Background-The astonishing thickness of the endothelial glycocalyx, which rivals that of endothelial cells in the microvasculature, was disclosed in the last 15 years. As already demonstrated, this structure plays a key role in the regulation of inflammation and vascular permeability. Methods and Results-Two components of the glycocalyx, syndecan-1 and heparan sulfate, were measured in arterial blood of 18 patients undergoing surgery of the ascending aorta with cardiopulmonary bypass (nϭ12 with and nϭ6 without deep hypothermic circulatory arrest) and of 14 patients undergoing surgery for infrarenal aortic aneurysm. Basal values of syndecan-1 (1.2 g/dL) and heparan sulfate (590 g/dL) of patients were similar to those of control subjects. Anesthesia and initiation of surgery caused no changes. Global ischemia with circulatory arrest (nϭ12) was followed by transient 42-and 10-fold increases in syndecan-1 and heparan sulfate, respectively, during early reperfusion (0 to 15 minutes). After regional ischemia of heart and lungs (cardiopulmonary bypass; nϭ6), syndecan-1 increased 65-fold, and heparan sulfate increased 19-fold. Infrarenal ischemia was followed by 15-and 3-fold increases, respectively (nϭ14). The early postischemic rises were positively correlated (rϭ0.76, PϽ0.001). Plasma concentrations of intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 did not change. Circulating polymorphonuclear granulocytes and the level of postischemic heparan sulfate corresponded negatively. Immunohistochemical imaging and immunoassay of isolated hearts (guinea pig) substantiated syndecan-1 and heparan sulfate as components of the endothelial glycocalyx released into the coronary venous effluent. Electron microscopy revealed shedding of the glycocalyx after ischemia/reperfusion. Conclusions-This study provides the first evidence in humans for shedding of the endothelial glycocalyx during ischemia/reperfusion procedures.

SUMMARY1. We have used non-invasive mercury in a silastic strain gauge system to assess the effect of pressure step size, on the time course of the rapid volume response (RVR) to occlusion pressure. We also obtained values for hydraulic conductance (Kf), isovolumnetric venous pressure (Pvi) and venous pressure (Pv) in thirty-five studies on the legs of twenty-three supine control subjects.2. The initial rapid volume response to small (953 + 045 mmHg, mean +S.E.M.) stepped increases in venous pressure, the rapid volume response, could be described by a single exponential of time constant 15-54 + 114 s.3. Increasing the size of the pressure step, to 49 8+ 1+ mmHg, gave a larger value for the RVR time constant (mean 77-3 + 11P6 s).4. We propose that the pressure-dependent difference in the duration of the rapid volume response, in these two situations, might be due to a vascular smooth musclebased mechanism, e.g. the veni-arteriolar reflex.5. The mean (+ S.E.M.) values for Kf, Pvi and Pv were 427+018 (units, ml min-(100 g)-1 mmHg-1 x 10-3), 21 50+0 81 (units, mmHg) and 9-11 +0-94 (units, mmHg), respectively.6. During simultaneous assessment of these parameters in arms and legs, it was found that they did not differ significantly from one another.7. We propose that the mercury strain gauge system offers a useful, non-invasive means of studying the mechanisms governing fluid filtration in human limbs.

Orthogonal polarization spectral imaging revealed no major changes of microvascular perfusion during uncomplicated hypothermic CPB. The slightly reduced functional capillary density during CPB may be caused by several factors all present during CPB, including hypothermia, the artificial extracorporeal perfusion, surgical trauma, hemodilution, and inflammatory reaction. The current data do not allow differentiation between the effects of those possible causes.

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The ability to investigate the microvascular structure and function is important in improving our understanding of pathophysiological processes in hypertension and related cardiovascular disease. A range of techniques are available or emerging for investigating different aspects of the microcirculation in animals and humans. Techniques such as experimental intravital microscopy and clinical intravital microscopy (e.g. orthogonal polarization spectral imaging) allow visualization at the level of single microvessels. Venous occlusion plethysmography can be used to measure blood flow in organs, and laser Doppler flowmetry to measure red cell flux in small areas of tissue. Positron emission tomography, myocardial contrast echocardiography, and magnetic resonance imaging provide three-dimensional imaging of local blood flow. The current and potential clinical usefulness of these different techniques is evaluated. The technical quality and availability for clinical use of some of the techniques should improve dramatically during the next few years. 'Molecular imaging'-the combination of these techniques with genetic, molecular, and computational approaches-offers great potential for use in research and in diagnosis and the monitoring of disease progression or the results of therapy. Closer attention to the microcirculation will ultimately improve the treatment and prevention of many of the most important forms of cardiovascular disease.

Venous congestion strain‐gauge plethysmography enables the non‐invasive assessment of arterial blood flow, fluid filtration capacity (Kf), venous pressure (Pv)and isovolumetric venous pressure (Pvi)in man. One of the major assumptions of this technique, that cuff pressure (Peuff) applied to the limb equals Pv at the level of the strain gauge, was tested in this study. In nine healthy male volunteers (mean age, 29.3 ± 1.2 years) the saphenous vein was cannulated with an 18‐gauge catheter proximal to the medial malleolus. The subjects were supine and Pv was continuously measured during the application of small step (8–10 mmHg) increases in congestion Pcuff (up to 70 mm Hg). Pcuff, changes in limb circumference and Pv were recorded by computer for off‐line analysis. Since the determination of Pv is influenced by the changes in plasma oncotic pressure, venous blood samples were obtained at the start of the study, when P& was raised to 30 mmHg and again to 65 mmHg and 4 min after deflation of the cuff. The relationship between Pv and Pcuff was linear over the range of 10–70 mm Hg (n= 9, 69 measurements, slope 0.9.1, r= 0.97, P. <<0.001). The non‐invasively measured calf Pv based on the intercept of the relationship between the vascular compliance component (Vv) and Pcuff, was 8.0±0.4mmHg, which was not significantly different from the corrected invasively measured Pv value of 8.8±0.3 mmHg P= 0.08). Venous blood lactate and haemoglobin concentrations, as well as colloid osmotic pressure, total protein and albumin concentrations were unchanged throughout the protocol, whereas significant decreases in Po2 and blood glucose concentration were observed when Pcuff reached 65 mmHg. Assuming a constant oxygen consumption, this may suggest a reduction in tissue perfusion. This study demonstrates the close correlation between Pcuff and Pvin the saphenous vein. Since the small congestion Pcuff step protocol does not cause significant increase in plasma oncotic pressure, we conclude that Pv as well as Kf can be accurately determined with this venous congestion plethysmography protocol.

