Casual and Basal Blood Pressures I. In British and Egyptian Men

Abstract

In the course of clinical investigations on healthy Egyptian men, we observed that during a period of rest in the sitting posture the systolic blood pressure often fell below 90 and usually below 100 mm. of mercury. This led to a study of the blood pressures of British subjects resident in Egypt and of others resident in London. The pressure found under the conditions described below is called basal* blood pressure because it was not found possible to reduce it appreciably below this level by rest or sleep. Our observations in a physiological type of low blood pressure may be of interest in relation to low blood pressure which is thought to be pathological. METHODMeasurements of the blood pressure were made by the auscultatory method, either with manometers in which the whole of the mercury column was visible, or with those of the Baumanometer type which had been checked by an ordinary mercury manometer. The diastolic pressure was taken at the moment when the arterial sound becomes muffled, usually 5 mm. higher than that at which the sound disappeared. The blood pressure was measured on the left arm with the subject sitting in a quiet, warm room. All subjects were instructed to find a comfortable posture, and then to remain still and with the mind blank throughout the half-hour or longer period during which the measurements were made. No conversation was allowed. The observer avoided unnecessary movement, and as a rule no third person entered the room during this time. To allay apprehension the subjects were informed that the investigation would be confined to the repeated measurement of blood pressure. Most subjects became somnolent but in general did not sleep.The blood pressure was measured as frequently as possible during the first three minutes after adopting the sitting posture. Blood pressure readings were then taken every few minutes throughout the half-hour period of rest, in order to habituate the subject to the procedure of blood pressure measurement. Without habituation of the subject by the continuous presence of the observer and by repeated measurements, the blood pressure falls are less than those we report. Towards the end of the half-hour period the measurements of the blood pressure were made at intervals of about one minute. RESULTSIn Fig. 1 are recorded systolic blood pressures and in Fig. 2

Masked Hypertension: A Review

“…They defined the casual pressure as the initial pressure taken without any rest, and the basal pressure was the minimum value obtained after a prolonged period of rest. Smirk's idea was that the basal pressure was the better predictor of cardiovascular risk (2). The difference between the casual and basal pressure was termed the supplemental pressure, and was roughly equivalent to what we now refer to as the white coat effect (WCE), as described below.…”

The Variation of Casual, Basal, and Supplemental Blood Pressures in Health and in Essential Hypertension

“…Except in the group of subjects in which an hypnotic drug was given the method of basal blood pressure determination which was used throughout this study was that outlined by Smirk (1945), namely a combination of the routine described by the combined committee on blood pressure measurement and that of Alam and Smirk (1943). The procedure was designed to measure the blood pressure when the subject was in the--basal metabolic state and was free from states of emotion or mental alertness.…”

“…It should be determined 10 to 12 hours after the last meal of the previous night and after resting for half an hour in a warmed room." Alam and Smirk (1938) indicated that they were using a basal blood pressure as a base-line in studies of blood pressure raising reflexes and later (1943) obtained results approximating to the basal blood pressure with a procedure which they termed emotional desensitization to the presence of the observer and to the process, of sphygmomanometry, with special attention to rest in a warm quiet room, but taking no special precautions as to the time of day or the time after the last meal. Alam and Smirk, from observations of blood pressure obtained by this method, suggested that readings obtained under ordinary clinical conditions should be called casual blood pressures, and those obtained under basal conditions, basal blood pressures; and that the difference between casual and basal blood pressure levels should be called the supplemental blood pressure.…”

Casual, Basal and Supplemental Blood Pressures in 519 First-Degree Relatives of Substantial Hypertensive Patients and in 350 Population Controls

“…This led to a study (Alam & Smirk, 1943;Smirk, 1944;Kilpatrick, 1948) of casual, basal and supplemental pressures. We introduced the term 'casual blood pressure' for the blood pressure as ordinarily measured.…”