N.T. Malan

Validation of the Finometer device for measurement of blood pressure in black women

The improved Finapres apparatus, known as the Fino-meter, measures finger blood pressure noninvasively on a beat-to-beat basis and gives waveform measurements similar to intra-arterial recordings. The Finometer measures brachial pressure and corrects for finger pressure accordingly. It also corrects for the hydrostatic height of the finger with respect to the heart level. The objective was to validate the Finometer according to the revised British Hypertension Society (BHS) protocol and the criteria of the Association for the Advancement of Medical Instrumentation (AAMI). We carried out a main validation test using a subject group of 102 black women, which was also divided into smaller groups, namely 24 hypertensives, 25 obese normotensive and 35 lean normotensive women. Finometer and mercury sphygmomanometer blood pressure (BP) measurements were taken early in the morning before breakfast, after the subjects stayed overnight in a research unit. Within the whole subject group, the Finometer satisfied the AAMI criteria for accuracy and achieved an overall A/B grading according to the BHS criteria. The sphygmomanometer measurements were 128±20/78±12 mmHg compared to 130±20/78±11 mmHg for the Finometer. The average differences between the mercury sphygmomanometer and Finometer readings for systolic and diastolic BP were, respectively, −1.83±6.8 and 0.88±7.5. Systolic readings of the Finometer device differed by less than 5 mmHg for 64%, by less than 10 mmHg for 86% and differed by less than 15 mmHg for 96% of all readings. A total of 63% of all diastolic readings of the Finometer by less than 5 mmHg, 85% by less than 10 mmHg and 94% of all readings differed by less than 15 mmHg. On the basis of these results, the Finometer device satisfied the validation criteria of AAMI and received an A/B grading according to the BHS protocol. It can therefore be recommended for measurements in the clinical set-up and for research purposes.

Leptin is independently associated with systolic blood pressure, pulse pressure and arterial compliance in hypertensive African women with increased adiposity: the POWIRS study

High leptin levels are often observed in human obesity and are implicated in obesity-related hypertension. Leptin levels have been found to be higher in hypertensive obese African-American women compared to normotensive African-American women, but a direct association between leptin and blood pressure could not be obtained. Additionally, increased adiposity has been associated with higher aortic stiffness in obese African-American women, but leptin was not included in the study. The effects of leptin on cardiovascular function in African women have not yet been determined. We hypothesised that leptin is directly associated with blood pressure and decreased arterial compliance and that leptin levels are significantly higher in hypertensive overweight/obese African women compared to normotensive overweight/obese African women. A case–case control study was performed which included 98 African women. The subjects were divided into lean normotensive (lean NT), overweight/obese normotensive (OW/OB NT) and overweight/obese hypertensive (OW/OB HT). The Finometer apparatus was used to obtain a more elaborate cardiovascular profile. Serum leptin and insulin levels as well as the HOMA-IR index were determined. Various anthropometric measures were obtained. Leptin levels were elevated (P⩽0.05) in the OW/OB NT and HT groups compared to the lean NT group, but were similar in the OW/OB NT and HT groups. After adjusting for obesity, insulin resistance, hyperinsulinaemia and age, a direct positive correlation was obtained between leptin and systolic blood pressure (SBP) (P⩽0.05; r=0.68) in the OW/OB HT group. Additionally, leptin also correlated negatively with arterial compliance (P⩽0.05; r=−0.76) and positively with pulse pressure (P⩽0.05; r=0.71) in the OW/OB HT group. In conclusion, even though leptin levels were the same in OW/OB HT and NT African women, leptin was directly and positively associated with SBP and pulse pressure and negatively with CW only in OW/OB HT African women, independent of obesity, insulin-resistance, hyperinsulinaemia and age.

