The influence of permanent impairment of the respiratory system is difficult to assess both objectively and reliably. One rating guideline has been prepared by American Medical Association (AMA) (¹), in which various respiratory diseases are described, followed by objective examples for users.

An impairment rating guideline was prepared by the Ministry of Health and Welfare (MOHW) and is now being used in Korea (²). However, it is based only on the parameters of oxygen tension and forced expiratory volume in 1 second (FEV₁). To better evaluate the various kinds of respiratory diseases that cause permanent impairment, more parameters should be included, and a new impairment rating system needs to be developed (^3-5).

In the case of chronic obstructive pulmonary disease (COPD), FEV₁ and diffusion capacity are the most important factors in an impairment rating, while forced vital capacity (FVC) is the basis of the impairment assessment in restrictive pulmonary diseases. A typical symptom in respiratory diseases is dyspnea, however, to objectively demonstrate it is difficult in an impairment assessment. Additionally, the degree of dyspnea and FEV₁ shows no clear relationship (⁶).

As respiratory impairment is caused by various diseases and situations, objectively scoring the degree of impairment using only two indicators is difficult. Thus, this study was conducted to make new objective and quantitative ratings using multiple indicators to represent impairment in varied respiratory diseases.

We set out a respiratory impairment rating guideline for Koreans, that relevant specialists can easily use, by removing the effects of subjective judgments from impairment ratings.

The most important issue to consider at the time of determining the respiratory impairment is patient's activity, established by the degree of patient's dyspnea. However, "dyspnea" is difficult to adequately define, although many have tried (⁸), and it could be argued that none of them is accurate. Dyspnea is subjective, as experienced by patients. Accordingly, dyspnea itself cannot be used to determine the impairment grade. It may seem natural for dyspnea to be included in assessing respiratory impairment, but it plays no part in this guideline for such determination.

It may also be argued that chest pain should be excluded from the rating determination because the degree of chest pain cannot be objectified. However, if the area of chest pain corresponds to thoracic trauma, and radiological and objective evidence exists to take analgesics to ease the pain, then chest pain is appropriately objective. Furthermore, chest pain is not rated alone, but is included in the impairment rating.

The existing respiratory impairment guidelines consider only FEV₁ and PaO₂ values. Thus, they give priority to chronic obstructive pulmonary disease, which is a weakness, because the guidelines do not adequately deal with impairment caused by other major chronic respiratory conditions such as interstitial lung disease, thorax and pleural diseases, and surgical lung resection.

The existing guidelines could be improved by including physiological impairment in patients with interstitial lung disease and emphysema, and by adding the FVC test to rate restrictive pulmonary function impairment, and the DLCO test to rate the exercise-induced hypoxemia. In our guidelines, DLCO was included, whereas DLCO/VA was excluded from the lost part of the lung parenchyma by lung resection and lung parenchymal destruction. A PaCO₂ test was added to rate ventilatory defects and physiological impairment caused by pulmonary hypertension. With the additional tests, the new guidelines reflect pathophysiological traits of various major chronic respiratory diseases that can cause respiratory impairment.

As previously stated, FEV₁ is representative of the degree of impairment in the case of obstructive lung disease, however, it is not completely objective. However, FEV₁ is still used because it is probably the best test available. When applied to some patients (that is, a score below 27), the impairment degree should be upgraded by one grade (data not shown).

Regarding restrictive lung disease, it can be argued that the value of diffusing capacity of the lungs used to determine impairment should be adjusted higher or lower than the value proposed here. For the impairment rating guideline to be applied reliably in the clinic, the values stated here should be used.

The final impairment rating by our guideline is determined by the lowest (most severe) rating among the five rating items. This is because impairment should not be determined by only one factor of respiratory disease. For example, in patients with serious emphysema, they often complain of dyspnea, but the condition might not be considered as one of impairment by only DLCO. Furthermore, the arterial blood gas test or FEV₁ findings may not fit the rating guidelines for serious impairment, and DLCO might have been reduced. For patients with idiopathic pulmonary fibrosis, the arterial blood gas test or FEV₁ may suggest no impairment rating based on spirometry findings. However, in such cases, DLCO will likely be considerably reduced, so that it can be the prime determinant of the impairment rating. In patients with pulmonary hypertension and clearly increased PaCO₂, this test alone can be used to make the determination of impairment.

We propose that impairment determinations should be made by specialists in departments of respiratory and thoracic surgery. However, some patients with asthma whose disease does not respond to respiratory relaxants may be treated at a COPD clinic. Thus, specialists in allergy departments treating patients with asthma should perhaps also be included to the list of practitioners who make impairment determinations.

The rating guideline for the disabled which was prepared by the AMA includes impairment guidelines fitted to each disease by defining diseases and describing diagnosis methods for each (¹). Accordingly, the grade is determined for each disease, and for airway disease, it is determined by the findings of pulmonary function tests. Of course, it would be ideal to define every disease and to set up the diagnosing methods and guidelines for grading impairments, nevertheless, it is too early to do so for many diseases in an economically effective manner.

We thank Miss Na Young Koo, Yonsei University, for arranging the meetings.