A method for determining respiration information, the method comprising: receiving a photoplethysmograph signal; identifying, using processing equipment, a plurality of time domain fiducial points in the PPG signal; defining, using the processing equipment, a plurality of fiducial-defined portions of the PPG signal between consecutive ones of the fiducial points; calculating, using the processing equipment, a plurality of morphology metric values, wherein each morphology metric value is associated with one of the fiducial-defined portions; generating, using the processing equipment, a morphology metric signal based at least in part on the plurality of morphology metric values; and determining, using the processing equipment, a respiration rate based at least in part on the morphology metric signal, characterized in that: either the morphology metric is a kurtosis metric of the first derivative of the PPG signal and each morphology metric value is calculated as the kurtosis of the first derivative of the associated fiducial-defined portion of the PPG signal, or the morphology metric is a delta of the second-derivative metric and each morphology metric value is calculated by subtracting the second derivative of the PPG signal at the later of the consecutive fiducial points of the associated fiducial-defined portion from the second derivative of the PPG signal at the earlier of the consecutive fiducial points of the associated fiducial-defined portion, respectively. receiving a photoplethysmograph signal; identifying, using processing equipment, a plurality of time domain fiducial points in the PPG signal; defining, using the processing equipment, a plurality of fiducial-defined portions of the PPG signal between consecutive ones of the fiducial points; calculating, using the processing equipment, a plurality of morphology metric values, wherein each morphology metric value is associated with one of the fiducial-defined portions; generating, using the processing equipment, a morphology metric signal based at least in part on the plurality of morphology metric values; and determining, using the processing equipment, a respiration rate based at least in part on the morphology metric signal, characterized in that: either the morphology metric is a kurtosis metric of the first derivative of the PPG signal and each morphology metric value is calculated as the kurtosis of the first derivative of the associated fiducial-defined portion of the PPG signal, or the morphology metric is a delta of the second-derivative metric and each morphology metric value is calculated by subtracting the second derivative of the PPG signal at the later of the consecutive fiducial points of the associated fiducial-defined portion from the second derivative of the PPG signal at the earlier of the consecutive fiducial points of the associated fiducial-defined portion, respectively. either the morphology metric is a kurtosis metric of the first derivative of the PPG signal and each morphology metric value is calculated as the kurtosis of the first derivative of the associated fiducial-defined portion of the PPG signal, or the morphology metric is a delta of the second-derivative metric and each morphology metric value is calculated by subtracting the second derivative of the PPG signal at the later of the consecutive fiducial points of the associated fiducial-defined portion from the second derivative of the PPG signal at the earlier of the consecutive fiducial points of the associated fiducial-defined portion, respectively.