Cooling the whole body to 32-34 degrees Centigrade from the normal of around 37 degrees Centigrade for 24 hours has been shown to be an effective way of reducing damage to brain function after return of spontaneous circulation when someone has been resuscitated from cardiac arrest. Cardiac arrest is a form of heart attack where the heart stops pumping.

The device is a prototype cooling vest. The investigators anticipate that this will be useful in ambulances, helicopters and emergency departments where there is a need for a portable, safe, easy-to-use, inexpensive, external, effective, readily-controlled and single-patient use device able to reduce body temperature by at least 1 degree Centigrade an hour to initiate cooling. What the investigators are doing in these trials is to demonstrate that the investigators can cool people and to get the best design possible for patient use. That means some of the initial prototypes will not resemble what we expect the eventual device to look like. The investigators will be undertaking the initial trials on 30 normal volunteers.

Inclusion Criteria:

Human volunteers aged over 18. The upper age limit, as is standard for risk mitigation in such studies, is 35. The volunteer must have capacity to understand the trial and give informed consent to participate. If the volunteer's first language is not English we will make use of Sussex Interpreting Services, a professional interpreting service.

Exclusion Criteria:

Pregnancy. Any disclosed medical condition. Any medical condition detected on examination. Core temperature outside stated parameters.

We will ask the volunteer to confirm that they are otherwise healthy, taking no regular medication (except the oral contraceptive pill), are not using recreational drugs and have no significant past medical history, in particular cardiovascular disease of any sort, thyroid disease, diabetes mellitus or other metabolic disease.