title: Diffusing capacity for carbon monoxide is linked to ventilatory demand in patients with chronic obstructive pulmonary disease.
abstract: Dyspnea is deemed to result from an imbalance between ventilatory demand and capacity. The single-breath diffusing capacity for carbon monoxide (DLCO) is often the best correlate to dyspnea in COPD. We hypothesized that DLCO contributes to the assessment of ventilatory demand, which is linked to physiological dead space /tidal volume (V(D)/V(T)) ratio. An additional objective was to assess the validity of non-invasive measurement of transcutaneous P(CO2) allowing the calculation of this ratio. Forty-two subjects (median [range] age: 66 [43-80] years; 12 females) suffering mainly from moderate-to-severe COPD (GOLD stage 2 or 3: n = 36) underwent pulmonary function and incremental exercise tests while taking their regular COPD treatment. DLCO% predicted correlated with both resting and peak physiological V(D)/V(T) ratios (r = -0.55, p = 0.0015 and r = -0.40, p = 0.032; respectively). The peak physiological V(D)/V(T) ratio contributed to increase ventilation (increased ventilatory demand), to increase dynamic hyperinflation and to impair oxygenation on exercise. Indirect (MRC score) and direct (peak Borg score/% predicted VO(2)) exertional dyspnea assessments were correlated and demonstrated significant relationships with DLCO% predicted and physiological V(D)/V(T) at peak exercise, respectively. The non-invasive measurement of transcutaneous P(CO2) both at rest and on exercise was validated by Bland-Altman analyses. In conclusion, DLCO constitutes and indirect assessment of ventilatory demand, which is linked to exertional dyspnea in COPD patients. The assessment of this demand can also be non invasively obtained on exercise using transcutaneous PCO(2) measurement.
authors.affiliation: AP-HP, Hôpital Européen Georges-Pompidou, Service de Physiologie -Clinique de la Dyspnée, Paris, France.
authors.forename: Bruno
authors.initials: B
authors.lastname: Mahut
authors.forename: Brigitte
authors.initials: B
authors.lastname: Chevalier-Bidaud
authors.forename: Laurent
authors.initials: L
authors.lastname: Plantier
authors.forename: Mohamed
authors.initials: M
authors.lastname: Essalhi
authors.forename: Etienne
authors.initials: E
authors.lastname: Callens
authors.forename: Semia
authors.initials: S
authors.lastname: Graba
authors.forename: Karine
authors.initials: K
authors.lastname: Gillet-Juvin
authors.forename: Judith
authors.initials: J
authors.lastname: Valcke-Brossollet
authors.forename: Christophe
authors.initials: C
authors.lastname: Delclaux
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001785:Blood Gas Monitoring, Transcutaneous; D002245:Carbon Dioxide / Q000097:blood*; D003430:Cross-Sectional Studies; D004417:Dyspnea / Q000503:physiopathology; D005080:Exercise Test; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D005082:Physical Exertion / Q000502:physiology; D011653:Pulmonary Diffusing Capacity / Q000502:physiology*; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology*; D012123:Pulmonary Ventilation / Q000502:physiology*; D012126:Respiratory Dead Space / Q000502:physiology; D013990:Tidal Volume / Q000502:physiology
chemical_list: D002245:Carbon Dioxide