What controls respiration and heart rate?

Control of Respiration and Heart Rate

The autonomic nervous system, primarily regulated by the hypothalamus and brainstem, controls both respiration and heart rate through complex interactions between the sympathetic and parasympathetic divisions.

Central Control Centers

• The hypothalamus serves as a key integrator of visceral sensory information and generates coordinated patterns of autonomic responses to internal and external stressors 1
• The brainstem contains critical nuclei for cardiorespiratory control, including the nucleus ambiguus and dorsal motor nucleus which are the origin of parasympathetic neurons controlling the heart 2, 3
• The reticular formation in the brainstem is the origin of sympathetic neurons that project to postganglionic neurons controlling heart function 3
• Local circuit neurons in intrathoracic ganglia and ganglionated plexi integrate signals from afferent and efferent neurons to provide additional regulatory control 3

Respiratory Control

• Respiration is regulated through a complex interplay between central pattern generators in the brainstem and peripheral chemoreceptors that detect changes in blood oxygen, carbon dioxide, and pH levels 3
• Respiratory sinus arrhythmia (RSA), the normal variation in heart rate during breathing (increasing during inspiration and decreasing during expiration), is primarily mediated by parasympathetic activity via the vagus nerve 3, 2
• During deep breathing, healthy individuals show pronounced heart rate variability, which is a sign of proper parasympathetic function 3
• Respiratory patterns can significantly influence heart rate variability measurements, with controlled breathing potentially inhibiting parasympathetic nerve activity 4, 5

Cardiac Control

• The heart is under dual control from the parasympathetic and sympathetic divisions of the autonomic nervous system, which generally oppose each other to maintain cardiac homeostasis 2, 6

• Parasympathetic control:

  • Originates from the nucleus ambiguus and dorsal motor nucleus in the brainstem 3, 2
  • Acts through the vagus nerve to slow heart rate and decrease conduction velocity 3, 2
  • Mediates high-frequency components of heart rate variability 3, 2
  • Can function independently of higher brain centers through postganglionic neurons in ganglionated plexi 3

• Sympathetic control:

  • Originates from the reticular formation in the brainstem 3
  • Increases heart rate and contractility when activated 7
  • Reduces overall heart rate variability during activation 3, 2
  • Can regulate heart dynamics even when disconnected from higher-order structures 3

Integration of Cardiorespiratory Control

• The neurovisceral integration model explains how the central nervous system dynamically interacts with the autonomic nervous system to control heart function 3
• Bidirectional coupling exists between respiration and parasympathetic control of heart rate, with the influence from respiration to heart rate being stronger 8
• During sympathetic activation, respiration increases in depth and frequency, but its influence on heart rate variability progressively decreases 3
• The prefrontal cortex and amygdala can regulate heart rate through pathways involving the nucleus ambiguus, dorsal nucleus of the vagus nerve, and the vagus nerve itself 3

Clinical Implications

• Beta-blockers like metoprolol demonstrate the importance of autonomic control by reducing heart rate and cardiac output through blockade of sympathetic influence 7
• Abrupt withdrawal of beta-blockers in patients with coronary artery disease can lead to severe exacerbation of angina, myocardial infarction, and ventricular arrhythmias due to sudden shifts in autonomic balance 7
• Autonomic dysfunction can manifest as abnormal heart rate responses during tests like the Valsalva maneuver and deep breathing test 3
• Restoring parasympathetic activity to the heart has been identified as a promising approach to treat cardiovascular conditions characterized by sympathetic hyperactivity and diminished parasympathetic activity 6

Common Pitfalls in Assessment

• Misinterpretation of heart rate variability can occur due to irregular respiratory patterns and verbalization during breathing, creating artificial low frequencies that may be mistaken for sympathetic overactivity 3
• The absolute power in the low-frequency region of heart rate variability should not be used as an index of sympathetic activity, as it decreases or remains unchanged during sympathetic activation 3, 2
• Controlled breathing at specific rates (particularly slow breathing at 6 breaths/min) can shift parasympathetic activity into lower frequencies, potentially leading to misinterpretation of autonomic balance 5, 4
• In cases of very low heart rate variability (2-4% of total variability found in healthy subjects), the interpretation of spectral components is affected by non-autonomic components 3