Abstract
ObjectiveThere is conflicting evidence about resting carbon dioxide levels in asthmatic individuals. We wanted to determine if transcutaneously measured carbon dioxide levels prior and during bronchial provocation testing differ according to asthma status reflecting dysfunctional breathing.MethodsWe investigated active firefighters and policemen by means of a validated questionnaire on respiratory symptoms, spirometry, bronchial challenge testing with methacholine (MCT) and measurement of transcutaneous blood carbon dioxide partial pressure (PtcCO2) at rest prior performing spirometry, one minute and five minutes after termination of MCT. A respiratory physician blinded to the PtcCO2 results assigned a diagnosis of asthma after reviewing the available study data and the files of the workers medical screening program.ResultsThe study sample consisted of 128 male and 10 female individuals. Fifteen individuals (11%) had physician-diagnosed asthma. There was no clinically important difference in median PtcCO2 at rest, one and five minutes after recovery from MCT in asthmatics compared to non-asthmatics (35.6 vs 35.7 mmHg, p = 0.466; 34.7 vs 33.4 mmHg, p = 0.245 and 37.4 vs 36.4 mmHg, p = 0.732). The median drop in PtcCO2 during MCT and the increase after MCT was lower in asthmatics compared to non-asthmatics (0.1 vs 3.2 mmHg, p = 0.014 and 1.9 vs 2.9 mmHg, p = 0.025).ConclusionsPtcCO2 levels at rest prior and during recovery after MCT do not differ in individuals with or without physician diagnosed asthma. The fall and subsequent increase in PtcCO2 levels are higher in non-asthmatics than in asthmatics and seems to be related with increased number of respiratory maneuvers during MCT.
Highlights
Asthma is associated with a chronic inflammation of the airways associated with symptoms such as cough, wheezing, sputum production and chest tightness
Thomas and co-workers have shown that dysfunctional breathing can be found in a third of asthmatic woman and a fifth of asthmatic men seen in general practice and in about 8% of the general population when evaluated with a questionnaire to detect functional breathing problems, the Nijmwegen Questionnaire [4,5]
The assumption that dysfunctional breathing might be associated with lower end-tidal carbon dioxide partial pressures (PETCO2) has led to the idea to offer asthmatics breathing retraining to raise PETCO2 [6]
Summary
Asthma is associated with a chronic inflammation of the airways associated with symptoms such as cough, wheezing, sputum production and chest tightness. Further several studies have shown an association between asthma and higher anxiety sensitivity scores and panic disorder [1,2,3]. The assumption that dysfunctional breathing might be associated with lower end-tidal carbon dioxide partial pressures (PETCO2) has led to the idea to offer asthmatics breathing retraining to raise PETCO2 [6]. It was shown in an experimental setting that increasing PETCO2 can decrease respiratory resistance while decreasing PETCO2 in turn led to an increase in resistance and decrease in airway reactance in asthmatic individuals [7]. We wanted to determine prospectively, if resting transcutaneous blood carbon dioxide partial pressures (PtCO2) prior and after bronchial challenge testing or the change in PtcCO2 were different in individuals with or without asthma
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