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Gastrointestinal blood flow‐measuring techniques

A. P. Shepherd, J. W. Kiel

10.1002/cphy.cp060137

Source: Supplement 16: Handbook of Physiology, The Gastrointestinal System, Motility and Circulation

Originally published: 1989

Published online: January 2011

Full Article on Wiley Online Library



Abstract

The sections in this article are:

1 Microsphere Technique
1.1 Principle of Measurement
1.2 Fractionation of Intramural Blood Flow in Intestine
1.3 Microsphere Studies in Gastric Circulation
2 Laser‐Doppler Velocimetry
2.1 History
2.2 Theory of Laser‐Doppler Blood Flowmetry
2.3 Evaluations in Gastrointestinal Tract
3 Aminopyrine Clearance and Other pH Trapping Techniques
3.1 Overview of pH Trapping Methods
3.2 Theoretical Background
3.3 Evaluation of Aminopyrine Clearance
4 Hydrogen Clearance
4.1 History
4.2 Principle of Measurement
4.3 Advantages and Disadvantages of Hydrogen Clearance
4.4 Locally Generated Hydrogen
5 Conclusions
Figure 1. Figure 1.

Size of microspheres determines their distribution within gut wall. Shown are percentages of each microsphere size (X) recovered in canine mucosa, submucosa, muscularis, and venous blood. Note reciprocal relation between mucosal and submucosal trapping of spheres.

From Maxwell et al. 84
Figure 2. Figure 2.

Size‐selective microsphere trapping in intestine. Shown is ratio of frequency of given sphere size in tissue sample to its frequency in injectate or among all spheres recovered. This ratio would be unity if sphere trapping were not size dependent.

From Maxwell et al. 84
Figure 3. Figure 3.

Microsphere migration induced by vasodilation. Mucosa‐to‐submucosal ratios of sphere deposition were increased by vasodilation with isoproterenol (no data points fell below line of identity). For both microsphere sizes, control and experimental data were significantly different.

From Maxwell et al. 83
Figure 4. Figure 4.

Microsphere sieving effect. Relative frequency distributions of injected spheres (filled square) and spheres recovered from venous blood (x). Injectate was mixture of commercial 9‐, 10‐, 15‐, and 20‐μm spheres.

From Maxwell et al. 82
Figure 5. Figure 5.

Predicted (+) and observed (x) relative frequency distributions of spheres recovered from venous blood. Injectate same as in Fig. 4. Assumptions in model were that microsphere delivery to capillaries was r4 function of capillary radius, that mean capillary diameter was 7.38 μm ± SD 1.4, and that frequency distribution was lognormal.

From Maxwell et al. 82
Figure 6. Figure 6.

Relative frequency distribution of intestinal capillary diameters . Frequency distribution calculated from injected and venous microsphere populations without assumptions regarding mathematical form of frequency distribution of intestinal capillary diameters.

From McMahan et al. 85
Figure 7. Figure 7.

Spatial distribution of microspheres within stomach wall. Deposition of spheres in gastric pits was inversely related to microsphere size, whereas their accumulation in lamina propria was directly proportional to sphere diameter.

Adapted from Varhaug et al. 143
Figure 8. Figure 8.

Doppler effect for sound waves. A: if both listener and sound source are stationary, listener hears Ct/Λ waves in t seconds, where C is speed of sound and Λ is wavelength. B: if listener moves toward source at velocity vL, he will hear additional vLt/Λ waves in time t.

Adapted from Magnin 80
Figure 9. Figure 9.

Typical optics for laser‐Doppler velocimetry in tissue. A: coherent light is guided to tissue surface by optical fiber, and one or more receiving fibers return light scattered by tissue to photo‐detector. B: depth or volume of tissue from which scattered photons are collected increases with greater separation between sending and receiving fibers.
Figure 10. Figure 10.

Interactions between photons and tissue. A: of photons returning to photodetector, most have been scattered by static tissue elements. B: a few photons have experienced a Doppler shift as a result of a single collision with a moving red blood cell. C: other photons experience multiple scattering by moving erythrocytes, but these events are infrequent except in large vessels.

Adapted from Bonner and Nossal 16
Figure 11. Figure 11.

