Hypertension Journal - MQ Special Issue

Abstract

The importance of the arterial blood pressure pulse has been recognized since ancient times, and from then to the present, the interaction of the observer and the patient has progressed in gradual steps. It evolved from the presence of a palpable arterial pulse, being accepted as a sign of life and health condition, to the registration of the features of the arterial pulse as the first ever graphical representation of any physiological parameter in medicine, culminating in the quantification of the tension in the arterial wall as a measurement of arterial “blood pressure.”[1] The current acceptance of high blood pressure (hypertension) as a major cardiovascular risk can claim to have part of its origins in the actuarial and data gathering endeavors of life insurance companies.[2] The ubiquitous use of the brachial cuff sphygmomanometer in the early 20th century enabled collection of numerical data on blood pressure over long periods. The accumulation of blood pressure measurements also enabled data to be collected across the whole human life span. This demonstrated that in the otherwise healthy population, that is, in the normal population with no symptoms of overt ill health, there was a wide range of blood pressure values. Systolic blood pressure varied much more than diastolic blood pressure but increased with age. Since blood pressure was thought to be related to (and drive) tissue and organ perfusion, the marked increase in blood pressure was thought to be essential for adequate blood flow, as is required for efficient organ function. Hence, the concept of “essential hypertension”[3] was used to describe this condition of elevated blood pressure as being due to the essential readjustment of the cardiovascular system to accommodate age-related changes that occur in the vasculature (such as reduced capillary density with sequelae of increased peripheral resistance, hence requiring a higher pressure for adequate tissue perfusion). However, calculations of risk of morbidity and mortality (perhaps related to the forecasting of life insurance premiums) showed that those with elevated diastolic pressure were at higher risk of clinical and multiorgan complications affecting their health. Hence, the accepted notion of how to qualitatively understand elevated blood pressure was that it was essential that mean blood pressure would increase with age (leading to essential hypertension, with no overt symptoms or identifiable cause), that systolic pressure was mainly related to the strength of cardiac contraction (and so related to stroke volume), and that hypertension-related health complications were mainly associated with high diastolic pressure,[4] presumably as diastolic pressure was thought to be more closely associated with total peripheral vascular resistance. However, with accumulation of information from many large epidemiological studies in the latter part of the 20th century, and in particular with longitudinal and generational data from the Framingham Heart Study,[5] it is now accepted that systolic pressure is the major blood pressure component that is related to cardiovascular risk of morbidity and mortality.[6] Systolic pressure shows a much more pronounced increase with age compared to diastolic pressure, and that, in fact, diastolic pressure actually tends to decrease in the latter two decades of life, with the majority of hypertension in the elderly being categorized as “isolated systolic hypertension.” This implies that it is the pulse pressure that shows the most pronounced increase with age, in particular after the sixth decade of life.[7] This marked increase in pulse pressure is not related to changes in stroke volume, which can also show a slight reduction with age, but rather to the known increase of arterial stiffness with age; and arterial stiffness itself has been shown to be an independent factor of cardiovascular risk.[8] While arterial blood pressure is perhaps the most widely measured physiological parameter in clinical medicine, with methods that have essentially not changed since the inception of the brachial sphygmomanometer in late 19th and early 20th century, it still presents formidable challenges in how to improve the understanding of the effects of high blood pressure on endorgan damage leading to health complications. It is some of these important challenges that are addressed in the series of comprehensive review articles and commentaries in this Special Issue of Hypertension Journal presented by investigators and G u e s t E d i t o r i a l