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Colored cold setting acrylic cement was injected through catheters into the arteries and veins of sixteen gravid uteri obtained from pigs at various stages of pregnancy. After the cement had set hard, the reproductive tracts were macerated in concentrated acid and the vascular casts resulting were washed clean of digested tissues. Small pieces of cast were coated with gold and viewed by means of a scanning electron microscope. Early in pregnancy the capillary network consists of low parallel ranks of ridges and troughs; later, cross ridging was observed which developed in complexity as pregnancy progressed. The density of capillaries comprising the microvascular network also increased towards term. No comparable changes were noted in the relatively less well vascularized areas surrounding the mouths of the uterine glands. This technique surmounted the problems of obtaining an adequate depth of focus for viewing the capillary network of the gravid uterus with the light microscope. The relationships that the blood vessels bore to the overlying epithelial layers were discussed and the inference tentatively drawn that blood flow at the capillary level was from ridge top to trough base.

Earlier studies of the vascular patterns around hair follicles revealed that actively growing follicles have an extensive microvasculature relative to that around quiescent follicles. In order to determine whether the establishment of the active perifollicular vascular pattern involves replication of endothelial and perivascular cells, we studied the 3H-thymidine labeling indices of these cells in autoradiographs of rat skin from regions containing either actively growing follicles or recently inactive follicles. In skin containing inactive follicles, the endothelial labeling index was 0.22%, a figure similar to those reported for the endothelium of small blood vessels in several other non-stimulated adult tissues. However, skin containing actively growing follicles displayed an endothelial labeling index of 2.35%. The labeling indices of perivascular cells paralleled those of the endothelial cells. Thus, endothelial and perivascular cells in vessels associated with actively growing follicles undergo significantly more DNA synthesis than those in vessels associated with inactive follicles. Replication of these cells apparently contributes to the extension of the microvascular network around growing follicles.

Erst 50 Jahre nach der Erstbeschreibung des Blutkreislaufes durch Harvey wurde das Kapillarsystem - von Marcello Malpighi an der Froschlunge - als Verbindungsglied zwischen arteriellem und venosem Kreislauf entdeckt. Seither ist gerade dieses mikrozirkulatorische Netzwerk Gegenstand zahlreicher, morphologischer und physiologischer Untersuchungen gewesen. Mit zunehmender Verfeinerung der technischen Moglichkeiten der Morphologie wurde eine sehr detailgetreue Darstellung der anatomischen Verhaltnisse moglich. Soweit dies die zellulare Ultrastruktur betrifft, fand bisher vor allem das variationsreiche Erscheinungsbild des Endothels Berucksichtigung. Aufgrund neuerer Erkenntnisse mussen besonders auf diesem Gebiet verschiedene - auch funktionell bedeutsame - Interpretationen revidiert werden. Fur die vorliegende Arbeit werden - unter Verwendung mehrerer, sich erganzender, morphologischer Techniken - neue Befunde der endonasalen Mikrozirkulation zusammengestellt und -soweit vertretbar - in ihrem funktionellen Kontext interpretiert. Harvey (1628) was the first to describe the blood circulatory system. 50 years later, the capillary system was discovered by Marcello Malpighi as a link between arteries and veins. Since then, the microvascular network has been examined abundantly by means of various morphological and physiological techniques. During the last decades the development of the technical equipment enabled us to receive detailed informations on the structural and ultrastructural aspects of the vasculature and - particularly - the capillary endothelium. New electron microscopic investigations are likely to revise earlier functional interpretations on the behaviour of this special cell system. In the present study we combined our own morphological results on the endonasal microcirculatory system - using different morphological techniques - to interpret these anatomical finding under functional aspects.

A bloodless method of isolating the sciatic nerve in rats, placing it on a light guide, and adapting the MBI-6 microscope for the intravital study of the microcirculation of blood in the epineurium of the sciatic nerve is described. Variations in the microvascular network of the epineurium in rats are demonstrated.

The histological structure and biochemical composition of human tumours is very varied, as is the structure of the microvascular network. It can be expected, therefore, that the extravasation, diffusion and convection of macromolecules will vary between tumours - and also between areas in the same tumour. The major factors influencing the intratumour distribution of injected antibody are reviewed and an attempt made to identify the tumour types in which therapeutic antibody, with or without a cytotoxin, will distribute most effectively.

