Ventilatory responses to carbon dioxide in asthmatics with previous carbon dioxide retention during severe asthma

Ventilatory responses to carbon dioxide (Sco2) were measured in 15 asymptomatic asthmatic patients in whom CO2 retention had been documented during a previous attack of acute asthma. At the time when Sco2 was measured, the patients had normal or only mildly impaired ventilatory function (vital capacity (VC) 3,5 +/- 0,19 I, 98,7 +/- 4% of predicted (mean +/- SE); forced expiratory volume in 1 second (FEV1) 2,37 +/- 0,161, 83,8 +/- 5,2% of predicted; and FEV1/VC 68 +/- 2,5%). Fifteen control subjects without lung disease were also studied (VC 4,38 +/- 0,28 I, 103 +/- 2,6% of predicted; FEV1 3,76 +/- 0,23 I, 112 +/- 4,4% of predicted; FEV1/VC 86 +/- 7,8%). Sco2 in the patients (1,21 +/- 0,14 l/min/mmHg, range 0,62 - 2,81) was significantly different (P less than 0,001) from that in controls (2,13 +/- 0,17 l/min/mmHg, range 1,13 - 3,17). Sco2 in a subgroup of 5 patients with normal pulmonary function was also significantly different from that in controls. Correction for lung size (Sco2/VC) did not detract from the significance of the difference between patients and controls, suggesting that inherently low respiratory centre sensitivities to CO2 may have played a role in the development of hypercapnia during severe asthma in these patients.