Statistical properties of simultaneously recorded fluctuations in pupil diameter and heart rate

Describes the relationship between fluctuations in pupil diameter (PD) and heart rate (HR). Simultaneous recording of PD, HR and instantaneous lung volume (ILV) has been made for ten normal healthy subjects. The spectral analysis showed that the cross phase spectrum between PD and HR fluctuations had a constant value -π/2 over fairly long frequency range (0.1-0.4 Hz). In addition to this, the authors have observed that the power spectrum of the PD fluctuations showed 1/f³ spectral pattern in the frequency range while the power spectrum of HR variability showed 1/f spectral pattern. This findings implies that HR variability is associated with the derivative of PD fluctuations and may be important for the characterization of PD fluctuations as an index to measure autonomic nervous activity