Repeated measurement variation and precision of laser Doppler flowmetry measurements

Venous stent placement ameliorates cutaneous microvascular function in iliocaval venous obstruction

BACKGROUND

The role of cutaneous microvascular dysfunction is well known in the development of chronic venous disease. However, the effects of venous obstruction on microcirculation have not been well investigated. The aim of this study was to assess cutaneous microvascular function in patients with iliocaval venous obstruction (ICVO) before and after venous stent placement.

METHODS

Endothelium-dependent and endothelium-independent vasodilator responses to iontophoretic administration of incremental doses of acetylcholine (ACh) and sodium nitroprusside (SNP) were evaluated using a laser Doppler scanner in the perimalleolar region in the supine and sitting positions in patients with ICVO (n = 11) and in healthy control subjects (n = 15). Cutaneous microvascular function, the Venous Clinical Severity Score (VCSS), and the Clinical, Etiology, Anatomy, and Pathophysiology (CEAP) clinical class were re-evaluated 3 months after stent placement in patients with ICVO.

RESULTS

The vasodilatory responses to ACh and SNP in the cutaneous microcirculation were lower in patients with ICVO than in healthy subjects in the sitting position (P < .05). Recanalization and stent placement were successful in all patients in the evaluation of VCSS and clinical class, and a significant decrease was determined in the signs and symptoms of the venous disease (P < .01). Stent placement resulted in a significant increase in vasodilation response to both ACh and SNP in the supine position and no improvement in the sitting position in patients with ICVO.

CONCLUSIONS

ICVO impairs endothelium-dependent and endothelium-independent vasodilation in the perimalleolar region. Iliocaval venous stent placement may recover microvascular dysfunction at different levels.

Acute skin trauma induces hyperemia, but superficial papillary nutritive perfusion remains unchanged

OBJECTIVES

Superficial skin papillary capillaries with blood supply from a superficial vascular plexus and regulated by local metabolic needs supply oxygen and nutrients for epithelial cell proliferation. A deep vascular plexus regulated by autonomous nerves serves body thermoregulation. In healthy volunteers, we assessed circulatory effects of a standardized skin trauma by CAVM, DRS, and LDPM to assess the measuring depth of the three techniques and to describe the acute trauma effects on nutritive and thermoregulatory perfusion.

METHODS

Volunteers (n=12) were examined at baseline and after induction of a 5.0 mm×1.0 mm incision on the forearm; 30 minutes after the trauma induction, data were collected at 0-1, 2-3 and 30 mm distances.

RESULTS

LDPM showed hyperemia at 2-3 mm distance (35.8±15.2 a.u.), but not at 30 mm distance (7.4±2.5 a.u.) compared to baseline (8.8±1.8 a.u.). The DRS saturation increased at 2-3 mm (71.2±4.8%), but not at 30 mm (49.8±7.9%) compared to baseline (45.8±7.4%). Capillary density and flow velocities were unaffected at all distances.

CONCLUSIONS

The results indicate that skin nutritive papillary capillary function can be assessed by CAVM and DRS, but not with LDPM because of its dependence of the deep plexus perfusion.

A methodological approach to non-invasive assessments of vascular function and morphology

The endothelium is the innermost lining of the vasculature and is involved in the maintenance of vascular homeostasis. Damage to the endothelium may predispose the vessel to atherosclerosis and increase the risk for cardiovascular disease. Assessments of peripheral endothelial function are good indicators of early abnormalities in the vascular wall and correlate well with assessments of coronary endothelial function. The present manuscript details the important methodological steps necessary for the assessment of microvascular endothelial function using laser Doppler imaging with iontophoresis, large vessel endothelial function using flow-mediated dilatation, and carotid atherosclerosis using carotid artery ultrasound. A discussion on the methodological considerations for each of the techniques is also presented, and recommendations are made for future research.

Skin microcirculation in healthy term newborn infants--assessment of morphology, perfusion and oxygenation

Despite microcirculation's fundamental role, assessments of its function are limited. We explored the applicability of Computer Assisted Video Microscope (CAVM), Laser Doppler Perfusion Measurements (LDPM) and Diffuse Reflectance Spectroscopy (DRS) to study skin microvascular morphology, perfusion and oxygen saturation in twenty-five healthy newborns day 1-3 of life.

RESULTS

Day 1-3 (mean (SD)): Microvascular density (CAVM; number of microvessels crossing a grid of lines/mm line, c/mm): Chest: 11.3 (1.5), 11.0 (1.7), 10.7 (1.6). Hand: 13.2 (2.0), 13.2 (1.9), 12.4 (1.6). Capillary density was significantly higher in the hand than in the chest each day (p <  0.001). Perfusion (LDPM; arbitrary units): Chest: 109.1 (26.0), 101.4 (24.6), 100.8 (25.3). Hand: 58.9 (17.5), 54.3 (15.8), 46.9 (14.8). Perfusion was significantly higher in the chest than in the hand each day (p <  0.01). Microvascular oxygen saturation (DRS; %): Chest: 88.1 (5.2), 87.8 (10.0), 86.7 (9.0). Hand: 79.9 (15.2), 82.7 (11.8), 82.2 (12.1) (p <  0.05). Capillary flow velocities (CAVM) were similar in the chest and hand: 60-70% capillaries had "continuous high flow" and 30-40% "continuous low flow".Multimodal skin microvascular assessments with CAVM, LDPM and DRS are feasible with reproducible data in newborns. The hand has lower perfusion, higher capillary density and higher oxygen extraction than the chest.

