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Triangularis sterni and phrenic nerve responses to progressive brain hypoxia.
L O Chae1, J E Melton, J A Neubauer
1Department of Medicine, University of Medicine and Dentistry of New Jersey-Robert Wood Johnson Medical School, New Brunswick 08903-0019.
Journal of Applied Physiology (Bethesda, Md. : 1985)
|April 1, 1992
Summary
Respiratory muscles active during normal breathing, like the phrenic (PHR) and triangularis sterni nerve (TSN), are equally vulnerable to hypoxic depression. Recovery shows significantly enhanced TSN expiratory activity.
Area of Science:
- Respiratory Physiology
- Neuroscience
Background:
- Eupneic respiratory muscles' vulnerability to hypoxia varies.
- Genioglossal and abdominal muscles are more susceptible to hypoxic depression than diaphragmatic activity.
Purpose of the Study:
- To investigate the vulnerability of eupneic respiratory muscles to isocapnic progressive brain hypoxia (PBH).
- To compare the hypoxic depression and recovery patterns of phrenic (PHR) and triangularis sterni nerve (TSN) activity.
Main Methods:
- Recorded PHR and TSN nerve activity in anesthetized, vagotomized, and ventilated cats.
- Induced isocapnic progressive brain hypoxia (PBH) by altering gas mixture and measuring arterial oxygen content (CaO2).
- Assessed nerve activity during hypoxia, apnea, and recovery periods with hypercapnia.
Main Results:
- PBH caused parallel decreases in PHR and TSN activity, leading to neural apnea.
- PHR activity ceased during gasping, while TSN remained silent.
- During recovery, PHR activity increased to 110% and TSN activity augmented to 269% of baseline.
Conclusions:
- Both TSN expiratory and PHR inspiratory activities are equally vulnerable to hypoxic depression.
- Recovery from severe hypoxia is marked by a substantial augmentation of TSN expiratory activity, exceeding that explained by hypercapnia alone.