By B. Roy. Amherst College. 2018.
Photopeak In an ideal situation cheap arcoxia 90mg with visa arthritis in dogs legs treatment, if the g-ray photon energy is absorbed by the photo- electric mechanism and each g-ray photon yields a pulse of the same height arcoxia 90 mg visa infective arthritis definition, then each g-ray would be seen as a line on the g-ray spectrum (Fig. In reality, the photopeak is broader, which is due to various statistical vari- ations in the process of forming the pulses. Because 20–30 light photons are produced for every keV of g-ray energy absorbed, there is a statistical variation in the number of light photons produced by the absorption of a given g-ray energy in the detector. As already stated, 7 to 10 light photons are required to release 1 to 3 photoelectrons from the photocathode. Therefore, the number of pho- toelectrons that one g-ray will produce may vary from one event to another. All of the preceding statistical ﬂuctuations in generating a pulse cause a spread in the photopeak (see Fig. Compton Valley, Edge, and Plateau When g-rays interact with the NaI(Tl) detector via Compton scattering and scattered photons escape from the detector, the Compton electrons result 90 8. A typical spectrum of the 662-keV g-ray of 137Cs illustrating the photopeak, Compton plateau, Compton edge, Compton valley, backscatter, characteristic lead K x-ray, and barium K x-ray peaks. The Compton electrons, however, can have variable energies from zero to Emax, where Emax is the kinetic energy of those electrons that are produced by the 180° Compton backscattering of the g-ray photons in the detector. At relatively high photon energy, Emax is given by the photon energy minus 256keV (Eq. Thus, the g-ray spectrum will show a continuum of pulses correspond- ing to Compton electron energies between zero and Emax. The peak at Emax is called the Compton edge, and the portion of the spectrum below the Compton edge down to about zero energy is called the Compton plateau (see Fig. The portion of the spectrum between the photopeak and the Compton edge is called the Compton valley, which results from multiple Compton scattering of a g-ray in the detector yielding a narrow range of pulses in this region. The relative heights of the photopeak and the Compton edge depend on the photon energy as well as the size of the NaI(Tl) detector. At low ener- gies, photoelectric effect predominates over Compton scattering, whereas at higher energies the latter becomes predominant. In larger detectors, g- rays may undergo multiple Compton scattering, which can add up to the absorption of the total photon energy identical to the photoelectric effect. This increases the contribution to the photopeak and decreases to the Compton plateau. Characteristic X-Ray Peak Photoelectric interactions of the g-ray photons in the lead shield around the detector can lead to the ejection of the K-shell electrons, followed by tran- Gamma-Ray Spectrometry 91 sition of electrons from the upper shells, mainly the L shell, to the K shell. The difference in binding energy between the K-shell electron (~88keV) and the L-shell electron (~16keV) appears as lead K x-ray of ~72keV. These characteristic x-ray photons may be directed toward the detector and absorbed in it and may appear as a peak in the g-ray spectrum (see Fig. These photons can be reduced by increasing the distance between the detector and the shielding material. Backscatter Peak When g-ray photons, before striking the detector, are scattered at 180° by Compton scattering in lead shielding and housing, and the scattered photons are absorbed in the detector, then a peak, called the backscatter peak, appears in the g-ray spectrum (see Fig. This peak can be mostly eliminated by increasing the distance between the shield and the detector. Iodine Escape Peak Photoelectric interaction of g-ray photons with iodine atoms of the NaI(Tl) detector usually results in the emission of characteristic K x-rays. These x- ray photons may escape the detector, resulting in a peak equivalent to photon energy minus 28keV (binding energy of the K-shell electron of iodine). This is called the iodine escape peak, which appears about 28keV below the photopeak (Fig. This peak becomes prominent when the energy of the photon is less than about 200keV, because, at energies above Fig. A spectrum of 111In with 171- and 245-keV photons showing a coincidence (sum) peak at 416keV. The b+- particles are annihilated to produce two 511-keV photons, which appear as photopeaks in the g-ray spectrum.
