The Power of Inversions: Heart and Circulation Upside Down
Roger Cole
See Roger Cole’s Instagram interview: click here
INTRODUCTION
Here’s a guide to deepening your experience of inverted asanas by applying science to practice. Inversions, when performed skillfully, redirect fluid flows and pressures in your body in ways that can improve your health and quiet your mind.
B.K.S. Iyengar famously said, “Yoga is a practical art,” meaning that when you practice, you reap practical benefits. You’ll get the most out of this guide if you do the quick practice demos suggested along the way.
We’ll focus narrowly on blood circulation and the heart because this lays the foundation for understanding how inversions also affect fluid flows in the lymphatic system, brain, lungs, and elsewhere. We’ll emphasize two of the most useful effects of inverted asanas (1) draining and filling, and (2) stimulating reflexes.
Draining and filling refers to draining fluids away from one part of the body and filling up another. For example, elevating the legs enhances circulation not only by helping blood drain out of leg veins, but also by increasing the pressure, and therefore the volume, of blood filling the heart.
Stimulating reflexes refers to activating fluid pressure sensors to trigger beneficial physiological responses. For example, increasing the volume of blood filling the heart triggers a set of reflexes that, over time, can reduce your body’s overall blood volume. Reducing the body’s blood volume can lower blood pressure.
Although inversions have well-documented, important physiological effects, there is not enough clinical evidence to justify making medical claims about them, and some inversions may be risky for some people. Only attempt poses that you know are safe for you, and only teach poses that you know are safe for your students.
If you have any doubts, or have a medical condition, or want to use yoga as therapy, please do it only with the approval and supervision of qualified medical professionals.
Practice Demo Round 1
Before we dig into the science, now would be a good time to do the first practice demo, if you are willing and able. It should only take a few minutes. It will help you intuitively understand the anatomy and physiology of inversions in ways that could never be expressed in words or pictures. We’ll revisit the same practice later.
To practice, simply get into the postures listed below one after another, doing the sequence first in forward order, then in reverse order. Stay in each position very briefly — just long enough to get a sense of how it feels, then move on to the next one and compare how it feels. (This is harder than it sounds, because the poses feel so good you’ll probably want to stay in them much longer.) If you can’t do all the poses, just do the ones you can. Set up your props in advance if possible (see photos).
Sequence (10 to 30 seconds per posture):
1. Tadasana
(standing upright)
2. Supported Savasana
(lying with legs and pelvis on the floor, back elevated on long folded blankets, head supported higher than the back.)
3. Savasana
(lying flat with legs, pelvis, trunk, and head all on the floor at the same level, or as close to level as you can comfortably manage)
4. Supported Urdhva Padasana
(lying flat with legs up a wall, and with pelvis, trunk, and head all on the floor at the same level)
5. Viparita Karani
(lying with pelvis elevated on stacked, folded blankets, legs up a wall, chest lifted, tops of shoulders and head on the floor)
5.5 Add a head support to Viparita Karani
6. Salamba Sarvangasana
(Shoulderstand with the back of the head on the floor, shoulders elevated on the edge of a stack of folded blankets or a comparable prop, and the shoulders, trunk, pelvis, and legs in a vertical line, or as close to vertical as you can comfortably manage)
7. Salamba Sirsasana I
(Headstand I, top of head and forearms on the floor, the rest of the body in a vertical line, or as vertical as you can comfortably manage)
8. Repeat the same sequence in reverse order
BASICS OF CIRCULATION
The heart pumps blood out through arteries, and blood returns to the heart through veins. This is circulation. The heart functions as if it were two pumps; one circulates blood through the lungs, the other circulates it through the rest of the body. Here, we’ll only talk about circulation through the rest of the body.
The heart pumps out blood to the body at high pressure. The blood exits the top of the heart through a single, giant artery called the aorta. The aorta branches into large arteries, which in turn branch into smaller and smaller arteries, which finally branch into fine capillaries that reach every cell.
The capillaries deliver oxygen, nutrients, water and other important molecules to the cells. The cells excrete carbon dioxide and other waste products into the fluid that surrounds them (the interstitial fluid).
On the path back to the heart, the venules converge into small veins, which converge into larger and larger veins, until all venous blood ends up in one of two giant veins, the superior vena cava or the inferior vena cava.
The blood from the capillaries begins its journey back to the heart in tiny veins called venules. The venules collect water and small molecules from the interstitial fluid. On the path back to the heart, the venules converge into small veins, which converge into larger and larger veins, until all venous blood ends up in one of two giant veins, the superior vena cava or the inferior vena cava (see illustration 1). These two veins deliver blood to the same receiving chamber of the heart, the right atrium.
