Changes in oxygen and carbon dioxide in umbilical cord arterial blood before and after the first breath of a newborn to explore the mechanisms of respiratory regulation

Abstract

The fetus has no actual respiration, and the newborn begins to breathe after birth. We assume that the first breath dominantly generated by hypoxia. In this study, the changes and lowest limit of blood oxygen partial pressure of umbilical artery (PuaO2) after chemoreceptor were analyzed to explore the mechanism of neonatal spontaneous breathing.MethodsWith signed consent form by all fetal parents before birth, 14 newborns successfully completed the umbilical artery or vein catheterization and drawn blood according to the heartbeat. All blood samples analyzed by blood gas analyzer, calculated and analyzed the similarities and differences between umbilical vein(Puv) and umbilical artery(Pua).ResultsAlthough we completed 14 newborns, there were only 9 cases of umbilical artery samples and 8 cases of umbilical vein samples were collected. Only 3 cases collected both Pua and Puv blood samples at the same tim (see serial paper II). PuaO2 in gradually decreased with time (heartbeat frequency), until Pua contracted after spontaneous breathing produced about 8‐10 heartbeats, and then could not get enough blood samples. Only 3 newborns were able to take blood samples after spontaneous breathing for 8‐10 heartbeats, and PuaO2 jumped to 93.8,137.0 and 93.8 respectively The mean value of PuaO2 was 25.94±6.79 (range 18.04‐37.55)mmHg, the highest value was 32.41±11.97 (range 23.0‐61.0) mmHg, and the lowest value was 22.18±6.35 (range 14.0‐33.6)mmHg. Although PuvO2 decreased gradually with time (heartbeat) too, most of them also showed the tendency of alternately rising and falling with the regularity of mother’s respiration. The mean value of PuvO2 was 50.35±21.35 (range 32.56‐100.73)mmHg, the highest value was 90.34±8.44 (range 43.4‐153.0)mmHg, and the lowest value was 36.96±14.90 (range 24.8‐73.8)mmHg, although.ConclusionPuaO2 decreases gradually with time before spontaneous breathing after the delivered fetus as a newborn, and it induces the first inhalation to start spontaneous breathing when it reaches the threshold of triggering breathing.