Limb blood flow

Hokanson D E, Sumner D S and Strandness D E Jr 1975 An electrically calibrated plethysmograph for direct measurement of limb blood flow IEEE Trans. Biomed. Eng. BME-22 25-9... 

The predominant actions of phenylephrine are on the cardiovascular system. Parenteral administration causes a rise in systolic and diastolic pressures due to peripheral vasoconstriction. Accompanying the pressor response to phenylephrine is a marked reflex bradycardia that can be blocked by atropine after atropine, large doses of the peripheral resistance is considerably increased. Circulation time is slightly prolonged, and venous pressure is slightly increased venous constriction is not marked. Most vascular beds are constricted renal, splanchnic, cutaneous, and limb blood flows are reduced, but coronary blood flow is increased. Pulmonary vessels are constricted, and pulmonary arterial pressure is raised. 

A series of bradykinin analogs containing the simple secondary amino acid, sarcosine, in place of the cyclic secondary structure, proline, was prepared to determine whether modification of the biologic activity of bradykinin might be related to steric factors. 2-Sarcosine bradykinin was the most active analog in increasing hind limb blood flow in the dog, although its activity was at most only about 30% that of synthetic bradykinin. The 3-sarcosine derivative of bradykinin... 

Quinterenol (XIII) was found to have g-adrenergic stimulant properties. Thus the drug increased hind limb blood flow and lowered total peripheral resistance in the dog to the same extent as did papaverine but had a considerably longer duration of action. All cardiovascular effects of quinterenol were blocked by the 8-receptor blocking agent, propranalol. 

Foop diuretics (furosemide, bumetanide, torsemide) are usually necessary to restore and maintain euvolemia in HF. In addition to acting in the thick ascending limb of the loop of Henle, they induce a prostaglandin-mediated increase in renal blood flow that contributes to their natriuretic effect. 

An additional contributing factor to the diuresis induced by osmotic diuretics is the increase in renal medullary blood flow that follows their administration. This medullary hyperemia reduces the cortex-meduUary osmolar gradient by carrying away interstitial Na+ and urea. This partial reduction of the osmolar gradient impairs normal reabsorption of tubular water, which occurs from the descending limb of Henle and the collecting duct. 

Intravenous regional anesthesia—injection of local anesthetic into a suitable vein supplying the limb to be anesthetized the blood flow from this limb is then restricted by a tourniquet... 

Administration of a cocktail containing eicosapentenoic acid and docosahexenoic acid to volunteers for up to 6 weeks, resulted in a significant depression in IL-1J3 (61%), IL-1 a (39%), and TNF (40%) synthesis. These levels returned to normal after a few weeks [99]. In vitro studies indicate that Pentoxifylline can block the effects of IL-1 and TNF on neutrophils [100]. It is a phosphodiesterase (PDE) inhibitor that causes increased capillary blood flow by decreasing blood viscocity and is used clinically in chronic occlusive arterial disease of the limbs with intermittent claudication. Denbufylline, a closely related xanthine, has been patented as a functional inhibitor of cytokines and exhibits a similar profile to Pentoxifylline [101]. Romazarit (Ro-31-3948) derived from oxazole and isoxazole propionic acids has been shown to block IL- 1-induced activation of human fibroblasts in vitro and in animal models reduces inflammation [102,103,104]. By using a spontaneous autoimmune MRL/lpr mouse model, a significant efficacy was shown [105]. Two-dimensional structures of some of these molecules are shown in Figure 14. 

These relationships imply that a wider tourniquet not only requires lower pressure applied to the limb to occlude blood flow, but lower pressure translates to less damage to nerves and tissue. A good design for a battlefield tourniquet should be flexible to allow different widths to accommodate the needs of soldiers with respect to the range of limb sizes. On the other hand it is recognized that the solider must carry a personal tourniquet of very limited size and weight, possibly worn within the uniform, so a narrow tourniquet may be necessary, and a wide tourniquet (e.g., 3-4 in.) may not be practical. 

The tourniquet must reliably occlude blood flow in large limbs up to 27 in. in... 

In the third and final step, the cinch-lever is lifted, as depicted in Figs. 5.36 and 5.37, to adjust the tension on the strap to that needed for occlusion of blood flow in the limb, distal to the tourniquet. The cinch-lever can be repeatedly lifted or partially lifted to achieve proper strap tension. 