Assessments of skin and tongue microcirculation reveals major changes in porcine sepsis

AIM

  To examine the relation between central hemodynamics, clinical severity and microvascular findings in tongue and skin during sepsis.

MATERIALS AND METHODS

  Skin and tongue microcirculation was examined using laser Doppler and video microscopy techniques before and 200 min after inducing sepsis in pigs (n=6) by inactivated Neisseria meningitides and in two control animals.

RESULTS

  All infected pigs developed clinical signs of sepsis. Pericapillary bleedings developed in the tongue in the two pigs with the most severe disease. Capillary density increased in the groin skin in infected pigs after 200 min as compared to baseline (P<0·02). In the same period, mean capillary flow velocity was reduced in groin skin and tongue in septic pigs (P<0·02). At 200 min a fraction of capillaries had developed 'no flow' or 'brisk flow', patterns hardly seen at baseline. Laser Doppler perfusion was reduced in ear and tongue after 200 min (P<0·02 for both). The described pathology was more pronounced in the pigs with the most severe sepsis.

CONCLUSION

  Capillary bleedings may be used as an early indication of severe sepsis. Examination of skin and tongue microcirculations may be used to characterize severity of sepsis and possibly to assess effect of treatment.

Intraoperative assessment of microperfusion with visible light spectroscopy for prediction of anastomotic leakage in colorectal anastomoses

PURPOSE

Anastomotic leakage is associated with increased morbidity and mortality. However, there is no accurate tool to predict its occurrence. We evaluated the predictive value of visible light spectroscopy (VLS), a novel method to measure tissue oxygenation [saturated O(2) (StO(2) )], for anastomotic leakage of the colon and the rectum.

METHOD

Oxygen saturation in the bowel was measured in 77 colorectal resections. The anastomosis was between 2 and 30 cm (mean 13 cm) from the anal verge. The oxygen saturation was measured in the colon and rectum before and after anastomosis construction. This was compared with a reference measurement in the caecum. Data on postoperative complications were prospectively collected.

RESULTS

Anastomotic leakage occurred in 14 (18%) patients. When compared with a leaking anastomosis, normal anastomoses showed rising O(2) values during the operation (mean StO(2) 72.1 ± 9.0-76.7 ± 8.0 vs 73.9 ± 7.9-73.1 ± 7.4) (P ≤ 0.05). There were also higher StO(2) values in the caecum compared with those which ultimately leaked (73.6 ± 5.7 normal anastomoses, 69.6 ± 5.6 anastomotic leaks) (P ≤ 0.05). Both StO(2) values were predictive of anastomotic leakage.

CONCLUSION

Tissue oxygenation O(2) appears to be a potentially useful means of predicting anastomotic leakage after colorectal anastomosis.

Local gingival blood flow at healthy and inflamed sites measured by laser Doppler flowmetry

BACKGROUND

This investigation aimed to: 1) develop a method to obtain reproducible laser Doppler flow readings (LDFRs) at the gingiva of the maxillary front teeth; 2) evaluate regional gingival blood flow (GBF) in healthy gingiva by laser Doppler flowmetry; 3) compare hand-held LDFR (H-LDFR) with splint LDFR (S-LDFR); and 4) monitor changes in GBF in experimental gingivitis (EG) and chronic gingivitis (CG).

METHODS

The LDFR, gingival index (GI), and plaque index (PI) were measured at 13 gingival sites (teeth #6 to #11) in 10 healthy volunteers (five males and five females), 23 to 34 years of age, over a period of 12.5 +/- 3.27 days employing a partial-mouth EG model and in 11 patients (three males and eight females), 20 to 63 years or age, with CG. LDFRs were obtained by S-LDFR or H-LDFR.

RESULTS

H-LDFRs were significantly higher than S-LDFRs (P <0.05). All EG subjects developed gingivitis (PI: 2.77 +/- 0.23; GI: 1.5 +/- 0.53). EG-LDFRs at diseased sites increased slightly but not significantly over the study period. All CG-patients had high plaque and inflammation scores (PI: 2.8 +/- 0.2; GI: 1.63 +/- 0.78). CG-LDFRs at sites with GI >1 were significantly higher than LDFRs at healthy sites (P <0.05). CG-LDFRs were significantly higher than EG-LDFRs at sites with a comparable GI (P <0.05).

CONCLUSIONS

LDFRs are positively correlated with the degree of gingival inflammation. GBF demonstrated significant differences in EG and CG. Modifications of the probe are needed to enhance its clinical applicability in clinical research of periodontal diseases.

