Vascular resistance

Calcium channel blockers reduce arterial blood pressure by decreasing calcium influx, resulting in a decrease in intracellular calcium (236,237). The arterial smooth muscle tone decreases, thereby decreasing total peripheral resistance. The increase in vascular resistance in hypertension is found to depend much on calcium influx. Calcium channel blockers reduce blood pressure at rest and during exercise. They decrease the transmembranous calcium influx or entry that lead to a net decrease of intracellular calcium and therefore the vascular tone falls, as does blood pressure. 

Class II drugs are classical (3-adrenoceptor antagonists such as propranolol, atenolol, metoprolol or the short-acting substance esmolol. These drugs reduce sinus rate, exert negative inotropic effects and slow atrioventricular conduction. Automaticity, membrane responsiveness and effective refractory period of Purkinje fibres are also reduced. The typical extracardiac side effects are due to (3-adrenoceptor blockade in other organs and include bronchospasm, hypoglycemia, increase in peripheral vascular resistance, depressions, nausea and impotence. 

DHPs are potent arterial vasodilators. They act on resistance vessels and therefore reduce peripheral vascular resistance, lower arterial blood pressure, and antagonize vasospasms in coronary or peripheral arteries. By reducing afterload, DHPs also reduce cardiac oxygen demand. Together with their vascular spasmolytic effect, this explains most of the beneficial actions of DHPs in angina pectoris. Most DHPs are only licensed for the therapy of hypertension, some of them also for the treatment of angina pectoris and vasospastic (Prinzmetal) angina. 

Monitoring the patient in shock requires vigilance on the part of the nurse The patient s heart rate, blood pressure, and ECG are monitored continuously. The urinary output is measured often (usually hourly), and an accurate intake and output is taken. Monitoring of central venous pressure via a central venous catheter will provide an estimation of the patient s fluid status. Sometimes additional hemodynamic monitoring is necessary with a pulmonary artery catheter. The use of a pulmonary artery catheter allows the nurse to monitor a number of parameters, such as cardiac output and peripheral vascular resistance The nurse adjusts therapy according to the primary health care provider s instructions. 

Phenylephrine 10-1000 pg/minute Seconds Bradycardia, coronary vasoconstriction, decreased renal perfusion, metabolic acidosis Alpha-1, increased cardiac output (CO), decreased systemic vascular resistance (SVR)... 

Bilde, T. and Dahlager, J.l. (1977). The effect of chlorproma-zine pretreatment on the vascular resistance in kidneys following warm ischaemia. Scand. J. Urol. Nephrol. 11, 21-26. 

Bilzer, M. and Lauterburg, B.H. (1991). Effects of hypoch-lorous acid and chloramines on vascular resistance, cell integrity, and biliary glutathione disulfide in the perfused rat liver modulation by glutathione. J. Hepatol. 13, 84-89. 

BP, blood pressure CO, cardiac output HR, heart rate PCWP, pulmonary capillary wedge pressure SVR, systemic vascular resistance T, increase 4, decrease 0, no or little change. 

Practitioners must have a good understanding of cardiovascular physiology to diagnose, treat, and monitor circulatory problems in critically ill patients. Eugene Braunwald, a renowned cardiologist, described the interrelationships between the major hemodynamic variables (Fig. 10-1).1 These variables include arterial blood pressure, cardiac output (CO), systemic vascular resistance (SVR), heart rate (HR), stroke volume (SV), left ventricular size, afterload, myocardial contractility, and preload. While an oversim-... 

PC After meals (post cibum) PVR Peripheral vascular resistance... 

SVRI Systemic vascular resistance index VT Ventricular tachycardia... 

SVR Supraventricular rhythm systemic vascular resistance VTE Venous thromboembolism... 

Afterload The force against which a ventricle contracts that is contributed to by the vascular resistance, especially of the arteries, and by the physical characteristics (mass and viscosity) of the blood. Afterload is the overall resistance to blood flow leaving the heart. 

Pulmonary artery catheter An invasive device used to measure hemodynamic parameters directly, including cardiac output and pulmonary artery occlusion pressure calculated parameters include stroke volume and systemic vascular resistance. 

Systemic vascular resistance The portion of resistance to blood flow leaving the heart that is determined by vascular tone (constriction or relaxation). Systemic vascular resistance = mean arterial blood pressure/cardiac output. 

Vasopressors Medications that cause constriction of blood vessels, increase in vascular resistance, and increase in blood pressure. 

NOx levels are increased in plasma and urine of septic animals. Many nonse-lective NO synthase inhibitors (e.g., L-NMMA) are used in several models with experimental induced sepsis (S40). In most studies it was shown that the cardiovascular abnormalities associated with sepsis were reversed, increasing blood pressure and systemic vascular resistance (F7, K9, M26, N5), together with a improvement in renal function (B42, H24). Also, selective inhibition of iNOS prolonged survival in septic rats (A7). 

Schneider, F Lutun, P Couchot, A., Bilbault, P., and Tempe, J, D., Plasma cyclic guanosine 3 -5 monophosphate concentrations and low vascular resistance in human septic shock. Intensive Care Med. 19,99-104(1993). 

An example of this type of reflex is the baroreceptor reflex (see Figure 1.2). Baroreceptors located in some of the major systemic arteries are sensory receptors that monitor blood pressure. If blood pressure decreases, the number of sensory impulses sent from the baroreceptors to the cardiovascular control center in the brainstem also decreases. As a result of this change in baroreceptor stimulation and sensory input to the brainstem, ANS discharge to the heart and blood vessels is adjusted to increase heart rate and vascular resistance so that blood pressure increases to its normal value. 

Understand Ohm s law and describe the relationship among blood flow, blood pressure, and vascular resistance... 

List the factors that affect vascular resistance and explain their physiological significance... 

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