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Biomedical subjects

M Reardon

Publications and source records attributed to M Reardon.

At least 19 recordsLinked to original sources
PubMed1998

Circadian variation of the QT interval in patients with sudden cardiac death after myocardial infarction.

To evaluate the potential prognostic value of the circadian variation of QT intervals in predicting sudden cardiac death (SCD) in patients after myocardial infarction (MI), 15 pairs of post-MI patients (15 died suddenly within 1 year after MI [SCD victims] and 15 remained event-free [MI survivors]) were studied (mean age 60 +/- 8 years; 24 men and 6 women). The pairs were matched for age, gender, infarct site, presence of Q wave, left ventricular ejection fraction, thrombolytic and beta-blocker therapy. Fourteen normal subjects served as controls (mean age 55 +/- 9 years; 12 men). A 24-hour Holter electrocardiographic (ECG) recording was obtained from each subject. All recordings were analyzed using a Holter ECG analyser. QT, RR, and heart rate-corrected QT intervals (QTc) were automatically calculated by the analyzer, and hourly and 24-hour mean values of each measurement were derived from each recording. There was a pronounced circadian variation in the QT interval in parallel with the trend in the RR interval in normal subjects and in MI survivors. Circadian variation in both indexes was blunted in SCD victims. The QT interval was significantly longer at night than during the day in normal subjects (388 +/- 28 vs 355 +/- 21 ms, p = 0.001) and in MI survivors (358 +/- 25 vs 346 +/- 15 ms, p = 0.008), but not in SCD victims (357 +/- 32 vs 350 +/- 31 ms, p = 0.6). The 24-hour mean value of the QT interval in SCD victims did not differ significantly from that in normal subjects or MI survivors. The QT interval at night was significantly shorter in SCD victims than in normal subjects (357 +/- 32 vs 388 +/- 28 ms, p = 0.02), but daytime values were similar. The QT interval in SCD victims did not differ significantly from that of MI survivors at any time. The QTc interval exhibited a small circadian variation in normal subjects. This variation was abolished in SCD victims and MI survivors. The 24-hour mean value of QTc was significantly longer in SCD victims than in normal subjects (424 +/- 25 vs 402 +/- 21 ms, p = 0.02), and in MI survivors (424 +/- 25 vs 404 +/- 32 ms, p < 0.05). The QTc interval of SCD victims differed from that of normal subjects during both the day (421 +/- 25 vs 400 +/- 17 ms, p = 0.02) and night (424 +/- 26 vs 403 +/- 23 ms, p = 0.03). Thus, blunted circadian variation in QT intervals, abolished circadian variation in QTc intervals, and prolonged QTc intervals may suggest an increased risk of SCD in patients after MI.

Circadian Rhythm↗
PubMed1998

Physiological effects of thermal stress on aviators flying a UH-60 helicopter simulator.

An evaluation of the physiological effects on aviators of heat stress (90 degrees F wet bulb globe temperature [WBGT]) versus a cooler condition (70 degrees F WBGT) when wearing either a MOPP0 (Mission-Oriented Protective Posture 0) uniform or a MOPP4 ensemble encumbered with a ballistic chest plate and overwater survival gear was performed at the United States Army Aeromedical Research Laboratory. The study used a repeated-measures design with 14 aviators flying 4-hour missions in a UH-60 helicopter simulator. Average crew endurance in the MOPP4-hot condition was reduced to one-third of the fully completed mission time of 309 minutes. For the hot condition, core temperature in the simulator rose 1.4 degrees F/hour when aviators wore the encumbered MOPP4 ensemble versus 0.27 degree F/hour when they wore the MOPP0 uniform. Sweating rate in the MOPP4-hot condition was 1,523 ml/hour, resulting in 2.5% dehydration, in contrast to 183 ml/hour and 0.9% dehydration in the MOPP4-cool condition. In this study, pilots flying realistic UH-60 simulator sorties rapidly incurred significant physiological heat strain when wearing an encumbered MOPP4 flight ensemble in hot cockpit conditions.

