Possible Physiological Role of the Cushing Response During Parturition
The Cushing response to elevated intracranial pressure (ICP) is often regarded as a defence mechanism of last resort when other mechanisms fail to maintain cerebral perfusion pressure. However, one physiological stress in which ICP may be commonly elevated is parturition. The fetus ordinarily is buoyed in amniotic fluid and uterine contractions produce equivalent increases in arterial pressure and ICP. However, once the head is engaged in the birth canal and begins to dilate the cervix, pressure on the skull is considerable. In the human fetus with its large, compliant skull, pressure on the equator of the skull may exceed amniotic fluid pressure by 50mm Hg or more (Lindgren 1960), and this pressure appears to be nearly fully transmitted intracranially (Schwarcz et al. 1969). Because fetal arterial pressure is only 40–50mm Hg greater than amniotic fluid pressure, cerebral ischemia might occur during intense labor. Even in non-human species with smaller skulls or closed fontanelles, the bone sutures usually are not fused and transient periods of elevated ICP are likely.
KeywordsArterial Pressure Cerebral Blood Flow Cerebral Perfusion Pressure Uterine Contraction Skin Blood Flow
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