The intercostal-to-phrenic inhibitory reflex in the human fetus near term.
Human fetal breathing movements (FBM) differ from neonatal breathing in that they are predominantly paradoxical and are not present all the time. Respiratory pauses are common in the fetus while prolonged apneas are life-threatening in the neonate. In the latter they occur during state 2 (active sleep) when paradoxical breathing is more frequent. Then the inward movement of the thoracic wall causes spreading of the caudal ribs which may elicit an intercostal-to-phrenic inhibitory reflex (IPIR) leading to apnea. This is not the case in state 1 (quiet sleep). In the fetus similar sleep states, state 2F and 1F respectively, have been identified and we investigated if the IPIR is already present before birth and if so, if the response is different between 1F and 2F. In 21 healthy fetuses between 37 and 40 weeks, two real time scanners and a cardiotocograph were used to asses the fetal behavioural state. If FBM were present, the caudo-lateral part of the fetal thoracic wall was shortly compressed manually and the period that FBM ceased measured. During the same epoch moments of sham-stimulation, i.e. control periods without actual compression were also carried out. In 15 out of 16 fetuses with FBM in 1F, and in 19 out of 19 fetuses in 2F, compressions were immediately followed by an apnea. In contrast, moments of sham-stimulation never induced apnea, indicating that the IPIR is indeed present in both behavioural states.(ABSTRACT TRUNCATED AT 250 WORDS)
Tas
B A
BA
Department of Obstetrics and Gynaecology, University Hospital St-Radboud, Nijmegen, The Netherlands.
Nijhuis
J G
JG
Lucas
A J
AJ
Folgering
H T
HT
D005314:Embryonic and Fetal Development; D005260:Female; D006801:Humans; D007367:Intercostal Nerves / Q000502:physiology*; D010791:Phrenic Nerve / Q000502:physiology*; D011247:Pregnancy; D012018:Reflex / Q000502:physiology*; D012119:Respiration / Q000502:physiology*; D012894:Sleep Stages / Q000502:physiology; D013900:Thoracic Nerves / Q000502:physiology*; D014463:Ultrasonography