When one looks at a particular colour for a long time and then turns one’s glance to another object order 60mg arcoxia with visa arthritis in feet fingers, this object seems to have the colour one has been looking at (459 b 11–13) generic arcoxia 90 mg overnight delivery arthritis in neck pinched nerve. When one has looked into the sun or at a brilliant object and subsequently closes one’s eyes, one still sees the light for some time: at ﬁrst, it still has the original colour, then it becomes crimson, then purple, then black, and then it disappears (459 b 13–18). When one has been exposed to strong sounds for a long time, one becomes deaf, and after smelling very strong odours one’s power of smelling is impaired (459 b 20–2). When a menstruating woman looks into a mirror, a red stain occurs on the surface of the mirror, which is difﬁcult to remove, especially from new mirrors (459 b 23–460 a 23). Wine and unguents quickly acquire the odours of objects near to them (460 a 26–32). While in earlier scholarship the authenticity of the passage was disputed, the discussion now focuses on the following issues: (1) the problem of the passage’s obvious counterfactuality; (2) is the theory of menstruation as expounded here in accordance with what Aristotle says elsewhere? Brieﬂy summarised, my view is (1) that what seems to be underlying the passage is a traditional belief (perhaps derived from magic or midwives’ tales) in the dangerous and polluting effects of menstrual blood, and that Aristotle must have accepted this story without checking it because he felt able to provide an explanation for it; such beliefs were not uncommon regarding menstruation (although most of the evidence dates from the Roman period); (2) there is no inconsistency regarding the cause of menstruation, for in 460 a 6–7 the words di taracn kaª flegmas©an a¬matikn must be connected with ¡ diafor... When one is under the inﬂuence of strong emotions, one is very susceptible to sensitive illusions (460 b 4–16). When one crosses two ﬁngers and puts an object between them, it is as if one feels two objects (460 b 22–3). When one is on a ship which is moved by the sea and looks at the land, it is as if the land moves (460 b 26–7). Weak stimuli of pleasure and pain are extruded by stronger ones and escape our attention (461 a 1–3). Dreams occur in a later stage of sleep; they are often distorted and unclear, but sometimes they are strong (461 a 18–27). Melancholics, drunk people and those suffering from fever have confused and monstrous dream images (461 a 21–2). When one presses a ﬁnger under one’s eye, one single object appears double (462 a 1). Sometimes, during sleep, one is aware of the fact that one is dreaming (462 a 2–8). At the moment of falling asleep and of awakening, one often sees images (462 a 10–11). Young people see in the dark all kinds of appearances when their eyes are wide open (462 a 12–15). In situations of half-sleep, one can have weak perceptions of light and sounds from one’s environment (462 a 19–25). Many people never had a dream in their whole lives; others ﬁrst got them after considerable advance in age (464 b 1–11;cf. This is a substantial list of empirical claims, some of which testify to Aris- totle’s sharp observational capacities (for example, nos. However, we also ﬁnd claims that are highly questionable from a modern point of view or for which the empirical basis can only be said to be very weak (e. It is difﬁcult to decide to what extent these ‘data’ (phainomena or sumbainonta, as Aristotle would call them) are derived from deliberate and purposeful observation by Aristotle and his pupils themselves, or just from common human experience (on the list, observations 15 and 25 are also found in other biological works of Aristotle, but they are evidently only a minority). Moreover, we should certainly take into account the pos- sibility that Aristotle has borrowed some of these data from other scientiﬁc writings, for example the psychological works of Democritus (whom Aris- totle mentions in Div. However, since this tradition has only been preserved in fragments, it is difﬁcult to assess the extent of his dependence on earlier sources. Yet when looking more closely at the way in which these empirical ‘data’ are used in Aristotle’s argument in On Dreams, it becomes clear that the treatise goes far beyond the level of empirical fact-ﬁnding. Aristotle does not present his theory as being built up, so to speak, inductively on the basis of a number of observations; on the contrary, the three research questions mentioned above ((i), (ii) and (iii)) are treated in a systematical and deductive way, and empirical ‘data’ are mentioned in the course of this theoretical argument – often in the form of examples or analogies – in order to support or clarify opinions and presuppositions which Aristotle already seems to take for granted. And although Aristotle’s style of reasoning seems very cautious and essayistic – the ﬁrst chapter, for example, is highly aporetic25 – it is, in fact, rather dogmatic. The general impression one gets is that empirical evidence is primarily mentioned when it suits the argument – and if not, it is either ignored or explained away in a questionable manner. Thus at the end of On Dreams, it turns out that the three questions raised at the beginning are to be answered as follows: (i) Dreams belong to the sensitive part of the soul qua imaginative part (459 a 21); dreaming is not an operation of sense-perception but of ‘imag- ination’, which is deﬁned by Aristotle as ‘the movement which occurs as a result of actual perception’ (459 a 17–18). This deﬁnition, together with Aristotle’s use of the words phantasia, phantasma, and phainesthai,isin broad agreement with his general theory of ‘imagination’ in On the Soul, to which he explicitly refers (459 a 15).
