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  • image The function of the lungs is to maintain the arterial partial pressure of oxygen (PaO2) and arterial partial pressure of carbon dioxide (PaCO2) within normal ranges (ie, normal ventilation-perfusion ratio).

  • image The air in the lung is divided into four compartments: tidal volume—air exhaled during non- exertional breathing; inspiratory reserve volume (IRV)—maximal air inhaled above tidal volume; expiratory reserve volume (ERV)—maximum air exhaled after tidal volume; and residual volume (RV)—air remaining in the lung after maximal exhalation. The sum of all four components is the total lung capacity (TLC). Pulmonary function tests will produce values consistent with normal lungs or an obstructive or restrictive disease: recognition of these values is key.

  • image Obstructive lung disease is defined as an inability to get air out of the lung. It is identified on spirometry when forced expiratory volume in the first second of expiration (FEV1) compared to the forced vital capacity (FVC) (total amount of air that can be exhaled during a forced exhalation) (FEV1/FVC) is less than 70% to 75% (0.70-0.75) in adults (or below the lower limit of normal (LLN) based on population studies).

  • image An increase in FEV1 of 12% (and greater than 0.2 L in adults) after an inhaled β-agonist suggests an acute bronchodilator response.

  • image Restrictive lung disease is defined as an inability to get enough air into the lung and is best defined as a reduction in TLC (usually less than 80% of predicted).

  • image Restrictive lung disease can be produced by a number of diseases, such as increased elastic recoil (interstitial lung disease), respiratory muscle weakness (myasthenia gravis), and mechanical restrictions (pleural effusion or kyphoscoliosis). It can also be the result of poor effort during the pulmonary function tests (PFTs).

  • image The shape of the flow-volume loop, which includes inspiratory and expiratory flow-volume curves, and the ratio of forced expiratory and inspiratory flow at 50% of VC (FEF50%/FIF50% greater than 1) may be useful in the diagnosis of upper airway obstruction.

  • image Cardiopulmonary exercise testing allows for the assessment of multiple organs involved in exercise.

  • image Spirometry and other pulmonary function tests in children are possible and can successfully be done with proper coaching methods and modified reference values.



Watch this brief video about when and how to perform spirometry: “Taking a Spirometry Test” from the National Heart Lung & Blood Institute: http://


The primary function of the respiratory system is to maintain normal arterial blood gases, that is, arterial partial pressure of oxygen (PaO2) and arterial partial pressure of carbon dioxide (PaCO2). To achieve this goal, several processes must be accomplished; including alveolar ventilation, pulmonary perfusion, ventilation-perfusion matching, and gas transfer across the alveolar-capillary membrane. Alveolar ventilation is achieved by the cyclic process of air movement in and out of ...

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