Spider Angiomas in Patients with Liver Cirrhosis: Role of Alcoholism and Impaired Liver Function

A study was undertaken to compare two new methods of capillary blood flow measurement, namely fluorescein flowmetry (FF) and laser Doppler flowmetry (LDF). The blood flow was measured in a pelvic pouch during its construction and in the completed ileoanal anastomosis in 12 patients. There was a high correlation between the two methods (correlation coefficient, 0.78) (p <0.01) when the blood flow was measured in the pelvic pouch. The correlation coefficient between the two methods for the difference between the blood flow in the pelvic pouch at the site of the planned anastomosis when the pouch resided in the abdomen and that in the completed ileoanal anastomosis was r = 0.99 (n = 12, p< 0.001); the reduction amounted to 25% as measured by FF and 27% as measured by LDF (n = 12, p < 0.01). All ileoanal anastomoses healed perfectly, the lowest FF and LDF values being 0.004 density units/sec and 0.3 V, respectively. The results indicate that either method can be considered for measuring capillary blood flow.     

The mucosal blood flow in pelvic pouches in man

Fluorescein flowmetry implies the measurement of capillary blood flow, expressed as an index between the maximum fluorescence after the first circulatory passage of sodium fluorescein (NaF) and the rise time, defined as the time interval between ten and 90 percent of the maximum fluorescence. A mathematic model based on fluorescein flowmetry was deduced to distinguish a mucosal and muscular blood flow in an intact (unopened) intestine during surgery in man. The hypothesis was that if, at a certain point in time, there is a fixed relationship between the seromuscular fluorescence and the mucosal maximum fluorescence, obtained during the first circulatory passage of NaF, and if the rise times were equal, then a mucosal blood flow could be calculated based on the seromuscular fluorescence. The model was tested in intestinal anastomoses on 16 patients. A fixed relationship between the numeric value of the mucosal maximum fluorescence and the seromuscular fluorescence was found. After five minutes, the ratio was 1:1 and the correlation coefficient at its highest (0.97). It was also found that the rise times were practically identical (r=0.92). The validity of the model was then tested by comparing it with fluorescein flowmetry, and the correlation coefficient was 0.85. The model was therefore accepted and named indirect mucosal fluorescein flowmetry. Indirect mucosal fluorescein flowmetry was applied to measure blood flow in pelvic pouches in 14 patients, and fluorescein flowmetry in the ileoanal anastomoses in eight patients. The mucosal blood flow in the reservoir, compared with the normal intestine, was reduced to 58 percent if the ileocolic artery or distal branches of the mesenteric artery were ligated, and to 88 percent if the vessels were left intact (P<0.05). In the ileoanal anastomosis the mucosal blood flow was reduced to 23 percent compared with the normal intestine (P<0.01). The results suggest that stretching and compressing the mesentery might be critical for circulation in the ileoanal anastomoses. Supported by the Serafimer Hospital Foundation and ELFA Radio and Television AB:s Foundation.     

Assessment of blood flow in the small intestine with laser Doppler flowmetry

Blood flow in the small intestine was assessed in 48 patients by laser Doppler flowmetry. Mucosal and serosal flowmeter signals were compared during 'resting' conditions, vascular occlusion, and reactive hyperemia. Serosal flowmeter recordings were compared with the total blood flow of a bowel segment as measured by venous collection. The magnitudes of the mucosal (n = 49) and serosal (n = 49) flowmeter signals were comparable throughout the whole range of flowmeter signals (r = 0.97; p less than 0.001). A correlation coefficient of 0.95 (n = 51; p less than 0.001) was obtained between serosal flowmeter signals and total blood flow during 'resting' and reduced blood flows. During vasodilatation after a vascular occlusion, blood flow was underestimated by the flowmeter. A calibration curve could be constructed for approximate interpretation of the flowmeter signals in absolute flow units. The present study underlines the potential of laser Doppler flowmetry in the assessment of blood flow in the human small intestine.     

