High Blood Pressure – disease or risk factor?

In the treatment or prevention of vascular disease the metabolic syndrome has recently attracted increasing interest. Our knowledge of the importance of this syndrome is, however, fairly superficial and it is only during the last decade that clinicians have realized its clinical importance. Slightly different factors have been suggested defining the syndrome. Hypertension, or elevated blood pressure, is, however, always present as one of the characteristics in different descriptions.

The arterial blood pressure, both what has been thought to be normal, and elevated blood pressure, has been the object of physiological and clinical studies for longer time than any other factor of the metabolic syndrome. More than sixty years ago, clinical studies were conducted on the treatment of hypertension, both malignant hypertension and what at that time was called benign hypertension. At that time the successful treatment was surgical, and some patients could be rescued through sympathectomy from the threatening complications, hypertensive encephalopathy, cerebral bleeding, heart failure or renal insufficiency 1.

Pharmacological treatment started, however, already before the middle of the twentieth century, the first approach being based on the same idea as surgical treatment. A new family of drugs, ganglionic blocking agents, were used to accomplish a medical sympathectomy. I am not going to dwell on the continuing extremely successful story of the pharmacologic treatment of hypertension as I only wanted to point out the wealth of information that exists about the arterial blood pressure in health and disease. The behaviour of the blood pressure and its regulation has been studied both by clinicians and physiologists for more than fifty years.

During the last decades, the clinical literature on hypertension has to a large extent been aimed at details of the treatment of high blood pressure rather than aspects as clinical picture, physiology or background. Two issues have mostly been in focus for the discussion, one being what figure for blood pressure should be thought of as normal, and the other, which type of drug should be the first choice in the treatment of a patient.

New or recent observations

Two observations have been done during the last decade regarding the importance of high blood pressure that so far has not received enough attention.

Is elevated blood pressure a disease?

The first observation is that the relation between blood pressure and subsequent vascular catastrophes – stroke, myocardial infarction or death – is the same within what has been thought to be normal pressure, as it is when the blood pressure is raised. This means that a systolic pressure of 140 mm Hg carries a higher risk than a pressure of 130 mm Hg, and a pressure of 130 mm Hg carries a higher risk than a pressure of 120 and so on 2.

This finding obviously confuses the issue of when to treat, as it does not seem possible to define a sharp cut-off point between what is normal, and what is a pressure necessitating treatment. MacMahon, Neil and Roberts have concluded from this observation that the aims of treatment ought to be changed. They do not find it reasonable that the treatment should depend on the presence or absence of hypertension (a disease?) 2. Instead treatment should be directed to lowering the blood pressure (a risk factor) regardless of its height – when the individual is deemed to be at a high risk of developing cardiovascular complications. With the many other factors of importance for developing vascular disease, the best way of using the blood pressure value would then be as a figure to enter into an equation, calculating the combined risk from all factors of importance, besides blood pressure, blood lipids, age, sex, smoking, diabetes, BMI.

Using the blood pressure this way, another question must be asked: Does elevation of the blood pressure really constitute a disease all by itself? Is hypertension really a disease entity?

Most individuals that today get a diagnosis of hypertension have only a slightly raised blood pressure and do not have any symptoms or signs of vascular engagement. Do they really have a disease sui genenris? When the blood pressure has been acting on the arterial wall during a longer period – years or decades – the resulting vascular changes are then as much a consequence of other factors –metabolic, immunologic or infectious mechanisms. The increased life span in the Western world gives the pure mechanical pressure effect longer time to influence the arterial wall.

If not a disease, what is it then? Isn't the blood pressure just a figure in a risk equation, or part of a syndrome, like the metabolic syndrome, rather than a disease entity? The patients we saw in the forties and fifties during the last century who had blood pressure of 260/160 mm Hg were symptomatic and presented with both vascular and organ changes. Some had the syndrome called malignant hypertension that was amenable to sympathectomy 1. However, this disease hardly exists today.

The blood pressure in the population is decreasing

The second observation is that the blood pressure decreases in the free-living population. The MIAMI trialist showed recently that the blood pressure in the populations they studied had decreased during the last years of observation 3. This decrease was spontaneous and was observed also in individuals who had never had any blood pressure lowering drug. They concluded that the spontaneous blood pressure decreased in these populations over time but could not explain why it behaved in this way 3.

