The Influence of Body Position on the Blood
Flow of Parenchymatous Organs: II. Kidneys
Human Physiology. Vol. 25. №2. 1999. pp. 203-209. Translated from Fiziologiya Cheloveka,
Vol. 25, №2. 1999. pp. 92-98. Original Russian Text Copyright © 1998 by Minvaleev,
Kuznetsov, Nozdrachev.
R. S. Minvaleev, A. A. Kuznetsov and A. D. Nozdrachev
To continue our earlier studies of the influence of hatha yoga positions on the intraorgan blood
flow [1], we have chosen kidneys as a parenchymatous organ involved in homeostasis. Our
choice was also based on the reports that the cobra position (bhujangasana in Sanscrit) had an
influence on the renal state and function [2] (Fig. 1).
Fig.1. Cobra position known in yoga exercises as bhujangasana
Note: This position appears as the vertebral column flexure when lying on one's belly without supporting
oneself by the arms. Unlike the usual flexure backwards, the correct performance of bhujangasana
should be characterized by the efforts to cave in the (inflexible!) vertebral region. And only such a
performance preconditions a correct reproducibility of our data on hemodynamic parameters in this
position.
HITACHI EUB-525
MATERIALS AND METHODS
The work was performed in three stages. The first stage included the study on nine subjects
(including seven women) aged from 20 to 45 who had been taught to perform exercise in the
cobra position. Using a HITACHI Eub-525 echo-chamber (Japan), blood flow in the interlobular
arteries of the left kidney was recorded before exercise, during its performance, and immediately
after it. The following parameters were determined: the maximum flow velocity (Vmax, cm/s): the
medium flow velocity (Vmed, cm/s); the flow velocity integral per one cardiac cycle and per
minute (FVI and Flow, cm and cm/min, respectively); the pulse and resistive indices (PI and RI,
respectively, conventional units) describing the muscular activity of the arterial wall; and the
heart rate (HR, beats/min). In the second stage, blood flow in the ascending aorta was determined
from the retrostemal approach during exercise in ten subjects (eight of them were women
between the ages of 20 and 50). In this case, only the index of flow velocity integral per minute
was recorded, which was calculated by the formula Flow/BSA = FVI · HR/BSA (cm/min·m²)
where BSA is the body surface area. In this work, we have abandoned the traditional calculation
of aortal flow volume because of difficulties in the measurement of its diameter.
Fig. 2. Scheme of normal blood flow in the renal vein.
Under these conditions, it would be improper to compare the central hemodynamics in different
subjects; therefore, we followed changes in the flow velocity integral separately in each subject
under study. We acknowledged that the aortal diameter should be unchangeable as the diameter
of a rigid elastic vessel. In the third stage, the influence of the exercise on the venous outflow
from the kidney was determined. A controlled volume of the Doppler signal was placed into the
renal vein at the level of renal hilum at the initial horizontal position on the belly, during
exercise, and at the horizontal position immediately after it. This examination was carried out in
22 subjects (including 14 women, aged from 26 to 63, 41.7 years on average). The central and
venous hemodynamics were studied with a KONTRON Sigma-44 echo-chamber (France). The
venous outflow was assessed according to changes in flow velocity during right-ventricular
systole (Vs, cm/s) and right-atrial systole (Va, cm/s) (Fig. 2); the heart rate (HR, beats/min) was
also recorded. When discussing the results, we also considered our clinical observations on the
venous renal outflow in patients with some renal diseases. Some of these studies were carried out
with Sinergy and System Five echo chambers (Vingmed, Norway). These echo-chambers were
available for our studies thanks to the employees of the St. Petersburg branch of VINGMEDSONOTRON, and we are grateful to them.
Fig. 3. Blood flow in the renal vein.
(а) Before exercise:
(б) during exercise.
RESULTS
The results were statistically treated using a STATGRAPHICS packet of applied programs, and
the significance of changes was evaluated with Student's t-test for coupled samples.
