Correlation between laser Doppler perfusion monitoring and hematocrit in hamster cheek pouch microcirculation

Arterial Network Geometric Characteristics and Regulation of Capillary Blood Flow in Hamster Skeletal Muscle Microcirculation

This study was aimed to characterize the geometric arrangement of hamster skeletal muscle arteriolar networks and to assess the in vivo rhythmic diameter changes of arterioles to clarify regulatory mechanisms of the capillary perfusion. The experimental study was carried out in male Syrian hamsters implanted with a plastic chamber in the dorsum skin under pentobarbital anesthesia. The skeletal muscle microvessels were visualized by fluorescence microscopy. The vessel diameters, lengths and the rhythmic diameter changes of arterioles were analyzed with computer-assisted techniques. The arterioles were classified according to a centripetal ordering scheme. In hamster skeletal muscle microvasculature the terminal branchings, differentiated in long and short terminal arteriolar trees (TATs), originated from anastomotic vessels, defined "arcading" arterioles. The long TATs presented different frequencies along the branching vessels; order 4 arterioles had frequencies lower than those observed in the order 3, 2, and 1 vessels. The short TAT order 3 arterioles, directly originating from "arcading" parent vessels, showed a frequency dominating all daughter arterioles. The amplitude of diameter variations in larger vessels was in the range 30-40% of mean diameter, while it was 80-100% in order 3, 2, and 1 vessels. Therefore, the complete constriction of arterioles, caused an intermittent capillary blood perfusion. L-arginine or papaverine infusion caused dilation of arterioles and transient disappearing of vasomotion waves and induced perfusion of all capillaries spreading from short and long TAT arrangements. Therefore, the capillary blood flow was modulated by changes in diameter of terminal arterioles penetrating within the skeletal muscle fibers, facilitating redistribution of blood flow according to the metabolic demands of tissues.

Retinal hemodynamic oxygen reactivity assessed by perfusion velocity, blood oximetry and vessel diameter measurements

PURPOSE

To test the oxygen reactivity of a fundus photographic method of measuring macular perfusion velocity and to integrate macular perfusion velocities with measurements of retinal vessel diameters and blood oxygen saturation.

METHODS

Sixteen eyes in 16 healthy volunteers were studied at two examination sessions using motion-contrast velocimetry and retinal oximetry with vessel diameter corrections. To test oxygen reactivity, participants were examined during normoxia, after 15 min of hyperoxia and finally after 45 min of normoxia. Repeatability was assessed by intraclass correlation coefficients (ICC) and limits of agreement.

RESULTS

Fifteen minutes of hyperoxia was accompanied by mean reductions in arterial and venous perfusion velocities of 14% and 16%, respectively (p = 0.0080; p = 0.0019), constriction of major arteries and veins by 5.5% and 8.2%, respectively (p < 0.0001), increased retinal arterial oxygen saturation from 95.1 ± 5.0% to 96.6 ± 6.4% (p = 0.038) and increased retinal venous oxygen saturation from 62.9 ± 6.7% to 70.3 ± 7.8% (p = 0.0010). Parameters returned to baseline levels after subsequent normoxia. Saturation and vessel diameter ICCs were 0.88-0.98 (range). For perfusion velocities, short-term ICCs were 0.79-0.82 and long-term ICCs were 0.06-0.11. Intersession increases in blood glucose were associated with reductions in perfusion velocities (arterial p = 0.0067; venous p = 0.018).

CONCLUSION

Oxygen reactivity testing supported that motion-contrast velocimetry is a valid method for assessing macular perfusion. Results were consistent with previous observations of hyperoxic blood flow reduction using blue field entoptic and laser Doppler velocimetry. Retinal perfusion seemed to be regulated around individual set points according to blood glucose levels. Multimodal measurements may provide comprehensive information about retinal metabolism.

Fiber optical spatial filter anemometry--intravital measurement of red blood flow velocity (RBCV) in the microcirculation

The fiberoptical spatial filter anemometry (SFA) is a common technique based on an optical grid to measure the velocity of corpuscular components in a multiphase flow, e.g. in the microvessels. The technical innovation is the analysis of flow velocities using an optical grid sensor and frequency analysis by Fast Fourier Transformation (FFT). This study describes a non-invasive, on-line technique to measure RBCV in the microcirculation. The sensor's validity was proven by in vitro measurements using a rotation disk of an exactly defined velocity with a correlation coefficient of 0.99967. For validation of RBCV measurements in the microcirculation in vivo, the setup was adapted to an intravital microscope. RBCV was measured in arterioles, capillaries, and postcapillary venules ranging from 8-140 microm diameter. As reference method for velocity measurements a computer assisted imaging system was used to measure the RBC-velocity in the identical vessels by frame to frame analysis. Both methods revealed a high significant correlation using transillumination technique for capillaries (r=0.986, p<0.001) and venules (r=0.952, p<0.001) as well as epiillumination technique (capillaries r=0.939, venules r=0.975, p<0.001).

