Which monitor uses a chest belt with a coiled wire and is considered the most accurate for tidal volume?

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

Answer: (C)

Tidal volume is best estimated by tracking how much the chest and abdomen expand during breathing, using a system that detects inductance changes as the body wall moves. Respiratory inductance plethysmography uses a chest belt with a coiled wire (and often a second abdominal belt) to measure these changes in circumference. The inductance changes are proportional to the volume of air being moved, and having belts on both the chest and abdomen lets the monitor separate chest wall from abdominal motion, improving the accuracy of the tidal volume estimate. Because this method directly relates a physical expansion to lung volume, it provides a more reliable correlate to tidal volume than other options. Impedance pneumography relies on overall thoracic impedance and can be affected by electrode placement, motion, and electrical noise, making it less precise for volume. Thermistors detect inspired gas temperature and mainly indicate breaths or rate, not volume. Electrical impedance tomography maps ventilation distribution across the chest but is more complex and not the standard method for accurate tidal volume measurement in routine monitoring.