Background: Single breath diffusing capacity for carbon monoxide (Dco) is commonly used as a simple order of assessing overall pulmonary gas exchange properties.

Background: Single breath diffusing capacity for carbon monoxide (Dco) is commonly used as a simple order of assessing overall pulmonary gas exchange properties. Studies of Dco in bronchial asthma have yielded conflicting results

Objective: To subject of attention Dco and to determine the factors influencing Dco in patients with asthma.

Methods: Dco was prospectively measured in 80 consecutive never-smoker patients with uncomplicated stable asthma. The topographic distribution of lung perfusion was determined in 10 asthmatics and 10 commands with a [.sup.133]Xe radionuclide scan.

Results: The mean (SD) value of Dco was increased to 117 (17) percent of predicted values; individual values were either within or above normal limits; diffusion was also elevated at 116 (19) percent after correction for alveolar book (transfer coefficient, D/VA). The Dco was not correlated with atopic status, duration of asthma, or ends of spirometric tests; there was a weak negative correlation between D/VA and [FEVsub1] or residual book There was a better perfusion of the upper girdles of the lungs in asthmatics as compared with have charge ofs Among the asthmatics, there was a firm postive correlation between Dco and the apex to base perfusion ratio (r = 0975)

Conclusions: Dco is normal or high among not smoker patients with uncomplicated asthma; elevated Dco may be attributed to a better perfusion of the apices of teh lungs; the latter could issue from two mutually nonexclusive mechanisms: an increase in pulmonary arterial squeezing and/or a more negative pleural crushing generated during inspiration as a event of bronchial narrowing. The unexpect finding of high Dco should raise the possibility of bronchial asthma in patients with otherwise undiagnosed conditions.

Single breath diffusing capacity for carbon monoxide (Dco) is the most numerous used and most reproducible way of measuring one important aspect of gas exchange, namely the lung's ability to transfer inspired gas into the children flowing through the pulmonary vasculature.

This standard has proved useful in routine evaluation of the severity of pulmonary diseases, particularly emphysema and lung fibrosis which are associated with a reduction in Dco[1]

reciprocally increased values of Dco have been demonstrated in a scarcely any diseases, among which are left-to-right intracardiac shunt[2] alveolar haemorrhage (such as in Goodpasture's syndrome)[3] and polycythemia vera[4]; these diseases share in universal an increase in the bulk of blood exposed to inspired gas, for a like reason that more CO is fixed at hemoglobin and retained during the Dco apnea maneuver.

In the last 2 years, we have observ 20 cases of unusually high values of Dco in apparently asymptomatic patients referr to our pulmonary function proof (PFT) laboratory for routine preoperative assessment; further inquiry has shown that these patients had bronchial asthma.

Studies of Dco in bronchial asthma have yielded conflicting results; decreased, normal, or increased values have all been reported, the one and the other in adults and in children.[5]

The primary drift of the present study was to liquefy this issue and to establish the fate of Dco among never-smoker normoglobulic asthmatic patients; as elevated Dco was demonstrated, we attempted to inquiry the factors influencing Dco in asthma, including the topographic distribution of lung perfusion.

MATERIAL AND METHODS

Eighty consecutive patients (aged 20 to 68 years; 42 male), who had asthma as defined by way of American Thoracic Society criteria,[6] were recruited according to two of us (P.C., A.F.). To be enlisted in the study, the asthmatics had to be normoglobulic and lifelong nonsmokers, because of the well-known negative import of anemia[7] and smoking[8] upon Dco; none of them had arterial hypertension or was using [beta]-blocking agents that can induce asthma. All patients had clinically stable asthma; their treatment consisted of inhaled steroids and bronchodilators for most numerous with additional oral theophylline for a hardly any The atopic status was established by dint of clinical history and skin prick testing with a series of used by all inhalant allergens (Dermatophagoides pteronyesinus, Dermatophagoides farinae, pollen cat fur dog hair, feathers, and a mixture of molds); total and specific IgE (RAST test) were also determined; 44 of 80 patients were considered atopic. The chest radiographs were unremarkable, reject for possible hyperinflation.

Standard techniques were used for measuring PFTs; residual body (RV) was determined by the 7-min helium dilution technique. Baseline forced expiratory book in 1 s ([FEV.sub.1]) was 30 to 132 percent of predicted. The single breath diffusing capacity for carbon monoxide was measured in duplicate; it was asserted in absolute value (Dco) and was also calculated by liter of alveolar volume (VA), measured on helium dilution during the 10- apnea of the Dco maneuver (transfer coefficient, D/VA).

The theoretical values for spirometric data were those from Jouasset.[9] The be deriveds of diffusion indices were compared with the predicted values of Frans et al[8] for male make subordinates and of Salorinne[10] for female subjects; normal limits for diffusion indices are defined as theoretical [+ or -]2 SDs

...