Cerebral haemodynamic responses to inspiratory muscle work

Fatiguing inspiratory work has been shown to evoke a sympathetically mediated reflex that has systemic cardiovascular consequences, including increases in heart rate and blood pressure and a decrease in resting limb vascular conductance. Moreover, the response to this reflex appears to be attenuated in females compared with males. It remains to be seen whether this respiratory muscle metaboreflex also exerts an effect on cerebral blood flow. Cerebral blood flow is tightly regulated to maintain homeostasis and critical function. Therefore, it stands to reason that cerebrovascular haemodynamics would not be compromised through this respiratory muscle metaboreflex. We hypothesized that fatiguing inspiratory work would reduce resting limb conductance, but cerebral blood flow would be minimally impaired. Females (34 ± 10 years old, n = 12) and males (31 ± 8 years old, n = 12) performed a 5 min, high-intensity bout of inspiratory pressure threshold loading (IPTL) designed to evoke the respiratory muscle metaboreflex. In response to IPTL, mean arterial pressure increased in both males and females (p < 0.001), and limb vascular conductance decreased to a greater degree in males than in females (p = 0.005). The cerebrovascular conductance index was higher in females (p = 0.007) but not affected by IPTL (p = 0.417). Our findings suggest that cerebral blood flow is spared from the redistribution of blood flow in response to fatiguing inspiratory work and that this protection is true in both males and females.