The lymphatic system runs roughly parallel to the venous system and also carries fluid back to the heart. It collects interstitial fluid containing waste (large molecules, bacteria, cellular debris, etc.) in lymphatic vessels. Once the fluid is inside the vessels it is called lymph. Lymphatic vessels, like veins, converge into larger vessels as they progress toward the heart. Along the way, lymph passes through nodes that filter and process it. All the processed lymph ultimately drains into the superior vena cava, where it becomes part of the venous blood that returns to the heart.
We’ll focus next on ways we can strategically use gravity in yoga to aid desirable draining and filling of arterial blood, venous blood, interstitial fluid, and lymph.
Unlike arterial (outbound) blood, the inbound venous blood and lymph operate at low pressure. They do not have a pump pushing them along. Several mechanisms move these fluids. One is the contraction of skeletal muscles that squeeze the veins and lymphatic vessels. Many of these vessels, especially in the legs and arms, have one-way valves, so squeezing them reliably propels venous blood and lymph toward the heart. Another mechanism is breathing. For example, the same vacuum- like negative pressure in the chest that draws air into the lungs during inhalation also helps draw venous blood and lymph toward the heart. A third factor, gravity, can be the most powerful driver of venous and lymphatic return to the heart under some conditions; however, under other conditions, it can be a strong impediment. We’ll focus next on ways we can strategically use gravity in yoga to aid desirable draining and filling of arterial blood, venous blood, interstitial fluid, and lymph.
DRAINING AND FILLING
Fluids flow downhill, so the first rule of draining and filling is to elevate the part of the body you want to drain above the part you want to fill. A crucial point to keep in mind is that the greater the height difference between the source of the fluid and its destination, the stronger the gravitational draining will be and the greater the pressure the fluid will exert below. The source of the fluid does not have to be directly above the destination, it just has to be higher. We’ll sometimes refer to the height difference as the “vertical drop” even when the fluid travels diagonally down or stairsteps down.
The second rule of draining and filling says that because all circulating blood comes from the heart and returns to the heart, the vertical drop that matters most in an asana is not the height difference between the feet and the head (although this still does matter), it is the height difference between the heart and whatever part of the body you want to drain or fill. For example, in any pose with the legs elevated, the strength with which gravity drains blood away from the feet depends much more
on how far the feet are above the heart than on how far the feet are above the head. Likewise, in poses with the head below the heart, the degree to which gravity increases blood pressure in the head depends mainly on how far the head is below the heart, with a much smaller influence of how far the head is below the feet.
The main reason for this lies in the venous system, because it contains three to five times more blood volume than the arterial system1. All venous blood returning from body regions below the heart (that is, the legs, pelvis, abdomen, and lower thorax) flows into the inferior vena cava, then into the heart. All venous blood returning from body regions above the heart (that is, the head, neck, upper chest, and arms) flows into the superior vena cava, then into the heart. There are no veins that go around the heart to connect blood in the lower body to blood in the upper body. Therefore, during an inversion venous blood from the lower body cannot drain into or put filling pressure on veins in the upper body, and during an upright posture, veins in the upper body cannot drain into, or put filling pressure on, veins in the lower body.
The situation in the arterial system is more complicated, so we won’t try to untangle it here, but the upshot is that standing upright increases arterial pressure in the legs far more than turning upside down increases arterial pressure in the head. We’ll see how this plays out when we discuss Tadasana and Salamba Sirsasana.
To make sense of how specific asanas affect draining and filling, it’s useful to know the general layout of some major arteries and veins (see illustrations 1 and 2). The aorta is attached to the top of the heart. It first travels up toward the head a short distance (this is the ascending aorta), then arches over (this is the aortic arch) and finally runs down the trunk to the abdomen (this is the descending aorta).
The first arteries that branch off the aorta come out of the top of the arch, then divide further to deliver blood to the head, neck, upper chest, and arms. Additional arteries branch off of the descending aorta at various levels to supply blood to the trunk. The lower (abdominal) end of the aorta splits into arteries that bring blood to the pelvis and legs.
When we are standing upright, as the heart pumps out blood, gravity opposes its upward flow, and this reduces its pressure. The higher the blood rises, the lower its pressure becomes; therefore, blood pressure systematically falls as blood rises through the ascending aorta, the top of the aortic arch, and the arteries of
the upper chest, neck, and head. Meanwhile, gravity accelerates and therefore increases the pressure of the downward flow of blood out of the aortic arch, down the descending aorta, and through all the arterial branches that serve the trunk, pelvis, legs, and feet. When we turn completely upside down, gravity exerts the opposite gravitational effects on the blood in the arteries, including the aorta itself.
It’s very important to understand how inversions affect blood flow and blood pressure in the head, so we’ll take a closer look at its pathways. Arterial blood travels through the neck to reach the head via two carotid arteries and two vertebral arteries. (The illustration shows just one carotid artery and omits the vertebral arteries). Each carotid artery splits into two branches within the neck. The internal carotid artery brings blood to the brain and other structures inside the skull. The external carotid artery brings blood to the face and other structures outside the skull. Venous blood exits the head mainly via two jugular veins. Each jugular vein has an internal and an external branch. (The illustration shows the two branches of one jugular vein.)
