Method Nosopharyngeal Tracheobronchial Pulmonary Pleural History
Questionnaire
Spirometry Exercise Chest X-ray
Some usefulness.
Moderately useful.
Highly useful.
The first approach is obviously the interview and the compilation of occupational and medical history. Further information on specified occupational diseases can be obtained using structured questionnaires. These two approaches are useful for identifying toxic effects in the nasopharyngeal compartment and, to a lesser extent, in the tracheobronchial compartment, as they elicit information on signs and symptoms.
As many of these symptoms are signs of an activated pulmonary defence system, standardised spirometry is useful for detecting disease in the tracheobronchial compartment. Measures such as FEV1 and FVC have been developed to indicate specific components of lung function, and have been used for many years by occupational physicians to measure lung function in workers. In addition, lung volume measurements can detect disease in the lung parenchyma and pleural space.
Damage to the pulmonary compartment can be assessed using gas exchange tests. The simplest test is to measure respiratory performance following exercise, using the step test, treadmill or bicycle ergonometer. Measures of pO2 and pCO2 can indicate changes in the cells in the gas exchange area. A combination of spirometry and gas exchange tests can
be very useful in defining damage to the respiratory system, especially as blood gases and pH are often normal at rest but become abnormal during exercise.
Finally, diseases of the pleural compartment and the lung parenchyma can be detected with chest X-rays. The X-ray is an indispensable aid in the evaluation of some diseases of the respiratory system, such as pneumoconiosis, but the limitations of the X-ray should be recognised: X-rays may be strikingly abnormal due to the presence of dusts, and there may be significant clinical impairment and extensive pathological changes in the presence of a normal X-ray. The chest X-ray should not be used to estimate the presence or extent of ventilatory impairment. However, workers exposed to respiratory hazards are often required to have an annual X-ray, and often serial X-rays are available to investigate the build up of respiratory disease.
Indeed, all these measures have developed to the stage that they are used as surveillance tools to detect disease from inhaled toxicants.
Summary
The very nature of the respiratory system places it at risk when it is exposed to airborne contaminants. In turn, a range of diseases of the lungs have been described based on properties of the inhaled material, the anatomy of the respiratory system itself, and the specialised defences it possesses.
Consideration of the tissue dose may help to identify the critical sites within the respiratory tract. The physical, chemical and biological properties of contaminants and their action within the lung helps identify the pathophysiological effects that might be anticipated. Knowledge of the pathophysiological consequences allows appropriate endpoints to be recognised and measured, and it can identify appropriate exposure monitoring, health surveillance and health surveillance protocols.
In conducting a risk assessment for a toxic inhaled material, the sequence of events that such materials progress can be used in the assessment:
■ How much is available in the air?
■ How much is inhaled?
■ What is the tissue dose?
■ What is the toxic effect?
■ What is the pathological effect?
■ What is the clinical outcome?
The range of effects of inhaled materials are fairly restricted to:
■ inflammatory reactions
Ultimately, impairment or damage to the respiratory system will impede the flow of air to the gas exchange system. The impairment of the flow of gases to the gas exchange regions can be classified into either obstructive or restrictive airway disease.
Restrictive diseases are typically characterised by a decrease in lung volumes (e.g.
vital and total lung capacities). Restrictive defects may occur when the elastic properties of the lung tissue are decreased and the lung becomes stiff (in fibrotic diseases such as silicosis, asbestosis and pneumonia).
Obstructive diseases are characterised by an obstruction to air flow. This increase in the resistance to air flow is characterised chiefly by a decrease in expiratory flow rate (e.g. FEV1).
An increasingly important concept in developing safe exposure to respiratory toxicants is the recognition of the role of protective mechanisms. If the exposure to a toxicant results in a tissue dose that does not overwhelm the protective response, then it is quite unlikely to cause adverse pathophysiological effects. However, disease can develop if these defences are overwhelmed and a range of normal biological responses becomes exaggerated (such as fibrosis, hypersensitivity or neoplasia) and possibly health-damaging or life-threatening.
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