Summary:  

​

From  Inverted positions  of the body are widely used in medical physical culture, in yoga therapy, and in the  yoga practice  in groups. Inverted postures have an effect on the different systems of the body:

​

• the impact of traction on the spine

• increased venous outflow from the lower limbs and pelvic organs

• decrease in blood pressure

• postural drainage, and other effects.
   

The study of the effect of  inverted postures  on the various body systems is necessary to avoid potential problems that can be caused by improper application of these techniques and their impact on the body. Thus, there have been many cases of spinal injuries, a sharp increase in blood pressure, progression of glaucoma by misusing reverse asanas without targeting an individual, but rather applied to all indiscriminately. In this article, we examine the effect of  reverse asanas  on the various parameters of blood circulation.
 

We will define the  reverse asanas  as a fixed, comfortable body position with a negative angle to the horizontal plane, and the body position in which the whole back and pelvis, or only part of the back touches the ground, and the feet and / or the pelvis are above the level of the heart.

In the lying position the angle is equal to 0º, in the standing position - 90º, standing on his head (Sirshasana) - -90º. Thus, through inverted asanas, we can define the following positions:

• lying on an inclined gymnastic bench, with the head lower than the body

• in the horizontal position lying on the back with the feet resting against the wall

• in the reverse position (Sirsasana)

• reverse positions with emphasis on the shoulder blades (Sarvangasana)

• and other versions of body positions as previously defined.
   

The modification of blood circulation parameters, during the practice of inverted postures, is influenced by the following factors:

• changes in hydrostatic pressure of blood and body tissues (due to a change in the position of the body in the gravitational field)

• regulating activity of the cardiovascular and nervous systems.

The impact of these factors leads to a change in blood circulation parameters:

• change in arterial and venous pressure in different parts of the body;

• change in filtration pressure in capillaries;

• change in venous outflow from different parts of the body;

• change in heart rate and cardiac output;

• change in blood flow to different parts of the body and organs;

• change in the redistribution of blood volume, mainly in the bloodstream (arteries and veins).

• change in the change in intracranial and intraocular pressure.
   

Now let's look at these factors and changes in detail.

Factors that affect the change in the parameters of blood circulation and which are due to the change in the position of the body:
 

hydrostatic pressure

The  pressure  hydrostatic - is a force acting on liquids under the influence of the gravitational field measured by  mmHg. The  hydrostatic pressure is the static pressure, at each point of the fluid in the hydraulic system; it acts in all directions. 

In an adult man, standing, the difference in pressure from the highest point of the head to the bottom of the foot is 140 mm Hg. This means an increase in hydrostatic pressure of the order of 2 mm of Hg for every 2.5 cm. (2) The difference between the hydrostatic pressure at two points located one above the other is called “differential hydrostatic pressure”.
 

In closed hydraulic systems there is a point where the hydrostatic pressure does not change when you change the position of the system relative to the lines of gravitational effects - these are the points of  constant hydrostatic pressure.

In the arterial and venous systems of the cardiovascular system, which also relates to a closed hydraulic system, there are such points.
In the arterial part of the circulatory system, in postures such as head down, standing or lying down, the point of constant hydrostatic pressure is at the level of the heart. Below this point the hydrostatic pressure increases, and above - it decreases.
 

Thus, in a standing position, the difference in hydrostatic pressure calculated from the arteries at the level of the feet and the heart is 115 mmHg; and that of the upper part of the head, then of the heart, indicates a pressure of 25 mm Hg.

If now we add to the average arterial pressure at the level of the heart (90 mm Hg.) the differential hydrostatic pressure for the arteries of the foot, the total pressure in the arteries of the foot will be 115 + 90 = 205 mm Hg., and in the arteries of the head;  90 - 25 = 65mm Hg.  (2)
 

In the venous system, when lying down, the point of constant hydrostatic pressure is at the level of the right atrium of the heart, and when standing it will be moved to a point a few centimeters below the level of the diaphragm. (3)
 

In moving from a standing position to a head-down position with straight legs, this point will be moved above the right atrium of the heart. (4) The position of the point of constant hydrostatic pressure is influenced by factors such as extensibility, quantity and components of the vascular system. Changing one or more of these components can change the position of the constant hydrostatic pressure point. This point is also affected by the  nervous and myogenic control. (4)
 