When you are upside down with the heart higher than the head, gravity helps push arterial blood downward into the head but it also hinders the flow of venous blood out of the head. The net result is that gravity does not increase blood flow through the head during inversions. It does, however, increase blood pressure in the head, in both the arteries and the veins. Blood vessels in the brain may be somewhat protected from increased pressure because the skull acts like a closed, fluid-filled box that makes it hard for arteries and veins to expand too much. Blood vessels in the face, nose, eyes, and other areas outside the skull are less protected from elevated pressure, but do have some defense mechanisms.
Gravity-induced changes in blood pressure trigger a number of important and interesting reflex responses.
BLOOD PRESSURE REFLEXES
Gravity-induced changes in blood pressure trigger a number of important and interesting reflex responses. We’ll look at three types of reflexes that inversions or other asanas can clearly trigger: the first are called high- pressure baroreflexes, the second are volume reflexes (also known as low-pressure baroreflexes), and the third are local arterial pressure reflexes. Each type of reflex is triggered by strategically-located stretch-sensors that send stronger signals when stretched by higher blood pressure and weaker signals when released due to lower blood pressure.
High Pressure Baroreflexes
The stretch sensors for high-pressure baroreflexes are called high-pressure baroreceptors, or just baroreceptors. The best known of these are nerves embedded in the arch of the aorta and in the carotid artery (see illustration). When these sensors are stretched by a rise in blood pressure, they elicit a set of responses that generally tend to lower blood pressure and otherwise calm the body and mind. When a fall in blood pressure reduces the amount of stretch on these sensors, they elicit a set of responses that generally tend to raise blood pressure and activate the body and mind. One consequence of this physiology is that when you go into poses that invert the heart, it often triggers a relaxation response. Another is that when you do standing poses, it activates you.
High-pressure baroreceptors don’t respond much, if at all, to small changes in blood pressure, but do respond to moderate-to-large changes (in a graded fashion). Many of these responses are fast-acting; for example, a rise in pressure at the baroreceptors almost immediately causes the heart to beat much more slowly, the heart muscle fibers to contract more gently, the smooth muscles that constrict most arteries and some veins to relax, and the body to breathe more slowly. Other responses are slower-acting; for example, the rise in pressure on the baroreceptors may gradually reduce the levels of several hormones that make the body retain salt and water, thereby tending to eventually reduce blood volume. Conversely, a substantial fall in pressure at high-pressure baroreceptors does the opposite: it greatly speeds up the heartbeat, makes the heart squeeze harder, constricts blood vessels, and so forth.
This means that finding ease and stillness in inversions can often be the key to unlocking their potency.
Perhaps the most interesting high-pressure baroreflex response, from a yoga perspective, is that stimulating the carotid or aortic baroreceptors can trigger a series of nerve signals that significantly slow down your brain waves. Although this has not been studied directly in yoga asanas, it is almost certainly one of the ways that supported inversions like Viparita Karani quiet your mind. If you want to take advantage of this calming reflex in yoga, it’s important to understand that it is easiest to trigger if your body and brain are already partly relaxed. This means that finding ease and stillness in inversions can often be the key to unlocking their potency. Finally, it’s useful to know that the calming baroreflex has an alerting counterpart: lowering blood pressure within the carotid artery and aortic arch can activate your brain; this may be one reason why standing poses generally wake you up.
Volume Reflexes (Low-Pressure Baroreflexes)
The stretch sensors for volume reflexes are called volume receptors, or sometimes low-pressure baroreceptors. Like their high-pressure cousins, they act to reduce load on the circulatory system when it’s high, and vice versa. The best known volume receptors are embedded in the right atrium, at the junctions where the superior and inferior venae cavae come in to deliver blood to the heart. When heart filling pressure increases, it stretches these sensors, and they in essence tell the body and brain that there is an increased volume of venous blood filling up the heart. This elicits a set of reflex responses that tend to reduce the volume load on the heart. A fall in filling pressure elicits opposite responses. One volume-unloading reflex response to the stretching of the heart’s volume receptors is immediate dilation of veins in the arms and elsewhere so they can, in effect, temporarily store excess blood. Another is increased urine production by the kidneys so the body excretes more liquid. Stretching these receptors can also induce several of the same volume-reducing hormonal responses that the high pressure baroreflexes do. In addition, stimulating the volume receptors signals the heart to secrete its own powerful, home-grown, volume- lowering chemical. There are no reports of volume reflexes affecting breathing or brain waves the way that high-pressure baroreceptors do, but this can’t be ruled out because it has not been studied.