Doppler frequency spectra recorded from canine intestinal mucosa. In absence of blood flow (artery occluded), instrument noise, imperceptible tissue motion, and unknown factors produce frequency shift in laser light. Average frequency is increased during control blood flow and increased still further during reactive hyperemia

A. P. Shepherd, G. L. Riedel, and J. W. Kiel, unpublished observations
Figure 12. Figure 12.

Idealized scheme of laser‐Doppler signal processing. Light returning from tissue consists chiefly of unshifted photons scattered by static tissue and a few Doppler‐shifted photons scattered by moving red blood cells. Thus, as the photons mix, a photodetector signal results that has a direct current (DC) offset and a superimposed alternating current (AC) component. A: signal for a single red cell moving at constant velocity. B: if more red cells were moving at same velocity, magnitude of AC component would increase as more photons are Doppler shifted. C: if other factors remained constant and red cell velocity increased, frequency (f) of signal would increase.

From Haumschild 47 Reprinted by permission. Copyright © Instrument Society of America 1986. From Biomedical Sciences Instrumentation, vol. 22
Figure 13. Figure 13.

Block diagram of microprocessor‐based laser‐Doppler blood flowmeter. Typical signal processing includes setting upper and lower frequency cutoff filters to maximize signal‐to‐noise ratio and calculations of relative red blood cell flux, local red cell concentration in tissue, and average red cell velocity.
Figure 14. Figure 14.

Linearity of laser‐Doppler blood flowmeter in intestine. Left: in isolated canine small bowel, raw laser‐Doppler velocimetry measurements were linearly related to total blood flow (r = 0.89). Right: normalizing data to flow values measured at perfusion pressure of 120 mmHg improved correlation (slope, 1.1; r = 0.97). Preparations were vasodilated with isoproterenol to eliminate autoregulation and unpredictable redistributions of blood flow.

From Shepherd and Riedel 120
Figure 15. Figure 15.

Linearity of laser‐Doppler velocimetric (LDV) measurements of gastric mucosal blood flow. Top: in chambered canine stomach flaps vasodilated with isoproterenol, LDV‐measured blood flow was linearly related to total gastric perfusion (r = 0.98). Flow was changed by altering perfusion pressure. Bottom: in preparations not vasodilated with isoproterenol, curve deviated from apparent linearity because gastric mucosal blood flow was autoregulated, as indicated by analysis of pressure versus flow relationship (not shown). For comparison, regression line from isoproterenol data is also shown.

From Kiel et al. 58
Figure 16. Figure 16.

Lack of reproducibility with laser‐Doppler blood flowmetry. Manipulating portal venous perfusion pressure to alter blood flow to isolated rat liver preparation resulted in highly linear relation between total hepatic perfusion and laser‐Doppler velocimetry‐measured blood on liver surface, but slopes of lines were not consistently reproducible.

From Shepherd et al. 125
Figure 17. Figure 17.

Reactive hyperemia and motility artifacts in laser‐Doppler blood flow tracings. In isolated loop of canine small bowel, spikes in laser‐Doppler velocimetry tracings during arterial occlusion are motility artifacts. Both mucosal and muscularis perfusion seem to undergo motility‐related oscillations (also see Fig. 18). Note that following arterial occlusion both total and mucosal blood flow tracings displayed characteristic reactive hyperemia, but reactive hyperemia was absent in muscularis.

From Shepherd and Riedel 122
Figure 18. Figure 18.

Motility artifacts or motility‐related oscillations in gastric blood flow? In chambered canine stomach flaps, laser‐Doppler blood flow tracings oscillate at same frequency as electrical activity in muscularis.

From Kiel et al. 58
Figure 19. Figure 19.

Two‐compartment model of the pH partition hypothesis. Gastric mucosa is represented as a plasma compartment and a gastric juice compartment separated by a lipoidal barrier selectively permeable to undissociated weak base. At plasma pH, weak base is predominantly undissociated, readily diffuses across barrier, and is “trapped” when dissociated in the low pH of gastric juice.
Figure 20. Figure 20.

