Relationship between sensitivity to carbon dioxide and clinical features in patients with chronic airways obstruction

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This study was designed to investigate the relationship between the different clinical features exhibited by patients with chronic airways obstruction and their responsiveness to carbon dioxide. In 19 patients pulmonary function was assessed by spirometry, lung volumes and arterial blood gases. Measurements of responsiveness to carbon dioxide were made and compared with responses obtained in five normal subjects. Assessed in terms of inspiratory mechanical work performed rather than ventilation achieved, it was shown that there was a highly significant positive correlation between work rate response and the level of dyspnoea, so that patients with poor response experienced little dyspnoea despite severe airways obstruction. Significant negative correlations were found between work rate response and the presence of oedema, polycythaemia and a raised resting arterial CO2 tension, and a positive correlation was found with radiographic evidence of emphysema. A reduced work rate response to CO2 was taken to signify diminished central sensitivity to carbon dioxide. The cause of the reduced sensitivity was not elucidated, but it was concluded that several of the clinical features associated with chronic airways obstruction were related to loss of CO2 sensitivity.

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