Mauricio Orozco - Levi and Esther

www.expert-reviews.com © 2012 Expert Reviews Ltd ISSN 1747-6348 10.1586/ERS.11.81 Any impairment in striated muscle function can interfere with the performance of daily activities, particularly for a patient already living with a respiratory disorder. However, the interaction between the respiratory and musculoskeletal systems is not always considered in the clinical management of these patients. Striated muscles are contractile elements that provide organisms with physiological functions, such as movement and generation of both airand blood-flow. The latter two functions are essential for respiratory gas exchange. The generation of airflow requires the action of inspiratory muscles. When this muscle group contracts, the changes in intrathoracic pressure allow air to enter the lungs. When these muscles relax, the air exits from the respiratory system. If additional effort is required to exhale, the expiratory muscle group contracts, increasing the alveolar–atmosphere pressure gradient. Although the diaphragm is the main inspiratory muscle, specifically in young and healthy subjects when they are at rest, other muscles progressively participate in the effort as ventilatory demands increase. These include external intercostals, parasternal and, to a lesser degree, the scalenes, sternocleidomastoid, latissimus dorsi, serratus and pectoralis muscles. The main expiratory muscles are the internal intercostals and those constituting the abdominal wall. Skeletal muscles located in the limbs (and also called peripheral muscles), are involved in the movements of the body. Any impairment in their function can interfere with the performance of daily activities. Muscle function becomes impaired in many different respiratory disorders, such as chronic obstructive pulmonary disease (COPD), cystic fibrosis, bronchial asthma, obstructive sleep apnea syndrome (OSAS), kyphoscoliosis and lung cancer. Although changes in respiratory mechanics in these diseases primarily target respiratory muscles, limb muscles can also be affected. In addition, respiratory and limb muscle dysfunction can occur in patients with myopathies, neurological and neuromuscular junction disorders, chronic heart failure, sepsis and other critical illness. In the intensive care unit (ICU), the condition called ICU muscle weakness is not only a limb problem but can also hamper weaning from mechanical ventilation. This review aims to brief ly present basic concepts of skeletal muscle physiology and to describe in-depth the muscle function impairment occurring in some of the most prevalent respiratory conditions, defining the factors and mechanisms involved in the etiopathogenesis of muscle dysfunction in this setting. Joaquim Gea*, Carme Casadevall, Sergi Pascual, Mauricio Orozco-Levi and Esther Barreiro