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DOI: 10.1183/09031936.00150907

Environmental temperature and relative humidity influence exhaled breath condensate pH
To the Editors: Exhaled breath condensate (EBC) is used to obtain information about the composition of airway surface lining fluid [1]. Acidificationof EBC has been reported in different inflammatory airway diseases [2]. Interpretation of data is compromised by the fact that condensate pH shows day-to-day variability, even in healthy subjects [3]. Coating of condensing surfaces [4] and salivary contamination of the condensate [5] have been proposed to influence exhaled biomarker levels. It was our aim to investigate whether environmentaltemperature and relative humidity could influence condensate pH and whether they could be responsible for the observed variability. EBC was collected from 12 healthy subjects with an R-Tube condenser (Respiratory Research Inc., Charlottesville, VA, USA) before and after the forecasted arrival of three cold, humid and two warm, dry meteorological fronts. In summer, on three occasions the room temperatureand relative humidity paralleled the outside conditions; in winter, on two occasions room temperature and relative humidity were maintained at 26uC and between 47–52%. EBC pH was determined using the carbon dioxide (CO2) standardisation method, as described previously [3]. Briefly, pH and CO2 were measured using a blood gas analyser (ABL 520; Radiometer, Copenhagen, Denmark) five timesconsecutively after 1-s CO2 load to the sample between each measurement. A pH–CO2 plot was created from the results. The pH at 5.33 kPa CO2 partial pressure was calculated using the logarithmic regression equity obtained from the plot. The arrival of forecasted meteorological fronts caused a pronounced change both in temperature and relative humidity of ambient air (table 1). In summer, when the study roomconditions paralleled the weather conditions outside, EBC pH decreased significantly with the humid, cold fronts and inversely increased with the dry, warm front. In winter, when room conditions were controlled, EBC pH was not affected significantly by either the humid, cold or the dry, warm fronts. The coefficient of variation of EBC pH was 3.0¡1.3 under uncontrolled room conditions in summer and1.8¡0.9 under controlled temperature and relative humidity of the room in winter (p,0.02). There was no correlation between pH and volume of condensates. The results have two possible readings, one clinical and the other pathophysiological. From a clinical point of view the results
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TABLE 1
Season

Effect of meteorological fronts on exhaled breath condensate (EBC) pHFront Day Temp. uC RH EBC pH p-value

Summer

Humid Humid Dry

Before After Before After Before After Before After Before After

29 18 30 23 23 31 16 5 1 12

53 74 38 53 40 36 53 83 55 42

6.11¡0.18 5.92¡0.19 5.96¡0.20 5.83¡0.13 5.88¡0.20 6.02¡0.16 6.00¡0.15 5.97¡0.16 5.98¡0.24 5.95¡0.14

0.008 0.030 0.015
NS

Winter

Humid Dry

NS

Temperature (temp.) and relativehumidity (RH) were registered at the time of collections. Study room temperature and RH paralleled the outside conditions in summer and were kept at 26uC and between 47–52% in winter. EBC pH values are presented as mean¡SD.
NS:

nonsignificant.

suggest that controlling room temperature and relative humidity should be part of standardisation of EBC collection. From a pathophysiological point of...