Cardiodynamic response to psychological and cold pressor stress: further evidence for stimulus response specificity and directional fractionation

Body composition and physical activity as mediators in the relationship between socioeconomic status and blood pressure in young South African women: a structural equation model analysis

OBJECTIVES

Varying hypertension prevalence across different socioeconomic strata within a population has been well reported. However, the causal factors and pathways across different settings are less clear, especially in sub-Saharan Africa. Therefore, this study aimed to compare blood pressure (BP) levels and investigate the extent to which socioeconomic status (SES) is associated with BP, in rural and urban South Africa women.

SETTING

Rural and urban South Africa.

DESIGN

Cross-sectional.

PARTICIPANTS

Cross-sectional data on SES, total moderate and vigorous physical activity (MVPA), anthropometric and BP were collected on rural (n=509) and urban (n=510) young black women (18-23 years age). Pregnant and mentally or physically disabled women were excluded from the study.

RESULTS

The prevalence of combined overweight and obesity (46.5% vs 38.8%) and elevated BP (27.0% vs 9.3%) was higher in urban than rural women, respectively. Results from the structural equation modelling showed significant direct positive effects of body mass index (BMI) on systolic BP (SBP) in rural, urban and pooled datasets. Negative direct effects of SES on SBP and positive total effects of SES on SBP were observed in the rural and pooled datasets, respectively. In rural young women, SES had direct positive effects on BMI and was negatively associated with MVPA in urban and pooled analyses. BMI mediated the positive total effects association between SES and SBP in pooled analyses (ß 0.46; 95% CI 0.15 to 0.76).

CONCLUSIONS

Though South Africa is undergoing nutritional and epidemiological transitions, the prevalence of elevated BP still varies between rural and urban young women. The association between SES and SBP varies considerably in economically diverse populations with BMI being the most significant mediator. There is a need to tailor prevention strategies to take into account optimising BMI when designing strategies to reduce future risk of hypertension in young women.

Analysing the socioeconomic determinants of hypertension in South Africa: a structural equation modelling approach

BACKGROUND

Epidemiological research has long observed a varying prevalence of hypertension across socioeconomic strata. However, patterns of association and underlying causal mechanisms are poorly understood in sub-Saharan Africa. Using education and income as indicators, we investigated the extent to which socioeconomic status is linked to blood pressure in the first wave of the National Income Dynamics Study--a South African longitudinal study of more than 15,000 adults--and whether bio-behavioural risk factors mediate the association.

METHODS

In a cross-sectional analysis, structural equation modelling was employed to estimate the effect of socioeconomic status on systolic and diastolic blood pressure and to assess the role of a set of bio-behavioural risk factors in explaining the observed relationships.

RESULTS

After adjustment for age, race and antihypertensive treatment, higher education and income were independently associated with higher diastolic blood pressure in men. In women higher education predicted lower values of both diastolic and systolic blood pressure while higher income predicted lower systolic blood pressure. In both genders, body mass index was a strong mediator of an adverse indirect effect of socioeconomic status on blood pressure. Together with physical exercise, alcohol use, smoking and resting heart rate, body mass index therefore contributed substantially to mediation of the observed relationships in men. By contrast, in women unmeasured factors played a greater role.

CONCLUSION

In countries undergoing epidemiological transition, effects of socioeconomic status on blood pressure may vary by gender. In women, factors other than those listed above may have substantial role in mediating the association and merit investigation.

Effects of brief rest periods upon heart rate in multiple baseline studies of heart rate reactivity

Although there has been some discussion regarding the appropriate length of time necessary for subjects to reach true resting heart rate prior to experimentation, the relevance of conclusions from that discussion for multiple baseline studies of heart rate has not been demonstrated. To investigate this issue, data were collected from 39 males and 33 females following a standard 15-minute adaptation period and then during a series of two-minute experimental phases including stressor tasks and rest periods. Results indicated that, while the group's heart rate during brief rest periods returned to postadaptation levels, there was a substantial subgroup of subjects for whom this was not the case. Implications for the use of multiple baseline procedures in research where heart rate is the dependent variable are discussed.

Effects of acute stress on lymphocyte beta 2-adrenoceptors in white males

The effects of acute cold pressor stress on peripheral blood cells and lymphocyte beta 2-adrenoceptor density and affinity were examined in 18 young, healthy normal white male volunteers. Blood samples were drawn two times before and three times after the stressor. The percents of lymphocytes and neutrophils, plasma cortisol and the beta 2-adrenoceptor density were significantly different among blood samples. There were no differences between samples in total white blood cell count, and percent of monocyte, basophil and eosinophil or beta 2-adrenoceptor affinity. The results suggest that cold pressor stress causes lymphocytosis and increases the lymphocytic beta 2-adrenoceptors concentration. Methodological issues, acute vs chronic condition effects, immune cell subset variations and the psychosomatic activity-affect model were discussed. Such adrenoceptor changes may provide one mechanism by which stress can affect the onset of cardiac/hypertensive disorders.