Postnatal maturation of respiration in intact and carotid body-chemodenervated lambs

Abstract

The contribution of the carotid body chemoreceptor to postnatal maturation of breathing was evaluated in lambs from 7 to 70 days of age. The study was conducted by comparing the eupneic ventilation and resting pneumograms in intact conscious lambs with those of lambs that were carotid body chemodenervated (CBD) at birth. In comparison to the 1-wk-old intact lambs, the CBD lambs had significant decreases in minute ventilation (VE, 313 vs. 517 ml/kg), tidal volume (VT, 7.2 vs. 10.5 ml/kg), respiratory rate (f, 44 vs. 51 breaths/min), and occlusion pressure (P0.1, 2.8 vs. 7.2 cmH2O). Arterial PO2's were 59 vs. 75 Torr (P less than 0.05) and arterial PCO2's 47 vs. 36 Torr (P less than 0.05), respectively, in CBD and intact lambs. In intact lambs from 7 to 70 days, resting VE decreased progressively from 517 to 274 ml/kg (P less than 0.01) due to a fall in VT, mean inspiratory flow (VT/TI), and f, whereas the ratio of inspiratory time to total breath duration remained constant. P0.1 decreased from 7.2 to 3.9 cmH2O from 7 to 42 days. In contrast the CBD lambs experienced only minimal changes in VE, VT, VT/TI, and f during the same period. VE only decreased from 313 to 218 and P0.1 from 2.8 to 2.4 cmH2O. In contrast to that of intact lambs the resting pneumogram of CBD lambs remained relatively fixed from 7 to 70 days. Three CBD lambs died unexpectedly, without apparent cause, in the 4th and 5th wk of life.(ABSTRACT TRUNCATED AT 250 WORDS)

The Influence of Acute Hypoxia and Carotid Body Denervation on Thermoregulation During Non‐Rapid Eye Movement Sleep in the Developing Lamb

“…Electrodes for recording ECG were implanted into all lambs, as well as electrodes for EEG into nuchal and thyroarytenoid muscles of six and nine lambs, respectively. When the lambs were 15 days old both carotid sinus nerves were sectioned as described by Bureau et al (1985). A 2 ml intra-muscular antibiotic injection (Streptopen; Glaxo Laboratories Ltd) was administered on the day of surgery and for 2 days post-operatively.…”

“…Control of thermoregulation following CBD CBD at 2 weeks of age results in a decrease in basal ventilation, thereby reducing Pa,Oµ and increasing Pa,COµ and resulting in a greatly reduced respiratory response to hypoxia (Bureau et al 1985). There was a fall in basal metabolic rate and altered ability of the lamb to respond to a thermoregulatory challenge, particularly when exposed to a further hypoxic challenge.…”

“…0·2-0·6 nÒ), as was a lamb which died at 24 days of age. These symptoms, resulting from the effects of CBD during development, suggest that failure of metabolic function may account for some of the lamb deaths observed following CBD, which previously were presumed to have been primarily of respiratory origin (Bureau et al 1985). However, homeostatic regulation during development involves an integration of temperature and metabolic regulation linked to thyroid function as well as respiratory control.…”

“…Dysfunction of any of these systems directly impinges on the others and a failure of their integration could cause death. The time course of such events is both critical and informative, in that death occurred between 19 and 24 days of age, irrespective of whether lambs were denervated at 2 weeks or 2 days of postnatal age (Bureau et al 1985). It has been shown that newborn lambs will establish effective breathing after birth following antenatal CBD and that the cool of the extra-uterine environment is an important thermal stimulus to breathing (Harned et al 1968;Harned & Ferreio, 1973).…”

“…The extent to which postnatal lambs are compromised by chronic hypoxia, as observed following carotid body denervation (CBD), appears to be directly linked to postnatal age (Bureau et al 1985). However, CBD only results in death after the third week of postnatal life and not in the neonatal period.…”