A theoretical study of intrinsic point defects and defect clusters in magnesium aluminate spinel.

Point and small cluster defects in magnesium aluminate spinel have been studied from a first principles viewpoint. Typical point defects that occur during collision cascade simulations are cation anti-site defects, which have a small formation energy and are very stable, O and Mg split interstitials and vacancies. Isolated Al interstitials were found to be energetically unfavourable but could occur as part of a split Mg-Al pair or as a three atom-three vacancy Al 'ring' defect, previously observed in collision cascades using empirical potentials. The structure and energetics of the defects were investigated using density functional theory (DFT) and the results compared to simulations using empirical fixed charge potentials. Each point defect was studied in a variety of supercell sizes in order to ensure convergence. It was found that empirical potential simulations significantly overestimate formation energies, but that the type and relative stability of the defects are well predicted by the empirical potentials both for point defects and small defect clusters.

Nonneurologic hand pain versus carpal tunnel syndrome: do psychological measures differentiate?

OBJECTIVE: To determine whether psychological measures would differentiate a group of patients with physician-diagnosed nonneurologic hand pain from patients with carpal tunnel syndrome (CTS). Many patients, who also displayed symptoms of psychological distress, were referred to an electrodiagnostic clinic with a diagnosis of possible CTS; they subsequently had normal nerve conduction studies. DESIGN: Sixty patients with hand pain were referred to either of two university clinics for electrophysiologic testing, were assigned to either the CTS or nonneurologic group, and were compared on a series of psychometric tests. RESULTS: The Beck Depression Inventory and McGill Pain Questionnaire showed that the physician-assigned nonneurologic patients have a greater degree of depression, use more affective adjectives, and choose more words on the McGill Pain Questionnaire than the physician-assigned CTS group. The nonneurologic group also scored higher on indices of self-reported disability on the Pain Disability Inventory in five of seven categories. Although the CTS group perceived more control over their pain, no differences were observed in the types of coping strategies used on the Coping Strategy Questionnaire. Finally, the nonneurologic group had more Workers' Compensation Board claims. CONCLUSION: Evidence of important psychological issues in some patients with hand pain suggests a need for greater awareness among treating physicians.

Postoperative pain expression in preschool children: validation of the child facial coding system.

OBJECTIVE: The purposes of the study were threefold: (a) to determine whether a measurement system based on facial expression would be useful in the assessment of post-operative pain in young children; (b) to examine construct validity in terms of structure, consistency, and dynamics of the facial display; and (c) to evaluate concurrent validity in terms of associations with global judgments of the children's pain. PATIENTS: One hundred children between the ages of 13 and 74 months were video-taped for a maximum of 1 hour after arrival in the postanesthesia care unit (PACU) at British Columbia's Children's Hospital. OUTCOME MEASURES: Videotapes were edited into 20-second blocks, randomly selected from each 2-minute time period taped during the hour following surgery, and coded for the presence or absence of 13 facial actions in the Child Facial Coding System (CFCS). RESULTS: Facial expressions were characterized primarily by the following constellation of actions: open lips, lowered brows, a deepened nasolabial furrow, mouth stretched wide in both horizontal and vertical directions, eyes squeezed shut or squinted, and raised cheeks. A principal components analysis indicated that these actions comprised a single factor, accounting for 55% of the variance in CFCS actions. Facial action summary scores were correlated with a visual analog rating of global pain, confirming that the CFCS has convergent validity. Facial action summary scores, i.e., pain displays, were at their lowest immediately after admittance to the PACU and just before the child's release from the PACU. CONCLUSIONS: The present study demonstrated that the CFCS serves as a valid measurement tool for persistent pain in children.

Biobehavioral responses to acute pain in adolescents with a significant neurologic impairment.

OBJECTIVE: To further understand acute pain response in children with a significant neurologic impairment (SNI), we undertook a descriptive hypothesis-generating study of the response to a routine vaccine among adolescents with SNI. DESIGN: Within-subject crossover design. SETTING: Tertiary care facility for children and adolescents with SNI. PATIENTS: Eight adolescents (mean age = 15 years). INTERVENTIONS: Mock and real vaccine injections. OUTCOME MEASURES: Quantitative measures of heart rate, videotaped facial action, Child Facial Coding System (CFCS), and Facial Action Coding System (FACS); observer ratings visual analog scale (VAS) were obtained before, during, and after a mock injection and routine annual influenza vaccine injection presented in a counterbalanced order. RESULTS: VAS scores were significantly higher during the injection phase than during the other time periods; however, there were no significant differences across study time periods when using the other outcome measures. CONCLUSIONS: Although the dampened behavioral and physiologic reactions to an acute noxious stimulus were similar to those of previous work with developmentally delayed children and frail elderly, it remains unclear what underlies the apparent reduced pain response in this setting. These findings have potentially important implications for the daily care of individuals with significant neurologic impairment and illustrate the compelling need tor further study of the unique character of the pain experience in this setting.

