Arterial pressure, mean

Mean arterial pressure and cardiac output, an expression of the amount of blood that the heart pumps each minute, are the key Indicators of the normal functioning of the cardiovascular system. Mean arterial pressure is strictly controlled, but by changing the cardiac output, a person can adapt, e.g., to increased oxygen requirement due to increased workload. Blood flow in vital organs may vary for many reasons, but is usually due to decreased cardiac output. However, there can be very dramatic changes in blood pressure, e.g., blood pressure plummets during an anaphylactic allergic reaction. Also cytotoxic chemicals, such as heavy metals, may decrease the blood pressure. 

In a third study the time course of the effects of intravenous and intracoronary injections of cysteinyl leukotrienes on metabolic parameters and systemic and coronary hemodynamics was examined in patients with normal coronary arteries [32]. LTD4 (3 nmol, injected into the left coronary artery) induced an early (20 s), transient fall in mean arterial pressure paralleled by rises in heart rate and plasma levels of epinephrine and norepinephrine, all of which had returned to baseline by 10 min. CVR rose at 10 and 15 min and myocardial oxygen extraction at 15 min. Thus, small doses of cysteinyl leukotrienes may induce both an early, transient fall in mean arterial pressure, with secondary sympathoadrenergic activation, and a later increase in small coronary arteriolar resistance. 

If PCWP between 15 and 18 mmHg and symptomatic o If adequate mean arterial pressure (MAP)... 

Reduce mean arterial pressure (MAP) by 20-25% or to a diastolic blood pressure of 110 mmHg in hypertensive emergencies... 

Aim for a 10-15% reduction in mean arterial pressure (MAP) ° Nitroprusside—0.25-0.5 mcg/kg/min continuous IV infusion increase in increments of 0.25-0.5 mcg/kg/min until desired hemodynamic effect. Usual doses up to 2-3 mcg/kg/min. High-alert medication—read package insert before use... 

Systolic blood pressure (SBP) <90 mmHg or a mean arterial pressure (MAP) <60 mmHg for >1 h or hypotension requiring vasopressor pharmacotherapy... 

FIGURE 10-4. Treatment algorithm for the management of moderate to severe hypovolemia. BP, blood pressure CVP, central venous pressure ECG, electrocardiogram MAP, mean arterial pressure PA, pulmonary artery PAOP, pulmonary artery occlusion pressure PRBCs, packed red blood cells SBP, systolic blood pressure. 

Systemic blood pressure correlates with glomerular pressure and elevations in both systemic blood pressure and glomerular pressure contribute to glomerular damage. The rate of GFR decline is related to elevated systolic blood pressure and mean arterial pressure. The decline in GFR is estimated to be 14 mL/minute per year with a systolic blood pressure of 180 mm Hg. Conversely, the decline in GFR decreases to 2 mL/minute per year with a systolic blood pressure of 135 mm Hg.11... 

Cardiovascular Increased stroke index, heart rate, and diastolic and mean arterial pressures Musculoskeletal Bone pain, muscle weakness Dermatologic Pruritus... 

Mean arterial pressure greater than or equal to 65 mm Hg... 

Aldosterone acts on the distal tubule of the nephron to increase sodium reabsorption. The mechanism of action involves an increase in the number of sodium-permeable channels on the luminal surface of the distal tubule and an increase in the activity of the Na+-K+ ATPase pump on the basilar surface of the tubule. Sodium diffuses down its concentration gradient out of the lumen and into the tubular cells. The pump then actively removes the sodium from cells of the distal tubule and into the extracellular fluid so that it may diffuse into the surrounding capillaries and return to the circulation. Due to its osmotic effects, the retention of sodium is accompanied by the retention of water. In other words, wherever sodium goes, water follows. As a result, aldosterone is very important in regulation of blood volume and blood pressure. The retention of sodium and water expands the blood volume and, consequently, increases mean arterial pressure. 

Understand the method by which mean arterial pressure is calculated... 

Explain why mean arterial pressure must be closely regulated... 

Explain how the autonomic nervous system alters cardiac output, total peripheral resistance, and therefore mean arterial pressure... 

Mean arterial pressure = cardiac output x total peripheral resistance... 

Figure 15.3 Factors that affect mean arterial pressure. Mean arterial pressure is determined by cardiac output and total peripheral resistance. Important factors that influence these two variables are summarized in this figure.

Figure 15.4 Effects of the autonomic nervous system on mean arterial pressure. The baroreceptors, chemoreceptors, and low-pressure receptors provide neural input to the vasomotor center in the brainstem. The vasomotor center integrates this input and determines the degree of discharge by the sympathetic and parasympathetic nervous systems to the cardiovascular system. Cardiac output and total peripheral resistance are adjusted so as to maintain mean arterial pressure within the normal range.

Notes CO cardiac output VR venous return HR heart rate SV stroke volume EDV end-diastolic volume ESV end-systolic volume O blood flow AP pressure gradient R resistance r vessel radius P systolic pressure Piiastoik- diastolic pressure MAP mean arterial pressure TPR total peripheral resistance, P venous pressure Era- right atrial pressure Rv venous resistance. 

Figure 15.5 Effects of sympathetic and parasympathetic nervous activity on mean arterial pressure. The parasympathetic nervous system innervates the heart and therefore influences heart rate and cardiac output. The sympathetic nervous system innervates the heart and veins and thus influences cardiac output. This system also innervates the arterioles and therefore influences total peripheral resistance. The resulting changes in cardiac output and total peripheral resistance regulate mean arterial pressure.

Glomerular capillary pressure is determined primarily by renal blood flow (RBF). As RBF increases, PGC and therefore GFR increase. On the other hand, as RBF decreases, PGC and GFR decrease. Renal blood flow is determined by mean arterial pressure (MAP) and the resistance of the afferent arteriole (aff art) ... 

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