0126 Metabolism And Energy Expenditure During Wake And Non-REM Sleep

Abstract

Energy expenditure is directly related to intensity of exercise, but has not been extensively evaluated during sleep. We undertook a pilot study to assess by indirect calorimetry the changes in energy expenditure during sleep. Nine patients undergoing polysomnograms were evaluated during an hour and a half of that study with application of the Cosmed K5 portable metabolic unit. The device performs a breath-by-breath analysis of inspired and expired O2 and CO2 to calculate the minute ventilation in liters/min (VE), minute oxygen consumption in ml/min (VO2), minute carbon dioxide production in ml/min (VCO2), from which are derived the metabolic equivalent (MET) and KCAL/min. After the polysomnogram was scored by AASM scoring criteria, stable five-minute intervals were selected of wake (eyes closed, alpha rhythm), N1, N2 and N3 for metabolic analysis. There were seven patients who did not demonstrate sleep apnea during the selected intervals, and they showed significant decreases from W to N1 in all 5 variables: VE 10.24/8.29/-1.95 (p < 0.01), VO2 347/312/-35 (p < 0.02), VCO2 259/212/-47 (p < 0.002), METS 1.19/1.00/-0.19 (p < 0.05), KCAL/min 1.62/1.45/-0.17 (p < 0.02). Two of those patients entered N2 and one entered N3, and they showed further decreases in all 5 variables from N1 to N2 and N1 to N3 respectively. Two of the nine patients had OSA throughout, one moderate and one severe, they showed increases in METS and KCAL/min from W (when there were no apneas) to N1 of 10–15% (patient with moderate OSA) and of 50% (patient with severe OSA) when apneas developed during sleep. Metabolic function can be recorded by indirect calorimetry in patients undergoing sleep studies. There is a significant decrease from W to N1, and a further decrease from N1 to N2 and N1 to N3 in these metabolic parameters. Patients with sleep apnea show an increase in metabolism. The study was performed during a 6-week loan of the device from the manufacturer.