Hyperbaric Oxygen Therapy and Insulin Resistance.

Visit 0 (Pre-clamp) and Visit 3 (Post-clamp) - Blood samples and subcutaneous adipose tissue biopsy: Subject will be seated comfortably in a chair for a 2-hour period. An IV cannula will be inserted into a vein in the forearm, and blood will be taken for analysis of fasting glucose and insulin time (t) = 0 min, and for cytokines at t = 0, 60 and 120 mins. The adipose tissue biopsy will then be performed. After cleansing the skin on the abdomen lateral to the umbilicus with chlorhexidine solution, and placing a fenestrated drape, anaesthesia will be administered (5ml of Xylocaine 2%, no adrenaline) via subcutaneous injection. A 0.75cm incision is made in the skin using a #11 scalpel, and a 5mm Bergstrom needle inserted to collect approximately 250mg of adipose tissue with suction. Two or three passes will be used to obtain approximately 500mg of adipose tissue. The sample is washed in sterile 0.9% saline and snap frozen in liquid nitrogen. Upon completion of the biopsy, pressure is applied and the incision closed with a sterile 'Steri-strip'. Visit 1 and Visit 2 - Hyperinsulinaemic euglycaemic clamp: Two intravenous cannulae are inserted into veins in contralateral forearms using local anaesthetic (lignocaine 1%). A baseline blood sample is taken to assess fasting glucose, and a primed insulin infusion is started for assessment of insulin sensitivity by hyperinsulinemic euglycemic clamp (80mU/m2/min) for 3.5 hours. Blood samples (<2mls) are obtained at 5-10 minute intervals so that blood glucose can be maintained at 5mmol/L with a variable infusion of 25% Dextrose, and a trained individual will be present for the duration of the clamping procedure. The steady state glucose infusion rate is calculated over the final 30 minutes of the clamp and adjusted for fat free mass by DXA. Immediately post-clamp, volunteers are given orange juice and high carbohydrate lunch, and the glucose infusion is maintained on a halving scale for 5 minutes each for at least 20 minutes. Blood sugar levels are monitored every 10-15 minutes for 45-60 minutes. Visit 2 and Visit 3 - Hyperbaric oxygen (HBO) therapy: Subject will be seated comfortably in a chair and wheeled into the chamber. The HBO session will involve compression to 2 atmospheres absolute, breathing 100% oxygen via a 'hood' gas delivery system for 90 minutes, and a linear decompression to 1 atmosphere absolute over 30 minutes. During visit 2, the 2-hour HBO treatment will occur during the second and third hours of the clamp. During visit 3, the HBO treatment will occur during the 2 hours immediately preceding the biopsy. Visit 4 - Blood samples: Subject will be seated comfortably, and a single blood sample will be taken for analysis of fasting glucose, insulin and cytokines. Visits 1 to 4 will occur on consecutive days, and visit 0 will occur 1 to 2 weeks beforehand.