The development of artificial blood requires the understanding of how blood behaves at the level of the microcirculation. A number of measuring systems have recently become available that allow analysis of the transport properties of blood and the microvessels in terms of pressure, flow, the dynamics of their diameter changes, and the rate and manner of oxygen delivery. Findings from this technology have led to the development of an analytical framework with which to assess the consequences of altering the physical properties of blood and to verify quantitatively theoretical predictions. Results show that blood viscosity and oxygen-carrying capacity are directly related, and must be jointly modified in a prescribed manner to maintain tissue oxygen delivery. The use of optical techniques to assess flow and oxygen delivery in experimental animal models show that the consumption of oxygen by the microvessel wall is an important determinant of tissue oxygenation. Furthermore, the viscosity of blood and/or the mixture of blood and an artificial substitute must achieve a viscosity that is close to normal. Low blood viscosity is not necessarily beneficial, unless blood flow velocity rises to maintain the shear stress at the wall needed for the generation of local vasodilators. Manipulating physical properties of currently available modified hemoglobins by mixing them with conventional plasma expanders yield fluids that may provide optimal blood replacements.

Biomedical Engineering↗

PubMedDate not supplied

Quantitative studies of microcirculatory function in malignant tissue: influence of temperature on microvascular hemodynamics during the early growth of the BA 1112 rat sarcoma.

Explore the source record for details and available documents.

Animals↗

PubMedDate not supplied

Site-specific PEGylation of hemoglobin at Cys-93(beta): correlation between the colligative properties of the PEGylated protein and the length of the conjugated PEG chain.

Increasing the molecular size of acellular hemoglobin (Hb) has been proposed as an approach to reduce its undesirable vasoactive properties. The finding that bovine Hb surface decorated with about 10 copies of PEG5K per tetramer is vasoactive provides support for this concept. The PEGylated bovine Hb has a strikingly larger molecular radius than HbA (1). The colligative properties of the PEGylated bovine Hb are distinct from those of HbA and even polymerized Hb, suggesting a role for the colligative properties of PEGylated Hb in neutralizing the vasoactivity of acellular Hb. To correlate the colligative properties of surface-decorated Hb with the mass of the PEG attached and also its vasoactivity, we have developed a new maleimide-based protocol for the site-specific conjugation of PEG to Hb, taking advantage of the unusually high reactivity of Cys-93(beta) of oxy HbA and the high reactivity of the maleimide to protein thiols. PEG chains of 5, 10, and 20 kDa have been functionalized at one of their hydroxyl groups with a maleidophenyl moiety through a carbamate linkage and used to conjugate the PEG chains at the beta-93 Cys of HbA to generate PEGylated Hbs carrying two copies of PEG (of varying chain length) per tetramer. Homogeneous preparations of (SP-PEG5K)(2)-HbA, (SP-PEG10K)(2)-HbA, and (SP-PEG20K)(2)-HbA have been isolated by ion exchange chromatography. The oxygen affinity of Hb is increased slightly on PEGylation, but the length of the PEG-chain had very little additional influence on the O(2) affinity. Both the hydrodynamic volume and the molecular radius of the Hb increased on surface decoration with PEG and exhibited a linear correlation with the mass of the PEG chain attached. On the other hand, both the viscosity and the colloidal osmotic pressure (COP) of the PEGylated Hbs exhibited an exponential increase with the increase in PEG chain length. In contrast to the molecular volume, viscosity, and COP, the vasoactivity of the PEGylated Hbs was not a direct correlate of the PEG chain length. There appeared to be a threshold for the PEG chain length beyond which the protection against vasoactivity is decreased. These results suggest that the modulation of the vasoactivity of Hb by PEG could be a function of the surface shielding afforded by the PEG, the latter being a function of the disposition of the PEG chain on the protein surface, which in turn is a function of the length of the PEG chain. Thus, the biochemically homogeneous PEGylated Hbs described in the present study, surface-decorated with PEG chains of appropriate size, could serve as potential candidates for Hb-based oxygen carriers.

Animals↗

PubMedDate not supplied

Effect of elevated C1-esterase inhibitor concentrations on white blood cell-endothelium interactions: a potential mechanism for steroid protection in contrast material reactions.

Purified human C1-esterase inhibitor (C1INH) infused into the circulation of rabbits caused an immediate drop in white blood cell (WBC) count and, simultaneously, a marked decrease in WBC adhesion to the endothelium in the microcirculation. Infusion of iodipamide caused a marked "carpeting" of the venous endothelium by WBC, and this condition was reversed by subsequent infusion of C1INH. The relationship of elevated C1INH to the protective effect of prednisolone on iodipamide toxicity in the rabbit is discussed.

Animals↗

PubMedDate not supplied

Oral administration of purified micronized flavonoid fraction suppresses leukocyte adhesion in ischemia-reperfusion injury: in vivo observations in the hamster skin fold.

