Non-invasive point-of-care optical technique for continuous in vivo assessment of microcirculatory function: Application to a preclinical model of early sepsis.

Increased amplitude of peripheral vasomotion is a potential early marker of sepsis-related microcirculatory impairment; however, previous reports relied on clinically unsuitable invasive techniques. Hyperspectral near-infrared spectroscopy (hsNIRS) and diffuse correlation spectroscopy (DCS) are non-invasive, bedside techniques that can be paired to continuously monitor tissue hemoglobin content (HbT), oxygenation (StO), and perfusion (rBF) to detect vasomotion as low-frequency microhemodynamic oscillations. While previous studies have primarily focused on the peripheral microcirculation, cerebral injury is also a common occurrence in sepsis and hsNIRS-DCS could be used to assess cerebral microcirculatory function.

Capillary oxygen regulates demand-supply coupling by triggering connexin40-mediated conduction: Rethinking the metabolic hypothesis.

Coupling red blood cell (RBC) supply to O demand is an intricate process requiring O sensing, generation of a stimulus, and signal transduction that alters upstream arteriolar tone. Although actively debated, this process has been theorized to be induced by hypoxia and to involve activation of endothelial inwardly rectifying K channels (K) 2.1 by elevated extracellular K to trigger conducted hyperpolarization via connexin40 (Cx40) gap junctions to upstream resistors.

Spectroscopy detects skeletal muscle microvascular dysfunction during onset of sepsis in a rat fecal peritonitis model.

Sepsis is a dysregulated host inflammatory response to infection potentially leading to life-threatening organ dysfunction. The objectives of this study were to determine whether early microvascular dysfunction (MVD) in skeletal muscle can be detected as dynamic changes in microvascular hemoglobin (MVHb) levels using spectroscopy and whether MVD precedes organ histopathology in septic peritonitis. Skeletal muscle of male Sprague-Dawley rats was prepared for intravital microscopy.

Optical method to determine in vivo capillary hematocrit, hemoglobin concentration, and 3-D network geometry in skeletal muscle.

Objective: The aim of this study was to develop a tool to visualize and quantify hemodynamic information, such as hemoglobin concentration and hematocrit, within microvascular networks recorded in vivo using intravital video microscopy. Additionally, we aimed to facilitate the 3-D reconstruction of the microvascular networks.

Methods: Digital images taken from an intravital video microscopy preparation of the extensor digitorum longus muscle in rats for 25 capillary segments were used.

Capillary module haemodynamics and mechanisms of blood flow regulation in skeletal muscle capillary networks: Experimental and computational analysis.

The capillary module (CM), consisting of parallel capillaries from terminal arteriole to post-capillary venule, is classically considered to be the building block of complex capillary networks. In skeletal muscle, CMs form interconnected columns spanning thousands of microns, which we recently described as the capillary fascicle. However, detailed evaluation of CM haemodynamics has not been described, and may provide insight into mechanisms of blood flow regulation in the microcirculation.

Low-flow intussusception and metastable VEGFR2 signaling launch angiogenesis in ischemic muscle.

Efforts to promote sprouting angiogenesis in skeletal muscles of individuals with peripheral artery disease have not been clinically successful. We discovered that, contrary to the prevailing view, angiogenesis following ischemic muscle injury in mice was not driven by endothelial sprouting. Instead, real-time imaging revealed the emergence of wide-caliber, primordial conduits with ultralow flow that rapidly transformed into a hierarchical neocirculation by transluminal bridging and intussusception.

Localized Oxygen Exchange Platform for Intravital Video Microscopy Investigations of Microvascular Oxygen Regulation.

Intravital microscopy has proven to be a powerful tool for studying microvascular physiology. In this study, we propose a gas exchange system compatible with intravital microscopy that can be used to impose gas perturbations to small localized regions in skeletal muscles or other tissues that can be imaged using conventional inverted microscopes. We demonstrated the effectiveness of this system by locally manipulating oxygen concentrations in rat muscle and measuring the resulting vascular responses.

Evidence for role of capillaries in regulation of skeletal muscle oxygen supply.

Unlabelled: How oxygen (O ) supply to capillaries is regulated to match the tissue's demand is unknown. Erythrocytes have been proposed as sensors in this regulatory mechanism since they release ATP, a vasodilator, in an oxygen saturation (SO )-dependent manner. ATP causes hyperpolarization of endothelial cells resulting in conducted vasodilation to arterioles.

The capillary fascicle in skeletal muscle: Structural and functional physiology of RBC distribution in capillary networks.

Key Points: The capillary module, consisting of parallel capillaries from arteriole to venule, is classically considered as the building block of complex capillary networks. In skeletal muscle, this structure fails to address how blood flow is regulated along the entire length of the synchronously contracting muscle fibres. Using intravital video microscopy of resting extensor digitorum longus muscle in rats, we demonstrated the capillary fascicle as a series of interconnected modules forming continuous columns that align naturally with the dimensions of the muscle fascicle.

