The standard technique of using thoracic body impedance to measure respiration can be unreliable due to patient movement, poor electrode connections, and interference from other medical devices in close proximity.

Patient Respiration Measurement Using a 3-Axis Accelerometer

Patient Respiration Measurement Using a 3-Axis AccelerometerMounting an ADXL330 3-axis iMEMS® accelerometer on the back side of the ECG electrode clip, or on the back of the electrode itself, enables more reliable respiration measurement. (Another design option is to replace a strain gage on a chest strap with an accelerometer.) The ADXL330 detects the rise and fall of the chest due to respiration and adjusts for patient movement. It is immune from other medical equipment leakage currents and poor electrode connections that can create measurement interference. This situation is particularly a problem in environments where multiple pieces of medical equipment are hooked up simultaneously to the patient.

The ADXL330 is a small, low power (180 μA at 1.8 V) accelerometer complete with signal conditioned voltage outputs on a single monolithic IC. The product measures acceleration with a minimum full-scale range of ±3 g. For tilt sensing, the device measures the static acceleration of gravity. It also measures dynamic acceleration resulting from motion, shock, or vibration. The ADXL330 is available in a small, 4 mm × 4 mm × 1.45 mm, 16-lead,
plastic LFCSP.

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