Interaction between the ventilatory and cerebrovascular responses to hypo‐ and hypercapnia at rest and during exercise

Abstract

Cerebrovascular reactivity to changes in the partial pressure of arterial carbon dioxide (P a,CO 2 ) via limiting changes in brain [H + ] modulates ventilatory control. It remains unclear, however, how exercise-induced alterations in respiratory chemoreflex might influence cerebral blood flow (CBF), in particular the cerebrovascular reactivity to CO 2 . The respiratory chemoreflex system controlling ventilation consists of two subsystems: the central controller (controlling element), and peripheral plant (controlled element). In order to examine the effect of exercise-induced alterations in ventilatory chemoreflex on cerebrovascular CO 2 reactivity, these two subsystems of the respiratory chemoreflex system and cerebral CO 2 reactivity were evaluated (n = 7) by the administration of CO 2 as well as by voluntary hypo-and hyperventilation at rest and during steady-state exercise. During exercise, in the central controller, the regression line for the P a,CO 2 -minute ventilation (V E ) relation shifted to higherV E and P a,CO 2 with no change in gain (P = 0.84). The functional curve of the peripheral plant also reset rightward and upward during exercise. However, from rest to exercise, gain of the peripheral plant decreased, especially during the hypercapnic condition (−4.1 ± 0.8 to −2.0 ± 0.2 mmHg l −1 min −1 , P = 0.01). Therefore, under hypercapnia, total respiratory loop gain was markedly reduced during exercise (−8.0 ± 2.3 to −3.5 ± 1.0 U, P = 0.02). In contrast, cerebrovascular CO 2 reactivity at each condition, especially to hypercapnia, was increased during exercise (2.4 ± 0.2 to 2.8 ± 0.2% mmHg −1 , P = 0.03). These findings indicate that, despite an attenuated chemoreflex system controlling ventilation, elevations in cerebrovascular reactivity might help maintain CO 2 homeostasis in the brain during exercise.

Cerebral blood flow and cerebrovascular reactivity at rest and during sub-maximal exercise: Effect of age and 12-week exercise training

“…An increase in hypercapnic cerebrovascular reactivity during exercise, as observed in this study, is similar to previous reports (Ogoh et al 2008;Rasmussen et al 2006;). The exact mechanisms responsible for the increased reactivity are unknown; however, increases in cerebral activation, core temperature (Rasmussen et al 2006) and CO 2 -induced increases in MAP (Ainslie et al 2005) have been suggested.…”

“…Similar to the findings from this study, Rasmussen et al (2006) observed an approximately twofold increase in hypercapnic reactivity during exercise at 67 % V Á O2 max. The exercise-induced elevations in reactivity observed by Ogoh et al (2008) were substantially less, at only 15-20 %, despite similar CBF measurement technique and CO 2 stimulus to that in the present study. However, in that study, participants were only exercising at~32 % V Á O2 max, potentially indicating a relationship with exercise intensity.…”

“…Only two studies have assessed the effect of age on the CBF response to sub-maximal exercise, and both observed no differential effect of age on the exercise-induced increase in CBF (Fisher et al 2008;Heckmann et al 2003). In addition to the CBF response, cerebrovascular CO 2 reactivity is also increased during exercise (Ogoh et al 2008;Rasmussen et al 2006). Although the effects of exercise on CBF Querido and Sheel 2007) and cerebrovascular reactivity (Ogoh et al 2008;Rasmussen et al 2006) have been relatively well documented in young individuals, any influencing effect of older age on these parameters has not been established.…”

“…In addition to the CBF response, cerebrovascular CO 2 reactivity is also increased during exercise (Ogoh et al 2008;Rasmussen et al 2006). Although the effects of exercise on CBF Querido and Sheel 2007) and cerebrovascular reactivity (Ogoh et al 2008;Rasmussen et al 2006) have been relatively well documented in young individuals, any influencing effect of older age on these parameters has not been established. Due to the conflicting evidence on the effect of age on cerebrovascular reactivity at rest, it is unclear what effect (if any) age has on cerebrovascular reactivity during exercise.…”

Cerebrovascular Reactivity is Increased with Acclimatization to 3,454 M Altitude

“…25 Moreover, an interaction of CVR and central chemoreceptormediated ventilatory drive has been suggested. 21,26,27 This interaction is manifested by changes in CVR, which affect the magnitude of hydrogen ion washout at the level of the central chemoreceptors that may consequently disturb the stability of the ventilatory response. 28,29 A blunted CVR, accordingly, leads to a diminished washout of brain tissue hydrogen ions, which subsequently facilitates a greater change in brain tissue PCO 2 for a given change in PaCO 2 .…”