Measurement of temperature and relative humidity in exhaled breath

Abstract Temperature (T) and relative humidity (RH) are two of the most important variables in breath analysis. Several studies have investigated the temperature range of exhaled breath, mostly in the context of respiratory disease diagnostics, but none of them inspected the correlation with clinical parameters, nor the effect of different geographic locations. In this study, we have built a tailor-made device for measuring temperature and relative humidity in exhaled breath. With it, we have carried out 340 measurements (265 in Paris/France and 75 in Haifa/Israel) from 31 participants. The results show that the temperature range of exhaled breath is 31.4-35.4 °C for Haifa’s participants and 31.4-34.8 °C for Parisian participants and the range of exhaled breath relative humidity is 65.0-88.6% and 41.9-91.0% for Haifa and Paris participants, respectively. Clinical and environmental effects were also inspected to give more information on the confounding factor. The results presented in this study contribute to the definition of the ranges of T and RH of exhaled breath in individuals, in addition to their correlation with clinical and environmental factors such as gender, BMI and age. These factors must be taken into consideration in order to increase the reproducibility and reliability of a wide variety of measurements in this particular field.