Carotid chemoreflex control of blood pressure at rest and during exercise in young-onset hypertension

Abstract

Despite reports of amplified carotid chemoreflex sensitivity to hypoxia in young adults with hypertension (<40 years), it is unclear whether this equates to a direct role of this reflex in maintaining high resting and exercise blood pressures (BP). The aim of this study was to examine whether tonic carotid chemoreflex activity contributes to high resting and exercise BP in young people with untreated hypertension compared to normotensives (NTN). In 14 NTN and 14 untreated hypertensives (HTN) (aged 27 ± 6 and 28 ± 5 years, respectively) the ventilatory and haemodynamic responses to hypoxia were measured using the transient hypoxic test at rest and during submaximal steady-state upright cycle exercise (40%–50% ${\dot{V}}_{O_2\mathrm{peak}}$). A double-blinded placebo-controlled systemic infusion of low-dose dopamine (2 mcg/kg/min) was used to inhibit the carotid chemoreflex and assess its tonic contribution to ventilation and BP at rest and submaximal exercise (mixed-model ANOVA). The hypoxic ventilatory response (HVR) at rest and submaximal cycle exercise were comparable between groups and were similarly blunted by dopamine infusion in both groups. However, at rest, there was a greater decrease in resting systolic BP (SBP) during carotid chemoreflex inhibition in the HTN group. Notably, during submaximal exercise, SBP was reduced during dopamine versus that during saline, but the decrease was similar between groups. The carotid chemoreflex appears to contribute to resting SBP in young people with untreated HTN but does not play a role in exaggerated exercise BP responses in this group.

Key points

• The role of the carotid chemoreflex in maintaining high resting and exercise blood pressures in young adults with untreated hypertension is unclear.
• Carotid chemoreflex sensitivity, assessed by the ventilatory response to hypoxia was similar between untreated young adults with hypertension (n = 14, age < 40 years) and age-matched normotensives (n = 14).
• During normoxic rest, there was a reduction in SBP during carotid chemoreflex inhibition with low-dose dopamine (2 mcg/kg/min; vs. saline) in people with hypertension which was not observed in the normotensive group.
• During submaximal cycle exercise, SBP was reduced during carotid chemoreflex inhibition, but this was similar between groups.
• These results suggest the carotid chemoreflex influences resting SBP in hypertensives but does not affect the exaggerated exercise BP response in this group.