Measurement of human nasal ventilation using an oxygen cannula as a pitot tube

A pressure transducer connected to a nasal oxygen cannula detects fluctuations of about 0.1 kPa (1 cm H2O) during nose breathing because the prongs act as two one-sided pitot tubes in parallel. We describe a digital technique for converting this signal to flow and volume records without encumbering the head except during calibration. The signal could be calibrated or validated using flow measured with a face mask by intubation of the nostrils or using a respiratory inductive plethysmograph. In many subjects, the calibration gave satisfactory results for as long as 30 min, but in some, more frequent checks were needed. Changes in the relative airflow in the two nostrils may upset the results, but this can be corrected by recording and calibrating the pressure from each side separately. The meaurements can be made at high ventilation rates of when oxygen is flowing along the cannula or when gas is being sucked out for analysis.