The invention relates to processing of physiological signal data in patient monitoring. In order to alleviate the problems caused by suppression waveforms in the analysis of physiological signal data, measurement data is derived from a segment of the time series of physiological signal data and valid measurement data is collected from the derived measurement data, thereby to form a set of valid measurement data. The collecting includes selecting measurement data that fulfills at least one predetermined threshold condition. Furthermore, at least a portion of the set of valid measurement data is supplied to a further processing stage when the amount of collected measurement data in the set is at least at a predetermined level. The deriving and collecting may be repeated for consecutive segments of the time series, in which case the supplying is performed for at least some of the consecutive segments of the time series.
