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Hypercapnic stimulation of respiratory activity in unanesthetized fetal sheep in utero. 1981

G Bowes, and M H Wilkinson, and M Dowling, and B C Ritchie, and V Brodecky, and J E Maloney

Respiratory responses to hypercapnia were studied in seven chronic in utero fetal lambs between 105 and 138 days' gestation (16 expts). Fetal arterial CO2 tension was raised (mean increase 9.9 Torr) by altering maternal inspired gas concentrations. Diaphragmatic electromyogram (EMG) was recorded as the index of respiratory activity. Electrocortical and electroocular activity (3 fetuses) were monitored in an attempt to define sleep state. Average respiratory rate increased (90%) and fetal apnea decreased (60%) during hypercapnia. Mean respiratory rate during "on" periods (greater than 6 EMG bursts/min) increased significantly during hypercapnia throughout the gestational epoch studied. Mean duration of the inspiratory time (TI) showed no significant change. Variability in both rate and TI decreased in response to CO2 at all gestations. Integrated EMG activity per burst divided by TI increased significantly at all gestations; however, no gestational increase in responsiveness to CO2 was seen. Sleep states were not able to be consistently identified, and a quantifiable electrocortical response to CO2 was not observed. These results indicate a relatively early functional maturation of fetal respiratory responses to CO2.

UI MeSH Term Description Entries
D011247 Pregnancy The status during which female mammals carry their developing young (EMBRYOS or FETUSES) in utero before birth, beginning from FERTILIZATION to BIRTH. Gestation,Pregnancies
D012119 Respiration The act of breathing with the LUNGS, consisting of INHALATION, or the taking into the lungs of the ambient air, and of EXHALATION, or the expelling of the modified air which contains more CARBON DIOXIDE than the air taken in (Blakiston's Gould Medical Dictionary, 4th ed.). This does not include tissue respiration ( Breathing
D002245 Carbon Dioxide A colorless, odorless gas that can be formed by the body and is necessary for the respiration cycle of plants and animals. Carbonic Anhydride,Anhydride, Carbonic,Dioxide, Carbon
D002540 Cerebral Cortex The thin layer of GRAY MATTER on the surface of the CEREBRAL HEMISPHERES that develops from the TELENCEPHALON and folds into gyri and sulci. It reaches its highest development in humans and is responsible for intellectual faculties and higher mental functions. Allocortex,Archipallium,Cortex Cerebri,Cortical Plate,Paleocortex,Periallocortex,Allocortices,Archipalliums,Cerebral Cortices,Cortex Cerebrus,Cortex, Cerebral,Cortical Plates,Paleocortices,Periallocortices,Plate, Cortical
D003964 Diaphragm The musculofibrous partition that separates the THORACIC CAVITY from the ABDOMINAL CAVITY. Contraction of the diaphragm increases the volume of the thoracic cavity aiding INHALATION. Respiratory Diaphragm,Diaphragm, Respiratory,Diaphragms,Diaphragms, Respiratory,Respiratory Diaphragms
D004576 Electromyography Recording of the changes in electric potential of muscle by means of surface or needle electrodes. Electromyogram,Surface Electromyography,Electromyograms,Electromyographies,Electromyographies, Surface,Electromyography, Surface,Surface Electromyographies
D005260 Female Females
D005333 Fetus The unborn young of a viviparous mammal, in the postembryonic period, after the major structures have been outlined. In humans, the unborn young from the end of the eighth week after CONCEPTION until BIRTH, as distinguished from the earlier EMBRYO, MAMMALIAN. Fetal Structures,Fetal Tissue,Fetuses,Mummified Fetus,Retained Fetus,Fetal Structure,Fetal Tissues,Fetus, Mummified,Fetus, Retained,Structure, Fetal,Structures, Fetal,Tissue, Fetal,Tissues, Fetal
D005865 Gestational Age The age of the conceptus, beginning from the time of FERTILIZATION. In clinical obstetrics, the gestational age is often estimated from the onset of the last MENSTRUATION which is about 2 weeks before OVULATION and fertilization. It is also estimated to begin from fertilization, estrus, coitus, or artificial insemination. Embryologic Age,Fetal Maturity, Chronologic,Chronologic Fetal Maturity,Fetal Age,Maturity, Chronologic Fetal,Age, Embryologic,Age, Fetal,Age, Gestational,Ages, Embryologic,Ages, Fetal,Ages, Gestational,Embryologic Ages,Fetal Ages,Gestational Ages
D006935 Hypercapnia A clinical manifestation of abnormal increase in the amount of carbon dioxide in arterial blood.

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