Sprouted grains are growing in popularity quality 120mg arcoxia arthritis in neck bone spurs, but I know of no research that clearly shows they have a higher nutrient content or are less sensitizing than whole grains cheap 120 mg arcoxia types of arthritis in back. When sprouting some of the starches turn to sugars—similar to what occurs during fermentation of grains in the traditional production of sourdough breads. That said, if you think you are sensitive to a grain, try a sprouted version for a month and see if you feel better. Extra-virgin olive oil is rich in monounsaturated fatty acids and phenolic antioxidant compounds. It is believed to be cardioprotec- tive and a good source of stable monounsaturated fatty acid. The more dark green and pungent the extra-virgin olive oil, the greater the concentration of antioxidant phenolic compounds. Compare these to the “bad” oils, which include refined fats, hydrogenated vegetable oils, or trans-fatty acids. Aside from be- ing calorie-dense foods and having more than twice the calories as carbohydrates and proteins (nine calories versus four calories per gram), trans-fatty acids get incorporated into the fatty cell membrane and can alter cell-to-cell communication, causing cel- lular dysfunction. Refined oils are exposed to more heat and can have more lipid peroxides (oxidized fat), which can damage tissue, including arteries. Hydrogenation, which adds hydrogen atoms to make the polyunsaturated fat more stable at room temperature, is not healthy either. I recommend keeping free oils to a minimum, even extra-vir- gin olive oil, flaxseed oil, or fish oil. Adding a food component that is more than twice the calories of an equivalent weight in carbohydrate or protein doesn’t make a lot of sense to me. To function properly the body requires several liters of water per day to avoid dehydration. This amount varies depending on the level of activity, temperature, humidity, and other factors. Many health experts recommend six to eight glasses of water daily as the minimum to maintain proper hydration, but the scientific backing for this recommendation is questionable. Sometimes the best way to really get a feel for whether something is good for you or not is to go on it completely, then off of it. If you fill containers at work and at home and then put them in the refrigerator, you may be more likely to drink them than by filling up on demand. Teas All teas (green, white, black, Oolong) have polyphenolic antiox- idant plant compounds in them called catechins, which belong to the flavonoid family. Green teas have received most of the notoriety and have been studied with positive effects on different chronic diseases, such as cardiovascular disease, cancer, and diabetes, and may even enhance fat loss. If you add a creamer or milk to the tea, however, you may be negating some of the effectiveness of these catechins. As I have admitted, the healthiest cultures in the world eat small amounts of animal foods. If you do eat meat, eat free-ranged, grass-fed, antibiotic-free animals or hunted wild game. Grass-fed, or grazing animals, take on the fat content of the vegeta- tion they eat, which generally has more omega-3 fatty acids and less omega-6 fatty acids. The need to take supplemental fish oils can be reduced dra- matically if you were to eat fewer foods that concentrate omega-6 fatty acids (arachidonic acid, linoleic acid), as in meat, egg, and dairy fat especially from animals fed grain (corn, wheat, etc. Grocery Shopping in the Fast Lane To shop healthfully is very simple and, in the right store, can be easily done in less than a half-hour with some very basic principles. While I am a big supporter of organic foods and eating seasonally and locally, I think it is incorrect to say America can’t improve its health dramatically by shopping for non-organic whole food in the basic grocery store. To improve health, you first have to stop eating processed foods that do you no good, and even harm you, then eat quality foods that are good for you. Shop the outside, or “perimeter,” of the grocery store where the whole, unprocessed foods are (fruit, vegetables, lean meats, etc. Buy the basics: vegetables (raw/frozen); fruit (raw/frozen); raw nuts and seeds; beans (canned/packaged); whole grains and sprouted whole grain (try non-glutinous whole grains such as brown rice, quinoa, millet, amaranth, buckwheat); water, mineral water, teas, and real juices (100 percent juice); ani- mal foods (optional): eggs, fish, lean fowl, and meat (free- ranged or grass-fed if possible). If you buy oils, get extra-virgin olive oil and/or cold-pressed canola oil for cooking and ground flaxseed or cold-pressed vegetable oils for salads and for cold sauces.
