Pressure blood

Four cardiovascular parameters of interest are stroke volnme, cardiac output (CO), total peripheral resistance of the systemic vasculature (TPR), and blood pressure. Measurements of both systolic blood pressnre (SBP) and diastolic blood pressure (DBP) are typically presented when discnssing blood pressnre. 

Stroke volume is the amount of blood pnmped into the aorta per heartbeat. It is typically measured in milliliters (ml), and a typical stroke volnme is around 60-100 ml. Cardiac output is the total amount of blood pnmped per nnit of time, typically 1 min. As is the case for heart rate, CO is nsnally represented in intervals of 1 min and is 

Along with CO, TPR is the second primary determinant of blood pressure. The simultaneous measuranent of blood pressure and CO allow the derivation of TPR. It is the resistance provided by the vasculature to the ejection of blood into the aorta. Blood pressure can be thought of as representing a manifestation of the interaction between the heart and the vasculature (Obrist 1981). A given change in blood pressure can be the result of a change in cardiac output, a change in TPR, or a combination of both. 

There is continuous pressure in arteries to propel blood through them. The level of blood pressure fluctuates during each cardiac cycle. Pressure is highest during systole (contraction) when blood is ejected from the left ventricle into the aorta this pressure is labeled SBP. Pressure is lowest during diastole (relaxation) and labeled 

4 Cardiac and Cardiovascular Diseases and Occurrences of Clinical Concern 

---

A base, formed by the bacterial degradation of histidine, and present in ergot and in many animal tissues, where it is liberated in response to injury and to antigen-antibody reactions. If injected it causes a condition of shock with dilatation of many blood vessels, loss of plasma from the capillaries to the tissues and a rapid fall in blood pressure. It is normally prepared from protein degradation products. 

Acts to constrict small arteries, thereby increasing blood pressure and to contract smooth muscle. Used in cases of peripheral vasomotor collapse. 

PGEi (a prostaglandin a small amount of PGEi lowers blood pressure significantly)... 

Physiological responses to prostaglandins encompass a variety of effects Some prostaglandins relax bronchial muscle others contract it Some stimulate uterine con tractions and have been used to induce therapeutic abortions PGEj dilates blood vessels and lowers blood pressure it inhibits the aggregation of platelets and offers promise as a drug to reduce the formation of blood clots... 

Hyperaldosteronism is accompanied by elevation of blood pressure (115), and can be treated with an aldosterone antagonist, eg, spironolactone (117) which... 

Nontraditional Hormones. Novel hormones identified ia cardiovascular tissue have profound effects on maintenance of blood pressure and blood volume ia mammals. Atrial natriuretic hormone (ANH) is a polypeptide hormone secreted from the atria of the heart. When the cardiac atrium is stretched by increased blood volume, secretion of ANH is stimulated ANH ia turn increases salt and water excretion and reduces blood pressure (6). Endothelin is a polypeptide hormone secreted by endothehal cells throughout the vasculature. Although endothelin is released into the circulation, it acts locally in a paracrine fashion to constrict adjacent vascular smooth muscle and increase blood pressure (7). 

The posterior lobe of the pituitary, ie, the neurohypophysis, is under direct nervous control (1), unlike most other endocrine organs. The hormones stored in this gland are formed in hypothalamic nerve cells but pass through nerve stalks into the posterior pituitary. As early as 1895 it was found that pituitrin [50-57-7] an extract of the posterior lobe, raises blood pressure when injected (2), and that Pitocin [50-56-6] (Parke-Davis) causes contractions of smooth muscle, especially in the utems (3). Isolation of the active materials involved in these extracts is the result of work from several laboratories. Several highly active posterior pituitary extracts have been discovered (4), and it has been deterrnined that their biological activities result from peptide hormones, ie, low molecular weight substances not covalendy linked to proteins (qv) (5). 

Sodium and Hypertension. Salt-free or low salt diets often are prescribed for hypertensive patients (57). However, sodium chloride increases the blood pressure in some individuals but not in others. Conversely, restriction of dietary NaCl lowers the blood pressure of some hypertensives, but not of others. Genetic factors and other nutrients, eg, Ca " and K", may be involved. The optimal intakes of Na" and K" remain to be estabUshed... 

