A quick and easy method of measuring the hypercapnic ventilatory response in patients with COPD.
BACKGROUND
Hypercapnic ventilatory response (HCVR) techniques have not previously been adequately validated in patients with chronic obstructive pulmonary disease (COPD). We have tested the hypothesis that end-tidal PCO(2) may be used to test the HCVR in COPD during non-steady-state rebreathing, despite the fact that large (arterial-end-tidal) PCO(2) differences (P(a-et)CO(2)) exist during air breathing.


METHODS
Eight patients and 11 healthy volunteers underwent steady-state HCVR testing and non-steady-state rebreathing HCVR testing, using Pa and PetCO(2).


RESULTS
In COPD patients, PetCO(2) was lower than PaCO(2) by a constant amount throughout steady-state HCVR, but equalised with PaCO(2) during non-steady-state HCVR. Consequently there were no differences in HCVR slope using either method (steady-state p=0.91; rebreathing p=0.73), or HCVR intercept in rebreathing (p=0.68) whether PaCO(2) or PetCO(2) was used. The steady-state HCVR intercept using PetCO(2) was greater than that using PaCO(2) (p=0.02). In healthy volunteers PetCO(2) equalised with PaCO(2) during steady-state HCVR, but was progressively greater than PaCO(2) during non-steady-state. Consequently, there was no difference in HCVR slope (p=0.21) or intercept (p=0.46) whether PaCO(2) or PetCO(2) was used. During non-steady-state there was a P(a-et)CO(2) difference in slope (p=0.03) and intercept (p=0.04).


CONCLUSIONS
In COPD patients non-steady-state HCVR using PetCO(2) is well tolerated, which is as accurate as PaCO(2). HCVR slope may be derived using PetCO(2) during steady-state testing, though there may be errors in intercept compared to use of PaCO(2). In healthy volunteers PetCO(2) may be used to estimate PaCO(2) during steady-state but not rebreathing HCVR.
Clinical and Academic Unit of Sleep and Breathing, National Heart and Lung Institute, Royal Brompton Hospital, Fulham Road, London SW3 6NP, UK. annabel@medex.org.uk
Annabel H
AH
Nickol
Helen
H
Dunroy
Michael I
MI
Polkey
Anita
A
Simonds
Jeremy
J
Cordingley
Douglas R
DR
Corfield
Mary J
MJ
Morrell
D000328:Adult; D001944:Breath Tests / Q000379:methods; D002245:Carbon Dioxide / Q000502:physiology*; D005260:Female; D006801:Humans; D006935:Hypercapnia / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology*; D013990:Tidal Volume / Q000502:physiology; D014692:Ventilation-Perfusion Ratio / Q000502:physiology*
D002245:Carbon Dioxide