Local Arterial Pressure Reflexes
The stretch sensors for local arterial pressure reflexes are located in the walls of certain arteries, for example in tiny arteries in the nasal passages. These reflexes can automatically constrict the arteries when they are filled up at high pressure. The constriction can expel excess blood and limit refilling. This may defend the arteries against damage if blood pressure gets too high during inversion.
With these reflexes, anatomical pathways and principles in mind, we’ll now explore how draining and filling work in the asanas of our demo sequence.
PRACTICE DEMO ROUND 2: EXPERIMENT AND FEEL
The focus of this round is to notice the specific sensations described in the observation instructions below, and to feel how they change when you transition quickly from one pose to the next (holding, again, for 10–30 seconds). It would be ideal to avoid interruptions by setting up the props for all the poses in advance, but if this is not practical, set up the props for two or three poses in a row, practice, then set up two or three more. Go back and forth between poses to better compare differences if you like.
There’s no need to try to figure out what is happening physiologically during this practice, just notice how things feel. We’ll analyze later.
Keep the instructions handy; refer to them frequently as you go along.
Observation Instructions for Practice Demo Round 2
1. Tadasana
Notice whether you experience these sensations:
elevated blood pressure in your feet and ankles;
no particular blood pressure sensation in your
heart, upper chest, neck, head, face, nasal
passages/sinuses, or eyes;
an alert mental state.
2. Supported Savasana
First, notice whether your nasal passages are clear, making it easier to breathe through your nose, and whether you feel reduced pressure in your sinuses.
Next, notice whether the sensation of pressure or fullness in your heart and upper chest are higher than they were in Tadasana.
Finally, notice what pressure, if any, you feel in your feet compared to Tadasana.
3. Savasana
Notice whether you feel an even distribution of pressure or fullness from your feet to your head, or perhaps a very slightly uneven distribution directing a bit more pressure and fullness toward your chest and head.
Notice whether your nostrils are less clear than in supported Savasana.
4. Supported Urdhva Padasana
Notice whether you feel:
a sense of blood draining from the feet — a distinct
drop in pressure — compared to Savasana;
moderately elevated pressure in the rest of your
body, distributed evenly from pelvis to head.
5. Viparita Karani
As you move directly from Urdhva Padasana to Viparita Karani, notice whether you feel:
increased pressure or fullness in the area of your heart, which then spreads to your upper chest, neck, face/head, and arms;
a distinct further drop in pressure in your feet.
Now try this first experiment while still in Viparita Karani
disturb the alignment of the pose by dropping your chest and laying your upper back on the floor (untucking your shoulder blades), then notice whether you feel a fall in pressure in your upper chest and neck;
return to the proper Viparita Karani alignment of lifting and opening your chest, lifting the lower tips of the shoulder blades high off the floor and pressing them into your back, and maximally rolling the tops of your shoulders far underneath you; notice whether you feel a restoration of pressure in your upper chest and neck.
5.5 Now try this second experiment while still in Viparita Karani
• elevate your head by placing a rather thick folded blanket under it, and notice whether this reduces pressure in your head and face, and/or reduces nasal congestion;
• remove the head support so your head is back on the floor, and notice whether this restores pressure to your head, face, and nasal passages.
Notice whether Viparita Karani feels especially relaxing.
6. Salamba Sarvangasana
As you move from Viparita Karani to Salamba Sarvangasana, notice whether you feel:
• a very strong increase in blood pressure focused especially in your upper chest;
• a strong increase in blood pressure in your neck, head, and face;
• a large further drop in blood pressure in the feet, legs, and pelvis compared to Viparita Karani; a more active brain, compared to Viparita Karani.
7. Salamba Sirsasana I
When you change from Salamba Sarvangasana to Salamba Sirsasana I, notice whether you feel:
• a distinct shift of blood pressure to the head itself, especially strong in regions nearest the floor (for example, the top of head, forehead, eyes);
• possibly less pressure in the neck and upper chest compared to Salamba Sarvangasana, but still high pressure there;
• either strong clogging or strong clearing of the nose and sinuses;
• similar or lower in pressure in the feet, legs, and pelvis compared to Salamba Sarvangasana; a more active brain, compared to Salamba Sarvangasana.
8. Repeat the same sequence in reverse order
9. After the final Tadasana, lie flat in Savasana again until you feel ready to move.
WHAT IS (PROBABLY) HAPPENING IN THE POSTURES
Here are proposed explanations of some of the things that may happen in each posture. They are grounded in science, but only a few of them are based on direct experimental measurements in yoga asanas. There are no fixed practice instructions for this section, but it’s extremely useful to revisit some of the poses as you read along.
1. Tadasana
Why there may be a feeling of pressure in the feet and ankles in Tadasana.
