By M. Kadok.
However generic cialis jelly 20mg online erectile dysfunction vitamin e, the method tends to cause artifacts due to underestimation of attenuation in the thorax area proven cialis jelly 20 mg erectile dysfunction caused by steroids. The source is placed in a holder mounted at the edge of the scanner bore and the holder is rotated by a motor so that data detected by all detector pairs can be acquired cheap cialis jelly 20mg overnight delivery causes of erectile dysfunction in 20 year olds. Normally buy discount cialis jelly 20 mg line laptop causes erectile dysfunction, a blank scan is obtained at the beginning of the day without any object or patient in the scanner. Next a transmission scan is obtained with the patient in the scanner for each patient. It takes 20 to 40min for acquisition of the transmission scan depending on the source strength. Two 511-keV annihilation photons traverse thicknesses a and b of tissues of an organ. However, attenuation of the two photons depends on the total thick- ness D of the organ regardless of a and b. Other approaches include post-injection transmission scanning (transmission scan after the emission scan) and simultaneous emission/transmission scanning, but each method suffers from various disadvantages of its own. This factor is assumed to be the same for all tissues except bone, which has a slightly higher mass attenuation coefﬁcient. Use of breath hold and water-based contrast agents helps mitigate these effects, respectively. Random Coincidences Random coincidence events occur when two unrelated 511-keV photons, arising from two different positron annihilation events, are detected by a detector pair within the same time window (Fig. Random coinci- dences are largely minimized in 2-D acquisition by septa, whereas in 3-D acquisition in the absence of septa, their contribution is high causing loss of image contrast. They increase with increasing pulse-height window, coin- cidence time window, and activity [varies as the square of the activity; see Eq. Corrections for random coincidences can be made by separately mea- suring two single count rates, R1 and R2, of a radioactive source by each of the detector pair and by using the following equation, Rc = 2tR1R2 (13. In another method, two coincidence circuits are employed in which one is set at a standard coincidence timing window (e. The counts in the standard time window contain true, scatter, and random events, whereas in the delayed time window, only random events and no true or scatter coincidence events are recorded, because true and scatter photons from the same annihilation decay arrive at the detectors within the short coincidence time window. The random counts will be the same in both coincidence and delayed coinci- dence windows. The true counts are then obtained by subtracting the delayed window counts from the standard window counts. Use of faster electronics and a shorter coincidence time window are some of the physi- cal techniques that are used to minimize random events. Random events are calculated by subtracting the low activity counts (true plus scatter) from the high activity counts (true plus scatter plus random). Positron Emission Tomography Scatter Coincidences Annihilation radiations may undergo Compton scattering while passing through the body tissue and, due to high energy of 511keV, they are mostly scattered forward without much loss of energy (Hoffman and Phelps, 1986). One or both of the 511keV photons from the same annihilation event may be scattered. Note that coincident counts of scattered photons from two separate annihilation events will be consid- ered as random counts. Background of the image is increased by these radi- ations with concomitant loss of image contrast. Scattering increases with the density and depth of tissue, the density of the detector material, the activity, and the pulse-height window. The use of septa in 2-D acquisition reduces the scatter events con- siderably, but in 3-D acquisition, this becomes a problem. Dead Time The effects of dead time and pulse pile-up have been discussed in Chapter 8. The effects of high-count rates on the performance of gamma cameras have been discussed in Chapter 10. The correction for dead time loss is made by measuring the observed count rates as a function of increasing concentrations of activity. The dead time is calculated from these data and then applied to actual data obtained in the patient’s scan- ning. Uses of high-speed electronics, buffers, and pulse pile-up rejection cir- cuits are some of the techniques that are employed to improve dead time loss. An off-center event (solid line) strikes the back of the detector pair tangentially. The X-, Y-positioning of the detec- tors (dashed line) is a distance d away from the actual location of the positron anni- hilation, causing the blurring of the image. Correction can be made for this effect by measuring light in the front and back of each detector and using the