Catharina Maria Theresia Fourie

Comparison of central pressure estimates obtained from SphygmoCor, Omron HEM-9000AI and carotid applanation tonometry

Background The Omron HEM-9000AI is the first automated tonometer to provide an estimate of central SBP (cSBP), which is considered to be more predictive of cardiovascular events than brachial pressure. However, considerable differences between the cSBP estimate of Omron and that of SphygmoCor have been reported, but not explained. This study assesses the sources of differences between both cSBP estimates and provides a handle on which estimate is closest to reality. Method For this purpose, aortic cSBP derived from calibrated carotid SBP was used as device- and algorithm-independent reference. Radial, brachial and carotid applanation tonometry were performed in 143 black South Africans, aged 39–91 years. Each individual was measured with an Omron HEM-9000AI and a SphygmoCor. Results When using both devices as advocated by their manufacturers, the corresponding cSBP estimates correlated strongly (r = 0.99, P < 0.001), but the Omron estimate was 18.8 (4.3) mmHg higher than the SphygmoCor estimate. Aortic SBP was in between both estimates: 11.7 (5.5) mmHg lower than cSBP-Omron and 7.1 (5.0) mmHg higher than cSBP-SphygmoCor. Alternative calibration of the radial SphygmoCor-curves with radial instead of brachial pressures yielded a cSBP that was 3.0 (4.2) mmHg lower than aortic SBP. The shape of the recorded pressure waves was similar in both devices: less than 5% of the observed cSBP difference was caused by differences in wave shape. Conclusion The results from this study demonstrate that the considerable difference between the central pressure estimates of Omron HEM-9000AI and SphygmoCor is due to algorithm differences, and suggest that the overestimation by Omron HEM-9000AI is larger than the underestimation by SphygmoCor.

Blood pressure variability is significantly associated with ECG left ventricular mass in normotensive Africans: The SABPA Study

The prognostic significance of blood pressure (BP) variability has lately enjoyed considerable attention. The need for early markers of cardiovascular dysfunction is imperative in black South Africans who have a significant risk for cardiovascular disease. We therefore compared 24-h BP variability with various traditional and advanced BP measurements, regarding their association with sub-clinical organ damage in black and white South Africans. The study included 409 African and Caucasian teachers aged 25–60 yrs. We measured office BP, 1-min continuous (finger) BP, ambulatory BP, BP reactivity and determined weighted 24-h BP variability. Albumin-to-creatinine ratio, Cornell product and carotid cross-sectional wall area (CSWA) were measures of organ damage. Africans had higher 24-h BP, BP variability, BP reactivity and sub-clinical organ damage (P<0.001). Correlations of BP variability with organ damage were overall weak when compared with other BP measurements. In normotensive groups, we found an independent association of 24-h systolic BP (SBP) variability with Cornell product only in Africans (r=0.37; P=0.01), confirmed in multiple regression models, with 24-h SBP included in the model. Only in hypertensive Caucasians, a significant correlation between CSWA and 24-h SBP variability was evident (r=0.30; P=0.01), although CSWA indicated stronger correlations with office or 24-h SBP than 24-h SBP variability. To conclude, 24-h SBP variability could potentially be an effective measure for the early detection of normotensive Africans at increased risk for the development of cardiovascular complications. Its usefulness based on associations with target organ damage in hypertensive groups seems to be less than traditional office or 24-h BP measurements.

Is HIV-1 infection associated with endothelial dysfunction in a population of African ancestry in South Africa?

Abstract The chronic infection status suffered by HIV-infected individuals promotes chronic arterial inflammation and injury, which leads to dysfunction of the endothelium, atherosclerosis and thrombosis. Although HIV-1 subtype C is prevalent in South Africa and accounts for almost a third of the infections worldwide, this subtype differs genetically from HIV-1 subtype B on which the majority of studies have been done. The objective of this study was to assess whether newly identified, never-treated, HIV-1-infected South African participants showed signs of endothelial dysfunction, accelerated atherosclerosis and increased blood coagulation. We compared 300 newly diagnosed (never antiretroviral-treated) HIV-infected participants to 300 age-, gender-, body mass index- and locality-matched uninfected controls. Levels of high-density lipoprotein cholesterol (HDL-C), triglycerides, interleukin-6 (IL-6), C-reactive protein (CRP), intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), fibrinogen and plasminogen activator inhibitor-1 (PAI-1), and carotid radialis pulse wave velocity (cr-PWV) were determined. The HIV-infected participants showed lower HDL-C and higher IL-6, CRP, ICAM-1 and VCAM-1 levels compared to the uninfected controls. No differences in fibrinogen and PAI-1 levels were detected. A continuous positive trend of increasing age with cr-PWV was detected in the HIV-infected group. Our findings suggest inflammatory injury of the endothelium, pointing to endothelial dysfunction of never-treated HIV-1-infected South Africans of African ancestry. Although no indication of a prothrombotic state could be detected, there was an indication of accelerated vascular aging and probable early atherosclerosis in the older HIV-infected participants.

