Human Gradient-Layer Calorimeter: Development of an Accurate and Practical Instrument for Clinical Studies

Abstract

A whole body gradient-layer calorimeter was designed for thermophysiologic studies in hospitalized patients. The instrument was assembled in a room adjoining a metabolic ward. The patient lies recumbent on a stretcher which is wheeled into the calorimeter on tracks. Once inside, the patient's head extends through one wall into a clear plastic canopy. The canopy is partially open on one side and is the entry point for fresh air into this open-circuit system. Heat flux transducers in the calorimeter walls, a thermopile in the exit air stream, and a platemeter in conjunction with wet and dry bulb thermometers allow measurement of total, wet, and dry heat losses from the subject. All calorimeter output signals are routed to a microcomputer system which processes the data and provides real-time output of results. A mannequin heat source is used to calibrate the gradient layer. Testing with a variety of wet/dry heat sources indicate total, wet, and dry heat measurements are accurate to within 2-3%. A typical study of resting energy expenditure requires 1 hr, and protocols of up to 6 hr are well tolerated. The calorimeter has proven to be reliable, accurate, and easy to operate. These qualities, combined with good patient tolerance, make it ideal for metabolic studies. (Journal of Parenteral and Enteral Nutrition 8:317-320, 1984)