HYPOPHOSPHATEMIA AND PHOSPHORUS DEPLETION IN RESPIRATORY AND PERIPHERAL MUSCLES OF PATIENTS WITH RESPIRATORY-FAILURE DUE TO COPD

In 22 patients (19 men, 3 women; mean [+/-SD] age, 63 +/- 6 years) wit h chronic obstructive pulmonary disease (COPD), phosphorus content was measured by spectrophotometric methods on muscle fragments of both pe ripheral (quadriceps femoris needle biopsy in 22 patients) and respira tory muscles (external intercostal muscle surgical biopsy in 14 patien ts). Thirty age- and sex-matched subjects were used as controls (19 fo r quadriceps femoris muscle biopsy and 11 for intercostal muscle biops y). Serum phosphorus levels, as well as the main determinants of overa ll phosphorus metabolism (dietary intake of phosphorus and renal phosp hate handling), were also obtained in all patients and control subject s. Muscle phosphorus content of both respiratory and peripheral muscle s was significantly reduced in the COPD patient group, no matter what reference index was used (fat-free dry muscle weight or muscle fragmen t DNA content); muscle phosphorus depletion was present in about 50 pe rcent of patients with COPD. In the same patient group, a significant relationship between muscle and serum phosphorus levels was demonstrab le in the case of peripheral muscles only. No relationship was found b etween phosphorus content of both types of skeletal muscles and dietar y phosphorus intake levels or with nutritional status, even though pat ients with COPD had significantly reduced anthropometric, biochemical, and immunologic indices as compared with controls. Renal phosphorus h andling indices of the COPD patient group were compatible with a condi tion of inadequacy of the renal compensatory mechanism to hypophosphat emia and phosphorus depletion (low percent tubular reabsorption of pho sphorus, low renal threshold concentration values). Our study suggests that phosphorus depletion occurs frequently in COPD, but in this clin ical condition serum phosphorus levels are not representative of cellu lar phosphorus levels. Phosphorus depletion, which is equally severe i n respiratory and peripheral muscles, could depend, at least in part, on malnutrition and a condition of renal phosphorus wasting possibly l inked to some drugs commonly used in patients with COPD (xanthine deri vatives, diuretics, etc).