Hyperbilirubinemia diminishes respiratory drive in a rat pup model.

Although apnea is common in premature babies, there is a paucity of information concerning the pathophysiologic basis of these episodes and their relationship to other perinatal conditions such as hyperbilirubinemia. Unconjugated hyperbilirubinemia in premature infants, even in moderately high levels, may cause encephalopathy affecting brainstem functions and has been linked to increased incidence of apnea in these infants. Thus, there is a need to clarify mechanisms by which bilirubin may alter respiratory control and induce apnea of prematurity. In this study, bilirubin or placebo was infused i.v. in 9-d-old rat pups (n = 36). Serum hyperbilirubinemia peaked in the first hours after bilirubin infusion. Twenty-four hours after bilirubin infusion, respiration was recorded by plethysmography at rest and under hypercapnic and hypoxic conditions. In treated pups, minute ventilation in room air was significantly reduced, hyperventilatory response to CO2 was blunted, and hypoxic ventilatory depression was increased, compared with placebo-injected rat pups. Brainstem bilirubin deposition and immunoreactivity to bilirubin was detected in the brainstem on histologic analysis. We speculate that high serum bilirubin levels may cause prolonged inhibition of brainstem autonomic function and that this could underlie the exacerbation of apnea noted in premature babies who have experienced jaundice.

Ventilatory mechanics and the effects of water depth on breathing pattern in the aquatic caecilian Typhlonectes natans.

The breathing pattern in the aquatic caecilian Typhlonectes natans was investigated by recording airflow via a pneumotachograph under unrestrained normal physiological conditions. Ventilatory mechanics were assessed using airflow and pressure measurements from the buccal cavity and trachea. The breathing pattern consisted of an expiratory phase followed by a series of 10-15 small buccal pumps to inflate the lung, succeeded by a long non-ventilatory period. T. natans separate the expiratory and inspiratory gases in the buccal cavity and take several inspiratory pumps, distinguishing their breathing pattern from that of sarcopterygians. Hydrostatic pressure assisted exhalation. The tracheal pressure was greater than the water pressure at that depth, suggesting that pleuroperitoneal pressure as well as axial or pulmonary smooth muscles may have contributed to the process of exhalation. The frequency of lung ventilation was 6.33+/-0.84 breaths h(-)(1), and ventilation occurred via the nares. Compared with other amphibians, this low ventilatory frequency suggests that T. natans may have acquired very efficient pulmonary respiration as an adaptation for survival in their seasonally fluctuating natural habitat. Their respiratory pathway is quite unique, with the trachea separated into anterior, central and posterior regions. The anterior region serves as an air channel, the central region is attached to the tracheal lung, and the posterior region consists of a bifurcated air channel leading to the left and right posterior lungs. The lungs are narrow, elongated, profusely vascularized and compartmentalized. The posterior lungs extend to approximately two-thirds of the body length. On the basis of their breathing pattern, it appears that caecilians are phylogenetically derived from two-stroke breathers.