The Effect Of Face Cooling On Brown Adipose Tissue Activation

BACKGROUND: Brown adipose tissue (BAT) is a thermogenic tissue that contributes to non-shivering thermogenesis during whole-body cooling and is sympathetically innervated. Additionally, immersing a hand in ice water increases BAT activity in humans. In humans, cooling the forehead, eyes, and cheeks (i.e., face cooling (FC)) stimulates the trigeminal nerve, increasing cardiac parasympathetic activity and sympathetic activity. It is not known whether FC activates BAT. PURPOSE: Test the hypothesis that BAT activation during 7 min of FC would be greater vs. a sham trial. METHODS: Six healthy adults (age: 25 ± 5 y; 1 woman) completed two randomized conditions: FC and sham. FC consisted of the application of a pliable plastic bag filled with an ice slurry (0.0 ± 0.1 °C) applied to the participants' forehead, eyes, and cheeks for 7 min while subjects rested supine. The sham trial was identical, except water temperature was 33.8 ± 0.2 °C. Both conditions were preceded by a 5 min baseline and separated by 20 min. BAT activity was estimated via supraclavicular skin temperature (Tsc; infrared thermography) every 30 s and expressed relative to shoulder skin temperature (thermocouple). The area under the curve (AUC) and the peak responses for relative Tsc during FC/sham were calculated. Heart rate (HR; 3-lead ECG) and beat-to-beat blood pressure (photoplethysmography) were measured throughout the visit. Data are reported as mean ± SD. RESULTS: Absolute Tsc (FC: 35.2 ± 0.73 vs sham: 34.9 ± 0.64 °C; trial: p = 0.319), shoulder skin temperature (FC: 32.3 ± 0.04 vs sham: 32.5 ± 0.03 °C; trial: p = 0.395), and relative Tsc did not differ between trials (FC: 2.90 ± 1.36 vs sham: 2.63 ± 1.02 °C; trial: p = 0.387). The AUC (FC: 3.54 ± 4.26 vs sham: 2.50 ± 3.86 °C x min; p = 0.258) and the peak responses for Tsc (FC: 3.17 ± 1.31 vs sham: 2.92 ± 0.93 °C; p = 0.428) also did not differ between trials. Mean arterial pressure (103.1 ± 2.3 vs 85.4 ± 1.6 mmHg; trial: p = 0.037) was greater during FC vs sham. HR did not differ between trials (FC: 63 ± 1 vs sham: 59 ± 1 bpm; trial: p = 0.260). DISCUSSION: Our preliminary results indicate that 7 min of FC does not activate BAT in humans. A different cooling stimulus (i.e., cooler or warmer) or other skin cooling locations, rather than the trigeminal nerve, might be better suited to acutely induce BAT activation.