[Physiopathology of respiratory muscles in malnutrition].

Objectives: a) To present the pathophysiological concepts behind undernutrition-related effects on respiratory muscle composition and function; b) to review the existing literature on the possible role of undernutrition-related effects on respiratory muscles as pathogenetic factors of ventilatory failure.

Data Sources: Selected recent references and pertinent literature in the english language dealing with the effects of undernutrition on respiratory muscle composition and function in the experimental and clinical settings.

Data Extraction: Peer-reviewed clinical or basic research journals.

Data Synthesis: Derangements of respiratory muscle function (fatigue and weakness) play a role in the pathogenesis of respiratory failure, as they are able to determine respiratory muscle pump failure and ventilatory insufficiency. Undernutrition negatively influences respiratory muscle function both through a direct effect of loss of contractile elements, and also indirectly, by worsening or inducing muscle composition derangements. Respiratory muscles are not spared by the process of wasting associated to undernutrition, and both experimental and clinical data are consistent with a decrease in respiratory muscle mass due to fiber size reduction. As respiratory muscle weakness in course of undernutrition is more than proportional to muscle mass decrease, the presence of alterations in the remaining muscle cell is likely. Derangements in both respiratory and skeletal muscle composition with particular regard to high energy phosphate compound depletion (low cell ATP and phosphocreatine content) and to cationic depletion (low muscle magnesium and potassium content), have been reported in patients with respiratory failure due to acute ot chronic lung disease; undernourished patients had the more severe derangements of muscle composition.

Conclusions: Undernutrition is associated with important alterations in respiratory muscle structure and function. Undernutrition-related effects on respiratory muscles, by inducing respiratory muscle weakness through derangements in muscle energy production, transport and utilization, could represent important "metabolic" factors in the pathogenesis of ventilatory failure.