MEASUREMENT OF RESPIRATORY RATE AND TIMING USING A NASAL THERMOCOUPLE

Objective. The aims of this study were to assess aspects of the respon se of a small thermocouple to temperature change, and to evaluate whet her such a thermocouple could be used intermittently to measure respir atory rate and timing by detecting the changes in nasal temperature oc curring with breathing. Methods. The study had three parts. First, thr ee similar, fast-responding thermocouples were immersed repeatedly in warm water. Second, the influence of atmospheric temperature on the si gnal of a thermocouple placed at different sites within the nasal orif ice was studied. The signals produced were continuously displayed and analyzed using a laptop computer to allow evaluation of the thermocoup les' response characteristics. Third, simultaneous respiratory recordi ngs were acquired using a nasal thermocouple and a nasal pneumotachogr aph in 12 teenaged subjects. The respiratory rate and the periods of t ime taken for inspiration (Ti) and expiration (Te) were calculated and compared. Results, The thermocouples' responses to the temperature ch anges associated with breathing and immersion into water were rapid an d consistent. The rate of the signals' decay, following the peak signa l marking expiration, was influenced by the atmospheric temperature. T he time constants of the thermocouples were similar (mean time constan t = 0.41 sec, standard deviation (SD) = 0.07). Optimal respiratory rec ordings were obtained, with least discomfort, when the thermocouple wa s positioned at 0 to 4 mm within the nasal orifice. In comparing the r espiratory recordings acquired simultaneously with a thermocouple and pneumotachograph, the respiratory rates were identical, and the Ti and Te values were similar (mean difference 0.04 sec (95% CI: -0.11 to 0. 21 sec) and -0.04 sec (95% CI: - 0.20 to 0.12 sec), respectively). Con clusions. Intermittent measurements of respiratory rate and timing usi ng a nasal thermocouple accurately reflected measurements obtained fro m nasal airflow using a pneumotachograph.