Blood pressure reactivity: pitfalls in methodology.

Two very different assumptions about the principles of blood pressure reactivity lead to quite different notions about hypertensive/normotensive behaviour. Both are referred to as the Law of Initial Value (LIV). Subsequent confusion about blood pressure reactivity vs resting level partly explains a number of inconsistencies between studies describing hypertensive behaviour. Here the validity of each assumption was tested. Young hypertensives and normotensives who had first been placed into a condition of arousal or relaxation performed a mental arithmetic task. Group behaviour and idiosyncratic paradoxical response phenomena were investigated. Results showed that the state of the subject immediately prior to the mental arithmetic task was more important in determining the reaction to that task than blood pressure category was: in an aroused subject blood pressure fell. The implications for both clinicians and researchers interested in blood pressure behaviour, in particular where stimuli have failed to elicit responses, are discussed.