Blood pressure measurement has been a standard practice in medicine for over a century, yet the numbers considered acceptable have changed dramatically over that time. This evolution reflects a deeper understanding of the relationship between blood pressure and long-term health outcomes. The medical standards of the 1920s provide a glimpse into a time when physicians operated with different assumptions about the human body and the aging process.
The 1920 Definition of Normal Blood Pressure
The prevailing medical consensus in the 1920s regarding a normal blood pressure often relied on formulas that incorporated the patient’s age. A common, though informally accepted, rule of thumb suggested that a person’s normal systolic pressure should be approximately 100 plus their age in years. Under this approach, a systolic reading of 160 millimeters of mercury (mm Hg) might have been viewed as acceptable for a 60-year-old patient. This perspective meant that higher blood pressure was generally seen as a natural, expected consequence of growing older, rather than a condition requiring intervention.
Despite this general medical acceptance, data from American life insurance companies in the early 20th century provided a more rigorous, financially motivated, definition of risk. These organizations performed large actuarial studies demonstrating that even modest elevations in blood pressure correlated with increased mortality. For individuals of working age, mean systolic pressures were found to be between 120 and 135 mm Hg. Insurance was often denied if a person’s systolic reading exceeded the average for their age group by more than 12 mm Hg. For instance, a systolic pressure exceeding 147 mm Hg was often grounds for denial for a 60- to 64-year-old.
Measuring Blood Pressure in the Early 20th Century
By the 1920s, blood pressure measurement relied on the manual sphygmomanometer. This device, often utilizing a column of mercury, involved an inflatable cuff placed around the upper arm. The cuff was inflated to temporarily stop blood flow in the brachial artery before being slowly deflated.
The key to reading both the systolic and diastolic pressures was using a stethoscope to listen for the specific Korotkoff sounds, first described by a Russian surgeon in 1905. The point at which the first tapping sound was heard corresponded to the systolic pressure. The disappearance of these sounds indicated the diastolic pressure. Standardization of measurement technique was less rigorous than it is today, meaning readings could vary based on factors like cuff size, arm position, and the practitioner’s skill.
The Paradigm Shift in Hypertension Understanding
The medical view of elevated blood pressure began a profound transformation later in the 20th century, moving away from the idea that it was an inevitable consequence of age. For decades, readings up to 200/100 mm Hg were sometimes categorized as “mild benign hypertension,” suggesting a less urgent need for treatment. This perception changed when large-scale epidemiological investigations and clinical trials provided undeniable evidence linking high blood pressure directly to severe cardiovascular events.
The Framingham Heart Study, which began in 1948, was fundamental in establishing that high blood pressure was a modifiable risk factor for conditions like coronary heart disease and stroke. Subsequent landmark trials, such as the Veterans Administration Cooperative Study in the late 1960s, confirmed that treating elevated blood pressure significantly reduced the incidence of stroke and heart failure. These studies demonstrated that rising blood pressure was not a harmless sign of aging but an active pathological process that could be treated to improve survival. This shift was the driving force behind the development of formal clinical practice guidelines, emphasizing the need for lower blood pressure targets to prevent disease.
Comparing Historical and Modern Blood Pressure Guidelines
The numerical differences between the 1920s perspective and contemporary guidelines illustrate the magnitude of this medical evolution. Today, a reading of less than 120/80 mm Hg is considered normal for most adults. A systolic pressure between 130 and 139 mm Hg, or a diastolic pressure between 80 and 89 mm Hg, is classified as Stage 1 hypertension, often prompting lifestyle changes and sometimes medication.
The modern threshold for Stage 1 hypertension is significantly lower than the values accepted as standard a century ago, such as the 160 mm Hg systolic reading for a 60-year-old suggested by the “age plus 100” rule. The current guidelines reflect a preventative approach, focusing on reducing long-term cardiovascular risk at much lower blood pressure levels. This means that a reading considered a minor variation in 1920 would now be an explicit target for intervention aimed at protecting the heart, brain, and kidneys.