Assessment of mucosal inflammation and blood flow in response to four weeks' intervention with probiotics in patients operated with a J-configurated ileal-pouch-anal-anastomosis (IPAA)

BACKGROUND

Pouchitis is a common and troublesome condition in patients operated on with ileal-pouch-anal-anastomosis (IPAA). A disturbed mucosal perfusion in the pouch has been suggested as a possible cause. Laser Doppler flowmetry (LDF) has been used successfully to measure gastric and colonic mucosal perfusion in humans. In a previous study, we demonstrated a reduced mucosal perfusion in the distal part of the pouch, during probiotic intervention, examined by LDF measurement. The aim of the present study was to confirm our previous results in a much larger material, and to compare the results of LDF measurements and inflammatory activity in ulcerative colitis (UC) patients with those in familial adenomatous polyposis (FAP) patients.

METHODS

Five hundred millilitres of a fermented milk product (Cultura), containing live lactobacilli (La-5) and bifidobacteria (Bb-12), was given daily for 4 weeks to 41 UC and 10 patients with FAP, operated on with IPAA. Mucosal perfusion was measured with LDF and the degree of inflammation was examined at predefined levels of the distal bowel by histology and faecal calprotectin measurements both before and after intervention. We also evaluated the applicability of a Pouchitis Disease Activity Index (PDAI).

RESULTS

The LDF measurements were reproducible in the pelvic pouch at each of the predefined levels, but did not change during intervention. Mucosal perfusion was significantly reduced in the distal compared to the proximal part of the pouch in the UC group (P < 0.05). The perfusion levels were higher in the FAP patients compared to the UC patientsat all predefined levels (P < 0.05). Calprotectin levels and histological score did not change significantlyafter intervention in any of the groups. The calprotectin level was significantly lower in the FAP compared to the UC group both before and after intervention. The PDAI decreased in both groups from alevel considered diagnostic for pouchitis to a level considered as not active pouchitis. The decreasewas significant for the UC patients.

CONCLUSIONS

The results did not demonstrate an effect of probiotics on histology, although a significant effect on the PDAI was achieved, which concurs with the previously reported effect on symptoms and endoscopic score. The significantly reduced blood flow in the UC group compared to the FAP group, operated on with the same procedure, and the significantly increased calprotectin levels in the UC group, are original findings. Both findings may be related to an increased risk for pouchitis among UC patients. The lack of effect of intervention on mucosal perfusion does not exclude a role for reduced circulation as a cause of pouchitis based on the reduced LDF measurements in the distal part of the pouch.

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.

A porcine model of systemic and renal haemodynamic responses to infrarenal aortic cross-clamping

OBJECTIVES

cross-clamping of the infrarenal aorta is associated with complex haemodynamic disturbances. Several experimental models of aortic cross-clamping (AXC) have been described with heterogeneous results. The main purpose of this study was to establish an animal model in which infrarenal AXC could reproduce similar systemic and renal haemodynamic changes to those observed in humans.

METHODS

eleven anaesthetised pigs underwent AXC just below the renal arteries. Renal blood flow was measured using clearance of (131)I hippuran. Systemic and renal parameters were collected at 3 consecutive 30-min periods.

RESULTS

AXC did not alter the extraction fraction of (131)I hippuran but was accompanied by significant (13%) decrease in cardiac index (p = 0.005) and a 23% increase in mean arterial pressure (p = 0.005). AXC induced significant 135% increase in renal vascular resistance (p = 0.012) and a 35% decrease in renal blood flow (p = 0.016). This worsened after removal of the aortic clamp, whereas systemic variables returned to baseline levels.

CONCLUSIONS

this AXC animal model reproduces the changes observed in humans. It provides a reliable animal model which allows to investigate the underlying mechanisms of renal vasoconstriction and the effect of new drugs.

Evaluation of a combined laser Doppler flowmetry and iontophoresis technique for the assessment of equine cutaneous microvascular function

A combined laser Doppler flowmetry and iontophoresis (LDFI) technique, used routinely to assess human microvascular function, was evaluated as a noninvasive technique for assessment of equine microvascular function, to facilitate the study of diseases such as laminitis. Baseline and vasoactive agonist-induced (acetylcholine and nitroprusside) microvascular flux was quantified at 2 sites (on the dorsal pastern adjacent to the coronary band and over the gluteals) in 6 clinically normal horses on 5 or 6 separate occasions under standardised conditions. Both agonists significantly increased microvascular flux. Skin pigmentation significantly attenuated the baseline flux, but not the magnitude of the agonist-mediated vasodilatory response. While LDFI was simple to perform, its value as a clinical and research tool for assessing the equine cutaneous microcirculation is limited by its poor reliability, as indicated by the marked intra- and intersubject variability in baseline and agonist-mediated microvascular flux.

