Abstract
In utero hypoxia may affect the development of the brain and result in altered respiratory responses postnatally. Using a barometric plethysmograph, we examined the effects of exposing pregnant guinea pigs to 200 ppm carbon monoxide (CO) for 10 h/d from d 23-25 of gestation until term(≈68 d) on the ventilatory responses of their 4-5-d-old neonates at rest, and during progressive asphyxia and steady state hypercapnia. Exposure to this concentration of CO produced significantly higher levels of carboxyhemoglobin(COHb) in maternal (8.53 ± 0.6% versus 0.25 ± 0.1%) and fetal blood (13.0 ± 0.4% versus 1.6 ± 0.1%) from CO-treated animals when compared with controls. Hematocrit was significantly higher in the CO-treated neonates (46.3 ± 1.0% versus 41.3± 0.9%) at 5-6 d of age, although no difference existed between the groups for COHb at this time. There was no difference between the groups for length of gestation, litter size, or birth weight, but CO-treated neonates were significantly smaller at 4 d of age (102.4 ± 3.7 g) compared with controls (132.0 ± 5.0 g). At 4-5 d of age there was no difference between the groups for either tidal volume (VT), respiratory frequency (f), or minute ventilation (VE) at rest, but during steady state hypercapnia (4 and 6% CO2) the CO-treated neonates had a significantly greater VT and VE (but not f) than did controls. During progressive asphyxia, CO-treated animals had a significantly greater VT than did controls from 1-8% CO2. There was a significant fall in f at 1 and 3% CO2 in CO-treated animals; however, this effect did not persist, resulting in a significantly increased VE from 3 to 8% CO2. The inspiratory flow rate(VT/expiratory time) was significantly increased in the CO-treated neonates during progressive asphyxia; this occurred in the absence of a difference in inspiratory time between the groups. These results indicate that prenatal exposure to CO increases CO2 sensitivity in 4-5-d-old guinea pigs. This may be due to developmental alterations in the areas of the brainstem responsible for respiratory control.
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Abbreviations
- COHb:
-
carboxyhemoglobin
- f:
-
respiratory frequency
- Hct:
-
hematocrit
- ppm:
-
parts per million
- TE:
-
expiratory time
- TI:
-
inspiratory time
- TTOTAL:
-
total cycle time between breaths
- TI/TTOTAL:
-
inspiratory duty cycle
- VE:
-
minute ventilation
- VT:
-
tidal volume
- VT/TI:
-
inspiratory flow rate
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Acknowledgements
The authors thank Phil Reynolds and Will Brenton for their assistance in designing and constructing the CO exposure chamber, Richard Carr for his assistance with data analysis, Dr. Sandra Rees and Mary Tolcos for providing neuroanatomical advice, and Prof. Richard Harding for reviewing this manuscript.
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Supported by a grant from the National Sudden Infant Death Council of Australia. H.P.M. was a Postgraduate Scholar of the Victorian Sudden Infant Death Research Foundation.
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McGregor, H., Westcott, K. & Walker, D. The Effect of Prenatal Exposure to Carbon Monoxide on Breathing and Growth of the Newborn Guinea Pig. Pediatr Res 43, 126–131 (1998). https://doi.org/10.1203/00006450-199801000-00019
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DOI: https://doi.org/10.1203/00006450-199801000-00019
