TenVoorde B J, Faes J C, Rompelman O
Vrije Universiteit, AZVU-Poli, Amsterdam, The Netherlands.
Med Biol Eng Comput. 1994 Jan;32(1):63-70. doi: 10.1007/BF02512480.
Beat-to-beat cardiovascular signals, e.g. a series of systolic pressure values, can be considered as time series which are pulse amplitude modulated (PAM) and pulse frequency modulated (PFM). The latter process, due to variations in heart rate, causes the series to become non-uniformly spaced in time. If PAM is to be quantified by spectral analysis, the influence of PFM must be known. An analytical expression is therefore derived for the spectrum of sinusoids which are sampled according to the output event series of a linear integral pulse frequency modulator (IPFM). We conclude that two spectral components arise at the difference and sum of the PFM and PAM frequencies, fp +/- fx, with amplitudes proportional to the PFM modulation depth. These components appear as a DC component and as a first harmonic if both modulating frequencies are equal. In addition, a cluster of spectral components appears around the mean pulse frequency fo (i.e. mean heart rate), at frequencies fo-nfp +/- fx, which may leak into the signal band. From these theoretical considerations, we conclude that the amplitude spectrum of a sinusoidally varying systolic blood pressure series can contain up to 20-30% spurious components, owing to the heart rate modulation process.
逐搏心血管信号，例如一系列收缩压值，可被视为经脉冲幅度调制（PAM）和脉冲频率调制（PFM）的时间序列。由于心率变化，后一过程会使该序列在时间上变得非均匀间隔。若要通过频谱分析对PAM进行量化，则必须了解PFM的影响。因此，针对根据线性积分脉冲频率调制器（IPFM）的输出事件序列进行采样的正弦波频谱，推导出了一个解析表达式。我们得出结论，在PFM和PAM频率之差与和处，即fp +/- fx，会出现两个频谱分量，其幅度与PFM调制深度成正比。如果两个调制频率相等，这些分量会表现为直流分量和一次谐波。此外，在平均脉冲频率fo（即平均心率）周围，在频率fo - nfp +/- fx处会出现一组频谱分量，它们可能会泄漏到信号频段。基于这些理论考量，我们得出结论，由于心率调制过程，正弦变化的收缩压序列的幅度频谱可能包含高达20% - 30%的虚假分量。