Inflammation, obesity and cardiovascular function in African and Caucasian women from South Africa: the POWIRS study

The integrated relationship between inflammation, obesity and cardiovascular disease is currently a subject of much research interest. These specific relationships, however, have not been studied in-depth in South African population groups in order to determine the role of ethnicity. It is known that Africans, compared to Caucasians, suffer from a high prevalence of hypertension. It was therefore hypothesized that the levels of inflammatory markers (high-sensitivity C-reactive protein (hsCRP), fibrinogen and leptin) are higher in Africans compared to Caucasians and are notably associated with cardiovascular dysfunction in Africans. Apparently healthy African (N=102) and Caucasian (N=115) women, matched for age and body mass index (BMI), were recruited. Leptin, hsCRP, fibrinogen and lipid levels, waist circumference (WC), BMI, systolic and diastolic blood pressure, cardiac output (CO), total peripheral resistance (TPR) and Windkessel compliance were measured. Results showed that the levels of leptin, hsCRP and fibrinogen were significantly higher (P<0.05) in the African women. The inflammatory markers correlated strongly with cardiovascular parameters, age and obesity (BMI, WC) in both groups, but after adjusting for age and obesity, none of the correlations were significant anymore. Multiple regression analyses (with leptin, hsCRP or fibrinogen as dependent variable) showed that only leptin levels of African women were explained by cardiovascular parameters (BP, TPR and CO). In conclusion, even though African women had significantly higher leptin, hsCRP, fibrinogen and blood pressure levels than Caucasian women, no cardiovascular parameters explained the variation in the inflammatory markers (except for leptin levels of African women).

Should obesity be blamed for the high prevalence rates of hypertension in black South African women

Hypertension is highly prevalent in South Africa, resulting in high stroke mortality rates. Since obesity is very common among South African women, it is likely that obesity contributes to the hypertension prevalence. The aims were to determine whether black African women have higher blood pressures (BPs) than Caucasian women, and whether obesity is related to their cardiovascular risk. African (N=102) and Caucasian (N=115) women, matched for age and body mass index, were included. Correlations between obesity (total body fat, abdominal obesity and peripheral fat) and cardiovascular risk markers (haemodynamic parameters, lipids, inflammatory markers, prothrombotic factors, adipokines, HOMA-IR (homoeostasis model assessment insulin resistance)) were compared between the ethnic groups (adjusted for age, smoking, alcohol and physical activity). Comparisons between low- and high-BP groups were also made for each ethnic group. Results showed that African women had higher BP (P<0.01) with increased peripheral vascular resistance. Surprisingly, African women showed significantly weaker correlations between obesity measures and cardiovascular risk markers when compared to Caucasian women (specifically systolic BP, arterial resistance, cardiac output, fibrinogen, plasminogen activator inhibitor-1, leptin and resistin). Interestingly, the latter risk markers were also not significantly different between low- and high-BP African groups. African women, however, presented significant correlations of obesity with triglycerides, C-reactive protein and HOMA that were comparable to the Caucasian women. Although urban African women have higher BP than Caucasians, their obesity levels are weakly related to traditional cardiovascular risk factors compared to Caucasian women. The results, however, suggest a link with the development of insulin resistance.

Aging influences the level and functions of fasting plasma ghrelin levels: the POWIRS-Study.

OBJECTIVE Ghrelin, known for its orexigenic activity, also have functions such as vasodilation and a growth hormone releasing action. It is uncertain whether these functions change with increasing age. This study aimed to determine whether ghrelin levels differ between young and older women with different levels of obesity; and secondly whether the associations of ghrelin with metabolic syndrome (MS) components, adipocytokines, coagulation factors, and cortisol change with increasing age. METHODS AND RESULTS Caucasian women (N=107) were divided into young (19-29 years) and older groups (30-56 years). Fasting ghrelin, leptin, adiponectin, glucose, insulin, cortisol, fibrinogen and plasminogen activator inhibitor-1 (PAI-1) levels were determined. Blood pressure (BP), body mass index and waist circumferences were measured. Older lean women showed lower levels of ghrelin (p<0.05) than young lean women, with no differences regarding BP, obesity, lipids, adipokines or insulin resistance (IR). Ghrelin levels of older women remained constant with increasing obesity, but younger women showed significantly reduced ghrelin levels in obese groups. Only younger women showed significant correlations between ghrelin and leptin, adiponectin, fibrinogen and PAI-1 (adjusted for age, obesity and menstrual phase), whereas both age groups showed significant correlations with IR. In younger women factor analysis grouped ghrelin with coagulation factors and all MS components. In older women ghrelin was absent from the MS cluster, but was associated with lower BP, cortisol and IR. CONCLUSIONS Ghrelin levels were not significantly elevated in lean older women, and did not change with increased obesity in older women--as were observed in younger women. The functions of ghrelin also seem to change with increased age since only in young women ghrelin was associated with obesity, coagulation factors and leptin.