Measurement of colonic blood flow with laser Doppler flowmetry

Colonic blood flow was measured with laser Doppler flowmetry during operation in 62 patients and during coloscopy in 15 patients. In 18 subjects mucosal and serosal laser Doppler signals were compared during 'resting' conditions, vascular occlusion, and reactive hyperemia. The mucosal (n = 36) and serosal (n = 36) flowmeter signals were of the same order of magnitude throughout the whole range of flowmeter signals (r = 0.96; p less than 0.001). In eight subjects total venous outflow from a colonic segment was measured simultaneously with flowmeter recordings from the serosal side. A correlation coefficient of 0.95 (n = 46; p less than 0.001) was obtained between total intestinal blood flow and serosal flowmeter signal during 'resting' and reduced blood flows. In this flow range a calibration curve was constructed for interpretation of the flowmeter signals in absolute flow units. The wall thickness of the bowel determined the quantitative relationship between flowmeter signal and total intestinal blood flow. It is concluded that laser Doppler flowmetry represents a potentially very interesting non-invasive, continuous method for the quantitative study of human intestinal blood flow.     

Assessment of mucosal inflammation and circulation in response to probiotics in patients operated with ileal pouch anal anastomosis for ulcerative colitis

BACKGROUND: Pouchitis is a common and troublesome condition, and a disturbed microbiological flora and mucosal blood flow in the pouch have been suggested as possible causes. Laser Doppler flowmetry (LDF) has been used successfully to measure gastric and colonic mucosal perfusion in humans. The aim of this study was to evaluate the effect of intervention with probiotics on ileal pouch inflammation and perfusion in the pouch, assessed by endoscopy, histology, fecal calprotectin and LDF. METHODS: A fermented milk product (Cultura; 500 ml) containing live lactobacilli (La-5) and bifidobacteria (Bb-12) was given daily for 4 weeks to 10 patients operated with ileal-pouch-anal anastomosis (IPAA) for ulcerative colitis (UC). Mucosal perfusion was measured with LDF and the degree of inflammation was examined at predefined levels of the distal bowel by endoscopy and histology. Stool samples were cultured for lactobacilli and bifidobacteria and calprotectin were measured before and after intervention. RESULTS: The LDF measurements were reproducible in the pelvic pouch at each of the predefined levels, but did not change after intervention. The mucosal perfusion was reduced in the distal compared to the proximal part of the pouch. Calprotectin levels did not change significantly after intervention. The median endoscopic score for inflammation was significantly reduced by 50% after intervention, whereas the histological score did not change significantly. CONCLUSION: The results suggest that probiotics primarily act superficially, with change of gross appearance of the mucosa at endoscopy, but without significant effect on histological picture, mucosal perfusion or faecal calprotectin, during a relatively short period of 4 weeks.     

Digital blood flow in cooled and contralateral finger in patients with Raynaud's phenomenon. Comparative measurements between photoelectrical plethysmography and laser Doppler flowmetry.

The effects of cooling of a hand on lateral and contralateral digital skin blood flow were investigated in 18 patients with primary or secondary Raynaud's phenomenon. The aim of the study was to compare photoelectrical plethsmography (PhEP) and laser Doppler flowmetry (LDF). PhEP and LDF were used simultaneously for skin blood flow measurements of the third finger of both hands. One hand was cooled in water from 33 degrees to 3 degrees C in steps of 3 degrees C, each step lasting four minutes. It was followed by a recovery period of ten minutes in room air of 24 degrees C. During stepwise cooling from 33 degrees to 9 degrees C the relative PhEP and LDF values, measured on the cooled hand, decreased to 6.2% +/- 3.2% and 10% +/- 12% respectively. The correlation coefficients between LDF and PhEP varied between 0.79 and 0.99. In the contralateral hand the relative PhEP and LDF values decreased to 38% +/- 30.% and 64% +/- 7.9% respectively. The correlation coefficients between LDF and PhEP values were lower on the contralateral hand and ranged from 0.26 to 0.95. By calculating the LDF/PhEP ratios during cooling and recovery, more specific changes in red blood cell velocities during cooling were studied. Increasing LDF/PhEP ratios suggest increasing red blood cell velocities during cooling at 9 degrees C and a difference in the measuring methods. For testing the severity of Raynaud's phenomenon and the effect of treatment the results of both methods show consistent and quite comparable results when measured on the cooled hand. The effect of indirect cooling on the contralateral hand is, however, less consistent.     