Mechanisms regulating hemodynamic parameters

The dynamic responses of the cardiovascular system to changes in the position of the body in space vary according to numerous mechanisms, including neurogenic and functional values of the veins. Redistribution of intravascular fluid leads to the activation of reflex responses, which mainly include the following types of receptors:  mechanoreceptors  aortics and carotids, cardiopulmonary mechanoreceptors,  osmoreceptors  hypothalamus and angiotensin receptors  II. (4)

Variation in blood circulation values
Capillary filtration of liquids

A constant exchange of substances and liquids takes place between the capillaries and the interstitial fluid. A change in the position of the body in space can affect this exchange. As discussed above, changing body position will lead to changes in  hydrostatic pressure. 

If the increase in hydrostatic pressure in the vessels is not compensated by an increase in hydrostatic pressure in the surrounding tissues, it will inevitably lead to edema. 
However, since the soft tissues of the body have the average water content is equal to  70%, when a change in body position, the hydrostatic pressure increases not only below the point of the  constant hydrostatic pressure, but also in the tissues surrounding the vessels. In this case, there are no pronounced edemas. (4)

When the position of the body changes from lying to standing, there is an increase in hydrostatic pressure that occurs in the abdominal cavity.
When moving from a lying position to a head down position, the hydrostatic pressure in the abdominal cavity will decrease. (5)

It has been found that the point of constant hydrostatic pressure in the cerebrospinal fluid system is located between C7 and T5 vertebrae. (6) 
The location of this point minimizes pressure variations within the central nervous system.

Blood volume and its distribution

The average blood volume of an adult is 5-5.5 liters per 70 kg for men. About 70% of the volume of blood is stored in the veins of the great circle of blood circulation, the blood vessels of the lungs and heart contain 15% of the blood, the arteries of the great circle of circulation - 10%, and about 5% in the capillaries.

During a change of position of the body, knowing that the redistribution of the hydrostatic pressure undergoes a change, a redistribution of the liquid also takes place. Most of these changes occur in the venous part of the cardiovascular system.
When moving from a lying position to a standing position, the vessels in the legs collect 400-600 ml of blood. (3)

Most of the volume is redistributed into the deep veins of the lower limbs. An additional volume of about 200-300 ml passes through the veins of the glutes and pelvic floor (7).  The increase in the volume of fluid in these areas is due to the veins of the chest and abdomen. (8)

It is observed that in the first hours after performing an inverted position at -5º, a significant reduction in the volume of the fluid containers of the legs occurs (veins and cells) - comparable to an increase in the volume of fluid in the legs. legs when the person stands up. (9)
 

Intravascular and intracardiac pressure

The intravascular pressure changes in different areas of the vascular system, and varies according to the position of the body. The average pressure in the arterial part of the vascular system in a standing position is as follows:
At the heart level - 100 mm Hg. 
at the level of the feet - 190 mm of Hg. 
at the level of the head - 70 mm Hg.

The average pressure in the venous part of the circulatory system in a standing position is:
- level of the feet - 90 mm Hg. 
- inferior vena cava  - 22 mm Hg. 
- superior vena cava  - 0 mm Hg. 
- superior vena cava at the confluence with the right atrium  - 4mm Hg.
- jugular vein  - 0 mm Hg. 
- longitudinal sinus (the head) - 10 mm Hg.
- subclavian vein - 6 mm Hg. 
- metacarpal veins (hands) - 35 mm Hg.

The pressure in the right atrium varies depending on the phase of the respiratory cycle. On average, it is negative and returns to -4 mm Hg. (3)
 

End diastolic pressure - this is the pressure exerted by blood on the walls of the chambers of the heart at the end of the  diastole. This pressure can vary depending on the position of the body, since in this case there is a change in the venous return, which activates the reflex mechanisms of the heart.
 

The presented diagrams are based on data from Katkov and Chestyuhine (rus). (10)
Let's look at the change in various parts of the cardiovascular system based on body position.

 

Diagram 1. The variation of pressure with changes in body position from 75º to -75º. LV - left ventricle, PA - pulmonary artery, RA - right atrium.

