Mark Corson

By O. Inog. Texas A&M University, Texarkana. 2018.

See if you can follow the calculation below purchase zanaflex 2mg online, using the table below zanaflex 4 mg low cost, to derive the relative resistance of the arterioles vs generic 4 mg zanaflex otc. Total Length Total (Mm) Cross- (Cm) Volume section (Cm²) al Area (Cm²) Aorta 10 1 0. To compare the resistance of the arteriolar bed to that of the capillary bed, we must start with the resistances of a single arteriole and capillary: Rart = (8/)Lart/rart4 Rcap = (8/)Lcap/rcap4 Taking the ratio between the two allows several factors to cancel out (we will assume that viscosity remains constant - a topic to be discussed later. However, the total resistance of a vascular bed is the combination of the resistances of all the individual vessels, which are organized in parallel. Thus, the total resistance is equal to the resistance of a single vessel divided by the number of vessels. Rart(total) = Rart/#arts Rcap(total) = Rcap/#caps Rart(total)/Rcap(total) = (Rart/Rcap)(#caps/#arts) Rart(total)/Rcap(total) = ( / )( / ) ~ 1. Given the larger cross-sectional area of the capillary bed and thus the much greater number of capillary vessels, the total resistance works out to be greater in the arteriolar bed by approximately 50%. Table 9 - Relative Resistance to Flow in the Vascular Bed: Calculated from Table 6 Poiseuille’s Law Aorta 4% Venules 4% Large arteries 5% Terminal veins 0. In the previous section we presented the conservation of mass and the resulting tradeoff between cross-sectional area and fluid velocity. In this section we will discuss the conservation of energy, where there is a balance between the potential energy and the kinetic energy of a fluid. This balance produces a tradeoff between pressure, a measure of potential energy, and velocity, a measure of kinetic energy. This will add to our understanding of the relationships among pressure, flow, velocity, and vessel geometry. Going back to our hot tub example, it takes "pressure work" to squeeze in under that pile in the tub. From the conservation of energy, the total energy (E) must remain constant as blood flows through the vascular tree. This, however, ignores any loss of energy due to frictional forces, which only applies over short distances where resistance is negligible. Just as we approximate the potential energy of a ball when we drop it from a height as equal to its kinetic energy when it hits the ground, we are applying conservation of energy to blood flow in order to gain a qualitative understanding of the relationship between pressure and velocity. This can be simplified by dividing by V: E/V = P + 1/2 v2 = constant Physics of Circulation - Michael McConnell, M. Equating the energies at two different points in the circulation yields: P1 + 1/2 v12 = P2 + 1/2 v22 G. First of all, gravity affects the hydrostatic pressure of any fluid, as we discussed at the very beginning: Pgrav = gd This causes the pressure to increase with depth, i. Note that the right atrium is used as the reference or zero point for the circulation, which is roughly the level where a blood pressure cuff is placed. While gravity does affect the hydrostatic blood pressure, that is not what determines blood flow. It is often assumed that pressure drives blood flow, such as from the high pressure arteries to the low pressure veins. If it were that simple then why, looking at the figure above, does blood flow from the aorta to the arteries in the feet, where the pressure is greater? Any increase in hydrostatic pressure from gravity is balanced by a decrease in gravitational potential energy and vice versa. Blood flows from the arteries to the veins because the total potential and kinetic energy is greater in the arteries than in the veins. Blood vessels are compliant, not rigid tubes, and can distend and collapse to changes in pressure. The farther above the heart the lower the hydrostatic pressure, and thus the more collapsed (less distended) the vessels are. Therefore, gravity does not effect the direction of blood flow, but it does decrease the hydrostatic pressure above the heart - decreasing vessel size, increasing resistance, decreasing flow - potentially resulting in ischemia. Previously we talked about resistance as an important property of the circulation. Another important physical property is compliance, which is the ability of a vessel to change its size relative to the pressure of the fluid inside it. On the arterial side, the heart pumps out a bolus of blood into the proximal or "elastic" arteries, which can distend and accommodate the ejected blood. The arteries store up energy as they distend and then return that energy when they elastically recoil, as shown in the figure below. If the arteries were stiff instead of compliant, the heart would have to generate a much higher pressure to eject an equal volume of blood, as though banging into a brick wall instead of hitting a wall made of rubber. Thus, individuals with less compliant arteries, as occurs with aging, have a higher pulse pressure (the difference between systolic and diastolic pressures) compared to individuals with very compliant arteries who have lower pulse pressure. The overall effect of arterial compliance is to reduce the work of the heart and provide a smooth, steady flow. The veins are also compliant, but they operate in a much lower pressure range, as shown below. Small changes in pressure on the venous side result in significant changes in vessel size and therefore substantial changes is venous blood volume. Thus, the compliance of the veins allows them to serve as the storage site for the vast majority of the blood volume. The force causing compliant vessels to stretch and distend is usually described as wall tension or wall stress.

