Cold-induced vasodilatation in the foot is not homogenous or trainable over repeated cold exposure

Cold-induced vasodilatation (CIVD) is proposed to be a protective response to preserve tissue integrity in the extremities during cold exposure, but little research exists on either the trainability or the spatial pattern of CIVD response in the foot. We investigated the thermal response across the foot with repeated cold exposure. Ten healthy subjects immersed their left foot to the ankle in 8 degrees C water for 30 min 5 days/week for 3 weeks. Skin temperature was recorded on the medial side of the nail bed of the 5 toes and the dorsum of the foot. The presence of CIVD, defined as an increase of 1 degrees C at any time during cooling, was rare with our protocol. While a CIVD response was observed at least once in 8 of the 10 subjects, only 122 instances of CIVD were observed out of a total of 900 possible observations (10 subjects x 6 sites x 15 trials). Furthermore, thermal habituation was not evident, with toe temperatures at the end of each immersion (8-11 degrees C) remaining near water temperature throughout the 15 sessions. Even within the two subjects exhibiting the most incidence of CIVD, high variability existed in the occurrence, magnitude, and/or onset times. Synchronicity was often observed where more than one toe exhibited CIVD, though the magnitude varied greatly (range 1-9 degrees C). We conclude that, under realistic conditions of whole-foot immersion in cold water, CIVD is not a common or trainable response.