Vessel Diameter Distribution Research Articles

Variability in Intracranial Vessel Diameters and Considerations for Neurovascular Models: A Systematic Review and Meta‐Analysis

BackgroundIn vitro experiments are critical for understanding the impact of medical devices and techniques on blood vessels and blood flow. However, their interpretation is often limited by anatomical models’ inability to capture the wide range of vessel sizes observed in real‐world practice. The current study aims to address this limitation by describing the distribution of vessel diameters in a real‐world population.MethodsThis systematic literature review using the PubMed database analyzed cerebral vessel diameters in patients from 2000 to 2022. The diameter measurements of various vessels within the neurovasculature were extracted. Random‐effects meta‐analyses were performed to synthesize vessel diameters across studies. Predicted distributions were generated from the meta‐analytical results.ResultsSeventy‐six studies were included in the analysis. The M1 segment, internal carotid artery (cervical and communicating segments), A1 segment, V2 segment, V4 segment, and basilar artery had sufficient data for generating predicted distributions of vessel diameters. Predicted mean diameters were as follows: M1 segment, 2.55 ± 0.42 mm (95th interpercentile range [IPR]: 1.71–3.38); internal carotid artery‐cervical segment, 4.74 ± 0.64 mm (95th IPR: 3.49–5.99); internal carotid artery‐communicating segment, 3.40 ± 0.64 mm (95th IPR: 2.15–4.66); A1 segment, 1.89 ± 0.34 mm (95th IPR: 1.23–2.55); V2 segment, 3.36 ± 0.67 mm (95th IPR: 2.05–4.67); V4 segment, 2.42 ± 0.74 mm (95th IPR: 0.98–3.86); and basilar artery, 2.96 ± 0.52 mm (95th IPR: 1.94–3.97).ConclusionCerebral vessel diameter measurements can vary substantially due to patient‐specific factors and imaging techniques. This literature review highlights the diverse range of vessel sizes observed in different patient populations, emphasizing the need for anatomical models that accurately represent clinical observations.

Association of Genetic Risk for Age-Related Macular Degeneration with Morphological Features of the Retinal Microvascular Network.

Age-related macular degeneration (AMD) is a multifactorial disease encompassing a complex interaction between aging, environmental risk factors, and genetic susceptibility. The study aimed to determine whether there is a relationship between the polygenic risk score (PRS) in patients with AMD and the characteristics of the retinal vascular network visualized by optical coherence tomography angiography (OCTA). 235 patients with AMD and 97 healthy controls were included. We used data from a previous AMD PRS study with the same group. The vascular features from different retina layers were compared between the control group and the patients with AMD. The association between features and PRS was then analyzed using univariate and multivariate approaches. Significant differences between the control group and AMD patients were found in the vessel diameter distribution (variance: p = 0.0193, skewness: p = 0.0457) and fractal dimension distribution (mean: p = 0.0024, variance: p = 0.0123). Both univariate and multivariate analyses showed no direct and significant association between the characteristics of the vascular network and AMD PRS. The vascular features of the retina do not constitute a biomarker of the risk of AMD. We have not identified a genotype-phenotype relationship, and the expression of AMD-related genes is perhaps not associated with the characteristics of the retinal vascular network.