High-fat diet pre-conditioning improves microvascular remodelling during regeneration of ischaemic mouse skeletal muscle.

Aim: Critical limb ischaemia (CLI) is characterized by inadequate angiogenesis, arteriolar remodelling and chronic myopathy, which are most severe in type 2 diabetic patients. Hypertriglyceridaemia, commonly observed in these patients, compromises macrovascular function. However, the effects of high-fat diet-induced increases in circulating lipids on microvascular remodelling are not established.

Hyperinsulinemia does not cause de novo capillary recruitment in rat skeletal muscle.

Objective: The effect of insulin on blood flow distribution within muscle microvasculature has been suggested to be important for glucose metabolism. However, the "capillary recruitment" hypothesis is still controversial and relies on studies using indirect contrast-enhanced ultrasound (CEU) methods.

Methods: We studied how hyperinsulinemia effects capillary blood flow in rat extensor digitorum longus (EDL) muscle during euglycemic hyperinsulinemic clamp using intravital video microscopy (IVVM).

Four-Dimensional Microvascular Analysis Reveals That Regenerative Angiogenesis in Ischemic Muscle Produces a Flawed Microcirculation.

Rationale: Angiogenesis occurs after ischemic injury to skeletal muscle, and enhancing this response has been a therapeutic goal. However, to appropriately deliver oxygen, a precisely organized and exquisitely responsive microcirculation must form. Whether these network attributes exist in a regenerated microcirculation is unknown, and methodologies for answering this have been lacking.

What is the efficiency of ATP signaling from erythrocytes to regulate distribution of O(2) supply within the microvasculature?

Erythrocytes appear to be ideal sensors for regulating microvascular O(2) supply as they release the potent vasodilator ATP in an O(2) saturation-dependent manner. Whether erythrocytes play a significant role in regulating O(2) supply in the complex environment of diffusional O(2) exchange among capillaries, arterioles, and venules, depends on the efficiency with which erythrocytes signal the vascular endothelium. If one assumes that the distribution of purinergic receptors is uniform throughout the microvasculature, then the most efficient site for signaling should occur in capillaries, where the erythrocyte membrane is in close proximity to the endothelium.

Mapping 3-D functional capillary geometry in rat skeletal muscle in vivo.

We have developed a novel mapping software package to reconstruct microvascular networks in three dimensions (3-D) from in vivo video images for use in blood flow and O2 transport modeling. An intravital optical imaging system was used to collect video sequences of blood flow in microvessels at different depths in the tissue. Functional images of vessels were produced from the video sequences and were processed using automated edge tracking software to yield location and geometry data for construction of the 3-D network.

Defects in oxygen supply to skeletal muscle of prediabetic ZDF rats.

In humans, prediabetes is characterized by marked increases in plasma insulin and near normal blood glucose levels as well as microvascular dysfunction of unknown origin. Using the extensor digitorum longus muscle of 7-wk inbred male Zucker diabetic fatty rats fed a high-fat diet as a model of prediabetes, we tested the hypothesis that hyperinsulinemia contributes to impaired O(2) delivery in skeletal muscle. Using in vivo video microscopy, we determined that the total O(2) supply to capillaries in the extensor digitorum longus muscle of prediabetic rats was reduced to 64% of controls with a lower O(2) supply rate per capillary and higher O(2) extraction resulting in a decreased O(2) saturation at the venous end of the capillary network.

Transfusion of stored red blood cells adhere in the rat microvasculature.

Background: Ex vivo storage of red blood cells (RBCS) for transfusions is associated with a "storage lesion," which decreases RBC deformability and increases RBC adhesiveness to vascular endothelium. This may impair microcirculatory flow with deleterious effects on oxygen delivery after transfusion. Previous studies have shown that human RBCs adhere to endothelial monolayers in vitro with prolonged storage and is reduced by prestorage leukoreduction (LR).

Effect of nitric oxide on capillary hemodynamics and cell injury in the pancreas during Pseudomonas pneumonia-induced sepsis.

Sepsis-induced nitric oxide (NO) overproduction has been implicated in a redistribution of flow from the pancreas making it vulnerable to ischemic injury in septic shock. To test this hypothesis in a remote injury model of normotensive sepsis, we induced Pseudomonas pneumonia in the rat and used intravital video microscopy (IVVM) of the pancreas to measure functional capillary density, capillary hemodynamics [red blood cell (RBC) velocity, lineal density, and supply rate], and lethal cellular damage (propidium iodine staining) at 6 and 24 h after the induction of pneumonia. With pneumonia, plasma nitrite/nitrate [NO2(-)/NO3(-)(NOx(-))] levels were doubled by 21 h (P < 0.