Mechanisms affecting exercise ventilatory inefficiency-airflow obstruction relationship in male patients with chronic obstructive pulmonary disease

Abstract

Abstract Background Exercise ventilatory inefficiency is usually defined as high ventilation ($$ \dot{\mathrm{V}}\mathrm{E} $$ V ̇ E ) versus low CO2 output ($$ \dot{\mathrm{V}}\mathrm{CO}2 $$ V ̇ CO 2 ). The inefficiency may be lowered when airflow obstruction is severe because $$ \dot{\mathrm{V}}\mathrm{E} $$ V ̇ E 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 (VD/VT), 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 $$ \dot{\mathrm{V}}\mathrm{E} $$ V ̇ E versus $$ \dot{\mathrm{V}}\mathrm{CO}2 $$ V ̇ CO 2 slope ($$ \dot{\mathrm{V}}\mathrm{E}/\dot{\mathrm{V}}\mathrm{CO}2\mathrm{S} $$ V ̇ E / V ̇ CO 2 S ) and intercept ($$ \dot{\mathrm{V}}\mathrm{E}/\dot{\mathrm{V}}\mathrm{CO}2\mathrm{I} $$ V ̇ E / V ̇ CO 2 I ) were obtained by linear regression. Arterial blood gas analysis was also performed in 47 of the participants during exercise tests. VD/VT and lactate level were measured. Results VD/VTpeak was moderately positively related to $$ \dot{\mathrm{V}}\mathrm{E}/\dot{\mathrm{V}}\mathrm{CO}2\mathrm{S} $$ V ̇ E / V ̇ CO 2 S (r = 0.41) and negatively related to forced expired volume in 1 sec % predicted (FEV1%) (r = − 0.27), and hence the FEV1%- $$ \dot{\mathrm{V}}\mathrm{E}/\dot{\mathrm{V}}\mathrm{CO}2\mathrm{S} $$ V ̇ E / V ̇ CO 2 S relationship was paradoxical. The higher the $$ \dot{\mathrm{V}}\mathrm{E}/\dot{\mathrm{V}}\mathrm{CO}2\mathrm{S} $$ V ̇ E / V ̇ CO 2 S , the higher the pH and PaO2, and the lower the PaCO2 and exercise capacity. $$ \dot{\mathrm{V}}\mathrm{E}/\dot{\mathrm{V}}\mathrm{CO}2\mathrm{I} $$ V ̇ E / V ̇ CO 2 I was marginally related to VD/VTrest. The higher the $$ \dot{\mathrm{V}}\mathrm{E}/\dot{\mathrm{V}}\mathrm{CO}2\mathrm{I} $$ V ̇ E / V ̇ CO 2 I , the higher the inspiratory airflow, work rate, and end-tidal PCO2peak. Conclusion 1) Dead space ventilation perturbs the airflow- $$ \dot{\mathrm{V}}\mathrm{E}/\dot{\mathrm{V}}\mathrm{CO}2\mathrm{S} $$ V ̇ E / V ̇ CO 2 S relationship, 2) increasing ventilation thereby increases $$ \dot{\mathrm{V}}\mathrm{E}/\dot{\mathrm{V}}\mathrm{CO}2\mathrm{S} $$ V ̇ E / V ̇ CO 2 S to maintain biological homeostasis, and 3) the physiology- $$ \dot{\mathrm{V}}\mathrm{E}/\dot{\mathrm{V}}\mathrm{CO}2\mathrm{S} $$ V ̇ E / V ̇ CO 2 S - $$ \dot{\mathrm{V}}\mathrm{E}/\dot{\mathrm{V}}\mathrm{CO}2\mathrm{I} $$ V ̇ E / V ̇ CO 2 I relationships are inconsistent in the current and previous studies. Trial Registration MOST 106–2314-B-040-025.