Inversions and Their Neuroendocrine Effects

Turning the Body Upside Down Changes the Brain

An inversion is any posture in which the heart is positioned above the head. This simple gravitational reversal produces a cascade of physiological effects that are disproportionate to the apparent simplicity of the intervention. When you go upside down — whether in Sirsasana (Headstand), Sarvangasana (Shoulderstand), Viparita Karani (Legs-Up-the-Wall), or Adho Mukha Svanasana (Downward-Facing Dog) — you change the hemodynamic, neuroendocrine, lymphatic, and autonomic conditions under which the entire body operates.

The effects are not mystical. They are mechanical and neurological, operating through well-characterized physiological pathways: the baroreceptor reflex, the renin-angiotensin-aldosterone system, lymphatic drainage, cerebrospinal fluid dynamics, and hypothalamic-pituitary axis modulation. What yoga has prescribed for millennia — that inversions are among the most important postures for health — finds increasingly precise validation in physiology.

Baroreceptor Activation and Cardiovascular Regulation

The baroreceptors are stretch-sensitive mechanoreceptors located in the carotid sinus (at the bifurcation of the common carotid artery) and the aortic arch. They continuously monitor arterial blood pressure and send afferent signals to the nucleus tractus solitarius (NTS) in the medulla oblongata, which orchestrates the autonomic response.

When blood pressure rises at the baroreceptors — as occurs during inversion, when the hydrostatic column of blood above the heart increases pressure in the carotid sinus — the baroreceptor reflex triggers:

1. Increased parasympathetic output via the vagus nerve, slowing heart rate (negative chronotropy)
2. Decreased sympathetic output to the heart and blood vessels, reducing cardiac contractility (negative inotropy) and peripheral vascular resistance
3. Reduced renin secretion from the juxtaglomerular cells of the kidneys, decreasing angiotensin II and aldosterone production
4. Increased atrial natriuretic peptide (ANP) release from cardiac atrial myocytes in response to atrial stretch

The net result is a reflex reduction in heart rate, blood pressure, and sympathetic tone. Klarner et al. (2016) demonstrated that even brief periods of head-down tilt produce measurable increases in heart rate variability (HRV) and shifts toward parasympathetic dominance. This is the baroreceptor reflex in action — a hardwired cardiovascular regulatory mechanism that inversions deliberately engage.

The therapeutic implications are significant. Individuals with chronic sympathetic overdrive — including those with hypertension, anxiety, insomnia, and PTSD — have tonically elevated sympathetic output and reduced baroreceptor sensitivity. Repeated activation of the baroreceptor reflex through inversions may improve baroreceptor sensitivity over time, restoring more normal autonomic balance. This is analogous to the mechanism by which aerobic exercise improves baroreceptor function (Monahan et al., 2000), but through a gravitational rather than metabolic pathway.

Sirsasana: The King of Asanas

Sirsasana (Headstand) is traditionally called the “king of asanas” — not for its difficulty but for the scope of its physiological effects. In Sirsasana, the entire body is inverted, with the head bearing weight through the forearms and crown.

Hemodynamic Effects

Full inversion increases cerebral blood flow by approximately 7-14% (Minhas et al., 2010). The increase is modulated by cerebral autoregulation — the brain’s intrinsic ability to maintain relatively constant blood flow despite changes in perfusion pressure. In healthy individuals, autoregulation buffers the increase, preventing dangerously elevated intracranial pressure. However, the modest, sustained increase in cerebral perfusion may have neurotrophic effects — promoting oxygen and nutrient delivery to neural tissue.

The venous drainage of the brain shifts during inversion. In the upright position, cerebral venous blood drains primarily through the internal jugular veins, assisted by gravity. In inversion, the jugular veins become compressed by increased intraluminal pressure, and drainage shifts to the vertebral venous plexus (Batson’s plexus) — an alternative pathway that may be underutilized in habitual upright posture. This alternation between drainage pathways may promote vascular health and prevent venous stasis.

Hormonal Effects

The hypothalamic-pituitary axis sits in the sella turcica at the base of the brain, directly above the sphenoid sinus. The hypothalamus receives blood supply from the superior hypophyseal arteries. Changes in cerebral blood flow during inversion alter the delivery of neurohormones from the hypothalamus to the anterior pituitary via the hypothalamic-hypophyseal portal system.

