Does 7 Minutes Of Face Cooling Induce Splenic Contraction In Non-breath Hold Divers?

Cold-water facial submersion combined with apnea triggers the human dive reflex, marked by bradycardia, peripheral vasoconstriction, and splenic contraction. Splenic contraction also occurs in response to other sympathetic stimuli like apneas alone, hypoxic breathing, and exercise. The effect of prolonged face cooling (FC), in the absence of apnea, on splenic contraction is unknown. Thus, the goal of this project was to explore the effects of prolonged FC on splenic contraction in non-breath hold divers. PURPOSE: Test the hypothesis that 7 min of FC will cause spleen contraction, and that the contraction is greater than maximal apnea induced splenic contraction. METHODS: In a preliminary analysis of a cross-over design, spleen volume, hemoglobin concentration (Hb), and hematocrit (Hct) were measured pre- and post- FC (0.0 ± 0.1 °C) and Sham (S, 33.8 ± 0.2 °C) conditions in 3 healthy adults (BMI: 26.0 ± 3.8,1 women). Pliable bags filled with water were applied to the participant’s forehead, cheeks, and eyes for 7 min, with order randomized and 20 min rest in between conditions. Participants were instructed to breathe at 15 breaths per minute with a metronome. Spleen volume was measured via (ultrasound) and calculated using the Pilström equation. Blood samples were obtained via finger stick. Results from this study were compared to previous data collected on splenic contraction following 5 maximal dry apneas, separated by 2 min, to compare the magnitude of spleen contraction between sympathetic stressors (n = 12). RESULTS: Spleen volume (FC = 231 ± 72, S = 229 ± 72 ml, p = 0.62), [Hb] (FC = 14.9 ± 1.0, S = 14.9 ± 1.0 g/dL, p = 0.99), and Hct (FC = 44 ± 2, S = 43 ± 2%, p = 0.67) were not different at baseline. Spleen volume decreased with FC (230 ± 72 ml, p = 0.07) and did not change with S (232 ± 73 ml, p = 0.53). [Hb] did not change with FC (15.0 ± 1.2 g/dL, p = 0.90) and S (14.8 ± 1.1 g/dL, p = 0.98). Hct did not change with FC (43 ± 3%, p = 0.44) and S (44 ± 3%, p = 0.92). The relative change in spleen volume was not different from apnea induced spleen reductions (FC = 72 ± 34, Apnea = 48 ± 20 ml, p = 0.13). CONCLUSION: These preliminary findings support that spleen volume is decreased during FC, which is likely of a similar magnitude to apnea induced splenic contraction. Supported by: Office of Naval Research (N00014-20-1-2593 and N00014-21-1-2276)