Factors influencing breath condensate volume

Abstract

Analysis of breath condensate (BC) has received interest recently due to the need for easy and repetitive monitoring or airway and pulmonary disease. While many authors have used custom built systems, commercial systems are now available and will probably be used more widely. Early studies of markers and mediators in BC have reported concentrations following varying periods of sampling time. However, factors that influence the generation of BC have not been analysed and it is unclear whether breathing rate, tidal volume, lung function, body weight, height or age influence the amount of BC collected. We therefore studied the influence of these factors on breath condensate volume and breath condensate urea and protein concentrations in 22 healthy volunteers and 23 COPD patients. A strong correlation of total respired volume and breath condensate volume was observed for both groups (volunteers: r=0.952, p < 0.0001, COPD: r=0.883, p < 0.001) while no significant correlation existed for breath condensate volume and TLC, RV, Vc, FEV1, R(tot), height or body weight, As long as ventilation remained fairly constant, breath condensate volume increased linearly with time. The fraction of breath condensate extracted from total vapour contained in the exhalate was estimated by measuring relative atmospheric humidity before and after the collecting tube. The amount calculated by the change in temperature and saturation corresponded closely to the amount actually collected. We conclude from these results that breath condensate volume is primarily dependent on V(E), and does not seem to depend on lung function parameters. For standardisation it is suggested to report breath condensate measurements per volume respired. Both, urea and protein are present in measurable quantities in breath condensate and protein as well as BCV may be helpful denominators for comparison with e.g. cytokines in lung disease.

Exhaled breath condensate: methodological recommendations and unresolved questions

“…This mediator is not age-dependent in children, but higher levels were found in older than younger adults [13,33,34]. Body weight or height do not affect EBC volume and H 2 O 2 concentration in adults [28]; however no data are available regarding other mediators.…”

“…Exhalation flow influences the level of exhaled H 2 O 2 ; at higher flows exhaled H 2 O 2 concentration is lower, but with the low flows during tidal breathing the effect is minor [19]. A strong correlation was found between total respired volume and breath condensate volume by different authors [11,28]. An animal study showed clear positive correlations not only between minute volume and EBC volume, but also to variables determining the breathing pattern (i.e.…”

“…Airway calibre and lung function EBC volume does not depend on lung function parameters including forced expiratory volume in one second and forced vital capacity (FVC) either in normal subjects or in patients with COPD [28]. At present there is no evidence to show that changes in airway calibre cause any difference in mediator release or dilution of EBC, but this question has not been studied systematically.…”

“…GESSNER et al [28] showed not only that EBC volume was linearly related to the volume expired, but also to the total protein and urea content found in EBC suggesting that these compounds accumulated in the collecting device by a similar mechanism as expired water vapour. This even distribution, however, is not necessarily true for all substances present in EBC and needs further study.…”

“…None of the available condensers collect all exhaled water vapour, since estimated water loss is around 30-35 mg?L -1 in a wide range of ambient air temperature and humidity [26,27]. One study estimated the water extraction by a cold trap integrated into the cooled head sampling unit and found that ,40% of water vapour was extracted with no difference in the efficiency of water vapour extraction in healthy subjects versus chronic obstructive pulmonary disease (COPD) patients [28]. Similar EBC volume was found by others using a 200 cm tubing connected to the expiratory port of a ventilator kept under saline-ice water [14].…”