Modelling hydraulic plasticity of mangroves

The hydraulic architecture of plants responds to their water availability, mediating between promoting water flow and providing hydraulic safety against embolism. Sites with a constant supply of water favor plants with large vessel diameters, while in dry conditions, narrower vessels are more advantageous. The characteristics of the vessels are primarily shaped by the species’ adaptation to its preferred habitat. However, physiological plasticity enables individual plants to undergo further adaptations to suit specific sites. Mangroves are constantly exposed to low water potentials and therefore hydraulic properties play a pivotal role. Reevaluating studies on vessel diameter distributions and xylem conductivities, we propose a two-parameter gamma distribution description of the hydraulic system. The shape parameter characterizes the species-specific component, and the rate parameter specifies the particular adaptation of the plant to the site salinity. Based on the Hagen–Poiseuille law, we can estimate the xylem conductivity of the plant. Applying this approach to the established single tree model BETTINA, we show the potential plant damage due to salinity shocks for stylized species with different hydraulic properties. Model results suggest that plants with a vessel diameter distribution similar to Rhizophora spp. have an advantage and grow faster under constant salinity conditions due to higher hydraulic conductivities compared to Avicennia-like diameter distributions. This comes at the cost of a higher hydraulic vulnerability to salinity changes of Rhizophora. This approach provides a mechanistic link between site conditions and the hydraulic properties of plants in terms of their ability to physiologically adjust to the site.

Revealing the uterine blood vessel network via virtual pathology.

The distribution of the blood vessel network at any point in time in any body tissue, may provide valuable information with regards to the tissue condition and its angiogenesis functionality. The blood vessel three-dimensional network of the endometrium goes through a process of change over a relatively short period of 4 weeks on average. It is well accepted that this angiogenesis is closely related to the success or failure of the implantation of the embryo Objective and rationale: Our study aims to present a method to follow the three-dimensional evolution of the superficial blood vessel distribution in the endometrium throughout the uterine cycle. This method utilizes differences in the observed broadband colors of the blood vessels in order to assess their depth coordinate below the endometrial tissue surface. We implemented the method using microscopic images of fresh, ex-vivo, endometrial samples of different cycle days to obtain the statistical evolution track of the superficial blood vessel population in both human and animal (swine) samples. In human samples we observed a systematic and consistent trend in the BV diameter distribution at different tissue depths. We demonstrate that the magnitude of this trend evolves throughout the course of the female cycle. This method has the potential to further our understanding of the mechanisms of angiogenesis in tissues other than the endometrium. We propose that this method may also contribute to more precise endometrial dating and may assist in more accurate determination of embryo transfer timing within IVF treatments.

The impact of xylem geometry on olive cultivar resistance to Xylella fastidiosa: An image‐based study

AbstractXylella fastidiosa is a xylem‐limited plant pathogen infecting many crops globally and is the cause of the recent olive disease epidemic in Italy. One strategy proposed to mitigate losses is to replant susceptible crops with resistant varieties. Several genetic, biochemical and biophysical traits are associated to X. fastidiosa disease resistance. However, mechanisms underpinning resistance are poorly understood. We hypothesize that the susceptibility of olive cultivars to infection will correlate to xylem vessel diameters, with narrower vessels being resistant to air embolisms and having slower flow rates limiting pathogen spread. To test this, we scanned stems from four olive cultivars of varying susceptibility to X. fastidiosa using X‐ray computed tomography. Scans were processed by a bespoke methodology that segmented vessels, facilitating diameter measurements. Though significant differences were not found comparing stem‐average vessel section diameters among cultivars, they were found when comparing diameter distributions. Moreover, the measurements indicated that although vessel diameter distributions may play a role regarding the resistance of Leccino, it is unlikely they do for FS17. Considering Young–Laplace and Hagen–Poiseuille equations, we inferred differences in embolism susceptibility and hydraulic conductivity of the vasculature. Our results suggest susceptible cultivars, having a greater proportion of larger vessels, are more vulnerable to air embolisms. In addition, results suggest that under certain pressure conditions, functional vasculature in susceptible cultivars could be subject to greater stresses than in resistant cultivars. These results support investigation into xylem morphological screening to help inform olive replanting. Furthermore, our framework could test the relevance of xylem geometry to disease resistance in other crops.

