Published in:
Open Access 01-12-2020 | Research
Mechanisms affecting exercise ventilatory inefficiency-airflow obstruction relationship in male patients with chronic obstructive pulmonary disease
Published in: Respiratory Research | Issue 1/2020
Login to get accessAbstract
Background
Exercise ventilatory inefficiency is usually defined as high ventilation (\( \dot{\mathrm{V}}\mathrm{E} \)) versus low CO2 output (\( \dot{\mathrm{V}}\mathrm{CO}2 \)). The inefficiency may be lowered when airflow obstruction is severe because \( \dot{\mathrm{V}}\mathrm{E} \) 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 \( \dot{\mathrm{V}}\mathrm{E} \) versus \( \dot{\mathrm{V}}\mathrm{CO}2 \) slope (\( \dot{\mathrm{V}}\mathrm{E}/\dot{\mathrm{V}}\mathrm{CO}2\mathrm{S} \)) and intercept (\( \dot{\mathrm{V}}\mathrm{E}/\dot{\mathrm{V}}\mathrm{CO}2\mathrm{I} \)) 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 \( \dot{\mathrm{V}}\mathrm{E}/\dot{\mathrm{V}}\mathrm{CO}2\mathrm{S} \) (r = 0.41) and negatively related to forced expired volume in 1 sec % predicted (FEV1%) (r = − 0.27), and hence the FEV1%- \( \dot{\mathrm{V}}\mathrm{E}/\dot{\mathrm{V}}\mathrm{CO}2\mathrm{S} \) relationship was paradoxical. The higher the \( \dot{\mathrm{V}}\mathrm{E}/\dot{\mathrm{V}}\mathrm{CO}2\mathrm{S} \), the higher the pH and PaO2, and the lower the PaCO2 and exercise capacity. \( \dot{\mathrm{V}}\mathrm{E}/\dot{\mathrm{V}}\mathrm{CO}2\mathrm{I} \) was marginally related to VD/VTrest. The higher the \( \dot{\mathrm{V}}\mathrm{E}/\dot{\mathrm{V}}\mathrm{CO}2\mathrm{I} \), the higher the inspiratory airflow, work rate, and end-tidal PCO2peak.
Conclusion
1) Dead space ventilation perturbs the airflow- \( \dot{\mathrm{V}}\mathrm{E}/\dot{\mathrm{V}}\mathrm{CO}2\mathrm{S} \) relationship, 2) increasing ventilation thereby increases \( \dot{\mathrm{V}}\mathrm{E}/\dot{\mathrm{V}}\mathrm{CO}2\mathrm{S} \) to maintain biological homeostasis, and 3) the physiology- \( \dot{\mathrm{V}}\mathrm{E}/\dot{\mathrm{V}}\mathrm{CO}2\mathrm{S} \)- \( \dot{\mathrm{V}}\mathrm{E}/\dot{\mathrm{V}}\mathrm{CO}2\mathrm{I} \) relationships are inconsistent in the current and previous studies.