Hence discount 120mg arcoxia with amex arthritis relief cream australia, making contact with local health visitors and delivering dental health messages via mother and toddler groups can be useful strategies 90 mg arcoxia otc arthritis pain for dogs treatment. Key Points • Parents should be encouraged to bring their children for a dental check-up as soon as the child has teeth (around 6 months of age). Ledermix) may be useful beneath such dressings, and over exposures/near-exposures of the pulp. The pulp chamber of abscessed teeth can sometimes be accessed by careful hand excavation, in which case placing a dressing of dilute formocresol on cotton wool within the pulp chamber will frequently lead to resolution of the swelling and symptoms. An acute and/or spreading infection or swelling may require the prescription of systemic antibiotics, although there is little rationale for the use of antibiotics in cases of toothache without associated soft tissue infection/ inflammation. Dental infection causing significant swelling of the face, especially where the child is febrile or unwell, constitutes a dental emergency and consideration should be given to referral to a specialized centre for immediate management. Therefore, early diagnosis and prompt instigation of appropriate treatment is important. Preschool children should be routinely examined for dental caries relatively frequently (at least 2-3 times per year). Approximal caries is common in primary molars so, in children considered to be at increased risk of developing dental caries and where posterior contacts are closed, a first set of bitewing radiographs should be taken at 4 years of age, or as soon as practically possible after that (Fig. In such children consideration should be given to repeating bitewings at least annually. The caries in the upper right molars would be clinically obvious but the early approximal lesions in the lower left molars would not. Bitewing radiographs not only enable an accurate diagnosis, but early lesions can be compared on successive radiographs to enable a judgement to made about caries activity and progression. There is often a failure to appreciate that those aspects of care we refer to as prevention are actually a fundamental part of the treatment of dental caries. Repairing the damage caused by dental caries is also important, but this will only be successful if the causes of that damage have been addressed. A structured approach to prevention should form a key part of the management of every preschool child. Key Point • Preventive measures are the cornerstone to the successful treatment of dental caries in children. For children considered to be at low risk of developing caries a toothpaste containing 450-600 p. Toothpastes with a lower fluoride concentration are available, but there is some question about their efficacy. Many authorities now support the prescribing of toothpastes containing higher concentrations of fluoride (around 1000 p. Where higher concentration toothpastes are prescribed for preschool children, parents should be counselled to ensure that brushing is supervised (see Section 7. Key Point • In areas without optimum levels of fluoride in the water supply, fluoride toothpaste is the most important method of delivering fluoride to preschool children. Such supplementation is only maximally effective if given long term and regularly. Unfortunately, studies have shown that long-term compliance with daily fluoride supplement protocols is poor. Parental motivation and regular reinforcement are essential for such measures to be effective. Dosage should follow the protocol advised by the British Society of Paediatric Dentistry (Table 7. No supplements should be prescribed if the water fluoride level is greater than 0. Professionally applied fluorides Site-specific application of fluoride varnish can be valuable in the management of early, smooth surface and approximal carious lesions (Fig. Hence, when using these products in young children great care should be taken to avoid overdosage (see below). Fluoride overdosage A dose of 1 mg of F/kg body weight can be enough to produce symptoms of toxicity and a dose of 5 mg of F/kg is considered to be potentially fatal. Subsequently, depression of plasma calcium levels results in convulsions, and cardiac and respiratory failure.
