The concept of a “normal” blood pressure reading is one of the most fundamental metrics in modern medicine, yet its definition has proven to be a moving target throughout history. The current standard of less than 120/80 mm Hg is the product of decades of research that fundamentally changed how physicians understand cardiovascular risk. To understand what was considered acceptable in the 1940s requires setting aside current knowledge and adopting a deeply contrasting medical philosophy. At that time, many doctors did not view mildly or even moderately elevated pressure as a disease requiring aggressive intervention.
The Clinical Definition of “Normal” in 1940
Physicians in the 1940s often operated under the informal, but widely accepted, standard known as the “100 plus age” rule for acceptable systolic pressure. This meant that a systolic reading of 140 mm Hg in a 40-year-old was generally not a cause for alarm, as the belief was that blood pressure naturally increased with age to help perfuse stiffening arteries. Consequently, the clinical threshold for high blood pressure was significantly higher than it is today.
Many medical texts of the era suggested that blood pressure was only considered genuinely “raised” when the systolic pressure reached 180 mm Hg or more, or the diastolic pressure was 110 mm Hg or higher. The common range that a physician might consider “mild benign hypertension” could be as high as <200/<100 mm Hg. This perspective meant that only the most severe elevations, often referred to as "malignant hypertension," were considered life-threatening conditions demanding treatment. Physicians paid particularly close attention to the diastolic pressure, the lower number, viewing it as the more significant indicator of continuous strain on the circulatory system. They often dismissed mild systolic elevation, the top number, as a benign consequence of aging. This acceptance of high readings meant that many patients were left untreated, even with pressures that would be classified as severe hypertension today.
Measurement Techniques and Diagnostic Tools of the Era
The technology used to derive these historical numbers was the mercury sphygmomanometer, a device that had been in use for several decades. This instrument, often a desk-standing unit, relied on a column of mercury to precisely measure the pressure exerted against the inflatable arm cuff. The reading, measured in millimeters of mercury (mm Hg), provided the systolic and diastolic values.
The actual measurement was determined through the auscultatory method, which involved the physician listening for Korotkoff sounds with a stethoscope placed over the brachial artery. The first sound heard as the cuff pressure was released indicated the systolic pressure, while the point at which the sounds disappeared or muffled marked the diastolic pressure.
This manual technique introduced significant variability into the readings. Accuracy was highly dependent on the skill and hearing of the individual physician or nurse administering the test. Factors like the speed of cuff deflation, stethoscope placement, and subjective interpretation of the sounds often led to inconsistent results. This contrasts sharply with the automated, digital devices commonly used today, which reduce observer bias.
The Shift from Age-Adjusted Norms to Risk-Based Thresholds
The complacent view of age-related pressure increases began to erode with the emergence of large-scale epidemiological studies after the 1940s. A pivotal moment came with the launch of the Framingham Heart Study in 1948, which began tracking thousands of residents over decades. This landmark research provided the first clear, long-term evidence challenging the prevailing medical wisdom.
The study demonstrated that cardiovascular risk was not a threshold phenomenon, but a continuous one. This meant that the risk of heart attack, stroke, and heart failure progressively increased across the entire range of blood pressure readings, directly contradicting the idea that a high-normal pressure was merely a harmless sign of getting older.
This new understanding revealed that the old definitions of “benign essential hypertension” were flawed. The medical community shifted its focus from treating only severe, life-threatening hypertension to preventing long-term cardiovascular damage, which moved the goalposts for “normal” dramatically lower and introduced the concept of risk-based thresholds.
Management and Treatment of Elevated Pressure in the 1940s
The management of elevated blood pressure in the 1940s was defined by the limited availability of effective and safe treatments. Non-pharmacological interventions were the first line of defense, most notably mandatory rest and significant dietary restrictions. Patients were often confined to a period of bed rest, sometimes for weeks, in an attempt to lower their pressure.
Strict dietary regimens, such as low-salt and low-protein diets, were frequently prescribed, including the famously restrictive Kempner rice-fruit diet. Early pharmacological options did exist, but they were largely ineffective and associated with severe side effects. Drugs like thiocyanates, which could be toxic, and Veratrum viride extracts, which often induced severe nausea and vomiting, offered poor therapeutic value.
For the most extreme and life-threatening cases of high blood pressure, radical surgical procedures were sometimes performed. The most notable of these was the extensive sympathectomy, a major operation that involved surgically cutting nerves in the sympathetic nervous system to reduce vascular tone and blood pressure. This procedure carried high morbidity and was only justified when all other limited options had failed.