difference to measure the depth of the photon interaction in the detector. It is nor- mally given by d at the face of the detector and by d/2 midway between the two detectors. A positron with energy travels a distance in tissue losing energy before it almost comes to rest and then combines with an elec- tron to produce two 511-keV photons. The locations of positron emission and annihilation are separated by the effective range of the positron (Fig. This error Rp increases with the positron energy and decreases with 18 the tissue density. Positrons at the end of their range still possess some resid- ual momentum and, therefore, the two annihilation photons are not emitted exactly 180°, but at slight deviation. This value deteriorates with the diameter of the ring and is estimated to be Ra = 0. Positrons travel a distance before annihilation in the absorber and the distance increases with positron energy. Because positrons with different energies travel in zigzag directions, the effective range is the shortest distance between the nucleus and the direction of 511-keV photons. Because there is some residual momentum associated with the positron, the two annihilation photons are not emitted exactly at 180°, but at a slight deviation from 180°. Two detectors detect these photons in a straight line, which is slightly deviated from the original annihi- lation line. If the ﬁlter backprojection method is used for reconstruction, the choice of ﬁlter with a selected cut-off frequency degrades spatial resolution. The use of block detectors rather than single detectors introduces an error in the (X, Y) positioning of the detector pair, which causes degradation of the spatial resolution. Positron Emission Tomography The transaxial spatial resolution typically ranges from 5mm to 7mm at 10 cm and the axial spatial resolution from 5. Commercial vendors give this in units of volume sensitivity, kcps/mCi/cc or cps/Bq/cc. Sensitivity depends on the geometric efﬁciency, detection efﬁciency of the detector, pulse-height window, and dead time of the detector. These factors have been discussed in detail in Chapter 10 for conventional cameras. The geometric efﬁciency depends on the distance d between the detector and the source, the diam- eter D of the ring, and the number of rings n in the scanner. Increasing the distance d and the diameter D reduces the solid angle subtended by the detector at the source and, thus, decreases the geometric efﬁciency. Noise Equivalent Count Rate As discussed in Chapter 10 under contrast, noise degrades the image con- trast and primarily arises from the statistical variation of the count rates.
Aristotle asserts that these people too cheap cialis jelly 20 mg otc impotence 19 year old, just like the irrational people discount 20 mg cialis jelly fast delivery erectile dysfunction pills otc, have a prophetic capacity which is swift discount 20mg cialis jelly otc icd 9 code erectile dysfunction neurogenic, but in them it actually is due to reason order 20mg cialis jelly fast delivery erectile dysfunction treatment natural way. Given this interpretation, Dirlmeier’s (1962a) emendation of m»non into m»nhn can be discarded. In any case n should certainly be retained, for the object of cr¦sqai (‘use’) is not tä skope±n (‘observation’), which is linguistically an awkward combination, but mantik (‘divination’; cf. The distinction between rational and irrational divination is made by Plato, Phaedrus 244 a–d; rational divination is referred to by Aristotle in Mem. Aristophanes, Wasps 515–17: katagelÛmenov mn oÔn oÉk pa¹eiv Ëpì ndrän, oÌv sÆ m»non oÉ proskune±v ll douleÅwn llhqav. Aristotle’s cautious reference to the idea, expressed by others, that divination is an pistmh lpistik (Mem. Aristotle on divine movement and human nature 255 This interpretation may seem over-subtle, but the interpretations in which m»non. To this it could be objected that perhaps they do not really belong there, and (1) we might have to clas- sify experience and habituation under the irrational form of the divination: then we would have the contrast, marked by ll, with tn p¼ toÓ l»gou (sc. However, on that interpretation (i) the connection with the previous sentence, marked by ka©, remains awkward, and (ii) it is hard to imagine how mpeir©a and sunqeia can be regarded as irrational activities, for they result in tcnh (‘technical skill’) whereas eutuchia is not founded on technical skill but on natural talent (fÅsiv) and on irrational impulses (¾rma©). Alternatively, one might consider (2) that mpeir©a is the rational form, sunqeia the irrational form of divination; but objection (i) would remain, and the word skope±n seems peculiar to rational divination; moreover it seems impossible to regard irrational eutuchia, based on natural impulses, as identical or comparable with mantik di sunqeian. In tä qeä d aÕtai we must understand a form of cr¦sqai, and tä qeä is the rc of line 32 (and of 23, 25 and 27). It is unnecessary to emend