While direct measurement of hormonal changes during Sirsasana is limited, indirect evidence is suggestive:

Cortisol: Inversion activates the baroreceptor reflex, which suppresses sympathetic output and may reduce HPA axis activation. Reduced cortisol is consistently reported in yoga practitioners (Riley & Park, 2015), though the specific contribution of inversions versus other poses is difficult to isolate.

Growth hormone: Brief periods of inverted posture have been shown to increase growth hormone secretion in preliminary studies, potentially through changes in hypothalamic blood flow or through the proprioceptive novelty of inversion, which activates hypothalamic arousal circuits.

Thyroid hormones: Sarvangasana (Shoulderstand) is specifically associated with thyroid effects due to the chin lock (Jalandhara Bandha) that compresses the thyroid gland and increases blood flow upon release. The theoretical mechanism is ischemic preconditioning: brief compression reduces blood flow to the thyroid, and subsequent release produces reactive hyperemia that floods the gland with oxygenated blood.

ANP and BNP: Atrial natriuretic peptide and brain natriuretic peptide, released in response to atrial stretch during inversion, have natriuretic (sodium-excreting), diuretic, and vasodilatory effects. They also suppress the renin-angiotensin-aldosterone system. This may explain the diuretic effect that practitioners sometimes report after inversion practice.

Sarvangasana: The Queen of Asanas

Sarvangasana (Shoulderstand) is traditionally called the “queen” or “mother” of asanas for its calming, restorative quality — in contrast to the stimulating quality of Sirsasana. The biomechanics are distinct: the cervical spine is in full flexion, creating a powerful chin lock (Jalandhara Bandha), while the rest of the spine is relatively straight, supported by the hands on the back.

The Jalandhara Bandha Effect

The chin lock compresses the carotid sinuses bilaterally, which intensifies the baroreceptor reflex beyond what simple inversion produces. This is a key difference between Sarvangasana and Sirsasana: in Sarvangasana, the baroreceptor activation is amplified by direct mechanical compression.

The vagal response is therefore stronger in Sarvangasana. Heart rate decreases more markedly, blood pressure drops more significantly, and the subjective experience is consistently described as calming and cooling — in contrast to the energizing quality of Sirsasana. This is why Iyengar and other teachers traditionally prescribe Sarvangasana as a counterpose to Sirsasana: the headstand stimulates, and the shoulderstand settles.

Thyroid and Parathyroid Effects

The compression of the anterior neck in Sarvangasana directly affects the thyroid and parathyroid glands. The thyroid gland lies anterior to the trachea at the level of C5-T1 — precisely the region compressed in Jalandhara Bandha.

The proposed mechanism is twofold:

1. Compression phase: Blood flow to the thyroid is reduced, creating a brief period of relative ischemia.
2. Release phase: Upon coming out of the pose, reactive hyperemia floods the thyroid with oxygenated blood, potentially stimulating thyroid hormone synthesis and release.

While controlled studies measuring TSH, T3, and T4 changes in response to Sarvangasana specifically are lacking, the broader yoga literature supports thyroid benefits. Nilakanthan et al. (2016) found that a six-month yoga practice that included Sarvangasana improved thyroid function in women with hypothyroidism, though the study could not isolate the contribution of Sarvangasana from the total practice.

In functional medicine, thyroid dysfunction is often traced to impaired blood flow to the thyroid gland, chronic inflammation, and HPA axis dysregulation — all of which inversions may address. The TCM perspective aligns: the Kidney meridian runs through the anterior neck, and the Kidneys govern the jing (essence) that supports endocrine function. Stimulating this region through Jalandhara Bandha is understood in TCM terms as nourishing Kidney essence.

Viparita Karani: The Accessible Inversion

Viparita Karani (Legs-Up-the-Wall) is the gentlest inversion and the most accessible to therapeutic populations. The practitioner lies supine with legs resting vertically against a wall, often with a bolster under the sacrum to create a mild pelvic inversion.

Despite its simplicity, Viparita Karani produces significant physiological effects:

Venous Return and Lymphatic Drainage

The lower extremities contain approximately 70% of the body’s blood volume in the upright position, pooled there by gravity. Elevating the legs reverses this gravitational pooling, promoting venous return to the heart. Increased venous return increases cardiac preload (the volume of blood entering the heart), which through the Frank-Starling mechanism increases stroke volume and cardiac output — temporarily and reflexively, before the baroreceptor reflex reduces heart rate to compensate.