The change in hydrostatic pressure leads to noticeable changes in pressure in different parts of the cardiovascular system. As shown in Diagram 1, in the 75º upright position, the mean pressure in the right atrium is minimal and negative.

The smaller the angle of inclination of the body, the less pressure there is: at 30º the pressure becomes 0 mm Hg. The lower the angle of inclination, the more the pressure increases,  until reaching 
9 mm Hg. for an inclination of -75º.

Similarly, the evolution of pressure changes in the pulmonary vein and the left ventricle. Of particular interest is that between the angles 0° to -30°  systolic pressure in the left ventricle remains practically unchanged, while end-diastolic pressure in the left ventricle - increases.

Let's look at the change in the pressure in the foot, depending on the evolution of the position of the body (10).

Diagram 2. The change in pressure in the vessels of the foot with changes in body position from 75º to -75º.

Mean Arteriovenous Gradient:  the mean blood pressure gradient.

As shown in Diagram 2, in  body position upside down at an angle of -75º, systolic arterial pressure, and mean venous pressure are lower than venous pressure in the feet, in the standing position at an angle of 75º.
In the head down position of the body at an angle of -75º the mean arteriovenous gradient (the difference between the mean arterial and venous pressure) is close to zero. It involves the almost complete cessation of blood circulation in the vessels of the feet.

Diagram 2 makes it possible to conclude that in the position of the body upside down, with a significant slope, blood circulation in the legs is significantly reduced.

The volume of blood propulsion by the heart

The rapid change in body position in space leads to a significant change in stroke volume, which is directly related to venous return. Thus, the passage from the lying position to the standing position changes the cardiac output by 25% (3) When passing from the lying position to a head-down position, the propulsion of the blood increases by 23%. In addition, the volume of systolic propulsion increases by 35%. (11)

Heart rate

The heart rate changes to respond to changes in the body's operating conditions, in the cardiovascular system. If you change the position of the body in space, the heart rate also changes, to ensure adequate volume flow demand. Most studies indicate that the transition of the body to the "head down" position -  decreases heart rate. (17, 20)

cardiac output

Cardiac output, or the volume of blood flow per minute - is the amount of blood ejected by the heart during 1 minute. It was found that in the position of the body at an angle -5º no change in blood pressure or in cardiac output occurs; on the other hand, a temporary increase in the volume of ejection occurs, which leads to a compensatory bradycardia. (12)

After 15 minutes in the body position at an angle of -20° no noticeable change was observed in right ventricular end-diastolic pressure, but there was a 15% increase in blood propulsion volume. Also a slight increase in heart rate and an increase in cardiac output of 27% were observed. (13)

Blood pressure in the heart

Changing body position causes changes in blood pressure. In the transition to the head down position at -90º an increase in systolic blood pressure and diastolic pressure occurs. (17, 18)

It appears that the increase in blood pressure occurs only in the first few minutes of inverted body positioning, and changes slightly thereafter. So, in the head-down position with an angle of inclination -90 °, and during the first 2.5 minutes, an increase in blood pressure in the subjects was observed. A further measurement 5 minutes later showed no significant increase in pressure. (18)

The arteriovenous difference in oxygen and blood flow

Variations in body position influence blood flow in different body parts and organs, as described above in the example of blood flow in the feet. Changes in blood flow are directly related to the arteriovenous difference in oxygen. 
Thus, the reduction of blood circulation in an organ, provided that it is not functionally overloaded, would increase the arteriovenous difference in oxygen.

Let's look at the arteriovenous difference in oxygen.

Diagram 3. Evolution of the arteriovenous oxygen difference. 
Heart - heart, Brain - the brain, Leg - Leg, Foot - Feet, Systemic - systemic difference.

As seen in Diagram 3, blood flow to vital organs (brain and myocardium) remains adequate at all times during changes in body position.

The brain

Oxygen consumption by the brain is not associated with a change in body position, as it is ensured by the combined action of several compensatory mechanisms, namely:

• effective self-regulation of blood circulation;

• changes in hydrostatic pressure in the cerebrospinal fluid system;

• anatomical and functional characteristics of intracranial veins. (14)

With a change in body position oxygen consumption is practically unchanged, cerebral blood flow undergoes a change due to gravitational stress. Thus, when changing from a lying position to a standing position, cerebral blood flow is reduced by 20%. (15)

The myocardium

When the position of the body changes, no significant variation in the oxygen consumption of the myocardium was found.