Assessment of gastric blood flow with laser Doppler flowmetry

The use of laser Doppler flowmetry (LDF) to measure gastric blood flow was evaluated in the cat and man. The reproducibility of laser Doppler flowmetry recordings was studied in the feline stomach. In five cats flowmeter signals and venous outflow of the stomach were simultaneously recorded. The flowmeter recordings were made during operation and gastroscopy in 140 patients by means of two different (PF1-4-kHz and PF2-12-kHz) laser Doppler systems. The flowmeter recordings were highly reproducible during the cat experiments, with a coefficient of variation varying between 4% and 13%. Angulation of the probe within 60-120 degrees against the tissue under study did not affect the flowmeter signal. Pressure of the probe against the studied tissue attenuated the flowmeter signal 42 +/- 13% (n = 10). A significant correlation coefficient (r = 0.76; p = 0.01; n = 30) was obtained between flowmeter signal and venous outflow of the stomach. In man the PF2-12-kHz system yielded a higher flowmeter signal (14.5 +/- 6.9 V; 32 patients) than the PF1-4-kHz system (7.9 +/- 2.5 V; 108 patients). Flow dimensions were calculated by using results previously obtained in the intestines. The estimated blood flow values amounted to 31 +/- 10 and 57 +/- 27 ml min-1 100 g-1 for the PF1-4-kHz and PF2-12-kHz systems, respectively. In conclusion, laser Doppler flowmeter is a promising technique for studying gastric perfusion during operation and endoscopy. Motion artifacts are the major drawback of the present laser Doppler systems.     

Endoscopic fluorescein flowmetry in the evaluation of gastric and duodenal mucosal blood flow

Fluorescein flowmetry (FF) implies the measurement of a relative capillary blood flow, expressed as an index--that is, the ratio between the maximum fluorescence, obtained during the first circulatory passage of sodium fluorescein (Na-F), and the rise time, defined as the time interval between 10% and 90% of the maximum fluorescence. The aim of this study was to develop FF to be used during endoscopy for the evaluation of ventricular and duodenal mucosal blood flow. FF was applied during gastroduodenoscopy in 38 patients with normal mucosa, as verified by histopathologic examination. The blood flow index did not differ significantly for the mucosa of the fundus, corpus, and antrum. However, when compared with the duodenal mucosa, the blood flow index of the ventricular mucosa was almost twice as high (P less than 0.01). This, in turn, was due to a significantly higher maximum fluorescence in the ventricular mucosa (P less than 0.01), indicating a denser capillary network than in the duodenal mucosa. Since FF is a reliable method, easy to perform and without complications, it is suitable whenever mucosal blood flow warrants measurement during endoscopy.     

Continuous measurement of gastric blood flow by laser-Doppler flowmetry during gastroscopy

Endoscopic laser-Doppler flowmetry (LDF) of gastric blood flow (GBF) was performed simultaneously with intragastric manometry to detect a possible correlation between GBF and luminal pressure during gastroscopy. By increasing luminal air pressure from 10 to 20 cm H2O a significant reduction in GBF was observed. Regional differences in GBF were also demonstrated. Variations in luminal air pressure have a significant influence on GBF as measured by LDF, and therefore intragastric manometry and standardization of intraluminal air pressure is necessary in endoscopic LDF measurements.     

Scanning laser-Doppler flowmetry of rat cerebral circulation during cortical spreading depression

Scanning laser-Doppler flowmetry (SLDF) generates two-dimensional images of blood flow. This study compared SLDF to conventional laser-Doppler flowmetry (LDF) in the cerebral circulation. Test stimuli were episodes of cortical spreading depression (CSD) elicited in brains of halothane anaesthetised rats (n = 9). The LDF instrument used two wavelengths of laser light to record relative changes of cerebral blood flow (CBF) up to an approximate depth of 250 microm (543 nm) and 500 microm (780 nm). Under resting conditions, SLDF images showed a heterogeneous pattern of flow in pial vessels with high flow rates in arterioles, and lower rates in venules and small vessels (<30 microm). Arterioles constituted about 6%, venules 12% and small vessels 2% of the image area, while approximately 80% were background with a laser-Doppler signal corresponding to zero calibration. During CSD, the relative increase of area was largest for small vessels and less for venules and arterioles. Similar changes were observed for blood flow in the three vessel structures. For both wavelengths of LDF, flow changes correlated with SLDF (r approximately 0.7). In conclusion, SLDF provides images of flow in pial vessels and capillaries at, or just beneath the cortical surface. SLDF and LDF are complementary, but cannot substitute for one another as they measure flow in different layers of the cortex.     

