Breathing He-O2 increases ventilation but does not decrease the work of breathing during exercise

We previously observed an increase in minute ventilation ((V) over dot E) with resistive unloading (He-O-2 breathing) in healthy elderly subjects with normal pulmonary function. To investigate the effects of resistive unloading in elderly subjects with mild chronic airflow limitation (FEV1/FVC: 61 +/- 4%), we studied 10 elderly men and women 70 +/- 3 yr of age. These subjects performed graded cycle ergometry to exhaustion, once breathing room air and once breathing a He-O-2 gas mixture (79% He, 21% O-2). (V) pver dotE, pulmonary mechanics, and PETCO2 were measured during each 1-min increment in work rate. Data were analyzed by paired t test at rest, at ventilatory threshold (VTh), and during maximal exercise. ire was significantly (p < 0.05) increased at VTh (3.4 +/- 4.0 L/min or 12 +/- 15% increase) and maximal exercise (15.2 +/- 9.7 L/min or 22 +/- 13% increase) while breathing He-Ol. Concomitant to the increase in (V) over dotE, PETCO2 was decreased at all levels (p < 0.01), whereas total work of breathing against the lung was not different. We concluded that (V) over dotE is increased during He-O-2 breathing because of resistive unloading of the airways and the maintenance of the relationship between the work of breathing and exercise work rate.