Introduction: Analysis of exhaled breath condensate (EBC) is a noninvasive method to access the epithelial lining fluid of\r\nthe lungs. Due to standardization problems the method has not entered clinical practice. The aim of the study was to assess\r\nthe comparability for two commercially available devices in healthy controls. In addition, we assessed different breathing\r\npatterns in healthy controls with protein markers to analyze the source of the EBC.\r\nMethods: EBC was collected from ten subjects using the RTube and ECoScreen Turbo in a randomized crossover design,\r\ntwice with every device - once in tidal breathing and once in hyperventilation. EBC conductivity, pH, surfactant protein A,\r\nClara cell secretory protein and total protein were assessed. Bland-Altman plots were constructed to display the influence of\r\ndifferent devices or breathing patterns and the intra-class correlation coefficient (ICC) was calculated. The volatile organic\r\ncompound profile was measured using the electronic nose Cyranose 320. For the analysis of these data, the linear\r\ndiscriminant analysis, the Mahalanobis distances and the cross-validation values (CVV) were calculated.\r\nResults: Neither the device nor the breathing pattern significantly altered EBC pH or conductivity. ICCs ranged from 0.61 to\r\n0.92 demonstrating moderate to very good agreement. Protein measurements were greatly influenced by breathing\r\npattern, the device used, and the way in which the results were reported. The electronic nose could distinguish between\r\ndifferent breathing patterns and devices, resulting in Mahalanobis distances greater than 2 and CVVs ranging from 64% to\r\n87%.\r\nConclusion: EBC pH and (to a lesser extent) EBC conductivity are stable parameters that are not influenced by either the\r\ndevice or the breathing patterns. Protein measurements remain uncertain due to problems of standardization. We conclude\r\nthat the influence of the breathing maneuver translates into the necessity to keep the volume of ventilated air constant in\r\nfurther studies.
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