The Pain Coping Questionnaire: preliminary validation.

A new measure of coping, the Pain Coping Questionnaire (PCQ), is presented and validated in two studies of children and adolescents. Factor analyses of data from healthy children and adolescents supported eight hypothesized subscales (information seeking, problem solving, seeking social support, positive self-statements, behavioral distraction, cognitive distraction, externalizing, internalizing/catastrophizing) and three higher-order scales (approach, problem-focused avoidance, emotion-focused avoidance). The subscales and higher-order scales were internally consistent. The pain coping scales were correlated in the expected directions with children's appraisals of pain controllability, self-rated coping effectiveness, emotional distress when in pain, and among high school students, pain thresholds and functional disability. The structure and internal consistency of the PCQ were replicated in a sample of children and adolescents experiencing recurrent pain (headache, arthritis), and their parents. Relations between child- and parent-ratings of children's coping were moderate (median r=0.34). Higher levels of emotion-focused avoidance were related to more emotional distress (both samples), less coping effectiveness (headache sample), and higher levels of pain (arthritis sample). Higher levels of approach coping were related to less disability (headache sample). Other relations between approach and distraction coping and the outcome variables were generally not significant. The PCQ is a promising instrument for assessing children's pain coping strategies. The items are simple and relatively few, making it useful for assessing coping across a wide age range. It can be administered to children as young as 8 years of age in approximately 15 min.

Social barriers to optimal pain management in infants and children.

OBJECTIVE: To examine the social barriers that lead to less than optimal management of pain in children. DESIGN: Recognizing the vulnerabilities of infants and children and their dependence on caring adults, a model of pain communication is proposed. The model examines (a) the pain experiences of children, including social determinants; (b) developmental variations in the capacity to encode the severity and qualities of pain as expressive behavior; (c) adult skills and deficiencies in decoding pain; and (d) the actions of adults predicated on the meaning and significance attached to children's actions. Limitations in care were examined. DATA SOURCES: The current research and professional literature were accessed through searches of the Psyclit and Medline databases for relevant investigations on the basis of our working knowledge of the literature. CONCLUSION: Numerous deterrents to optimal care are identified in the domains of commonplace beliefs about the nature of pain in infants and children: failure to recognize the impact of socialization in familial and cultural modes of experience and expression; needs for age-specific assessment instruments; the limited capacity to use available evidence concerning pain; the need to employ clinicians, parents, and other adults more effectively in delivering care; and structural problems in the health care system.

The influence of early repolarization variant on the exercise electrocardiogram: a correlation with coronary arteriograms.

Sixteen adult patients with S-T segment elevation in their resting electrocardiograms characteristic of early repolarization variant (ERV) and chest pain syndromes of possible myocardial ischemia were evaluated with both treadmill exercise electrocardiography and coronary arteriography. Of 14 patients with normal coronary arteriograms, 13 had their resting S-T elevation return ("normalize") to the isoelectric baseline with physical exercise, while one patient with normal arteriograms and normal left ventricular contractility but moderately elevated left ventricular end-diastolic pressure of unknown etiology developed significant S-T depression with exercise. Two patients with significant coronary atherosclerotic occlusive lesions developed "ischemic" S-T depression during treadmill testing. Symptoms developed during treadmill exercise did not distinguish patients with coronary artery disease from those without. Thus, while ERV at rest may be "normalized" by graded physical exercise in the absence of significant coronary atherosclerosis, the presence of ERV does not prevent the usual electrocardiographic manifestations of exercise-induced myocardial ischemia.

Echocardiographic study of cardiac dimensions and function in the endurance-trained athlete.

Adaptive cardiac responses to isotonic training were studied with echocardiographic measurement of cardiac dimensions and function in 20 endurance runners whose maximal aerobic capacity on the treadmill was 4.88 +/- 0.13 (mean standard error of mean) liters of oxygen/min. They were compared with 26 young sedentary control subjects whose capacity was 3.34 +/- 0.11 liters of oxygen/min (P less than 0.001). A modest degree of right and left ventricular chamber enlargement and left ventricular hypertrophy was observed in endurance runners (left ventricular mass index 140 +/- 6 g/m2 compared with 107 +/- 4 g/m2 in sedentary control subjects, (P less than 0.001). Resting heart rate was slower in endurance runners (51 +/- 2 versus 62 +/- 2 beats/min, P less than 0.001) and resting left ventricular function as evaluated with ejection fraction and maximal posterior wall shortening velocity and mean circumferential shortening velocity (VCF) was comparable or slightly depressed in endurance runners (0.98 +/- 0.03 versus 1.02 +/- 0.05 circumferences/sec [difference not significant]). This study suggests that isotonic training results in adaptive changes in ventricular volume and mass, slower heart rates that may be associated with more efficient pumping function (that is, increasing stroke volume) and insignificant alterations in resting ejection phase indexes of left ventricular function.

