Which apnea monitor uses a piezoelectric buckle around the chest that generates a voltage as the chest moves and does not require a battery?

• A. Respiratory inductance plethysmography
• B. Piezoelectric plethysmography
• C. Fiberoptic plethysmography
• D. Thermistors

Answer: (B)

Relying on chest wall movement to generate a signal without a separate power source is the hallmark of piezoelectric plethysmography. A buckle around the chest contains a piezoelectric crystal that is strained as the chest expands and contracts during breathing. That mechanical deformation produces a voltage from the crystal itself, so the sensor loop can provide a signal to the apnea monitor without needing its own battery. The other methods use different sensing principles: inductance plethysmography requires powered circuitry to detect changes in inductance; fiberoptic plethysmography depends on light transmission and detection with powered components; thermistors measure temperature rather than mechanical chest movement.