE showed similar (end-) test results for all measurements, except for a higher carbon dioxide production, venous lactate concentration, and respiratory quotient after CE. However, lactate concentration was also significantly increased after WT. Severe and prolonged desaturation was shown during walking in most patients.


CONCLUSIONS
The physiological stress evoked during the WT is close to the stress developed at an incremental symptom-limited test and the relatively high metabolic and ventilatory stress is sustained from at least 4 to 12 minutes during the WT. This study has shown that anaerobic metabolism not only occurs during incremental cycle ergometry, but also during the WT.
Baarends
E M
EM
Department of Pulmonology, University of Limburg, Maastricht, The Netherlands.
Schols
A M
AM
Mostert
R
R
Janssen
P P
PP
Wouters
E F
EF
D001784:Blood Gas Analysis; D004734:Energy Metabolism; D005080:Exercise Test / Q000009:adverse effects / Q000379:methods*; D017079:Exercise Tolerance; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D019344:Lactic Acid / Q000097:blood; D008173:Lung Diseases, Obstructive / Q000175:diagnosis / Q000378:metabolism* / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D010101:Oxygen Consumption; D012119:Respiration; D013990:Tidal Volume; D013997:Time Factors
D019344:Lactic Acid