Exercise blood flow during

Table 9-4). Activation of 32 receptors in skeletal muscle contributes to increased blood flow during exercise. Under physiologic conditions, epinephrine functions largely as a hormone after release from the adrenal medulla into the blood, it acts on distant cells. Norepinephrine (levarterenol, noradrenaline) is an agonist at both 0 and tx2 receptors. Norepinephrine also activates receptors with similar potency as epinephrine, but has relatively little effect on 32 receptors. Consequently, norepinephrine increases peripheral resistance and both diastolic and systolic blood pressure. Compensatory baroreflex activation tends to overcome the direct positive chronotropic effects of norepinephrine however, the positive inotropic effects on the heart are maintained (Table 9-4). 

Drury AN, Szent-Gyorgyi A (1929) The physiological activity of adenine compounds with especial reference to their action upon the mammalian heart. J Physiol 68(3) 213-237 Duncker DJ, Bache RJ (2008) Regulation of coronary blood flow during exercise. Physiol Rev 88(3) 1009-1086... 

The level of plasma albumin-bound fatty acids increases when lipolysis rates are high. The tissue uptake of fatty acids is proportional to their concentration in plasma and is therefore largely dependent on blood flow. During intense exercise, the flow of blood through the splanchnic bed is reduced and more fatty acids are available to skeletal muscle. With the exception of nerve tissue and blood cells, tissues can use fatty acids by /3-oxidation and by the TCA cycle. Fatty acid uptake is not regulated by hormones or intracellular effectors. Free fatty acids readily diffuse across the plasma membrane of cells where they are used strictly in response to supply and demand. This is illustrated for cardiac muscle in Figure 22-20. 

Bradley SJ, Kingwell BA, McConell GK. 1999. Nitric oxide synthase inhibition reduces leg glucose uptake but not blood flow during dynamic exercise in humans. Diabetes 48 1815-1821. 

Some P-adrenoceptor blockers have intrinsic sympathomimetic activity (ISA) or partial agonist activity (PAA). They activate P-adrenoceptors before blocking them. Theoretically, patients taking P-adrenoceptor blockers with ISA should not have cold extremities because the dmg produces minimal decreases in peripheral blood flow (smaller increases in resistance). In addition, these agents should produce minimal depression of heart rate and cardiac output, either at rest or during exercise (36). 

Paulsson, B., Bende, M., and Ohim, P. (1985). Nasal mucosal blood flow at rest and during exercise. Acta Otolaryngol. (Stockh.) 99, 140-143. 

The primary goal of the circulatory system during exercise is to increase blood flow to the working muscles. This is accomplished by increasing MAP and decreasing local vascular resistance ... 

Exercise tolerance (stress) testing (ETT) is recommended for patients with an intermediate probability of CAD. Results correlate well with the likelihood of progressing to angina, occurrence of acute MI, and cardiovascular death. Ischemic ST-segment depression during ETT is an independent risk factor for cardiovascular events and mortality. Thallium myocardial perfusion scintigraphy may be used in conjunction with ETT to detect reversible and irreversible defects in blood flow to the myocardium. 

An implication of the high degree of hepatic extraction is that clearance of nicotine should be dependent on liver blood flow. Thus, physiological events, such as meals, posture, exercise, or drugs perturbing hepatic blood flow, are predicted to affect the rate of nicotine metabolism. Meals consumed during a steady state infusion of nicotine result in a consistent decline in nicotine concentrations, the maximal effect seen 30-60 min after the end of a meal (Gries et al. 1996 Lee et al. 1989). Hepatic blood flow increases about 30% and nicotine clearance increases about 40% after a meal. 

Blood-bome fuels are glucose, which is derived from liver glycogen, and fatty acids derived from adipose tissue. Uptake depends on the flow of blood through the muscle, the concentration of the fuel in the blood and the demand for ATP within the muscle. During sustained exercise the flow of blood to the muscle can increase up to 50-fold and the rate of utilisation of the fuel can increase to a similar extent, yet the concentration of the fuels in blood remains remarkably constant (Table 13.5). 

During very brief but very high-intensity exercise (sprinting, running upstairs), when there is not sufficient time for the arterioles to dilate to permit increased blood flow to the muscle. 

Atherosclerosis in a coronary artery can lead to an infarct (see below). If the atherosclerosis is less severe, the reduction in the blood flow cannot provide enough oxygen in some conditions to support the work of the heart, for example during exercise or acute anxiety, and the resulting pain, angina pectoris, if frequent reduces the quality of life of the patient (Box 22.2). 

Lindbjerg IF (1966) Leg muscle blood-flow measured with 133-xenon after ischaemia periods and after muscular exercise performed during ischaemia. Clin Sci, 30(3) 399-408. 

The caliber of arteriolar resistance vessels controls blood flow through the coronary bed. Arteriolar caliber is determined by myocardial 02 tension and local concentrations of metabolic products, and is automatically adjusted to the required blood flow (B, healthy subject). This metabolic autoregulation explains why anginal attacks in coronary sclerosis occur only during exercise (B, patient). At rest, the pathologically elevated flow resistance is... 

Typically, angina occurs when patients who have narrowed coronary vessels start to exercise. Exercise increases heart rate and cardiac output, increasing the myocardial requirement for oxygen. Narrowed coronary arteries may not be able to dilate sufficiently to permit the increased blood flow and oxygen delivery required by cardiac muscle during exercise. The most common reason for narrowed coronary blood vessels is the build-up of fatty deposits (atheroma) on the inner wall of coronary vessels, which reduces the space available for blood flow. 

As noted previously, like skeletal muscle, glycogen depletion in liver during endurance exercise is much less in trained animals and in animals who have had free fatty acids artificially elevated. No evidence exists that the mechanism proposed by Randle to account for the inhibition of carbohydrate metabolism in muscle by oxidation of fatty acids is operative in the liver. Thus other factors must be responsible for the slower rate of liver glycogen depletion in these situations. Such factors may include a smaller increase in catecholamine levels, a smaller reduction in insulin levels, and a smaller reduction in blood flow to the liver during exercise (19,20). 

An exception for coffee drinkers came from work done by Swiss investigators, who found that drinking two cups of caffeinated coffee decreases blood flow to the heart during exercise, especially at high altitudes. On a practical level, it seems that we should keep coffee drinking to just one cup before exercise and avoid it entirely while climbing or hiking in the mountains. 

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