The lymphatic system, unlike the cardiovascular system, has no central pump. Lymphatic fluid is moved by skeletal muscle contraction, respiratory diaphragm movement, and — critically — gravity. In the upright position, lymphatic drainage from the lower extremities must work against gravity, traveling upward through the inguinal lymph nodes to the cisterna chyli and thoracic duct. Elevating the legs reverses this gravitational challenge, promoting lymphatic drainage from the legs and pelvis.

This is therapeutically significant for:

• Chronic venous insufficiency: Leg elevation is a standard medical recommendation for varicose veins and chronic edema
• Lymphedema: Post-surgical or idiopathic lymphedema of the lower extremities responds to elevation-based protocols
• Post-exercise recovery: Athletic recovery protocols incorporate leg elevation to promote venous return and lymphatic clearance of metabolic waste

The Parasympathetic Shift

Viparita Karani is consistently associated with a strong parasympathetic shift. The mechanism combines baroreceptor activation (from increased carotid pressure), reduced gravitational demand on the heart (the heart no longer works against gravity to perfuse the brain), and the restorative context in which the pose is typically practiced (dim room, closed eyes, bolster support).

Khattab et al. (2007) measured HRV during Shavasana (Corpse Pose) and found significant increases in high-frequency HRV — the parasympathetic marker. Viparita Karani, which adds the hemodynamic effects of inversion to the restorative context of Shavasana, would be expected to produce an even stronger parasympathetic response.

In polyvagal terms (Porges, 2011), Viparita Karani creates the conditions for ventral vagal engagement: physical safety (supine, supported), reduced metabolic demand (no muscular effort), and enhanced vagal tone (baroreceptor activation). This makes it an ideal practice for individuals stuck in sympathetic overdrive or dorsal vagal shutdown — the two maladaptive autonomic states that Porges identifies.

Lymphatic System and Inversions

The lymphatic system processes approximately 3 liters of fluid per day, filtering it through approximately 600 lymph nodes before returning it to the venous system via the thoracic duct and right lymphatic duct. The system has no pump; it relies on intrinsic lymphatic vessel contractions, skeletal muscle contraction, respiratory movements, and gravity.

Inversions affect lymphatic drainage through multiple mechanisms:

1. Gravitational reversal: Fluid that has pooled in the lower extremities drains toward the central lymphatic system when the legs are elevated above the heart.

2. Thoracic pressure changes: During inversion, the weight of the abdominal organs rests on the diaphragm, which may enhance diaphragmatic excursion during breathing. The diaphragm is the primary pump for the thoracic duct, which collects lymph from three-quarters of the body.

3. Venous pressure changes: Increased central venous pressure during inversion creates back-pressure in the lymphatic-venous junction (where the thoracic duct empties into the left subclavian vein), which may temporarily slow lymphatic drainage. However, upon returning to upright, the pressure gradient reverses and drainage is accelerated — another example of the compression-release principle.

Lymphatic drainage is relevant to immune function, as lymph nodes contain dense concentrations of lymphocytes. Enhanced lymphatic circulation increases the exposure of immune cells to antigens and pathogens, theoretically supporting immune surveillance. While direct evidence linking inversions to improved immune function is limited, the lymphatic mechanism is physiologically sound.

Cerebrospinal Fluid Dynamics

Cerebrospinal fluid (CSF) is produced by the choroid plexus in the ventricles of the brain at a rate of approximately 500 ml per day. It circulates through the ventricular system, around the brain and spinal cord in the subarachnoid space, and is reabsorbed through the arachnoid granulations into the venous sinuses.

CSF circulation is driven by arterial pulsations, respiratory movements, and body position. Inversion alters CSF dynamics by changing the hydrostatic pressure gradient along the spinal axis. In the upright position, CSF pressure is lowest in the cranial vault and highest in the lumbar cistern. Inversion reverses this gradient.

Recent research on the glymphatic system — the brain’s waste-clearance system, active primarily during sleep — has revealed that CSF permeates the brain parenchyma through perivascular channels, clearing metabolic waste including amyloid-beta (the protein implicated in Alzheimer’s disease) (Iliff et al., 2012). Body position affects glymphatic clearance: Xie et al. (2013) demonstrated that the glymphatic system is most active during sleep, and Lee et al. (2015) showed that lateral sleeping position enhances glymphatic clearance compared to supine or prone positions.

While inversions have not been directly studied in the context of glymphatic clearance, the alteration of intracranial pressure dynamics and CSF flow patterns during inversion is a plausible mechanism for enhanced waste clearance. This is speculative but physiologically grounded — and represents a promising research direction.