Adult↗
PubMed1997

Variation in emergency department use of cervical spine radiography for alert, stable trauma patients.

OBJECTIVE: To, assess the emergency department use of cervical spine radiography for alert, stable adult trauma patients in terms of utilization, yield for injury and variation in practices among hospitals and physicians. DESIGN: Retrospective survey of health records. SETTING: Emergency departments of 6 teaching and 2 community hospitals in Ontario and British Columbia. PATIENTS: Consecutive alert, stable adult trauma patients seen with potential cervical spine injury between July 1, 1994, and June 30, 1995. MAIN OUTCOME MEASURES: Total number of eligible patients, referral for cervical spine radiography (overall, by hospital and by physician), presence of cervical spine injury, patient characteristics and hospitals associated with use of radiography. RESULTS: Of 6855 eligible patients, cervical spine radiography was ordered for 3979 (58.0%). Only 60 (0.9%) patients were found to have an acute cervical spine injury (fracture, dislocation or ligamentous instability); 98.5% of the radiographic films were negative for any significant abnormality. The demographic and clinical characteristics of the patients were similar across the 8 hospitals, and no cervical spine injuries were missed. Significant variation was found among the 8 hospitals in the rate of ordering radiography (p < 0.0001), from a low of 37.0% to a high of 72.5%. After possible differences in case severity and patient characteristics at each hospital were controlled for, logistic regression analysis revealed that 6 of the hospitals were significantly associated with the use of radiography. At 7 hospitals, there was significant variation in the rate of ordering radiography among the attending emergency physicians (p < 0.05), from a low of 15.6% to a high of 91.5%. CONCLUSIONS: Despite considerable variation among institutions and individual physicians in the ordering of cervical spine radiography for alert, stable trauma patients with similar characteristics, no cervical spine injuries were missed. The number of radiographic films showing signs of abnormality was extremely low at all hospitals. The findings suggest that cervical spine radiography could be used more efficiently, possibly with the help of a clinical decision rule.

Adolescent↗
PubMed1997

Variation in ED use of computed tomography for patients with minor head injury.

STUDY OBJECTIVE: To determine the frequency of utilization, yield for brain injury, incidence of missed injury, and variation in the use of computed tomography (CT) for ED patients with minor head injury. METHODS: This retrospective health records survey was conducted over a 12-month period in the EDs at seven Canadian teaching institutions. Included in this review were adult patients who sustained acute minor head injury, defined as witnessed loss of consciousness or amnesia and a Glasgow Coma Scale score of 13 or greater. Data were collected by research assistants who were trained to select cases and abstract data in a standardized fashion according to a resource manual. Subsequently, patient eligibility was reviewed by the study coordinator and principal investigator. RESULTS: Of the 1,699 patients seen, 521 (30.7%) were referred for CT, and 418 (79.8%) of these scans were negative for any type of brain injury. Overall, 105 (6.2%) of these patients sustained acute brain injury, including 9 (.5%) with an epidural hematoma Cochran's Q test for homogeneity demonstrated significant variation between the seven centers for rate of ordering CT (P < .0001), from a low of 15.9% to a high of 70.4%. All five cases of "missed" hematoma occurred at the institutions with the highest and third highest rates of CT use. After controlling for possible differences in case severity and patient characteristics at each hospital, logistic regression analysis revealed that five of seven hospitals were significantly associated with the use of CT (respected odds ratios [OR], .4, .5, .5, 3.2, and 4.7). Three of the centers (two with the highest ordering rates) showed significant heterogeneity in the ordering of CT among their attending staff physicians, from a low of 6.5% to a high of 80.0%. CONCLUSION: There was considerable variation among institutions and individual physicians in the ordering of CT for patients with minor head injury. Although emergency physicians were selective when ordering CT, the yield of radiography was very low at all hospitals. None of the cases of "missed" intracranial hematoma came from the lowest ordering institutions, indicating that patients may be managed safely with a selective approach to CT use. These findings suggest great potential for more standardized and efficient use of CT of the head, possibly through the use of a clinical decision rule.

