Luft's syndrome: O₂ cost of exercise and chemical control of breathing

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 increased 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 l/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 P(CO₂) and ventilatory response to CO₂ were normal, while ventilatory response to hypoxia was four times the predicted value. The data confirm, in vivo, the normal respiratory efficiency of skeletal muscles in this disorder; suggest that in vitro estimates of the extent to which mitochondrial respiration can be stimulated may not correlate with in vivo determinations; and suggest that hypermetabolism per se can cause the ventilatory adjustments which are associated with exercise in normal subjects.