The role of different chemical modifications of superoxide dismutase in preventing a prolonged muscular ischemia/ reperfusion injury

It is well know that a long period of ischemia followed by reperfusion can create an irreversible tissue damage, also due to the excessive generation of oxygen-derived free radicals. A possibility for avoiding this syndrome is represented by the use of free radical scavengers, such as the superoxide dismutase (SOD). The current authors compared the results achieved through different modifications of this enzyme in an experimental rat hind limb model of ischemia/reperfusion. 60 rats that had a 4 hour and 30 minute ischemia of the left hind limb were divided into four groups of 15 each and treated using a physiological solution (control group), native SOD, monomethoxypolyethylene-glycol-SOD (mPEG-SOD) or poly(acryloilmorpholine)-SOD (PAcM-SOD). The outcomes obtained in terms of limb survival (p < 0.05), as well as histomorphologic studies (p < 0.0005), revealed a superior capacity of mPEG-SOD when compared with the other three substances.

Guidelines for visualization of cutaneous blood flow by laser Doppler perfusion imaging. A report from the Standardization Group of the European Society of Contact Dermatitis based upon the HIRELADO European community project

This report reviews how to set up a laser Doppler perfusion imaging system intended for visualization of skin blood perfusion, capture images and evaluate the results obtained. A brief summary of related papers published in the literature within the areas of skin irritant and allergy patch testing, microdialysis and skin tumour circulation is presented, as well as early applications within other fields such as diabetology, wound healing and microvascular research.

Influence of Helicobacter pylori infection and cetraxate on gastric mucosal blood flow during healing of endoscopic mucosal resection-induced ulcers

BACKGROUND AND AIM

Helicobacter pylori (H. pylori) infection is known to affect the gastric microcirculation, and cetraxate is reported to accelerate gastric ulcer healing, possibly by augmenting gastric mucosal blood flow (MBF). The aim of this study is to clarify the effect of H. pylori infection and cetraxate on MBF during gastric ulcer healing.

METHODS

Forty-two patients who had undergone endoscopic mucosal resection (EMR) were studied. Mucosal blood flow was measured by the use of a laser Doppler flowmeter in the surrounding mucosa and at the ulcer margin, before, 1 day, 1 week and 4 weeks after EMR. Helicobacter pylori infection was confirmed by the use of bacterial culture and histology. After EMR, patients were randomly assigned to receive 30 mg lansoprazole (u.i.d; L-regimen) or 30 mg lansoprazole (u.i.d.) with 200 mg cetraxate (q.i.d; LC-regimen) for 4 weeks.

RESULTS

The MBF ratio (MBF at ulcer margin/MBF in surrounding mucosa) 1 week after EMR was significantly lower than that before or 4 weeks after EMR only in H. pylori-positive patients treated with the L-regimen. No such decrease in MBF was observed after 1 week in H. pylori-positive patients treated with the LC-regimen or in H. pylori-negative patients.

CONCLUSION

A transient decrease in MBF was detected at the ulcer margin during healing of EMR-induced ulcers in H. pylori-infected patients. Cetraxate seemed to prevent this decrease in MBF.

On the number of measurement sites required to assess regional cerebral blood flow by laser-Doppler scanning during cerebral ischemia and reperfusion

The aim of this study was to determine whether the number of measurement sites affected the precision of regional cerebral blood flow (CBF) assessment by Laser-Doppler (LD). A simulation study was applied based on data obtained by scanning the cortex in 25 rats during baseline conditions, 15 min global cerebral ischemia and reperfusion. Random samples were repeatedly collected from 1 to 100 locations and deviations from the median of the entire CBF data pool (800 locations) were determined. Single location CBF measurements missed the true median by 24.8+/-2.2 LD-units (baseline conditions, n=100 simulations, mean+/-SEM), 2.7+/-0.6 LD-units (ischemia), and 31.9+/-2.4 LD-units (30th min reperfusion), which can be reduced to 10.9+/-1.0 LD-units (baseline), 0.9+/-0.1 LD-units (ischemia), and 15.5+/-1.3 LD-units (30th min reperfusion) by scanning ten locations. Reliability is further improved by scanning 30 sites with deviations of 6.1+/-0.6 LD-units (baseline), 0.4+/-0.0 LD-units (ischemia), and 8.9+/-0.7 LD-units (30th min reperfusion). Single location CBF assessment was sufficient during global ischemia only. In order to keep the deviation from the true flow below 10 LD-units, at least 15 locations are recommended during baseline conditions and 25 during reperfusion. Laser-Doppler scanning improves the reliability and reduces the variability of CBF measurements.

Laser Doppler scanning: how many measurements are required to assess regional cerebral blood flow?

This study was initiated to determine the optimal number of measuring sites necessary to estimate regional cerebral blood flow (CBF) under pathophysiological conditions. 25 rats were exposed to 15 minutes of global cerebral ischemia. Local CBF was sequentially measured by laser Doppler (LD) at 32 locations during baseline conditions, ischemia and reperfusion using a computer-controlled scanning technique. A simulation study was performed based on 800 local measurements at each time point: random samples (size 1-100) were repeatedly drawn to estimate the variability of median flow. Accuracy was defined as probability that the simulated median differed less than +/- 5 LD-units from the true median of the 800 data. Above a single location, CBF was measured with an accuracy of 21.6 +/- 0.4% (baseline conditions, n = 100 simulations, mean +/- SEM), 85.8 +/- 0.4% (ischemia) and 11.1 +/- 0.3% (30th min. reperfusion). Accuracy increases to 75.2 +/- 0.5% (baseline conditions), 100 +/- 0% (ischemia) and 41.8 +/- 0.6% (30th min. reperfusion) if 24 locations are scanned. Scanning, therefore, improves accuracy and reduces variability of CBF measurements. With enough local CBF measurements laser Doppler assessment of regional CBF is possible. Single location CBF assessment is sufficiently accurate only during ischemia. During reperfusion, when accuracy is half reduced compared to baseline conditions, larger sample sizes are required.

