Performance of Continuous Glucose Monitoring Systems at Altitude

10 healthy volunteers will undergo the controlled lowering of their blood glucose level at sea level and a simulated altitude of 8,000 feet, to test the hypothesis that continuous glucose monitoring system measurement of blood glucose is as accurate at altitude as at sea level.

To assess reliability of continuous glucose monitoring system at sea level whilst subject undergo's a hyperinsulinaemic glucose clamp study.

To assess reliability of continuous glucose monitoring system at a simulated altitude of 8,000 feet whilst the participant undergo's a hyperinsulinaemic glucose clamp study.

Study participants will have their blood glucose stabilized between 5 - 6 mmol/L by the delivering of a controlled rate insulin/glucose infusion. Participants will have their blood glucose level reduced by conducting a controlled two step hyperinsulinaemic glucose clamp. The clamp procedure will take a total of 120 minutes and will reduce the blood glucose level to below 3 mmol/L. During this time blood tests will be obtained for analysis, physical observations recorded and cognitive function tests performed at regular intervals. Participants will have been fitted at least 12 hours prior to the intervention with 2 real time continuous glucose monitoring systems which will remain in place for the duration of the clamp procedure, however participants will be blinded to their glucose readings.

To evaluate the accuracy of CGMS for glucose measurement at altitude (8,000 ft) in healthy volunteers.

To examine the effect of high altitude (8,000 ft) on the recognition of hypoglycaemia in healthy volunteers.

Inclusion Criteria: Age 18 - 60 years. No known medical conditions or concomitant medication. Exclusion Criteria: Pregnancy. Marine diving in preceding 24 hours. Unable to provide written informed consent.