Low-frequency respiratory rhythms in infants during the first six months of life

Piezoelectric vibrator-stimulated potential and heart rate accelerations detected from the fetus

OBJECTIVES

The fetus is well known to have a substantial capacity for sound recognition in the uterine environment. The aim of this study was to develop a sound stimulus system equipped with a piezoelectric vibrator (PV), record the PV-stimulated potential (PVSP) of the fetus and monitor changes of the fetal heart rate (FHR) under PV stimulation.

METHODS

The relationship between the input voltage applied to a piezoelectric vibrator and the sound pressure generated in the uterus was calibrated based on a model of the maternal abdomen. Fourteen fetuses for the measurement of the PVSP and 22 fetuses for the measurement of the heart rate changes from low-risk pregnant women were recruited.

RESULTS

The PVSP responses were obtained in 9 out of 14 fetuses. All the tested fetuses accelerated the FHR after the 2 kHz tone stimulation at 70 dB intensity generated by PV from 32 to 37 weeks gestational age.

CONCLUSIONS

Using a newly developed sound stimulus system equipped with PV, the electric responses of a fetus recorded from electrodes placed on the mother's abdomen may be closely related to the auditory evoked response. Significant accelerations of FHR were objectively, accurately and readily obtained after the sound stimulation.

Basic values for heart and respiratory rates during different sleep stages in healthy infants

The aim of this study was to systematically register data for respiratory and heart rates (RR and HR, respectively) during different sleep stages [active (AS, i.e., rapid eye movement) and quiet (QS, i.e., non-rapid eye movement) sleep] and age in a large number of healthy infants (277) during the first year of life to simplify polysomnography. The reference values in this age group differ significantly between the number of patients and age at time of investigation. According to strict inclusion and exclusion criteria, the measurement of polysomnography included HR (beats per minute, or bpm), RR (breaths per minute, or breaths/min), brain waves, SO2, sound, and video. Data recording and evaluation occurred via Alice 3®/3.5®(Respironics®), classification into AS and QS sleep according to maturity. For RR, the 5th-95th percentiles during AS decreased from 25.8-47.7 breaths/min (1st month) to 17.8-27.7 breaths/min (>9 months). During QS, RR ranged from 27.4-51.5 breaths/min (1st month) to 17.8-29.2 breaths/min (>9 months). HR decreased during AS from 118.3-150.6 bpm (1st month) to 100.9-126.4 bpm (>9 months). During QS, HR decreased from 116.0-149.9 bpm (1st month) to 93.7-119.8 bpm (>9 months). The mean HR and RR significantly decreased with age in both sleep stages (p<0.05). The mean HR is significantly lower during QS compared with AS (p<0.05). Our data may serve as basic values for HR and RR in different sleep stages during the first year of life.