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Urinary Bladder Blood Flow Changes During the Micturition Cycle in a Conscious Pig Model
~5347/9s/1565-1858$03.00/0
vol. 156, 1858-1861,November
1996 Printed in U S A .
THe JOURNAL OF UROLCGY Copyright 0 1996 by AMERICANUROUXIICAL ASSOCIATION, INC.
URINARY BLADDER BLOOD FLOW CHANGES DURING THE MICTURITION CYCLE IN A CONSCIOUS PIG MODEL J. E. GREENLAND*
AND
A. F. BRADING
From the University Department of Pharmacology, Oxford University and the Department of Urology, Churchill Hospital, Headington, Oxford, United Kingabm
ABSTRACT
Purpose: TO develop a method using laser Doppler flowmetry in conscious pigs, which allows the accurate simultaneous measurement of cystometric and cardiovascular parameters together with changes in vesical blood flow. The animal model was then used to investigate the changes in blood flow in the urinary bladder which occur during the micturition cycle. Materials and Methods: Seven large white female pigs were subjected to chronically implanted vascular access and urodynamic catheters as well as a n intramural vesical laser Doppler probe. The animals underwent repeated conscious urodynamics with simultaneous measurement of cardiovascular, urodynamic and vesical blood flow parameters. Results: The model shows both compliant and low-compliance behavior and allows greater investigation of the effects of intravesical pressure on blood flow. Blood flow is not altered, during compliant filling and voiding transiently decreases flow to 38% of resting levels, with a rapid return to normal. Low-compliance filling results in a progressive fall in blood flow to a minimum of 45% of normal. At all times a n inverse relationship between intravesical pressure and blood flow is maintained. Conclusions: The pig model proved to be well suited to the experimental conditions and provided reproducible results. The principal determinant of blood flow within the wall of the bladder is the pressure within its lumen. During normal filling the blood supply of the bladder is able to adapt to the large increase in surface area which occurs, maintaining blood flow until the pressure increases. KEY WORDS:swine, regional blood flow, physiology, perfusion, laser-Doppler flowmetry
At present we know little of how blood flow within the wall of the urinary bladder is affected by the changes that occur during the phases of the micturition cycle. Even less is known of the effects of disease on vesical blood flow. To date vesical blood flow has not been investigated in conscious subjects. Some investigators have reported that bladder filling decreases blood flow in the wall of the bladder’-7 while others have reported a n increase.8.9 or no effect.”J Only 1 of these studies was performed in humansf the others used a variety of animal models. The techniques employed include the use of radiolabelled microspheres,4.5.10 radiolabelled tracer washout,2~3.5.10venous drop counting8 and laser Doppler flowmetry.6.7.9 All have been performed under general anesthesia, and only a few have accurately correlated the changes seen with recorded changes in intravesical pressure.2. 4-6, lo Where this has been done, all report a negative correlation. To date there have been no reports as to the changes that occur during normal micturition. Pelvic nerve stimulation has been used to produce bladder contraction with conflicting results: Andersson et al. reported a n increase in blood flow? Siroky et al.7 reported a decrease, and Hofmann et al.11 found no effect. In the present study we have developed a method of recording relative vesical blood flow during the micturition cycle normalized to prevoid values in conscious pigs using laser Doppler flowmetry (LDF). The laser Doppler flowmeter measures blood flow within the microcirculation by quantifying the amount of a laser light beam which is frequency shifted and reflected by a moving column of blood. The reading produced, expressed in flux units, is proportional to both
the numbers and velocity of red blood cells passing within a small distance of the probe tip.12.13 MATERIALS AND METHODS
Seven large white female pigs (weight range 58 to 95 kg.) were used. Under halothane general anesthesia each animal had silicone catheters with subcutaneous Dacronm cuffs tunnelled from entry sites in the dorsal mid-line to the abdominal cavity ( ~ 3 and ) neck (X2). Two of the abdominal lines were inserted through the dome of the bladder and sutured in place so that their tips lay free within its lumen. The third abdominal line was left free in the peritoneal cavity posterior to the bladder. One of the neck lines was placed in the descending thoracic aorta via the common carotid artery and the other in the superior vena cava via the internal jugular vein. Both were held in place by sutures passed through Dacron” “wings” positioned at the site of vessel entry. A 0.5 mm. diameter, bare plastic optical fiber sheathed in a Dacron” cuffed silicone catheter was tunnelled into the abdominal cavity as for the other lines. The distal 3 cm. of a 0.58 mm. i.d. nylon tube 5 cm. long was introduced into the wall of the bladder with a 14-gauge intravenous cannula needle as a trocar so that its tip was lying in the detrusor muscle layer. The laser fiber was then introduced through this polythene tubing which was subsequently withdrawn to leave approximately 2 mm. of laser fiber exposed within the detrusor (fig. 1).All of these components were then firmly anchored to the wall of the bladder with multiple 2-zero silk sutures taking care to avoid placing any sutures within 2 to 3 cm. of the fiber tip or around any visible blood vessels. Accepted for publication April 4,1996. Following surgery each animal had its vascular lines * Requests for reprints: Department of Urolo Churchill Hospital, Headington, Oxford OX3 7 U , United Kinggm. flushed with heparinized saline and received long-acting in1858
BLADDER BLOOD FLOW DURING THE MICTURITION CYCLE
Silicone Tubing
Laser Fibre Tip
\
1859
\
I Po‘ythene Tube
FIG.1. Schematic representation of arrangement of laser fiber and polythene tubing within bladder wall. Laser light beam is directed parallel to detrusor muscle layer.
