Effects of sex and ageing on the human respiratory muscle metaboreflex

Intense inspiratory muscle work evokes a sympathetically mediated pressor reflex, termed the respiratory muscle metaboreflex, in which young females demonstrate an attenuated response relative to males. However, the effects of ageing and female sex hormones on the respiratory muscle metaboreflex are unclear. We tested the hypothesis that the pressor response to inspiratory work would be similar between older males and females, and higher relative to their younger counterparts. Healthy, normotensive young (26 +/- 3 years) males (YM; n = 10) and females (YF; n = 10), as well as older (64 +/- 5 years) males (OM; n = 10) and females (OF; n = 10), performed inspiratory pressure threshold loading (PTL) to task failure. Older adults had a greater mean arterial pressure (MAP) response to PTL than young (P < 0.001). YF had a lower MAP compared to YM (+10 +/- 6 vs. +19 +/- 15 mmHg, P = 0.026); however, there was no difference observed between OF and OM (+26 +/- 11 vs. +27 +/- 11 mmHg, P = 0.162). Older adults had a lower heart rate response to PTL than young (P = 0.002). There was no effect of sex between young females and males (+19 +/- 9 and +27 +/- 11 bpm, P = 0.186) or older females and males (+17 +/- 7 and +20 +/- 7 bpm, P = 0.753). We conclude the respiratory muscle metaboreflex response is heightened in older adults, and the sex effect between older males and post-menopause females is absent, suggesting an effect of circulating sex hormones.

Automated summary

The effects of ageing and female sex hormones on the respiratory muscle metaboreflex are unclear. Our study found that older adults have a heightened pressor response to inspiratory work, and there is no difference in this response between older males and post-menopause females.