Blood Pressure and Obesity

Body Size Predicts Cardiac and Vascular Resistance Effects on Men's and Women's Blood Pressure

Key Points Summary We report how blood pressure, cardiac output and vascular resistance are related to height, weight, body surface area (BSA), and body mass index (BMI) in healthy young adults at supine rest and standing.Much inter-subject variability in young adult's blood pressure, currently attributed to health status, may actually result from inter-individual body size differences.Each cardiovascular variable is linearly related to height, weight and/or BSA (more than to BMI).When supine, cardiac output is positively related, while vascular resistance is negatively related, to body size. Upon standing, the change in vascular resistance is positively related to size.The height/weight relationships of cardiac output and vascular resistance to body size are responsible for blood pressure relationships to body size.These basic components of blood pressure could help distinguish normal from abnormal blood pressures in young adults by providing a more effective scaling mechanism. Introduction: Effects of body size on inter-subject blood pressure (BP) variability are not well established in adults. We hypothesized that relationships linking stroke volume (SV), cardiac output (CO), and total peripheral resistance (TPR) with body size would account for a significant fraction of inter-subject BP variability. Methods: Thirty-four young, healthy adults (19 men, 15 women) participated in 38 stand tests during which brachial artery BP, heart rate, SV, CO, TPR, and indexes of body size were measured/calculated. Results: Steady state diastolic arterial BP was not significantly correlated with any index of body size when subjects were supine. However, upon standing, the more the subject weighed, or the taller s/he was, the greater the increase in diastolic pressure. Systolic pressure strongly correlated with body weight and height both supine and standing. Diastolic and systolic BP were more strongly related to height, weight and body surface area than to body mass index. When supine: lack of correlation between diastolic pressure and body size, resulted from the combination of positive SV correlation and negative TPR correlation with body size. The positive systolic pressure vs. body size relationship resulted from a positive SV vs. height relationship. In response to standing: the positive diastolic blood pressure vs. body size relationship resulted from the standing-induced, positive increase in TPR vs. body size relationship. The relationships between body weight or height with SV and TPR contribute new insight into mechanisms of BP regulation that may aid in the prediction of health in young adults by providing a more effective way to scale BP with body size.

Assessing factors related to waist circumference and obesity: application of a latent variable model

Background. Because the use of BMI (Body Mass Index) alone as a measure of adiposity has been criticized, in the present study our aim was to fit a latent variable model to simultaneously examine the factors that affect waist circumference (continuous outcome) and obesity (binary outcome) among Iranian adults. Methods. Data included 18,990 Iranian individuals aged 20–65 years that are derived from the third National Survey of Noncommunicable Diseases Risk Factors in Iran. Using latent variable model, we estimated the relation of two correlated responses (waist circumference and obesity) with independent variables including age, gender, PR (Place of Residence), PA (physical activity), smoking status, SBP (Systolic Blood Pressure), DBP (Diastolic Blood Pressure), CHOL (cholesterol), FBG (Fasting Blood Glucose), diabetes, and FHD (family history of diabetes). Results. All variables were related to both obesity and waist circumference (WC). Older age, female sex, being an urban resident, physical inactivity, nonsmoking, hypertension, hypercholesterolemia, hyperglycemia, diabetes, and having family history of diabetes were significant risk factors that increased WC and obesity. Conclusions. Findings from this study of Iranian adult settings offer more insights into factors associated with high WC and high prevalence of obesity in this population.

Sex differences in the contributions of visceral and total body fat to blood pressure in adolescence

Excess body fat deposited viscerally rather than elsewhere in the body is associated with higher risk for hypertension; this relationship is stronger in men than in women. Here we investigated whether similar sex dimorphism exists already in adolescence. A population-based sample of adolescent boys (n=237) and girls (n=262), age 12 to 18 years, was studied. Total body fat (TBF) was assessed with multifrequency bioelectrical impedance, and visceral fat (VF) was quantified with MRI. Blood pressure (BP) was measured beat by beat during an hour-long protocol, including supine, standing, sitting, mental stress, and poststress sections. Multivariate mixed-model analysis was used to assess the relative contributions of TBF and VF to BP during these sections. In boys, BP was strongly positively associated with VF (P<0.0001), whereas it was less strongly and negatively associated with TBF (P=0.004); these relationships did not substantially vary during the protocol. In contrast, in girls, BP was strongly positively associated with TBF (P=0.0006), whereas it was not associated with VF (P=0.08); the relationship with TBF varied during the protocol and was most apparent during mental stress (TBF*section interaction: P=0.002). Furthermore, when waist circumference was included in multivariate models instead of VF, it was not associated with BP in either sex; this indicates that waist circumference may not be an appropriate surrogate for VF. Thus, in adolescence, adiposity-related BP elevation is driven mainly by visceral fat in males and by fat deposited elsewhere in females. This dimorphism suggests sex-specific mechanisms of obesity-induced hypertension and the need for sex-specific criteria of its prevention.