this to tä qe©w, as Verdenius (1971), following Spengel, pro- poses. Moreover, as xiv is implicitly rejected as a possible cause of eÉtuc©a in 1247 a 7–13, it is unlikely that sunqeia, which is closely connected with xiv (cf. In any case, both irrational and rational divination are caused by ¾ qe»v; also the fr»nimoi kaª sofo© use the divine movement, and this conclusion can, as we have seen above, be read as a plain reference to the distribution argument of 1247 a 28–9. Only then can it be understood that Aristotle says that God moves also (ka©) in those whose l»gov is disengaged, and that he moves more strongly («scÅein mllon)63 in those: he does not say that God does not move in the fr»nimoi kaª sofo©. First, in 1247 a 28–9 Aristotle speaks of ‘being loved’ (file±n) by the gods; eutuchia is, 63 The words «scÅein and polÅesqai seem to form a contrast here, but it remains obscure what exactly Aristotle means when he says that ‘reason is disengaged’ (l»gov polu»menov), and through what cause it is supposed to be so. The example of the blind in 1248 b 1–2 points to a physical defect, but perhaps we should not press the analogy too far (see my note 65 below). In view of this obscurity it is questionable whether the traditional reading oÕtov should be emended into oÌtwv, for this vague reference can only be to the way in which the eÉtuce±v succeed logoi Àntev. On the contrary, if rational divination did not consult God,¨ many elements in the text (lines 26–9 and 34–8) would be out of place. The difﬁculty is poluqntev toÓ pr¼v to±v e«rhmnoiv e²nai t¼ mnhmoneÓon, for which many emendations have been proposed, none of which are free from dif- ﬁculties. The simplest solution is that suggested by von Fragstein (1974) 377: poluqntev tä pr¼v to±v e«rhmnoiv e²nai t¼ mnhmoneÓon; but how can the blind be called poluqntev without further qualiﬁcation (although the aorist participle, after poluomnou, is striking)? Dirlmeier (1962a) and Woods (1982) propose tä poluqntov toÓ pr¼v to±v ¾rwmenoiv [sc. It is safer, though not free from difﬁculties either, to read poluqntov toÓ pr¼v to±v ¾rwmnoiv e²nai t¼ mnhmoneÓon. Anyhow, the point must be, as Woods (1982, 219) puts it, that ‘just as the blind man has better powers of memory as a result of lack of preoccupation with the visible, the power of divination is improved when reason is in abeyance’. Then the text runs as printed by Susemihl, who emends faner¼n into faner¼n d, but for Spengel’s conjecture in 1248 b 4 ¡ d fÅsei which is certainly wrong (see n. He is the one who succeeds in accordance with impulse, the other succeeds contrary to impulse; but both are irrational. But his contra-predestinarian remark ‘Weiterdenken darf man hier nicht, also nicht fragen, warum Gott in solchen Seelen nicht tatig wird’, is certainly¨ out of place, for God is moving in all souls: the second form also occurs with people who have the ﬁrst form, but in them its cause is different. Aristotle on divine movement and human nature 257 in the theory criticised there, a speciﬁc form of divine dispensation (qe©a mo±ra), whereas in 1248 a 32ff. Aristotle is thinking of a process which does not consist in such a divine dispensation but in people making use of a universal divine causality. The only difference is that the Eudemian Ethics explicitly mentions ‘God’ (¾ qe»v) as the starting-point (rc) of the process, whereas in On Div- ination in Sleep Aristotle seems to reject any divine inﬂuence whatsoever. But the reason for this is that in On Divination in Sleep he combats a theory which is comparable with the view, rejected in Eth. The reason why he does not explicitly mention the divine aspect of the process of interaction is that the subtleties of Eth. In the Eudemian Ethics, however, the argument does not breathe the polemi- cal atmosphere of On Divination in Sleep. It seems that Aristotle is arguing here positively in defence of a view which is unlikely to be accepted by an audience who, in accordance with the main tenets of Aristotle’s ethical the- ory, tend to reject any possible cause of human success which is not within human control (fì ¡m±n) and who will cling to a rational way to success based on l»gov and fr»nhsiv. On the other hand, it has now become clear why Aristotle repeatedly stresses the existence of an eutuchia which is based neither on reason nor on chance (a 32, 34, 39,b4), and why he explains that it is not proﬁtable for the ‘irrationally lucky’ people to use deliberation (boÅleusiv) – on the contrary, they owe their success to the very fact that their reasoning faculty is disengaged (polu»menov). In this chapter, then, I have tried to solve a problem of textual consistency both within Eth. As a result of this interpretation, the concept of eutuchia has become much less isolated from Aristotle’s ethical and theological ideas in general than used to be assumed. Other discussions of this chapter can be found in Bodeus (´¨ 1992); Verbeke (1985); Kenny (1992); and Johnson (1997). None of these publications, however, have led me to change my interpretation of the text of Eth. Whether its title, Ëpr toÓ m gennn (‘On Sterility’, ‘On Failure to Pro- duce Offspring’), is authentic or not, the work transmitted as ‘Book 10’of Aristotle’s History of Animals (Hist. It sets out by saying that these causes may lie in both partners or in either of them, but in the sequel the author devotes most of his attention to problems of the female body. Thus he discusses the state of the uterus, the occurrence and modalities of menstruation, the condition and position of the mouth of the uterus, the emission of ﬂuid during sleep (when the woman dreams that she is having intercourse with a man), physical weakness or vigour on awakening after this nocturnal emission, the occurrence of ﬂatulence in the uterus and the ability to discharge this, moistness or dryness of the uterus, wind-pregnancy, and spasms in the uterus. Then he brieﬂy considers the possibility that the cause of infertility lies with the male, but this is disposed of in one sentence: if you want to ﬁnd out whether the man is to blame, the author says, just let him have intercourse with another woman and see whether that produces a satisfactory result. There is some discussion of animal sexual behaviour in chapter 6, but compared to the rest of History of Animals, the scope of the work is anthropocentric, and the lengthy discussion of the phenomenon of mola uteri with which the work concludes is also human-orientated. Apart from numerous difﬁculties of textual transmission and interpretation of particular passages, the main issues are (1) whether the work is by Aristotle and, if so, (2) whether it is part of History of Animals as it was originally intended by Aristotle or not,4 or, if not, (3) what the original status of the work was and how it came to be added to History of Animals in the later tradition. From the eighteenth century onwards the view that the work is spurious seems to have been dominant,5 with alleged doctrinal differences between ‘Hist. These concerned issues such as the idea that the female contributes seed of her own to produce offspring, the idea that pneuma draws in the mixture of male and female seed into the uterus, the idea that heat is responsible for the formation of moles, and the idea that multiple offspring from one single pregnancy is to be explained by reference to different places of the uterus receiving different portions of the seed – views seemingly advocated in ‘Hist. In addition, arguments concerning style (or rather, lack of style), syntax and vocabulary, as well as the observation of a striking number of similarities with some of the Hippocratic writings, have been adduced to demonstrate that this work could not possibly be by Aristotle and was more likely to have been written by a medical author. This view has in recent times been challenged by at least two distin- guished Aristotelian scholars. For some briefer discussions see Aubert and Wimmer (1868) 6; Dittmeyer (1907) v; Gigon (1983) 502–3; Louis (1964–9) vol. Aristotle On Sterility 261 of Generation of Animals would beneﬁt from accepting ‘Hist. Quite recently, Sabine Follinger,¨ in her monograph on theories of sexual differentiation in an- cient thought, once again advocated scepticism with regard to the question of authenticity. It seems to me that many of Follinger’s objections to Balme’s analysis are¨ justiﬁed and that her cautious attitude to the question of authenticity is prudent, because in the present state of scholarship (i. However, this does not necessarily mean that scepticism is the only acceptable position.
In our studying experiment generic cialis jelly 20mg on-line erectile dysfunction treatment drugs, we manipulate study time because we think that longer studying causes fewer errors order cialis jelly 20mg without a prescription erectile dysfunction doctors in coimbatore. Or buy generic cialis jelly 20 mg line impotence icd 9, in an experiment to determine whether eating more chocolate causes people to blink more discount cialis jelly 20mg erectile dysfunction doctors in baltimore, the experimenter would manipulate the Understanding Experiments and Correlational Studies 23 independent variable of the amount of chocolate a person eats. You can remember the independent variable as the variable that occurs independently of the participants’ wishes (we’ll have some participants study for 4 hours whether they want to or not). Technically, a true independent variable is manipulated by doing something to par- ticipants. However, there are many variables that an experimenter cannot manipulate in this way. For example, we might hypothesize that growing older causes a change in some behavior. Instead, we would manipulate the variable by selecting one sample of 20-year-olds and one sample of 40-year-olds. Similarly, if we want to examine whether gender is related to some behavior, we would select a sample of females and a sample of