Mice having prenatal exposure to the drug show reduced social interaction zanaflex 2 mg with mastercard, and males are more aggressive than normal buy zanaflex 2 mg on line. Clinicians have observed alprazolam to increase the hormone that prepares female breasts for milk production 2mg zanaflex. When combined with the pain reliever tramadol and the antidepressant citalopram, alprazolam has been known to cause excessive milk flow. Alprazolam passes into milk, and nursing is not recommended for mothers taking the drug. In one case an infant even exhib- ited drug withdrawal symptoms when a nursing mother who was receiving alprazolam ceased nursing. These mushrooms are found in much of the Northern Hemisphere and are known to grow elsewhere. Due to the possibility that an effective dose is close to a poisonous dose, and because of variations in potency, these mush- rooms are easily poisonous and have even been mixed with milk as bait to kill flies. Persons seeking amanita sometimes accidentally ingest Amanita phal- loides, also called Death Cap and Death Cup, which can be deadly poisonous to the kidneys and liver. Confusion with other dangerous mushrooms has also harmed people seeking Amanita muscaria. The Amanita muscaria mushroom has been used to treat alcohol overdose and to relieve nervousness, fever, and pain of sore throat, nerves, and joints. The natural product contains muscimol, a chemical that initially acts as a stim- ulant but that can later produce temporary loss of muscular control as the drug action proceeds. In various animal species muscarine chloride can cause spasms and constrictions and lower blood pressure. The relevance of those studies to humans is unclear; for example, a dose that would poison a human leaves a monkey unfazed. The ibotenic acid in amanita can produce hallucinations; a case report mentions visual hallucinations lasting for days after ingesting the mushroom. The mush- room is said to produce euphoria and to cause changes in sensory perceptions. Some persons consume the fungus for spiritual purpose, a practice that some authorities date back to ancient Buddhist times, with the Buddhists perhaps learning the custom from still older examples among forest peoples in north- ern Europe and Asia. One user describes the experience as lacking in feelings of hap- piness, or love, or sexual impulses—a lack that sets amanita apart from many drugs that are used recreationally. A scientist who engaged in self- experimentation had similar results of emptiness. Of 6 subjects who received the mushroom in an experiment, all were nauseated, 2 vomited, 1 had hal- lucinations, and several had sensory distortions. The supervising researcher wondered if variations in supplies of the natural product explained why the experiment’s results differed so greatly from hallucinations and pleasures reported by other persons. Personality, ex- pectations, and surrounding environment can shape the experience. A re- searcher interviewed 18 persons who ate Amanita muscaria or Amanita pantherina; half had eaten the mushrooms deliberately, and half thought they were consuming something else. In contrast, the mushroom’s effects were enjoyed by every individual who deliberately ate it. Because active chemicals from the natural product are excreted into urine, people can dose themselves again by drinking their own urine, a dosage method that may horrify Americans but that a few other cultures have ac- cepted calmly. Unwanted amanita effects can include twitching, cramps, abdominal dis- comfort, sweating, nausea, vomiting, diarrhea, dizziness, confusion, rapid heartbeat, difficulty in moving around, high body temperature, and convul- sions. Users can become manic and then sleepy, with those conditions alter- nating back and forth until a person collapses. Scientific journals contain many articles about brain damage caused by ibotenic acid, although conditions of experiments do not necessarily duplicate what happens when mushrooms are eaten. A person who received a dose of ibotenic acid in an experiment de- veloped a headache for two weeks. Under laboratory conditions amanita ex- tracts cause red blood cells to clump together. They are about the size of a cherry and come from palm trees in the Indian Ocean region, grown in countries such as India, China, and the Philippines. The product is used not only as a drug but also as a dye and in the leather tanning industry. Drug use of areca nut is common in South Africa, India, Taiwan, and other areas of South Asia and the Pacific basin. The product has been unfamiliar in the United States, but is available and is used in some immigrant communities. Areca nut is a popular recreational stimulant relieving tension and produc- ing euphoria, regularly used by perhaps 200 million to 600 million persons, making it one of the most popular substances in the world. Effects may be unpleasant for new chewers: nausea, dizziness, burning sensation in the mouth, a closing sensation in the throat. As with alcohol, in lands ranging from India to New Guinea areca nut has a place in religious and other ceremonies (engagements to marry, offerings to spirits), but the product’s main use is secular. In some places, areca nut is a social lubricant, much as beer is used in the United States. Paraphernalia involved with consuming areca nut may be either utilitarian or highly decorated functional artwork. As with tobacco quids, users typically spit out areca nut juice, staining walls or other targets. Because such a practice may potentially promote the spread of disease, in some places large cans are lined with plastic bags and used as spittoons.