I ~
tramuscular cephalexin injections on a daily basis. Urine was taken for microscopy and culture 1 week following bladder line insertion and then subsequently if indicated. Four to 5 days postoperatively it was possible to commence urodynamic investigation combined with LDF. It was possible to repeat the investigation on multiple days over a time period of up to 3 weeks. For investigation the animals were lightly sedated with a n infusion of propofol(2 to 8 mg./kg./hr.) via the vena cava line. One of the bladder catheters was used to fill the bladder with 0.9% saline at 38C at rates ranging from 20 to 110 ml. per minute. Experience showed that filling at 50 ml. per minute produced reproducible results that did not differ significantly from those obtained at other filling rates. As a result, most of the data presented below were obtained by filling at 50 ml. per minute. The other bladder line and the peritoneal line were connected via fluid filled catheters to pressure transducers to allow measurement of P,,, and Pabdo,respectively, and subtraction to give Pdet.The systemic blood pressure (P,) was measured in similar fashion from the aortic line. The laser fiber was connected via a n optical connector to an MBF3 laser Doppler flowmeter (Moor Instruments, Axminster, United Kingdom) to allow simultaneous measurement of blood flow (at a sampling frequency of 10 Hz) in the detrusor expressed in “flux units.” All parameters were displayed on a six-channel pen recorder and also recorded on digital audio tape for subsequent recording (at 10 Hz) and analysis with an eight-channel MacLab.? The MacLab software allows specified blocks of data to be identified and the mean values for each of the variables within the block to be calculated. Following sacrifice of the animal Sudan black dye was injected through the nylon laser fiber introducer sheath and the position of its tip in the wall of the bladder confirmed histologically.
FIG.2. Cystometrogram, blood pressure and vesical blood flow recordings from female ig showing normal pattern of compliance. Shaded areas A, B, C anXD correspond to blocks of data described in text as prefdling, prevoid, void and peak void.
obtain the best signal available. Sedation of the animals with low doses (<4 mg./kg./hr.) of propofol did not affect their P, significantly or the characteristics of their cystometrograms (CMG) (fig. 2) compared with those obtained in nonsedated animals and was necessary to protect the optical connection and minimize the movement artifact produced by the external portion of the optical pathway. If the dose of the propofol was increased to >6 mg./kg./hr., then all of the CMGs showed a “low-compliance”picture (fig. 3). As a result it was possible to obtain blood flow data in each animal both with normal and low compliance. A rise in Pdet of >10 cm. H,O from baseline prior to voiding was used as a cut-off to define those cycles showing low compliance. The data presented were normally distributed and are expressed as the mean (standard error of the mean [SEMI). Normal compliance. Figure 2 shows a typical “compliant“ CMG. The MacLab software was used to produce mean values for the 30-second blocks of data occurring immediately before the onset of bladder filling (prefilling) and the voiding contraction (prevoid). Another block of data coincident with the duration of the voiding contraction (void) was analyzed, as was a 5-second data block centered on the peak of the contraction (peak void). The data from 28 micturition cycles
RESULTS
NO significant morbidity was experienced as a result of the surgical procedure. The urine of each animal became colonized with low counts (<106/ml.) of bacteria without detectable numbers of leukocytes. Histology confirmed that the tip of each laser fiber lay within the detrusor muscle layer. There was minimal collagen deposition around the fiber tip. During the period of fiber implantation the relative changes recorded by the fiber probe did not alter, indicating that collagen deposition did not affect the results. Rapid signal recording and analysis showed that the flux signal oscillated synchronously with the cardiac cycle. Breaking and remaking the optical connection to the laser Doppler flowmeter signififantly affected the magnitude of, but not the relative changes the flux signal. The connection was always adjusted to
t AD Instruments Pty, NSW, Australia.
