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To the Editor:
In their very interesting study recently published in the Journal, Elbehairy and colleagues established that VD is increased during exercise in smokers with mild obstructive pulmonary disease, leading to a compensatory increase in minute ventilation to keep alveolar ventilation constant (1). This in turn resulted in early dyspnea and exercise limitation. We would like to present the view that this study reveals an intriguing picture in which the breathing pattern adopted by these patients, and thus the way their breathing is regulated, contributes to the observed high ventilatory output.
1. The patients display a significant increase in their breathing frequency at any given work rate (1). This is true at 60 W, but also at 100 W, averaging 23 versus 42 c/min in the control and the patie:nt group, respectively. The consequences on VD ventilation (VD) must be considered regardless of the VD values: Breath:ing at 23 versus 42 cycles (c)/min at a CO2 production (VCO2) of about 1.5 L/min (100 W) requires the same alveolar ventilation (50 L/min for the sake of simplicity) to keep PaCO constant. This implies that if the control subjects and patients had the same VD (200 ml), an...