Quantitative estimates of angiogenic and anti-angiogenic activity by laser Doppler flowmetry (LDF) and near infra-red spectroscopy (NIRS)

The use of laser Doppler flowmetry (LDF) and near-infra-red spectroscopy (NIRS) for non-invasive in vivo measurements of angiogenic and anti-angiogenic activity in nude mice was evaluated. Angiogenic foci were induced in the skin by implantation of slow release pellets containing 200 ng basic fibroblast growth factor (bFGF). LDF and NIRS recordings from induced foci were significantly higher than placebo implants (P<0.05) and controls (P<0.001), proving that LDF and NIRS provide measures of angiogenic activity. Correspondingly, by these methods, an anti-angiogenic activity was significantly demonstrated in bFGF-stimulated animals treated with either the specific anti-angiogenic compound TNP-470 (P<0.05) or the anti-inflammatory agent dexamethasone (P<0.001). We conclude that LDF and NIRS, alone or in combination, are useful non-invasive tools for early evaluation of angiogenic and anti-angiogenic activity in vivo.

Intraoperative assessment of colonic perfusion using scanning laser Doppler flowmetry during colonic resection

BACKGROUND

Ischemia occurring on mobilization and mesenteric division is thought to be a major factor in the etiology of anastomotic dehiscence after colorectal resection. This study assessed the ability of the new technique of scanning laser Doppler flowmetry to measure changes in human colonic perfusion during mobilization at and adjacent to the anastomotic site.

STUDY DESIGN

Colonic perfusion was measured in 10 patients undergoing large-bowel resection by making laser Doppler scans of the proximal bowel before mobilization, after mobilization and mesenteric division, and after resection of the specimen. Mean perfusion was calculated within 1-cm2 regions of interest, each of which contained 1,750 individual measurements of perfusion. These regions represented the anastomosis site and adjacent areas 1 cm and 2 cm proximal and distal to this. The results were expressed as mean perfusion units (PUs).

RESULTS

After mobilization, there were significant decreases in perfusion in all the subjects between each time point and in all areas of the colon scanned. Median perfusion at the anastomosis site was 491 PUs before mobilization, and this fell to 212 PUs after mobilization, representing a decrease of 57%; the median within-person decrease was also 57% (p < 0.01). There was a gradient of reduced perfusion between the area 2 cm proximal to the mesenteric division (median within-person fall 25%; p < 0.05) and the area 2 cm distal to the mesenteric division (median within-person fall 84%; p < 0.01). After resection of the specimen, perfusion increased slightly at the anastomosis site to a median of 240 PUs (median within-person fall 41%; p < 0.01), but 2 cm proximal to this, median perfusion remained depressed at 330 PUs.

CONCLUSIONS

This new technique can be used intraoperatively and appears to overcome the limitations of single-point laser Doppler flowmetry. In this small preliminary study, it measured large decreases in colonic perfusion during mobilization, and it may have widespread clinical applications.

Laser Doppler evaluation of microcirculation behaviour during an ischaemia-reperfusion injury

Laser Doppler flowmetry (LDF) was tested in an experimental ischaemic model on rat limbs to evaluate the degree of ischaemia and to find a possible correlation with values obtained with this device and prognosis. Under general anaesthesia, 40 Wistar rats were submitted to 4 h and 30 min of ischaemia of the left hind limb. Ten rats formed the control group (group 1). Two enzymes, native superoxide dismutase (SOD) and SOD modified with polyethylene glycol, were employed in 15 rats each (groups 2 and 3). Data were collected by means of LDF both in the sole and muscles before ischaemia (steady state), during ischaemia and at the beginning of reperfusion, and only in the sole after 1 h of reperfusion. A range of predictive (95%) perfusion values (PU) for limb healing or necrosis was identified at the beginning of reperfusion. During ischaemia, PU changed from 0 to 10, both in the sole and in the muscle. A three-factor ANOVA (site, group, time) did not show interaction of these factors with PU (F = 1.655; p = 0.195), even if every single effect was significant (p < 0.0005). A two-factor ANOVA (group, time) showed a significant interaction of these factors with PU (F = 4.079; p = 0.019). The logistic regression between the reperfusion PU of each site and the survival of the limb was observed at the beginning and after 1 h of reperfusion in the sole only. Furthermore, a correlation between sole and muscle PU at the steady state and at the beginning of the reperfusion period was observed. The results showed the effectiveness of LDF, which can be considered a quite reliable tool to evaluate the degree of ischaemia and to have a good correlation with prognosis in this kind of experiments.