Hypertension: genes and environment

Hypertension can be classified as either Mendelian hypertension or essential hypertension, on the basis of the mode of inheritance. The Mendelian forms of hypertension develop as a result of a single gene defect, and as such are inherited in a simple Mendelian manner. In contrast, essential hypertension occurs as a consequence of a complex interplay of a number of genetic alterations and environmental factors, and therefore does not follow a clear pattern of inheritance, but exhibits familial aggregation of cases. In this review, we discuss recent advances in understanding the pathogenesis of both types of hypertension. We review the causal gene defects identified in several monogenic forms of hypertension, and we discuss their possible relevance to the development of essential hypertension. We describe the current approaches to identifying the genetic determinants of human essential hypertension and rat genetic models of hypertension, and summarise the results obtained to date using these methods. Finally, we discuss the significance of environmental factors, such as stress and diet, in the pathogenesis of hypertension, and we describe their interactions with specific hypertension susceptibility genes.

[Methodologic evaluation of the relation of blood pressure and skinfold thickness: an epidemiologic approach]

The empirical evidence concerning the relationship between blood pressure and anthropometric characteristics (triceps skinfold, adiposity, and arm circumference) was assessed by means of meta-analysis. Different studies were evaluated critically for strength of design, methods and associations. It was found that the association between blood pressure and triceps skinfold holds for three different demographic categories. The question as to the independence of these associations remained unsolved. The effect of arm adiposity on the measurement of blood pressure was also discussed. Recommendations are give in order to standardize blood pressure measurements in clinical and research settings.

Indirect auscultatory blood pressure measurement at two sites in the arm

The purpose of this research was to describe and compare indirect auscultatory blood pressure measurement at the forearm site with values obtained at the traditional upper arm site. The forearm site has been suggested as an alternative site for more accurate measurement of blood pressure in obese patients. This study explores differences in data obtained at the two sites on 98 female subjects, aged 18 to 25 years, with nonobese arms and without history of cardiovascular-renal disease. Data were analyzed using a paired t test (p less than .05). Results indicate that statistically significant differences exist between the sites based on the lower systolic values and higher diastolic values obtained at the forearm site. Additional study is recommended to further clarify differences and to include obese subjects.

Anaesthesia in the morbidly obese. A comparison of anaesthetic and analgesic regimens for upper abdominal surgery

Seventy morbidly obese patients presented for upper abdominal surgery; 17% had pre-existing cardiovascular disease and 23% pre-existing respiratory disease. Twenty-eight patients received general anaesthesia, plus narcotic analgesia postoperatively, and 42 general anaesthesia plus thoracic epidural analgesia intra- and postoperatively. Aspects of anaesthetic management are discussed and compared with previous similar reports. Doses of local anaesthetic for induction of epidural analgesia were less than those for the non-obese but doses of local anaesthetic for maintenance of epidural analgesia were similar to those in non-obese patients. Patients who had thoracic epidural analgesia required less volatile anaesthesia than the group who had general anaesthesia and narcotic analgesics. Postoperative respiratory complications were more common in patients with pre-existing cardiovascular and respiratory disease, and occurred less frequently in patients who had thoracic epidural analgesia.

