Effects of sex and ageing on the human respiratory muscle metaboreflex.

KEY POINTS
The arterial blood pressure response to the respiratory muscle metaboreflex is greater in older males and females. Compared to sex-matched young individuals, there is no sex differences in the blood pressure response between older males and post-menopause females. Our results suggest the differences between males and females in the cardiovascular response to high levels of inspiratory muscle work is abolished with reduced circulating female sex hormones.


ABSTRACT
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 y) males (YM; n = 10) and females (YF; n = 10), and older (64±5 y) 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 (HR) 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. Abstract figure legend Young females demonstrate an attenuated cardiovascular response to the respiratory muscle metaboreflex relative to males; however, the effects of ageing and female sex hormones 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. Using inspiratory, pressure-threshold loading, we found a greater mean arterial pressure response in older adults. Additionally, the arterial pressure response was similar between older males and females. We interpret the findings to mean that 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. This article is protected by copyright. All rights reserved.