The initial parameters of blood flow in the interlobular renal arteries in test patients were similar
to values published for healthy subjects [3]. The maximal and average flow velocities were
0.28±0.01 and 0.17±0.01 cm/s, respectively: FVI and Flow were 0.16± 0.01 and 10.0±0.6 cm,
respectively; PI was 1.12±0.05 c.u., and RI was 0.67±0.01 c.u. The initial heart rate (HR) was
62.8±1.0 beats/min. During exercise, HR sharply increased (up to 106±4.6 beats/min, p<0.001),
the velocity integral of one pulse wave FVI considerably decreased to (0.10±0.01 cm, p<0.01),
whereas the flow velocity integral per minute (Flow) did not change (10.0±0.07, p<0.05). Other
parameters were stable. After the exercise, all parameters did not differ from those observed
initially (Table 1). The parameters of venous outflow from the kidney (Table 2 and Fig. 3)
indicated that during exercise the flow velocity in the renal vein in the right-ventricular systole,
VS did not change (-14.4±1.4 and -16.0±1.8 cm/s, p<0.05), whereas the outflow in atrial systole,
Va , significantly increased (from -4.5±1.4 to -10.2±1.2 cm/s, p<0.01). The heart rate increased
from 78.5±2.9 to 112.8±4.3 beats/min, p<0.001). After exercise, these parameters were restored
to their initial values.
Fig. 4. Changes in the index of flow velocity integral per minute in the ascending aorta
before (1) and during exercise (2) (n=10).
Table 1. Changes in the parameters of renal arterial inflow in the cobra position (n=9)
Parameters
Initialy
Position
After the Exercise
X±m
X±m
p
X±m
p
Vmax cm/s
0.28±0.01
0.26±0.02
n/d
0.31±0.02
n/d
Vmed cm/s
0.17±0.01
0.17±0.01
n/d
0.18±0.01
n/d
FVI, cm
0.16±0.01
0.10±0.01
**
0.18±0.01
n/d
Flow, cm/s
10.0±0.6
10.0±0.7
n/d
10.9±0.6
n/d
PI, c.u.
1.12±0.05
0.98±0.06
n/d
1.13±0.06
n/d
RI, c.u.
0.67±0.01
0.62±0.02
n/d
0.67±0.02
n/d
HR, beats/min
62.8±1.0
106.0±4.6
**
61.4±1.6
n/d
Note: Here and in Table 2: n/d, diflerences are absent. * p <0.01, **p <0.001.
Table 2. Changes in the parameters ol renal venous outflow in the cobra position (n=22)
Parameters
Initially
Position
After the Exercise
X±m
X±m
p
X±m
p
Vs , cm/s
-14.4±1.4
-16.0±1.8
n/d
-15.6±1.6
n/d
VA , cm/s
-4.5±1.4
-10.2±1.2
*
-6.8±0.9
n/d
HR, beats/min
78.5±2.9
112.8±4.3
**
84.3±4.3
n/d
hanges in the index of flow integral in the ascending aorta (Flow/BSA, cm/min·m²) seemed to be
similar to the cardiac index. During exercise, this parameter decreased in all test subjects (Fig.
4). Based on this observation, it was suggested that the stroke volume of the left ventricle
decreased so markedly during exercise that the minute flow volume significantly decreased,
despite the development of tachycardia (Fig. 5).
Fig. 5. Blood flow in the ascending aorta
before (A) and during exercise (B).
DISCUSSION
It seems that the significantly decreased pulse filling in the interlobular renal arteries (FVI) observed
during exercise was compensated for by increased heart rate until the minute organ blood filling (Flow)
was stable. This occurred along with decreased minute general blood flow because of the sharp fall of
the left-ventricular beat. Thus, exercise-induced redistribution of arterial blood in favor of kidneys was
suggested. The general renal and surface cortical blood flow is known to be regulated by the
sympathetic nerves, and their stimulation caused arteriospasm in these regions [4]. It is clear that
tachycardia during exercise could be induced by increased sympathetic influences that also involved the
kidneys. According to the data presented in [5], the decreased vagal effects on the heart were
accompanied by increased renal vascular resistance. However, we failed to detect arteriospasm in the
kidneys because the PI and Rl parameters did not change in test subjects.
Fig. 6. Blood flow in the renal vein in a patient with pyelonephritis
during the voluntary urine retention test:
(а) during urine retention,
(б) after emptying the urinary bladder.
Presently, the intrarenal mechanisms of changes in the arterial blood flow parameters are rather
well known. Thus, they are significantly changed in cases of renal sinus cysts and
hydronephrosis [6]. The parameters of muscular activity of the arterial wall are increased in
acute glomerulonephritis and during exacerbation of chronic glomerulonephritis: in acute and
chronic renal failure [7-9]; with rejection of renal allograft [10-12]; in diabetic
nephroangiopathia [13]; and in renal colic, especially in proximal obstruction of the ureter and
signs of pyelonephritis [14]. Essential hypertension also raises the tonus of resistive renal vessels
[15, 16]. A certain inconsistency of the literature data seems to be due to the different
mechanisms of changes observed. In particular, at the height of renal disease blood flow in the
juxtamedullar glomeruli increased along with the partially ceased blood flow in the cortex. This
picture is associated with decreased PI and RI values. In more severe disease, when the
juxtaglomerular apparatus is also changed and the blood cannot pass through it, the PI and Rl
values again increase. This was observed in cases of irreversible damage to kidney glomeruli
[17]. In stenosed renal arteries, the PI and Rl values were lower than normal [18,19]. No changes
were detected in the muscular tone of renal artery during exercise. And since the velocity
parameters of the vascular blood flow correlate with the renal creatine clearance [20], it is
suggested that this posture does not affect functions of the glomerular apparatus.
