This is a continuation of the previous post titled “Baroreflex – the secret behind Inverted Yoga poses like Sirsasana”. In that post, we covered the role of a Neuroscience reflex called “Baroreflex” in making Yoga inversions effective in bringing relaxation and calmness.
Many readers may find this post too technical, but this the intention. This is written on the requests from many readers asking for the background and scientific evidence of what we covered in the previous post – and so, here we go!
We will cover:
1. Baroreceptor stimulation for relaxation response through activation of the parasympathetic nervous system. This is of significance in inverted Yoga poses and poses involving Jalandhar Bandh (Chin Lock).
2. Baroreflex influence on the Cerebral Blood Flow (CBF). This negates the popular belief that inverted Yoga poses (like Sirsasana) increase the blood supply to the brain to promote relaxation and calmness.
Let’s first have a look at a little bit of history. In modern Neuroscience, the first reference to the use of pressure on carotid sinus for lowering the heart rate, which is now called “Baroreflex”, dates back a couple of centuries. It is primarily attributed to Johann Nepomuk Czermak (1828-1873) and was popularly known as “Czermak’s Vagus pressure”. Since the days of Czermak, it was known to the medical science that the pressure over the Vagus nerve (Cranial nerve X) in the neck produces cardiac slowing of varying degree. During that time, this effect was attributed to mechanical excitation of the Vagus nerve, and NOT to the Carotid sinus as is known today.
Later, Heinrich Ewald Hering (1866-1948) in his research paper in 1924, excerpt and English translation of which is available here at, reported his finding that it is not the Vagus nerve but the Carotid sinus located in the Glossopharyngeal nerve (Cranial nerve IX), that produces this effect. In the paper, he writes – “Using the so-called Czermak’s vagal pressure test, I found that its effects are not the result of pressure on the vagal nerve and the mechanical irritation of its heart inhibitory fibers, but due to a reflex from the carotid sinus, which is located at the origin of the internal carotid artery. I also found a second reflex emanating from the carotid sinus, which has a quite vigorous effect on reducing the blood pressure. Both reflexes, the heart-inhibitory and vasodilatory, disappeared after denervation of the carotid sinus”.
Hering showed that the Carotid Sinus wall can be manipulated to activate the Baroreceptors. They are innervated not by the Vagus nerve but by the Hering branch of the Glossopharyngeal Nerve – commonly referred to as the Carotid Sinus nerve or Hering’s nerve. The Baroreceptors located in Carotid Sinus trigger the Baroreflex to the brain which in turn tries to stabilize the blood pressure through the change in heart rate. A reference to this can also be found in the research paper “Stimulation of the Vagus Nerve and Carotid Sinus” by I.G.W Hill et.al. from the year 1932. The paper describes how Carotid Sinus massage stimulates cardiac slowing by forceful pressing of Carotid Sinus area. This explains the relaxation effect of Jalandhar Bandh in Yoga poses – particularly those in inversions like Sarvangasana, in which the blood flow is throttled by a chin lock.
Stimulation of the carotid body and sinus via Hering’s nerve has clinical significance in modern medicine with respect to regulation of blood pressure and Hypoxia. The procedure called “Carotid Sinus Massage” or “Czermak-Hering Test” or “Vagal Maneuver” consists of the application of external pressure to the Carotid Sinus. This is typically performed at the patient’s bedside by imposing moderate pressure with the fingers, repeatedly massaging the carotid arteries. This is being used in the diagnosis and treatment of many conditions like Tachycardia – many times in an emergency. (NOTE: Only experts and certified practitioners should attempt this).
So far, we covered the Baroreflex stimulation affecting the heart rate and activating the parasympathetic relaxation response. Now about the Baroreflex stimulation and its effect on Cerebral Blood Flow. Such stimulation may happen either because of the change in pressure (due to manual intervention described above) or change the position of heart with respect to the head (i.e. the brain) affected by gravity.
These research papers rule out the old belief that an increase in the cerebral blood flow in Yoga inversions are the cause of calmness. But it is the Baroreflex effect that stimulates the parasympathetic response triggering relaxation and calmness.
We hope you like this post!