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

We previously observed an increase in minute ventilation (V̇E) with resistive unloading (He-O₂ 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-O₂ gas mixture (79% He, 21% O₂). V̇E, pulmonary mechanics, and PET_CO2 were measured during each 1-min increment in work rate. Data were analyzed by paired t test at rest, at ventilator/threshold (VTh), and during maximal exercise. V̇E 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-O₂. Concomitant to the increase in V̇E, PET_CO2 was decreased at all levels (p < 0.01), whereas total work of breathing against the lung was not different. We concluded that V̇E is increased during He-O₂ breathing because of resistive unloading of the airways and the maintenance of the relationship between the work of breathing and exercise work rate.