[Chronic hypercapnia at rest or exercise-induced and ventilatory patterns in patients suffering from chronic...

The authors review the recent literature on hypercapnia at rest and on exertion in patients suffering from chronic airflow obstruction. At rest, the data in the literature has shown that for varying degrees of airflow obstruction, chronic hypercapnic patients show similar occlusion pressures to normocapnic patients. (The occlusion pressure is an index of the amplitude of neuro-muscular signals coming from the respiratory centre). However, their respiratory profile is characterised by a smaller tidal volume due to a reduction of the inspiratory time and often of a more rapid respiratory rate at a lower minute ventilation (VE). This pattern alone could explain CO2 retention by alveolar hypoventilation. On effort, various authors have shown that hypercapnic patients, or those becoming so during exercise, differ from normals by adopting a ventilatory pattern characterised by a reduction in ventilation linked to their airflow obstruction and a smaller tidal volume. The limited increase in tidal volume on effort is dependent on the duration of inspiration and the reduction of vital capacity and inspiratory capacity. As at rest, the two populations cannot be distinguished in terms of occlusion pressure.