Response to music on the nonlinear dynamics of human fetal heart rate fluctuations: A recurrence plot analysis

Music has been shown to influence physiological functions in humans, but its effects on fetal heart rate variability (fHRV) are not well understood. This study aimed to assess the response of classical music exposure on the nonlinear behavior of fetal heart rate fluctuations in fetuses between 32 and 40 weeks of gestation using recurrence quantification analysis (RQA). We collected R-R time series from 37 fetuses in the third trimester following a study into four stages: PRE (baseline), STIM1 (first musical piece), STIM2 (second musical piece), and POST (post-exposure). The fetal R-R time series from each stage were evaluated using RQA indices such as determinism (DET), average diagonal line length (L), maximum line length (LMAX), entropy (ENTR), and trapping time (TT), as well as conventional linear indices like SDRR (standard deviation of R-R intervals). Results revealed three main points. First, there was an increase in DET, L, LMAX, and TT, with a decrease in ENTR in the POST stage compared to PRE, indicating more regular and predictable patterns. Second, the STIM2 stage enhanced the predictability and stability of cardiac dynamics compared to PRE, as indicated by L, LMAX, and TT. Third, no significant changes were observed in conventional indices, except for an increase in SDRR in the POST stage compared to STIM1. These findings suggest a reduction in complexity and nonlinear behavior of fHRV patterns after musical stimulus. The increase in SDRR during the POST stage appears to coincide with fetal movements, as indicated by the number of fetal accelerations found.