Intraoperative scanning laser Doppler flowmetry in the assessment of gastric tube perfusion during esophageal resection

BACKGROUND

Ischemia from tissue hypoperfusion in the gastric tube after esophagectomy is believed to contribute significantly to postoperative complications associated with anastomotic failure. This study assessed the ability of the new technique of laser Doppler flowmetry to measure differential levels of blood flow in human gastric tubes during esophagectomy.

STUDY DESIGN

Gastric perfusion was measured in 16 patients undergoing esophagectomy by making laser Doppler scans of the stomach before mobilization and after formation of the gastric tube. Mean perfusion was calculated within the whole anterior surface of the stomach or tube and within 1 cm2 regions of interest, each of which contained 1,750 individual measurements of perfusion. These regions represented the cephalic end of the gastric tube, 10 adjacent 1 cm2 regions distally along the tube, and the proposed anastomosis site. Results were expressed as mean perfusion units, and tissue blood flow from each scan in each region was compared.

RESULTS

There were significant decreases in gastric perfusion measured with the scanning laser Doppler in all patients after formation of the gastric tube. Mean perfusion of the stomach fell 41% (p<0.0005) after mobilization. In all patients there was a gradient of perfusion from the proximal end of the tube where flow was poor, to more distal areas where it was higher. At the proximal end of the tube perfusion fell by a mean of 72%, 5 cm distally the mean fall was 44%, and 10 cm from the proximal end of the tube the mean fall was 28%. At the anastomosis site mean perfusion fell 55%.

CONCLUSIONS

This new technique can be used intraoperatively and appears to overcome the limitations of single point laser Doppler flowmetry. It has measured large differences in perfusion at different sites within the gastric tubes and could therefore have widespread clinical applications.

Scanning laser Doppler is a useful technique to assess foot cutaneous perfusion during femoral artery cannulation

BACKGROUND: Measurement of cardiac output and extravascular lung water in critically ill patients using femoral artery double-indicator dilution involves femoral artery catheterization. The potential risk of vascular compromise to the limb may be exacerbated in patients receiving vasopressors. The utility of scanning laser Doppler flowmetry to measure changes in pedal perfusion following catheterization was assessed. RESULTS: There were no significant changes in mean occlusion pressures or in cutaneous perfusion between either leg or between measurement time points, immediately after or 24 h following insertion of the catheters. CONCLUSIONS: Scanning laser Doppler flowmetry is easily used to assess changes in foot perfusion and the effect of interventions that may reduce blood flow to the skin of the foot. Femoral artery catheterization for double-indicator dilution measurements does not reduce calf occlusion pressures or foot skin perfusion in patients receiving vasopressor drugs.

Effect of heart transplantation on impaired peripheral microvascular perfusion and reactivity in congestive heart failure

Whether reduced peripheral blood flow in congestive heart failure is reversed after heart transplantation, has not been closely examined. We therefore studied skin microvascular resting perfusion and reactivity in patients pre- and postoperatively. Resting digital skin perfusion, together with the responses to cold pressor test, postocclusive reactive hyperemia and direct skin heating were examined with laser Doppler perfusion measurements. We examined 28 patients with congestive heart failure and 14 of these patients after heart transplantation and compared them to 13 healthy controls. Measurements were performed within 3 months preoperatively and 12 days, 1, 2, 3 and 6 months postoperatively. Patients with congestive heart failure had significantly lower resting perfusion levels than controls and demonstrated attenuated responses to both stimuli of vasodilation (all P<0.01). While peak hyperemic responses improved significantly after transplantation, postocclusive area under the hyperemic curve decreased further, and none of these variables were normalized after 6 months. In contrast, minimal perfusion during cold pressor test increased from a significantly lower level in the patients with congestive heart failure (P<0.05), to a level similar to that of the controls within 12 days postoperatively. Thus, skin microvascular perfusion and reactivity improve, but are not normalized within 6 months of transplantation. Both pre- and postoperative factors may be involved in maintaining a dysfunction of the peripheral microcirculation, which may contribute to exercise intolerance and hypertension in heart transplant recipients.

Human en bloc double-lung transplantation: bronchial artery revascularization improves airway perfusion

BACKGROUND

Ischemic airway complications are common after en bloc double-lung transplantation with tracheal anastomosis. The aim of this study was to evaluate the effects of a direct revascularization of the donor bronchial artery with the recipient internal thoracic artery on airway perfusion.

METHODS

Seven patients undergoing double-lung transplantation with tracheal anastomosis were investigated intraoperatively and postoperatively (12 to 36 hours) with endoscopic laser Doppler flowmetry. Sixteen patients undergoing coronary artery bypass grafting served as a control group.

RESULTS

Two patients who had double-lung transplantation with tracheal anastomosis died of sepsis and multiorgan failure 1 week after transplantation. In the remaining 5 patients healing of the anastomosis was excellent during the observation period of 3 to 52 months. In 5 patients clamping of the attached internal thoracic artery induced a reduction of the laser Doppler flowmetry signal from 10% to 60%. In the 2 patients with the highest graft perfusion level, no clamping effect could be detected. Compared with the control group, perfusion was significantly higher in the transplanted airways intraoperatively, at 71 versus 55 arbitrary perfusion units (p < 0.01). Postoperative transplant airway perfusion values were not significantly different from the intraoperative value. The coefficient of variation of repeated measurements was higher in the transplanted airways, with a coefficient of variation of 0.22 versus 0.17 in the control group (p < 0.01), indicating heterogeneous transplant airway perfusion.

