Airflow dynamics and exhaled-breath temperature following cold-water ingestion.

Drinking cold water evokes decreases in spirometric indices of lung function. We studied whether this could be explained by changes in exhaled-breath temperature (EBT), airflow dynamics, and spirometer measurement sensitivity. In a randomized/crossover design, 10 healthy adults consumed 1000 mL refrigerated water (2.1 ± 0.64 °C) or water at room temperature (19.4 ± 0.5 °C), with EBT assessed at baseline and at 5, 10, 15 and 30-min post-ingestion. The influence of EBT on pneumotachograph measurement characteristics was modelled using computational fluid dynamics (CFD). At 5-min post-ingestion, EBT was lower (p < 0.001) following the ingestion of cold water versus water at room-temperature (31.7 ± 1.1 vs. 33.0 ± 0.9 °C), and remained lower until 30-min post-ingestion. At a flow of 8 L s-1, a decrease in EBT of 2.1 °C (as observed following cold-water ingestion) was modelled to underpredict lung volume by 0.7%. Cold water reduces EBT below baseline but effects pneumotachograph measurements only negligibly. Therefore, decreased lung function following cold-water ingestion likely has a physiological explanation which warrants further study.