Associations between reactive oxygen species, blood pressure and arterial stiffness in black South Africans: the SABPA study

Many mechanisms, including oxidative stress, contribute to hypertension. This study investigated the possible associations between oxidative stress, blood pressure and arterial stiffness in black South Africans. Ambulatory blood pressure measurements were taken for 101 black South African men and 99 women. The stiffness indices included ambulatory arterial stiffness index (AASI) and pulse pressure (PP). Reactive oxygen species (ROS) levels (P<0.0001) were higher in the African women compared with men. ROS levels were also higher in hypertensive compared with normotensive men. The 24 h systolic blood pressure (SBP; P<0.01), 24 h diastolic blood pressure (DBP; P<0.0001) and pulse wave velocity (PWV; P<0.01) were significantly higher in African men compared with women. There were unadjusted positive associations of 24 h SBP (r=0.33; P=0.001), 24 h DBP (r=0.26; P=0.008) and 24 h PP (r=0.29; P=0.003) with ROS in African men only. A positive association between AASI and ROS existed only in hypertensive men (r=0.27; P=0.035), but became nonsignificant (B=0.0014; P=0.14) after adjustments. Adjusted, positive associations of 24 h SBP (B=0.181; P=0.018) and 24 h PP (B=0.086; P=0.050) with ROS were again only evident in African men. ROS is positively associated with SBP and PP in African men, suggesting that increased ROS levels may contribute to hypertension in this population group.

Dietary risk markers that contribute to the aetiology of hypertension in black South African children: the THUSA BANA study

Although clinical hypertension occurs less frequently in children than in adults, ample evidence supports the concept that the roots of essential hypertension extend back to childhood. Since little is available in the literature on causal dietary factors of hypertension in children, this study hypothesised that certain dietary factors can be identified as risk markers that might contribute to the aetiology of hypertension in black children. Children aged 10–15 years were randomly selected from 30 schools in the North West Province from 2000 to 2001. These children comprised 321 black males and 373 females from rural to urbanised communities, of which 40 male and 79 female subjects were identified with high-normal to hypertensive blood pressure. Blood pressure was measured with a Finapres apparatus and data were analysed with the Fast Modelflo software program to provide systolic, diastolic and mean blood pressure. A 24-h dietary recall questionnaire and weight and height measurements were taken. In a stepwise regression analysis, the following variables were significantly associated (P⩽0.05) with blood pressure parameters of hypertensive males: biotin, folic acid, pantothenic acid, zinc and magnesium. Energy, biotin and vitamin A intakes were significantly associated with blood pressure parameters of hypertensive females. No significant dietary markers were indicated for any of the normotensive groups. Dietary intakes of all of these nutrients were well below the dietary reference intakes. In conclusion, the dietary results coupled with the cardiovascular parameters of this study identified folic acid and biotin as risk markers that could contribute to the aetiology of hypertension in black persons. The low intakes of these nutrients, among others, is a matter of serious concern, as is the increasing tendency towards urbanisation.

