PURPOSE: Ingesting cold-water evokes decreases in spirometric indices of pulmonary function. However, given that most commercial spirometers assume an exhaled-breath temperature (EBT) of 37 °C, a cold-water-induced decrease in EBT may influence the accuracy of flow-volume measurements. Accordingly, the aims of this study were: i) to assess whether cold-water ingestion was sufficient to reduce EBT in healthy subjects; and ii) to model the influence of EBT on pneumotachograph airflow dynamics.
METHODS: Ten healthy, recreationally-active adults (5 male, 5 female), with normal pulmonary function, volunteered to participate (age=36±7 y; mass=87.4±31.8 kg; stature=1.74±0.8 m). In a randomized crossover design, subjects consumed either 1000 mL of refrigerated water (2.1±0.64 °C) or water at room temperature (19.4±0.5 °C), with exhaled-breath temperature assessed (via the tidal breathing method) at baseline and at 5, 10, 15, and 30 min post-ingestion. The influence of exhaled-breath temperature on the measurement characteristics of a non-heated pneumotachograph, was modelled using computational fluid dynamics (CFD).
RESULTS: Baseline EBT was not different between the two conditions (33.8±0.4 vs. 33.7±0.54 °C; p=0.269, d=0.25). Following the ingestion of cold-water, EBT fell below baseline and remained so until the final measure at 30 min (p<0.01). When compared to water at room temperature, EBT was significantly lower following the ingestion of cold-water at 5 min (31.7±1.1 vs. 33.0±0.9 °C; p<0.001, d=1.34), 10 min (32.6±0.6 vs. 33.2±0.6 °C; p<0.001, d=1.06), and 15 min post-ingestion (32.5±0.6 vs. 33.3±0.5 °C; p<0.001, d=1.46). A mean decrease in EBT of 2.1 °C (as observed acutely following cold-water ingestion) was modelled to under-predict flow by 0.84% and volume by 0.78%.
CONCLUSIONS: Cold-water reduces exhaled-breath temperature for at least 30 min post-ingestion, and to a greater extent than water at room-temperature. The mean decrease in EBT resulted in a negligible effect on calculated flow-volume variables. Accordingly, a measured change in lung function that follows cold-water ingestion likely has a physiological explanation which warrants further study. These data may also have implications for the clinical assessment of EBT in monitoring pathological processes of the airway.