The limiting factors to exercise performance in COPD at sea level are controversial. We studied the effect of the hipoxemia imposed on these patients by the altitude of Bogotá.
Pulmonary function test and symptom-limited incremental exercise testing on a cycle ergometer were done in 115 stable COPD patients, GOLD stage I to IV and 25 healthy subjects. Oxygen uptake (VO2), minute ventilation (VE), tidal volume (VT), inspiratory capacity (IC), heart rate (HR) and arterial blood gases were measured at rest and peak exercise.
FEV1 % 51±18.6. In COPD at peak exercise: VO2 % 69.9±20.9; HR % 77.9±11.8; VE L/m 54.5±20.5; IC % 63.3±16.9; PaO2 mmHg 54.6±10.5; SaO2 % 83.7±8.3, lower than control subjects. In the univariate analysis the variable at rest best correlated with peak VO2 was the FEV1 % (r 0.63 p <0.001). At peak exercise variables best correlated were VT % (r 0.60 p <0.001), VE L/m (r 0.53 p <0.001), IC % (r 0.57 p <0.001), PaO2 mmHg (r 0.51 p <0.001), SaO2 % (r 0.43 p <0.001) and VE/VCO2 (r 0.44 p <0.001). In the multivariate analysis adjusted for FEV1, peak VO2 was best described by the combination of peak VT %, VE/VCO2 and PaO2 (model r 0.78, r2 0.61 p <0.001). Peak VT was determined primarily by the degree of dynamic hyperinflation evaluated by the IC % at peak exercise (r 0.78 p<0.001).
In patients with COPD at the altitude of Bogotá the combination of hipoxemia, increased ventilatory demand and abnormal dynamic ventilatory mechanics (dynamic hyperinflation), are the determinant factors of the limitation to exercise performance. The correlation of hipoxemia with peak VO2 is independent of the severity of the airways obstruction (FEV1 %).
The demonstration of the role played by hipoxemia as a limiting factor to exercise performance at the altitude of Bogotá, independent of the severity of the obstruction, supports the importance of an adequate evaluation and correction of hipoxemia in all the patients with COPD.
Mauricio Gonzalez, No Financial Disclosure Information; No Product/Research Disclosure Information