TOTAL-ENERGY EXPENDITURE AND PHYSICAL-ACTIVITY MEASURED WITH THE BICARBONATE-UREA METHOD IN PATIENTS WITH HUMAN-IMMUNODEFICIENCY-VIRUS INFECTION

1. Our objectives were to measure total energy expenditure, the daily variation in total energy expenditure and the physical activity level in a group of HIV-positive subjects using the bicarbonate-urea method. The study also aimed to assess the practicalities of using the bicarb onate-urea technique in free-living conditions. 2. Total energy expend iture was measured with the bicarbonate-urea method over 2 consecutive days (1 day in one subject) in 10 male patients with HIV infection (m edian CD4 count=30). Resting energy expenditure was measured by indire ct calorimetry. Physical activity level (total energy expenditure/rest ing energy expenditure) was calculated from these measurements and fro m activity diaries. 3. Resting energy expenditure was found to be 7.46 +/-0.87 MJ/day, 5% higher than predicted values. Total energy expendit ure was 10.69+/-1.95 MJ/day with an intra-individual day-to-day variat ion of 6+/-6%. The measured physical activity level was 1.42+/-0.14, h igher than the diary estimate of 1.34+/-0.16 (P=0.029), and there were large intermethod differences in individual values. The subcutaneous infusion of bicarbonate was well tolerated and did not seem to restric t normal activities. 4. Total energy expenditure was not elevated in t he group of HIV-positive subjects when compared with reference values for normal subjects. The physical activity level of the patients in th is study was lower than that measured using other techniques in health y young men, but was compatible with that expected for people leading a sedentary lifestyle. Reductions in physical activity in patients wit h HIV are likely to contribute to the wasting process and physical act ivity level may thus be a clinically useful measure. This study has al so provided the first tracer estimate of the day-to-day variation in t otal energy expenditure. The bicarbonate-urea method represents an imp ortant new investigative tool for measuring total energy expenditure w hich has previously only been possible within the confines of a whole- body calorimeter or using the expensive doubly labelled water method.