Integration of micro-CT and histology data for vasculature morpho-functional analysis in tissue regeneration

The demand for artificial or bioartificial engineered tissues is increasing today in regenerative medicine techniques to replace and restore the physiological function of damaged tissues. Such engineered constructs hold different properties depending on the tissue to be replicated. As for vascularized tissues, complex biocompatible structures, namely scaffolds, play a key role in supporting oxygen and nutrient supply, thus sustaining tissue neoformation and integration with the host. Scaffold architecture significantly impacts its regenerative potential, while preclinical trials are essential to define scaffold-host interactions. In compliance with the 3 R principle, there is a clear need to optimize both the procedures to evaluate scaffold performance and the analysis methodology decreasing the number of animals required to gain consistent data. In parallel, current technologies used in preclinical research generate huge amounts of data that need to be elaborated and interpreted correctly. Therefore, we designed this study to evaluate the results of scaffold integration with the host tissue after implantation in a mouse subcutaneous pocket model. We evaluated the angiogenic response developed by the host and the degree of scaffold integration by using a combined morphometric approach based on both histological and micro-CT analyses. Six-layer scaffolds, made of polycaprolactone (PCL) microspheres, with an ordered structure were produced by thermal sintering. Scaffolds were then implanted in BALB/c mice and retrieved 21 days post-implantation when the animals were deeply anesthetized and perfused with Microfil, a contrast agent for micro-CT. Here, we describe a method to extract quantitative data from micro-CT reconstructions such as (i) total vessel volume; (ii)% of vessel penetration; (iii) distribution of vessel diameters. The general principle of this approach is the refinement of the region of interest (ROI), thus producing a volume of interest (VOI) that matches scaffold volume. This VOI serves as a dataset from which to extract volumetric information. Then VOIs are divided into three identical parts, proximal, median, and distal, to follow the vessel progression into the scaffold, thus obtaining their depth of penetration (DoP). By this methodology, we observed in mean, among the analyzed samples, a vessel invasion for 1,38 mm3 corresponding to the 1,53% of the scaffold volume. We then looked at the diameter distribution being this value a key indicator of vessel maturity, highlighting that 55% of vessels fall into the range from 5,99–53.99 µm while the remaining 45% are distributed into intervals from 54 to 136 µm. In parallel, to evaluate tissue integration in detail, histological and immunofluorescent analyses were performed to look at vessel distribution and collagen synthesis. Histological results strongly correlate with the micro-CT data providing, however, an overview of the ingrowth tissues. In addition, by immunofluorescent analysis we demonstrate that newly formed vessels are mature at the considered time point and tissue collagen deposition is widespread within the scaffolds. Collectively, we propose a new method to track vessel formation by using a multi-modal approach posing the basis for: i) the fabrication of novel scaffolds for Tissue Engineering; ii) the integration of detailed information for a wide range of morphological and functional analyses.

Stenosis Detection in Internal Carotid and Vertebral Arteries With the Use of Diameters Estimated from MRI Data

Background. Magnetic resonance imaging (MRI) offers the opportunity to quantify the vessel diameters in vivo. This technique can have a breakthrough impact on the evaluation, risk stratification and therapeutical planning in hemodynamic-related pathologies, e.g., arterial stenosis. However, its applicability in clinics is limi­ted due to the complex post-processing required to extract the information and the difficulty to synthesize the obtained data into clinical useful parameters.Objective. In this work, we use the vessel diameter distribution along its central line obtained with the use of MRI technology in order to detect the existence of stenosis in internal carotid arteries (ICA) and vertebral arteries (VA) with the minimal amount of False Negative predictions and to estimate the efficiency of therapy.Methods. Special normalized and smoothed characteristics will be used to develop the stenosis detection criteria which can be used for every artery separately and for both vessels simultaneously. Linear and non-linear characteristics were used to increase the reliability of diagnostics. Study is based on the Receiver Operating Characteristics (ROC) and optimization methods. Real diameter data of 10 patients (80 data sets) were used.Results. To detect stenosis, three different criteria have been proposed, based on the optimal smoothing parameters of vessel diameter distributions and the corresponding threshold values for linear and nonlinear characteristics. The use of the developed criteria allows increasing the reliability of stenosis detection.Conclusions. Different linear, non-linear, smoothed and non-smoothed parameters and ROC were applied to detect stenosis in internal carotid and vertebral arteries. It was shown that smoothed data are necessary for VA and the criterion applicable both for VA and ICA. For ICA it is possible to use initial (unsmoothed) data. Only one False Positive case was detected for every artery. Results of application of proposed criteria are presented, tested and discussed. For VA it is possible to use criteria 1 and 2 and smoothed normalized diameter data. For ICA criterion 2 can be recommended to detect long enough narrowing areas. To detect short zones of stenosis in ICA, the criterion 3 is useful, since it uses the non-smoothed diameter data.

