BackgroundFetal heart rate variability (fHRV) of normal-to-normal (NN) beat intervals provides high-temporal resolution access to assess the functioning of the autonomic nervous system (ANS).AimTo determine critical periods of fetal autonomic maturation. The developmental pace is hypothesized to change with gestational age (GA).Study designProspective longitudinal observational study.Subjects60 healthy singleton fetuses were followed up by fetal magnetocardiographic heart rate monitoring 4–11 times (median 6) during the second half of gestation.Outcome measureFHRV parameters, accounting for differential aspects of the ANS, were studied applying linear mixed models over four predefined pregnancy segments of interest (SoI: <27; 27+0–31+0; 31+1–35+0; >35+1 weeks GA). Periods of fetal active sleep and quiescence were accounted for separately.ResultsSkewness of the NN interval distribution VLF/LF band power ratio and complexity describe a saturation function throughout the period of interest. A decreasing LF/HF ratio and an increase in pNN5 indicate a concurrent shift in sympathovagal balance. Fluctuation amplitude and parameters of short-term variability (RMSSD, HF band) mark a second acceleration towards term. In contrast, fetal quiescence is characterized by sequential, but low-margin transformations; ascending overall variability followed by an increase of complexity and superseded by fluctuation amplitude.ConclusionsAn increase in sympathetic activation, connected with by a higher ability of parasympathetic modulation and baseline stabilization, is reached during the transition from the late 2nd into the early 3rd trimester. Pattern characteristics indicating fetal well-being saturate at 35 weeks GA. Pronounced fetal breathing efforts near-term mirror in fHRV as respiratory sinus arrhythmia.

Acoustic or visual warning signals for workers in hazardous situations might fail under loud and/or lowvisibility work situations. A warning system should be developed that uses electrocutaneous stimulation through textile electrodes. Previous work investigated suitable stimulation parameters using TENS electrodes. The aim of this study was to compare TENS and textile cuff electrodes in terms of sensation thresholds, qualitative and spatial sensation. A study on 30 healthy volunteers (f=13, m=17) of mean age of 26.7 years was conducted applying bi-phasic rectangular current pulses to electrodes attached to the upper right arm. The study revealed that perception, attention and intolerance thresholds, qualitative and spatial perception are comparable indicating that future studies with the textile cuff electrodes can be generally based on the previous results with TENS electrodes.

Our long-term goal is the development of a wearable warning system that uses electrocutaneous stimulation. To find appropriate stimulation parameters and electrode configurations, we investigate perception amplitude thresholds and qualitative perceptions of electrocutaneous stimulation for varying pulse widths, electrode sizes, and electrode positions. The upper right arm was stimulated in 81 healthy volunteers with biphasic rectangular current pulses varying between 20 and $$2000\,\upmu \hbox {s}$$ 2000 μ s . We determined perception, attention, and intolerance thresholds and the corresponding qualitative perceptions for 8 electrode pairs distributed around the upper arm. For a pulse width of $$150\,\upmu \hbox {s}$$ 150 μ s , we find median values of 3.5, 6.9, and 13.8 mA for perception, attention, and intolerance thresholds, respectively. All thresholds decrease with increasing pulse width. Lateral electrode positions have higher intolerance thresholds than medial electrode positions, but perception and attention threshold are not significantly different across electrode positions. Electrode size between $$15 \times 15\,\hbox {mm}^{2}$$ 15 × 15 mm 2 and $$40\times 40\,\hbox {mm}^{2}$$ 40 × 40 mm 2 has no significant influence on the thresholds. Knocking is the prevailing perception for perception and attention thresholds while mostly muscle twitching, pinching, and stinging are reported at the intolerance threshold. Biphasic stimulation pulse widths between $$150\,\upmu \hbox {s}$$ 150 μ s and $$250\,\upmu \hbox {s}$$ 250 μ s are suitable for electric warning wearables. Within the given practical limits at the upper arm, electrode size, inter-electrode distance, and electrode position are flexible parameters of electric warning wearables. Our investigations provide the basis for electric warning wearables.

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