Differential responses to CO2 and sympathetic stimulation in the cerebral and femoral circulations in humans

  title={Differential responses to CO2 and sympathetic stimulation in the cerebral and femoral circulations in humans},
  author={Philip N. Ainslie and Jon C. Ashmead and Kojiro Ide and Barbara J Morgan and Marc J. Poulin},
  journal={The Journal of Physiology},
The relative importance of CO2 and sympathetic stimulation in the regulation of cerebral and peripheral vasculatures has not been previously studied in humans. We investigated the effect of sympathetic activation, produced by isometric handgrip (HG) exercise, on cerebral and femoral vasculatures during periods of isocapnia and hypercapnia. In 14 healthy males (28.1 ± 3.7 (mean ±s.d.) years), we measured flow velocity (; transcranial Doppler ultrasound) in the middle cerebral artery during… 
Hypercapnia elicits differential vascular and blood flow responses in the cerebral circulation and active skeletal muscles in exercising humans
It is demonstrated that hypercapnia‐induced vasomotion in active skeletal muscles is opposite to that in the cerebral circulation, suggesting that differential vascular responses may cause a preferential rise in cerebral blood flow.
Cerebral vasoreactivity during hypercapnia is reset by augmented sympathetic influence.
The sensitivity of cerebral vasoreactivity to hypercapnia, in terms of the rate of increases in MCAV and in ScO(2), is diminished by LBNP-stimulated sympathoexcitation.
Differential responses to sympathetic stimulation in the cerebral and brachial circulations during rhythmic handgrip exercise in humans
The data indicate that while the marked vasoconstrictor responses to sympathetic activation in the skeletal muscle vasculature are blunted by handgrip exercise, the modest cerebrovascular responses to a cold pressor test remain unchanged.
Cerebral and myocardial blood flow responses to hypercapnia and hypoxia in humans.
It is demonstrated, compared with coronary circulation, that the cerebral circulation is more sensitive to hypercapnia but similarly sensitive to hypoxia.
Differential sensitivities of cerebral and brachial blood flow to hypercapnia in humans.
It is confirmed that Vp has a greater sensitivity than BBF in response to hypercapnia and show an adaptive response of BBF that is not evident in Vp.
The effect of hypercapnia on static cerebral autoregulation
The findings indicate that hypercapnia impairs static autoregulation, such that higher blood pressures are translated into the cerebral circulation.
Interaction between the ventilatory and cerebrovascular responses to hypo‐ and hypercapnia at rest and during exercise
Findings indicate that, despite an attenuated chemoreflex system controlling ventilation, elevations in cerebrovascular reactivity might help maintain CO2 homeostasis in the brain during exercise.
Cerebrovascular and corticomotor function during progressive passive hyperthermia in humans.
The results indicate that descending voluntary drive becomes progressively impaired as Tc is increased, presumably due, in part, to reductions in CBFv and to hyperthermia-induced hyperventilation and subsequent hypocapnia.
Alterations in cerebral autoregulation and cerebral blood flow velocity during acute hypoxia: rest and exercise.
The data indicate that increases in cerebral neurogenic activity and/or sympathoexcitation during hypoxic exercise can potentially outbalance the hypocapnia-induced lowering of MCAV, which can potentially compromise cerebral autoregulation and oxygenation.
Enhanced cerebral CO2 reactivity during strenuous exercise in man
The results suggest that during exercise changes in cerebral blood flow are dominated by the arterial carbon dioxide tension.


Baroreflex‐induced sympathetic activation does not alter cerebrovascular CO2 responsiveness in humans
Cerebrovascular CO2 responsiveness was not altered by baroreflex‐induced sympathetic activation, challenging the concept that sympathetic activation restrains cerebrov vascular responses to alterations in CO2 pressure.
Interaction of Carbon Dioxide and Sympathetic Nervous System Activity in the Regulation of Cerebral Perfusion in Humans
Changes in sympathetic tone have a limited effect on cerebral blood flow at normal Paco2 levels, however, the sympathetic nervous system seems to attenuate the CO2-induced increase in cerebralBlood flow.
Sympathetic neural discharge and vascular resistance during exercise in humans.
  • D. Seals
  • Biology
    Journal of applied physiology
  • 1989
It is demonstrated that muscle sympathetic nerve discharge and vascular resistance in the lower leg are tightly coupled during and after isometric arm exercise in humans.
Dissociation of muscle sympathetic nerve activity and leg vascular resistance in humans.
It was concluded that control of leg muscle vascular resistance is sensitive to changes in arterial pressure and can be dissociated from sympathetic factors.
Mechanisms of the cerebrovascular response to apnoea in humans
It is concluded that apnoea‐induced fluctuations in CFV were caused primarily by increases and decreases in arterial partial pressure of CO2 (Pa,CO2) and that sympathetic nervous system activity was not required for either the initiation or the maintenance of the cerebrovascular response to hyper‐ and hypocapnia.
Cerebral hemodynamic changes induced by sympathetic stimulation tests.
  • Y. Sohn
  • Medicine, Biology
    Yonsei medical journal
  • 1998
The results suggest that sympathetic activation increases MCA flow velocities, related with a reduction in small vessel resistance and/or a constriction of large arteries.
Ventilatory, cerebrovascular, and cardiovascular interactions in acute hypoxia: regulation by carbon dioxide.
The between-individual variability in AHVR is shown to be firmly linked to the variability in V(p) and MAP responses to hypoxia, demonstrating a linkage of individual sensitivities of ventilation and cerebral blood flow to the interaction of Pet(CO(2)) and Hypoxia.
Fast and slow components of cerebral blood flow response to step decreases in end-tidal PCO2 in humans.
The cerebral blood flow response to hypocapnia was characterized by a significant (P < 0.001) slow progressive adaptation in P.VIWM, with gs = 1.26 %/Torr and taus = 427 s, that persisted throughout the hypocapnic period.
Evaluation of the cerebral hemodynamic response to rhythmic handgrip.
The data suggest that the cerebral blood flow (CBF) response to rhythmic handgrip is heterogeneous and that middle cerebral artery flow can decrease in some subjects, in agreement with prior studies using the Kety-Schmidt technique.