Within-Site Variability of Liana Wood Anatomical Traits: A Case Study in Laussat, French Guiana

Research Highlights: We investigated the variability of vessel diameter distributions within the liana growth form among liana individuals originating from a single site in Laussat, French Guiana. Background and Objectives: Lianas (woody vines) are key components of tropical forests. Lianas are believed to be strong competitors for water, thanks to their presumed efficient vascular systems. However, unlike tropical trees, lianas are overlooked in field data collection. As a result, lianas are often referred to as a homogeneous growth form while little is known about the hydraulic architecture variation among liana individuals. Materials and Methods: We measured several wood hydraulic and structural traits (e.g., basic specific gravity, vessel area, and vessel diameter distribution) of 22 liana individuals in a single sandy site in Laussat, French Guiana. We compared the liana variability of these wood traits and the correlations among them with an existing liana pantropical dataset and two published datasets of trees originating from different, but species-rich, tropical sites. Results: Liana vessel diameter distribution and density were heterogeneous among individuals: there were two orders of magnitude difference between the smallest (4 µm) and the largest (494 µm) vessel diameters, a 50-fold difference existed between extreme vessel densities ranging from 1.8 to 89.3 vessels mm−2, the mean vessel diameter varied between 26 µm and 271 µm, and the individual theoretical stem hydraulic conductivity estimates ranged between 28 and 1041 kg m−1 s−1 MPa−1. Basic specific gravity varied between 0.26 and 0.61. Consequently, liana wood trait variability, even within a small sample, was comparable in magnitude with tree surveys from other tropical sites and the pantropical liana dataset. Conclusions: This study illustrates that even controlling for site and soil type, liana traits are heterogeneous and cannot be considered as a homogeneous growth form. Our results show that the liana hydraulic architecture heterogeneity across and within sites warrants further investigation in order to categorize lianas into functional groups in the same way as trees

Engineered human myocardium with local release of angiogenic proteins improves vascularization and cardiac function in injured rat hearts

Heart regeneration after myocardial infarction requires new cardiomyocytes and a supportive vascular network. Here, we evaluate the efficacy of localized delivery of angiogenic factors from biomaterials within the implanted muscle tissue to guide growth of a more dense, organized, and perfused vascular supply into implanted engineered human cardiac tissue on an ischemia/reperfusion injured rat heart. We use large, aligned 3-dimensional engineered tissue with cardiomyocytes derived from human induced pluripotent stem cells in a collagen matrix that contains dispersed alginate microspheres as local protein depots. Release of angiogenic growth factors VEGF and bFGF in combination with morphogen sonic hedgehog from the microspheres into the local microenvironment occurs from the epicardial implant site. Analysis of the 3D vascular network in the engineered tissue via Microfil® perfusion and microCT imaging at 30 days shows increased volumetric network density with a wider distribution of vessel diameters, proportionally increased branching and length, and reduced tortuosity. Global heart function is increased in the angiogenic factor-loaded cardiac implants versus sham. These findings demonstrate for the first time the efficacy of a combined remuscularization and revascularization therapy for heart regeneration after myocardial infarction.

Xylem anatomy needs to change, so that conductivity can stay the same: xylem adjustments across elevation and latitude in Nothofagus pumilio.