RG. 3. Cystometrogram, blood pressure and vesical blood flow re
cordings from female pig showing l o w a m liance picture. Shaded
blocks reDresent 2 %second blocks, separated\y another similarblack, as analy&d by MacLab software.
1860
BLADDER BLOOD FLOW DURING THE MICTURITION CYCLE
Blood flow during filling and voiding Mean Pder(SEMI (cm. H,OI Mean Pa, (SEMI (cm. H,O) Mean blood flow tSEM) ('2 Prefilling) * p (0.01.
Prefilling
F'revoid
Voiding
Peak void
2.45 (0.46) 161.77 (4.431 100 (0)
4.14 (0.43)* 163.36 (4.11) 96.32 (2.48)
18.63 (1.29)* 160.93 (4.26) 50.15 (2.34)*
21.85 l1.09)* 160.22 (4.541 37.89 (2.06)'
from the 7 animals are presented in the table, where the blood flow is expressed as a percentage of the prefilling value. Compliance was 619.9 (159.9)~ m . ~ / c m H,O. . Low compliance. Figure 3 shows a typical low-compliance CMG. The data for 19 such filling cycles from the 7 animals were analyzed in consecutive 30 second blocks. Bladder comH,O. . Prior to voiding, blood pliance was 58.66 (5.821~ m . ~ / c m flow fell to 44.53 (4.151%compared with the initial value (p <0.001, t test). The Pearson correlation coefficient for each series of data (Pdetversus blood flow) was -0.81 (0.03). To allow the relationship between changes in Pdetand blood flow to be quantified, it was necessary to normalize Pdetbecause the bladder compliance varied significantly from animal to animal. Figure 4 shows 3 representative plots of percent change in Pdetagainst percent change in blood flow together with the regression line for each series of data; the corresponding data from the normal compliance series are also plotted [slope -0.62 (-0.02)]. The mean slope of the regression lines was -0.53 (-0.05). There was no significant correlation between Pa, and either of the other variables. DISCUSSION
We believe that this method of measuring blood flow in the wall of the bladder offers significant advantages over those used previously. Chief among these is the fact that it can be carried out repeatedly in conscious large animals, which are believed to offer the best available model of the human lower urinary tract.14-16 In contrast to previous authors we are able to accurately describe the changes in Pd,t which occur, and furthermore the presence of low-compliance behavior has allowed the relationship between Pdet and blood flow to be further characterized. While LDF does not allow quantitative measurement of blood flow, this technique is able to adequately demonstrate, in semiquantitative fashion, the dynamic changes in blood flow within the detrusor muscle itself and not in the whole thickness of the bladder wall or indeed in the whole organ. We feel that this is important since it is
-Q-
Slope=4.5
----*--Slope = 4.63 d-- Slope = 4.52
-20
.
0
-70, . 0
. .
.
-Slam
%
, . . . . , . . . . , 25
50
75
= 4.53
,
. . ....... . . 0, 1W
%Change I'det
FIG. 4. Representative plots taken from 3 animals (A,c?, and 0) to show relationship between Pdetand blood flow under low-com liance conditions together with their respective regression lines a n i mean Corresponding plots ( 0 )of means for comregression line (-). pliant data series are also shown.