This is, however, not a new observation. In the repeated Gothenburg population studies of 50 year old men, it has been shown that representative population samples of men, born 1913, when examined 1963, 50 years of age, had a higher blood pressure than a similar sample of men born 1943, examined when fifty years of age 1993. The difference between these two samples amounted to 10/9 mm Hg. These were thus free-living healthy men studied in exactly the same manner by the same team.

Furthermore, Harald Eliasch (pers. comm.) has followed the pilots in the Swedish Air Force during several decades. Each age group consisted of around 200 to 300 healthy men, recruited as pilots in the Air Force, who were followed with half-yearly cardiovascular investigations as a routine procedure. This made it possible to compare the blood pressure taken under standardized conditions – and also other features of interest – in healthy men at the same age at different time periods. As shown in Table I, between the 1970s and 1990s blood pressure was lower by approximately 10 mm Hg systolic and around 6 mm Hg diastolic in the 1990s compared to the 1970s.

Table I.  Blood pressure in pilots in the Swedish Air Force, investigated half-yearly.

			Blood pressure, mm Hg
Age group	Time period	Number	Systolic	Diastolic
24–26	1965–1974	290	29.2 + / − 11.5	78.1 + / − 6.5
	1975–1984	160	123.7 + / − 10.0	75.7 + / − 5.8
	1985–1994	260	116.4 +/ − 11.1	72.0 + / − 4.8
24–26
Decrease	1970–1990		12.8	6.1
39–41	1965–1974	233	128.8 + / − 11.7	81.1 + / − 6.7
	1975–1984	320	122.1 + / − 10.8	77.3 + / − 6.5
	1985–1994	252	118.6 + / − 11.3	74.6 + / − 6.5
39–41
Decrease	1970–1990		10.2	6.5
48–52	1965–1974	183	130.5 + / − 13.7	83.3 + / − 8.0
	1975–1984	187	125.6 + / − 13.3	80.2 + / − 7.8
	1985–1994	417	120.7 + / − 13.1	77.0 + / − 7.8
48–52
Decrease	1970–1990		9.8	6.3
After Eliasch

The decrease was similar in all age groups, though the blood pressure was slightly higher in the older men. It is of interest that serum cholesterol also was lower late in the century, while body weight and BMI was slightly higher (not showed). Also the MIAMI group found that the BMI increased while the blood pressure decreased.

Taken together, MIAMI, 50 year old men in Gothenburg, and the Swedish Air Force pilots demonstrate that the spontaneous blood pressure in different populations has decreased during the end of the last century. Why it is so is unclear? However, the changes in the way people are living are large when you compare the fifties with the present. Tunstall-Pedoe and associates suggest:

“Possibilities, apart from measurement errors, include cohort effects, dietary factors, and other lifestyle and environmental factors.”

It has been demonstrated that socioeconomic factors play an important role for health in Western societies 4. The arterial pressure is the result of the interplay of the peripheral vascular resistance and the cardiac output, both of which are influenced by the autonomic nervous system. This may act directly or through hormonal influences from the adrenals, the kidneys and the brain. It is conceivable that the socioeconomic situation, or the daily stresses of life, may exert some influence on the autonomic and hormonal regulation of the arterial blood pressure. This is, of course, pure speculation, but the idea is accessible to investigation in patients with blood pressure in different ranges.

The most important conclusion of these observations, is, however, that information from or medical knowledge gained in studies of populations or patients born before the first world war may not be applicable to people born after the second world war, with all the societal changes that have occurred during the latter part of the last century.

Another conclusion – mostly directed to those interested in clinical research – is that less attention should be directed to large multicenter studies of treatment of high blood pressure with different drugs. A much more challenging task would be to study why a common characteristic like the blood pressure has been changing over time in the western populations. This would probably necessitate detailed studies of the clinical and physiological features of blood pressure regulation. The combination of the many different physiological and metabolic factors in the metabolic syndrome ought to also be analyzed more in depth, rather than just constructing an equation to make the treatment of patients easier. Even though such an equation may seem to solve most problems for the general physician treating patients with high blood pressure, helping him to administer medicines without thinking, it also makes his patient contacts less personal and less rewarding for both patient and doctor.