Plants have the potential to adjust the configuration of their hydraulic system to maintain its function across spatial and temporal gradients. Species with wide environmental niches provide an ideal framework to assess intraspecific xylem adjustments to contrasting climates. We aimed to assess how xylem structure in the widespread species Nothofagus pumilio varies across combined gradients of temperature and moisture, and to what extent within-individual variation contributes to population responses across environmental gradients. We characterized xylem configuration in branches of N. pumilio trees at five sites across an 18° latitudinal gradient in the Chilean Andes, sampling at four elevations per site. We measured vessel area, vessel density and the degree of vessel grouping. We also obtained vessel diameter distributions and estimated the xylem-specific hydraulic conductivity. Xylem traits were studied in the last five growth rings to account for within-individual variation. Xylem traits responded to changes in temperature and moisture, but also to their combination. Reductions in vessel diameter and increases in vessel density suggested increased safety levels with lower temperatures at higher elevation. Vessel grouping also increased under cold and dry conditions, but changes in vessel diameter distributions across the elevational gradient were site-specific. Interestingly, the estimated xylem-specific hydraulic conductivity remained constant across elevation and latitude, and an overwhelming proportion of the variance of xylem traits was due to within-individual responses to year-to-year climatic fluctuations, rather than to site conditions. Despite conspicuous adjustments, xylem traits were coordinated to maintain a constant hydraulic function under a wide range of conditions. This, combined with the within-individual capacity for responding to year-to-year climatic variations, may have the potential to increase forest resilience against future environmental changes.

Lack of association between acupoint sensitization and microcirculatory structural changes in a mouse model of knee osteoarthritis: A pilot study.

As a stimulating point in acupuncture, acupoint has unique microcirculatory features, and its dynamics vary greatly depending on health status. Acupoint sensitization is defined as the transformation of an acupoint from a “silenced status” (healthy) to an “activated status” (disease). Our previous study demonstrated that acupoint sensitization is associated with an increase in the level of local blood perfusion. However, the structural changes in microcirculation during acupoint sensitization have yet to be elucidated because the high‐resolution microcirculation imaging of acupoints has been difficult to obtain. In this study, the structural changes in microcirculation at the Zusanli (ST36), Yanglingquan (GB34) and nonacupoint sites on days 0, 7 and 21 were dynamically observed during acupoint sensitization in an experimental knee osteoarthritis mouse model by using optical‐resolution photoacoustic microscopy. The results showed that no significant differences in microvessel density, the distribution of vessel diameters or vascular tortuosity were observed at the GB34, ST36 or nonacupoint sites among days 0, 7 and 21. We proposed that acupoint sensitization may not be associated with the structural changes in microcirculation and that the microcirculatory changes during acupoint sensitization are more likely to be functional. The functional characteristics of the sensitized acupoints warrant further investigation.

Correction: Corrigendum: Organ-wide 3D-imaging and topological analysis of the continuous microvascular network in a murine lymph node

Understanding of the microvasculature has previously been limited by the lack of methods capable of capturing and modelling complete vascular networks. We used novel imaging and computational techniques to establish the topology of the entire blood vessel network of a murine lymph node, combining 63706 confocal images at 2 μm pixel resolution to cover a volume of 3.88 mm3. Detailed measurements including the distribution of vessel diameters, branch counts, and identification of voids were subsequently re-visualised in 3D revealing regional specialisation within the network. By focussing on critical immune microenvironments we quantified differences in their vascular topology. We further developed a morphology-based approach to identify High Endothelial Venules, key sites for lymphocyte extravasation. These data represent a comprehensive and continuous blood vessel network of an entire organ and provide benchmark measurements that will inform modelling of blood vessel networks as well as enable comparison of vascular topology in different organs.

Organ-wide 3D-imaging and topological analysis of the continuous microvascular network in a murine lymph node.

