Blood pressure is the measurement of the force exerted by circulating blood against artery walls, and its definition of “normal” has shifted significantly over time. Historical medical standards changed in response to new research and technology, making the “normal” reading in the 1920s very different from today’s ideal numbers. This history reveals a medical philosophy that was far more tolerant of elevated blood pressure than current guidelines allow, providing context for today’s much stricter standards of cardiovascular health.
The Prevailing Definition of “Normal” Blood Pressure in the 1920s
The medical community in the 1920s used a definition of normal blood pressure that was far more permissive, especially for older patients. A common rule of thumb for acceptable systolic pressure was “100 plus the patient’s age.” This meant a 60-year-old could have a systolic reading of 160 millimeters of mercury (mm Hg) and still be considered acceptable. This guideline reflected a broader medical philosophy that high blood pressure was a natural consequence of aging.
Physicians frequently viewed an elevated reading not as a disease requiring aggressive treatment, but as a necessary compensatory mechanism. They believed higher pressure might be needed to adequately perfuse aging organs, such as the brain and kidneys, through stiffened arteries. Some authorities suggested the greatest danger was the discovery of high blood pressure, fearing a physician might “try and reduce it.” This passive approach meant a systolic reading up to 160 mm Hg was often considered “benign” or not a cause for alarm if the patient showed no severe symptoms.
Life insurance companies, however, did not share this relaxed view and were much more rigorous in their risk assessments. Actuarial data showed a clear link between elevated blood pressure and increased mortality, even at levels the medical community deemed acceptable. Insurance was often denied if a person’s systolic pressure exceeded the age-specific average by only 12 mm Hg. These statistical findings, though known, did not immediately translate into widespread aggressive treatment by most physicians.
Measuring Blood Pressure a Century Ago
The ability to obtain a quantitative measurement of blood pressure became routine in the 1920s, relying on technology developed shortly before the turn of the century. The primary instrument was the mercury sphygmomanometer, a device consisting of an inflatable cuff, a pump bulb, and a column of mercury to indicate pressure. This device was considered revolutionary because it allowed for non-invasive measurement, a significant advance from earlier methods.
The technique used was the auscultatory method, standardized by Russian surgeon Nikolai Korotkoff in 1905. A physician would inflate the cuff to stop blood flow and then slowly release the pressure while listening over the brachial artery with a stethoscope. The first distinct tapping sound, known as the Korotkoff sound, marked the systolic pressure. The point where the sound disappeared or became muffled indicated the diastolic pressure.
Despite the standardized technique, the accuracy of readings in the 1920s was often inconsistent. Measurements depended highly on the skill and hearing of the practitioner and the calibration of the mercury column. The concept of “white coat hypertension”—elevated readings due to anxiety—was recognized, though not formally named. Furthermore, non-standardized cuff sizes and a lack of rigorous training meant the numbers recorded were not always precise or reproducible.
The Shift in Medical Understanding Since the 1920s
The permissive standards of the 1920s were gradually discredited by large-scale epidemiological research beginning in the mid-20th century. A pivotal moment came with the launch of the Framingham Heart Study in 1948, which aimed to identify factors contributing to cardiovascular disease. This long-term study demonstrated that even moderately elevated blood pressure, far below the historical “100 plus age” threshold, dramatically increased the risk of heart attacks and strokes.
The Framingham findings, published over subsequent decades, established that the risk from high blood pressure was a continuous, graded phenomenon. This meant there was no safe cutoff point where risk suddenly began. This evidence fundamentally contradicted the earlier medical belief that high blood pressure was a benign part of aging. The studies showed that aggressive intervention was necessary to prevent catastrophic cardiovascular events.
The ability to treat the condition also changed the definition of normal, as new pharmaceutical treatments became available starting in the 1950s. The combination of epidemiological data and effective medications led medical guidelines to progressively lower the target blood pressure over the following decades. Today’s standard of less than 120/80 mm Hg for most adults reflects this dramatic shift. This moved the standard from one that accepted high readings to one that actively seeks to prevent the long-term vascular damage caused by even slightly elevated pressure.