Do respiratory influences on cardiovascular regulation provide early markers of hypertension in young adults with a family history of hypertension?

Al Enazi, Fahad Holil S ORCID: 0000-0003-0209-2191 (2023). Do respiratory influences on cardiovascular regulation provide early markers of hypertension in young adults with a family history of hypertension? University of Birmingham. Ph.D.

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Abstract

Background: Hypertension is the well-known leading cause of the majority of cardiovascular diseases. Individuals with a parental history of hypertension (FH+) have a two-fold greater risk of developing hypertension than those without parental hypertension (FH-).

Objective: This PhD project had three main aims. First, to elucidate whether young normotensive adult FH+ already have disturbed autonomic regulation of arterial blood pressure (ABP) relative to FH- at rest and in response to everyday stressors such as postural manoeuvres and environmental stressors. Second, to investigate whether slow breathing normalises autonomic dysregulation in FH+. Third, to assess whether slow breathing acutely or following training reduces ABP and restores autonomic regulation in normotensives and hypertensives.

Methods: The first and second aims were explored by recording arterial blood pressure (ABP), a range of haemodynamic variables, heart rate variability (HRV) and baroreceptor reflex sensitivity (BRS), in young normotensive FH+ and FH- men and women at rest, during and following acute mental stress (Stroop colour-word test) and during acute slow breathing at 6 breaths/minute. The third aim was evaluated by a systematic review and meta-analysis on the effects of the device- and non-device-guided slow breathing acutely and by training for ≥4 weeks on ABP and autonomic regulation of ABP in normotensives and hypertensive.

Results and Conclusion: The experimental studies showed no differences between FH+ and FH- at rest. However, FH+ showed exaggerated increases in ABP and total peripheral resistance to mental stress relative to FH-. On the other hand, HRV, which mainly reflects vagal influences on the heart, was reduced during mental stress in FH+ and FH- and consistent with inhibition of the baroreceptor reflex being a characteristic of the defence response, vagal BRS was also reduced in FH+ and FH-. However, sympathetic BRS to a fall in ABP assessed by the squat-to-stand test was depressed by mental stress in FH- but not FH+. These findings provide novel evidence that sympathetic control of ABP is disturbed in young adult FH+ such that repeated exposure to mental stressors would be expected to increase their risk of hypertension. Acute slow breathing reduced ABP in both FH+ and FH- but reduced TPR in FH- only. Concomitantly, HRV was increased in both groups, while vagal BRS was increased in FH+ only. These novel results suggest that FH+ are more resistant to the ability of slow breathing to reduce sympathetic tone, but that vagal influences are normalised. Importantly, the systematic review and meta-analysis, demonstrated that slow breathing is effective in both hypertensives and normotensives in lowering ABP, enhancing HRV, and improving BRS, at least in normotensives. Thus, collectively the results indicate that slow breathing training should help to reduce abnormal autonomic regulation in young FH+ by increasing vagal regulation of the heart and decreasing sympathetic activity to the heart and vasculature, so lowering their future risk of hypertension.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):