Which apnea monitor modality measures respiratory rate with chest electrodes and cannot detect obstructive apnea?

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

Answer: (B)

The main idea is that this modality tracks breathing by sensing chest wall movement, not airflow. Chest impedance changes as the chest expands and contracts with each breath, so the device derives respiratory rate from these impedance oscillations. Because it reflects how the chest moves (effort) rather than whether air is actually moving in and out, it will still show breathing during obstructive apnea, when the airway is blocked but chest muscles continue to work. In obstructive apnea, airflow ceases but respiratory effort often persists, so impedance-based monitoring may miss the lack of airflow. Central apnea, by contrast, involves no respiratory effort, and would be detected as absent impedance changes. To truly detect obstructive events, airflow or CO2 monitoring is needed.