CONCLUSIONS

This study has documented that revascularization with the internal thoracic artery supplies the transplanted airway with additional oxygenated blood.

Effect of probe design and bandwidth on laser Doppler readings from vital and root-filled teeth

Laser Doppler flowmetry has been shown to be useful in assessing blood flow in teeth. This study investigated the effect of probe design and bandwidth on laser Doppler readings from vital and root-filled teeth using an 810 nm light source, and established the sensitivity and specificity of each probe/bandwidth combination. Readings were taken from 20 human subjects with a root-filled tooth and a vital contralateral tooth using each of the probes with 0.125 mm, 0.375 mm and 0.5 mm fibre separations and three bandwidths (3.1 kHz, 14.9 kHz and 20 kHz). Ten pairs of traces from each group were examined by 10 trained observers who indicated whether the traces had come from a vital or root-filled tooth. The sensitivity and specificity of each combination were calculated from the accuracy of their replies. This was repeated for five observers but with additional information from Fourier analysis. Median readings from vital teeth were higher than those from root-filled teeth for all combinations. This difference was only significant at the 95% confidence level for the 0.5 mm probe with the two lower bandwidths. The 0.125 mm fibre separation probe showed good specificity. The other two probes had better sensitivity but poor specificity. The best specificity and sensitivity was shown by the 0.5 mm probe/3.1 kHz bandwidth combination. All sensitivities and specificities increased when additional information from Fourier analysis was available, but the 0.5 mm probe/3.1 kHz combination still had the best sensitivity and specificity.

Peptic ulcer pathophysiology: acid, bicarbonate, and mucosal function

The previously accepted role of gastric acid hypersecretion in peptic ulcer disease has been modified by studies showing no correlation between acid output and clinical outcome of ulcer disease, or between ulcer recurrence rate after vagotomy and preoperative acid secretion. At the same time, studies have been unable to demonstrate increased acidity in the duodenal bulb in patients with duodenal ulcer, and consequently more emphasis has been given to the mucosal protecting mechanisms. The existence of an active gastric and duodenal mucosal bicarbonate secretion creates a pH gradient from the luminal acid to near neutrality at the surface of the epithelial cells, thereby acting as an important mucosal defence mechanism. The regulation of bicarbonate secretion is a complex process related to motility and neural activity. Stimulation is by acid, PGE2, NO, VIP, cAMP, and mucosal protective agents. Bicarbonate secretion is inhibited by atropine, muscarinic antagonists, alpha-adrenoceptor agonists, indomethacin, bile acids, tobacco smoking, and probably also by infection by Helicobacter pylori. Apart from mucus and bicarbonate, the mucosal defence is supported by a hydrophobic epithelial lining, rapid cell removal and repair regulated by epidermal growth factor. Sufficient mucosal blood flow, including a normal acid/base balance, is important for subepithelial protection. In today's model of ulcer pathogenesis, gastric acid and H. pylori work in concert as aggressive factors, with the open question being: why does only a fraction of the infected population develop an ulcer?

Laser doppler-recorded reactive hyperaemia in the forearm skin during the menstrual cycle

OBJECTIVE

By means of laser Doppler flowmetry to describe the changes in resting microvascular perfusion and post-occlusive reactive hyperaemia in skin of the forearm and finger pulp throughout the menstrual cycle.

DESIGN

Prospective descriptive study.

SETTING

University Hospital of Tromso, Norway.

SAMPLE

Fifteen nonsmoking healthy women were studied in the follicular (days 2 to 7) and the luteal (days 19 to 24) phase of the menstrual cycle.

RESULTS

Resting perfusion in forearm and finger pulp as well as post-occlusive reactive hyperaemia in finger pulp were unchanged from the follicular to the luteal phase. The peak perfusion value of the reactive hyperaemic response after 1 min of arterial occlusion was significantly reduced from the follicular to the luteal phase (P<0.01) in forearm skin. The repayment for the blood flow debt, which is the hyperaemic response in percentage of the ischaemic build-up, was also reduced (P<0.01). After 3 min of arterial occlusion, significant reductions in peak post-occlusive flow (P<0.01), recovery time, which is the total duration of the hyperaemic response (P<0.01), and the repayment (P<0.01) were observed. A significant correlation was found between the ratio serum oestradiol/progesterone and repayment after 3 min of arterial occlusion in forearm skin (r=0.71,P<0.001).

CONCLUSIONS

Vascular reactivity is altered during the menstrual cycle. In the luteal phase, significant reductions in peak perfusion, repayment and recovery time were seen. The mechanisms behind these findings are unclear, but probably involve changes in both serum oestradiol and progesterone levels.