If so safe arcoxia 60 mg juvenile arthritis in dogs, the sample will have characteristics that are only somewhat similar to those of the population purchase arcoxia 60mg with mastercard arthritis diet eating plan, and although may be 500, the sample mean will not be 500. In the same way, depending on the scores we happen to select, any sample may not be perfectly representative of the population from which it is selected, so the sample mean will not equal the population mean it is representing. The statistical term for communicating that chance produced an unrepresentative sample is to say that the sample reflects sampling error. Sampling error occurs when random chance produces a sample statistic (such as X) that is not equal to the popula- tion parameter it represents (such as ). Sampling error conveys that the reason a sam- ple mean is different from is because, by chance, the sample is unrepresentative of the population. That is, because of the luck of the draw, the sample contains too many high scores or too many low scores relative to the population, so the sample is in error in representing the population. The problem is that then the sample appears to come from and represent that other population. Thus, although a sample always represents some population, we are never sure which population it represents: Through sampling error the sample may poorly represent one population although it doesn’t look like it represents that one, or the sample may accurately represent some other popula- tion altogether. Therefore, we should have obtained a sample mean of 500 if our sample was perfectly representative of this population. Maybe because of the luck of the draw, we selected too many students with high scores and not enough with low scores so that the sam- ple mean came out to be 550 instead of 500. Thus, it’s possible that chance produced a less than perfectly representative sample, but the population being represented is still that ordinary population where is 500. After all, these are Prunepit students, so they may belong to a very different population of students, having some other. For example, maybe Prunepit students belong to the population where is 550, and their sample is perfectly representing this population. The solution to this dilemma is to use inferential statistics to make a decision about the population being represented by our sample. The next chapter puts all of this into a research context, but in the following sections we’ll examine the basics of deciding whether a sample represents a particular population. Therefore, we can determine whether our sample is likely to come from and thus represent a particular population. If chance is likely to produce our sample from the population, then we decide that our sample does come from and represent that population, although maybe with a little sampling error. However, if chance is unlikely to produce our sample from the population, then we decide that the sample does not represent that population, and instead represents some other population. It’s possible that some quirk of chance produced such an unrepresentative sample, but it’s not likely: I type errorless words only 20% of the time, so the probability of an errorless paragraph is extremely small. Thus, because chance is unlikely to produce such a sample from the population of my typing, you should conclude that the sample represents the population of a competent typist where such a sample is more likely. Deciding Whether a Sample Represents a Population 195 On the other hand, say that there are typos in 75% of the words in the paragraph. This is consistent with what you would expect if the sample represents my typing, but we have a little sampling error. Although you expect 80% typos from me over the long run, you would not expect precisely 80% typos in every sample. Rather, a sample with 75% errors seems likely to occur simply by chance when the population of my typing is sampled. Therefore, you can accept that this paragraph represents my typing, albeit somewhat poorly. As you’ve seen, we determine the probability of a sample mean by computing its z-score on the sampling distribu- tion of means. Therefore, think of a sampling distribution as a “picture of chance,” showing how often chance produces different sample means when we sample a particular raw score population. The next step is to calculate the z-score for our sample mean of 550 so that we can determine its likelihood.