Patients should be informed that tablets should not be removed from blisters until immediately before administration generic zanaflex 4mg on-line. Deterioration It is important to be familiar with the normal aspects of each drug (colour purchase zanaflex 2 mg mastercard, odour purchase 4mg zanaflex free shipping, solubility, consistency) in order to detect changes, which may indicate its deterioration. It is important to know that deterioration does not always lead to a detectable external modification. The principal consequence of deterioration is a reduction of therapeutic activity, which leads to more or less grave consequences for the individual and/or community. For example, the use of expired antibacterials does not cure an infection and also favours the emergence of resistant strains. It is not recommended to compensate for a possible reduction of activity by a random increase in the usual dose, as there is a real danger of overdose when using toxic drugs. In time, certain drugs undergo a deterioration leading to the development of substances much more dangerous, thus an increase in toxicity. Tetracycline is the principal example: the pale, yellow powder becomes brownish and viscous, its use therefore being dangerous even if before the expiry date. An increase in allergen strength has been observed in certain drugs such as penicillins and cephalosporins. Updated: February 2017 Drug quality and storage Suppositories, pessaries, creams and ointments that have been melted under heat should not be used. Oral rehydration salts may be used as long as they keep their aspect of white powder. Humidity transforms them into a compact mass, more or less brownish and insoluble. Expiration Drugs deteriorate progressively and according to various processes, even if stored in adequate conditions. In most countries, regulations impose an obligation on manufacturers to study the stability of their products in standardised conditions and to guarantee a minimum shelf life period. The expiry date indicated by manufacturers designates the date up to and including which the therapeutic effect remains unchanged (at least 90% of the active ingredient should be present and with no substantial increase in toxicity). The expiry date indicated on the label is based on the stability of the drug in its original and closed container. Expired drugs Expiry dates are to be respected due to legal obligations and considerations of therapeutic responsibility. In cases where the only available drugs have expired, a doctor may be led to take on the responsibility of using these drugs. It is evident that a drug does not become unfit for consumption the day after its expiry date. If a product has been stored in adequate conditions (protected from humidity and light, packaging intact and at a medium temperature) and if modification of aspects or solubility have not been detected, it is often preferable to use the expired drug than to leave a gravely ill patient without treatment. Expiry dates for drugs that require very precise dosage should be strictly respected due to a risk of under-dosage. This is the case for cardiotonic and antiepilectic drugs, and for drugs that risk becoming toxic, such as cyclines. Destruction of expired or unusable drugs and material It is dangerous to throw out expired or unusable drugs or to bury them without precaution. Limiting the use of injectable drugs Numerous patients demand treatment with injectable drugs, which they imagine to be more effective. Certain prescribers also believe that injections and infusions are more technical acts and thus increase their credibility. When both oral and injectable drugs are equally effective, parenteral administration is only justified in case of emergency, digestive intolerance or when a patient is unable to take oral medication. Oral drugs should replace injectable drugs as soon as possible during the course of treatment. Limiting the use of syrups and oral suspensions Taking liquid drugs is often easier, especially for young children and more so if they are sweetened or flavoured. It is, however, recommended to limit their use for numerous reasons: – Risk of incorrect usage Outside of hospitals, determining the correct dosage is hazardous: spoons never contain standard volumes (soup spoons, dessert spoons, tea spoons). Oral suspensions should be prepared with a specified amount of clean water, and well shaken prior to administration. Some oral suspensions must be kept refrigerated; their storage at room temperature is limited to a few days, and with syrups there is a risk of fermentation. Confusion between cough mixtures and antibacterial suspensions or syrups is common. Even using a powder for subsequent reconstitution, the costs may be 2 to 7 times higher than an equivalent dose due to the cost of the bottle itself and higher transportation costs due to weight and volume. Prescription, cost, compliance Studying the choice of treatment regimens The choice of a treatment regimen often influences compliance and cost. The shortest and least divided (1 to 2 doses per day) treatments are most often recommended. Considering non-essential medicines and placebos In developing countries as in industrialised countries, patients with psychosomatic complaints are numerous. The problems that motivate their consultations may not necessarily be remedied with a drug prescription. Is it always possible or desirable to send these patients home without a prescription for a symptomatic drugs or placebo? When national drug policy is strict and allows neither the use of placebos nor non-essential symptomatic drugs, other products are often used in an abusive manner, such as chloroquine, aspirin, and even antibacterials. This risk is real, but seems less frequent, which makes the introduction of placebos on a list of essential drugs relevant. Their composition generally corresponds to preventive treatment of vitamin deficiency and they have no contra–indications.