Multifractality and scale invariance in human heartbeat dynamics

Area of Science:

• Physiology
• Complex Systems Analysis
• Nonlinear Dynamics

Background:

• Human heart rate (HR) displays complex fluctuations, with evidence of multifractality in healthy states.
• Multifractality in HR variability may manifest as scale-dependent probability density functions (PDFs) of interbeat interval increments.
• Previous studies reported scale invariance in detrended HR increments, but the precise nature requires clarification.

Purpose of the Study:

• To clarify the nature of scale invariance in detrended human heart rate fluctuations.
• To differentiate between scale invariance in interbeat interval increments versus sums of detrended intervals.
• To investigate the general applicability of observed dynamics in both healthy and pathological human heartbeats.

Main Methods:

• Analysis of probability density functions (PDFs) of detrended interbeat interval increments.
• Examination of the scale or n-dependence of these PDFs.
• Comparison of dynamics in healthy and pathological human heart rate data.

Main Results:

• Scale invariance is exhibited by the PDFs of the sum of n detrended interbeat intervals, not the increments themselves.
• Detrended healthy interbeat interval increments show scale or n-dependence, consistent with multifractality.
• The n-independence of the PDFs of summed detrended intervals is a universal characteristic of human heartbeat dynamics.

Conclusions:

• The reported scale invariance in detrended HR dynamics pertains to the sums of detrended interbeat intervals.
• Human heartbeat dynamics exhibit multifractality, characterized by scale-dependent PDFs of increments.
• The scale invariance of summed detrended intervals is a robust feature across healthy and pathological human heart rate fluctuations.