A pial window model for the intracranial study of human glioma microvascular function

A new model for human brain tumor uses the intracranial placement of tumor xenografts under transparent glass cranial windows in nude rats, which require no immunosuppression for tumor engraftment. Adult male nude rats underwent implantation of human anaplastic astrocytomas (D-54 MG in 10 rats, D-317 MG in 11 rats). The tumors were placed on the pial surface of the left cerebral hemisphere under a glass cranial window overlying the cranium. Six control animals underwent cranial window placement alone. Tumor volumes were estimated from direct measurements of tumor dimensions, revealing a mean doubling time of 1.58 days for the D-54 MG tumors and 2.62 days for the D-317 MG tumors. When tumor volume estimates reached 35 mm3, photomicrographs revealed tumor vasculature in each tumor cell line that was distinct from both the other xenograft and the normal brain parenchyma. Qualitative differences in vascular appearance were supported by length/density coefficient calculations in each study group, with D-317 MG demonstrating the highest vascular density. Vessel caliber tended to be smaller in D-54 MG tumors than in D-317 MG tumors. Laser-Doppler measurements of local blood flow in tumors and normal parenchyma revealed significantly lower blood flow in both tumor cell lines than in control brain. Evaluation of leukocyte/endothelial cell interactions indicated more leukocyte rolling in D-54 MG tumors than in D-317 MG tumors; no evidence of this cell interaction was found in normal pial vasculature. This model allows direct serial inspection of human brain tumor growth and vascular function in an experimental animal and could be used to study tumor vascular and inflammatory responses to a variety of therapeutic manipulations.

The significance of probe design in evaluation of colonic perfusion with laser Doppler flowmetry

The significance of probe design for laser Doppler flowmetry measurement depth and variation was investigated by determining flux versus pressure relations and spatial variability with various probes placed on the serosal surface of porcine sigmoid colon. For two large probes (three optical fibers with diameter and center separation > or = 500 microns) the flux versus pressure relations showed autoregulation, indicating that the mucosal perfusion contributed to the flux signal. The curves were reproducible between individuals. With two smaller probes linear flux versus pressure relations were obtained, indicating a shallow measurement not influenced by the autoregulated mucosal perfusion. The spatial variation expressed as coefficients of variation of repeated recordings at each pressure level was significantly greater with the smaller probes (p < 0.001). For clinical use the larger probes should be preferred. These include all wall layers, and only 3 repeated recordings are needed to obtain a reproducible mean flux value within +/- 10%, as opposed to 10 with the smaller probes.

Perfusion of the human distal colon and rectum evaluated with endoscopic laser Doppler flowmetry. Methodologic aspects

The aim of this study was to evaluate methodologic aspects of colonoscopic laser Doppler flowmetry. A Periflux PF1d flowmeter, set to 4 kHz/0.2 sec, with an endoscopic probe (PF 109) was used. In 20 patients, with a median age of 70 years and without colonic disease, flux was recorded at 10, 40, 30, 20, and again at 10 cm from the anal verge. A median of three repeated recordings were made at each level, to calculate average flux and spatial variation. Median flux was 158 (150-167) perfusion units, and the coefficient of variation of repeated recordings 0.14 (0.12-0.17). There was no regional variation, and no increase in flux at 10 cm from the start until the end of the procedure. Pressure of the probe against the bowel wall and severe distention significantly reduced the flux. The interference of light from the endoscopic light source on the flux could not be predicted. It differed with different light sources, and also with the length of probe coming out of the colonoscope--that is, the distance from the light to the measurement point. To avoid the problem, the light source should be turned off while recording.

Intraoperative prediction of ischaemic injury of the bowel: a comparison of laser Doppler flowmetry and tissue oximetry to histological analysis

Intraoperative diagnosis of inadequate colonic perfusion would contribute to prevention of ischaemic colitis after abdominal aortic reconstructions. The aim of this study was to evaluate laser Doppler flowmetry (LDF) and tissue oximetry (TpO2) as predictors of the development of bowel necrosis. Devascularised loops of colon and ileum in anaesthetised pigs were divided into 10-20 mm segments and measurements of laser Doppler flux and TpO2 were performed in each segment. After 7 h of ischaemia the segments were resected for histological and biochemical analysis. In 65 colonic and 58 ileal segments a significantly lower flux was found in segments with necrosis of greater than or equal to 30% of the mucosal thickness compared to segments with necrosis of less than or equal to 10% (p less than 0.01). The discriminant flux value was 50 perfusion units, confirming a previous clinical study. The specificity was 0.96 and the sensitivity 0.94. Flux was inversely correlated to tissue lactate concentration. Significantly lower TpO2 was found in 19 colonic segments with necrosis of greater than or equal to 30% of mucosa compared to 19 colonic segments with necrosis of less than or equal to 10% (p less than 0.01). Using a discriminant value of 5kPa, a specificity of 0.79, and a sensitivity of 0.95 were calculated. In 27 ileum segments no significant difference in TpO2 between different histological groups was found (p greater than 0.30). The results show that LDF and TpO2 can predict ischaemic injury of the colon, and LDF also of the small bowel.