The effect of a clinically used purified micronized flavonoid fraction (90% diosmin and 10% hesperidin) on leukocyte-endothelial cell interaction during ischemia-reperfusion injury was studied in the microcirculation of unanesthetized hamsters fitted with a skin fold window chamber. The drug was given orally in suspension with arabic gum (30 mg/kg) 8 h prior to induction of 4-hour tourniquet ischemia in the chamber window. Leukocyte-endothelial cell interaction was observed using fluorescence intravital microscopy in postcapillary venules (15-70 microns in diameter) at control and during reperfusion at 30 min and 2 and 24 h. Leukocytes were classified according to their flow pattern as (1) 'passers', including 'free flowing' leukocytes and those which were 'flowing with endothelial contact', and (2) 'immobilized' leukocytes. Untreated animals exhibited a significant increase of 'immobilized' leukocytes and of those 'flowing with endothelial contact' during reperfusion. Flavonoid-treated animals displayed a statistically significant lower number of 'immobilized' leukocytes at all time points during reperfusion. There was no change in the number of leukocytes 'flowing with endothelial contact' relative to the untreated animals. Since firm leukocyte attachment to the endothelial wall and subsequent emigration of leukocytes into the interstitium is a mechanism for tissue damage during inflammation, attenuation of this phenomenon during conditions of ischemia-reperfusion can in part explain previous observations that this purified micronized flavonoid fraction decreases edema formation.

Administration, Oral↗

PubMedDate not supplied

Microvascular vasomotion: origin of laser Doppler flux motion.

Intravital microscopy and laser Doppler fluxmetry (LDF) were used to assess vasomotion and flux motion in skeletal muscle microcirculation. To clarify the relation between vessel type and LDF signals, arterioles, capillaries, and venules were sequentially studied. We used as an experimental model the hamster skin fold window preparation to record vasomotion and flux motion under control conditions and after injection of an alpha 2-adrenoceptor antagonist, yohimbine, since terminal arterioles appear to be subserved primarily by alpha 2-adrenoceptors. LDF signals were characterized by using an autoregressive modeling power spectrum technique. This analysis indicated that the flux motion fundamental frequency of terminal arterioles coincided with order 2 arteriole vasomotion fundamental frequency. The LDF fundamental frequency of order 3 arterioles was synchronous with the vasomotion frequency in the same-order vessels. The LDF fundamental frequency of order 3 venules corresponded to the frequency component coincident with the respiratory rate. The pattern of LDF oscillations was peculiar for each type of vessels, and the total power was greater in larger arterioles than in venules. Yohimbine reduced frequency and amplitude of vasomotion and flux motion in terminal arterioles, but it was possible to detect LDF oscillatory patterns due to the activity of parent vessels with a low frequency. In conclusion, the flux motion is fundamentally dependent on the type of vessel from which it originates and is directly related to the vasomotion of the arterioles.

Animals↗

PubMedDate not supplied

Induced periodic hemodynamics in skeletal muscle of anesthetized rabbits, studied with multiple laser Doppler flow probes.

Periodic fluctuations, regular slow-wave flowmotion, were induced in the skeletal muscle of six mature anesthetized New Zealand White rabbits by acute femoral artery pressure reduction from a median control value of 78 to 36 mm Hg. This phenomenon was monitored simultaneously with four laser Doppler flowmetry (LDF) probes placed over the gastrocnemius muscle in a linear array with a spacing of 5 mm. The median relative peak-to-trough amplitude of the oscillatory flow patterns was 47%, white a frequency of approximately 2.5 cycles per minute (cpm), which remained relatively stable over an observation period of 1 h (+/- 15-20%). Application of two frequency analysis methods, Welch's FFT method and Prony Spectral Line Estimation yielded similar results and showed a correlation coefficient of r = +0.84. Spectral coherence between pairs of regular slow-wave flowmotion records decreased with increasing probe separation (0.28 at 5 mm; 0.01 at 15 mm). However, patterns of frequency fluctuation over time were significantly correlated between concurrent record pairs regardless of probe separation. These results suggest that the regular slow-wave flowmotion signal originates in regions that are independently regulated by local vasoactive sites, which may be called pacemakers. These sites may also be influenced by an additional common control mechanism, which may be myogenic/metabolic or central in nature.

Anesthetics, Intravenous↗

PubMedDate not supplied

Capillary flow impairment and functional capillary density.

Functional capillary density is variable in both normal and diseased tissue. When this parameter is defined as the number of capillaries that possess red blood cell transit, changes in functional capillary density reflect mechanisms that modulate the entrance of red blood cells into the capillaries. These mechanisms have anatomical origin, whereby the capillary diameter changes, and may also be hydrodynamic, when flow conditions prevent red blood cells from entering a capillary branch. An intrinsic feature of both processes is that capillaries undergo lumenal changes. Capillary lumen is determined by a composite of mechanical and cellular factors, where intravascular pressure is one of the principal determinants affecting diameter as a consequence of the elastic properties of the capillary/tissue system. The hydration of the surrounding tissue and the cellular volume regulation of the endothelium are additional factors. There is increasing evidence that capillaries possess contractility and that this phenomenon has spontaneous components. Consequently, functional capillary density is the resultant of both passive and active processes present at the level of individual vessels.

Animals↗