Reduction of magnetic resonance spectroscopy brain temperature by convective head cooling in healthy humans

This pilot study assessed the effect of forced convective head and neck cooling on brain temperature, measured by magnetic resonance spectroscopy (MRS), in five healthy adult humans (three males).

Following a 10-minute baseline, subjects received 30 minutes head cooling followed by 30 minutes head and neck cooling. The cooling device delivered air at 11°C and 15 m/s through a hood and separate neck collar made of a double layer of nylon sheeting, the inner layer pierced with holes. Subjects wore a windproof waistcoat taped round the base of their neck and were wrapped in blankets from the base of the neck down. Bilateral foot warming with chemical hot packs was used to encourage heat loss in the presence of normothermia.

MRS temperature data were collected at the level of the basal ganglia over the baseline and the last 10 minutes of each cooling intervention. MRS detects naturally occurring brain metabolites and interpretation of the relative frequencies of N-acetyl aspartate and water allows estimation of tissue temperature in 1 cm³ voxels. For assessment of regional cooling, voxels lying within the region formed by joining the tips of the lateral ventricles were defined as 'core', voxels within approximately one voxel of the brain surface were defined as 'outer', and all other voxels were defined as 'intermediate'. The oesophageal temperature was measured continuously with a fluoroptic thermometer.

The mean baseline-corrected MRS brain temperature over all voxels reduced by -0.45°C (SD 0.23°C, P = 0.01, 5% CI -0.74 to -0.17°C) with head cooling and -0.37°C (SD 0.30°C, P = 0.049, 95% CI -0.74 to 0.00°C) with head and neck cooling. Head cooling reduced the mean baseline-corrected MRS brain temperature in core voxels in all subjects. The formal test for gradient was not significant (P = 0.43; 95% CI -0.15 to 0.29°C). Head and neck cooling reduced the temperature in core voxels in three subjects; the test for gradient was not significant (P = 0.07; 95% CI -0.03 to 0.58°C). The mean baseline-corrected oesophageal temperature reductions for the last 10 minutes of each intervention were -0.16°C (SD 0.04°C) with head cooling and -0.36°C (SD 0.12°C) with head and neck cooling.

Forced convective head cooling reduced the MRS brain temperature at an equivalent of 1.35°C per hour in healthy subjects, and the reduction was apparent across the brain.