Dissociation of gastric secretion and aminopyrine clearance. In a histamine‐stimulated Heidenhain pouch, a low dose of isoproterenol greatly increased aminopyrine clearance but did not change gastric volume secretion. However, the higher dose depressed both aminopyrine clearance and gastric secretion. R, concentration ratio.

Adapted from Jacobson et al. 53
Figure 21. Figure 21.

Dissociation of total gastric blood flow and aminopyrine clearance during stimulated acid secretion. In Heidenhain pouch, graded gastrin infusion greatly increased aminopyrine clearance without changing total blood flow.

Adapted from Swan and Jacobson 137
Figure 22. Figure 22.

Dissociation of total gastric blood flow and aminopyrine clearance during inhibition of acid secretion. In chambered canine stomach flap stimulated with histamine, thiocyanate poisoning greatly depressed aminopyrine clearance and secretion of gastric juice but did not alter total blood flow.

Adapted from Moody 91
Figure 23. Figure 23.

Dissociation of gastric oxygen consumption and aminopyrine clearance during inhibition of acid secretion. In chambered canine stomach flap stimulated with histamine, thiocyanate poisoning depressed aminopyrine clearance nearly to zero without altering either total blood flow or gastric oxygen uptake.

Adapted from Moody 92
Figure 24. Figure 24.

Comparison of gastric mucosal blood flow measurements by aminopyrine clearance and microspheres. During infusions of histamine or isoproterenol, aminopyrine clearance values showed significant linear correlation with microsphere determinations in chambered canine stomach flaps. However, slopes of regression lines show that aminopyrine clearance consistently underestimated blood flow measured by microspheres. Furthermore discrepancy between the two methods was even greater in the absence of acid secretion (isoproterenol). Linear regression lines are shown; data points omitted for clarity.

Adapted from Archibald et al. 3
Figure 25. Figure 25.

Effect of acid secretion rate on ratio of microsphere‐measured mucosal blood flow to aminopyrine clearance (MMF/APC). If two techniques measured same quantity, ratio would equal one. Most data points lie above solid line showing aminopyrine clearance underestimated microsphere determinations. Note disparity increased markedly at low rates of acid secretion.

Adapted from Archibald et al. 3
Figure 26. Figure 26.

Comparison of aminopyrine clearances determined spectrophotometrically and with 14C‐labeled aminopyrine. Although measurements were highly correlated, slope of regression line, which is significantly different from 1.0, indicates that spectrophotometric method overestimated [14C]aminopyrine clearance. Spectrophotometric method requires much higher plasma concentrations of aminopyrine than isotope method.

Data from Tague and Jacobson 138
Figure 27. Figure 27.

Aminopyrine clearance overestimates gastric mucosal blood flow during stimulated acid secretion. In rabbits, pentagastrin increased blood flow measured by all 3 techniques. Measurements by electromagnetic flow probe and hydrogen clearance showed similar increases in blood flow (17% and 22%, respectively), but an inordinate increase in aminopyrine clearance (216%) occurred that was quantitatively inconsistent with the other two measurements. Flow units are left gastric artery, ml/min; aminopyrine and hydrogen clearance, ml · min−1 · 100 g−1.

Data from Leung et al. 71
Figure 28. Figure 28.

Sequestration of aminopyrine by isolated parietal cells. Parietal cells accumulate significant quantities of aminopyrine; this sequestration is enhanced by agents listed.

Adapted from Sonnenberg et al. 130
Figure 29. Figure 29.

Hydrogen gas clearance values significantly correlated with microsphere‐measured gastric mucosal blood flow. In anterior corpus of canine stomach at gastrotomy, hydrogen underestimated microsphere‐measured gastric mucosal perfusion as indicated by slope of regression line.

From Ashley and Cheung 5
Figure 30. Figure 30.

Principle of hydrogen clearance technique for measuring blood flow. If instantaneous arterial (Cin) and venous (Cout) concentrations of indicator gas were known, blood flow could be determined from either tissue uptake or washout of hydrogen, but in practice only relative tissue hydrogen concentration is recorded. Also see Figs. 31 and 32.
Figure 31. Figure 31.

Blood flow determined from tissue saturation or uptake of indicator. Blood flow could be determined from tissue uptake of hydrogen if instantaneous arterial (Cin) and venous (Cout) concentrations of hydrogen were known.
Figure 32. Figure 32.

