An apparatus and method for detecting phrenic nerve stimulation (PNS) including computing a power spectral density (PSD) of spatial data of a sensor determining two spectral magnitudes from the PSD computing a ratio of the two spectral magnitudes and comparing the ratio to a threshold to detect PNS. In one example, detecting PNS includes computing a PSD of spatial data of an externally placed sensor determining a diaphragmatic spectral magnitude and a respiratory motion spectral magnitude from the PSD and computing a ratio of the diaphragmatic spectral magnitude to the respiratory motion spectral magnitude to detect PNS. In one example, detecting PNS includes computing an oscillation amplitude of spatial data of a sensor computing a baseline wander amplitude of the spatial data of the sensor computing a ratio of the oscillation amplitude to the baseline wander amplitude and comparing the ratio to a threshold to detect PNS.
