Responses of the autonomic nervous system (ANS) to short-term functional loads (calculation in mind, deep breathing) were studied in healthy pregnant (P) and non-pregnant (NP) age matched women (average 20.4 + 1.4 yrs). As markers of ANS were used statistical, spectral and non-linear measures of heart rate variability (HRV). At rest increased mean heart rate was recorded in P (90.5 + 11.4 beat per min) in comparison with NP (77.6 + 8.0 beats permin, p < 0.05) causing relatively lower HRV values in pregnant women. Most prominent distinction between P and NP groups consisted in changes of cardiac interval variation range (Var) and of LF HRV spectral component against deep breathing (P: Var decrease -6 %, NP: Var increase +36 %, p < 0.05; P: LF increase: +4 %, NP: LF increase +37 %, p < 0.01). These changes were observed in subgroups of women with initially predominant vagotonic type of neuroautonomic control. It has been concluded that normal pregnancy is characterized by paradoxically attenuated barorefl ex responsiveness despite of higher parasympathetic tone in part (approximately 1/3) of women.
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