this layer which not only contains the smooth muscle but also contains many of the nerve fibers and ganglia of the autonomic nerves that innervate it.15.17 Certain forms of detrusor instability are associated with damage to the postganglionic neurones in the detrusor, and we believe that this model may be used to investigate a putative relationship between this neuronal loss and disturbances in blood flow patterns in disease states.18 We have shown that the principal determinant of blood flow within the wall of the bladder is the pressure within its lumen; at all times a negative relationship between these 2 variables is maintained. Blood flow is preserved during normal compliant filling despite the large increase in bladder surface area that occurs. I t is important that the bladder is able to act as a low pressure reservoir since, under abnormal low-compliance conditions, blood flow decreases significantly during filling. We feel that the confusion which exists in the literature regarding the effects of bladder filling on blood flow is due largely to a failure to accurately report the changes in intravesical pressure which are occurring.1.3.5-7-9Those authors who report a fall due to filling are really seeing the effects of rising intravesical pressure under their experimental conditions.l.3.5~7In agreement with our results in which pressure is accurately reported, a rise in intravesical pressure leads to a fall in blood flow.2.4.6 The mechanism by which the bladder's blood supply is able to adapt to the marked increase in surface area during filling is unknown. There is lack of information regarding the vascular anatomy of the urinary bladder. Braithwaitelg describes the macroscopic anatomy and Sarma20 the microangiographic details, including the presence of well-developed extramural, intramural and submucosal plexi. Neither advances any suggestion as t o how the blood supply adapts during filling. REFERENCES
1. Mehrotra, R. M.L.: An experimental study of the vesical circulation during distension and in cystitis. J. Pathol. Bacteriol., 6 6 79, 1953. 2. Dunn, M.: A study of the bladder blood flow during distension in rabbits. Br. J. Urol., 41:67, 1975. 3. Finkbeiner, A.and Lapides, J.: Effect of distension on blood flow in dog's urinary bladder. Invest. Urol., 1 2 210, 1974. 4. Nemeth, C. J., Khan, R. M., Kirchner, P. and Adams, R.: Changes in canine bladder perfusion with distension. Invest. Urol., 15 149, 1977. 5. Nielsen, K.K.,Nielsen, S. L., Nordling, J. and Kromann, A. B.: Rate of urinary bladder blood flow evaluated by 133Xe washout and radioactive microspheres in pigs. Urol. Res., 19:387, 1991. 6. Bellringer, J. F., Ward, J. and Fry, C. H.: Evaluation of a laser Doppler technique for the measurement of bladder blood flow in the anaesthetised rabbit. Proceedings International Continence Society, p. 89, 1993. 7. Siroky, M.B., Krane, R. J., Pontari, M. and Azadzoi, K.: Effect of bladder filling and contraction on bladder microcirculation. Neurourol. Urodyn., 12: 400, 1993. 8. Anderson, P. O.,Bloom, S. R., Mattiasson, A. and Uvelius, B.: Bladder vasodilatation and release of vasoactive intestinal polypeptide from the urinary bladder of the cat in response to pelvic nerve stimulation. J. Urol., 138 671, 1987. 9. Irwin, p. and Galloway, N. T.: Impaired bladder perfusion in interstitial cystitis: a study of blood supply using laser Doppler flowmetry. J. Urol., 149:890, 1993.
BLADDER BLOOD FLOW DURING THE MICTURITION CYCLE 10. Kroyer, K., Bulow, J., Nielsen, S. L. and Kromann, A. B.: Urinary bladder blood flow. I. Comparison of clearance of locally injected 99m-technetium pertechnate and radioactive microsphere technique in dogs. Urol. Res., 18 223, 1990. 11. Hofmann, R., Gomez, R., Schmidt, R. and Tanagho, E. A,: Effects of nerve stimulation on blood flow in the urinary bladder, urethra and pelvic floor in the dog. J. Urol., 150 1945, 1993. 12. Tyml, K. and Ellis, C. G.: Simultaneous assessment of red cell perfusion in skeletal muscle by laser Doppler flowmetry and video microscopy. Int. J. Microcirc. Clin. Exp., 4: 397, 1985. 13. Smits, G. J., Roman, R. J. and Lombard, J. H.: Evaluation of laser-Doppler flowmetry as a measure of tissue blood flow. J. Appl. Physiol., 61:666, 1986. 14. Sibley, G. N.: An experimental model of detrusor instability in the obstructed pig. Br. J. Urol., 57: 292, 1985.
1861
15. Crowe, R. and Burnstock, G.: A histochemical and immunohistochemical study of the autonomic innervation of the lower urinary tract of the female pig. Is the pig a good model for the human bladder and urethra? J. Urol., 141:414, 1989. 6. Guan, Z., Kiruluta, G., Coolsaet, B. and Elhilali, M.: Concious minipig model for evaluating the lower urinary tract. Neurourol. Urodyn., 13 147, 1994. 7. Gosling, J. A. and Dixon, J. S.: The structure and innervation of smooth muscle in the wall of the bladder neck and proximal urethra. Br. J. Urol., 47:549, 1975. 18. Brading, A. F. and Turner, W. H.: The unstable bladder: towards a common mechanism. Br. J. Urol., 73:3, 1994. 19. Braithwaite, J. L.: The arterial supply of the male urinary bladder. Br. J. Urol., 24:64, 1952. 20. Sarma, K P.: Microangiography of the bladder in health. Br.J. Urol., 53: 237, 1981.
vol. 156, 1858-1861,November
1996 Printed in U S A .
THe JOURNAL OF UROLCGY Copyright 0 1996 by AMERICANUROUXIICAL ASSOCIATION, INC.
