Thermographic variables and rewarming classification

The mean of index-, middle- and ring fingertip temperatures (Tfi) was determined for the following five points in time: baseline temperature, the end of 10 min cooling, and after 5 min, 10 min and 19 min of cold recovery, similar to Brändström et al. (2008). Even though water immersion duration and water temperature differed between their and our study, we used their criteria to make a subdivision in normal, moderate or slow rewarmers, which corresponds to the subdivision in the study by Dupuis (1987). This classification is based on the percentage of the 19-min rewarming period while vasodilation of the fingertips was present (%VD), which was the case when fingertip temperature was at least 0.1 °C greater than finger base temperature (Anderson et al. 2007; Schuhfried et al. 2000). Rewarming categories include: normal rewarming, Tfi_,19 > 20 °C and %_VD > 50%; moderate rewarming, either Tfi_,19 > 20 °C and %_VD ≤ 50%, or Tfi_,19 < 20 °C and %_VD ≥ 5%; and slow rewarming, Tfi_,19 < 20 °C and %_VD < 5%. In addition to the classification of rewarming groups, rewarming amplitude (ΔT_REWARMING) is also measured. ΔT_REWARMING equals the temperature difference between the beginning (Tfi_,0) and the end (Tfi_,19) of the rewarming period. Since ΔT_REWARMING is measured over a period of 19 min in all subjects, it is an indicator of rewarming speed (°C/min). This procedure is followed for both ΔT_REWARMING after short immersion and ΔT_REWARMING after the CIVD response.