Alveolar volume determined by single-breath helium dilution correlates with the high-resolution computed tomography-derived nonemphysematous lung volume.
BACKGROUND
The alveolar volume (V(A)), determined by single-breath helium dilution, is a measure for the total lung capacity (TLC) that is very sensitive to ventilatory disturbances. In chronic obstructive pulmonary disease (COPD), the emphysematous lung parts are less accessible to test gas; therefore, the V(A) is smaller than TLC measured by multiple-breath helium dilution (TLC(He)).


OBJECTIVE
The aim of this study was to investigate whether the V(A) represents the nonemphysematous lung parts.


METHODS
We measured V(A) as part of the diffusing capacity for carbon monoxide (DL(CO)), TLC(He) and spirometry in 50 patients with COPD. High-resolution computed tomography (HRCT) scans of all subjects were analyzed with the density mask method, where parts with an attenuation of less than -950 Hounsfield units were considered as emphysematous.


RESULTS
A strong correlation was observed between the V(A) (mean 5.2 liters) and nonemphysematous HRCT lung volume (mean 5.2 liters, r(2) = 0.9) and between the TLC(He) (mean 6.6 liters) and total HRCT lung volume (mean 6.4 liters, r(2) = 0.9). Bland-Altman plots showed considerable disagreement between the V(A) and the nonemphysematous HRCT lung volume. A weak correlation between the forced expiratory volume in 1 s (mean 46% predicted) and DL(CO) (mean 46% predicted) versus the HRCT emphysema ratio (nonemphysematous/total HRCT lung volume) was observed (r(2) = 0.3 and 0.3, respectively).


CONCLUSIONS
We concluded that the V(A) correlates with the nonemphysematous HRCT lung volume, although the two measurements are not equivalent, possibly due to technical factors.
van der Lee
I
I
Department of Pulmonary Diseases, Heart Lung Centre Utrecht, St. Antonius Hospital, Nieuwegein, The Netherlands.
van Es
H W
HW
Noordmans
H J
HJ
van den Bosch
J M M
JM
Zanen
P
P
D000280:Administration, Inhalation; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D004646:Emphysema; D005260:Female; D006371:Helium / Q000008:administration & dosage / Q000493:pharmacokinetics*; D006801:Humans; D008176:Lung Volume Measurements; D008297:Male; D008875:Middle Aged; D011650:Pulmonary Alveoli / Q000503:physiopathology*; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology*; D013902:Radiography, Thoracic; D012016:Reference Values; D012907:Smoking / Q000503:physiopathology; D014057:Tomography, X-Ray Computed
D006371:Helium