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Characterizing the breath‐to‐breath hypercapnic ventilatory response in neonatal rats
Author(s) -
Cummings Kevin James,
Frappell Peter B.
Publication year - 2008
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.22.1_supplement.955.9
Subject(s) - hyperoxia , peripheral , anesthesia , medicine , washout , hypercapnia , steady state (chemistry) , ventilation (architecture) , respiration , respiratory system , chemistry , lung , anatomy , physics , thermodynamics
The delay in the appearance of the central component of the ventilatory (V E ) response to CO 2 depends on the model. A 2–3 s delay has been demonstrated in anesthetised and decerebrate adult cats, versus a 10–20 s delay in awake lambs and dogs. Our aim was to characterise the peripheral and central components of the V E response to CO 2 in neonatal rats. A near‐square wave challenge of 8% CO 2 in both air and 90% O 2 was administered to P4 rats (n=10) for 1 min, with 2 min washout between randomized tests. The air‐CO 2 and hyperoxia‐CO 2 V E responses were measured with a pneumotach and the slope determined over each breath of the rising phase. Compared to CO 2 ‐hyperoxia, the V E response in CO 2 ‐air occurred about 4 breaths sooner, and the slope of the immediate V E on‐response to CO 2 in air was significantly greater than in hyperoxia (P=0.04). Steady‐state responses, determined by comparing the average responses in the last 60 breaths, were not different. These data suggest that for neonatal rats, the carotid bodies contribute significantly to the immediate V E response to CO 2 , but not to the steady‐state response, and that the central component is delayed only a few breaths relative to the peripheral component. For comparisons between models having different mass‐specific rates of metabolic CO 2 production, it may be more appropriate to express the V E delays in terms of breaths rather than absolute time.