Responses of the autonomic nervous system (ANS) to moderate mental (calculating in mind) and respiratory (deep breathing) loading tests were studied in pregnant women with clinical signs of threatening preterm labor (PL, n = 52) and healthy pregnant women with uncomplicated gestation course (NP, n = 97). Total mean age and gestational term were respectively 24.9 ± 4.4 years and 20.9 ± 5.6 weeks. Measures of maternal heart rate variability (HRV) were used as of ANS sympathetic (S) and parasympathetic (PS) subsystems and also of the baroreflex activity (Bar) estimations. Differentiated changes of the vago-sympathetic index (as a ratio of HF to VLF spectral components of HRV) against respiratory probe were shown in subgroups of women having high rest activity of S (NP – decrease by 3 %, PL – increase by 62 %, p < 0.05) and Bar (NP – decrease by 10 %, PL – increase by 26 %, p < 0.01). The qualitatively same-type reactive changes under hyperventilation were found concerning the parameter of Detrended Fluctuation Analysis (DFA). It has been concluded that shifts of maternal vago-sympathetic ratio and cardiac non-linear dynamics against hyperventilation might be used as criterion for prediction of PL at early time of gestation.
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