Cardiovascular effects of obesity and hypertension

Although often coexisting in the same patient, obesity and essential hypertension exert disparate cardiovascular effects. An excess of adipose tissue augments cardiac output, stroke volume, and left ventricular filling pressure, expands intravascular volume, and lowers total peripheral resistance. In contrast, essential hypertension in a non-obese patient is associated with a contracted intravascular volume, high total peripheral resistance, and normal cardiac output, but increased left ventricular stroke work due to high afterload. Left ventricular adaptation will consist of eccentric hypertrophy in the obese (irrespective of arterial pressure) and concentric hypertrophy in the non-obese hypertension patient. The combination of obesity and hypertension burdens the heart with high preload and high afterload, thereby greatly enhancing the risk of congestive heart failure. Peripheral resistance and intravascular volume may be normal in mildly hypertension obese patients because of the mutually antagonising effects of the increase in arterial pressure and the increase in body weight. The fall in arterial pressure associated with weight loss seems to be caused by a decrease in adrenergic activity which leads to a fall in cardiac output without change in vascular resistance. Obesity hypertension may be the result of an inappropriately raised cardiac output in the presence of a relatively restricted arterial capacity due to the low vascularity of adipose tissue. In morbid obesity increased blood viscosity may contribute to the raised arterial pressure.

The experimental evidence for weight-loss treatment of essential hypertension: a critical review

The empirical evidence concerning the therapeutic effects of weight loss for hypertension treatment was reviewed. Interventions were critically reviewed for strength of measures and experimental design. Six of 21 intervention studies proved to be methodologically strong. However, only one study was considered a randomized clinical trial, testing the combined effects of weight reduction and pharmacological treatment of hypertension. Average blood pressure decrease obtained from the methodologically strongest studies was -21 mmHg and -13 mmHg, for systolic and diastolic measures, respectively. This magnitude change suggests that weight loss may be a clinically and statistically significant treatment. Confounding and bias variables, such as adherence to diet, medication, salt consumption, etc., were discussed and future areas of research were outlined. It was concluded that weight loss appears to be an effective and safe treatment of hypertension.

Hypertension in obese patients: hemodynamic and volume studies

Distinct hemodynamic and volume characteristics have been suggested for established hypertension in severe obesity, namely, a high cardiac output, and expanded blood volume, and a normal peripheral resistance. To evaluate whether hypertension in moderately obese patients represents a separate entity that can be defined by hemodynamic and volume profiles, we studied these in 50 such patients and compared results with those obtained in 59 nonobese essential hypertensives and 25 normal subjects. Both obese and nonobese hypertensives had a normal cardiac index (men, 2.8 +/- 0.1 vs 2.8 +/- 0.09 liter/min/m2; women, 2.9 +/- 0.1 vs 2.8 +/- 0.1 liter/min/m2, respectively) and similarly elevated total peripheral resistance (men, 47.1 +/- 2.3 vs 46.5 +/- 1.9 U . m2; women, 45.0 +/- 2.4 vs 44.0 +/- 1.3 U . m2, respectively) as compared to normals (cardiac index: men, 2.9 +/- 0.09 liter/min/m2, women, 3.4 +/- 0.2 liter/min/m2; total peripheral resistance: men, 29.4 +/- 1.0 U . m2, women, 28.3 +/- 2.8 U. m2). Volume measurements corrected to body surface area showed that both obese and nonobese hypertensive patients had lower blood volume (men, 2.6 +/- 0.05 vs 2.5 +/- 0.05 liter/m2; women, 2.2 +/- 0.05 vs 2.3 +/- 0.05 liter/m2, respectively) than normals (men, 2.9 +/- 0.08 liter/m2; women, 2.5 +/- 0.08 liter/m2). The results of this study suggest that hypertension in moderately obese subjects is similar in its hemodynamic and volume profiles to hypertension in the nonobese and that the presence of obesity does not alter the hemodynamic characteristics of established essential hypertension.

The massively obese hypertensive patient: an analysis of blood pressure response to weight reduction with supplemented fasting

A 42.4% incidence of hypertension was seen in 783 massively obese patients admitted to a supplemented fasting program between February 1974 and November 1976. Chosen for this study were the 99 hypertensives who had not received any antihypertensive medication before admission. The blood pressure response after 1 week of inhospital fasting was compared with that at the end of a period of outpatient fasting. Reduction in blood pressure was noted in 85 patients by the end of the first week; by the end of the fasting period, 68 patients were normotensive. We conclude that the elevated blood pressure common in a high percentage of massively obese patients is primarily volume-dependent.