Yogic agnisara increases blood flow in the superior mesenteric artery.

OBJECTIVES
Medieval yoga texts claim that a special exercise of the muscles of the anterior abdominal wall, called agnisara, improves digestive function. Main objective of the study was to demonstrate change in the blood flow through superior mesenteric artery (if any) after performance of agnisara.


METHODS
Ultrasound examination of the linear and volumetric indicators of blood flow in the superior mesenteric artery (SMA) before and after performing the agnisara yoga exercise 100 times was carried out in 12 healthy volunteers of both sexes (8 of them women).


RESULTS
A significant increase in the diameter of the SMA, peak systolic and diastolic velocities, and blood flow in the superior mesenteric artery after performing the agnisara exercise 100 times was found, which contrasts with the established data on a decrease in splanchnic blood flow in humans in response to normal physical activity.


CONCLUSION
Properly performed agnisara increases blood flow to the splanchnic region, registered by the SMA, which should contribute to adequate blood supply to the gastrointestinal tract for successful performance of digestive function.


Introduction
In the course of our ultrasound studies of yogic postural in uences on intracardiac [1] and intraorganic blood ow [2,3], we decided to evaluate the blood ow to the gastrointestinal tract during the agnisara, or vahnisara, yoga exercise, since in medieval texts on yoga a direct in uence on gastrointestinal function is attributed to this exercise [4]. Consequently, modern guidelines for yoga practice repeat the above instruction and yoga practitioners believe they are increasing their digestive activity.
The activation of the digestive tract function must be accompanied and is, indeed, accompanied by a natural increase in its blood supply, which is well established in case of postprandial blood ow to the celiac region by various independent methods [5,6], including Doppler owmetry [7]. The superior mesenteric artery (SMA), which supplies the whole of small intestine, is often studied, because the anatomy of this vessel lends itself to examination by a noninvasive Doppler ultrasound method [8]. The adapting of noninvasive Doppler techniques has made it possible to develop reproducible measurements of celiac and superior mesenteric arteries blood ow, which are the main contributors to the gastrointestinal vasculature [9].
In a recent study of cerebral blood ow during inverted yoga pose (shirshasana), we found a decrease in the blood ow to the brain through the internal carotid artery, contrary to the prevailing opinion among yoga practitioners [10], which makes the problem statement relevant for testing other yoga practices.
Since it remains unclear how agnisara increases digestive function while physical exercise in general reduces celiac blood ow by distributing cardiac output in favor of working skeletal muscles [11], we decided to evaluate celiac blood ow using ultrasound examination of the SMA before and after doing the agnisara exercise multiple (100) times.

Compliance with Ethical Standards
This study was approved by the Institutional Review Board of Saint Petersburg State University (IRB00003875, irb@spbu.ru). Written informed consent was translated into all relevant languages and cross translated to assure accuracy. Consent was signed by all participants after all questions had been answered by the scienti c team.

Subjects And Methods
A total of 12 healthy volunteers of both sexes (including 8 women) at the age from 34 to 57 years old were examined (see Table 1 for details). Table 1.
All subjects had varying levels of yoga experience and were trained to do the agnisara exercise.
A short description of this exercise is presented, for example, in the medieval instruction on yoga practice called "Gheranda-samhita" [4]: "Move the navel plexus to the spinal column one hundred times. This gets rid of intestinal diseases and increases the digestive re. This Vahnisara (Agnisara) brings about success in Yoga for yogis…" (Chapter 1. 18-20). Outwardly, it looks like alternate, forceful retractions and protrusions of the abdominal wall, performed along a 20-30 s period of apnea after a full exhalation (Fig.   1). Interestingly, an outwardly similar exercise called "vacuum" has become widespread in Western training systems such as tness and bodybuilding, with a direct indication that this exercise is adopted from yoga.
We performed ultrasound examination of the blood ow of the superior mesenteric artery using an expert class ultrasound machine Fuji lm Sonosite Edge (Bothell, Washington). For sagittal visualization of the abdominal aorta and the superior mesenteric artery extending from it, a C60x convex probe with a scanning frequency of 2-5 MHz was used (Fig. 2).
Power and Pulsed Wave Doppler owmetry of the superior mesenteric artery blood ow was consistently carried out in all subjects in the morning on an empty stomach in the supine position with knees bent to relax the abdominal muscles. Power Doppler was used to con rm vascular ow and angle of SMA takeoff. Pulsed Wave Doppler was used to generate a spectral image of ow in SMA at takeoff. Waveform generated and assessed for quality (Quality was determined by lack of spectral broadening in arterial wave form). Scale was adjusted to t wave form onto image display. Quality image and Doppler wave form with arterial pattern in obtained within 1cm of SMA takeoff. Calipers are used to measure peak systole and peak diastole. Calculation function is used to measure the SMA diameter at the area where Doppler wave form obtained at SMA take off. Volume ow was calculated by measuring peak to peak and converted to ml/min. Immediately after this, each subject, in a sitting position with their legs crossed, performed the agnisara exercise, holding their breath after a full exhalation, as many times as possible (Fig. 1). In total, three to four exercise cycles were performed each time after a new exhalation, in order to obtain a total of 100 propulsive movements of the anterior abdominal wall. Immediately after completing the agnisara exercise 100 times, the ultrasound of the SMA blood ow was repeated.
The results of measuring the actual diameter (in cm), peak velocities at the times of systole and diastole (in cm/s), and the total estimate of the volumetric blood ow (in ml/min) in the superior mesenteric artery were read from the obtained sonograms (Fig. 3).
Statistical processing of the numerical results obtained was carried out using the paired samples t test.