Adolescent↗
PubMed1997

Heart rate variability in idiopathic dilated cardiomyopathy: relation to disease severity and prognosis.

OBJECTIVE: To assess the clinical importance of heart rate variability (HRV) in patients with idiopathic dilated cardiomyopathy (DCM). PATIENTS AND METHODS: Time domain analysis of 24 hour HRV was performed in 64 patients with DCM, 19 of their relatives with left ventricular enlargement (possible early DCM), and 33 healthy control subjects. RESULTS: Measures of HRV were reduced in patients with DCM compared with controls (P < 0.05). HRV parameters were similar in relatives and controls. Measures of HRV were lower in DCM patients in whom progressive heart failure developed (n = 28) than in those who remained clinically stable (n = 36) during a follow up of 24 (20) months (P = 0.0001). Reduced HRV was associated with NYHA functional class, left ventricular end diastolic dimension, reduced left ventricular ejection fraction, and peak exercise oxygen consumption (P < 0.05) in all patients. DCM patients with standard deviation of normal to normal RR intervals calculated over the 24 hour period (SDNN) < 50 ms had a significantly lower survival rate free of progressive heart failure than those with SDNN > 50 ms (P = 0.0002, at 12 months; P = 0.0001, during overall follow up). Stepwise multiple regression analysis showed that SDNN < 50 ms identified, independently of other clinical variables, patients who were at increased risk of developing progressive heart failure (P = 0.0004). CONCLUSIONS: HRV is reduced in patients with DCM and related to disease severity. HRV is clinically useful as an early non-invasive marker of DCM deterioration.

Adolescent↗
PubMed1996

Atrial fibrillation in the elderly.

The prevalence of atrial fibrillation is 11% in persons older than 70 years and rises to 17% in those aged 84 years or more. One-year mortality ranges from 0.2 to 16%, being highest in elderly patients, and is associated with a 4.8-fold increased risk of stroke. Atrial fibrillation can be cardioverted to normal sinus rhythm electrically or pharmacologically and rapid ventricular rate can be controlled with drugs. While anti-coagulation prevents embolic events in those with atrial fibrillation, the decision to anticoagulate should be based on an assessment of the risk/benefit ratio.

Age Factors↗
PubMed1996

QT interval change with age in an overtly healthy older population.

BACKGROUND: Prolonged QT interval on the surface electrocardiogram (ECG) is known to be associated with arrhythmias, coronary heart disease, and sudden cardiac death. Increased QT dispersion has also been related to arrhythymias which are more frequent in the elderly. HYPOTHESIS: This study investigated the relationship between aging, QT interval, and QT dispersion. METHODS: Normal resting ECGs were recorded from 96 healthy subjects (73 women, age range 40-102 years). No subject had symptoms or signs of heart disease and none was on medication affecting cardiac function. All had normal heart size on chest x-ray and normal electrolytes. Using a digitizing board, the RR and QT intervals were measured on each lead of each ECG, excluding only the leads in which the T wave was not visible. Mean RR, mean QT interval, and heart rate-adjusted QTc interval (standard Bazet's formula) were obtained from these measurements. Further, QT dispersion was calculated for each ECG as (1) the difference between the maximum and minimum QT interval, and (2) as the coefficient of variance of QT interval of all measurable leads. RESULTS: A significant correlation between aging and prolonged QTc was noted in the total population (r = 0.43, p < 0.05), as well as in men (r = 0.4, p < 0.05) and women (r = 0.23, p < 0.05) separately. There was no association between QT dispersion and increasing age regardless of the method of calculation (r = -0.04, r = -0.08 respectively, both NS). CONCLUSION: The rate-adjusted QT interval is prolonged with increasing age and may contribute to the increased risk of ventricular arrhythmias and cardiac mortality in elderly patients.

