As I understand this study, the researchers had subjects with primary open angle glaucoma (POAG) breathe through their right nostril only (by closing off their left nostril) for 20 minutes. There is a common breathing technique in Yoga know as "alternate nostril breathing" or Nadi Shodhana in sanskrit. The aim of alternating the open nostrils is to create balance in the physiology.

The study below used exclusive breathing through the right nostril; such techniques have been long used in Ayurvedic medicine for treating certain conditions, although they are not commonly practiced as part of Yoga.

The researchers of this study point out that breathing exclusively through the right nostril increases activation in the left brain hemisphere. This left brain activation induces increased activity in the sympathetic nervous system (the fight or flight nervous system).

The researchers use the term "functional vagotomy." A vagotomy is a surgical removal of, or severing part of, the vagus nerve. A "functional vagotomy" is therefore a non-surgical technique that functions (temporarily) in a similar manner to reduce parasympathetic activation.

The vagus nerve is part of the parasympathetic nervous system. Therefore, what the authors intend to imply by the term "functional vagotomy" is that they used the right nostril-only breathing technique to shift the physiology's balance toward sympathetic nervous system activation.

I should also note that, even without closing one (either) nostril, when we inhale, the vagus nerve activity is impeded and heart rate begins to increase. When we exhale this pattern is reversed.

With that background, here is the abstract of the study:

A functional vagotomy induced by unilateral forced right nostril breathing decreases intraocular pressure in open and closed angle glaucoma

J Backon, N Matamoros, M Ramirez, RM Sanchez, J Ferrer, A Brown and U Ticho
Mount Pleasant Hospital, Addiction Studies Foundation, Jerusalem, Israel.

There is evidence of the central regulation of intraocular pressure, and it has been suggested that vagal tone might be increased in glaucoma simplex (POAG).The nasal cycle, the simultaneous congestion-decongestion response in thenasal cavities, reflects the dynamic lateralisation of the autonomicnervous system. Since this lateralisation presents with sympatheticactivity induced by left brain hemisphere stimulation and parasympatheticactivity induced by right hemisphere stimulation, it was subsequentlydemonstrated that forced unilateral nostril breathing induces selectivecontralateral hemispheric stimulation as measured by relative increases inthe electroencephalographic amplitude in the contralateral hemisphere aswell as alternating lateralisation of plasma catecholamines. Using thisfunctional vagotomy, we report that left hemispheric stimulation by 20 minutes of forced unilateral right nostril breathing led to a significantbilateral decrease of 4.6 mmHg (25%) in intraocular pressure in 46 patientswith open and closed angle glaucoma. However, it significantly increasedthe IOP in three patients with neovascular, one with juvenile onset, andone with closed angle glaucoma.

British Journal of Ophthalmology, 1990, Vol 74, 607-609