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Intrathoracic pressures in fetal sheep
Journal of Developmental Physiology
|August 1, 1982
Summary
Fetal sheep studies reveal positive tracheal pressure during apnea, not caused by breathing effort. This pressure is likely due to continuous lung fluid production and outflow resistance.
Area of Science:
- Physiology
- Fetal Development
- Respiratory System
Background:
- Intrathoracic pressure dynamics are crucial for understanding fetal respiratory function.
- Previous research has not fully elucidated the mechanisms behind positive tracheal pressure in the fetal state.
Purpose of the Study:
- To investigate intrathoracic pressures in late-gestation sheep fetuses.
- To determine the source and characteristics of positive tracheal pressure during fetal apnea.
Main Methods:
- Measurements of tracheal, intrapleural, and amniotic cavity pressures using catheters and manometers in sheep fetuses (122-145 days gestation).
- Validation of pressure measurements with differential water manometry and pressure transducers.
- Assessment of the effect of tubocurarine hydrochloride on pressure dynamics and diaphragmatic activity.
Main Results:
- During apnea, tracheal pressure exceeded intrapleural pressure by 2.1-2.6 torr.
- This positive tracheal pressure was primarily due to intratracheal pressure (1.8-2.0 torr), with a minor negative intrapleural pressure component (0.2-0.7 torr).
- Muscle paralysis with tubocurarine abolished breathing efforts but did not reduce the positive tracheal pressure.
Conclusions:
- The positive tracheal pressure observed in fetal sheep during apnea is not generated by respiratory muscle activity.
- It is hypothesized that continuous fetal lung fluid production and resistance to its outflow maintain this positive pressure.
- These findings offer insights into fetal lung development and fluid dynamics.