Bleeding, clotting, and functional disability following Beall prosthetic mitral valve replacement.

The incidence of fatal and nonfatal thromboemboli and bleeding episodes was compared in 53 patients who received sodium warfarin and in 17 successive patients who received no sodium warfarin after Beall mitral valve replacement. Actuarial curves showed that by 12 months postoperatively patients not receiving sodium warfarin had a greater incidence of emboli (P less than 0.01). This significant difference remained when the combined incidence of emboli and hemorrhage was considered (P less than 0.05). Deaths due to emboli or hemorrhage, however, were not statistically different in the two groups. The quality of control of prothrombin times (percent of prothrombin times two to two and a half times control) did not significantly influence the incidence of ebmoli although the numbers were small. However, fatal and nonfatal hemorrhagic episodes which did occur were almost invariably associated with prothrombin times greater than three to eight times control. Results of pre- and post-operative graded treadmill exercise tests in 39 patients receiving a Beall mitral valve replacement showed significant postoperative improvement in exercise tolerance. Nevertheless, the patients' postoperative working capacity was only 55% to 57% of that of age- and sex-matched sedentary controls. The present study supports the use of sodium warfarin therapy and strict anticoagulation control in Beall mitral valve replacement patients. It also documents a significant residual impairment in physical working capacity.

The pathophysiology of idiopathic mitral valve prolapse.

Left ventricular structure, function, and the coronary circulation were studied in a subset of patients with mitral valve leaflet prolapse. This group of 26 patients (21 females, five males, with mean age of 46 years), had the syndrome identified as idiopathic mitral valve prolapse (IMVP), which was characterized by a systolic click-murmur, clinical symptoms that were highly variable in duration and intensity, angiographically-documented mitral prolapse, and no obvious associated systemic or cardiovascular disease. Mitral regurgitation was of moderate degree in four, mild in 14, and absent in eight. The left ventricular (LV) end-diastolic volume index was elevated in ten of 25 (40%), the LV mass index was elevated in six of 17 (35%), but the LV anterior wall thickness was increase in only one of 17. Three major patterns of ventricular contraction were identified: 1) normal in seven; 2) abnormal, usually an inferior deformity and/or anterior asynergy, in eight; and 3) hyperkinetic in 11. Normal resting left ventricular function, assessed as an ejection fraction greater than 55%, was present in 17 of 25 (68%). Selective coronary arteriography was essentially normal in all 25 patients studied. An ischemic ECG response was detected during only one of 12 maximal treadmill exercise tests and in none of ten atrial pacing stress tests (AP). Myocardial lactate extraction did not change significantly during AP in six patients. We conclude that cardiomyopathy does not appear to be a primary cause or an important associated component of the IMVP syndrome. Abnormalities of the coronary circulation or of myocardial metabolism were not demonstrated by available methods. A proposed pathophysiological mechanism to explain the clinical and angiographic findings in IMVP is discussed.

Antihypertensive effect of a dopamine beta hydroxylase inhibitor, bupicomide: a comparison with hydralazine.

The cardiovascular effects of a new antihypertensive drug, bupicomide, were compared with those of hydralazine in 6 patients with mild to moderate hypertension. The mean supine arterial pressure of patients was reduced 15.2 mm Hg by bupicomide (900 to 2,000 mg/day) and 15.7 mm Hg by hydralazine (300 to 600 mg/day). Heart rate increased an average of 11.3 bpm during bupicomide and 14.5 bpm by hydralazine. Neither drug was associated with a postural decrease in mean arterial pressure. The heart rate response during maximum tolerated treadmill exercise was not diminished by either drug. Cardiac index was increased during administration of both drugs. Bupicomide and hydralazine reduced forearm vascular resistance, while renal blood flow and renal vascular resistance were not significantly modified. Evidence of equivalent augmentation of sympathetic nervous activity during administration of both drugs consisted of equal and significant increases in heart rate and urinary norepinephrine excretion, and decreases in duration of the pre-ejection period. The absolute values of these parameters were correlated with mean arterial pressure, which may indicate that the increase in sympathetic nervous activity was mediated by baroreceptor reflexes. Although bupicomide inhibits dopamine beta-hydroxylase, our results suggest that it is acting as a direct vasodilator.