The vertical distance from the heart to the feet is maximal in Tadasana, so gravity creates a very strong increase in arterial pressure as blood travels down the descending aorta through the leg arteries to the feet. For example, one study found that in people who are standing up, arterial blood pressure measured at the ankle averaged 222/142 mm Hg, while arterial blood pressure measured at the arm averaged 129/79 mm Hg.5 Over time, this high pressure in the lower legs and feet can push excess fluid out of the capillaries into the interstitial space, causing swelling.
Meanwhile, the great vertical distance between the heart and the feet in Tadasana also increases downward pressure in the venous system. This makes it harder
for the veins and lymph vessels to collect fluid from the interstitial space and send it upward toward the heart. In addition, the downward pressure causes the veins to expand, so a large volume of blood pools in the venous system of the legs and feet. You may see veins in your feet become distended in this pose.
All the factors above may contribute to a feeling of pressure in the feet in Tadasana.
Why there may not be any marked feeling of low pressure or fullness in the heart, upper chest, neck, head, face, nasal passages/sinuses, or eyes inTadasana.
The circulatory system has several mechanisms for moving blood upward against gravity while standing. Let’s look separately at moving venous blood up from the feet to the heart and pushing arterial blood up from the heart to the head.
When we stand upright, pooling of venous blood
and interstitial fluid in the abdomen, pelvis and legs effectively removes about 10–20% of our total blood volume from circulation.6 This reduces the amount of venous blood available to fill the heart from below via
the inferior vena cava. However, in Tadasana, strong action of the leg muscles squeezing the leg veins, plus constriction of smooth muscle in the walls of some leg veins, aided by one-way valves, helps push a sufficient amount of venous blood up through the legs to increase blood volume in the abdomen. There, strong breathing takes over to help draw a sufficient amount of venous blood upward through the inferior vena cava into the heart to achieve partial filling. Meanwhile, since the head, neck, and upper chest are above the heart in Tadasana, gravity assists the return of venous blood from these regions to the heart via the superior vena cava. This partially offsets the reduced venous-filling pressure from below, so although heart-filling pressure and volumeare likely to be somewhat low in Tadasana compared to other poses, it is high enough for us to function normally. This may be partly why there is no marked feeling of low pressure in the heart in this pose. (The pressure is, in fact, somewhat low, but our body can deal with it, so it feels normal.)
In Tadasana, the head is as far above the heart as it can be, so the heart has to work extra hard to pump arterial blood upward with sufficient pressure to supply the head, especially the brain. When we move from lying down to standing, there is an immediate, large fall in blood pressure in the aortic arch and carotid artery, and this quickly triggers strong high-pressure baroreflexes. These increase the pressure of blood being pumped upward out of the heart to the upper chest, neck, head, face, nasal passages, sinuses, and eyes, partially or completely offsetting the tendency of gravity to lower pressure in these locations. This is the main reason that there is no marked feeling of low pressure in regions above the heart in Tadasana.
Why you may feel an alert mental state in Tadasana The same baroreceptors that activate your
cardiovascular system also activate your brain.
2. Supported Savasana
Why the nasal passages and sinuses often clear, making it easier to breathe through the nose in supported Savasana. The nasal passages and sinuses clear out when
more fluid drains out of them than comes into them. Supported Savasana elevates the head above the heart, causing gravity to both increase fluid drainage out of the nasal region and reduce fluid flow into it. Specifically, elevating the head helps venous blood flow downhill out of the nasal region toward the heart, while it also makes it harder for arterial blood to be pushed uphill out of the heart into the nasal region. This usually clears the nose and sinuses. A similar process probably tends to reduce fluid pressures in all parts of the face and head during supported Savasana.
However, there is a paradox. Tadasana elevates the
head much farther above the heart than supported Savasana does, yet it does not reliably drain the sinuses or clear the nasal passages, and sometimes it may even clog them. One reason for this may be that, whereas Tadasana triggers a very strong high-pressure baroreflex that helps maintain or increase blood flow to the nasal region, supported Savasana may not be steeply enough upright to trigger a high-pressure baroreflex at all, so there is not an increase in arterial pressure to offset the gravitational drainage the pose provides.
Why sensations of pressure in your heart and upper chest may be higher in supported Savasana than they were in Tadasana, and why you may feel no pressure, or only slight pressure, in your feet in supported Savasana compared to Tadasana.
The short answer is that, whereas the large vertical drop from the head to the feet in Tadasana causes strong gravitational drainage of blood from the upper body and strong gravitational filling of the feet, the small vertical drop in supported Savasana produces much less gravitational drainage of the upper body and puts very little filling pressure on the legs and feet.
