Vasoconstriction and Age

Innovations in house construction that lead to reduced energy consumption
require accurate models for predicting human thermal comfort. Physiological
models predicting thermal comfort simulate body temperatures and incorporate
human thermoregulatory mechanisms, such as skin blood flow, shivering and
sweating. However, model structure is based on physiological theory, the
parameter values used, for instance in the skin blood flow module, lack a
physiological base. The formulation of skin perfusion incorporates
physiological stimulation by the central nervous system and vascular
sensitivity to its mediators. The module predicts that vascular sensitivity to
vasomotive mediators is dependent on temperature. To our knowledge this effect
has not yet been studied nor observed. Together little is known of the effects
of ageing on vascular sensitivity and comfort levels under equal body
temperature distributions. Therefore incorporation of age effects in models of
human thermoregulation and comfort levels may enlarge the scope of the models
applicability as well as the understanding of the physiological processes.
Individual responses to cold exposure are partly dependent on body composition.

Study of the effect of age on vasoconstrictive sensitivity to vasoconstrictor
tone, study of the effect of temperature on vasoconstrictive sensitivity to
vasoconstrictor tone, and a comparison of body temperature distribution during
thermal (dis)comfort between young and elderly.

Analyse two groups of 15 volunteers each (young and elderly) by means of local
iontophoresis of exogenous norepinephrine while controlling for endogenous
release of noradrenergic vesicles. Together local cutaneous perfusion is
measured through laser Doppler flowmetry. This proces is repeated for a range
of local temperatures. Thermal comfort is measured through a questionnaire

Iontophoresis:
Iontophoresis is a technique to enhance the transport of a drug across a tissue
barrier. It is based on the principle that a charged molecule migrates under
the influence of an applied electrical field toward electrodes of opposite
charge.

Pre-synaptic blockade of sympathetic noradrenergic nerve terminals:
Bretylium tosylate is a positively charged, anti-adrenergic agent that is taken
up by adrenergic neurons. Once within the nerve terminal the drug blocks the
release of noradrenergic vesicles without interfering with axon transmission.
It is delivered through iontophoresis

Exogenous application of norepinephrine:
Positively charged NE-ions are transported transdermally through iontophoresis.
The response on perfusion is measured.

Skin temperature
Whole body cutaneous temperature of subjects is controlled by a water perfused
suit. Skin temperatures will be held at two levels: 27C (cool) and 33C
(neutral).

All measurements are noninvasive and easy to perform. Possible reactions such
as itching, erythema and general irritation of the iontophoretic skin surface
are common. Which is considered a low risk.