Early Versus Late Morning Measurement of Blood Pressure in Healthy Men. A Potential Source of Measurement Bias?

Standardization of blood pressure (BP) measurement is important for both clinical and epidemiological purposes. The aim of the present study was to investigate early vs late morning measurements of BP and heart rate in healthy subjects. During the years 1972-75, healthy men aged 40-59 years (n = 2014) participated in a cardiovascular survey in Oslo. Two to four men underwent the examination program per day; it included height/weight, a spirographic study, chest X-ray, a number of blood tests, case history, clinical examination, resting ECG and physical exercise testing. BP and heart rate measurements were meticulously standardized. When adjusting for age, smoking habits and season of year we found that men who were examined as number one in the row of two to four subjects each morning had higher systolic BP (3.6 mmHg, p < 0.001) and heart rate (3.6 beats/min, p < 0.001) at rest compared to others. They were virtually identical in all other aspects. These differences in systolic BP and heart rate at rest disappeared during bicycle exercise. Thus, we suggest that the increased BP and heart rate at rest represent a stress reaction to being number one in a row of subjects to be examined, i.e. a bias in BP and heart rate measurements, possibly of both clinical and epidemiological importance.