“How we get there…”: Heart Rate Variability and Blood Pressure Response to Physical Challenge in Māori and New Zealand European Pākehā

Abstract

Chronically elevated blood pressure (hypertension) poses an important threat to health, both globally and within Aotearoa New Zealand. However, hypertension does not affect all ethnic groups equally. Within New Zealand populations Māori experience a disproportionate burden of hypertension and hypertension related illness when compared with New Zealand European/Pākehā. This disparity in hypertension is long standing and the New Zealand academic community acknowledges the urgent need for research to support evidence-based practice in reducing cardiovascular disparities between Māori and New Zealand European/Pākehā. Despite this call to action, there appears to be no research considering the physiological and psychological mechanisms which underlie these disparities. This cross-sectional study aimed to experimentally investigate the underlying physiological mechanisms involved in blood pressure regulation for self-identified Māori (n = 21) and New Zealand European/Pākehā participants (n = 22), from a multi-dimensional perspective. To this end, participants completed a three-part protocol, which included a five minute baseline period, a five minute physical challenge (standing) and a final five minute recovery period. At the end of each period, participants completed a self-reported mood measure. The physical challenge in this protocol necessitates initiation of blood pressure regulatory mechanisms. Changes in these underlying blood pressure mechanisms were monitored throughout the protocol for both Māori and New Zealand European/Pākehā participants. The results of the study showed no significant difference in systolic, diastolic or mean arterial pressure levels in young adult (mean age = 23 years) Māori and New Zealand European/Pākehā. Analysis of underlying blood pressure parameters showed that Māori and New Zealand European/Pākehā participants regulated blood pressure via different hemodynamic mechanisms. Specifically, Māori participants exhibited greater use of centrally mediated blood pressure regulation (greater cardiac output and stroke volume) than New Zealand European/Pākehā participants; while New Zealand European/Pākehā showed greater use of peripheral mechanisms for blood pressure regulation (greater total peripheral resistance) than Māori participants across all conditions. When controlling for baseline differences in BMI across ethnic groups, BMI was shown to be positively correlated with negative mood, and negatively correlated with positive mood directly after physical challenge. In sum the results of the study indicate that young adult populations of Māori and New Zealand European/Pākehā show no disparity in absolute blood pressure levels. In fact, Māori participants showed patterns of blood pressure regulation which are considered more adaptive than those exhibited by New Zealand European/Pākehā. These results do not dispute hypertension disparities between Māori and New Zealand European/Pākehā evident at the population level. Instead, these findings suggest that population level hypertension disparities are likely to be the result of differential ‘break-down’ in blood pressure regulatory mechanisms for Māori and New Zealand European/Pākehā individuals in middle- or olderadulthood. These results provide the motive for future research concerning changes in these physiological blood pressure mechanisms across the life-course.