Respiratory chemosensitivity evaluated by respiratory drive and breath holding

Ventilatory response to CO2 (delta VE/delta PCO2), respiratory drive (delta P0.1/delta PCO2), breath-holding time (BHT) on 100% O2 and log BHT/PCO2 slope during CO2 rebreathing was assessed, in 19 control subjects and in 22 patients with chronic obstructive pulmonary disease (COPD) with hypercapnia (PCO2 greater than 50 mm Hg). The log BHT/PCO2 slope was expressed as the PCO2 increment to half the BHT. We found no correlation between BHT on 100% O2 and delta VE/delta PCO2 or delta P0.1/delta PCO2 in controls and COPD subjects. delta PCO2 halving BHT had an inverse statistical significant correlation with delta VE/delta PCO2 and delta P0.1 delta PCO2 in controls and patients. In contrast to delta P0.1/delta PCO2, the delta PCO2 halving BHT increased in COPD patients and there are patients with normal respiratory drive but prolonged delta PCO2 halving BHT. The delta PCO2 halving BHT as delta VE/delta PCO2 cannot be substituted for delta P0.1/delta PCO2 in the clinical assessment of respiratory chemosensitivity in COPD patients.