males. In our discussions, we will call such variables independent variables because the experimenter controls them by controlling a characteristic of the samples. In essence, a participant’s “score” on the independent variable is assigned by the experimenter. In our examples, we, the researchers, decided that one group of students will have a score of 1 hour on the variable of study time or that one group of people will have a score of 20 on the variable of age. Conditions of the Independent Variable An independent variable is the overall variable that a researcher examines; it is potentially composed of many different amounts or categories. A condition is a specific amount or category of the independent vari- able that creates the specific situation under which participants are examined. Thus, although our independent variable is amount of study time—which could be any amount—our conditions involve only 1, 2, 3, or 4 hours. Likewise, 20 and 40 are two conditions of the independent variable of age, and male and female are each a condi- tion of the independent variable of gender. A condition is also known as a level or a treatment: By having participants study for 1 hour, we determine the specific “level” of studying that is present, and this is one way we “treat” the participants. The Dependent Variable The dependent variable is used to measure a partici- pant’s behavior under each condition. A participant’s high or low score is supposedly caused or influenced by—depends on—the condition that is present. Thus, in our studying experiment, the number of test errors is the dependent variable because we believe that errors depend on the amount of study. If we manipulate the amount of chocolate people consume and measure their eye blinking, eye blinking is our depend- ent variable. Or, if we studied whether 20- or 40-year-olds are more physically active, then activity level is our dependent variable. The behavior that is to be influenced is measured by the dependent variable, and the amounts of the variable that are present are indicated by the scores. Drawing Conclusions from Experiments The purpose of an experiment is to produce a relationship in which, as we change the conditions of the independent vari- able, participants’ scores on the dependent variable tend to change in a consistent fash- ion. To see the relationship and organize your data, always diagram your study as shown in Table 2. Each column in the table is a condition of the independent variable (here, amount of study time) under which we tested some participants. Each number in a column is a participant’s score on the dependent variable (here, number of test errors). To see the relationship, remember that a condition is a participant’s “score” on the independent variable, so participants in the 1-hour condition all had a score of 1 hour paired with their dependent (error) score of 13, 12, or 11. Likewise, participants in the 2-hour condition scored “2” on the independent variable, while scoring 9, 8, or 7 errors. Now, look for the relationship as we did previously, first looking at the error scores paired with 1 hour, then looking at the error scores paired with 2 hours, and so on. Essentially, as amount of study time increased, participants produced a different, lower batch of error scores. Thus, a relationship is present because, as study time increases, error scores tend to decrease. For help envisioning this relationship, we would graph the data points as we did pre- viously. Notice that in any experiment we are asking, “For a given condition of the in- dependent variable, I wonder what dependent scores occur? Likewise, we always ask, “Are there consistent changes in the dependent variable Diagram of an as a function of changes in the independent variable? Understanding Experiments and Correlational Studies 25 For help summarizing such an experiment, we have specific descriptive procedures for summarizing the scores in each condition and for describing the relationship. For exam- ple, it is simpler if we know the average error score for each hour of study. Notice, how- ever, that we apply descriptive statistics only to the dependent scores. Above, we do not know what error score will be produced in each condition so errors is our “I Wonder” variable that we need help making sense of. We do not compute anything about the con- ditions of the independent variable because we created and controlled them. Then the goal is to infer that we’d see a similar relationship if we tested the entire population in the experiment, and so we have specific inferential procedures for exper- iments to help us make this claim. If the data pass the inferential test, then we use the sample statistics to estimate the corresponding population parameters we would ex- pect to find. Therefore, we would infer that if the population of students studied for 1 hour, their scores would be close to 12 also. But our sample produced around 8 errors after studying for 2 