Here is a more detailed explanation. It has four parts. (1) In supported Savasana, although the torso and head are higher than the legs, the vertical drop is much smaller than in Tadasana. The smaller vertical drop causes less gravitationally-driven draining of the head and trunk and less filling of the legs and feet. (2) In supported Savasana, the legs are horizontal and the pelvis rests at the same level, so fluid pressure is distributed fairly evenly from the feet to the hips. (There is no concentrated pressure in or near the feet as there is in Tadasana). (3) The relatively small vertical step up from the level of the legs and pelvis to the level of the heart makes it much easier in supported Savasana than in Tadasana for respiratory action to draw venous blood up from the pelvis and abdomen to the heart. This tends to make cardiac-filling pressure and volume higher in supported Savasana than in Tadasana. (4) The elevation of the head and neck in supported Savasana increases drainage of venous blood and other fluids into large veins in the upper chest, applying pressure that helps to push these fluids into the superior vena cava and then into the heart. In this way, the lifted head position causes increased filling of the veins above the heart and the heart itself.
The four factors above, in various combinations, probably account for the slightly greater sensation of pressure and fullness in the heart and upper chest and lesser sensation of pressure and fullness in the feet in supported Savasana compared to Tadasana.
Bear in mind, though, that supported Savasana is still a head-up, feet-down posture because the head is above the heart while the pelvis, legs and feet are below the heart. The pose still favors an overall gravity-driven shift of fluids away from the head and toward the feet, even though the effect is very mild.
3. Savasana
Why you may feel an even distribution of pressure and fullness from your feet to your head, or perhaps a very slightly uneven distribution directing a bit more pressure and fullness toward your chest and head in Savasana compared to supported Savasana.
In flat Savasana, the legs, pelvis, trunk (including the heart), and head are all at the same level (or as close to level as is practical), and the heart itself lies horizontal, so there is no gravitational bias pushing or pulling body fluids toward or away from the head or feet. This is why fluid distribution may feel even from head to toe. However, our circulatory system is structurally biased to systematically push fluids away from the feet and toward the head, even when we are lying down. This is why, when you lie flat in Savasana, you may feel a slightly higher pressure and fullness in your chest and head.
Why your nostrils may be less clear in Savasana than in supported Savasana.
When we lie flat, the natural, structural push of fluids toward the head is unopposed by gravity, so it may gently push excess fluid into the nostrils, leaving less space for air to pass through. This does not occur in supported Savasana because the overall slant of the pose, especially the elevation of the head, may produce enough gravitational push of fluids away from the head to overcome the natural push toward the head.
4. Supported Urdhva Padasana
Why you may feel draining of fluids and a distinct drop in pressure in your feet in Urdhva Padasana, compared to Savasana.
In Urdhva Padasana the vertical drop from the feet to the heart is relatively large (the full length of the legs), causing fairly strong gravity-driven drainage of fluids from the feet and legs into the pelvis. You may see veins in your feet recede in this pose.
Why you may feel moderately elevated pressure and fullness in the rest of your body, distributed evenly from pelvis to head, in supported Urdhva Padasana.
The fluids draining from the feet and legs first fill the veins and lymphatic vessels in the pelvis, then over several heartbeats end up spreading relatively evenly through the pelvis, torso, and head because these body parts are all on the same level, with no gravitational bias pushing fluids toward one part or another.
Moments after you elevate your legs in Urdhva Padasana, the gravitational push of fluids draining out of them puts excess filling pressure on the heart. This usually stimulates the volume reflex that immediately dilates veins in your arms and elsewhere to accommodate part of the excess blood volume coming out of the legs. You might notice veins in your forearms or hands becoming more prominent in this pose.
Filling of the heart remains higher than normal as long as the legs remain elevated, and this causes the volume receptors to trigger the slower-acting body responses that may eventually reduce overall blood volume. It may take 10–20 minutes in the pose to develop some of these responses, and it may take repeated practice to produce a significant reduction in blood volume. Reduced blood volume can lower blood pressure, so theoretically, consistent, extended daily practice of Urdhva Padasana or other inversions that increase cardiac filling might help reduce blood pressure. However, this has not been proven clinically.
5. Viparita Karani
Why you may feel increased pressure in the area of your heart, which then spreads to your upper chest, neck and face/head, when you transition from Urdhva Padasana to Viparita Karani.
When you transition directly from Urdhva Padasana to Viparita Karani without bringing the legs down you elevate your pelvis and abdomen well above your heart. This causes an immediate increase in the volume of venous blood draining from the pelvis and abdomen through the inferior vena cava and pushing into the heart. That is why you may feel an immediate increase in the sensation of pressure and fullness in the heart. Over the next few heartbeats, the higher volume of blood going into the heart comes out on the arterial side, filling the upper chest, neck, face, and the rest of the head with a higher volume of blood than they had before.
That is one of the reasons you may feel the sensation of pressure spread to these areas. The pelvis and abdomen end up with lower blood volume, and regions from the heart to the head end up with higher blood volume for as long as you stay in the pose.
Why lifting your chest in Viparita Karani increases pressure in your upper chest and neck.
