Prolonged Hypoxemia Enhances and Acute Hypoxemia Attenuates Laryngeal Reflex Apnea in Young Lambs

Abstract

ABSTRACT. To determine the influence of an altered carotid body function on the laryngeal chemoreflex (LCR) response, reflex apnea was induced by laryngeal water stimulation during normoxia or acute hypoxia in unanesthetized awake lambs in which the ventilatory response to acute hypoxia was attenuated by prolonged postnatal hypoxemia. Prolonged hypoxemia (H) was induced in seven lambs for 12 d after birth through exposure to 0.10 fraction of inspired oxygen. Five control lambs were kept in 0.21 fraction of inspired oxygen. Studies were performed repeatedly during the first 7 wk after birth. The ventilatory response to LCR stimulation, expressed as a percent decrease in minute ventilation, was tested in 0.21, 0.14, and 0.10 fraction of inspired oxygen. H after birth resulted in a markedly increased inhibition of ventilation in response to LCR stimulation and postponed the age-related decrease in LCR response. A potential failure to recover from apnea occurred only in the H lambs, and in these lambs there was a significantly greater requirement for mechanical ventilation after LCR stimulation. Acute hypoxemia preceding LCR stimulation significantly attenuated the ventilatory response in both control and H lambs, with a stronger effect in the H lambs. There was no difference between the two groups in heart rate response to LCR stimulation. Acute hypoxemia significantly augmented reflex bradycardia in the H lambs. These results show that there is a relationship between H immediately after birthwhich is known to delay resetting of carotid chemoreceptors-and augmented ventilatory inhibition in response to LCR stimulation. They do not confirm the theory that acute hypoxia reinforces reflex apnea. (Pediatr Res 34: [813][814][815][816][817][818][819][820]1993)

Impaired Cardiorespiratory Recovery after Laryngeal Stimulation in Nicotine-Exposed Young Lambs

“…Although not apparent in the C group in this study, it has previously been shown that the magnitude of cardiorespiratory inhibition in response to LCR stimulation is strongest in the newborn period and decreases thereafter (8,9,33). Both these factors would imply that the most marked effects of nicotine are to be seen early.…”

“…Sladek et al (8), Grogaard et al (9), and Grogaard and Sundell (13) could demonstrate that surgical denervation of the CB chemoreceptors resulted in extreme prolongation of LCR-induced apnea, whereas stimulation of CB chemoreceptors by hypoxemia or ␤-adrenergic agonists shortened LCR-induced apnea and the postapneic respiratory depression. We therefore compared the LCR response in room air with the response during CB chemoreceptor stimulation with mild hypoxia.…”

“…The lambs were instrumented with placement of a tracheal window and arterial and venous catheters at the age of 1-3 d (7,8). When not studied, tracheal patency was reestablished with a piece of endotracheal tube (Portex, Keene, NH, U.S.A.).…”

“…We used chronically instrumented, unanesthetized lambs, an animal model used in our laboratory in a number of studies addressing the mechanisms of hypoxic defense, LCR response, and effects of nicotine (7)(8)(9).…”

Laryngeal reflex apnea in neonates: Effects of CO2 and the complex influence of hypoxia

“…Here, too, the results with respect to hypoxia are complex: the duration of apnea with intralaryngeal water instillation has generally been shortened by acute hypoxia (Sladek et al,1993; Milerad and Sundell, 1999; Sundell et al, 2003), although not significantly at all ages. As pointed out by Milerad and Sundell (1999), the apneic response to laryngeal stimulation during acute hypoxia may be attenuated by carotid chemoreceptor mediated ventilatory drive, but enhanced by the attendant hypocapnia.…”