Pulmonary Function Assessment of Respiratory Muscle Strength


Pulmonary Function Assessment of Respiratory Muscle Strength, Findings of Impending Respiratory Failure, Negative Inspiratory Flow, Maximal Inspiratory Pressure, Maximal Inspiratory Force, Inspiratory Force, Respiratory Muscular Pressure

  • Definitions
  1. Negative Inspiratory Flow (NIF) or Maximal Inspiratory Pressure (MIP)
    1. Maximal inspiratory effort measured as the pressure generated against an occluded airway
    2. Maximal Inspiratory Pressure (MIP) and Negative Inspiratory Flow (NIF) represent the same measure
      1. MIP is typically reported as positive, while NIF is reported as negative
  • Indications
  1. Progressive Neuromuscular Disease (e.g. Guillain Barre Syndrome, Myasthenia Gravis)
  2. Ventilator Weaning
  • Interpretation
  • Findings of Impending Respiratory Failure
  1. Physical findings
    1. Tachypnea with decreased chest excursion
    2. Hypophonia
    3. Accessory Muscle use (e.g. intercostal retractions, abdominal Muscle use)
    4. Paradoxical breathing
  2. Quantitative Tests
    1. Single Breath Counting <10 to 15
    2. Vital Capacity <15-20 ml/kg
    3. Tidal Volume <5 ml/kg
    4. Maximum expiratory force <40 cm H2O (normal may be as high as 100 cm H2O)
    5. Negative Inspiratory Flow (NIF) less negative than -20 to -30 cm H2O (normal may be < -100 cm H2O)
      1. NIF less negative than-25 cmH2O may predict Ventilator Weaning failure