It is widely accepted that cold exposure increases peripheral vascular resistance
and arterial blood pressure (BP) and, hence, increases cardiovascular risk primarily
in the elderly. However, there is a lack of concomitantly longitudinal recordings
at personal level of environmental temperature (PET) and cardiophysiological variables
together with skin temperatures (STs, the “interface-variable” between the body core
and ambient temperature). To investigate the intra-individual temporal relationships
between PET, STs and BP 60 healthy young women (52 completed the entire study) were
prospectively studied in a winter/summer design for 26 h under real life conditions.
The main hypothesis was tested whether distal ST (Tdist)mediates the effect of PET-changes
on mean arterial BP (MAP). Diurnal profiles of cardiophysiological variables (including
BP), STs and PET were ambulatory recorded. Daytime variations between 0930 and 2030
h were analyzed in detail by intra-individual longitudinal path analysis. Additionally,
time segments before, during and after outdoor exposure were separately analyzed.
In both seasons short-term variations in PET were positively associated with short-term
changes in Tdist (not proximal ST, Tprox) and negatively with those in MAP. However,
long-term seasonal differences in daytime mean levels were observed in STs but not
in BP leading to non-significant inter-individual correlation between STs and BP.
Additionally, higher individual body mass index (BMI) was significantly associated
with lower daytime mean levels of Tprox and higher MAP suggesting Tprox as potential
mediator variable for the association of BMI with MAP. In healthy young women the
thermoregulatory and BP-regulatory systems are closely linked with respect to short-term,
but not long-term changes in PET. One hypothetical explanation could serve recent
findings that thermogenesis in brown adipose tissue is activated in a cool environment,
which could be responsible for the counter-regulation of cold induced increase of
BP in winter leading to no seasonal differences in MAP. Our findings suggest that
the assessment of diurnal patterns of STs and PET, in addition to the conventional
ambulatory BP monitoring, might improve individual cardiovascular risk prediction.