Blood flow determined from washout of hydrogen. If it can be assumed that hydrogen reaches equilibrium with tissue (C∞), blood flow can be determined by monitoring only instantaneous tissue hydrogen concentration and integrating area under washout curve.
Figure 33. Figure 33.

FIG. 33. Proposed method for measuring blood flow by local generation of hydrogen. One electrode measures local H2 concentration while a second electrode connected to a constant current source generates hydrogen electrochemically. Tissue is first saturated with hydrogen, then H2‐generating current is shut off, and washout curve is recorded.


Figure 1.

Size of microspheres determines their distribution within gut wall. Shown are percentages of each microsphere size (X) recovered in canine mucosa, submucosa, muscularis, and venous blood. Note reciprocal relation between mucosal and submucosal trapping of spheres.

From Maxwell et al. 84


Figure 2.

Size‐selective microsphere trapping in intestine. Shown is ratio of frequency of given sphere size in tissue sample to its frequency in injectate or among all spheres recovered. This ratio would be unity if sphere trapping were not size dependent.

From Maxwell et al. 84


Figure 3.

Microsphere migration induced by vasodilation. Mucosa‐to‐submucosal ratios of sphere deposition were increased by vasodilation with isoproterenol (no data points fell below line of identity). For both microsphere sizes, control and experimental data were significantly different.

From Maxwell et al. 83


Figure 4.

Microsphere sieving effect. Relative frequency distributions of injected spheres (filled square) and spheres recovered from venous blood (x). Injectate was mixture of commercial 9‐, 10‐, 15‐, and 20‐μm spheres.

From Maxwell et al. 82


Figure 5.

Predicted (+) and observed (x) relative frequency distributions of spheres recovered from venous blood. Injectate same as in Fig. 4. Assumptions in model were that microsphere delivery to capillaries was r4 function of capillary radius, that mean capillary diameter was 7.38 μm ± SD 1.4, and that frequency distribution was lognormal.

From Maxwell et al. 82


Figure 6.

Relative frequency distribution of intestinal capillary diameters . Frequency distribution calculated from injected and venous microsphere populations without assumptions regarding mathematical form of frequency distribution of intestinal capillary diameters.

From McMahan et al. 85


Figure 7.

Spatial distribution of microspheres within stomach wall. Deposition of spheres in gastric pits was inversely related to microsphere size, whereas their accumulation in lamina propria was directly proportional to sphere diameter.

Adapted from Varhaug et al. 143


Figure 8.

Doppler effect for sound waves. A: if both listener and sound source are stationary, listener hears Ct/Λ waves in t seconds, where C is speed of sound and Λ is wavelength. B: if listener moves toward source at velocity vL, he will hear additional vLt/Λ waves in time t.

Adapted from Magnin 80


Figure 9.

Typical optics for laser‐Doppler velocimetry in tissue. A: coherent light is guided to tissue surface by optical fiber, and one or more receiving fibers return light scattered by tissue to photo‐detector. B: depth or volume of tissue from which scattered photons are collected increases with greater separation between sending and receiving fibers.



Figure 10.

Interactions between photons and tissue. A: of photons returning to photodetector, most have been scattered by static tissue elements. B: a few photons have experienced a Doppler shift as a result of a single collision with a moving red blood cell. C: other photons experience multiple scattering by moving erythrocytes, but these events are infrequent except in large vessels.

Adapted from Bonner and Nossal 16


Figure 11.

Doppler frequency spectra recorded from canine intestinal mucosa. In absence of blood flow (artery occluded), instrument noise, imperceptible tissue motion, and unknown factors produce frequency shift in laser light. Average frequency is increased during control blood flow and increased still further during reactive hyperemia

A. P. Shepherd, G. L. Riedel, and J. W. Kiel, unpublished observations


Figure 12.

Idealized scheme of laser‐Doppler signal processing. Light returning from tissue consists chiefly of unshifted photons scattered by static tissue and a few Doppler‐shifted photons scattered by moving red blood cells. Thus, as the photons mix, a photodetector signal results that has a direct current (DC) offset and a superimposed alternating current (AC) component. A: signal for a single red cell moving at constant velocity. B: if more red cells were moving at same velocity, magnitude of AC component would increase as more photons are Doppler shifted. C: if other factors remained constant and red cell velocity increased, frequency (f) of signal would increase.