Understanding of the microvasculature has previously been limited by the lack of methods capable of capturing and modelling complete vascular networks. We used novel imaging and computational techniques to establish the topology of the entire blood vessel network of a murine lymph node, combining 63706 confocal images at 2 μm pixel resolution to cover a volume of 3.88 mm3. Detailed measurements including the distribution of vessel diameters, branch counts, and identification of voids were subsequently re-visualised in 3D revealing regional specialisation within the network. By focussing on critical immune microenvironments we quantified differences in their vascular topology. We further developed a morphology-based approach to identify High Endothelial Venules, key sites for lymphocyte extravasation. These data represent a comprehensive and continuous blood vessel network of an entire organ and provide benchmark measurements that will inform modelling of blood vessel networks as well as enable comparison of vascular topology in different organs.

Abstract 17797: Noninvasive Optical Imaging of Response to On-Demand Antioxidant Therapy in a Model of Peripheral Arterial Disease

Peripheral arterial disease is often modeled by surgical induction of hind limb ischemia (HLI) in mice to study collateral vessel development. However, there is a need for methodologies that provide intravital, multifunctional, quantitative data on ischemic recovery for robust evaluation of new therapeutics. Here, we apply hyperspectral imaging and optical coherence tomography (OCT) to longitudinally assess hemoglobin oxygen saturation (SaO 2 ) and vessel morphology in response to a novel therapy. Injectable microspheres loaded with curcumin were synthesized from reactive oxygen species (ROS)-responsive poly(propylene) sulfide (PPS) to provide “on demand”, local release of the antioxidant drug curcumin to reduce tissue-damaging oxidative stress in a mouse model of diabetic HLI. Curcumin-PPS microspheres significantly reduced intracellular ROS in LPS-activated RAW 264.7 macrophages and rescued viability of 3T3 fibroblasts treated with cytotoxic levels of H 2 O 2 in vitro . HLI was induced in FVB mice with streptozotocin-induced diabetes, and curcumin-PPS or blank-PPS microspheres were injected into the ischemic limb. Curcumin-PPS significantly improved recovery of SaO 2 in the ischemic footpad relative to blank-PPS and vehicle (saline) groups over a one week time course evaluated with hyperspectral imaging (n≥8/group, p<0.05). Vessel structure in the gastrocnemius was imaged noninvasively with OCT at day 7 (Figure), revealing trends toward increased vessel area density and vessel length fraction in the curcumin-PPS group (n=5/group). The vessel diameter distribution was also extracted from OCT data. Our collective data indicate that sustained, on demand curcumin delivery has significant therapeutic promise for improving ischemic tissue recovery. Also, the hyperspectral and OCT imaging methods showcased provide quantitative, noninvasive monitoring of vasculature and can accelerate screening of novel therapies.

Multi-parametric quantitative microvascular imaging with optical-resolution photoacoustic microscopy in vivo

Many diseases involve either the formation of new blood vessels (e.g., tumor angiogenesis) or the damage of existing ones (e.g., diabetic retinopathy) at the microcirculation level. Optical-resolution photoacoustic microscopy (OR-PAM), capable of imaging microvessels in 3D in vivo down to individual capillaries using endogenous contrast, has the potential to reveal microvascular information critical to the diagnosis and staging of microcirculation-related diseases. In this study, we have developed a dedicated microvascular quantification (MQ) algorithm for OR-PAM to automatically quantify multiple microvascular morphological parameters in parallel, including the vessel diameter distribution, the microvessel density, the vascular tortuosity, and the fractal dimension. The algorithm has been tested on in vivo OR-PAM images of a healthy mouse, demonstrating high accuracy for microvascular segmentation and quantification. The developed MQ algorithm for OR-PAM may greatly facilitate quantitative imaging of tumor angiogenesis and many other microcirculation related diseases in vivo.