We studied human lower limbs to test the hypothesis that the application of small cumulative venous congestion pressure steps is associated with a reduction in precapillary resistance. Strain gauge plethysmography was performed on twenty‐one young subjects (22.7 ± 0.6 years). At each of the small cumulative pressure steps, limb blood flow was estimated from the initial slope of the volume response to transient (10 s duration) elevations of venous congestion pressure to 90 mmHg, after which the congestion pressure was returned to the previous value. The blood flow at each pressure was also expressed as a percentage of the initial control value. Peak tibial arterial blood flux was assessed, in four of the subjects, using colour duplex ultrasonography and the same congestion pressure protocol. We used Darcy's Law to predict the limb arterial blood flow and blood flux at each venous congestion pressure, assuming that both mean arterial blood pressure and precapillary resistance remained constant. The mean ± s.e.m. control arterial blood flow at the lowest venous congestion pressure, 4.8 ± 0.1 mmHg, was 2.77 ± 0.18 ml min−1 (100 ml)−1. At the highest venous congestion pressure, 59.2 ± 0.2 mmHg, arterial blood flow was 2.45 ± 0.35 ml min−1 (100 ml)−1 (121.6 ± 16.9 % of the initial value). This did not differ significantly from the initial control value, but was significantly greater than the predicted value of 0.77 ± 0.13 ml min−1 (100 ml)−1 (28.6 ± 2.1 % of the initial value) calculated assuming constant resistance and sustained mean arterial pressure. The tibial arterial peak blood flux at 58.3 mmHg venous congestion pressure was 102.2 ± 2.3 % of the control value, which was significantly greater than the predicted 17.2 ± 1.3 % of control, calculated for this pressure, assuming constant resistance and sustained mean arterial pressure. Our data show that lower limb arterial blood flow is sustained when venous congestion pressure is raised using small cumulative steps, even at congestion pressures approaching mean arterial blood pressure. These data support the notion that precapillary resistance is influenced by signals generated at the microvascular and post microvascular levels and transmitted via the endothelium.

Little is known about the microvascular perfusion of the skin postnatally. Skin microvascular parameters can be assessed noninvasively with orthogonal polarization spectral imaging (OPS), a technique where, through the use of special optics, a virtual light source is created at a depth of 1 mm within the tissue. The light is absorbed by the Hb, yielding an image of the illuminated Hb-carrying structures in negative contrast. In nine term (weight 2100 -4470 g) and 28 preterm infants (weight 550 -2070 g; gestational age 24 -33 wk) red blood cell velocity and vessel diameter and density were determined off-line with the CapImage program in vessels video-recorded by OPS near the axilla on d 1 and 5 of life. Blood pressure, heart rate, hematocrit, and body and incubator temperature were noted. Vessel diameter ranged from 6 to 24 m, vessel density from 219 to 340 cm/cm 2 with no change between d 1 or 5 and no difference between term and preterm infants. Red blood cell velocity increased in preterm infants from d 1 [median 528 m/s, 95% confidence interval (CI) 486 -564 m/s] to d 5 (median 570 m/s; 95% CI 548 -662 m/s; p ϭ 0.001) and correlated with the decrease in median hematocrit from 44% (CI 40%-60%) to 39% (CI 37%-43%) with r 2 ϭ Ϫ0.37 with a 95% CI Ϫ0.59 to Ϫ0.11, p ϭ 0.006. Hematocrit correlates with red blood cell velocity in the microvessels of the skin. The new technology can be used to assess quantitative changes in the microvessels and thus allows noninvasive assessment of tissue perfusion in term and preterm infants. At birth, the skin is richly supplied by a dense subepidermal plexus that shows relatively little regional variation. Even the middle and deep dermis are richly endowed with vasculature. The mature pattern of capillary loops and of the subpapillary venous plexus is not present at birth. With exception of the palms, soles, and nail beds, the skin at birth has almost no papillary loops, but demonstrates a disorderly capillary network. By the end of the first week of life, the capillary network assumes a more orderly pattern. Papillary loops begin to appear as small superficial dilatations or buds in the second week and cooling of the skin appears to encourage maturation. The skin architecture in newborns is notably different from those of an adult. Whereas the latter regularly shows loops of capillaries running orthogonal to the surface of the skin, the neonate has a more horizontal structure, which is readily seen through the very thin upper layers (1-4).Cardiac output normalized to mass is much higher in the newborn than in the adult. Because of the high resting cardiac output of neonates there is limited reserve to further augment blood flow under stress. Perfusion pressure is maintained by redistributing marginal cardiac output and oxygen supply to brain, heart, and adrenal gland. Under no stress conditions the skin has high blood flow in relation to its oxygen requirement. Assessment of skin perfusion is therefore of great interest, but there is only very scant data about the microcirculator...