Despite intensive study, the relation between insulin's action on blood flow and glucose metabolism remains unclear. Insulin-induced changes in microvascular perfusion, independent from effects on total blood flow, could be an important variable contributing to insulin's metabolic action. We hypothesized that modest, physiologic increments in plasma insulin concentration alter microvascular perfusion in human skeletal muscle and that these changes can be assessed using contrastenhanced ultrasound (CEU), a validated method for quantifying flow by measurement of microvascular blood volume (MBV) and microvascular flow velocity (MFV). In the first protocol, 10 healthy, fasting adults received insulin (0.05 mU ⅐ kg ؊1 ⅐ min ؊1 ) via a brachial artery for 4 h under euglycemic conditions. At baseline and after insulin infusion, MBV and MFV were measured by CEU during continuous intravenous infusion of albumin microbubbles with intermittent harmonic ultrasound imaging of the forearm deep flexor muscles. In the second protocol, 17 healthy, fasting adults received a 4-h infusion of either insulin (0.1 mU ⅐ kg ؊1 ⅐ min ؊1 , n ‫؍‬ 9) or saline (n ‫؍‬ 8) via a brachial artery. Microvascular volume was assessed in these subjects by an alternate CEU technique using an intra-arterial bolus injection of albumin microbubbles at baseline and after the 4-h infusion. With both protocols, muscle glucose uptake, plasma insulin concentration, and total blood flow to the forearm were measured at each stage. In protocol 2 subjects, tissue extraction of 1-methylxanthine (1-MX) was measured as an index of perfused capillary volume. Caffeine, which produces 1-MX as a metabolite, was administered to these subjects before the study to raise plasma 1-MX levels.In protocol 1 subjects, insulin increased muscle glucose uptake (180%, P < 0.05) and MBV (54%, P < 0.01) and decreased MFV (؊42%, P ‫؍‬ 0.07) in the absence of significant changes in total forearm blood flow. In protocol 2 subjects, insulin increased glucose uptake (220%, P < 0.01) and microvascular volume (45%, P < 0.05) with an associated moderate increase in total forearm blood flow (P < 0.05). Using forearm 1-MX extraction, we observed a trend, though not significant, toward increasing capillary volume in the insulin-treated subjects. In conclusion, modest physiologic increments in plasma insulin concentration increased microvascular blood volume, indicating altered microvascular perfusion consistent with a mechanism of capillary recruitment. The increases in microvascular (capillary) volume (despite unchanged total blood flow) indicate that the relation between insulin's vascular and metabolic actions cannot be fully understood using measurements of bulk blood flow alone.

Ultrasound examination during microbubble infusion can be used to quantify total organ as well as regional nutrient blood flow to the kidney.

Background-Albumin microbubbles that are used for contrast echocardiography persist within the myocardial microcirculation after ischemia/reperfusion (I-R). The mechanism responsible for this phenomenon is unknown. Methods and Results-Intravital microscopy of the microcirculation of exteriorized cremaster muscle was performed in 12 wild-type mice during intravenous injections of fluorescein-labeled microbubbles composed of albumin, anionic lipids, or cationic lipids. Injections were performed at baseline and after 30 to 90 minutes of I-R in 8 mice and 2 hours after intrascrotal tumor necrosis factor-␣ (TNF-␣) in 4 mice. Microbubble adherence at baseline was uncommon (Ͻ2/50 high-power fields). After I-R, adherence increased (PϽ0.05) to 9Ϯ5 and 5Ϯ4 per 50 high-power fields for albumin and anionic lipid microbubbles, respectively, due to their attachment to leukocytes adherent to the venular endothelium. TNF-␣ produced even greater microbubble binding, regardless of the microbubble shell composition. The degree of microbubble attachment correlated (rϭ0.84 to 0.91) with the number of adhered leukocytes. Flow cytometry revealed that microbubbles preferentially attached to activated leukocytes. Albumin microbubble attachment was inhibited by blocking the leukocyte ␤ 2 -integrin Mac-1, whereas lipid microbubble binding was inhibited when incubations were performed in complement-depleted or heat-inactivated serum rather than control serum. Conclusions-Microvascular attachment of albumin and lipid microbubbles in the setting of I-R and TNF-␣-induced inflammation is due to their ␤ 2 -integrin-and complement-mediated binding to activated leukocytes adherent to the venular wall. Thus, microbubble persistence on contrast ultrasonography may be useful for the detection and monitoring of leukocyte adhesion in inflammatory diseases. (Circulation. 2000;101:668-675.)

After attaching to activated neutrophils and monocytes, microbubbles are phagocytosed intact. Despite viscoelastic damping, phagocytosed microbubbles remain responsive to ultrasound and can be detected by ultrasound in vivo after clearance of freely circulating microbubbles from the blood pool. Thus, contrast ultrasound has potential for imaging sites of inflammation.

CBF reserve can be measured in humans using MCE. This method may allow the noninvasive assessment of coronary stenosis severity and the detection of microvascular dysfunction.