URINARY BLADDER BLOOD FLOW CHANGES DURING THE MICTURITION CYCLE IN A CONSCIOUS PIG MODEL J. E. GREENLAND*
AND
A. F. BRADING
From the University Department of Pharmacology, Oxford University and the Department of Urology, Churchill Hospital, Headington, Oxford, United Kingabm
ABSTRACT
Purpose: TO develop a method using laser Doppler flowmetry in conscious pigs, which allows the accurate simultaneous measurement of cystometric and cardiovascular parameters together with changes in vesical blood flow. The animal model was then used to investigate the changes in blood flow in the urinary bladder which occur during the micturition cycle. Materials and Methods: Seven large white female pigs were subjected to chronically implanted vascular access and urodynamic catheters as well as a n intramural vesical laser Doppler probe. The animals underwent repeated conscious urodynamics with simultaneous measurement of cardiovascular, urodynamic and vesical blood flow parameters. Results: The model shows both compliant and low-compliance behavior and allows greater investigation of the effects of intravesical pressure on blood flow. Blood flow is not altered, during compliant filling and voiding transiently decreases flow to 38% of resting levels, with a rapid return to normal. Low-compliance filling results in a progressive fall in blood flow to a minimum of 45% of normal. At all times a n inverse relationship between intravesical pressure and blood flow is maintained. Conclusions: The pig model proved to be well suited to the experimental conditions and provided reproducible results. The principal determinant of blood flow within the wall of the bladder is the pressure within its lumen. During normal filling the blood supply of the bladder is able to adapt to the large increase in surface area which occurs, maintaining blood flow until the pressure increases. KEY WORDS:swine, regional blood flow, physiology, perfusion, laser-Doppler flowmetry
At present we know little of how blood flow within the wall of the urinary bladder is affected by the changes that occur during the phases of the micturition cycle. Even less is known of the effects of disease on vesical blood flow. To date vesical blood flow has not been investigated in conscious subjects. Some investigators have reported that bladder filling decreases blood flow in the wall of the bladder’-7 while others have reported a n increase.8.9 or no effect.”J Only 1 of these studies was performed in humansf the others used a variety of animal models. The techniques employed include the use of radiolabelled microspheres,4.5.10 radiolabelled tracer washout,2~3.5.10venous drop counting8 and laser Doppler flowmetry.6.7.9 All have been performed under general anesthesia, and only a few have accurately correlated the changes seen with recorded changes in intravesical pressure.2. 4-6, lo Where this has been done, all report a negative correlation. To date there have been no reports as to the changes that occur during normal micturition. Pelvic nerve stimulation has been used to produce bladder contraction with conflicting results: Andersson et al. reported a n increase in blood flow? Siroky et al.7 reported a decrease, and Hofmann et al.11 found no effect. In the present study we have developed a method of recording relative vesical blood flow during the micturition cycle normalized to prevoid values in conscious pigs using laser Doppler flowmetry (LDF). The laser Doppler flowmeter measures blood flow within the microcirculation by quantifying the amount of a laser light beam which is frequency shifted and reflected by a moving column of blood. The reading produced, expressed in flux units, is proportional to both
the numbers and velocity of red blood cells passing within a small distance of the probe tip.12.13 MATERIALS AND METHODS
Seven large white female pigs (weight range 58 to 95 kg.) were used. Under halothane general anesthesia each animal had silicone catheters with subcutaneous Dacronm cuffs tunnelled from entry sites in the dorsal mid-line to the abdominal cavity ( ~ 3 and ) neck (X2). Two of the abdominal lines were inserted through the dome of the bladder and sutured in place so that their tips lay free within its lumen. The third abdominal line was left free in the peritoneal cavity posterior to the bladder. One of the neck lines was placed in the descending thoracic aorta via the common carotid artery and the other in the superior vena cava via the internal jugular vein. Both were held in place by sutures passed through Dacron” “wings” positioned at the site of vessel entry. A 0.5 mm. diameter, bare plastic optical fiber sheathed in a Dacron” cuffed silicone catheter was tunnelled into the abdominal cavity as for the other lines. The distal 3 cm. of a 0.58 mm. i.d. nylon tube 5 cm. long was introduced into the wall of the bladder with a 14-gauge intravenous cannula needle as a trocar so that its tip was lying in the detrusor muscle layer. The laser fiber was then introduced through this polythene tubing which was subsequently withdrawn to leave approximately 2 mm. of laser fiber exposed within the detrusor (fig. 1).All of these components were then firmly anchored to the wall of the bladder with multiple 2-zero silk sutures taking care to avoid placing any sutures within 2 to 3 cm. of the fiber tip or around any visible blood vessels. Accepted for publication April 4,1996. Following surgery each animal had its vascular lines * Requests for reprints: Department of Urolo Churchill Hospital, Headington, Oxford OX3 7 U , United Kinggm. flushed with heparinized saline and received long-acting in1858
BLADDER BLOOD FLOW DURING THE MICTURITION CYCLE
Silicone Tubing
Laser Fibre Tip
\
1859
\
I Po‘ythene Tube
FIG.1. Schematic representation of arrangement of laser fiber and polythene tubing within bladder wall. Laser light beam is directed parallel to detrusor muscle layer.