Fig. 7. Blood flow in the renal vein in a patient with the remaining hydronephrotic kidney after removal of the
other kidney.
The increased intra-abdominal and intrarenal pressure is likely to be one of the mechanisms
responsible for the effect of exercise in the cobra position on the kidneys. More than twofolddecreased cortical blood flow in the kidneys was found in dogs [21], along with an increase in
the intra-abdominal pressure from 0 to 15 mm Hg. and a high correlation was found between
renal blood flow and pressure in the abdominal cavity (r=0.897). In our case, the flow volume
did not change in the blood vessel under observation, which suggests a relatively insignificant
compression of the kidney at the backward flexure of the loins during exercise. However, it was
sufficient to markedly decrease pulsations in venous outflow from the kidney due to the
significantly increased blood flow during right-atrial systole (Va). And, in the more highly
trained subjects, fluctuations in the venous blood flow completely disappeared when the velocity
spectrum became monophase (Fig. 3). Unfortunately, the published data on the blood outflow
from the kidneys are very scarce. A turbulent flow was described in the renal vein under
conditions of its compression after a kidney transplantation [22]. Studies of the syndrome of
compression of the left renal vein by the superior mesenteric artery and the abdominal aorta
(Nutcracker syndrome) revealed a moderate decrease in the peak velocity of venous outflow in
the renal hilum and a sharp acceleration of blood flow in the compressed region of the vein. No
data have been reported on the minimal velocity of blood outflow from the kidney [23, 24].
Therefore, we turned to our own findings mentioned above. A monophase venous outflow was
detected by the voluntary urine retention test in patients with chronic pyelonephritis complicated
with pyeloureteral reflux (Fig. 6), in patients with hydronephrosis (Fig. 7), in a patient with acute
ischuria because of neoplasia in the small pelvis (Fig. 8), and in the case of kidney damage
associated with cirrhosis of the liver (Fig. 9). Based on the data. we suggest that disorders
accompanied by the increased compression of the renal veins should result in venous outflow
with either markedly smoothed fluctuations or in completely monophase outflow. And changes
in this parameter preceded changes in the arterial bed that indicated the more severe damage to
the kidneys.
Fig. 8. Blood flow in the renal vein in a patient with acute
ischuria caused by a voluminous process in the small pelvis.
We believe that the influence of exercise in the cobra position is within the limits of
physiological fluctuations in the transmural pressure on the intra- and extrarenal blood vessels.
And, naturally, the renal veins are more sensitive to such gentle effects. Following the logic of
our previous studies, we determined the influence of the exercise on the venous outflow from the
kidneys under conditions of the initially disturbed renal blood circulation. When choosing
subjects suitable for our studies, one of the yoga instructors was found to have a changed
monophase blood flow in the renal vein. The changes were unilateral. The yoga exercise test was
clearly positive (fluctuations in the blood flow were completely restored). Examination of the
repeated dopplerograms of venous outflow after purposeful yoga exercises in the cobra position
(Fig. 10) within three months showed fluctuations in the initial blood flow and its transformation
into the monophase type during exercise (this indicated a correct exercise performance).
Fig. 9. Blood How in the renal vein in a patient
with cirrhosis of the liver.
After the exercise, the fluctuations increased. Some observations of this kind seem promising
with respect to the favorable effects of the exercise in the cobra position on the blood outflow in
the renal veins.
CONCLUSION
(1) During the exercise in the cobra position, cardiac output significantly decreases in the
background of tachycardia.
(2) When the minute blood flow volume drops under the influence of exercise in the cobra
position, the arterial blood supply to the kidneys remains stable.
(3) This exercise significantly increases linear flow velocity in the renal veins during right-atrial
systole. and this is accompanied by a decrease or disappearance of blood pulsations in these
veins.
(4) The preliminary results indicate that the initially changed venous outflow from the kidneys is
restored after exercise in the cobra position.
Fig. 10. Changes in blood flow in the renal vein:
(A) before exercise,
(B) during exercise,
(C) after exercise.
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