1. Some patients with the emphysematous type of tobacco-related chronic obstructive pulmonary disease are hypermetabolic. Since the likely mechanism is the increased work of breathing, other groups of patients with chronic obstructive pulmonary disease should be similar. We have now measured basal metabolic rate and diet-induced thermogenesis in six patients with chronic obstructive pulmonary disease with an arterial partial pressure of CO2 of <5kPa (emphysematous), nine patients with chronic obstructive pulmonary disease with an arterial partial pressure of CO2 of >6kPa (bronchitic), eight patients with chronic obstructive pulmonary disease due to chronic asthma and seven control subjects. Diet-induced thermogenesis was measured for 4h after a meal of 87% carbohydrate, 11% protein and 2% fat as energy, with a total energy content of 40% of basal metabolic rate.
2. There was no difference between measured and predicted basal metabolic rate in the control (5541 ± 272 versus 5881 ± 245 kJ/24h) or emphysematous (5552 ± 370 versus 6239 ± 197 kJ/24 h) groups, but measured basal metabolic rate was significantly higher than predicted in the bronchitic (6126 ± 387 versus 5405 ± 250 kJ/24 h) and asthmatic (6293 ± 197 versus 5701 + 245, mean ± SEM, P<0.01) groups. All the control subjects had measured basal metabolic rates within 10% of predicted, whereas two out of six emphysematous patients, four out of nine bronchitic patients and five out of eight asthmatic patients were hypermetabolic. The contributions of fat, carbohydrate and protein oxidation rates to the overall basal metabolic rate were similar between groups.
3. Diet-induced thermogenesis was similar between groups. The postprandial fuel mix oxidized was also similar between all four groups.
4. Thus, some patients with both types of smoking-related chronic obstructive pulmonary disease and other patients with chronic asthma were hypermetabolic. This could not be predicted from detailed lung function tests, arterial blood gases or anthropometric measurements, and suggests that the increased work of breathing may not be the only cause of the hypermetabolism and weight loss seen in these patients.