I ~
tramuscular cephalexin injections on a daily basis. Urine was taken for microscopy and culture 1 week following bladder line insertion and then subsequently if indicated. Four to 5 days postoperatively it was possible to commence urodynamic investigation combined with LDF. It was possible to repeat the investigation on multiple days over a time period of up to 3 weeks. For investigation the animals were lightly sedated with a n infusion of propofol(2 to 8 mg./kg./hr.) via the vena cava line. One of the bladder catheters was used to fill the bladder with 0.9% saline at 38C at rates ranging from 20 to 110 ml. per minute. Experience showed that filling at 50 ml. per minute produced reproducible results that did not differ significantly from those obtained at other filling rates. As a result, most of the data presented below were obtained by filling at 50 ml. per minute. The other bladder line and the peritoneal line were connected via fluid filled catheters to pressure transducers to allow measurement of P,,, and Pabdo,respectively, and subtraction to give Pdet.The systemic blood pressure (P,) was measured in similar fashion from the aortic line. The laser fiber was connected via a n optical connector to an MBF3 laser Doppler flowmeter (Moor Instruments, Axminster, United Kingdom) to allow simultaneous measurement of blood flow (at a sampling frequency of 10 Hz) in the detrusor expressed in “flux units.” All parameters were displayed on a six-channel pen recorder and also recorded on digital audio tape for subsequent recording (at 10 Hz) and analysis with an eight-channel MacLab.? The MacLab software allows specified blocks of data to be identified and the mean values for each of the variables within the block to be calculated. Following sacrifice of the animal Sudan black dye was injected through the nylon laser fiber introducer sheath and the position of its tip in the wall of the bladder confirmed histologically.
FIG.2. Cystometrogram, blood pressure and vesical blood flow recordings from female ig showing normal pattern of compliance. Shaded areas A, B, C anXD correspond to blocks of data described in text as prefdling, prevoid, void and peak void.
obtain the best signal available. Sedation of the animals with low doses (<4 mg./kg./hr.) of propofol did not affect their P, significantly or the characteristics of their cystometrograms (CMG) (fig. 2) compared with those obtained in nonsedated animals and was necessary to protect the optical connection and minimize the movement artifact produced by the external portion of the optical pathway. If the dose of the propofol was increased to >6 mg./kg./hr., then all of the CMGs showed a “low-compliance”picture (fig. 3). As a result it was possible to obtain blood flow data in each animal both with normal and low compliance. A rise in Pdet of >10 cm. H,O from baseline prior to voiding was used as a cut-off to define those cycles showing low compliance. The data presented were normally distributed and are expressed as the mean (standard error of the mean [SEMI). Normal compliance. Figure 2 shows a typical “compliant“ CMG. The MacLab software was used to produce mean values for the 30-second blocks of data occurring immediately before the onset of bladder filling (prefilling) and the voiding contraction (prevoid). Another block of data coincident with the duration of the voiding contraction (void) was analyzed, as was a 5-second data block centered on the peak of the contraction (peak void). The data from 28 micturition cycles
RESULTS
NO significant morbidity was experienced as a result of the surgical procedure. The urine of each animal became colonized with low counts (<106/ml.) of bacteria without detectable numbers of leukocytes. Histology confirmed that the tip of each laser fiber lay within the detrusor muscle layer. There was minimal collagen deposition around the fiber tip. During the period of fiber implantation the relative changes recorded by the fiber probe did not alter, indicating that collagen deposition did not affect the results. Rapid signal recording and analysis showed that the flux signal oscillated synchronously with the cardiac cycle. Breaking and remaking the optical connection to the laser Doppler flowmeter signififantly affected the magnitude of, but not the relative changes the flux signal. The connection was always adjusted to
t AD Instruments Pty, NSW, Australia.