Lifting your chest and rolling your shoulders under increases arterial and venous pressure in the neck and upper chest by raising the heart a little higher and tilting it nearly upside down. These actions combine to increase the vertical drop from the heart to the aortic arch, carotid artery, superior vena cava, jugular vein, and other blood vessels. The greater vertical drop increases the filling pressure of all these vessels, which probably amplifies feelings of pressure in the upper chest, neck, and head in Viparita Karani.
Why you may feel a distinct further drop in pressure in your feet when you transition from Urdhva Padasana to Viparita Karani.
When you lift your pelvis up from Urdhva Padasana to Viparita Karani you also raise your legs and feet higher above your heart. The increased vertical distance causes lower pressure of blood flowing upward in the arteries that supply the feet and stronger draining of venous blood and lymph traveling downward out of the feet.
Why elevating your head in Viparita Karani may reduce feelings of pressure in your head and face, and/or reduce nasal congestion, and why bringing your head back down to the floor may restore pressure and/or congestion.
Viparita Karani can increase blood pressure in the face and promote nasal congestion because it places the head below the heart. In this position, gravity increases the pressure of arterial blood flowing downhill from the heart to the head and also increases back-pressure (pressure against the direction of flow) on venous blood flowing uphill from the head to the heart. Elevating the head close to or above heart level reduces the pressure of arterial blood pushing into it and increases ease of drainage of venous blood out of it. Both of these factors may reduce feelings of pressure and fullness in your head and face, and/or reduce nasal congestion. Lowering the head back down below heart level restores the vertical drop that may have caused the feelings of pressure and congestion in the first place.
Why Viparita Karani may feel especially relaxing.
We have seen that the elevation and upside down tilt of the heart in Viparita Karani raise blood pressure in the aortic arch and carotid artery. This increases pressure on the baroreceptors located there. This may trigger the high-pressure baroreflex response that slows your brain waves, making you feel more relaxed. This response works best when you are already partly relaxed, comfortable, and give it some time to develop. Viparita Karani usually provides all of these conditions.
6. Salamba Sarvangasana
Why you might feel a very strong increase in blood pressure focused especially in your upper chest, and a strong increase in blood pressure in your neck, head, and face as you move from Viparita Karani to Salamba Sarvangasana.
In Salamba Sarvangasana, but not Viparita Karani (1) the legs, pelvis, and abdomen are as high above the heart as they can be, so gravity pushes venous blood from the lower body as strongly as possible into the heart through the inferior vena cava, and this high volume of blood gets pumped out of the heart into the aorta within a few beats, (2) in a fully vertical Salamba Sarvangasana, the heart is completely upside down and as high above the aortic arch and other arteries of the upper chest as it can be, so as the heart pumps out blood, gravity maximally increases its pressure on these arteries, (3) the heart is also as high above the superior vena cava and other veins of the upper chest as it can be, so gravity maximally increases pressure on blood in these veins, (4) although there is a greater vertical drop from the upper chest to the head in Salamba Sarvangasana than in Viparita Karani, the drop is not large in absolute terms, so gravity only weakly drains blood away from the upper chest into the head; the four factors above suggest that both arterial and venous blood pressure and blood volume in the upper chest may be higher in Salamba Sarvangasana than in any other pose in this series, and (5) in Salamba Sarvangasana, the vertical drop from the heart to the head is greater than in Viparita Karani, so Salamba Sarvangasana puts greater fluid pressure in the neck, face and the rest of the head than Viparita Karani does.
Why you might feel a large further drop in pressure in the feet, legs, and pelvis as you move from Viparita Karani to Salamba Sarvangasana.
When you lift your pelvis up from Viparita Karani to Salamba Sarvangasana you also raise your legs and feet higher above your heart. The increased vertical distance causes stronger draining of fluids from the feet and legs, which you may feel as a drop in pressure.
Why you might feel a more active brain in Salamba Sarvangasana compared to Viparita Karani.
This may seem paradoxical at first. Salamba Sarvangasana puts more pressure on the aortic and carotid baroreceptors than Viparita Karani does and is therefore theoretically capable of producing a stronger brain-quieting baroreflex response. However, this response can be blocked or reversed by muscular effort, mental effort, or discomfort, all of which are more common in Salamba Sarvangasana than in Viparita Karani. One might expect that skilled practitioners who can practice Salamba Sarvangasana with minimal effort and great comfort might experience a greater brain-quieting baroreflex. Likewise, anyone who can get comfortable in supported Salamba Sarvangasana, which requires little muscular or mental effort, may be able to enjoy this quieting experience.
Incidentally, it has been proposed that the flexed position of the neck in Salamba Sarvangasana may somehow stimulate the carotid baroreceptors. This hypothesis awaits evidence.
7. Salamba Sirsasana I
Why you might feel a distinct shift of blood pressure to the head itself, especially strong in regions nearest the floor (for example, the top of head, forehead, eyes) when you change from Salamba Sarvangasana to Salamba Sirsasana.
