Introduction:  Impairments caused by the chronic disorder of the respiratory system generally result
                  from irreversible loss of pulmonary functional capacity (ventilatory impairment, gas
                  exchange impairment, or a combination of both). The most common symptom attributable
                  to these disorders is dyspnea on exertion. Cough, wheezing, sputum production, hemoptysis,
                  and chest pain may also occur, but need not be present. However, since these symptoms
                  are common to many other diseases, evaluation of impairments of the respiratory system
                  requires a history, physical examination, and chest roentgenogram to establish the
                  diagnosis of a chronic respiratory disorder. Pulmonary function testing is required
                  to provide a basis for assessing the impairment, once the diagnosis is established
                  by appropriate clinical findings.
               
               
               Alteration of ventilatory function may be due primarily to chronic obstructive pulmonary
                  disease (emphysema, chronic bronchitis, chronic asthmatic bronchitis) or restrictive
                  disorders with primary loss of lung volume (pulmonary resection, thoracoplasty, chest
                  cage deformity as seen in kyphoscoliosis), or infiltrative interstitial disorders
                  (diffuse fibrosis). Impairment of gas exchange without significant airway obstruction
                  may be produced by interstitial disorders (diffuse fibrosis). Primary disease of pulmonary
                  circulation may produce pulmonary vascular hypertension and, eventually, heart failure.
                  Whatever the mechanism, any chronic progressive pulmonary disorder may result in cor
                  pulmonale or heart failure. Chronic infection caused, most frequently by mycobacterial
                  or mycotic organisms, may produce extensive lung destruction resulting in marked loss
                  of pulmonary functional capacity. Some disorders such as bronchiectasis and asthma
                  may be characterized by acute, intermittent illnesses of such frequency and intensity
                  that they produce a marked impairment apart from intercurrent functional loss, which
                  may be mild.
               
               
               Most chronic pulmonary disorders may be adequately evaluated on the basis of history,
                  physical examination, chest roentgenogram, and ventilatory function tests. Direct
                  assessment of gas exchange by exercise arterial blood gas determination or diffusing
                  capacity is required only in specific relatively rare circumstances, depending on
                  the clinical features and specific diagnosis.