REACTIVITY TO MULTIPLE STRESSORS - A COURSE IN SYNERGISM

This paper proposes a model for the study of ''synergism'' and ''additivity'' of physiological responses to multiple stressors and evaluates the model with the data of a previously published study. Five distinct types of effects on responses of multiple compared to single stressors are defined: inhibition, hierarchy, overlap, independence, and enhancement. Three stressors (mental arithmetic, cold pressor, and physical exercise) were administered to 54 mole subjects either alone, in all possible pairs, or all at once. Variables measured were heart rate, cardiac output, RZ-time, respiration rate, respiratory minute volume, oxygen uptake, and blood pressure. Using simple t-tests for repeated measurements, physiological variables were classified according to the effect type that governed their responses. Furthermore, an additive model was suggested which allows separate testing of the main effects of stressors and their interactions in order to quantify this classification. In terms of effect types, systolic blood pressure was affected by multiple stressors independently and diastolic blood pressure hierarchically. The other variables were affected differently, mostly hierarchically, overlapping, or independently. No variable corresponded to the effect type of inhibition, and only RZ-time and oxygen uptake in the triple stressor condition responded according to the enhancement type of effect. Theoretical explanations of the synergistic effects of multiple stressors are discussed.