hours, so we would infer the population would also make around 8 errors when in this condition. As this illustrates, the goal of any experiment is to demonstrate a relationship in the population, describing the different group of dependent scores associated with each condition of the independent variable. Then, because we are describing how everyone scores, we can return to our original hypothesis and add to our understanding of how these behaviors operate in nature. In a correlational study we simply measure participants’ scores on two variables and then determine whether a relationship is present. Unlike in an experiment in which the re- searcher actively attempts to make a relationship happen, in a correlational design the researcher is a passive observer who looks to see if a relationship exists between the two variables. Or, we would have a correlational design if we asked people their career choices and measured their personality, asking “Is career choice related to personality type? As usual, we want to first describe and understand the relationship that we’ve observed in the sample, and correlational designs have their own descriptive statistical procedures for doing this. Then, to describe the relationship that would be found in the population, we have specific correlational inferential procedures. Finally, as with an experiment, we would translate the relationship back to the original hypothesis about studying and learning that we began with, so that we can add to our understanding of nature. In an experiment, the ______ is changed by the ures participants’ behavior using the dependent researcher to see if it produces a change in partici- variable. To see if drinking influences one’s ability to drive, participants on two variables. In an experiment, the ______ variable reflects after they’ve been in a darkened room for either 10, participants’ behavior or attributes. This is an experiment because the researcher controls the length of time in the room. We measure the age and income of 50 people to independent variable is length of time, the conditions see if older people tend to make more money. This is not necessarily true (people who weigh more tend to be taller, but being heavier does not make you taller!
A 16-year-old patient visits his dentist for a patient displays flight of ideas as he jumps from routine checkup discount 20mg cialis jelly fast delivery erectile dysfunction causes natural treatment. Which of the following is associated with on using an agent that has good analgesic and lithium use? A first-year surgery intern has rotated on (E) Isoflurane numerous surgical services during the first year generic cialis jelly 20mg with amex erectile dysfunction ear, including general surgery generic 20 mg cialis jelly with amex gonorrhea causes erectile dysfunction, cardiothoracic sur- 11 order 20mg cialis jelly erectile dysfunction venous leak. A 6-year-old child was badly burned when gery, urology, surgical oncology, trauma sur- his house caught on fire. He has gotten thickness burns on approximately 40% of his quite used to liberally ordering morphine for body. This drug has (B) Myocardial infarction been associated with which of the following (C) Acute pulmonary edema adverse reactions? A 5-year-old child is admitted to the hospital (D) Malignant hyperthermia with a low-grade fever and a persistent cough (E) Distortion of reality and terrifying dreams that has resulted in vomiting episodes following prolonged coughing spells. A patient sees an otolaryngologist with com- negative, his fever has resolved, and all that is plaints of recurrent sinusitis. He is discharged from the decides to perform sinus surgery to debride the hospital by the pediatrician who recommends scarred sinus tissue. Which surgeon elects to use an agent that has good of the following does he recommend? A 28-year-old alcoholic woman learns that abdomen for their eventual incision when the she is pregnant after missing her last two men- attending physician enters the operating room strual periods. She received poor prenatal care, and asks the anesthesia resident if the patient is missing many of her appointments. Which of the following is the most tologist that cared for her child at birth learned reliable sign that surgical anesthesia has been that the mother did not refrain from her normal reached? Which of the following is the most likely (B) Amnesia consequence of such abuse to the child during (C) Loss of consciousness pregnancy? A 31-year-old lawyer is transferred to the emergency room after collapsing at a party. A 16-year-old boy is brought to the emer- complained of chest pain, and an electrocardio- gency room at 4 am by his friends, who report gram demonstrated ventricular fibrillation, for that the patient was at an all-night rave party which he received cardioversion. A close pills, which his friends thought were ‘‘ecstasy’’ friend accompanied the patient and confides in (methylenedioxymethamphetamine). Which