Vasopressin decreases intestinal mucosal perfusion: a clinical study on cardiac surgery patients in vasodilatory shock

BACKGROUND

Low to moderate doses of vasopressin have been used in the treatment of cathecholamine-dependent vasodilatory shock in sepsis or after cardiac surgery. We evaluated the effects of vasopressin on jejunal mucosal perfusion, gastric-arterial pCO2 gradient and the global splanchnic oxygen demand/supply relationship in patients with vasodilatory shock after cardiac surgery.

METHODS

Eight mechanically ventilated patients, dependent on norepinephrine to maintain mean arterial pressure (MAP) > or = 60 mmHg because of septic/post-cardiotomy vasodilatory shock and multiple organ failure after cardiac surgery, were included. Vasopressin was sequentially infused at 1.2, 2.4 and 4.8 U/h for 30-min periods. Norepinephrine was simultaneously decreased to maintain MAP at 75 mmHg. At each infusion rate of vasopressin, data on systemic hemodynamics, jejunal mucosal perfusion, jejunal mucosal hematocrit and red blood cell velocity (laser Doppler flowmetry) as well as gastric-arterial pCO2 gradient (gastric tonometry) and splanchnic oxygen and lactate extraction (hepatic vein catheter) were obtained.

RESULTS

The cardiac index, stroke volume index and systemic oxygen delivery decreased and systemic vascular resistance and systemic oxygen extraction increased significantly, while the heart rate or global oxygen consumption did not change with increasing vasopressin dose. Jejunal mucosal perfusion decreased and the arterial-gastric-mucosal pCO2 gradient increased, while splanchnic oxygen or lactate extraction or mixed venous-hepatic venous oxygen saturation gradient were not affected by increasing infusion rates of vasopressin.

CONCLUSIONS

Infusion of low to moderate doses of vasopressin in patients with norepinephrine-dependent vasodilatory shock after cardiac surgery induces an intestinal and gastric mucosal vasoconstriction.

Vasopressors and intestinal mucosal perfusion after cardiac surgery: Norepinephrine vs. phenylephrine

OBJECTIVES

To evaluate the potential differential effects of norepinephrine, an alpha1-, beta1-, and beta2-receptor agonist, to the alpha1-agonist phenylephrine on jejunal mucosal perfusion, gastric-arterial PCO2 gradient, and the global splanchnic oxygen demand-supply relationship after cardiac surgery.

DESIGN

A randomized, prospective, interventional crossover study.

SETTING

A university cardiothoracic intensive care unit.

PATIENTS

Ten patients were studied during propofol sedation and mechanical ventilation after uncomplicated coronary artery bypass surgery.

INTERVENTIONS

Each patient received randomly and sequentially norepinephrine (0.052+/-0.009 microg/kg/min) and phenylephrine (0.50+/-0.22 microg/kg/min) to increase mean arterial blood pressure by 30%.

MEASUREMENTS AND MAIN RESULTS

Data on jejunal mucosal perfusion, jejunal mucosal hematocrit, and red blood cell velocity (laser Doppler flowmetry) as well as gastric-arterial Pco2 gradient (tonometry) and splanchnic oxygen extraction were obtained before (control) and during a 30-min drug infusion period after the target mean arterial blood pressure was reached. The procedure was sequentially repeated for the second vasopressor. Both drugs induced a 40-46% increase in systemic vascular resistance with no change in cardiac index. Neither jejunal mucosal perfusion, jejunal mucosal hematocrit, red blood cell velocity, nor gastric-arterial Pco2 gradient was affected by any of the vasopressors. Splanchnic oxygen extraction increased from 38.2% to 43.1% (p<.001) with norepinephrine and from 39.3% to 47.5% (p<.001) with phenylephrine. This increase was significantly more pronounced with phenylephrine compared with norepinephrine (p<.05). Mixed venous-hepatic vein oxygen saturation gradient increased with both drugs (p<.01), and the increase was more pronounced with phenylephrine (p<.05). Splanchnic lactate extraction was not significantly affected by any of the vasopressors.

