Expiratory muscle function in amyotrophic lateral sclerosis

Am J Respir Crit Care Med. 1998 Sep;158(3):734-41. doi: 10.1164/ajrccm.158.3.9710072.


Few data exist concerning expiratory muscle function in amyotrophic lateral sclerosis (ALS). We studied 26 patients with ALS (16 with respiratory symptoms and 10 without) and measured the maximal static expiratory mouth pressure (MEP), the gastric pressure during a maximal cough (Cough Pga), and the gastric pressure after magnetic stimulation of the lower thoracic nerve roots (Tw Pga). These measurements were related to the ability to generate transient supramaximal flow during a cough (cough spikes), to arterialized capillary blood gases, and to inspiratory muscle strength. Vocal cord motion was examined endoscopically in 11 of the 16 symptomatic patients. Expiratory muscle weakness was related to inability to generate cough spikes with a threshold effect such that spikes were absent for Cough Pga < 50 cm H2O (p = 0.009) or Tw Pga < 7 cm H2O (p = 0.006) and was usually associated with inspiratory muscle weakness. However, in multivariate analysis, PaCO2 was only significantly associated with the maximal sniff esophageal pressure (p = 0.02). Symptomatic patients had significantly lower inspiratory muscle strength, whereas, of the expiratory muscle tests, only Tw Pga was significantly lower (p = 0.0009) in symptomatic patients. Abnormal vocal cord motion was observed in two of the 11 patients examined. We conclude that abdominal muscle weakness in ALS, when substantial, results in an inability to generate transient supramaximal flow during a cough. However, the primary determinant of both ventilatory failure and respiratory symptoms seems to be inspiratory muscle weakness.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Amyotrophic Lateral Sclerosis / complications
  • Amyotrophic Lateral Sclerosis / physiopathology*
  • Capillaries / physiopathology
  • Carbon Dioxide / blood
  • Cough / physiopathology
  • Female
  • Humans
  • Inhalation / physiology
  • Laryngoscopy
  • Magnetics
  • Male
  • Maximal Expiratory Flow Rate / physiology
  • Middle Aged
  • Multivariate Analysis
  • Muscle Contraction / physiology
  • Muscle Weakness / complications
  • Muscle Weakness / physiopathology
  • Oxygen / blood
  • Pressure
  • Pulmonary Ventilation / physiology
  • Respiratory Insufficiency / etiology
  • Respiratory Muscles / physiopathology*
  • Spinal Nerve Roots / physiopathology
  • Stomach / physiopathology
  • Vocal Cords / physiopathology


  • Carbon Dioxide
  • Oxygen