Results
At the initial stage of the examination, unidirectional changes in SMA blood ow were found in response to performing the agnisara exercise 100 times in most subjects, which made it possible to draw a preliminary conclusion about an increase in linear and volumetric parameters of SMA blood ow after this exercise. However, in the test subject ES (female), in response to performing the agnisara exercise 100 times, a decrease in diameter and an almost twofold decrease in volumetric blood ow in the SMA was discovered. After conversations with her and with other participants, it turned out that their techniques of performing agnisara were different. Namely, subject ES performed agnisara in strict accordance with the instructions given in the Gheranda Samhita, pressing the front abdominal wall against the spine, while the rest of the participants, who had received yoga training from another trainer, performed uddiyana bandha (Sanskrit: ' ying up'), in which the front abdominal wall is pulled not to the spine, but up to the diaphragm raised while holding the breath after exhalation (see Fig. 1). On the next day, during the repeated ultrasound examination, subject ES performed uddiyana bandha before each abdominal retraction, and the direction of changes in SMA blood ow after performing agnisara 100 times was equal to that of the main group (see Table 2). Table 2.
Since all other subjects (n = 11) performed the agnisara yoga exercise with the preliminary performance of uddiyana bandha, their measurement results, including the results of repeated measurements in subject ES, were summarized in Table 3 and subjected to statistical processing. Table 3.
Following the guidelines, we give 95% con dence intervals (CI) for signi cant changes in the studied indicators: 1. mean difference in diameter was 0.04 cm (95% CI 0.073 -0.01 cm) or 6.6% mean increase; 2. mean difference in systolic blood ow in the SMA was 18.31 cm/s (95% CI 35. 5 Table 3 shows a signi cant (with a probability of type 1 error less than 0.05) increase in all indicators of linear and volumetric blood ow through the SMA after the 100-fold execution of a speci c agnisara exercise, despite the statistical invariance of the resistance index (highlighted in gray in Table 3).

Discussion
Moreover, the amount of blood owing through the SMA per minute increased with a probability close to 1.
The latter contrasts with the established data on a decrease in mesenteric blood ow in humans in response to various sympatho-adrenal activations, including physical activity. In other words, a performance of the special physical exercise agnisara 100 times should have reduced the blood ow through the superior mesenteric artery, like any other physical activity, which has been found in many studies [12,13,14,15]. This is exactly what happened in subject ES when performing agnisara without uddiyana bandha. When we added the performance of uddiyana bandha before each propulsive movement of the anterior abdominal wall during agnisara, the volumetric ow of arterial blood along the SMA increased (see Table 2), which allows us to indicate a speci c retraction of the anterior abdominal wall up to the diaphragm, called in yoga the uddiyana bandha, as a key element for the correct performance of agnisara.
In 2003, we described a shift in the autonomic tone towards the predominance of parasympathetic in uences when performing uddiyana bandha [16]. The same cholinergic re ex mediates an increase in blood ow to the SMA after a meal [17]. Thus, the correct agnisara reproduces/imitates the vegetative support of the digestive process before meals, preparing the digestive tract to perform its function.
Interestingly, even at the initial stage of digestion, blood ow in the SMA also increased from as early as the rst minute after a meal, that is, even before the chyme entered the intestine, or, in other words, preventively [18]. We observed a similar more than 30% increase in blood ow in the SMA when performing the correct agnisara, of course, outside the meal, which allows us to prove the capacity of a correctly performed agnisara to activate gastrointestinal function through an increase in the SMA. Another coincidence with our data (see table 3) was that the increase in the mesenteric blood ow after a meal was mainly due to an increase in velocity and volume, the increase in the vessel diameter was less important [17].
Thus, an increase in blood ow to the SMA after repeating this yoga exercise 100 times can be seen as a sign of performing the exercise correctly. Then, our ultrasound experimental data can be seen as a con rmation of the ancient description of agnisara as the practice of "kindling the digestive re" [4].

Conclusion
Correctly performed agnisara (with the obligatory performance of uddiyana bandha before each propulsive movement of the anterior abdominal wall) increases blood ow to the splanchnic area, by the SMA, which should contribute to an increased blood supply to the gastrointestinal tract for the corresponding improvement of the digestive function.    Ultrasound visualization of SMA.

Figure 3
Typical sonogram of linear and volumetric blood ow in the superior mesenteric artery after performing the agnisara exercise.