Until the mid-20th century, clinicians' concern was directed mainly to the
systolic component of blood pressure.(1) Later, however, when systolic bloo
d pressure was found to be elevated with advancing age and decreased compli
ance of the arterial wall,(1,2) it began to be considered an inevitable con
sequence of aging.(1-3) Based on this belief, physicians often concluded th
at only the diastolic blood pressure elevation, which reflected peripheral
vascular resistance,(4,5) was harmful, while systolic hypertension was inno
cuous.(6) Therapeutic intervention was practiced mainly for diastolic hyper
tension, and research protocols were based on the levels of diastolic blood
pressure alone.(7-10) In the 1950s, even when life insurance companies' ac
tuarial data revealed that systolic and diastolic blood pressure elevations
were hazardous to health,(11) few clinicians took heed. In 1962, the World
Health Organization also defined hypertension as a blood pressure level of
165/95 mm Hg or higher for intervention purposes.(12) However, until the 1
991 Systolic Hypertension in the Elderly Program (SHEP) trial, many physici
ans were reluctant to pay credence to the need for therapy of elevated syst
olic blood pressure (vide infra).