OXYGEN COST OF BREATHING IN PATIENTS WITH EMPHYSEMA OR CHRONIC-BRONCHITIS IN ACUTE RESPIRATORY-FAILURE

This study compared the oxygen cost of breathing (VoverdotO(2) resp) i n 19 patients with severe chronic obstructive pulmonary disease intuba ted for acute respiratory failure. Ten patients showed radiologic (X-r ay and/or computed tomographic scan) evidence of emphysema. The remain ing ones were considered as having chronic bronchitis. Measurements we re made just before extubation. Despite si mi lar expiratory airflow o bstruction, patients with emphysema exhibited significantly higher Vov erdotO(2) resp than patients with chronic bronchitis (109 +/- 61 versu s 42 +/- 26 ml/min/m(2), respectively; p < 0.006). Moreover, emphysema was associated with nutritional depletion assessed through decreases in body mass index (emphysema 17.9 +/- 3.5 kg/m(2); chronic bronchitis : 28.8 +/- 8.2 kg/m(2); p < 0.005). This seemed to affect somatic stor es (significant decreases in arm muscular circumference and triceps sk infold thickness, whereas visceral stores were preserved (no decreases in serum albumin, serum prealbumin, and retinol binding protein). Mal nutrition appeared to be the consequence of a hypermetabolic state of the respiratory muscles, with a significant negative correlation betwe en VoverdotO(2) resp and body mass index, arm muscular circumference, and triceps skinfold thickness (p < 0.05). Total oxygen consumption no rmalized for body surface was similar in the two groups. Thus, in emph ysematous patients, the oxygen available for tissues other than respir atory muscles was significantly reduced (emphysema: 124 +/- 51 ml/min/ m(2); chronic bronchitis: 207 +/- 78 ml/min/m(2); p < 0.02). This coul d explain nutritional differences observed between patients with emphy sema and those with chronic bronchitis.