Is early evidence of cardiovascular and respiratory disease already present in young healthy South Asians or White Europeans: could respiratory training lead to improvement?

Alqahtani, Mobarak Khalid M. (2023). Is early evidence of cardiovascular and respiratory disease already present in young healthy South Asians or White Europeans: could respiratory training lead to improvement? University of Birmingham. Ph.D.

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Abstract

Background: Hypertension is well-known as the forerunner of most cardiovascular diseases. The prevalence of hypertension, coronary artery diseases, and other cardiovascular diseases has been reported to be higher among men and women of South Asian ethnicity than White Europeans. Further, South Asians have lower lung function than White Europeans, and poor lung function has been reported as a risk for developing future hypertension and cardiovascular disease.

Objective: The overall objective of this PhD project was to investigate whether young healthy normotensive South Asian adults show early markers of autonomic dysfunction at rest and in response to mental stress that may lead to future hypertension and to assess whether acute or long-term slow breathing may have beneficial effects on autonomic regulation of arterial blood pressure (ABP), especially in South Asians.

Methods: Three studies were conducted to test the hypothesises. The first compared haemodynamic variables, heart rate variability (HRV) which largely reflects vagal influences on HR and baroreceptor reflex sensitivity (BRS) between young normotensive South Asian and White European adults at rest, in response to acute slow breathing at 6 breaths/ minute and acute mental stress. The second tested whether there were sex-dependent differences in these responses within and between ethnicities. Thirdly, a systematic review was performed to evaluate the effects of acute slow breathing and slow breathing training on autonomic regulation of ABP in healthy, normotensive South Asians.

Results and Conclusions: Young South Asians showed a pronounced pressor response to mental stress associated with greater peripheral vasoconstriction than occurred in White Europeans, vasoconstriction being most prevalent in South Asian women. These novel findings are consistent with mental stress facilitating development of hypertension in South Asians. Further, White Europeans showed the characteristic inhibition of the vagal and sympathetic component of BRS in mental stress, but both components of BRS to falls in ABP were preserved in South Asians, possibly protecting them against vasovagal syncope but facilitating their risk of hypertension. By contrast, acute slow breathing decreased ABP and increased HRV in both young South Asians and White Europeans but decreased tonic peripheral vasoconstriction in WEs only. These new findings suggest that South Asians may be more resistant to the beneficial effects of slow breathing on sympathetic activity. However, the systematic review and meta-analysis showed that both acute slow breathing and four weeks of slow breathing training were able to decrease ABP and increase HRV in healthy normotensive South Asians. Thus, these outcomes are consistent with our hypotheses. Importantly, considered together with our experimental findings they suggest that a study should be performed to evaluate whether slow breathing can provide a beneficial therapeutic intervention for young normotensive South Asians and reduce their risk of future hypertension and cardiovascular disease.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):