The slope of phase 3 and three noninvasively determined dead space estimates derived from the expiratory carbon dioxide tension (PCO 2 ) versus volume curve, including the Bohr dead space (VD,Bohr), the Fowler dead space (VD,Fowler) and pre-interface expirate (PIE), were investigated in 28 healthy control subjects, 12 asthma and 29 emphysema patients (20 severely obstructed and nine moderately obstructed) with the aim to establish diagnostic value.Because breath volume and frequency are closely related to CO 2 elimination, the recording procedures included varying breath volumes in all subjects during self-chosen/natural breathing frequency, and fixed frequencies of 10, 15 and 20 breaths·min -1 with varying breath volumes only in the healthy controls.From the relationships of the variables with tidal volume (VT), the values at 1 L were estimated to compare the groups. The slopes of phase 3 and VD,Bohr at 1 L VT showed the most significant difference between controls and patients with asthma or emphysema, compared to the other two dead space estimates, and were related to the degree of airways obstruction. Discrimination between no-emphysema (asthma and controls) and emphysema patients was possible on the basis of a plot of intercept and slope of the relationship between VD,Bohr and VT. A combination of both the slope of phase 3 and VD,Bohr of a breath of 1 L was equally discriminating. The influence of fixed frequencies in the controls did not change the results.The conclusion is that Bohr dead space in relation to tidal volume seems to have diagnostic properties separating patients with asthma from patients with emphysema with the same degree of airways obstruction. Equally discriminating was a combination of both phase 3 and Bohr dead space of a breath of 1 L. The different pathophysiological mechanisms in asthma and emphysema leading to airways obstruction are probably responsible for these results.

D Do oe es s p ph ha as se e 22 o of f t th he e e ex xp pi ir ra at to or ry y P PC CO O 2 2 v ve er rs su us s v vo ol lu um me e c cu ur rv ve e h ha av ve e d di ia ag gn no os st ti ic c v va al lu ue e i in n e em mp ph hy ys se em ma a p pa at ti ie en nt ts s? ? The volumes between 25-50% (V25-50) and 25-75% (V25-75) of the expiratory carbon dioxide tension versus volume curve were determined in 29 emphysematous patients (20 severely obstructed and 9 moderately obstructed), 12 asthma patients in exacerbation of symptoms, and 28 healthy controls. Discriminant analysis was used to examine whether these diagnostic groups could be separated.With regard to phase 2 of the expiratory CO 2 versus volume curve (mixture of anatomic deadspace and alveolar air), a plot of intercept versus slope of the relationships of (V25-50) and (V25-75) versus inspiratory volume (VI) from functional residual capacity (FRC), obtained during natural breathing frequency, proved to be most discriminating in the separation between healthy controls and severely obstructed emphysema patients. Separating healthy controls and severely obstructed emphysema pat-ients on the basis of the discriminant line for V25-50, 9 of the 12 asthma patients in exacerbation were classified as normal, and only 5 of the 9 moderately obstructed emphysema patients as emphysematous. For V25-75 involvement of phase 3 of the curve (alveolar plateau) in asthma patients in exacerbation caused a marked overlap with the severely obstructed emphysema patients. In the healthy controls, a fixed breathing frequency of 20 breaths·min -1 led to an increase of both volumes. For V25-50, this resulted in an overlap with the severely obstructed emphysematous patients.We conclude that V25-50 and V25-75 are not useful in the diagnosis of emphysema. This indicates that the ventilatory inhomogeneity as reflected by Phase 2 of the expiratory carbon dioxide tension versus volume curve is not sensitive enough for diagnostic application.

Ta ble1:Accuracyparametersofthe Vidas and AutoDimer D-dimerassay. Vidas A utoDimer Parameter ≤ 500 ng/ml ≤ 189 ng/ml ≤ 110 ng/ml sensitivity %(95% CI) 9 8(92-99) 92 (84-97) 97 (90-99) sensitivity %(95% CI) 4 1(36-47) 52 (46-58) 32 (27-38) NPV%(95%CI) 98 (94-100) 96 (91-98) 97 (91-99) PPV%(95%CI) 33 (28-39) 36 (30-43) 30 (25-35) NPV,negativepredictivevalue; PPV,positivepredictivevalue.