Evaluation of endoscopic laser Doppler flowmetry for measurement of human gastric blood flow. Methodologic aspects

Endoscopic measurement of gastric blood perfusion by laser Doppler flowmetry (LDF) has been evaluated in 28 patients and 15 healthy volunteers. During the recordings it was necessary to keep the probe in light contact with the mucosa to obtain stable curves and to avoid artificial Doppler signals caused by relative movements between the gastric wall and the probe. Gastric distention by air insufflation did not influence the recorded flow level significantly when air insufflation was moderate. The intravenous injection of 0.6 mg atropine did not cause any significant alteration in recorded blood flow, and this drug may be used as premedication before endoscopic blood flow measurements. Recordings with both 4- and 12-kHz bandwidth of the LDF instrument showed a relative constant relationship for different flow levels, the flow values measured with 12 kHz being about twice the corresponding values measured with 4 kHz. With 12-kHz bandwidth more of the disturbance signal is recorded, which makes analysis of endoscopic recorded flow curves difficult and inaccurate. It is therefore recommended to use 4-kHz bandwidth during endoscopic measurements in conscious humans. Blood flow measurements from both sides of the gastric wall were consistently of the same order of magnitude (r = 0.91), and the endoscopically recorded output signal increased in three of five patients when a reflecting mirror was placed at the serosal side. The results indicate that endoscopic LDF usually represents blood perfusion in all layers of the gastric wall.     

Laser Doppler flowmetry for assessing localized scleroderma in children

OBJECTIVE: Assessment of disease activity is a major challenge in the management of children with localized scleroderma. The aim of this study was to evaluate the role of laser Doppler flowmetry (LDF) in comparison with infrared thermography in the detection of scleroderma disease activity. METHODS: In 41 children with localized scleroderma, 111 lesions were assessed on 2 separate occasions, by clinical examination, LDF, and thermography. Measurements from contralateral areas of unaffected skin served as intrapatient controls, and differences in blood flow and temperature were calculated between the corresponding sites. The sensitivity and specificity to detect clinically active lesions were compared between LDF and thermography. RESULTS: Seventy-five active lesions (34%) and 147 inactive lesions (66%) were identified clinically. The median relative increase in blood flow measured by LDF was +89% (range -69% to +449%) for clinically active lesions and +11% (range -46% to +302%) for clinically inactive lesions (P < 0.001). Thermography showed a median difference in temperature of +0.5 degrees C (range -0.1 degrees C to +4.1 degrees C) and +0.3 degrees C (range -1.9 degrees C to +2.7 degrees C) for clinically active lesions and clinically inactive lesions, respectively (P = 0.024). Using a cutoff level of 39% to indicate increase in blood flow, a sensitivity of 80% and specificity of 77% to detect clinically active lesions were observed; for thermography, no useful cutoff level was identified. The correlation between differences in blood flow and differences in temperature was small, but significant (r2 = 0.120, P < 0.001). CONCLUSION: LDF is a helpful, noninvasive diagnostic technique that can be used to discriminate disease activity in children with localized scleroderma, and is more accurate than thermography for this purpose.     

A controlled study of human resting gastric mucosal blood flow by endoscopic laser-Doppler flowmetry

We investigated regional variation in resting focal gastric mucosal blood flow obtained by endoscopic laser-Doppler flowmetry in patients with symptoms of dyspepsia or peptic ulcer (N = 12) and asymptomatic healthy volunteers (N = 6). Mucosal blood flow was measured for 1 min at the duodenum (first part), prepylorus, antrum and body (anterior and posterior walls), angularis, mid-greater curvature, fundus, and distal esophagus. At all sites, mean +/- SE blood flow in patients was 71.88% of the corresponding value in volunteers (1.15 +/- 0.10 and 1.60 +/- 0.13 volts, p less than 0.02, t test). In both groups, blood flow was highest in the fundus, followed by the body and lowest in the antrum; the angularis had a high blood flow, second only to the fundus. There was no correlation between age and blood flow. We conclude that regional variation in resting gastric mucosal blood flow exists in health and disease.     

Simultaneous recording of fingertip skin blood flow changes by multiprobe laser Doppler flowmetry and frequency-corrected thermal clearance

We compared the results of skin blood flow (SBF) measurements, obtained simultaneously in adjacent fingertips by laser Doppler flowmetry (LDF) and thermal clearance (TC) probes, having approximately the same spatial and temporal characteristics. Experiments were performed in nine healthy volunteers during rest at room temperature (26-28 degrees C). A time resolution equal to about a second was achieved by speeding up the response of the thermal measurement circuit by applying the computer simulation software of the MATLAB package. The comparison revealed that the frequency-corrected TC signal correlated well with the multiprobe LDF signal (median correlation coefficient = 0.90, range = 0.84 to 0.96). At the same time the individual slope values of the regression equation ranged from 0.58 to 1.61, revealing the difficulties encountered in obtaining the invariant scaling factor between the TC and LDF measurements. The relationship between the frequency-corrected TC signal and the multiprobe LDF signal was found to be linear in the range of SBF changes of about three- to fourfold. In the case of larger fluctuations in SBF, excessive acceleration at high SBF rates was noted.     

