Rapid and selective brain cooling method using vortex tube: A feasibility study

Selective Brain Cooling: A New Horizon of Neuroprotection

Therapeutic hypothermia (TH), which prevents irreversible neuronal necrosis and ischemic brain damage, has been proven effective for preventing ischemia-reperfusion injury in post-cardiac arrest syndrome and neonatal encephalopathy in both animal studies and clinical trials. However, lowering the whole-body temperature below 34°C can lead to severe systemic complications such as cardiac, hematologic, immunologic, and metabolic side effects. Although the brain accounts for only 2% of the total body weight, it consumes 20% of the body's total energy at rest and requires a continuous supply of glucose and oxygen to maintain function and structural integrity. As such, theoretically, temperature-controlled selective brain cooling (SBC) may be more beneficial for brain ischemia than systemic pan-ischemia. Various SBC methods have been introduced to selectively cool the brain while minimizing systemic TH-related complications. However, technical setbacks of conventional SBCs, such as insufficient cooling power and relatively expensive coolant and/or irritating effects on skin or mucosal interfaces, limit its application to various clinical settings. This review aimed to integrate current literature on SBC modalities with promising therapeutic potential. Further, future directions were discussed by exploring studies on interesting coping skills in response to environmental or stress-induced hyperthermia among wild animals, including mammals and birds.

A novel selective cooling system for the brain: feasibility study in rabbits vs piglets

Background

Selective brain cooling (SBC) methods could alleviate the complications associated with systemic hypothermia. The authors (MFB, LK, and T-YL) have developed a simple and an effective nasopharyngeal SBC method using a vortex tube. The primary focus of the study is to evaluate the effectiveness of this approach on rabbits and compare it with our previous published finding on piglets, which are mammals without and with a carotid rete, respectively.

Methods

Experiments were conducted on six rabbits. Body temperature was measured continuously using an esophageal temperature probe while brain temperature was measured with an implanted thermometer. Two successive experiments were performed on each animal. In the first experiment, brain cooling was initiated by blowing room temperature air from the hospital medical air outlet, at a flow rate of 14–15 L/min into both nostrils for 60 min. The second series of measurements and brain cooling was performed in the same manner as the first one but blowing cold air (− 7 °C) at the same flow rate.

Results

One hour post cooling with room temperature air at a flow rate of 14–15 L/min, the brain temperature was 34.2 ± 1.2 °C which resulted in mean brain cooling rates of 3.7 ± 0.9 °C/h. Brain temperature could be reduced more rapidly at mean rates of 5.2 ± 1.9 °C/h, while the body temperature as measured by the esophageal temperature probe was maintained above 36 °C during cooling and maintaining period.

Conclusions

We have demonstrated that using the vortex tube allows initial rapid and SBC in rabbits. Moreover, comparing results between piglets and rabbits demonstrates clearly that the lack of a carotid rete does not prevent specific cooling of the brain by means of the nasopharyngeal method.

A new approach to selective brain cooling by a Ranque-Hilsch vortex tube

Background

Target temperature management is the single most effective intervention and the gold standard in post-resuscitation care today. However, cooling the whole body below 33–34 °C can cause severe complications. Therefore, developing a selective brain cooling (SBC) approach which can be initiated early to induce rapid cooling and maintain the target temperature over 12–24 h before slowly rewarming brain temperature by itself alone would be advantageous. Vortex tubes are simple mechanical devices generating cold air from a stream of compressed air without applied chemical or energy. This study investigated whether blowing cooled air from a vortex tube into the nasal cavities is safe and effective to selectively reduce and maintain before slowly rewarming brain temperature back to normal temperature.

Methods

Experiments were conducted on ten juvenile pigs. Body temperature was measured using an esophageal and a rectal temperature probe while brain temperature with an intraparenchymal thermocouple probe. Cerebral blood flow (CBF) was measured with CT perfusion.

Results

Brain temperature dropped below 34 °C within 30–40 min while a brain-esophageal temperature difference greater than 3 °C was maintained over 6 h. There was no evidence of nasal or nasopharynx mucosal swelling, necrosis, or hemorrhage on MRI examination. CBF first decreased and then stabilized together with brain temperature before increasing to the baseline level during rewarming.

Conclusions

SBC was accomplished by blowing cold air from a vortex tube into the nasal cavities. Due to its portability, the method can be used continuously in resuscitated patients in both in- and out-of-hospital situations without interruption.