Adult↗
PubMed1996

Changes in heart rate variability with age.

Depressed heart rate variability (HRV) after a myocardial infarction is associated with increased mortality. This is thought to be due to reduced parasympathetic activity and heightened sympathetic activity. Aging is associated with depressed HRV, but little is known of the affect of aging on parasympathetic activity. This study examined 56 healthy subjects (age range 40-102 years; 39 women). None had a history of heart disease or were on medication that would affect cardiac function. All had normal resting ECGs, normal heart size on chest X ray, and normal electrolytes. In all subjects, 24-hour Holter recordings were performed and used to measure HRV. In particular, the study examined the affect of age on HRV triangular index, which gives an estimate of overall HRV, and on RMSSD (square root of the mean squared differences of successive normal-to-normal RR intervals), which gives an estimate of short-term components of HRV and is thought to reflect the overall extent of vagal modulations of heart rates. Both these parameters were compared in patients younger and older than 70 years. Each recording lasted at least 17 hours; the majority of recordings were longer than 20 hours. There was a significant decrease in HRV triangular index with age (r = -0.4, P < 0.05) and no significant change in RMSSD with age(r = -0.08, P = NS). There was a significant difference in HRV index in those > 70 years compared with those < 70 years (38.0 +/- 9.3 vs 31.0 +/- 11, respectively, P < 0.02). There was no significant difference in RMSSD between the two age groups (26.7 +/- 8.2 ms vs 28.4 +/- 11.3 ms, respectively, P = NS). Thus, the study concludes that aging reduces the global measure of HRV and may reflect reduced responsiveness of autonomic activity to external environmental stimuli with age. However, the time-domain short-term components of HRV are not affected by age and, therefore, the fast and presumably vagal modulations of heart rate appear to be maintained.

Adult↗
PubMed1995

A survey of domiciliary consultations in medicine for the elderly.

The objective of this study was to assess the value of domiciliary consultations carried out by two hospital physicians for care of the elderly, using the resulting admission rates as one of the criteria. The action taken by the physicians on domiciliary visits was also studied. Data were collected retrospectively from all the domiciliary consultations done by the two departmental physicians from January 1992 to December 1992. From totals of 184 and 268 domiciliary consultations only 14.1% and 11.2% of patients seen respectively by consultant 1 and consultant 2 were admitted acutely to hospital. Overall, consultant 1 had something to offer in 92.4% of his domiciliary visits and consultant 2 took action in 81.3% of his domiciliary consultations. Most of the GP practices in the area used the service and only one practice was responsible for more than 10% of one consultant's domiciliary consultations. Domiciliary consultations form a useful service in medicine for the elderly and admission rates to hospital from these visits are low.

Aged↗
PubMed1993

Decision rules for the use of radiography in acute ankle injuries. Refinement and prospective validation.

OBJECTIVE: To validate and refine previously derived clinical decision rules that aid the efficient use of radiography in acute ankle injuries. DESIGN: Survey prospectively administered in two stages: validation and refinement of the original rules (first stage) and validation of the refined rules (second stage). SETTING: Emergency departments of two university hospitals. PATIENTS: Convenience sample of adults with acute ankle injuries: 1032 of 1130 eligible patients in the first stage and 453 of 530 eligible patients in the second stage. MAIN OUTCOME MEASURES: Attending emergency physicians assessed each patient for standardized clinical variables and classified the need for radiography according to the original (first stage) and the refined (second stage) decision rules. The decision rules were assessed for their ability to correctly identify the criterion standard of fractures on ankle and foot radiographic series. The original decision rules were refined by univariate and recursive partitioning analyses. MAIN RESULTS: In the first stage, the original decision rules were found to have sensitivities of 1.0 (95% confidence interval [CI], 0.97 to 1.0) for detecting 121 maleolar zone fractures, and 0.98 (95% CI, 0.88 to 1.0) for detecting 49 midfoot zone fractures. For interpretation of the rules in 116 patients, kappa values were 0.56 for the ankle series rule and 0.69 for the foot series rule. Recursive partitioning of 20 predictor variables yielded refined decision rules for ankle and foot radiographic series. In the second stage, the refined rules proved to have sensitivities of 1.0 (95% CI, 0.93 to 1.0) for 50 malleolar zone fractures, and 1.0 (95% CI, 0.83 to 1.0) for 19 midfoot zone fractures. The potential reduction in radiography is estimated to be 34% for the ankle series and 30% for the foot series. The probability of fracture, if the corresponding decision rule were "negative," is estimated to be 0% (95% CI, 0% to 0.8%) in the ankle series, and 0% (95% CI, 0% to 0.4%) in the foot series. CONCLUSION: Refinement and validation have shown the Ottawa ankle rules to be 100% sensitive for fractures, to be reliable, and to have the potential to allow physicians to safely reduce the number of radiographs ordered in patients with ankle injuries by one third. Field trials will assess the feasibility of implementing these rules into clinical practice.