Blood cells flowing in the coronary microvascular network are responsible for oxygen supply to myocardial cells. Among these cells, white cells (WBCs) are more spherical, larger, and less deformable than red cells (RBCs) [1]. For this reason, WBCs may have an important influence on the microcirculation, especially at a low perfusion pressure. In fact, according to intravital microscopic observation of microcirculation in the s~eletal muscle, one or several WBCs may block the capillary flow during hemorrhagic shock [2]. There is also histological evidence that WBC plugging may cause mechanical obstruction of coronary capillaries in myocardial ischemia [3].

Publisher Summary This chapter discusses a study in which the distribution of RBC velocity in the capillaries of resting skeletal muscle was examined to understand the regulation of oxygen supply to both cardiac and skeletal muscle. Using the television-computer method, velocity in 53 capillaries selected randomly from 24 frogs for periods of 5 to 50 min was measured. The temporal distribution of RBC velocity in four of these capillaries as represented by histograms containing from 1500 to 20,000 velocity measurements was shown. The overall range of velocity values for all capillaries measured extended from 0 to 0.83 mm/s, with mean velocity values for individual capillaries ranging from 0.03 to 0.48 mm/s. The histogram on the mean velocity axis represents the distribution of mean velocities, but it does not necessarily represent a spatial velocity distribution because this histogram depends also on any animal-to-animal variation. Changes in the shape of the histogram measured at different times would reflect changes in the distribution of blood flow within the microvascular network.

A systematic investigation of the distribution of red cell velocity throughout the hierachy of the rat pulp microvascular network was performed. Luminal diameters (D) of microvessels ranging in size from 8 to 72 micron were measured in situ by an electronic video image shearing technique. Intravascular red cell velocities (Vrbc) were simultaneously measured by a variation of the "two-slit" photometric technique and intravascular volumetric flow rates (Q) were calculated. It was found that red cell velocity decreased monotonically throughout successive arteriolar divisions to attain capillary values of 1/10 those in the feeding arterioles. A slight rise in Vrbc was found in the venous confluences, however, a maximum value of Vrbc of only 1/5 large arteriolar values was evident in the large collecting venules. In contrast, the calculated volumetric flow rate distribution was found to be nearly parabolic from arterioles (40 micron) and their paired (72 micron) collecting venules. This behavior was attributed to the dominance of microvessel cross-sectional areas as a determinant of Q.

A system designed faithfully to record intra-luminal pressure from small arteries or veins (90–150 μ radius) has been perfected, tested, and used extensively. The system utilizes a modified Statham strain gauge, PE tubing (594 μ in diameter) and a small stainless-steel needle. Dynamic response (N.F. = 40–120 cps) is tested and recorded before each use, and can be deliberately adjusted by changing needle length, tubing length, etc. Frequent zero pressure references and static calibration in situ are possible. Continuous recordings of duration up to 3 hr are obtainable

Background: Preterm infants are at increased risk for hypertension in adolescence. Microcirculatory dysfunction has been identified as an underlying cause for cardiovascular disease. Our goal was to document the development of the cutaneous microcirculation in preterm infants during the first weeks of life and to compare it to the situation in term infants at birth. Methods: In 20 preterm infants, microcirculatory parameters were obtained prospectively by Sidestream Dark Field (SDF) Imaging at the upper inner arm once a week until discharge or 37 weeks of gestational age. A single microcirculatory measurement was obtained in 30 term infants during the first 3 days of life. Videos were blinded and analyzed with the AVA software. Results: Microcirculatory parameters in preterm infants differ significantly from term infants with a lower vessel surface (VS), a lower percentage of large and medium but higher percentage of small vessels, a higher Functional Vessel Density (FVD), and a higher Microcirculatory Flow Index (MFI). In multivariable linear regression models we could demonstrate a statistically significant association between the dependent microcirculatory variables (VS, diameter distribution, MFI) and gestational age as independent predictor variable while adjusting for postnatal days of life. Looking at the longitudinal follow-up data of preterm infants by means of a multivariable mixed-effects linear regression model adjusting for clinical variables, there is a significant decrease in FVD with increasing postnatal age, however no other significant changes in microcirculatory parameters over time. Accordingly, comparing the microcirculatory parameters of near term former preterm infants with term born neonates, we could still find significant differences with a higher FVD, lower VS and differences in vessel diameters in the former premature group. Conclusion: Infants born prematurely exhibit distinct microcirculatory alterations compared to term neonates with gestational age at birth being associated with microvascular parameters. Interestingly, this premature vascular phenotype persists even close to corrected term age. In view of the known increased cardiovascular risk of former preterm infants, our observations might have important clinical impact. The factors governing the development of the microvascular network in preterm infants and the contribution of microcirculatory changes observed here to vascular pathology in later life need to be further investigated.