Abstract
BACKGROUND: Exercise ventilatory inefficiency is usually defined as high ventilation ([Formula: see text]) versus low CO(2) output ([Formula: see text]). The inefficiency may be lowered when airflow obstruction is severe because [Formula: see text] cannot be adequately increased in response to exercise. However, the ventilatory inefficiency-airflow obstruction relationship differs to a varying degree. This has been hypothesized to be affected by increased dead space fraction of tidal volume (V(D)/V(T)), acidity, hypoxemia, and hypercapnia. METHODS: A total of 120 male patients with chronic obstructive pulmonary disease were enrolled. Lung function and incremental exercise tests were conducted, and [Formula: see text] versus [Formula: see text] slope ([Formula: see text]) and intercept ([Formula: see text]) were obtained by linear regression. Arterial blood gas analysis was also performed in 47 of the participants during exercise tests. V(D)/V(T) and lactate level were measured. RESULTS: V(D)/V(Tpeak) was moderately positively related to [Formula: see text] (r = 0.41) and negatively related to forced expired volume in 1 sec % predicted (FEV(1)%) (r = - 0.27), and hence the FEV(1)%- [Formula: see text] relationship was paradoxical. The higher the [Formula: see text], the higher the pH and P(a)O(2), and the lower the P(a)CO(2) and exercise capacity. [Formula: see text] was marginally related to V(D)/V(Trest). The higher the [Formula: see text], the higher the inspiratory airflow, work rate, and end-tidal PCO(2peak). CONCLUSION: 1) Dead space ventilation perturbs the airflow- [Formula: see text] relationship, 2) increasing ventilation thereby increases [Formula: see text] to maintain biological homeostasis, and 3) the physiology- [Formula: see text]- [Formula: see text] relationships are inconsistent in the current and previous studies. TRIAL REGISTRATION: MOST 106-2314-B-040-025 .