Contraindications: When Not to Invert

Inversions are contraindicated in several conditions:

Uncontrolled hypertension: Inversion increases intracranial pressure and systemic blood pressure at the level of the brain. In individuals with uncontrolled hypertension, this may increase stroke risk.

Glaucoma: Intraocular pressure increases during inversion (Baskaran et al., 2006). In glaucoma, where intraocular pressure is already elevated, inversions may worsen the condition and accelerate optic nerve damage.

Cervical spine pathology: Sirsasana and Sarvangasana place significant load on the cervical spine. Cervical disc herniation, stenosis, or instability are contraindications to these weight-bearing inversions. Viparita Karani, which does not load the cervical spine, remains safe.

Acute sinus infection or inner ear disorders: Inversion increases congestion in the sinuses and may exacerbate vertigo in individuals with vestibular dysfunction.

Menstruation: Traditional yoga teaching advises against inversions during menstruation, on the grounds that they reverse the downward flow (apana vayu) that governs menstruation. While the physiological evidence for harm is weak, many women report discomfort with inversions during menses. The traditional guidance errs on the side of caution and aligns with the broader principle of practicing with, not against, the body’s natural rhythms.

Retinal detachment or recent eye surgery: Increased intraocular pressure during inversion may be dangerous.

A Therapeutic Inversion Sequence

This sequence progresses from the gentlest to the most demanding inversions:

1. Viparita Karani (Legs-Up-the-Wall): 5-15 minutes. The foundation of any inversion practice. Accessible to nearly everyone. Bolster under the sacrum for a mild pelvic inversion.

2. Setu Bandha Sarvangasana (Supported Bridge): A supported bridge with a block under the sacrum creates a mild inversion of the pelvis while keeping the head below the heart. 3-5 minutes. Beneficial for individuals who are not ready for full inversions.

3. Adho Mukha Svanasana (Downward-Facing Dog): A semi-inversion that places the heart above the head without full body inversion. Hold 1-2 minutes. This transitions the body toward greater inversion while maintaining muscular engagement.

4. Sarvangasana (Shoulderstand): 3-5 minutes. Use blankets under the shoulders to protect the cervical spine. Focus on Jalandhara Bandha for thyroid and baroreceptor effects.

5. Sirsasana (Headstand): 1-5 minutes (advanced practitioners). Use the wall for support if needed. Focus on axial alignment and steady breathing.

6. Return to Viparita Karani: After active inversions, return to the passive inversion to allow the nervous system to integrate and settle.

The Four Directions Perspective

In the Four Directions framework, inversions represent a fundamental reversal of perspective — the willingness to see the world differently by literally changing one’s relationship to gravity. The North — the direction of wisdom, of the elder, of seeing from above — is accessed when we go upside down and view our habitual patterns from a new orientation. The East — new beginnings, fresh perspective — is embodied in the physiological renewal that inversions promote: enhanced circulation, hormonal reset, lymphatic clearance.

The willingness to go upside down also requires trust — trust in one’s own body, trust in the support of the ground. This mirrors the South’s domain of instinct, embodiment, and grounded presence. One cannot sustain an inversion without being simultaneously grounded (through the foundation points) and elevated (through the rest of the body). This paradox — grounded elevation — is the essence of the inversion’s teaching.

References

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• Heusch, G. (2015). Molecular basis of cardioprotection: signal transduction in ischemic pre-, post-, and remote conditioning. Circulation Research, 116(4), 674-699.
• Iliff, J. J., Wang, M., Liao, Y., Plogg, B. A., Peng, W., Gundersen, G. A., … & Bhatt, D. L. (2012). A paravascular pathway facilitates CSF flow through the brain parenchyma and the clearance of interstitial solutes, including amyloid-beta. Science Translational Medicine, 4(147), 147ra111.
• Khattab, K., Khattab, A. A., Ortak, J., Richardt, G., & Bonnemeier, H. (2007). Iyengar yoga increases cardiac parasympathetic nervous modulation among healthy yoga practitioners. Evidence-Based Complementary and Alternative Medicine, 4(4), 511-517.
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• Nilakanthan, S., Metri, K., Raghuram, N., & Hongasandra, N. (2016). Effect of 6 months intense yoga practice on lipid profile, thyroxine medication and serum TSH level in women suffering from hypothyroidism: a pilot study. Journal of Complementary and Integrative Medicine, 13(2), 189-193.
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