A similar distinction between more or less theoretical approaches in the sciences is made in Metaphysics 1 discount arcoxia 60mg otc arthritis in back l4 l5. Perhaps the distinction of charientes iatroi also has a social aspect arcoxia 120mg lowest price arthritis fingers crooked, in that they belong to a higher class. The use of the word pepaideumenos by Aristotle usually has to do with an awareness of the methodological limits of a certain discipline (see Jori 1995), whereas the word charieis is used to refer to people who enrich their discipline by crossing its boundaries; on the other hand, in the passage from Nicomachean Ethics 196 Aristotle and his school Aristotle also recognises that the latter are often more successful in practical therapy than the former. The passage from On Respiration further mentions differences between distinguished doctors and distinguished students of nature. These are not explained by Aristotle, but they probably have to do with the difference between theoretical and practical sciences mentioned above (differences of interest, such as the lack of therapeutic details in the account of the natural scientist, as well as different degrees of accuracy). Moreover, his remark that the more distinguished natural philosophers ‘end by studying the principles of health and disease’, whereas distinguished doctors are praised for starting with principles derived from natural science, seems to imply a certain hierarchy or priority of importance, which is hardly surprising given Aristotle’s general preference for theoretical knowledge. This would correspond with the fact that the discussion of health and disease (Peri hugieias kai nosou) was apparently planned by Aristotle at the end of the series of treatises which we know as the Parva naturalia. The treatise has not survived, and it is not even certain that it was ever written. But it would no doubt refrain from worked-out nosological descriptions and from extended and detailed prescriptions on prognostics and therapeutics. He obviously approves of doctors who build their practice on principles of natural science, but he also acknowledges that more empirically minded doctors often have greater therapeutic suc- cess. He further praises those liberal-minded students of nature (among whom he implicitly counts himself) who deal with the principles of health and disease. He obviously prefers the study of nature rather than medicine, because the former is concerned with universals, the latter with particu- lars, and because the former reaches a higher degree of accuracy, but he quoted above Aristotle credits the liberal-minded student of politics with a similar awareness of a limited degree of accuracy in his interest in psychology: one might say that this implies a comparable awareness with the distinguished doctors with regard to their use of principles derived from the study of nature. Aristotle on sleep and dreams 197 also recognises that even medicine may contribute to the study of na- ture (a fact he hardly could ignore, given the large amount of anatomi- cal and physiological information preserved in the Hippocratic writings). Having considered his theoretical position on the relationship between medicine and the study of nature, let us now turn to the practice of the ‘inquisitive non-specialist’ Aristotle in his discussion of the prognostic value of dreams. For although the distinguished doctors’ opinion is a reputable view and as such an important indication that there are, in fact, dreams which play the part of signs of bodily events, the rational justiﬁcation (eulogon) for the natural scientist’s sharing this view does not lie in the doctors’ authority, but in the fact that he can give an explanation for it. The explanation which follows makes use of empirical claims but is also based on Aristotle’s own theory of dreams. For the fact is that movements occurring in the daytime, if they are not very great and powerful, escape our notice in comparison with greater movements occurring in the waking state. But in sleep the opposite happens: then it is even the case that small movements appear to be great. This is evident from what often happens during sleep: people think that it is lightning and thundering, when there are only faint sounds in their ears, and that they are enjoying honey and sweet ﬂavours when a tiny bit of phlegm is running down their throats, and that they go through a ﬁre and are tremendously hot when a little warmth is occurring around certain parts of the body. But when they wake up, they plainly recognise that these things are of this nature. Consequently, since of all things the beginnings are small, it is evident that also of diseases and of other affections which are going to occur in the body, the beginnings are small. It is obvious, then, that these are necessarily more clearly visible in sleep than in the waking state. If the dream is correctly interpreted, it can be reduced to its cause, which can be recognised as the cause of an imminent disease. Aristotle pays no attention to the rules for such a correct interpretation of dreams; he only analyses the causal structure of the relationship between the dream and the event foreseen in it. The ﬁrst is one of the corner stones of his theory of dreams as set out in On Dreams (460 b 28ff. This principle is demonstrated by means of a number of examples derived from common experience (no. The second principle is that the origins of all things (including diseases) are small and therefore belong to the category of small movements. The two principles are combined in the form of a syllogism at the end of the paragraph. These points are most relevant for an assessment of what Aristotle is do- ing in the passage under discussion. It has, of course, long been recognised by commentators that the sentence 463 a 4–5 may very well be a reference to the Hippocratic treatise On Regimen, the fourth book of which deals with dreams and which I quoted at the beginning of this chapter. Although the Hippocratic Corpus contains several examples of the use of dreams as prognostic or diagnostic clues,49 we nowhere ﬁnd such an explicit theoret- ical foundation of this as in this book. It is chronologically possible and plausible that Aristotle knew this treatise, because other places in the Parva naturalia show a close similarity of doctrine to On Regimen.
