1. Sympathetic vasoconstrictor responses to inspiratory gasp and contralateral arm cold challenge were assessed in fingertip skin in relation to age and were correlated with vasoconstrictor ability during body cooling. The above relationship was also examined in diabetic patients in whom vasoconstrictor responses to inspiratory gasp and contralateral arm cold challenge had been shown previously to be markedly impaired.
2. Vasoconstrictor responses to inspiratory gasp and contralateral arm cold challenge, measured by laser Doppler flowmetry, were significantly reduced in the elderly group, although individual responses varied from normal to absent, and they also had a considerably greater variability as measured on three separate occasions than seen in young subjects. Discriminant analysis showed that, from each of three occasions, 65% of vasoconstrictor responses were abnormal in the elderly group.
3. Body cooling was performed by reducing the environmental temperature from 40°C to 12°C, and the time taken for blood flow to fall to 75%, 50% and 25% of the pre-cooling level (VC75, VC50, VC25, respectively) was calculated. Vasoconstriction was rapid in young subjects and was consistent with good vasoconstrictor responses to inspiratory gasp and contralateral arm cold challenge. In the elderly group, vasoconstriction was slower, but only the VC25 value differed significantly [elderly group, 13.3(7.9–31.0) min, young group, 5.7(2.7–15.5) min; median (interquartile range); P < 0.05]. A poor vasoconstrictor response to contralateral arm cold challenge did not always correlate with an impaired response to body cooling in the elderly group, but, importantly, a diminished vasoconstrictor response to body cooling, with no spontaneous sympathetic vasoconstrictor bursts, was associated with an impaired vasoconstrictor response to contralateral arm cold challenge. Diabetic patients all had markedly reduced vasoconstrictor responses to inspiratory gasp, contralateral arm cold challenge and body cooling.
4. It is concluded that elderly subjects have diminished sympathetic vasoconstrictor responses. This may be a significant factor contributing to thermoregulatory impairment in the elderly, thereby rendering them more susceptible to the harmful effects of cold weather.