CONCLUSIONS

Phenylephrine induced a more pronounced global alpha1-mediated splanchnic vasoconstriction compared with norepinephrine. Neither of the vasoconstrictors impaired perfusion of the gastrointestinal mucosa in postcardiac surgery patients. The lack of norepinephrine-induced, alpha1-mediated impairment of gastrointestinal perfusion is not explained by a beta2-mediated counteractive vasodilation but instead by possible mucosal autoregulatory escape.

Cardiopulmonary bypass in humans--jejunal mucosal perfusion increases in parallel with well-maintained microvascular hematocrit

BACKGROUND

An imbalance between splanchnic oxygen supply and demand occurs during cardiopulmonary bypass (CPB) in man, which might disrupt the intestinal mucosal barrier function. The aim of the present study was to evaluate the effects of mild hypothermic CPB on intestinal mucosal perfusion in man undergoing cardiac surgery. Additionally we aimed to identify variables, which independently could predict changes of intestinal mucosal microcirculatory variables during CPB.

METHODS

Jejunal mucosal perfusion (JMP), jejunal mucosal hematocrit (JMHt), red blood cell (RBC) velocity and arteriolar vasomotion using endoluminal jejunal laser Doppler flow metry were studied in eight cardiac surgical patients before and during CPB at a temperature of 34 degrees C.

RESULTS

Cardiopulmonary bypass and the accompanied hemodilution (25-30%) induced a 44% increase in JMP (P < 0.05) and a 42% increase in RBC velocity (P < 0.01), with no change in JMHt. The oscillation amplitude of JMP, at a fundamental frequency of 2.8 cycles min(-1), increased with 175% (P < 0.05) during CPB. Splanchnic oxygen extraction increased by 64% during CPB (P < 0.05). Stepwise multiple regression analysis identified systemic hematocrit, arterial O2 and CO2 tension and splanchnic oxygen extraction as independent predictors of RBC velocity during CPB (R2=0.63, P < 0.001). The oscillation amplitude of JMP was predicted by RBC velocity and splanchnic oxygen extraction (R2= 0.68, P <0.0001).

CONCLUSIONS

The increase in RBC velocity and enhanced arteriolar vasomotion, as well as maintained jejunal mucosal hematocrit, are microcirculatory, compensatory mechanisms for the splanchic oxygen supply/demand mismatch seen during cardiopulmonary bypass in humans.

Volumetric flow mapping for microvascular networks by bimodality imaging with light microscope and Laser Doppler imager

A method was developed to produce a composite image of microvascular networks with grayscales proportional to volumetric flows. Velocities in arterioles and venules were assessed with a high-resolution laser Doppler imager (LDI). The vascular structures were quantified from the micrograph with a computerized vessel detection algorithm. After registering the detected vascular network with the LDI scan, volumetric flows were calculated along the centerlines of the vessels. In vivo data were obtained from the hamster cheek pouch in 6 studies. Flow continuity of the flow map was evaluated by comparing the main flow (Q) with the sum of branch flows (Qs), averaging over the respective vessel segments incident to each bifurcation. The method was reproducible across the 6 studies with the correlation coefficient (r) between Qs and Q ranging from 0.913 to 0.986. In all, over 20,000 flow estimates from 360 vessel segments (24-160 microm in diameter) at 166 bifurcations were analyzed. With flow normalized between 0 and 1, the linear regression yielded: Qs = 1.03 Q + 0.006; r = 0.952, n = 166, P < 0.0005. The bimodality imaging method exploits a large amount of velocity and diameter data, and therefore should be useful for studying heterogeneous flows in the microvasculature.

Miniaturization: an overview of biotechnologies for monitoring the physiology and pathophysiology of rodent animal models

Recent advances in bioengineering technologies have made it possible to collect high-quality reproducible data quantitatively in a wide range of laboratory animal species, including rodents. Several of these technologies are incorporated into a plan called Miniaturization, which aims to design, develop, and maintain rodent animal models to study the pathophysiology and therapy of human diseases. Laser Doppler flowmetry, digital sonomicrometry, bioelectrical impedance, and microdialysis are some of the most widely used methods under the plan because they cause minimal pain and distress, reduce the number of animals used in biomedical research, and allow chronic, nonterminal assessment of physiological parameters in rodents. An overview of each of these technologies and their major applications in rodents used for biomedical research is provided.

Jejunal and gastric mucosal perfusion versus splanchnic blood flow and metabolism: an observational study on postcardiac surgical patients

OBJECTIVES

To evaluate the association between changes in total splanchnic and mucosal perfusion, assessed either by gastric tonometry or jejunal laser Doppler flowmetry in postcardiac surgical patients.

DESIGN

A prospective, observational study.

SETTINGS

A general intensive care unit in a tertiary care center.

