| Abstract: | The oxygen cost of exercise and chemical control of breathing were studied in a subject with Luft's syndrome, a disorder in which skeletal muscle mitochondria have a high "resting" O2 consumption which is imcreased only slightly by stimulation with excess phosphate acceptor, but a normal P/O ratio. The O2 consumption was more than three times normal (1.05 1/min) at rest but could be doubled when stimulated by maximal exercise. The O2 cost of exercise was similar to that of normal subjects. At rest, arterial blood PCO2 and ventilatory response to CO2 were normal, while ventilatory response to hypoxia was four times the predicted value. The data 1) confirm, in vivo, the normal respiratory efficiency of skeletal muscles in this disorder; 2) suggest that in vitro estimates of the extent to which mitochondrial respiration can be stimulated may not correlate with in vivo determinations; and 3) suggests that hypermetabolism per se can cause the ventilatory adjustments which are associated with exercise in normal subjects. |