From Haumschild 47 Reprinted by permission. Copyright © Instrument Society of America 1986. From Biomedical Sciences Instrumentation, vol. 22


Figure 13.

Block diagram of microprocessor‐based laser‐Doppler blood flowmeter. Typical signal processing includes setting upper and lower frequency cutoff filters to maximize signal‐to‐noise ratio and calculations of relative red blood cell flux, local red cell concentration in tissue, and average red cell velocity.



Figure 14.

Linearity of laser‐Doppler blood flowmeter in intestine. Left: in isolated canine small bowel, raw laser‐Doppler velocimetry measurements were linearly related to total blood flow (r = 0.89). Right: normalizing data to flow values measured at perfusion pressure of 120 mmHg improved correlation (slope, 1.1; r = 0.97). Preparations were vasodilated with isoproterenol to eliminate autoregulation and unpredictable redistributions of blood flow.

From Shepherd and Riedel 120


Figure 15.

Linearity of laser‐Doppler velocimetric (LDV) measurements of gastric mucosal blood flow. Top: in chambered canine stomach flaps vasodilated with isoproterenol, LDV‐measured blood flow was linearly related to total gastric perfusion (r = 0.98). Flow was changed by altering perfusion pressure. Bottom: in preparations not vasodilated with isoproterenol, curve deviated from apparent linearity because gastric mucosal blood flow was autoregulated, as indicated by analysis of pressure versus flow relationship (not shown). For comparison, regression line from isoproterenol data is also shown.

From Kiel et al. 58


Figure 16.

Lack of reproducibility with laser‐Doppler blood flowmetry. Manipulating portal venous perfusion pressure to alter blood flow to isolated rat liver preparation resulted in highly linear relation between total hepatic perfusion and laser‐Doppler velocimetry‐measured blood on liver surface, but slopes of lines were not consistently reproducible.

From Shepherd et al. 125


Figure 17.

Reactive hyperemia and motility artifacts in laser‐Doppler blood flow tracings. In isolated loop of canine small bowel, spikes in laser‐Doppler velocimetry tracings during arterial occlusion are motility artifacts. Both mucosal and muscularis perfusion seem to undergo motility‐related oscillations (also see Fig. 18). Note that following arterial occlusion both total and mucosal blood flow tracings displayed characteristic reactive hyperemia, but reactive hyperemia was absent in muscularis.

From Shepherd and Riedel 122


Figure 18.

Motility artifacts or motility‐related oscillations in gastric blood flow? In chambered canine stomach flaps, laser‐Doppler blood flow tracings oscillate at same frequency as electrical activity in muscularis.

From Kiel et al. 58


Figure 19.

Two‐compartment model of the pH partition hypothesis. Gastric mucosa is represented as a plasma compartment and a gastric juice compartment separated by a lipoidal barrier selectively permeable to undissociated weak base. At plasma pH, weak base is predominantly undissociated, readily diffuses across barrier, and is “trapped” when dissociated in the low pH of gastric juice.



Figure 20.

Dissociation of gastric secretion and aminopyrine clearance. In a histamine‐stimulated Heidenhain pouch, a low dose of isoproterenol greatly increased aminopyrine clearance but did not change gastric volume secretion. However, the higher dose depressed both aminopyrine clearance and gastric secretion. R, concentration ratio.

Adapted from Jacobson et al. 53


Figure 21.

Dissociation of total gastric blood flow and aminopyrine clearance during stimulated acid secretion. In Heidenhain pouch, graded gastrin infusion greatly increased aminopyrine clearance without changing total blood flow.

Adapted from Swan and Jacobson 137


Figure 22.

Dissociation of total gastric blood flow and aminopyrine clearance during inhibition of acid secretion. In chambered canine stomach flap stimulated with histamine, thiocyanate poisoning greatly depressed aminopyrine clearance and secretion of gastric juice but did not alter total blood flow.

Adapted from Moody 91


Figure 23.