Portal vein blood flow measurements using pulsed Doppler and electromagnetic flowmetry in dogs: a comparative study

Comparative measurements of portal vein blood flow were performed at laparatomy in anesthetized dogs using either a pulsed Doppler echo system or electromagnetic flowmeters. Three hundred four simultaneous determinations were obtained under baseline conditions and during vasopressin and glucagon infusions. In each dog, serial triplicate measurements were taken within 10 min of each other. In all the cases, flow changes induced by vasoactive drugs followed the same direction regardless of the method used. Portal vein blood flow as measured by electromagnetic flowmetry ranged from 85 to 1570 ml/min. Portal vein blood flow values obtained with Doppler and electromagnetic flowmeters were not significantly different (609 +/- 335 vs. 600 +/- 370 ml/min; p = NS) and were highly correlated (r = 0.918, p less than 0.001). The difference between values obtained by the two techniques was -3 +/- 159 ml/min or -1.0% +/- 21.2% (mean +/- SD). This difference was not influenced by the portal vein diameter but increased slightly as a function of the angle of insonation. When considering the mean of triplicate measurements, we also found a highly significant correlation between data obtained by the two techniques (r = 0.934, p less than 0.001; n = 63). The mean difference was 11 ml/min, but limits of agreement between these methods were -267 and +239 ml/min. This relative discrepancy was explained by a coefficient of variation higher in Doppler measurements than in electromagnetic measurements (10.9% vs. 5.9%). These data demonstrate that under our experimental conditions, Doppler flowmetry is probably not an ideal method to measure absolute portal vein blood flow values, and that more sophisticated equipment is needed to improve its reproducibility and accuracy. In humans, however, this method might be a useful tool to assess the direction of portal flow changes in the same individual.     

The function of the intestinal microflora in patients with ulcerative colitis before and after colectomy

The function of the intestinal microflora was studied in patients with ulcerative colitis before and after colectomy. The following six microflora-associated characteristics (MACs) were investigated: formation of coprostanol and urobilinogen; degradation of mucin, water-soluble protein, and beta-aspartylglycine; and presence of faecal tryptic activity. In 12 unoperated patients without sulphasalazine as maintenance therapy the six MACs were similar to those in normal subjects. In 12 unoperated patients receiving sulphasalazine the formation of coprostanol and urobilinogen was significantly lower (p less than 0.01 and p less than 0.001, respectively) and the level of faecal tryptic activity was significantly higher (p less than 0.01) than in normal subjects. The functional capacity of the microflora in operated patients treated by colectomy combined with one of four surgical procedures (ileorectal anastomosis, ileoanal anastomosis with pelvic pouch, Kock's continent ileostomy, or conventional ileostomy) was disturbed with regard to all six MACs. The disturbance was most pronounced in patients with conventional ileostomy.     

Evaluation of laser Doppler flowmetry in the assessment of intestinal blood flow in cat

Laser Doppler flowmetry with a differential detector system has been used in the assessment of blood flow in the feline small intestine. Simultaneous mucosal and serosal laser Doppler flowmeter recordings were compared with total blood flow of a bowel segment measured by an optical drop-recorder unit in 6 cats. Blood flow through the muscularis layer was estimated using the 85Kr washout technique. A correlation coefficient of r = 0.96 (mucosal recordings = 90, serosal recordings = 80, p less than 0.001) was obtained between laser Doppler flowmeter output signals and total blood flow at different levels of vascular tone, regardless of whether the flowmeter recordings were made from the mucosal or the serosal side of the bowel wall. At intense vasodilation, the flowmeters showed a tendency to underestimate blood flow. The flowmeter signals were at variance with the muscularis blood flow but were clearly correlated to the calculated mucosal-submucosal blood flow. The uneven blood flow distribution in the intestinal wall did not affect the ability of the flowmeters to reflect total blood flow from either side of the bowel wall. A calibration curve could be constructed for approximate interpretation of the laser Doppler signals in absolute flow units. However, further experiments in humans and further development of the technique must be performed to elucidate clinical applications of the method.     

