Short-term modulation of the exercise ventilatory response in younger and older women

The exercise ventilatory response (EVR; defined as the slope of the relationship between ventilation and CO2 production) is reversibly augmented within a single exercise trial with increased respiratory dead space (DS) in both younger (Wood, H.E., Mitchell, G.S., Babb, T.G., 2008. Short-term modulation of the exercise ventilatory response in young men. J. Appl. Physiol. 104, 244-252) and older (Wood, H.E., Mitchell, G.S., Babb, T.G., 2010. Short-term modulation of the exercise ventilatory response in older men. Respir. Physiol. Neurobiol. 173, 37-46) men. The neural mechanism accounting for this augmentation is known as short-term modulation (STM) of the EVR. Since the effects of female sex hormones on STM are unknown, we examined the capacity for STM in healthy adult women of two age groups; nine younger (29 ± 3 yrs, eumenorrheic) and seven older (69 ± 3 yrs, postmenopausal) women were studied at rest and during cycle exercise (10 W, 30 W; not randomized) in control conditions and with added external DS (200 mL, 400 mL; randomized). Within groups, the main effects of DS and work rate on EVR were analyzed with a two-way repeated measures ANOVA; EVR comparisons between groups were made with unpaired t-tests. In both groups, EVR increased progressively with increasing DS volume (e.g. at 10 W 31 ± 4 and 35 ± 6 in control, 40 ± 11 and 40 ± 6 with 200 mL, 48 ± 12 and 49 ± 11 with 400 mL DS in younger and older women, respectively). In younger women, the effects of DS on EVR differed between work rates (significant interaction, p < 0.05), although this was not the case for older women. In both groups, PCO2 regulation was similar between DS and control; hence, increased EVR was not due to altered chemoreceptor feedback from rest to exercise. EVR with and without added DS did not differ between age groups. We conclude that the capacity for STM of the EVR with added DS is similar in healthy younger and older women.