Pressure transmural

Vasodilating molecule(s) liberated from vascular endothelial cells in response to chemical substances (i.e., Acetylcholine, bradykinin, substance P, etc.) or mechanical stimuli (i.e., shear stress, transmural pressure, etc.). The EDRF includes NO, prostaglandin J2 (prostacyclin), and endothelium-derived hypeipolarizing factor (EDHF). 

The release of NO from the endothelium is induced by various chemical substances, including acetylcholine polypeptides such as substance P, bradykinin, and arginine vasopressin histamine ATP/ADP a2-adrenoceptor agonists thrombin and Ca2+ iono-phores. NO formed in response to mechanical stimuli like shear stress or transmural pressure plays an important role in maintaining basal blood flow. Endothelial NO causes vasodilatation, decreased... 

Compliancy Measures the ability of an artery to increase its section (and obviously the volume of blood, which can be contained in a given segment of this artery) upon an increase of TransMural Pressure (PTM) compliancy is expressed as AV/V) x 100)/AP as % per mmg Hg. 

Fry, D.L. (1983) Effect of pressure and stirring on in vitro aortic transmural 125I-albumin transport. Am. J. Physiol., 245, H977-H991. 

Naughton MT, Rahman M A, Hara K, Floras JS, Bradley TD (1995) Effect of continuous positive airway pressure on intrathoracic and left ventricular transmural pressures in patients with congestive heart failure. Circulation 91 1725-1731... 

Figure 12.4 shows the relation between the equilibrium transmural pressure Peq and the normalized arteriolar radius r for different values of the muscular activation xj/. Fully drawn curves represent the results of a numerical integration of the active and passive stress components across the arteriolar wall, and the dashed curves represent the analytic approximation Eq. (17). 

Nevens, F., Sprengers, D., Fevery, J. The effect of different doses of a bolus injection of somatostatin combined with a slow infusion on transmural oesophageal variceal pressure in patients with cirrhosis. J. Hepatol. 1994 20 27-31... 

The advantages of the isolated vessel technique in defining microvascular physiologic and pathophysiologic mechanisms are 1) The vessels are studied in the absence of a neurohumoral and parenchymal tissue environment, 2) it allows for direct assessment of vascular responses in defined segments, 3) transmural pressure is controlled, 4) hormones and drugs can be added to the bathing media or luminal perfusate, 5) intracellular ion concentrations can be measured by fluorescence microscopy and membrane potentials can be recorded with microelectrodes. 

The hmitations of the preparation are ) autocoid production and vascular reactivity may be altered in vitro, 2) the absence of flow dynamics may alter endothelial cell function, 3) the small amount of tissue limits biochemical measurements, 4) isolated arterioles do not exhibit myogenic responses to changes in transmural pressure. 

Yoshioka T, Rennke HG, Salant DJ, et al. Role of abnormally high transmural pressure in the permselectivity defect of glomerular capillary wall a study in early passive Heymann nephritis. Circ Res 1987 61 531-538. 

However, 50 xM barium has little effect on membrane potential in rabbit middle cerebral artery (Brayden, 1990), or on diameter in rat posterior cerebral arteries pressurized to half the mean systolic blood pressure (McCarron and Halpern, 1990a). Clearly, factors such as membrane potential, transmural pressure, vasoconstrictors, and vasodilators, as well as possible differences in channel distribution and density, are likely to influence the contribution of the Kjp channel to the membrane potential. 

Harder, D.R., Gilbert, R., and Lombard, J.H. (1987) Vascular muscle cell depolarization and activation in renal arteries on elevation of transmural pressure. American Journal of Physiology, 253 F778-F781... 

Factors that change with growth. Pp pleural pressure P m transmural pressure (intra-airway pressure-pleural pressure) Pjilyialveolar pressure P Intra-airway pressure. Modified from Wohl (4)... 

The primary functions of albumin are to help maintain the osmotic (oncotic) transmural pressure differential that ensures proper mass exchange between blood and interstitial fluid at the capillary level and to serve as a transport carrier molecule for several hormones and other small biochemical constituents (such as some metal ions). The primary function of the globulin class of proteins is to act as transport carrier molecules (mostly of the a and p class) for large biochemical substances, such as fats (lipoproteins) and certain carbohydrates (muco- and glycoproteins) and heavy metals (mineraloproteins), and to work together with leukocytes in the body s immune system. The latter function is primarily the responsibflity of the y class of immunoglobulins, which have antibody activity. The primary function of fibrinogen is to work with thrombocytes in the formation of a blood clot — a process also aided by one of the most abundant of the lesser proteins, prothrombin (MW 62,000). 

The first condition occurs when the inlet and outlet transmural pressures are positive. [Transmural pressure is defined as the pressure gradient across the vessel waU (Pinside Toutside)-] In this instance, the vein can be treated as discussed above for an artery. A second condition occurs when the inlet and outlet transmural pressures are negative. In this instance, the vein will coUapse, and flow will stop or be greatly reduced. 

The conduit characteristics of the venous system primarily depend on the anatomy of the system. Valves in the veins of the limbs are crucial for reducing the pressure in dependent parts of the body. Even small movements from skeletal muscle activity tend to compress the veins and move blood toward the heart. A competent valve then blocks back flow, thus reheving the pressure when the movement stops. Even a few steps can reduce the transmural venous pressure in the ankle from as much as 100 mmHg to about 20 mmHg. Without this mechanism, transcapillary movement of fluid into the extravascular spaces results in edema. Varicose (swollen) veins and peripheral pooling of blood can result from damage to the venous valves. During exercise, the rhythmic contraction of the skeletal muscles, in conjunction with venous... 

Unstressed volume (Vq) is the volume in the vascular system when the transmural pressure is zero. It is a calculated volume obtained by extrapolating the relatively hnear segment of the pressure-volume relationship over the normal operating range to zero transmural pressure. Many studies have shown that reflexes and drugs have quantitatively more influence on Vb than on the compHance. 

The stressed volume (V ) is the volume of blood in the vascular system that must be removed to change the computed transmural pressure from its prevailing value to zero transmural pressure. It is computed as the product of the vascular compHance and transmural distending pressure Vs = C x P. The total contained blood volume at a specific pressure (P) is the sum of stressed and unstressed volume. The unstressed volume is then computed as the total blood volume minus the stressed volume. Because of the marked nonlinearity around zero transmural pressure and the required extrapolation, both Vb and Vs are virtual volumes. 

For estimating the capacitance parameters of the veins, contained volume, rather than flow, and transmural pressure, rather than the longitudinal pressure gradient, must be measured. Pressures are measured as described above. For the desired pressure-volume relationship the total contained volume must be known. 

Most of our knowledge of the mechanics of the microvascular wall comes from in vivo or in vitro measurements of vessel diameter as a function of transmural pressure [ 4 ]. Development of isolated microvessel preparations has made it possible to precisely control the transmural pressure during experiments. In addition, these preparations allow one to separate the effects of metaboHc factors and blood flow rate from the effect of pressure by controlling both the chemical environment and the flow rate through the vessel. Arterioles and venules exhibit vascular tone, that is, their diameter is maximal when smooth muscle is completely relaxed (inactivated). When the vascular smooth muscle is constricted, small arterioles may... 

Krogh tissue cylinder model A cylindrical volume of tissue supplied by a central cylindrical capillary. Myogenic response Vasoconstriction in response to elevated transmural pressure and vasodilation in response to reduced transmural pressure. 

Starling s Law The relationship between water flux through the endothelium and the difference between the hydraulic and osmotic transmural pressures. 

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