Gains and losses with stapling and omission of loop ileostomy in pelvic pouch surgery: a matched control study

After 10 years experience of pelvic pouch surgery with handsewn pouch and ileoanal anastomosis, mucosectomy, and covering loop ileostomy, the surgical technique was altered. Twenty patients were operated on with staple technique in pouch and ileoanal anastomosis but without mucosal proctectomy and loop ileostomy. This study group was compared with a matched control group of patients from our previous series with respect to duration of surgery, blood loss, hospital stay, complications, and functional outcome after 2 months, 12 months, and 60 months. It was found that staple technique significantly reduced the duration of surgery and the need of blood transfusions. Length of hospital stay after pouch surgery did not differ between the two groups, but omitting loop ileostomy reduced total hospital stay by about 2 weeks. Ileoanal anastomotic insufficiency occurred in two patients in the study group. Treatment by establishment of a defunctioning loop ileostomy, local saline perfusion, and administration of antibiotics was successful; the anastomosis healed within 2 weeks, and the long-term functional outcome did not differ from the average. Increased temperature persisted postoperatively in seven patients in the study group. Transient peroneal paresis occurred in three patients in the control group. Only in the control group was there stenosis in the ileoanal anastomosis requiring dilatation and fibrosis at the levator plane demanding emptying by a catheter. Concerning functional outcome, nighttime continence was significantly better in the study group than in the control group. The evacuation rate per 24 h was significantly higher in the study group after 2 and 12 months but not after 60 months. The outcome concerning other functional parameters such as urgency to evacuate, capacity to discriminate between gas and stool, deferral time, and perianal symptoms, did not differ significantly. Staple technique without mucosal proctectomy and loop ileostomy thus results in shorter duration of surgery and shorter hospital stay. In patients with increased risk of insufficiency of the anastomosis, however, covering loop ileostomy may be justified because of the risk for more serious consequences if anastomotic leakage occurs. Accepted: 18 June 1999     

Assessment of myocardial perfusion in the empty beating porcine heart with laser Doppler flowmetry

Laser Doppler flowmetry was applied to the empty beating heart of six pigs. Cardiopulmonary bypass was instituted and the preparation allowed continuous and simultaneous measurement of coronary sinus blood flow and local tissue perfusion. An epicardial and an intramuscular probe were used. Significant linear correlation coefficients were obtained between changes of laser Doppler signal and coronary sinus blood flow changes in all seven experiments in four animals (r from 0.71 to 0.94, p less than 0.005) and between laser Doppler signal and changes of extracorporeal bypass in five out of six experiments in four animals (r from 0.82 to 0.99, p less than 0.001). The correlation between coronary sinus flow and bypass flow of four pigs was significant (r from 0.81 to 0.98, p less than 0.001), the coronary flow being about 10% of bypass flow. Muscular activity of the heart contributed to the laser Doppler signal, the magnitude of this "noise level" varying between different experiments even in the same animal. A key question for the applicability of laser Doppler flowmetry to the beating heart is whether it will become possible to discriminate between flow and muscular contribution to the laser Doppler output.     

Comparison of blood flow measurements by hydrogen gas clearance and laser Doppler flowmetry in the rat duodenum

This report examines the relationship between hydrogen gas clearance and laser Doppler flowmetry measurements in the duodenum of fasted, anesthetized rats under conditions of 1) reduced perfusion due to graded levels of hemorrhagic hypotension or 2) hyperemia due to perfusion with step doses of acid. There was a significant correlation between hydrogen gas clearance and laser Doppler flowmetry measurements (r = 0.73, p less than 0.01; n = 32 data points in 16 rats). The change in laser Doppler flowmetry values from the period immediately before to the period during the 3 min of acid perfusion was significantly correlated with the dose of acid used (r = 0.51, p less than 0.01; n = 27 rats). The changes in hydrogen gas clearance and laser Doppler flowmetry values from the 30-min period before to the 30-min period after acid perfusion were not correlated with the dose of acid used (r = 0.30 and 0.33, respectively). We conclude that in the rat duodenum 1) the significant linear correlation between hydrogen gas clearance and laser Doppler flowmetry when blood flow is reduced suggests that the countercurrent exchange mechanism is unlikely to modulate significantly hydrogen gas clearance measurements, and 2) the dose-related acid-induced duodenal hyperemia is transient rather than persistent when the rat duodenum is exposed to hydrochloric acid (0.03 to 0.1 N) for 3 min.