RG. 3. Cystometrogram, blood pressure and vesical blood flow re
cordings from female pig showing l o w a m liance picture. Shaded
blocks reDresent 2 %second blocks, separated\y another similarblack, as analy&d by MacLab software.
1860
BLADDER BLOOD FLOW DURING THE MICTURITION CYCLE
Blood flow during filling and voiding Mean Pder(SEMI (cm. H,OI Mean Pa, (SEMI (cm. H,O) Mean blood flow tSEM) ('2 Prefilling) * p (0.01.
Prefilling
F'revoid
Voiding
Peak void
2.45 (0.46) 161.77 (4.431 100 (0)
4.14 (0.43)* 163.36 (4.11) 96.32 (2.48)
18.63 (1.29)* 160.93 (4.26) 50.15 (2.34)*
21.85 l1.09)* 160.22 (4.541 37.89 (2.06)'
from the 7 animals are presented in the table, where the blood flow is expressed as a percentage of the prefilling value. Compliance was 619.9 (159.9)~ m . ~ / c m H,O. . Low compliance. Figure 3 shows a typical low-compliance CMG. The data for 19 such filling cycles from the 7 animals were analyzed in consecutive 30 second blocks. Bladder comH,O. . Prior to voiding, blood pliance was 58.66 (5.821~ m . ~ / c m flow fell to 44.53 (4.151%compared with the initial value (p <0.001, t test). The Pearson correlation coefficient for each series of data (Pdetversus blood flow) was -0.81 (0.03). To allow the relationship between changes in Pdetand blood flow to be quantified, it was necessary to normalize Pdetbecause the bladder compliance varied significantly from animal to animal. Figure 4 shows 3 representative plots of percent change in Pdetagainst percent change in blood flow together with the regression line for each series of data; the corresponding data from the normal compliance series are also plotted [slope -0.62 (-0.02)]. The mean slope of the regression lines was -0.53 (-0.05). There was no significant correlation between Pa, and either of the other variables. DISCUSSION
We believe that this method of measuring blood flow in the wall of the bladder offers significant advantages over those used previously. Chief among these is the fact that it can be carried out repeatedly in conscious large animals, which are believed to offer the best available model of the human lower urinary tract.14-16 In contrast to previous authors we are able to accurately describe the changes in Pd,t which occur, and furthermore the presence of low-compliance behavior has allowed the relationship between Pdet and blood flow to be further characterized. While LDF does not allow quantitative measurement of blood flow, this technique is able to adequately demonstrate, in semiquantitative fashion, the dynamic changes in blood flow within the detrusor muscle itself and not in the whole thickness of the bladder wall or indeed in the whole organ. We feel that this is important since it is
-Q-
Slope=4.5
----*--Slope = 4.63 d-- Slope = 4.52
-20
.
0
-70, . 0
. .
.
-Slam
%
, . . . . , . . . . , 25
50
75
= 4.53
,
. . ....... . . 0, 1W
%Change I'det
FIG. 4. Representative plots taken from 3 animals (A,c?, and 0) to show relationship between Pdetand blood flow under low-com liance conditions together with their respective regression lines a n i mean Corresponding plots ( 0 )of means for comregression line (-). pliant data series are also shown.