A significant decline in IGF-I may predispose young Africans to subsequent cardiometabolic vulnerability

OBJECTIVES Low serum IGF-I is an independent risk factor for diabetes and cardiovascular disease. These noncommunicable diseases are extremely common in urban black South Africans, but their IGF-I concentration is unknown. We aimed to compare serum IGF-I concentrations of African and Caucasian people, investigate their age-related IGF-I decline, and determine whether IGF-I could account, at least in part, for the high prevalence of noncommunicable diseases in black Africans. RESEARCH DESIGN AND METHODS This cross-sectional study involved 211 African and 316 Caucasian men and women (aged 20-70 yr). Fasting glucose, insulin, lipids, albumin, creatinine, liver enzymes, cotinine, high-sensitivity C-reactive protein, reactive oxygen species, IGF-I, blood pressure (BP), and pulse wave velocity were determined. RESULTS IGF-I was lower in Africans (P < 0.001) and in both ethnicities declined significantly by age quartiles (P < 0.001). In African men and women, IGF-I declined significantly from age quartile 1 to 2 (r = -0.65, P < 0.001), not seen in young Caucasian men and women (r = -0.08, P = 0.45; r = -0.10, P = 0.34). This was confirmed after adjustment for BP, insulin resistance, high-sensitivity C-reactive protein, cotinine, gamma-glutamyl transferase, and reactive oxygen species. Only young Africans showed significant negative correlations of IGF-I with BP, pulse wave velocity, and high-density lipoprotein cholesterol. CONCLUSIONS Africans presented lower IGF-I levels than Caucasians due to an accelerated decline in serum IGF-I concentration prior to 40 yr of age. Strong associations of low serum IGF-I with blood pressure and arterial stiffness in young Africans suggest that the loss of cardiometabolic protection by IGF-I could predispose them to earlier disease onset.

Arterial stiffness, ambulatory blood pressure and low-grade albuminuria in non-diabetic African and Caucasian men: the SABPA study

Recent evidence suggests that low-grade urinary albumin excretion is a marker of early general attenuation of vascular function, but studies are limited to Caucasian population groups. We compared low-grade urinary albumin excretion (<3.5 mg mmol−1 or 30 μg mg−1) between non-diabetic African (aged, 41.7 years; n=70) and Caucasian (aged, 44.6 years; n=91) men and ethnic-specific associations thereof with arterial stiffness and ambulatory blood pressure. The albumin-to-creatinine ratio (ACR) was determined from an 8 h overnight urine collection. We recorded ambulatory blood pressure over 24 h during a typical workday and the carotid–dorsalis pedis pulse wave velocity measured the next morning after a controlled overnight stay. ACR was higher in Africans compared with Caucasians (P<0.001), also after adjusting for 24 h systolic blood pressure, diastolic blood pressure and hypertension prevalence (P<0.001) or when grouped by similar 24 h mean arterial pressures (P<0.01 for all categories). Daytime (P=0.002) and night time (P< 0.001) systolic and daytime (P<0.001) and night time (P<0.001) diastolic blood pressures were higher in Africans compared with Caucasians, but no differences existed for daytime and night time pulse pressure and pulse wave velocity. In African men only, after adjustment for covariates, night time systolic blood pressure (β=0.347; P=0.003), diastolic blood pressure (β=0.298; P=0.010) and mean arterial pressure (β=0.331; P=0.004) correlated positively with ACR. In addition, daytime (β=0.265; P=0.032) and night time (β=0.258; P=0.038) pulse pressure as well as pulse wave velocity (β=0.271; P=0.032) correlated positively with ACR. In conclusion, arterial stiffness and ambulatory blood pressure are already associated with low-grade albuminuria in non-diabetic African men with normal kidney function.