Two AT-II receptors, AT and AT2 are known and show wide distribution (27). The AT receptor has been cloned and predominates ia regions iavolved ia the regulation of blood pressure and water and sodium retention, eg, the aorta, Hver, adrenal cortex, and ia the CNS ia the paraventricular nucleus, area postrema, and nucleus of the soHtary tract. AT2 receptors are found primarily ia the adrenal medulla, utems, and ia the brain ia the locus coeruleus and the medial geniculate nucleus. AT receptors are GCPRs inhibiting adenylate cyclase activity and stimulating phosphoHpases C, A2, and D. AT2 receptors use phosphotyrosiae phosphatase as a transduction system. 

Potassium [7440-09-7] K, is the third, element ia the aLkaU metal series. The name designation for the element is derived from potash, a potassium mineral the symbol from the German name kalium, which comes from the Arabic qili, a plant. The ashes of these plants al qili) were the historical source of potash for preparing fertilisers (qv) or gun powder. Potassium ions, essential to plants and animals, play a key role in carbohydrate metaboHsm in plants. In animals, potassium ions promote glycolysis, Hpolysis, tissue respiration, and the synthesis of proteins (qv) and acetylcholine. Potassium ions are also beheved to function in regulating blood pressure. 

Nitrous oxide produces respiratory depression (38,39). It has been shown to produce a direct myocardial depressant effect in dogs (40) and in humans breathing a 40% N2O/60% oxygen mixture (41) however, this may be offset by the activation of the sympathetic nervous system (42). The combination of nitrous oxide and opioids can produce decreases in myocardial contractiHty, heart rate, and blood pressure (43). 

Isoflurane is a respiratory depressant (71). At concentrations which are associated with surgical levels of anesthesia, there is Htde or no depression of myocardial function. In experimental animals, isoflurane is the safest of the oral clinical agents (72). Cardiac output is maintained despite a decrease in stroke volume. This is usually because of an increase in heart rate. The decrease in blood pressure can be used to produce "deHberate hypotension" necessary for some intracranial procedures (73). This agent produces less sensitization of the human heart to epinephrine relative to the other inhaled anesthetics. Isoflurane potentiates the action of neuromuscular blockers and when used alone can produce sufficient muscle relaxation (74). Of all the inhaled agents currently in use, isoflurane is metabolized to the least extent (75). Unlike halothane, isoflurane does not appear to produce Hver injury and unlike methoxyflurane, isoflurane is not associated with renal toxicity. 

Desflurane is less potent than the other fluorinated anesthetics having MAC values of 5.7 to 8.9% in animals (76,85), and 6% to 7.25% in surgical patients. The respiratory effects are similar to isoflurane. Heart rate is somewhat increased and blood pressure decreased with increasing concentrations. Cardiac output remains fairly stable. Desflurane does not sensitize the myocardium to epinephrine relative to isoflurane (86). EEG effects are similar to isoflurane and muscle relaxation is satisfactory (87). Desflurane is not metabolized to any significant extent (88,89) as levels of fluoride ion in the semm and urine are not increased even after prolonged exposure. Desflurane appears to offer advantages over sevoflurane and other inhaled anesthetics because of its limited solubiHty in blood and other tissues. It is the least metabolized of current agents. 

Aerosol adniinistration of isoproterenol produces a prompt (2—5 minutes) intense bronchodilatation of relatively short (1 h) duration. The lack of P2-selectivity leads, in many cases, to tachycardia and blood pressure elevation. Also, use of isoproterenol, like all other known P-agonists, results in a down-regulation, or desensitization, of P-adrenergic receptors. This desensitization is only partial, and after time (depending on dose, patient, and agent), a stable, less responsive state is achieved in which P-agonists remain effective. Isoproterenol has been widely used for many years. 

Statement on the Eole of Dieta Management in Hypertension Control, National High Blood Pressure Education Program and Coordinating Committee, Bethesda, Md., 1979. 

---