Influence of unequal ventilation on the single breath K(CO) in COPD revealed by comparison with the rebreathing K(CO).
In 16 patients with chronic obstructive pulmonary disease (COPD) we investigated the relation between unequal ventilation and diffusion by means of lung volumes and Krogh factors (K(CO)) using the single breath (SB) and the rebreathing (RB) methods. We used both methods because the SB measurement is sensitive to unequal ventilation and diffusion whereas the RB measurement is not. Because K(CO) depends on inspired volume (VI), the SB and RB measurement have to be performed at the same VI. We therefore determined K(CO)SBm by making a SB measurement at VI equal to the mean inspired volume during the RB measurement and then calculated K(CO)RBm by dividing the RB transfer factor for CO by the mean RB lung volume. In 10 patients K(CO)SBm/K(CO)RBm, a parameter determined by the combined effect of unequal ventilation and diffusion, was almost equal to unequal ventilation, the quotient of the SB and mean RB lung volumes (VSBm/VRBm), just as in normal subjects (Jansons et al., Respiration 67 (2000) 383). This finding means that we can correct for the effects of unequal ventilation by dividing K(CO)SBm by VSBm/VRBm. We suggest that the SB measurement of K(CO) at vital capacity can be corrected in a similar way.
Jansons
H
H
Lung Function Department of the Heart Lung Division and Centre of Biostatistics, Utrecht University, Utrecht, The Netherlands. jansons.h@planet.nl
Fokkens
J K
JK
Tweel van der
I
I
Lammers
J-W
JW
Folgering
H
H
D000328:Adult; D000367:Age Factors; D000368:Aged; D002248:Carbon Monoxide / Q000032:analysis; D006801:Humans; D007320:Inspiratory Capacity / Q000502:physiology; D008875:Middle Aged; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology*; D012123:Pulmonary Ventilation / Q000502:physiology*; D012044:Regression Analysis; D012129:Respiratory Function Tests / Q000379:methods / Q000706:statistics & numerical data; D014797:Vital Capacity / Q000502:physiology
D002248:Carbon Monoxide