Casual and Basal Blood Pressures Iv. Their Relationship to the Supplemental Pressure with a Note on Statistical Implications.

In an article entitled Casual and Basal Blood Pressures in Essential Hypertension (Alam and Smirk, 1943, b), two statements were made in the discussion upon which it is desired to offer further evidence. 1. " It seems desirable to regard the casual blood pressure as made up of two parts, namely, the relatively stable basal blood pressure and a variable supplemental pressure. The supplemental pressure is the part of the casual blood pressure that is elevated as the result of the patient's physical, mental, and emotional activity, chiefly the latter; the elevation of the basal blood pressure in essential hypertension requires some other explanation." This statement that the supplemental pressure varies and the basal pressure is relatively constant refers, as is indicated in the last sentence, to the individual and not to comparisons between different individuals. Measurements of the basal pressure, whatever technique be adopted to obtain it, aim at removing these known causes of variation and at measuring a pressure that has been obtained under standard conditions of mental and physical rest. There is a high probability, therefore, that basal readings obtained under standard conditions will be more constant for the individual than casual readings taken under a variety of conditions. This has now been shown, experimentally, by Kilpatrick. 2. " The lability of the blood pressure in a case of essential hypertension may be judged by the degree of difference between the casual and basal pressures." In Fig. 4 of the paper referred to above the relationship of this difference, which we call the supplemental pressure, to the casual and basal pressures is set out graphically. It was suggested by the authors that the patients with the higher supplemental pressures are in general those with higher casual blood pressures, but their basal pressures are no higher than those of essential hypertension patients with lower supplemental pressures. The object of the present paper is to describe some further observations that confirm the views previously expressed as to the relationship of the basal and supplemental pressures in essential hypertension, to study this relationship in health, to rediscuss the conditions under which the basal blood pressure should be measured, and to make reference to the significance which this conception has in relation to the statistical analysis of the ordinary casual (clinical) readings of the blood pressure. The opportunity is taken of referring to a comment by the editor of the British Heart Journal upon a statement in a previous paper (Alam and Smirk, 1943, b), which was to the effect that our results shown in Fig. 4 did not seem to support one of our conclusions. The basal and supplemental pressures have a practical importance which should make their separate determinations a matter of clinical routine in certain classes of patient.