Differentiation between human fetal breathing patterns by investigation of breathing-related tracheal fluid flow velocity using Doppler sonography

Abstract

We report our results from the analysis of Doppler measurements of breathing-related fluid flow velocity waveforms in the trachea in human fetuses. Our aim was to determine whether, using the proposed method, reproducible patterns can be recognized over the latter half of gestation. Breathing-related tracheal fluid flow velocity of 47 normal fetuses at 20-39 weeks' gestation were analysed. Colour Doppler was used to document 'streaming' of fluid in the trachea, followed by spectral Doppler to record flow velocity waveforms. More than 40 (median 94; range 42-725) continuous breathing cycles (inspiration+expiration) were obtained in each case. Although breathing-related fetal tracheal fluid flow waveforms were found to be highly variable, we were able to distinguish by visual analysis between a regular and an irregular pattern. Among the regular patterns, we further differentiate between a regular symmetric (sinusoidal type) and a regular asymmetric (deep inspiration with expiratory flow retardation) pattern. The regular pattern occurred consistently in all age groups studied and there were no significant (p<0.05) differences in the occurrence rate of the regular symmetric and asymmetric pattern. The incidence of the regular pattern increased significantly (p<0.05) from 11.74+/-3.38% (mean +/- SEM) at 24-27 weeks to 20.72+/-1.75% at 28-31 weeks of gestation and remained constant thereafter. This study shows that the proposed method can provide detailed information on breathing-related tracheal fluid flow velocity as early as 20 weeks of gestation. The information that a regular symmetric pattern was observed throughout the second half of gestation is important. Hence, a higher standardization of on-going fetal breathing movements studies may be achieved by measuring breathing-related tracheal fluid flow velocity waveform parameters only during this pattern.

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“…Previous Doppler ultrasound‐based studies have investigated fetal breathing movements indirectly, by extrapolation of parameters23, 24. In our study, however, we investigated fetal breathing movements through direct measurements of the musculoskeletal components of fetal breathing and used an algorithm to determine the parameters of each breathing movement.…”

Does fetal tracheal fluid flow during fetal breathing movements change before the onset of labour?

“…The approach, which we have previously termed pulmonary Doppler ultrasonography 13 is a major advance over other modalities to assess fetal breathing movements for the following reasons. First, it is sensitive enough to allow a differentiation between distinct fetal breathing patterns as early as the second trimester 14 . Hence, standardised sets of measurements can be obtained by considering exclusively the regular symmetric pattern and overcome bias due to the great variability of fetal breathing movements.…”

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“…As a result, the chest wall collapses as the diaphragm contracts during individual FBMs, resulting in little if any change in lung volume [24]. This is particularly evident in fetal sheep, but studies in human fetuses have reported the movement of up to 2mls of liquid with each breath; measured in the trachea and at the nose using ultrasonography [25,26]. The reason for the discrepancy between humans and sheep is unknown, but may relate to a slower breathing movement rate in humans [27].…”