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Mechanisms mediating the heart rate response to hypoxemia
H Kato1, A S Menon, A S Slutsky
1Department of Medicine, Mount Sinai Hospital Research Institute, University of Toronto, Ontario, Canada.
Circulation
|February 1, 1988
Summary
The Hering-Breuer reflex significantly influences heart rate responses to low oxygen levels (hypoxemia). Stronger reflex activity correlates with greater heart rate variability during hypoxemia, explaining inter-dog differences.
Area of Science:
- Cardiovascular Physiology
- Respiratory Reflexes
Background:
- Pulmonary afferent information influences heart rate (HR).
- The Hering-Breuer reflex modulates respiratory control.
- Variability exists in heart rate responses to hypoxemia.
Purpose of the Study:
- To investigate the role of phasic pulmonary afferent signals in heart rate regulation during hypoxemia.
- To assess the relationship between the Hering-Breuer reflex and heart rate changes during reduced oxygen saturation (SaO2).
Main Methods:
- Studied anesthetized, paralyzed dogs under controlled ventilation.
- Evaluated the Hering-Breuer reflex using the apnea duration to expiratory time ratio (dT).
- Compared heart rate responses during spontaneous breathing versus constant-flow ventilation (CFV) to eliminate phasic afferent activity.
Main Results:
- Heart rate response to SaO2 reduction varied widely during spontaneous breathing (mean delta HR/delta SaO2 = 0.62).
- A strong correlation was observed between delta HR/delta SaO2 and dT (r = .79).
- During CFV, the mean HR response to hypoxemia was significantly blunted (-1.32 bpm/%) compared to spontaneous breathing (0.23 bpm/%).
Conclusions:
- Phasic pulmonary afferent input significantly impacts heart rate regulation during hypoxemia.
- The strength of the Hering-Breuer reflex is a key determinant of heart rate variability during hypoxemia.
- This reflex mechanism may explain the substantial inter-dog variability in heart rate responses to reduced oxygen saturation.