Postural effects on blood pressure reactivity: implications for studies of laboratory-field generalization

This study was designed as an in-laboratory evaluation of the significance of postural blood pressure (BP) adjustments in the investigation of laboratory-field generalization. Blood pressure responses were monitored while 20 subjects completed a mental arithmetic task in two postures, seated and standing. Baseline data were also collected in each posture. The standing challenge was regarded as a laboratory representation of real-world standing challenges. Reactivity scores for the seated stressor were calculated as seated task level minus seated baseline level. For the standing stressor, they were calculated in two ways; standing task level minus standing baseline, and standing task level minus seated baseline. It was hypothesized that the standing reactivity scores calculated from standing baselines (i.e. from the same-posture baselines) would be more highly correlated with seated reactivity than would the standing reactivity scores calculated using sitting baselines. This was not found to be the case for either SBP or DBP. Absolute task SBP levels were very similar in both postures, while they were significantly different for DBP, with standing task levels being higher. It was concluded that ignoring posture will not mask SBP reactivity associations between laboratory and field, but that it may do so for DBP, particularly in future studies as our overall understanding of laboratory-field generalization increases.