Four factors contribute to the ability to concentrate urine (1) Active reabsorption of Na+, K+, and CF without water reabsorption by the thick ascending limb of the loop of Henle results in interstitial hypertonicity and hypoosmotic tubular fluid. (2) Selective permeability to water, but not small electrolytes, in the descending thin limb of the loop of Henle allows passive reabsorption of water, facilitated by interstitial hypertonicity. (3) Relatively low medullary blood flow maintains medullary hypertonicity, allowing continued elaboration of concentrated urine. (4) In the presence of ADH, the distal tubule and collecting ducts are permeable to water so that water may diffuse out of the tubular lumen into the medullary, and papillary inter-stitium. Because of the ability of the thick ascending limb of the loop of Henle to move solutes but not water into the medullary interstitium, the medullary, and papillary interstitium are hyperosmotic and hypertonic compared to plasma and cortical interstitium (Figure 29.5). 

The aim has been to produce peripheral arteriolar vasodilatation without a concurrent significant drop in blood pressure, so that an increased blood flow in the limbs will result. Drugs are naturally more useful in patients in whom the decreased flow of blood is due to spasm of the vessels (Raynaud s phenomenon) than where it is due to organic obstructive changes that may make dilatation in response to drugs impossible (arteriosclerosis, intermittent claudication, Buerger s disease). 

As the ascending limb of the loop re-enters the renal cortex, sodium continues to be removed from the tubular fluid by the sodium pump, accompeinied electrostatically by chloride. Both ions pass into the interstitial tissue (site 3) from which they are rapidly removed because cortical blood flow is high and there are no vasa recta present consequently the urine becomes more dilute. Thiazides act principally at this cortical diluting segment of the ascending limb, preventing sodium reabsorption. They inhibit the NaCl co-transporter (called NCCT). 

Birds (and reptiles) have a well-developed renal portal system that drains blood from the caudal portion of the body. Consequently, drugs administered parenterally in the lower extremities (hind limbs) of those species pass through the kidneys before entering the systemic circulation. This feature of blood flow to the kidneys provides the opportunity for first-pass excretion of water-soluble ionized drugs (e.g., p-lactam and aminoglycoside antibiotics) to occur. 

Ten patients with peripheral arterial occlusive disease were scheduled to undergo elective percutaneous transluminal angioplasty after a single dose of ciprofloxacin 400 mg (66). Antibiotic concentrations were significantly reduced in ischemic lesions compared with healthy adipose tissue. However, improvement of arterial blood flow in the affected limb was associated with increased cure rates of soft tissue infections. 

Dextran 70, so-called because its molecules have an average weight of 70 kDa, is used as a plasma substitute, as is dextran 40. Dextran 40 has been used to improve blood flow in ischemic limbs. Dextran 40 and dextran 70 have been used to prevent deep venous thrombosis. Dextran 1 is used as a desensitizer to prevent allergic reactions to dextrans of larger molecular weight. After reproductive surgery 32% dextran 70 is sometimes administered... 

Verapamil s major effect is on the slow Ca channel. The result is a slowing of AV conduction and the sinus rate. This inhibition of the action potential inhibits one limb of the reentry circuit believed to underlie most paroxysmal. supraventricular tachycardias that use the A V node as a reentry point. It is categorized as a class IV antiarrhythmie drug (see Classes of Antiarrhythmie Drugs" below). Hemodynami-cally. verapamil causes a change in the preload, afterload, contractility, heart rate, and coronary blood flow. The drug reduces systemic vascular resistance and mean blood pressure, with minor effects on eardiae output. 

Intravenous regional ane.sthesia is used to anesthetize a large region, such us a limb. The anesthetic is injected into a suitable vein in a limb that has had its blood flow restricted by a tourniquet. The efficiency and safety of the technique depends on preventing arterial flow for the duration of the anesthesia. Lignocaine is frequently used to produce intravenous regional anesthesia, but bupivacaine is not approved for this purpose because of its long duration of action. 

Most first-aid measures are of little value and some are dangerous. The use of ice to prevent the spread of the venom has been linked to an increased frequency of limb amputations and should never be employed. Field procedures such as fang mark incisions may result in vein or artery damage and improperly placed tourniquets may impede blood flow. Electric shock directed at the site of envenomation has not been proven effective and is a dangerous procedure. 

The kidneys receive the largest blood flow (22-24% of cardiac output) of any organ, relative to the percentage body weight they constitute (cattle, 0.24% horse 0.36% dog, 0.61%). The functional unit of the kidney is the nephron, which comprises a renal corpuscle (glomerulus and Bowman s capsule), proximal convoluted tubule, descending and ascending limbs of the loop of... 

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