The natural history of borderline isolated systolic hypertension

Aortic wall properties in normotensive and hypertensive rats of various ages in vivo

The distensibility of the arterial system, which is partly determined by arterial wall structure, smooth muscle tone, and actual pressure level, decreases with aging and hypertension. Our aim was to compare aortic wall properties in 3- and 6-month-old normotensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) at comparable blood pressures in vivo. During ketamine/xylazine anesthesia in rats we performed ultrasound arterial wall tracking and invasive pressure measurements to determine, at the level of the thoracic aorta, diastolic pressure, diastolic lumen area, changes in pressure and lumen area during the cardiac cycle, and indexes of compliance and distensibility. These observations were combined with histological measurements for determination of media cross-sectional area and thickness and the incremental elastic modulus under conditions as expected in situ. Anesthesia abolished the difference in diastolic pressure between SHR and WKY. Between 3 and 6 months of age in WKY, diastolic area and incremental elastic modulus increased significantly, distensibility decreased, and all other recorded variables were not modified. Between 3 and 6 months of age in SHR, diastolic area and incremental elastic modulus increased, distensibility of the aortic wall decreased, and all other mechanical and structural properties did not change significantly. At both ages, diastolic area and compliance were significantly smaller in SHR than WKY. The other mechanical and structural properties measured or calculated at comparable pressure did not differ between strains. Differences between the aorta of 3- and 6-month-old rats and between strains observed in vivo at comparable pressures can largely be attributed to differences in lumen caliber.(ABSTRACT TRUNCATED AT 250 WORDS)

Medical care utilization among older HMO members with and without hypertension

OBJECTIVES

To compare hospital utilization, health status, and sociodemographic characteristics of older persons with and without hypertension and to examine the nature of the association of hypertension with medical care utilization.

DESIGN

A retrospective, nonexperimental study.

SETTING

A large health maintenance organization (HMO), located in the Portland, Oregon and Vancouver, Washington areas, that provides comprehensive, prepaid benefits to its members.

PARTICIPANTS

Approximately 4200 older (> or = 65 years) members enrolled in the Social HMO Demonstration Project.

MEASUREMENTS

The dependent variables were (1) whether a member was hospitalized (0 = no; 1 = yes) and (2) the number of hospitalizations during the 12-month period before the return of the Health Status Form, a mail questionnaire. The predictor variables were high blood pressure and other medical conditions, health status, and sociodemographic characteristics. Patients classified as hypertensive were those who self-reported high blood pressure and who received two or more dispensings for antihypertensive medications.

RESULTS

Older hypertensives were more likely than older nonhypertensives to have been hospitalized (odds ratio (OR) = 1.14 (95% CI 1.01, 1.27)), self-report their health as only good or fair (P < .001), self-report IADL functional limitations (P < .001), and to be younger than nonhypertensives (P < .001). Utilization differences were similar after controlling for patients' age and gender. Factors independently associated with an increased likelihood of hospitalization were male gender (OR = 1.14 (1.00,1.31)), age (OR = 1.35 (1.00,1.81)), poor (OR = 1.32 (1.02,1.72)) or fair (OR = 1.20 (1.01,1.44)) self-rated health status, functional limitations in activities of daily living (OR = 1.74 (1.48,2.03), and self-reported heart trouble (OR = 1.50 (1.34,1.68)), stroke (OR = 1.37 (1.15,1.64)), or cancer (OR = 2.89 (1.72,4.84)). Factors independently associated with a decreased likelihood of hospitalization were excellent self-reported health (OR = 0.65 (0.47,0.90)), no physical impairments (OR = 0.59 (0.48,0.72)), and no circulation problems (OR = 0.85 (0.74,0.98)).

CONCLUSIONS

Older hypertensive patients had poorer self-reported health, more functional limitations, used more hospital services, and were not as old as nonhypertensive older patients. To the extent that general health is improved by treatment of hypertension, appropriate treatment of high blood pressure may not only improve health, it may also reduce medical care utilization. Our findings offer further support for hypertension prevention, detection, and treatment programs designed to reduce or minimize hypertension's later medical complications and to reduce future utilization.

systolic flow augmentation in hearts ejecting into a model of stiff aging vasculature. Influence on myocardial perfusion-demand balance

Age-related arterial stiffening and widening of the pulse pressure elevates ventricular systolic wall stress while it lowers diastolic coronary perfusion pressure. These changes are thought to adversely alter the balance between myocardial work load and blood supply. To test this hypothesis, the native compliant thoracic aorta was surgically bypassed by a stiff tube in reflex-blocked anesthetized dogs. Ventricular outflow was directed into either native aorta or the bypass; the latter resulting in an increase in arterial pulse pressure from 37.8 to 107.5 mm Hg (P < .001), with minimal change in mean pressure and flow. Cardiac work load was assessed by pressure-volume area (PVA), which combines external and internal left ventricular work and is linearly related to myocardial oxygen consumption (MVO2), and by MVO2 itself. Regional phasic and mean coronary flow were measured in the left anterior descending coronary artery, and global flow was assessed by radiolabeled microspheres. Myocardial supply-demand balance was assessed by comparing flow at matched PVA or MVO2, flow-PVA relations, and endocardial-to-epicardial flow ratios. When blood flow was directed into the stiff bypass tube, peak systolic pressure, wall stress, and PVA all rose nearly 50%, yet diastolic perfusion pressure fell by 20 mm Hg (all P < .01). Rather than being compromised, however, mean coronary flow rose by 34%, maintaining the same endocardial-to-epicardial flow ratio (approximately 1.1). Flow augmentation persisted when data were compared at matched work load (PVA or MVO2), and mean arterial pressure, as well as over a range of work loads (P < .001 from ANCOVA of flow-PVA relations). The increased flow resulted from enhanced systolic perfusion, which nearly equaled diastolic flow when ejection passed into the stiff bypass. These data counter the notion that cardiac coupling with a stiff arterial system (as with aging) necessarily compromises myocardial flow versus metabolic demand. However, the data highlight a greater role of systolic flow under such conditions and also raise the novel suggestion that enhanced pulsatility of the arterial pressure waveform may itself augment coronary perfusion.

Salt, hypertension and renal disease: comparative medicine, models and real diseases

Dogs are well established as experimental animals for the study of both renal disease and hypertension, but most work is based on surgical or pharmacological models and relatively little on spontaneous diseases. This review argues for the latter as an underexploited aspect of comparative medicine. The most important feature of canine hypertension may not be the ease with which models can be produced but the fact that dogs are actually rather resistant to hypertension, and perhaps to its effects, even when they have chronic renal failure. The importance of natural models of chronic renal failure is strengthened by the evidence that self-sustaining progression is a consequence of extreme nephron loss, that is, a late event, rather than the dominant feature of the course of the disease. The role of salt in hypertension is discussed and emphasis given to the importance of understanding the physiological basis of nutritional requirement and recognizing that it is unlikely to exceed 0.6 mmol/kg/day for most healthy adult mammals except during pregnancy or lactation. Such a perspective is essential to the evaluation of experiments, whether in animals or humans, in order to avoid arbitrary definitions of 'high' or 'low' sodium intake, and the serious misinterpretations of data which result. An age-related rise in arterial pressure may well be a warning of excess salt intake, rather than a normal occurrence. Problems of defining hypertension in the face of variability of arterial pressure are also discussed.