End-organ damage in urbanized Africans with low plasma renin levels: the SABPA study

Abstract The purpose of this study was to evaluate whether active renin concentration is associated with markers of end-organ damage in urbanized Africans. This study forms part of the Sympathetic Activity and Ambulatory Blood Pressure in Africans (SABPA) study. For this study, 81 men and 74 women were divided into low- and high-renin groups. Ambulatory blood pressure measurements were conducted. A resting 12-lead ECG was determined in order to determine the gender-specific Cornell voltage. Cardiovascular variables were continuously recorded with the Finometer. Carotid-dorsalis pedis pulse wave velocity was obtained with the Complior acquisition system. The carotid intima-media thickness (CIMT) was obtained with the SonoSite MicroMaxx. Blood samples were collected; serum and plasma were stored at −80 °C for analysis. Anthropometric measurements were taken using standard methods. A general health questionnaire was also completed. The urinary creatinine was determined with a calorimetric method and albumin with a turbidimetric method. The serum sodium and potassium were determined by making use of the Konelab TM 20i Sequential Multiple Analyzer Computer (SMAC). The concentration of active renin in the plasma was analyzed by making use of a high-sensitivity radio-immunometric assay. A negative association (r = −0.29, p < 0.01) exists between renal function (ACR) and plasma renin in the low-renin group (<6.18 pg/mL), which was not observed in Africans with high-renin levels. It seems evident that low renin in black South Africans may result in sub-clinical renal damage and impaired vascular function in a group of urbanized black South Africans.

Associations of cholesterol and glucose with cardiovascular dysfunction in black Africans: the SABPA study

The aim was to determine whether blood glucose or cholesterol is the more prominent contributor to cardiovascular dysfunction in 101 African men and 99 African women. We measured ambulatory daytime blood pressure (BP), carotid intima-media thickness (CIMT), and determined blood glucose and lipids in serum. High-density lipoprotein cholesterol (HDL) (p = 0.002) and HDL: total cholesterol (HDL:TC) (p ≤ 0.001) were significantly lower, while serum glucose (p ≤ 0.001) was significantly higher in men. In single, partial, and multiple regression analysis, BP correlated positively with blood glucose in men. Furthermore, CIMT (B = −0.50; p = 0.009) correlated negatively with HDL:TC in men. While in women CIMT (B = 0.346; p = 0.015) correlated positively with glucose. In conclusion, subclinical atherosclerosis is significantly related to an unfavorable HDL profile in men, whereas in women, this link is stronger with fasting glucose.

The usefulness of γ-glutamyltransferase as a marker of cardiovascular function in Africans and Caucasians: the SABPA study.

Aim. Serum γ-glutamyltransferase (GGT) is increasingly regarded as a marker of vascular function. However, the usefulness of this marker is in dispute. Gender and ethnic differences, as well as the serum level range where correlations with vascular function will emerge, may complicate the usefulness of GGT. The aim is to compare correlations with markers of vascular function between African and Caucasian groups. Methods. This cross-sectional target population study involved four groups of African and Caucasian men and women of 100 participants each. Fasting lipids, GGT, C-reactive protein (CRP), reactive oxygen species, and glycosylated hemoglobin (HbA1c) were determined as well as blood pressure, carotid intima-media thickness (CIMT), and left ventricular hypertrophy. Results. γ-Glutamyltransferase levels were significantly higher in Africans compared with Caucasians and also higher in men than in women. γ-Glutamyltransferase correlated with triglycerides in all four groups and after adjusting the correlations sustained in the male groups but disappeared in women. Correlations existed between GGT and blood pressure, except for the African women. After adjustments, CIMT correlated with GGT in Caucasian men (r = 0.29; P < .01). Glycosylated hemoglobin was associated with GGT in Caucasian women (r = 0.26; P = .01) as well as CRP (r = 0.36; P < .01). When the groups were divided into low and high GGT groups by median split, most of the correlations disappeared in the high GGT groups. Conclusions. Gender and ethnic-specific associations occurred regarding GGT and variables associated with cardiovascular function. With high levels of GGT the correlations diminished. The usefulness of GGT as a marker of vascular dysfunction seems limited.