Early Microvascular Changes with Loss of the Glycocalyx in Children with Type 1 Diabetes

To evaluate the microcirculation of children with type 1 diabetes mellitus who demonstrate no clinical signs of diabetic microangiopathy for the presence of microvascular alterations and glycocalyx perturbation. Images of sublingual vessels were obtained in 14 children with diabetes (ages 12.8 ± 2.8 years, diabetes duration 6.7 ± 4.3 years) and 14 control patients (ages 11.8 ± 2.8 years) by the use of sidestream dark field imaging and analyzed for total vessel density, vessel surface coverage, vessel diameter distribution, mean flow index, and glycocalyx thickness. Wilcoxon rank sum test and Pearson correlation were used for statistical analysis. We observed profound microcirculatory changes in children with diabetes compared with control patients, with a significant reduction of glycocalyx thickness (0.38 μm vs 0.60 μm; P = .013), which was inversely correlated with blood glucose levels (r = -0.55; P = .003). Furthermore, the percentage of large vessels (>20 μm diameter) was significantly increased (11% vs 6%; P = .023) at the expense of capillaries (<10 μm diameter) with consequent increase in total vessel surface coverage (30% vs 26.0%; P = .041). No differences were seen in total vessel density and mean flow index. Microvascular alterations, including changes in microvessel distribution and loss of the glycocalyx, can be detected in children with type 1 diabetes mellitus before clinically apparent vascular complications. Our results disclose the glycocalyx as a possible monitoring measurement for earlier detection of diabetic microangiopathy and may provide a basis for new therapeutic strategies aiming at protection or restoration of the glycocalyx.

Shoot hydraulic characteristics, plant water status and stomatal response in olive trees under different soil water conditions

To evaluate the impact of the amount and distribution of soil water on xylem anatomy and xylem hydraulics of current-year shoots, plant water status and stomatal conductance of mature ‘Manzanilla’ olive trees. Measurements of water potential, stomatal conductance, hydraulic conductivity, vulnerability to embolism, vessel diameter distribution and vessel density were made in trees under full irrigation with non-limiting soil water conditions, localized irrigation, and rain-fed conditions. All trees showed lower stomatal conductance values in the afternoon than in the morning. The irrigated trees showed water potential values around −1.4 and −1.6 MPa whereas the rain-fed trees reached lower values. All trees showed similar specific hydraulic conductivity (K s) and loss of conductivity values during the morning. In the afternoon, K s of rain-fed trees tended to be lower than of irrigated trees. No differences in vulnerability to embolism, vessel-diameter distribution and vessel density were observed between treatments. A tight control of stomatal conductance was observed in olive which allowed irrigated trees to avoid critical water potential values and keep them in a safe range to avoid embolism. The applied water treatments did not influence the xylem anatomy and vulnerability to embolism of current-year shoots of mature olive trees.

Periosteal microvascular reorganization after tibial reaming and intramedullary nailing in rats

BackgroundIntramedullary reaming and nailing of long bones impairs the endosteal circulation, often causing necrosis of the inner region of the bone cortex. We hypothesized that compensatory hypertrophy of the periosteal microcirculation may develop in response to mechanical destruction of the endosteum, and that this may affect bone survival in these circumstances. In these studies, nailing was performed with materials that affect regeneration of the endosteum differently, and the effects on the tibial periosteal microvasculatory organization were examined. MethodsIn male Wistar rats, the right tibia was reamed and implanted with an inert titanium nail or a less osseointegrative polyethylene nail; the contralateral tibial endosteum was destroyed by reaming. Reaming without nailing or sham operation was performed on both extremities in two other groups of rats. Twelve weeks later, the anteromedial and anterolateral surfaces of the tibias were exposed by a microsurgical technique. The structural characteristics of the periosteal microcirculation (vessel density and distribution of vessel diameters) were determined by intravital videomicroscopy and computer-assisted analysis. The stability of the implants was assessed on the basis of grades 0–2 on a qualitative scale. ResultsTibial reaming alone caused significant increases in overall blood vessel and capillary densities in the periosteum compared with those of the intact tibias. Implantation with a titanium nail resulted in firm embedding of the nail and caused changes in the periosteal vasculature similar to those after reaming alone. In contrast, implantation of a polyethylene nail was followed by the development of marked instability of the endomedullary implant and significant increases in the percentage of capillaries and the vessel density in the periosteum. ConclusionsDestruction of the endosteal microcirculation per se brings about an increase in periosteal vascular density, which is further augmented if implantation is performed with a material which delays regeneration of the endosteal circulation.