this layer which not only contains the smooth muscle but also contains many of the nerve fibers and ganglia of the autonomic nerves that innervate it.15.17 Certain forms of detrusor instability are associated with damage to the postganglionic neurones in the detrusor, and we believe that this model may be used to investigate a putative relationship between this neuronal loss and disturbances in blood flow patterns in disease states.18 We have shown that the principal determinant of blood flow within the wall of the bladder is the pressure within its lumen; at all times a negative relationship between these 2 variables is maintained. Blood flow is preserved during normal compliant filling despite the large increase in bladder surface area that occurs. I t is important that the bladder is able to act as a low pressure reservoir since, under abnormal low-compliance conditions, blood flow decreases significantly during filling. We feel that the confusion which exists in the literature regarding the effects of bladder filling on blood flow is due largely to a failure to accurately report the changes in intravesical pressure which are occurring.1.3.5-7-9Those authors who report a fall due to filling are really seeing the effects of rising intravesical pressure under their experimental conditions.l.3.5~7In agreement with our results in which pressure is accurately reported, a rise in intravesical pressure leads to a fall in blood flow.2.4.6 The mechanism by which the bladder's blood supply is able to adapt to the marked increase in surface area during filling is unknown. There is lack of information regarding the vascular anatomy of the urinary bladder. Braithwaitelg describes the macroscopic anatomy and Sarma20 the microangiographic details, including the presence of well-developed extramural, intramural and submucosal plexi. Neither advances any suggestion as t o how the blood supply adapts during filling. REFERENCES
1. Mehrotra, R. M.L.: An experimental study of the vesical circulation during distension and in cystitis. J. Pathol. Bacteriol., 6 6 79, 1953. 2. Dunn, M.: A study of the bladder blood flow during distension in rabbits. Br. J. Urol., 41:67, 1975. 3. Finkbeiner, A.and Lapides, J.: Effect of distension on blood flow in dog's urinary bladder. Invest. Urol., 1 2 210, 1974. 4. Nemeth, C. J., Khan, R. M., Kirchner, P. and Adams, R.: Changes in canine bladder perfusion with distension. Invest. Urol., 15 149, 1977. 5. Nielsen, K.K.,Nielsen, S. L., Nordling, J. and Kromann, A. B.: Rate of urinary bladder blood flow evaluated by 133Xe washout and radioactive microspheres in pigs. Urol. Res., 19:387, 1991. 6. Bellringer, J. F., Ward, J. and Fry, C. H.: Evaluation of a laser Doppler technique for the measurement of bladder blood flow in the anaesthetised rabbit. Proceedings International Continence Society, p. 89, 1993. 7. Siroky, M.B., Krane, R. J., Pontari, M. and Azadzoi, K.: Effect of bladder filling and contraction on bladder microcirculation. Neurourol. Urodyn., 12: 400, 1993. 8. Anderson, P. O.,Bloom, S. R., Mattiasson, A. and Uvelius, B.: Bladder vasodilatation and release of vasoactive intestinal polypeptide from the urinary bladder of the cat in response to pelvic nerve stimulation. J. Urol., 138 671, 1987. 9. Irwin, p. and Galloway, N. T.: Impaired bladder perfusion in interstitial cystitis: a study of blood supply using laser Doppler flowmetry. J. Urol., 149:890, 1993.
BLADDER BLOOD FLOW DURING THE MICTURITION CYCLE 10. Kroyer, K., Bulow, J., Nielsen, S. L. and Kromann, A. B.: Urinary bladder blood flow. I. Comparison of clearance of locally injected 99m-technetium pertechnate and radioactive microsphere technique in dogs. Urol. Res., 18 223, 1990. 11. Hofmann, R., Gomez, R., Schmidt, R. and Tanagho, E. A,: Effects of nerve stimulation on blood flow in the urinary bladder, urethra and pelvic floor in the dog. J. Urol., 150 1945, 1993. 12. Tyml, K. and Ellis, C. G.: Simultaneous assessment of red cell perfusion in skeletal muscle by laser Doppler flowmetry and video microscopy. Int. J. Microcirc. Clin. Exp., 4: 397, 1985. 13. Smits, G. J., Roman, R. J. and Lombard, J. H.: Evaluation of laser-Doppler flowmetry as a measure of tissue blood flow. J. Appl. Physiol., 61:666, 1986. 14. Sibley, G. N.: An experimental model of detrusor instability in the obstructed pig. Br. J. Urol., 57: 292, 1985.
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15. Crowe, R. and Burnstock, G.: A histochemical and immunohistochemical study of the autonomic innervation of the lower urinary tract of the female pig. Is the pig a good model for the human bladder and urethra? J. Urol., 141:414, 1989. 6. Guan, Z., Kiruluta, G., Coolsaet, B. and Elhilali, M.: Concious minipig model for evaluating the lower urinary tract. Neurourol. Urodyn., 13 147, 1994. 7. Gosling, J. A. and Dixon, J. S.: The structure and innervation of smooth muscle in the wall of the bladder neck and proximal urethra. Br. J. Urol., 47:549, 1975. 18. Brading, A. F. and Turner, W. H.: The unstable bladder: towards a common mechanism. Br. J. Urol., 73:3, 1994. 19. Braithwaite, J. L.: The arterial supply of the male urinary bladder. Br. J. Urol., 24:64, 1952. 20. Sarma, K P.: Microangiography of the bladder in health. Br.J. Urol., 53: 237, 1981.