Age-Dependent Changes in Breathing Stability in Rats

Abstract

The respiratory control system rapidly develops during the perinatal period in mammalian species. Therefore, premature birth prevents the completion of important neurological maturation processes, which can cause periodic breathing and apneas. The ventilatory response to hypoxia (HVR) is among the test that have been used to study the immature respiratory control system in human and animal subjects (Carroll 2003; Cohen and Katz-Salamon 2005). This response is biphasic because the early increase in the HVR of newborn mammals is not sustained as in adults but decreases to below baseline values (Bissonnette 2000; Cohen and Katz-Salamon 2005; Niane and Bairam 2011). In a preliminary report, we have suggested that rats at postnatal days 1, 4, 7 and 12 (P1, P4, P7 and P12) may be selected to represent the postnatal changes in the biphasic HVR pattern (peak and steady state) and apnea frequency (Niane and Bairam 2011). To better understand the relationship between the maturation of respiratory control and the decreased apnea frequency with age (Niane and Bairam 2011), we re-analyzed our data in P1-, P4-, P7-, P12-, P21- and P90-day-old rats. The following two parameters were studied as an index of respiratory stability during development: the coefficient of variation of minute ventilation and the apnea types (spontaneous vs. post-sigh). The correlation between apnea types and the coefficient of variation of minute ventilation under baseline and steady-state conditions of HVR were assessed.