To define the role of capillaries in the control of coronary blood flow (CBF) reserve, we developed a model of the coronary circulation and evaluated experimental data in its context. Our model comprised three compartments connected in series (arterial, capillary, and venous), each with its own resistance. The resistance in each vascular compartment was derived from the model based on hemodynamic data obtained in nine dogs during baseline and stenosis, both at rest and during hyperemia. The capillary hydrostatic pressure was assumed to be constant in all stages. Although in the absence of stenosis, the contribution of capillaries to total myocardial vascular resistance was only 25 +/- 5% at rest, it increased to 75 +/- 14% during hyperemia, despite the total myocardial vascular resistance decreasing by 51 +/- 13%. In the presence of a noncritical stenosis, total myocardial vascular resistance decreased by 22 +/- 10% at rest, with no change in capillary resistance. During hyperemia, total myocardial vascular resistance increased by 58 +/- 50% in the presence of the noncritical stenosis. In this situation, because arteriolar and venular resistances were already minimal, the increase in myocardial vascular resistance was due to increased capillary resistance, making it the predominant source (84 +/- 8%) of total myocardial vascular resistance. Myocardial video intensity (VI) on myocardial contrast echocardiography (MCE), which reflects capillary blood volume, decreased distal to the stenosis during hyperemia. In the presence of a flow-limiting stenosis at rest, myocardial VI also decreased, indicating that decrease in CBF was associated with an increase in capillary resistance. Our findings also provide an alternative explanation for the critical coronary closing pressure. Thus, contrary to previously held notions, capillaries play a vital role in the regulation of CBF.

Abstract-Homeostasis in the pulmonary vasculature is maintained by the actions of vasoactive compounds, including nitric oxide (NO). NO is critical for normal development of the pulmonary vasculature and continues to mediate normal vasoregulation in adulthood. Loss of NO bioavailability is one component of the endothelial dysfunction and vascular pathology found in pulmonary hypertension (PH). A broad research effort continues to expand our understanding of the control of NO production and NO signaling and has generated novel theories on the importance of pulmonary NO production in the control of the systemic vasculature. This understanding has led to exciting developments in our ability to treat PH, including inhaled NO and phosphodiesterase inhibitors, and to several promising directions for future therapies using nitric oxide-donor compounds, stimulators of soluble guanylate cyclase, progenitor cells expressing NO synthase ( Key Words: nitric oxide Ⅲ pulmonary vasculature Ⅲ pulmonary hypertension treatment T he low resting tone of the pulmonary circulation is established at birth 1 and is modulated by the balance of vasoconstrictors (endothelin-1, thromboxane A 2 , and serotonin) and vasodilators (prostacyclin and NO) produced by the pulmonary endothelium (reviewed in 2 ). Vasoconstriction of the pulmonary vasculature in response to acute hypoxia is the clearest divergence from the systemic vasculature, which is characterized by hypoxic vasodilation in the periphery. The acute hypoxic response in the pulmonary bed is thought to be critical for matching ventilation with perfusion. Disruption of the balance of pulmonary vasodilators and vasoconstrictors, for example by environmental stress (eg, prolonged hypoxia) or endothelial dysfunction, can lead to the pulmonary vasoconstriction, vascular smooth muscle cell (VSMC) proliferation, and in situ thrombosis that characterize pulmonary hypertension (PH).NO is a free radical gas that diffuses from its site of production in the endothelial cell to its target, soluble guanylate cyclase (sGC), in the VSMC. In this classical NO signaling pathway, activation of sGC enhances cyclic guanosine monophosphate (cGMP) production, which in turn mediates vasodilatation. Alternative NO signaling pathways involve the oxidation of NO to nitrite 3 or reactions of NO with protein thiols to form S-nitrosothiols (SNOs), 4 NO derivatives that can function as vasodilators or as posttranslational modifiers of protein function. Intriguing new theories are founded on the interaction of nitrite and SNOs with hemoglobin (Hb): by exploiting the allosteric nature of Hb within red blood cells (RBCs), the NO signal is transported to the periphery, where its vasodilator potential enables selective delivery of oxygenated blood to hypoxic tissue.

Background Individually, heart failure (HF) and Alzheimer Disease (AD) are severe threats to population health, and their potential coexistence is an alarming prospect. In addition to sharing analogous epidemiological and genetic profiles, biochemical characteristics, and common triggers, we recently recognized common molecular and pathological features between the 2 conditions. Whereas cognitive impairment has been linked to HF through perfusion defects, angiopathy, and inflammation, whether patients with AD present with myocardial dysfunction, and if the 2 conditions bear a common pathogenesis as neglected siblings is unknown. Objectives Here we investigated if amyloid beta (Aβ) protein aggregates are present in the hearts of patients with a primary diagnosis of AD, affecting myocardial function. Methods We examined myocardial function in a retrospective cross-sectional study from a cohort of AD patients and age-matched controls. Imaging and proteomics approaches were used to identify and quantify Aβ deposits in AD heart and brain specimens compared to controls. Cell shortening and calcium transients were measured on isolated adult cardiomyocytes. Results Echocardiographic measurements of myocardial function suggest that patients with AD present with an anticipated diastolic dysfunction. As in the brain, Aβ40 and Aβ42 are present in the heart, and their expression is increased in AD. Conclusions Here we provide the first report of the presence of compromised myocardial function and intramyocardial deposits of Aβ in AD patients. Our findings depict a novel biological framework in which AD may be viewed either as a systemic disease or as a metastatic disorder leading to heart, and possibly multiorgan failure. AD and HF are both debilitating and life-threatening conditions, affecting enormous patient populations. Our findings underline a previously dismissed problem of a magnitude that will require new diagnostic approaches and treatments for brain and heart disease, and their combination.