Prolactin, testosterone and cortisol as possible markers of changes in cardiovascular function associated with urbanization

People living in large informal settlements in South Africa showed a significant increase in cardio/cerebrovascular disease. This study was undertaken to compare the cardiovascular and endocrine parameters of urbanized and rural black female and males. The hormone levels such as prolactin, cortisol and testosterone may also change with urbanization and could make a contribution to the high rate of hypertension. For this study, 1202 black subjects were selected from 37 randomly selected rural and urbanized settlements. Resting blood pressure was recorded with a Finapres apparatus. Cardiac output, stroke volume, heart rate, total peripheral vascular resistance and compliance had been obtained with the Fast Modelflow software program. An acute laboratory stressor (hand dynamometer exercise) was applied to challenge the cardiovascular system and the measurements were repeated. Blood sampling was done and hormone levels were determined by biochemical analyses. For females, significant lower levels of cortisol were found in the urban strata in comparison with the rural strata. The testosterone levels were significantly lower and the prolactin levels significantly higher for females in the informal settlements compared with the rural strata. It is noticeable that most cardiovascular parameters showed the highest changes with the application of the stressor in the informal settlement strata and the lowest in people living on farms for both male and female. The prolactin levels in males are significantly higher in the informal settlement stratum. Subjects living in informal settlements showed a noticeable endocrine pattern of ongoing stress that can be associated with changes in the cardiovascular parameters with urbanization. This can partly explain the reported high rate of cardio/cerbrovascular disease in black South Africans living in informal settlements.

Classifying Africans with the Metabolic Syndrome

This study was aimed to compare prevalences of the metabolic syndrome in Africans using five definitions as proposed by the World Health Organization (WHO), the European Group for the Study of Insulin Resistance (EGIR), the National Cholesterol Education Program Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults [Adult Treatment Panel (ATPIII)], the American College of Endocrinology (ACE), and the International Diabetes Federation (IDF). A further objective was to identify difficulties in classifying Africans with the metabolic syndrome and to suggest specific areas where criteria adjustments for identifying Africans should be made. A case-case-control cross-sectional study involved 102 urban African women. Except for microalbumin data, all data necessary for classification of the metabolic syndrome were collected, including fasting and 2-h glucose and insulin, anthropometric measurements, blood pressure, and lipids. The metabolic syndrome prevalences ranged from 5.4% (EGIR), 15.7% (ATPIII), >or=19.4% (WHO), 24.8% (IDF) to 25.5% (ACE). Only 2.9% (n=3) had a triglyceride level >or=1.69 mmol/l, but 58.8% (n=60) had a HDL-level <1.29 mmol/l, whereas 27% (n=26) were insulin resistant, 22.3% (n=21), had a blood pressure >or=140/90 or used hypertension medication. It seems as if the classification of hypertension, insulin resistance and hyperglycemia might have been adequate, but body composition and dyslipidemia criteria need adjustment for Africans. Since neither definition seems completely suitable for Africans it is suggested that clinical emphasis should rather be on treating any specific cardiovascular disease risk factor that is present, than on diagnosing a patient with the metabolic syndrome.

Leptin is favourably associated with vascular function in obese Caucasians, but not in obese Africans

The comparison of the associations between chronically elevated leptin levels and cardiovascular function in obese Africans and Caucasians has not yet been determined. Therefore, the aim of this study was to compare leptins associations with cardiovascular function in obese African and obese Caucasian women to determine whether leptins associations differ between these two groups. This study consisted of two case–case control studies. The first study included a sample of 102 apparently healthy African women and the second, 115 apparently healthy Caucasian women. All lean and obese subjects were selected from each study. The Finometer apparatus was used to obtain a more elaborate cardiovascular profile. Serum leptin levels, insulin levels and the lipid profile were determined. Stroke volume (SV) and cardiac output (CO) were significantly (P⩽0.01) elevated in both obese African and Caucasian groups compared to their lean controls. Total peripheral resistance (TPR) was significantly decreased and arterial compliance (CW) significantly increased in both obese African and Caucasian groups. In the obese Caucasian group, diastolic blood pressure (DBP) was significantly (P⩽0.01) lower, SV and CW significantly higher (P⩽0.01) and TPR significantly lower compared to the age, body mass index (BMI), and leptin-matched obese African group. After adjusting for age and BMI, leptin correlated negatively with DBP (P⩽0.05; r=−0.33) and TPR (P⩽0.05; r=−0.36) in the obese Caucasian group, but not in the obese African group. Even though leptin levels were similar in obese African and Caucasian women, leptin is favourably associated with vascular function in obese Caucasians, but not in obese Africans.