Which device detects airflow by sensing temperature changes at the nose and mouth, with accuracy affected by ambient temperature or skin contact?

• A. Thermistors
• B. Piezoelectric plethysmography
• C. Impedance pneumography
• D. Electrical impedance tomography

Answer: (A)

Temperature-based airflow sensing near the nose and mouth uses a thermistor to detect breaths. A small temperature sensor placed at the airway experiences cooling when air is inspired and warming when air is exhaled. The thermistor’s resistance changes with temperature, producing a signal that tracks the breathing cycle.

Accuracy depends on ambient conditions and skin contact because the sensor’s reading is influenced by external temperature and heat transfer from the body. If the surroundings are very cold or warm, the baseline temperature around the sensor shifts, making it harder to discern the breath-related temperature changes. Similarly, if the sensor is in contact with skin, body heat can alter the sensor’s temperature independently of airflow, reducing fidelity of the detected breath signal.

Other methods detect breathing through chest wall movement or changes in electrical impedance, not by airway temperature, so they don’t rely on temperature differences between inspired and expired air. This temperature-based approach is the reason thermistors fit the description.