Adolescent↗
PubMed1993

Attempted homicide in hospital.

Strychnine poisoning is reported in a patient who was the victim of attempted homicide in his home and in a General hospital. The diagnosis proved to be an elusive one over five months. The question of a primary psychiatric diagnosis, raised by the patient's wife proved to be an attempt by her to cover her crime. Medico-legal issues relating to the management of attempted homicide in hospital are discussed.

Family↗
PubMed1990

Expression of key enzymes of purine and pyrimidine metabolism in a hepatocyte-derived cell line at different phases of the growth cycle.

The effect of growth phase on enzymatic activities of the de novo and salvage pathways for purine and pyrimidine nucleotide synthesis was studied in a hepatocyte-derived cell line from the rat. The cells were in lag phase after plating for 36 h; log phase started at 48 h and persisted up to 120 h of culture. Then the cells stopped growing and entered into plateau phase (144 h). In non-proliferating cells (144 h of culture) the basal activities of the enzymes of purine de novo biosynthesis were 1.7- to 6.8-fold higher than in normal rat liver, those of pyrimidine de novo synthesis showed 0.6- to 30-fold increase in activity. The purine salvage enzymes were unchanged, and the pyrimidine salvage enzymes were 3.1- to 7.4-fold higher compared to normal liver. During the growth cycle all enzymes except the purine salvage enzymes, which did not change, showed a peak in activity at 72 h of culture (log phase). The increase in activity in log phase compared to plateau phase was 1.3- to 2.4-fold for purine de novo synthetic enzymes, 1.1- to 2.4-fold for pyrimidine de novo enzymes, and 1.4- to 4.7-fold for pyrimidine salvage enzymes. The specific activities of the enzymes in exponentially growing cells were comparable either to that in 24-h regenerating liver, or to that in hepatomas of low or medium growth rate. It was concluded that the enzymatic pattern and metabolic state of the cells shared some features with regenerating liver, others with tumors, although they were not tumorigenic after transplantation into athymic nude mice.

Animals↗
PubMed1990

The relationship between conductance and functional residual capacity during drug-induced bronchoconstriction.

UNLABELLED: We wondered if the inverse changes in airway conductance (Gaw) and functional residual capacity (FRC) during histamine (H) and acetylcholine (ACH) challenge are interrelated or occur at random. In 14 normal and 14 asthmatic subjects, we determined FRC and Gaw changes corresponding to changes in specific airway conductance (SGaw) around -40 percent produced by an aerosol of H or ACH inhaled quantitatively and with measured lung deposition. We also assessed the elastic recoil following H inhalation (5A). We found that in 11 normal and nine asthmatic subjects, after H or nine normal and 11 asthmatic subjects after ACH, Gaw and 1/FRC were linearly and directly related (p less than 0.05). The steepness of this slope was directly related to the resting Gaw values. A similar relation was uncovered in the literature for asthmatic patients at rest or during recovery from natural asthma. As the elastic recoil was normal and did not change after H, it could not explain delta FRC at delta SGaw of -40 percent. IN CONCLUSION: (1) during H or ACH challenge, Gaw-FRC relationship in normal or asthmatic subjects tends to be hyperbolic and dependent on resting Gaw; (2) such a relationship is seemingly present in other bronchoconstrictor responses with a different pathogenesis; and (3) during bronchoconstriction, as Gaw vs FRC is no longer linear, SGaw becomes volume dependent.

