Diphasic ventilatory response to hypoxia in newborn lambs

Area of Science:

• Neonatal Physiology
• Respiratory Control
• Hypoxia Response

Background:

• The ventilatory response to hypoxemia in newborns is critical for survival.
• Previous studies indicated a diphasic response in some species.
• Understanding age-related changes in respiratory control is essential.

Purpose of the Study:

• To evaluate the ventilatory response of newborn lambs to hypoxemia at different ages (2 and 7 days).
• To investigate the characteristics of the diphasic ventilatory response in neonatal lambs.
• To determine the role of chemoreceptor strength and respiratory center responsiveness.

Main Methods:

• Two groups of seven awake newborn lambs were studied at 2 and 7 days of life.
• Minute ventilation (VE) and airway occlusion pressure (P0.1) were monitored.
• Lambs were exposed to room air, 12% O2, 7% O2, and room air sequentially.

Main Results:

• Two-day-old lambs showed a diphasic ventilatory response (hyperventilation followed by depression) to 12% and 7% O2.
• Seven-day-old lambs displayed a clear diphasic response only to 7% O2.
• Respiratory centers remained responsive to hypoxia during the ventilatory depression phase.
• A strong inverse relationship was found between immediate VE response to hypoxia and VE depression magnitude (R = 0.81, P < 0.001).

Conclusions:

• Lambs, like other neonates, exhibit an age-related diphasic ventilatory response to hypoxemia.
• Respiratory centers maintain responsiveness to acute hypoxia even during ventilatory depression.
• Chemoreceptor weakness in newborns is a significant determinant of the diphasic ventilatory response.