of you that the patient was ‘‘doing’’ an illicit sub- the following describes the mechanism of this stance at the party. Venlafaxine and some tricyclic antidepressants are used in the management of chronic pain. Promethazine and prochlorperazine are two dopamine receptor blockers, without antipsychotic activity, used to treat nausea and vomiting. Trazodone is an atypical antidepres- sant that is highly sedating and has been associated with orthostatic hypotension and priapism. Both fluoxetine and paroxetine inhibit cytochrome P-450 and thus need to be used with caution as they can potentiate the action of other drugs metabolized by this system. Bupropion is an atypical antidepressant that is useful as an aid in smoking ces- sation. Mirtazapine is another atypical agent used in the treatment of depression that blocks both serotonin and a-adrenergic receptors. Buspirone is an antianxiety drug useful in situations where nonsedating agents are favored. Lithium use is associated with a fine tremor that can often be successfully man- aged with b-blockers. Likewise, the other choices are opposite what might be expected with lithium use, as patients ex- perience weight gain and hypothyroidism. Lithium has a narrow therapeutic margin, with thera- peutic doses not too much lower than toxic doses. Opioids are contraindicated in cases of head trauma, as they increase cerebral vascular pressure and may cause hemorrhage and/or herniation. Morphine is used during myo- cardial infarction, as it decreases cardiac preload and chest pain. Renal colic, pain due to a kidney stone passing through the ureter, or biliary colic, which is a similar pain associated with gallstones passing through biliary ducts, are both well managed with morphine. Dextromethorphan is an opioid isomer available in over-the-counter cough remedies. Tramadol is a weak l- opioid-receptor agonist, which also blocks serotonin and norepinephrine uptake and is used for neuropathic pain. Propoxyphene is a weak opioid agonist usually used in combination with as- pirin or acetaminophen. Loperamide is an opioid that does not cross the blood–brain barrier 148 Chapter 5 Drugs Acting on the Central Nervous System 149 and is used for the treatment of diarrhea. Nitrous oxide is an anesthetic gas that has good analgesic and sedative proper- ties without the skeletal muscle–relaxing effects. It is often used in the vignette setting but can be used along with other inhaled agents, decreasing their concentrations and thus their side effects. Enflurane produces anesthesia, hypnosis, and muscle relaxation, as do the others, and is very pungent. Isoflurane is associated with more rapid induction and recovery than halothane and may have some benefits in patients with ischemic heart disease. Its use is associated with distortions of reality, terrifying dreams, and delirium, more commonly in adults. Malignant hyperthermia may be associated with any of the inhaled anesthetics, such as halothane, in ge- netically prone individuals. Des- fluramine is especially irritating to airways, and enflurane can reduce cardiac output. Cocaine is ideal for such surgery because of its topical activity; it does not require the addition of epinephrine, as it has intrinsic vasoconstrictive activity that aids in hemo- stasis. Like cocaine, procaine and tetracaine are both ester-type compounds; however, procaine is not topically active and tetracaine is used primarily for spinal anesthesia and ophthalmologic procedures. Lidocaine is an amide anesthetic preferred for infiltrative blocks and epidural anes- thesia. Mepivacaine is another amide local anesthetic, although not topically active, which, like all such agents, acts by blocking sodium channels. Fetal alcohol syndrome is a leading cause of congenital abnormalities, espe- cially microcephaly, growth retardation, and congenital heart defects. Abruptio placentae and learning difficulties are more typical with maternal use of cocaine during pregnancy. Spina bifida and orofacial defects are associated with valproic acid use during pregnancy, and the anti- convulsant phenytoin is associated with fetal growth retardation, microcephaly, and craniofacial abnormalities. Fetal hemorrhage and bone malformation are a consequence of warfarin use during pregnancy. Like other amphetamines, ecstasy increases the release of dopamine and nor- epinephrine. Its use is becoming more common in more affluent areas and is often associated with parties. Marijuana causes euphoria, uncontrol- lable laughter, loss of time perception, and increased introspection. Nicotine is a powerful stimulant in tobacco products and works by mimicking the effects of acetylcholine. Cocaine causes vasoconstric- tion, and snorting the drug causes necrosis and eventual perforation of the nasal septum. Marijuana causes euphoria, laughter, a loss of time perception, and increased introspection. Autocoids, Ergots, chapter Anti-inflammatory Agents, 6 and Immunosuppressive Agents I.