This method is used for measuring a subject’s O2 consumption and CO2 production during a stay in the respiration chamber. The measurements can be used for:
- Derivation of energy expenditure from O2 consumption and CO2 production, which is called indirect calorimetry, through a choice of equations. The standard choice is the Brouwer equation with correction for not measuring metabolic Nitrogen production1, please note that also the Weir equation3 can be used. It is the researchers responsibility to choose the equation that best fits the study objective.
- Calculation of carbohydrate, fat, and protein oxidation by using oxygen consumption, carbondioxide production, and urinary nitrogen losses with the equations of Brouwer.1 To calculate nitrogen losses in urine, 24-hour urine must be collected during the stay in the respiration chamber.
The 2-step hyperinsulinemic-euglycemic clamp is the gold standard method for assessment of hepatic and peripheral (skeletal muscle) insulin sensitivity. Briefly, a cannula is inserted into a superficial dorsal hand vein for sampling of arterialized blood and in an antecubital vein of the contralateral forearm for insulin (40 mU/m2/min), glucose (20%), and glucose tracer (D2 glucose) infusion. During the first step (LOW INSULIN infusion), the insulin-mediated suppression of hepatic glucose production (hepatic insulin sensitivity) can be determined. During the second step (HIGH INSULIN infusion), the whole-body glucose disposal rate (peripheral insulin sensitivity) can be determined.
A small amount of blood is drawn from the dorsal hand vein every 5 min throughout the clamp to determine glucose concentration. The glucose infusion rate is adapted (variable 20% glucose infusion) to maintain euglycemia at 5.0 mmol/l. Based on the rate of appearance and rate of disappearance of the glucose tracer during the steady-state of each step (last 30 min of each step), hepatic and peripheral insulin sensitivity can be determined, respectively.