Respiratory Impairment and Disability

A. H. Mehrparvar, M.D.

References

Anderson, Cocchiarella; Guides to the evaluation of permanent impairment, 5th edition, 2001.“Guidelines for the evaluation of impairment / disability in patients with asthma”, ATS criteria, 2003.W. N. Rom; Environmental and occupational medicine, 3rd. Edition, 1997.Abramson, Burden, Field; “Evaluation of impairment, disability, and handicapcaused by respiratory disease” Thoracic society of Australia and New Zealand, 1992.

Respiratory system consists of:

Tracheobronchial tree

Pulmonary parenchyma

Rib cage

Impairment and Disability

Impairment: a loss, loss of use, or derangement of any body part, organ system or organ function (a medical issue)

Disability: absence from work or loss of work attributed to a medical condition (a non-medical issue) (disability is a term used to indicate the total effect of impairment on the patient’s life)

Impairment percentage or rating

Estimates that reflect the severity of the medical condition and the degree to which the impairment decreases an individual’s ability to perform common daily activities, excluding work.

Important data for impairment evaluation

History (occupational and non- occupational)

Physical examination

Imaging

Lab data

PFT

Symptoms associated with respiratory diseases

Dyspnea: The most common, non-specific

Cough, Sputum, Hemoptysis

Wheezing

Thoracic cage abnormalities

Examinations

Respiratory rate

Use of accessory muscles

Respiratory sounds (crakle, Wheezing,…)

Respiratory pattern (e.g. pursed lips,…)

Chest wall abnormalities

And …

Imaging

Chest X ray (AP and lateral in full inspiration)

CT, HRCT

Other tests

Spirometry (the most beneficial test in evaluating functional changes)

DLCO

Cardiopulmonary exercise testing (VO2 max)

ABG

Cardiopulmonary exercise testing (Vo2 max)

Exercise capacity is measured by oxygen consumption per unit time (Vo2) in ml/(kg.min) or in metabolic equivalents (METS)

1 METS = 3.5 ml/(kg.min)An individual can sustain a work level equal

to 40% of Vo2 max for an 8-hour period.

Cardiopulmonary exercise testing (Vo2 max, Cont.)

Work intensity O2 consumption Excess energy expenditure

Light work 7ml/kg; 0.5 L/min <2 METS

Moderate work 8-15ml/kg; 0.6-1.0L/min 2-4 METS

Heave work 16-20 ml/kg; 1.1-1.5L/min 5-6 METS

Very heavy work 21-30ml/kg; 1.6-2.0L/min 7-8 METS

Arduous work >30ml/kg; >2.0 L/min >8 METS

Permanent impairment due to respiratory disorders

(whole person)

Class 1 (0% impairment)

Class 2 (10%– 25% impairment)

Class 3 (26%– 50% impairment)

Class 4 (51%-100% impairment)

Class 1

FVC and FEV1 and FEV1/FVC lower limit ≧of normal

And

DLCO lower limit of normal≧Or

VO2 max 25 ml/ kg.min (7.1 METS)≧

Class 2

FVC or FEV1 60% of predicted ≧and < lower limit of normal

or

DLCO 60% of predicted and < lower limit of ≧normal

or

20 V≦ O2 max < 25 ml/ kg.min (5.7-7.1 METS)

Class 3

51% FVC 59% of predicted ≦ ≦or

41% FEV≦ 1 59% of predicted ≦or

41% DL≦ CO 59% of predicted ≦or

15 V≦ O2 max 20 ml/ kg.min (4.3 < METS < 5.7)≦

Class 4

FVC 50% of predicted ≦or

FEV1 40% of predicted ≦or

DLCO 40% of predicted ≦or

VO2 max< 15 ml/ kg.min (< 4.3 METS)

Asthma

Diagnosis of asthma requires:

1. Relevant symptoms and signs (cough, sputum, wheeze,…)

2. Evidence of airflow obstruction (partially or completely reversible)

or airway reactivity to methacholine

Evaluation of impairment in asthma

1. Spirometry (before and after bronchodilator)

2. Challenge test

Measurement of spirometry

Spirometric measurements should be made after withholding inhaled bronchodilators for 8 hours and long-acting bronchodilators for 24 hours.

Antiinflammatory drugs such as cromolyn, inhaled or systemic corticosteroids should not be withheld.

Measurement of spirometry (Cont.)

FEV1, FVC and FEV1/FVC is measured

If: FEV1/FVC < lower limit of normal

Then: repeat spirometry after administration of an inhaled bronchodilator

Improvement in FEV1 of 12%, with an absolute change of 200 ml from baseline indicates reversibility

Measurement of spirometry (Cont.)

If: improvement in FEV1 <12%

Then: Begin steroid therapy (>800 mcg beclomethasone /day)

Improvement in FEV1 of 20%, indicates reversibility

Airway hyperresponsiveness (bronchial challenge test)

Measurement of airway responsiveness is needed for diagnosis and impairment rating if subject has no current evidence of airflow limitation.

The test should be done after withholding inhaled short-acting bronchodilators for 6 hours and long-acting for 24 hours.

The provocation concentration to cause a fall in FEV1 of 20% (PC20).

Airway hyperresponsiveness (bronchial challenge test, Cont.)

If PC20 is 8 mg/ml methacholine or ≦histamine, hyperresponsiveness is considered.

Parameters for impairment evaluation in asthma

FEV1

% of FEV1 change (reversibility)

PC20 mg/ml

Minimum medications

Score 0

FEV1 lower limit of normal≧Reversibility <10%

PC20 > 8 mg/ml

No medication

Score 1

FEV1 70% of predicted≧10% < Reversibility < 19%

0.6 mg/ml < PC20 < 8 mg/ml

Occasional but not daily bronchodilator or cromolyn

Score 2

60% < FEV1< 69%

20% <Reversibility < 29%

0.125 mg/ml <PC20 < 0.6 mg/ml

Daily bronchodilator or cromolyn or daily low-dose inhaled corticosteroid

Score 3

50% < FEV1< 59%

20% Reversibility ≦PC20 0.125 mg/ml ≦Bronchodilator (PRN) or daily high-dose inhaled corticosteroid (800mcg beclomethasone) or occasional systemic corticosteroid

Score 4

FEV1 < 50% of predicted

Bronchodilator (PRN) or daily high-dose inhaled corticosteroid (>1000 mcg beclomethasone) or daily or every other day systemic corticosteroid

Impairment rating for asthma

Total asthma score

% Impairment Class

Imp. Of the whole person

0 1 0%

1-5 2 10-25%

6-9 3 26-50%

10-11 (or asthma uncontrollable despite maximal treatment)

4 51-100%

Types of impairment/disability in asthma

1. Temporary: after diagnosis of occupational asthma, the patient is 100% impaired for the job that has caused the symptoms and treatment is to remove the worker from exposure.

2. Permanent: assessment for permanent impairment should be done 2 years after the removal from exposure.

Sleep apnea

For grading sleep apnea:

1. Number of apnea / hypopnea episodes in polysomnography

2. Severity of hypoxia

There is no standard for impairment rating. , only judgment of a sleep specialist is important.