Mauricio Orozco-Levi

Relevance of assessing quadriceps endurance in patients with COPD

The aims of this study were to investigate whether the impairment in endurance of limb muscles is a general finding in chronic obstructive pulmonary disease (COPD) patients, affecting even those with mild-to-moderate disease or relatively normal physical activity. In addition, this study aimed to determine the physiopathology of exhaustion in local endurance tests and whether the reduction in quadriceps endurance can be predicted from muscle strength measurements. A total of 75 volunteers were assigned to one of two groups according to pulmonary function tests: COPD patients or healthy age-matched controls. Functional assessment included both quadriceps strength (maximum voluntary contraction (QMVC)), and quadriceps endurance (contractions against a load equivalent to 10% QMVC until task failure or for up to a limiting time of 30 min (QTlim)). COPD patients showed a decrease of ∼43% in QMVC and ∼77% in QTlim compared with controls. Task failure occurred only in COPD patients and was due to muscle fatigue, since limiting symptoms were associated with a decrease in the median frequency of quadriceps electromyographical signal and a reversible decrease in QMVC. The impairment in skeletal muscle endurance was present even in patients with mild-to-moderate airflow obstruction and individuals with relatively normal physical activity, and was irrespective of lung function variables, anthropometrical data or quadriceps strength. Peripheral muscle endurance was impaired in chronic obstructive pulmonary disease patients, even in those with relatively normal physical activity and mild-to-moderate airflow obstruction. This impairment associated with an early onset of muscle fatigue and could not be predicted from the severity of the disease or the reduction in quadriceps strength.

Upregulation of pro-inflammatory cytokines in the intercostal muscles of COPD patients

Muscle dysfunction is a characteristic feature of chronic obstructive pulmonary disease (COPD). Recent studies suggest that cytokines may operate as local regulators of both muscle function and regeneration. The aim of the present study was to characterise the expression of different cytokines in the external intercostal muscle of COPD. Muscle biopsies were obtained from 25 stable COPD patients and eight healthy controls. Local tumour necrosis factor (TNF)-α, interleukin (IL)-1β, -6 and -10 expressions (real-time PCR and ELISA), sarcolemmal damage (immunohistochemistry), and the transcript levels of CD18 were assessed. Muscle TNF-α and IL-6 transcripts were significantly higher in COPD patients compared with controls, and IL-1β and sarcolemmal damage showed a strong tendency in the same direction. Similar results were observed at protein level. The CD18 panleukocyte marker was similar in COPD and controls. Respiratory muscle function was impaired in COPD patients and it correlated to both the severity of lung function impairment and TNF-α muscle expression. Chronic obstructive pulmonary disease is associated with the upregulation of pro-inflammatory cytokines in the intercostal muscles. This phenomenon might be involved in respiratory muscle dysfunction.

Non-invasive Functional Evaluation of the Reserve in Fatigue and the Diaphragm Structure using Transthoracic Echography in B and M Modes

a b s t r a c t The diaphragm is the principal respiratory muscle. Its special characteristics have made it difficult to design instruments capable of performing a non-invasive evaluation of its structure and function in humans. The present study was designed to evaluate the potential use of ultrasound as a non-invasive method to fulfil these objectives. Methods: The study consisted of three phases: (1) ultrasound study in autopsy samples (n=10) of a segment of the thoracic-abdominal wall, from the bottom to the parietal peritoneum (i.e., thoracic wall, diaphragm, pleura and peritoneum structures), (2) static ultrasound study of the previous structures and the diaphragm in healthy subjects (n=10) to standardised lung volumes; and (3) dynamic ultrasound study of the contraction-relaxation of the diaphragm in the same subjects, calculating its maximum velocity of relaxation (MVrdi, mm/sec) during a specific inspiratory resistance test. Results: The ultrasound enabled the pleural and peritoneal limits of the diaphragm to be identified, and quantify its thickness (Tdi), both ex-vivo and in-vivo, in all cases. The dynamic study of the Tdi showed a linear increase directly associated with the lung volume measurement, as well as a cyclical increase during inspiratory movements at rest. In the resistance test, the MVrdi was maximal with low loads and gradually decreased until reaching a minimum nadir (∆≈ -70% of the initial value) in claudication (fatigue). The MVrdi has a high precision in diagnosing claudication. Conclusions: Transthoracic ultrasound of the diaphragm is a non-invasive method that gives promising results in the structural and functional evaluation (i.e. fatigue risk) of that muscle. These findings are of pathophysiological interest and could be of use in the clinical care context.

Evaluación funcional no-invasiva de la reserva ante la fatiga y la estructura del diafragma mediante ecografía transtorácica en modos B y M

UNLABELLED The diaphragm is the principal respiratory muscle. Its special characteristics have made it difficult to design instruments capable of performing a non-invasive evaluation of its structure and function in humans. The present study was designed to evaluate the potential use of echography as a non-invasive method to fulfil these objectives. METHODS The study consisted of three phases: (1) echographic study in autopsy samples (n=10) of a segment of the thoracic-abdominal wall, from the bottom to the parietal peritoneum (i.e., thoracic wall, diaphragm, pleura and peritoneum structures), (2) static echographic study of the previous structures and the diaphragm in healthy subjects (n=10) to standardised lung volumes; and (3) dynamic echographic study of the contraction-relaxation of the diaphragm in the same subjects, calculating its maximum velocity of relaxation (MVrdi, mm/sec) during a specific inspiratory resistance test. RESULTS The echography enabled the pleural and peritoneal limits of the diaphragm to be identified, and quantitate its thickness (Tdi), both ex-vivo and in-vivo, in all cases. The dynamic study of the Tdi showed a linear increase directly associated with the lung volume measurement, as well as a cyclical increase during inspiratory movements at rest. In the resistance test, the MVrdi was maximal with low loads and gradually decrease until reaching a minimum nadir (Δ≈-70% of the initial value) in claudication (fatigue). The MVrdi has a high precision in diagnosing claudication. CONCLUSIONS Transthoracic echography of the diaphragm is a non-invasive method that gives promising results in the structural and functional evaluation (i.e. fatigue risk) of that muscle. These findings are of pathophysiological interest and could be of use in the clinical care context.