Whole-body active heating does not preserve finger temperature or manual dexterity during cold-water immersion

Background: Cold-water immersion impairs manual dexterity when finger temperature is below 15ºC. This exposes divers to increased risk of error. We hypothesized that whole-body active heating would maintain finger temperatures and dexterity during cold-water immersion. Methods: Twelve subjects (six males) (22±2 years old; BMI 23.9±2.5; body fat 16±6%) completed 60-minute head-out water immersion (HOWI) wearing a 7mm wetsuit and 3mm gloves in thermoneutral water (TN 25ºC) and cold water (CW 10ºC)while wearing a water-perfused suit (WP) with 37ºC water circulated over the torso, arms, and legs. Gross (Minnesota Manual Dexterity Test [MMDT]) and fine (modified Purdue Pegboard [PPT]) dexterity were assessed before, during and after immersion. Core body and skin temperatures were recorded every 10 minutes. Results: MMDT (TN -25±14%; CW -72±23%; WP -67±29%; p<0.05) and PPT (TN -16±9%; CW: -45±10%; WP: -38±13%; p<0.05) performance decreased during immersion. MMDT and PPT did not differ between CW and WP. Immediately following immersion gross dexterity was recovered in all conditions. Post-immersion fine dexterity was still impaired in CW (p<0.01), but not WP or TN. Core and skin temperatures decreased during immersion in CW and WP (p<0.05) but did not differ between CW and WP. Conclusions: Manual dexterity decreased during immersion. Dexterity was further impaired during cold-water immersion and was not maintained by water perfusion active heating. Warm water perfusion did not maintain finger temperature above 15ºC but hand temperature remained above these limits, suggesting a need to reassess thermal thresholds for working divers in cold-water conditions.