Peripheral muscle composition and health status in patients with COPD

Summary

Study objective

The present study evaluated the relationship between health status (HS) and peripheral muscle histochemical characteristics in chronic obstructive pulmonary disease (COPD), and identified selected independent respiratory and extrapulmonary variables that predicted the HS of these patients.

Design

Cross-sectional study.

Setting

Outpatient respiratory clinic of a university hospital.

Patients and methods

We studied 29 patients (63±10 yrs) with a forced expiratory volume in 1 s (FEV₁) of 39±12%. All patients underwent vastus lateralis muscle biopsies for histochemical analysis. They also had spirometry, arterial blood gas analysis, body mass index (BMI), dyspnea determined with the MMRC scale and responded to the St. George's Respiratory Questionnaire (SGRQ) for HS assessment.

Results

SGRQ total score correlated with fiber type distribution. A stepwise multiple regression identified three independent predictors of SGRQ total score: type I fiber proportion, BMI, and FEV₁; $r=0.78$ and $r^2=0.61$.

Conclusions

These results indicate that impaired HS in COPD is related to the peripheral muscle changes characterized by less type I fibers proportion. The findings argue in favor of an important contribution of the systemic consequences on the HS in COPD independently from the airflow limitation severity, and help to explain the observation of the poor correlation between the degree of airflow limitation and SGRQ total score.