Muscles

It was found that when the angle of inclination of the body reaches -75º, the blood circulation in the feet almost completely stops.

Kidneys

About 20% of blood passes through the kidneys when the body is at rest. Changing the position of the body has a significant effect on blood flow in the kidneys. Thus, during the transition from lying to standing, renal blood flow was decreased by 30%. (2) In the inverted position, an increase in blood pressure in the kidneys was recorded. (4)

Pressure in the vessels of the eye and intraocular pressure

Normally, the average intraocular pressure is around 16 mmHg. and ranges from 12 to 20 mm Hg. When intraocular pressure is above 20 mm Hg, it enters a dangerous zone in which the emergence and development of glaucoma is possible. In this disease, the intraocular pressure of the eye becomes abnormally high, sometimes reaching the level of 70 mm Hg. The increase in intraocular pressure by 25 - 30 mm Hg.. can lead to the loss of vision, if it remains high for several years. (19)

Conclusion

Changing the position of the human body leads to significant changes in the parameters of blood circulation. Understanding these changes in the cardiovascular system will allow a professional yoga instructor, or  yoga-therapist, to choose adapted inverted asanas, which will make it possible to achieve the above-named objectives with the practitioners, in full knowledge.

Bibliography:

Patanjali. Yoga Sutras
THOMAS J. COONAN, CHARLES E. HOPE. Cardio-respiratory effects of change of body position.
Schmidt R., G.Thews “Human Physiology”.
C. Gunnar Blomquvist, H. Lowell Stone. Cardiovascular Adjustments to Gravitational Stress.
Rushmer, RF The nature of intraperitoneal and intrarectal pressures.
HAMILTON, WF, R A. WOODBURY, AND HT HARPER, JR. Physiologic relationships between intrathoracic, intraspinal and arterial pressures.
LUDBROOK, J. Aspects of Venous Function in the Lower Legs.
CULBERTSON, J. W., RW WILKINS, FJ INGELFlNGER, AND SE BRADLEY. Effects of the upright posture upon hepatic blood flow in normotensive and hypertensive subjects.
BLOMQVIST, CG, J . V. NIXON, R L. JOHNSON, JR., AND JH MITCHELL. Early cardiovascular adaptation to zero gravity simulated by head-down tilt.
KATKOV, VE, AND VV CHESTUKHIN. Blood pressures and oxygenation in different cardiovascular compartments of a nonnal man during postural exposures.
NIXON, JV, RG MURRAY, P . P. LEONARD, JH MITCHELL, AND CG BLOMQVIST. Effects of large variations in preload on left ventricular performance characteristics in normal subjects.
BLOMQVIST, CG, J . V. NIXON, R L. JOHNSON, JR., AND JH MITCHELL. Early cardiovascular adaptation to zero gravity simulated by head-down tilt.
KATKOV, VE, VV CHESTUKHIN, VA LAPTEVA, VM MIKHAILOV, O. KH. ZYBIN, AND VV UTKIN. Central and cerebral hemodynamics of the healthy man during head-down tilting.
HENRY, JO GAUER, S. KETY, AND K. KRAMER. Factors maintaining cerebral circulation during gravitational stress.
GAUER OH, THRON HL Postural changes in the circulation.
SHENKIN HA, SCHEUERMAN EB, SPITZ EB, GROFF RA Effect of change of posture upon cerebral circulation of man.
ESTHER M HASKVITZ, WILLIAM P HANTEN. Blood Pressure Response to Inversion Traction.
MICHAEL ZITTO. Artery Pressure Rate, Systolic Brachial Pressure, and Ophthalmic Effects of Two Gravity Inversion Methods on Heart.
GUYTON AC Textbook of Medical Physiology.
STEPHEN A. SOUZA. Cardioperipheral Vascular Effects of Inversion on Humans.
DIMITER ROBERT BERTSCHINGER, EFSTRATIOS MENDRINOS, ANDRE´ DOSSO. Yoga can be dangerous— glaucomatous visual field defect worsening due to postural yoga.

​

​

Author: Kiril Polojivec (Belorussia)
Translated by: A. Papin