Climate, altitude, and blood pressure

Human Biology, Aug 1999 by Hanna, Joel M

Acclimation to the cold pressor response has been documented with repeated exposures over a period of several days (Glaser and Whittow 1957; LeBlanc 1975; Savourey et al. 1996). The major aspect of acclimation was a change in vascular reactivity. Blood flow to the exposed area was increased, temperature of the exposed area also increased, pain was reduced, and heart rate and blood pressure responses were lessened. The level of stress and the stress-induced response appeared to be reduced. Unlike total body acclimation, there is a decrease in plasma catecholamines, suggesting a habituation response (Savourey et al. 1996). With continued exposure of the extremities, acclimatized individuals often experience a temperature cycling as blood flow increases and decreases. This cold-induced vasodilation probably reflects a combination of autoregulation and central regulation to reduce distress and prevent injury (LeBlanc 1975).

Laboratory results are supported by examples of natural acclimatization. Several investigations have documented the cold pressor responses of men whose occupations require regular exposure of the extremities to cold air or cold water. Arctic fishermen (LeBlanc 1975) and British fish filleters (Nelms and Soper 1962), who frequently immerse their hands in ice water, provide examples. When given the cold pressor test, their hand temperatures remain relatively high and their systolic and diastolic blood pressures show only minor increases. Eskimos (LeBlanc 1975), Arctic Indians (Elsner et al. 1960), Andean Indians (Little et al. 1973), and Lapps (Krog et al. 1960) show similar reduced responses. The Ama do not differ from unacclimatized control subjects in blood pressure during cold pressor tests (Paik et al. 1972). The investigators attribute this to differences between whole body acclimatization and local acclimatization.

Sex and age are potentially important factors in response to intense local cold; however, recent research suggests that men and women respond to the cold pressor test in similar manners. Although men begin the test with higher pretest pressures, the magnitude of increase is similar for men and women (Lash et al. 1991; Kilgour and Carvalho 1994; Jones et al. 1996). There is some evidence that the duration of increased blood pressure may be longer in men (Kilgour and Carvalho 1994). The higher absolute blood pressures reached by men and their attenuated response time may account for their higher mortality during natural intense cold exposure (Gyllerup et al. 1991; Macey and Schneider 1993).

By virtue of their smaller size, children are at greater risk from local exposure than are adults. Adults experience a greater increase in blood pressure with a lesser increase in heart rate than children (Matthews and Stoney 1988). This is evident even in well-acclimatized children (Steegmann 1975). In adults the effect of age on blood pressure in the cold has been discussed by Collins (1987). Although the elderly are heterogeneous in response, agerelated changes in control of vasomotor tone seem clear. As noted, the elderly experience a substantially greater increase in systolic and diastolic blood pressures when exposed to more severe cold (Collins et al. 1985). Their responses were also more sluggish.