Increased systolic blood pressure after mild cold and rewarming: relation to cold-induced thermogenesis and age.

Aim: Higher winter mortality in elderly has been associated with augmented systolic blood pressure (SBP) response and with impaired defense of core temperature. Here we investigated whether the augmented SBP upon mild cold exposure remains after a rewarming period, and whether SBP changes are linked to thermoregulation. Therefore, we tested the following hypotheses: cold-induced increase in SBP a) remains augmented after rewarming in elderly compared to young adults b) is related to non-shivering thermogenesis upon mild cold c) is related to vasoconstriction upon mild cold. Methods: BP, energy expenditure (EE), skin and core temperature, skin perfusion (abdomen, forearm, both sides of hand) and % body fat were measured in 12 young adults (Y) and 12 elderly (E). Supine subjects were exposed to a thermoneutral baseline 0.5h (T(air) =30.1 degrees C), 1h mild cold (T(air) =20.7 degrees C), 1h rewarming (T(air) =34.8 degrees C) and 1h baseline (T(air) =30.5 degrees C). Results: Upon mild cold only the young adults showed significant non-shivering thermogenesis (NST) (Y:+2.5+/-0.6W/m(2) ,p<0.05). No significant age effects in vasoconstriction were observed. After rewarming %DeltaSBP remained significantly increased in both age groups and was augmented in elderly (Y:+5.0%+/-1.2%vs.E:+14.7%+/-3.1%,p<0.05). Regression analysis revealed that %DeltaSBP significantly related to DeltaEE upon mild cold (p<0.01,r(2) =0.35) and in elderly also to %body fat (p<0.02, r(2) =0.57). Conclusion: Individual changes in SBP after rewarming correlate negatively to non-shivering thermogenesis (NST). Elderly did not show NST, which explains the greater SBP increase in this group. In elderly a relatively large %body fat protected against the adverse effects of mild cold.