M ost episodes of repetitive ventricular tachycardia respond to intravenous drugs such as lidocaine 120 mg arcoxia free shipping treatment for arthritis in the knee at home, procainam ide or am iodarone allow ing for oral loading w ith an antiarrhythm ic agent in a m ore controlled fashion cheap 120mg arcoxia fast delivery arthritis knee weight loss. Lim itations and late com plications of third-generation autom atic cardioverter-defibrillators. Sara Thorne The m anagem ent of a pregnant w om an w ith dilated cardio- m yopathy should be considered in term s of m aternal risk, and risk to the fetus. M aternal risk This relates to the degree of ventricular dysfunction and the ability to adapt to altered haem odynam ics. They m ay thus contribute to prem ature labour • W arfarin – see Q 93 (page 196) and Q 95 (page 202). Failure of adjusted doses of sub- cutaneous doses of heparin to prevent throm boem bolic phenom ena in pregnant patients w ith m echanical cardiac valve prostheses. Sara Thorne Native or tissue valves In general, regurgitant lesions are w ell tolerated during pregnancy, w hereas left sided stenotic lesions are not (increased circulating volum e and cardiac output lead to a rise in left atrial pressure). Nitrates m ay be useful, but should be used w ith caution in those w ith aortic stenosis. M echanical valves Anticoagulation is the issue here: in particular, the risk of w arfarin em bryopathy vs risk of valve throm bosis. The patient m ust be fully inform ed, and involved in deciding her m ode of anticoagulation (m edicolegal im plications). Failure of adjusted doses of sub- cutaneous doses of heparin to prevent throm boem bolic phenom ena in pregnant patients w ith m echanical cardiac valve prostheses. The key here is to leave the m other off w arfarin for the m inim um tim e possible. An elective section is perform ed at 38 w eeks’ gestation, replacing the w arfarin w ith unfractionated heparin for the m inim um tim e possible • Severe aortic or m itral stenosis. If the m other’s life is at risk, section follow ed by valve replacem ent m ay be necessary. Controversy rem ains over w hether the follow ing patients should undergo elective Caesarean section: 1 Cyanotic congenital heart disease w ith im paired fetal grow th. Section m ay help to avoid further fetal hypoxaem ia, but at the 100 Questions in Cardiology 199 expense of excessive m aternal haem orrhage to w hich cyanotic patients are prone. A balance has to be m ade betw een a spontaneous vaginal delivery w ith the m other in the lateral decubitus position to attenuate haem odynam ic fluctuations, forceps assistance and the sm aller volum e of blood lost during this type of delivery, and the controlled tim ing of an elective section. Probably m ore im portant than the route of delivery is peri-partum planning and team w ork: delivery m ust be planned in advance, and the patient intensively m onitored, kept w ell hydrated and not allow ed to drop her system ic vascular resistance. Consultant obstetric and anaesthetic staff experienced in these conditions should be present, and the cardiologist readily available. Rachael James All anticoagulant options during pregnancy are associated w ith potential risks to the m other and fetus. Any w om an on w arfarin w ho w ishes to becom e pregnant should ideally be seen for pre- pregnancy counselling and should be involved in the anti- coagulation decision as m uch as possible. Potential risks to the fetus need to be balanced against the increased m aternal throm - botic risk during pregnancy. Anticoagulation for m echanical heart valves in pregnancy rem ains an area of som e controversy. The use of w arfarin during pregnancy is associated w ith a low risk of m aternal com plications1 but it readily crosses the placenta and em bryopathy can follow exposure betw een 6–12 w eeks’ gestation, the true incidence of w hich is unknow n. A single study has reported that a m aternal w arfarin dose 5m g is w ithout this em bryopathy risk. Conversion to heparin in the final few w eeks of pregnancy is recom m ended to prevent the delivery of, w hat is in effect, an anticoagulated fetus. Studies have been criticised for the use of inadequate heparin dosing and/or inadequate therapeutic ranges4 although a recent prospective study w hich used heparin in the first trim ester and in the final w eeks of pregnancy reported fatal valve throm boses despite adequate anticoagulation. Use in pregnancy is m ainly for throm boprophylaxis rather 100 Questions in Cardiology 201 than full anticoagulation but experience is increasing. M anagement W om en w ho do not w ish to continue w arfarin throughout preg- nancy can be reassured that conceiving on w arfarin appears safe but conversion to heparin, to avoid the risk of em bryopathy, needs to be carried out by 6 w eeks. Possible regim es include: • W arfarin throughout pregnancy until near term and then conversion to unfractionated heparin.