Hypertension in Capsule
High blood pressure, in the form of a “hard pulse,” was tied to mortality risk from the time of ancient Chinese medicine. Diet, body weight, nutrients and the intake of sodium, potassium, and calcium have been central to questions about the causes of hypertension only since indirect arterial blood pressure became easily measured at the turn of the last century. Afterward, it was clinically related to cardiac hypertrophy and failure and to stroke. But it was massive data from insured lives collected in the early 20th century that established the strong relation of blood pressure to the risk of cardiovascular and all-causes death. Despite these clear data, the Pickering-Platt debate raged throughout two decades, Pickering considering blood pressure and its associated risk continuous, Platt maintaining separate universes of the healthy and the hypertensive.
Thus, blood pressure was a natural candidate among the risk characteristics measured in health in the early longitudinal studies of cohorts that took off in mid-20th century. By 1956, the prospective data identified the independent predictive power of blood pressure for CVD risk, which was relatively stronger for stroke than for coronary disease, and had, at least, an additive role with cholesterol level and smoking. With the Hammond-Horn Red Cross study, the AHA Pooling Project in the late 1970s, and such subsequent huge cohort studies as that in 370,000 MRFIT screenees, was the smoothly rising, continuous relation of blood pressure level to CVD risk thoroughly established.
The prospective studies, led by Framingham data, established, by the 1980s, that often-ignored systolic pressure levels were superior to the clinically used diastolic levels in defining the risk of hypertensive “complications.”
A series of clinical trials was mounted when safe and effective anti-hypertensive therapy became available in the late 1960s, resulting in progressive evidence that severe, then moderate, then mild hypertension, then isolated systolic hypertension in the elderly, could be safely and effectively treated to prevent CVD events.
Public health programs began in the U.S. in 1973 and worldwide thereafter to screen, treat, and control hypertension, with improved coverage and a significant influence on CVD risk and rates in the population. Meanwhile, despite relentless upward trends in body mass index in most industrial countries, the mean value and distribution of blood pressure shifted downward, only in part explained by improved medical control. These values remained high, however, in many Eastern block and developing countries.
In regions of high pressure, as in Japan, the steady improvement in control, and apparent improvement in nutrition, have resulted in diminished pressure levels and falling deaths from stroke, especially hemorrhagic stroke.
Until today, much of the medical community has not accepted evidence of the individual or public health importance of salt consumption in blood pressure regulation and risk of developing hypertension, throughout the usual range of intake in industrial countries. The finding at the extremes of intake, as in Japan versus primitive Ecuadorian groups with their contrast in hypertension, have not proved persuasive. Thus, Intersalt and Intermap, major cross-sectional contrasts across the range of electrolyte intake, remain important epidemiological contributions to the continuing debate. (Henry Blackburn)
Intersalt Cooperative Research Group. 1988. Intersalt: an international study of electrolyte excretion and blood pressure. Results for 24 hour urinary sodium and potassium excretion. Br Med J 297: 319-28.
Stamler, J., Kesteloot, H., Ueshima, H., and Zhou, BF. 2003 INTERMAP: background, aims, design, methods, and descriptive statistics (nondietary) for the INTERMAP Research Group, Journal of Human Hypertension 17: 591-608.