PATIENTS

Twelve, postoperative cardiac surgery patients were studied.

INTERVENTIONS

Patients were treated according to clinical routine. Total splanchnic blood flow (indocyanine green extraction), jejunal mucosal perfusion (laser Doppler flowmetry), gastric mucosal-arterial PCO2 gradients, and splanchnic lactate uptake were studied during four 30-min measurements periods, each separated by a period of 1 hr.

MEASUREMENTS AND MAIN RESULTS

There was no consistent association between either total splanchnic and local mucosal perfusion or between gastric and jejunal perfusion as assessed by two different techniques. The PCO2 gradient increased from 0.73+/-0.21 kPa to 1.15+/-0.30 kPa (p < .05), and splanchnic oxygen extraction increased from 40%+/-9% to 49%+/-14% (p < .01).

CONCLUSIONS

In this observational study on postcardiac surgical patients, local mucosal perfusion did not reflect total splanchnic blood flow and vice versa. Either changes in gastric and jejunal mucosal perfusion were different or increasing tissue metabolism was responsible for the observed lack of association between tonometry, laser Doppler flowmetry, and total splanchnic blood flow. Increasing mucosal arterial PCO2 gradient and splanchnic oxygen extraction may reflect a mismatch between splanchnic perfusion and metabolic demands.

Differential effects of dopamine, dopexamine, and dobutamine on jejunal mucosal perfusion early after cardiac surgery

OBJECTIVE

To evaluate the potential differential effects of dopamine, dopexamine, and dobutamine on jejunal mucosal perfusion, assessed by endoluminal laser Doppler flowmetry in uncomplicated postcardiac surgical patients.

DESIGN

A prospective, blinded, randomized, crossover study.

SETTING

A cardiothoracic intensive care unit in a tertiary care center.

PATIENTS

A total of ten postoperative cardiac surgical patients were studied.

INTERVENTIONS

Each patient received sequentially, randomly, and in a blinded fashion 2.7+/-0.2 microg x kg(-1) x min(-1) dopamine, 0.7+/-0.1 microg x kg(-1) x min(-1) dopexamine, and 2.7+/-0.1 microg x kg(-1) x min(-1) dobutamine. Each inotropic agent was titrated to increase cardiac output by 25% from baseline. Data on jejunal mucosal perfusion, splanchnic lactate, and oxygen extraction were obtained during a 5-min control period and a 5-min drug infusion period after the target cardiac output was reached. The procedure was sequentially repeated for each agent, and there was a 20- to 30-min washout period between each agent.

MEASUREMENTS AND MAIN RESULTS

Dopamine, dopexamine, and dobutamine increased jejunal mucosal perfusion by 27% (p < .01), 20% (p < .001), and 7% (p < .001), respectively. The increase in jejunal mucosal perfusion by dopamine and dopexamine were significantly more pronounced compared with dobutamine (p < .05 and p < .01, respectively), whereas there was no difference between dopamine and dopexamine. Splanchnic oxygen extraction decreased to the same extent with all three drugs. Splanchnic lactate extraction did not change for any of the drugs. The effects on central hemodynamics were similar for the three inotropic agents.

CONCLUSIONS

Endoluminal laser Doppler flowmetry is a new tool for the detection of perfusion changes at the local intestinal mucosal level. Dopamine, dopexamine, and dobutamine have differential effects on jejunal mucosal perfusion probably because of their different receptor stimulating properties. These findings may be of clinical importance when the therapeutic goal is to improve gut mucosal perfusion.

Evaluation of enhanced high-resolution laser Doppler imaging in an in vitro tube model with the aim of assessing blood flow in separate microvessels

An enhanced high-resolution laser Doppler imaging (EHR-LDI) technique intended for visualization of separate microvessels was evaluated by use of in vitro flow models. In EHR-LDI, a laser beam focused to a half-power diameter less than 40 microm successively scans the tissue under study in steps of 25 microm. Spatial blood flow variations within microvascular structures of 1.5 x 1.5 mm are rendered by 64 x 64 measurement sites. Individual microvessel diameters could be estimated and an average difference of 11 microm compared to microscopic measurements was obtained. For the flow algorithm used, the LDI output signal was found to scale linearly with average velocity (0-3.5 mm/s) when a plastic tube of inner diameter 175 microm was perfused with human blood (correlation coefficient 0.99). The LDI output signal was further found insensitive to hematocrit variations in the range 16-44%. Due to the limited laser light penetration in blood, a reduction in the LDI output signal was observed as the inner tube diameters were successively changed from 280 to 1400 microm.