Vessel size index measurements in a rat model of glioma: comparison of the dynamic (Gd) and steady‐state (iron‐oxide) susceptibility contrast MRI approaches

Vessel size index (VSI), a parameter related to the distribution of vessel diameters, may be estimated using two MRI approaches: (i) dynamic susceptibility contrast (DSC) MRI following the injection of a bolus of Gd-chelate. This technique is routinely applied in the clinic to assess intracranial tissue perfusion in patients; (ii) steady-state susceptibility contrast with USPIO contrast agents, which is considered here as the standard method. Such agents are not available for human yet and the steady-state approach is currently limited to animal studies. The aim is to compare VSI estimates obtained with these two approaches on rats bearing C6 glioma (n = 7). In a first session, VSI was estimated from two consecutive injections of Gd-Chelate (Gd(1) and Gd(2)). In a second session (4 hours later), VSI was estimated using USPIO. Our findings indicate that both approaches yield comparable VSI estimates both in contralateral (VSI{USPIO} = 7.5 ± 2.0 µm, VSI{Gd(1)} = 6.5 ± 0.7 µm) and in brain tumour tissues (VSI{USPIO} = 19.4 ± 7.1 µm, VSI{Gd(1)} = 16.6 ± 4.5 µm). We also observed that, in the presence of BBB leakage (as it occurs typically in brain tumours), applying a preload of Gd-chelate improves the VSI estimate with the DSC approach both in contralateral (VSI{Gd(2)} = 7.1 ± 0.4 µm) and in brain tumour tissues (VSI{Gd(2)} = 18.5 ± 4.3 µm) but is not mandatory. VSI estimates do not appear to be sensitive to T(1) changes related to Gd extravasation. These results suggest that robust VSI estimates may be obtained in patients at 3 T or higher magnetic fields with the DSC approach.

Changes of hydraulic conductivity during dehydration and rehydration in Quercus serrata Thunb. and Betula platyphylla var. japonica Hara: the effect of xylem structures

Xylem cavitation and its recovery were studied in 1-year-old stems of ring-porous Quercus serrata Thunb. and diffuse-porous Betula platyphylla var. japonica Hara. The Q. serrata had 5-100 microm vessel diameter in the functional current xylem and 5-75 microm in nonconducting 1-year-old xylem; B. platyphylla had a narrower range of vessel diameters of 5-55 microm and more than double the number of vessels in both functional growth rings. Although hydraulic conductivity of Q. serrata appeared to decrease after release of moderate water stress of a half loss of native hydraulic conductivity--about -2 MPa in xylem water potential--no significant recovery of hydraulic conductivity was observed, probably because of intraspecific variation in vessel diameter distribution, which induced variable vulnerability to cavitation. Furthermore, in terms of xylem anatomy, larger and more efficient vessels of the current xylem did not show obvious refilling. In B. platyphylla, after release of water stress, rapid (1 h) recoveries of both hydraulic conductivity and water potential were apparent after rewatering: so-called 'novel refilling'. During that time, a high degree of vessel refilling was observed in both xylems. At 12 h after rewatering, embolized vessels of the current xylem had refilled completely, although about 20% of vessels were still embolized in 1-year-old xylem. This different pattern of vessel refilling in relation to xylem age for B. platyphylla might be attributable to structural faults in the 1-year-old xylem, such as pit degradation or perhaps xylem aging itself. Results show that Q. serrata performs water conduction using highly efficient large vessels instead of unclear vessel refilling. In contrast, B. platyphylla transports water via less efficient but numerous vessels. If cavitation occurs, B. platyphylla improves water conduction by increasing the degree of vessel refilling.