Dissociation of gastric oxygen consumption and aminopyrine clearance during inhibition of acid secretion. In chambered canine stomach flap stimulated with histamine, thiocyanate poisoning depressed aminopyrine clearance nearly to zero without altering either total blood flow or gastric oxygen uptake.

Adapted from Moody 92


Figure 24.

Comparison of gastric mucosal blood flow measurements by aminopyrine clearance and microspheres. During infusions of histamine or isoproterenol, aminopyrine clearance values showed significant linear correlation with microsphere determinations in chambered canine stomach flaps. However, slopes of regression lines show that aminopyrine clearance consistently underestimated blood flow measured by microspheres. Furthermore discrepancy between the two methods was even greater in the absence of acid secretion (isoproterenol). Linear regression lines are shown; data points omitted for clarity.

Adapted from Archibald et al. 3


Figure 25.

Effect of acid secretion rate on ratio of microsphere‐measured mucosal blood flow to aminopyrine clearance (MMF/APC). If two techniques measured same quantity, ratio would equal one. Most data points lie above solid line showing aminopyrine clearance underestimated microsphere determinations. Note disparity increased markedly at low rates of acid secretion.

Adapted from Archibald et al. 3


Figure 26.

Comparison of aminopyrine clearances determined spectrophotometrically and with 14C‐labeled aminopyrine. Although measurements were highly correlated, slope of regression line, which is significantly different from 1.0, indicates that spectrophotometric method overestimated [14C]aminopyrine clearance. Spectrophotometric method requires much higher plasma concentrations of aminopyrine than isotope method.

Data from Tague and Jacobson 138


Figure 27.

Aminopyrine clearance overestimates gastric mucosal blood flow during stimulated acid secretion. In rabbits, pentagastrin increased blood flow measured by all 3 techniques. Measurements by electromagnetic flow probe and hydrogen clearance showed similar increases in blood flow (17% and 22%, respectively), but an inordinate increase in aminopyrine clearance (216%) occurred that was quantitatively inconsistent with the other two measurements. Flow units are left gastric artery, ml/min; aminopyrine and hydrogen clearance, ml · min−1 · 100 g−1.

Data from Leung et al. 71


Figure 28.

Sequestration of aminopyrine by isolated parietal cells. Parietal cells accumulate significant quantities of aminopyrine; this sequestration is enhanced by agents listed.

Adapted from Sonnenberg et al. 130


Figure 29.

Hydrogen gas clearance values significantly correlated with microsphere‐measured gastric mucosal blood flow. In anterior corpus of canine stomach at gastrotomy, hydrogen underestimated microsphere‐measured gastric mucosal perfusion as indicated by slope of regression line.

From Ashley and Cheung 5


Figure 30.

Principle of hydrogen clearance technique for measuring blood flow. If instantaneous arterial (Cin) and venous (Cout) concentrations of indicator gas were known, blood flow could be determined from either tissue uptake or washout of hydrogen, but in practice only relative tissue hydrogen concentration is recorded. Also see Figs. 31 and 32.



Figure 31.

Blood flow determined from tissue saturation or uptake of indicator. Blood flow could be determined from tissue uptake of hydrogen if instantaneous arterial (Cin) and venous (Cout) concentrations of hydrogen were known.



Figure 32.

Blood flow determined from washout of hydrogen. If it can be assumed that hydrogen reaches equilibrium with tissue (C∞), blood flow can be determined by monitoring only instantaneous tissue hydrogen concentration and integrating area under washout curve.



Figure 33.

FIG. 33. Proposed method for measuring blood flow by local generation of hydrogen. One electrode measures local H2 concentration while a second electrode connected to a constant current source generates hydrogen electrochemically. Tissue is first saturated with hydrogen, then H2‐generating current is shut off, and washout curve is recorded.

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Article Title: Gastrointestinal blood flow‐measuring techniques
 

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A. P. Shepherd, J. W. Kiel. Gastrointestinal blood flow‐measuring techniques. Compr Physiol 2011, Supplement 16: Handbook of Physiology, The Gastrointestinal System, Motility and Circulation: 1335-1370. First published in print 1989. doi: 10.1002/cphy.cp060137