Salamba Sirsasana creates the maximum possible vertical drop from feet to head and from heart to head, so it causes maximal shift of all body fluids toward the head, with the maximum fluid pressure in the parts of the head nearest the floor.
It appears that no one has scientifically measured actual blood pressure in the head in Salamba Sirsasana, but we can make an educated guess about it. Extrapolating from a 1963 study7 a rough estimate is that a person whose arterial blood pressure while standing in Tadasana is 104/75 mm Hg at heart level and 213/178 mm Hg at the ankle might have a pressure of 148/113 mm Hg at forehead level while in Salamba Sirsasana.
Why you might feel less pressure, but still high pressure, in the upper chest in Salamba Sirsasana compared to Salamba Sarvangasana.
Salamba Sirsasana takes the head and most of the neck substantially further below the upper chest than Salamba Sarvangasana does, so gravity drains fluids away from the upper chest into the neck and head more strongly in Salamba Sirsasana than in Salamba Sarvangasana. This may account for the sensation of lower pressure in the upper chest that may occur in Salamba Sirsasana.
Why you might feel either strong clogging or strong clearing of the nose and sinuses in Salamba Sirsasana.
In Salamba Sirsasana, the nose and sinuses are as far below the feet and heart as they can be, so filling pressure there is maximal. This can cause nasal and sinus tissues to swell with fluid. However, blood vessels of the nose and sinuses may have the local arterial reflex that causes them to automatically constrict and expel fluid when they are filled up at high pressure. Some people experience strong clearing of the nose and/or sinuses in Salamba Sirsasana; it is possible that this may be caused by such a local reflex. It seems plausible that when this occurs, the reflex might help protect the arteries against damage from excessive blood pressure, but it would require careful study to demonstrate convincingly if and when this is true.
Why you might feel similar or lower in pressure in the feet, legs, and pelvis in Salamba Sirsasana compared to Salamba Sarvangasana.
The vertical drop from the feet to the heart is about the same in Salamba Sirsasana and Salamba Sarvangasana. This means that gravity probably aids venous drainage from the feet to the heart about the same amount in both poses, so the feet may feel similar, low pressure in the two poses. On the other hand, the lower head position relative to the heart in Salamba Sirsasana makes it harder for venous blood
to return from the head to the heart than in Salamba Sarvangasana. This could reduce the volume of blood filling the heart, making it harder for the heart to
pump arterial blood all the way up the feet in Salamba Sirsasana than in Salamba Sarvangasana. This could hypothetically cause a sensation of lower pressure (and actual lower pressure) in the feet in Salamba Sirsasana.
Why you might feel a more active brain in Salamba Sirsasana compared to Salamba Sarvangasana.
The carotid baroreceptors are further below the heart in Salamba Sirsasana than in Salamba Sarvangasana, so one might expect blood pressure on these receptors to be higher in Salamba Sirsasana, and this could cause a stronger baroreflex-mediated quieting response in the brain. However, practicing Salamba Sirsasana typically requires more muscular effort and attention to balance than practicing Salamba Sarvangasana does, and these factors might make it more challenging to fully activate the baroreceptor-mediated calming effect in Salamba Sirsasana.
8. Repeat the same sequence in reverse order
9. After the final Tadasana, lie flat in Salamba Savasana again until you feel ready to move.
Why is it recommended to lie flat in Savasana after the final Tadasana?
Tadasana is an activating pose and not ideal for putting the mind and body in a rested, balanced state at the end of practice. Savasana is the most neutral pose with respect to gravitational effects, mental effort, and muscular effort, so it helps restore both physiological and mental balance.
The practice demo sequence we did here was designed to teach about the physiology of inversions. It was not a typical inversions practice sequence. It is often good for a typical inversions practice sequence to end with supported Savasana, a restful, head-up pose, as a counterpose to all the head-down poses. This could theoretically help speed draining of waste fluids (venous blood and lymph) that could have accumulated in the head, neck, and upper chest in the head-down poses. Flat Savasana would also support such draining, but it would probably be slower.
FURTHER PRACTICE
Here are some ways you can use knowledge about inversions in practice.
Experiment with longer durations in the poses of the demo sequence.
Experiment with variations of the poses, see and feel what happens, and think about why. For example, practice Eka Pada Sarvangasana and Eka Pada Sirsasana, feel the difference between the foot of the down leg and the up leg, then compare the feet when you bring them back together.
Experiment with poses that invert one part of the body but not another, such as Adho Mukha Svanasana, Uttanasana, and Setu Bandha Sarvangasana. Think about what parts of the body are below the heart and what parts are above the heart in these poses, and notice associated sensations.
Design and adjust asanas to achieve specific draining and filling effects. For example, try to design a pose that helps drain swollen ankles while also reducing nasal congestion, then actually set it up, practice it, and adjust it so it works best.
See Roger Cole’s Instagram interview: click here
References