The impairment of pulmonary gas exchange results in metabolic disturbances of the tissue cells due to O
2 deficit and CO
2 retention. The changes in O
2 and CO
2 tension, and pH in the arterial blood, therefore, are recognized as the most useful sign to suggest the impairment.
Factors which affect pulmonary gas exchange are one or more of the followings; 1) airway obstruction; 2) alveolar hypoventilation; 3) change in mechanical properties of the thorax and the lung; 4) uneven pulmonary capillary blood flow; 5) right-to-left shunts.
In a patient with respiratory disorder, shortness of breath should be realized as a somatic expression of effort to overcome these handicaps.
Patterns of altered pulmonary function observed in patients with chest disease were listed, and their patho-physiological significances were discussed. In addition, the usefulness of some integrated tests, f. e. analysis of flow-volume curve or expiratory CO
2 concentration curve and so on, were also interpreted.
Finally, it was emphasized that the necessity to find the impairment of pulmonary gas exchange, in its early stage, must be kept in mind in order to check further advancement of the disease.
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