experiments, where various “stressful” tasks are evaluated (see for example,
Pickering and Gerin 1990 ; Linden et al. 2003 ; Kamarck et al. 2003 ; James 2013 ).
Specifically, in laboratory experiments, a baseline condition is established and then
the subject undertakes a series of defined“stressful”tasks. The difference between
the baseline measurements and those during the tasks determines the extent of
stress-related blood pressure reactivity (James 2013 ). Laboratory experiments have
numerous controls built into them, including standardizing the conditions and the
number of measurements at baseline and during each task. All participants expe-
rience the exact same protocol (James 2013 ). As has been noted, moving this
experimental paradigm to a“natural”setting (e.g., into real life and outside the
laboratory) requires modification because no true baseline can be established (e.g.,
James 2013 ). However, a“natural experiment” can be designed where blood
pressure changes can be evaluated as people move from microenvironment to
microenvironment (such as their work and home situations) during the course of
their everyday lives (James 1991 , 2007a, b, 2013). As described in many of my
previous studies of women who lived and worked in the greater New York City
urban area, those who commuted to their Manhattan workplace every day have a
structured, urban work environment where economic-related activities occur, where
social interactions take place with non-relative co-workers, and where a specific
occupational hierarchy dictates the nature of social relationships (James 1991 ,
2013 ; James et al. 1993 ; James and Bovbjerg 2001 ). This work environment
contrasts sharply with that of their home environment, where domestic tasks and
leisure activity happen in a social context where interactions are with relatives and
neighbors. The allostatic variation in blood pressure required to adapt to the
changes between these relatively predictable microenvironments are assessed by
comparison with the average blood pressure during overnight sleep, or more
specifically, while lying quietly in a dark room acting as a pseudo-baseline (see
Fig.8.3) (from James2007a).
Fig. 8.3 Comparison of laboratory reactivity experimental design with natural experimental
design for assessing circadian ambulatory blood pressure variation (modified from James2007a)
8 Continuous Blood Pressure Variation: Hidden Adaptability 151