Acetylcholine↗
PubMed1989

The effects of hypoxemia on myocardial blood flow during exercise.

We evaluated the adequacy of regional and transmural blood flow during exercise and rapid pacing after 1 wk of hypoxemia. Seven mature mongrel dogs were made hypoxemic (mean O2 saturation = 72.4%) by anastomosis of left pulmonary artery to left atrial appendage. Catheters were placed in the left atrium, right atrium, pulmonary artery, and aorta. Atrial and ventricular pacing wires were placed. An aortic flow probe was placed to measure cardiac output. Ten nonshunted dogs, similarly instrumented, served as controls. Recovery time was approximately 1 wk. Cardiac output, mean aortic pressure, and oxygen saturation were measured at rest, with ventricular pacing, atrial pacing, and with treadmill exercise. Ventricular and atrial pace and exercise were at a heart rate of 200. Right ventricular free wall, left ventricular free wall, and septal blood flow were measured with radionuclide-labeled microspheres. Cardiac output, left atrial blood pressure, and aortic blood pressure were similar between the two groups of dogs in all testing states. Myocardial blood flow was significantly higher in the right and left ventricular free wall in the hypoxemic animals during resting and exercise testing states. Myocardial oxygen delivery was similar between the two groups of animals. Pacing resulted in an increase in myocardial blood flow in the control animals but not the hypoxemic animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Regulation of carbamoyl-phosphate synthase II.

Evidence was provided that in rat liver synthase II activity, amount and turnover were regulated primarily by insulin. When rats were starved, synthase II activity and the immunotitratable enzyme amount markedly decreased; refeeding restored enzyme activity and amount to normal range. The changes in activity and amount were paralleled with alterations in the level of circulating insulin in the plasma. When starved rats were treated with anti-insulin serum before and during refeeding, the animals consumed the food, but the rise in synthase II activity was prevented. In diabetic rats, the activity and amount of synthase II in the liver markedly decreased and insulin treatment restored them to normal range. Actinomycin treatment prevented the refeeding and the insulin-induced rise in synthase II activity and amount. Study of the turnover of synthase II showed that in starvation the rate of synthesis decreased and refeeding restored the enzyme synthetic and degradation rates to normal range. In the diabetic rat, synthase II synthetic rate markedly decreased, and the degradation rate increased. Insulin returned the synthetic and catabolic rates to normal livers. In rapidly growing rat hepatoma 3924A, synthase II activity and amount were elevated 9- to 10-fold. Turnover studies showed that the synthetic rate in hepatoma 3924A was approximately 10-fold higher than that of normal liver. The catabolic rates of synthase II were similar in the liver and hepatoma. Thus, the increased activity and amount of synthase II in the hepatoma was due primarily to an increased rate of enzyme biosynthesis. Evidence was presented that in starvation and diabetes and on refeeding and insulin administration there is very little or no change in the enzymic activity, amount and turnover of hepatoma synthase II. The marked contrast between the turnover rate of hepatoma 3924A synthase II activity and that of the normal liver enzyme in starvation and in diabetes is under investigation. This overview of the behavior of activity, amount and turnover of synthase II in liver and hepatoma 3924A provides evidence of the important role of insulin in regulation of liver synthase II and of the apparent lack of responsiveness of the hepatoma enzyme to insulin concentrations. The precise details of the experimental procedures and the enzymic results will be published elsewhere.

Animals↗