PubMed Health⌕ Search

Biomedical subjects

P M Clarkson

Publications and source records attributed to P M Clarkson.

At least 19 recordsLinked to original sources
PubMed1992

Predictors of long-term survival with Ebstein's anomaly of the tricuspid valve.

In patients with Ebstein's anomaly of the tricuspid valve, predictors of death and indications for surgery are poorly defined. We retrospectively reviewed 48 patients with Ebstein's anomaly, 17 (35%) of whom presented in the first week of life. Duration of follow-up extended to 32 years (greater than 10 years in 35%). Twenty of the 48 patients (42%) died, 6 in the first week of life and 1 at age 5 months. Thirteen of the 41 patients surviving to age 6 months subsequently died, 50% probability of survival being reached at 47 years. Significant (p less than or equal to 0.05) predictors of death in this group were: male sex, cardiothoracic ratio greater than or equal to 0.65, New York Heart Association class III or IV, breathlessness and the absence of Wolff-Parkinson-White syndrome. Eight patients died suddenly. A cardiothoracic ratio greater than or equal to 0.65 was a better predictor of sudden death than functional status. All who developed atrial fibrillation died within 5 years. Other atrial arrhythmias were not helpful in predicting sudden death. In view of these findings, tricuspid valve surgery is recommended before the cardiothoracic ratio reaches 0.65, regardless of the symptomatic state.

Actuarial Analysis↗
PubMed1992

Exercise-induced muscle damage: effects of light exercise on damaged muscle.

The effects of performing light eccentric exercise (LB) during the period of recovery from a heavy eccentric exercise bout (HB) were studied. An experimental and a control group, each consisting of nine college age volunteers (seven women, two men) performed two HB--HB1 and HB2--14 days apart, using the elbow flexor and extensor muscles of one arm. The experimental group performed an additional LB on the day following the first HB. HB1 resulted in muscle soreness, muscle weakness, changes in elbow joint flexibility, and large delayed increases in serum creatine kinase (CK) activity. The HB2 produced smaller changes in all parameters, indicating that adaptation to the effects of eccentric exercise had occurred in the muscle. The LB did not alter muscle soreness, strength or elbow flexibility, but did reduce or delay CK activity increase after HB1. The LB had no apparent effect on adaptation to HB2.

Adult↗
PubMed1992

Robust adaptive parameter estimators in arrhythmia detection.

The authors consider the statistical analysis of threshold crossing intervals, as applied to estimation of tachycardia rates from intracavitary electrograms. The authors developed a class of robust algorithms designed to produce minimum variance estimates for tachycardia rates. The authors formulated the algorithms using order statistic filters, and obtained the minimum variance unbiased order statistic estimator. The potential gain in efficiency achieved by this approach is demonstrated via a representative example. The results indicated that the order statistics operator can produce dramatic reductions for typical errors in error variance as compared to linear estimators.

Algorithms↗
PubMed1992

Relationship between post-exercise plasma CK elevation and muscle mass involved in the exercise.

The purpose of this study was to investigate whether a larger post-exercise increase in plasma creatine kinase (CK) activity would be produced when a larger amount of muscle is damaged by eccentric exercise. Twenty-two non-weight trained females were placed into two groups; Group A (n = 12) and Group B (n = 10). Both groups performed 24 maximal eccentric actions of the forearm flexors on each bout. The right and left arm were exercised on the same day for Group A (24 eccentric actions per arm, a total of 48 actions). In contrast, Group B performed 24 actions with either the right or the left arm on the first bout and performed 24 eccentric actions with the opposite arm on the second bout 3-5 weeks later. Blood samples were taken before and for 5 days after each exercise and plasma CK activity was determined. Forearm flexion isometric force (ISO), range of motion evaluated by relaxed elbow joint angle (RANG) and flexed elbow joint angle (FANG), and perceived muscle soreness (SOR) were also examined to indirectly assess muscle damage. All of the muscle damage indicators changed significantly over time (p < 0.01) for both groups, but changes were not significantly different between arms or between groups. Because it seemed that both arms were equally "damaged" for each group, it was expected that Group A (two arms were exercised on the same day) should show an approximate two-fold increase in plasma CK compared to Group B when one arm was exercised on each bout.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1992

Changes in plasma zinc following high force eccentric exercise.

This study was done to determine whether eccentric exercise that causes muscle damage will produce an increase in plasma levels of zinc. Changes in total plasma zinc concentration (Zn) were examined following an eccentric and concentric exercise of the forearm flexors. Eight female subjects performed 24 maximal concentric actions (CON) with one arm and 10-14 days later performed 24 maximal eccentric actions (ECC) with the other arm. Maximal isometric force, elbow joint angles at a relaxed (RANG) and flexed position (FANG), muscle soreness, and plasma creatine kinase activity (CK) were measured as indicators of muscle damage. Zn levels were determined at the same time as CK. Maximal isometric force, RANG, FANG, and muscle soreness showed large changes after ECC but little if any change after CON. CK increased significantly after ECC but did not change after CON. Neither ECC nor CON showed significant changes in Zn following exercise. It is concluded that exercise-induced muscle damage does not appear to produce an increase in plasma zinc levels.

Adult↗
PubMed1992

Muscle function after exercise-induced muscle damage and rapid adaptation.

This brief review focuses on the time course of changes in muscle function and other correlates of muscle damage following maximal effort eccentric actions of the forearm flexor muscles. Data on 109 subjects are presented to describe an accurate time course of these changes and attempt to establish relationships among the measures. Peak soreness is experienced 2-3 d postexercise while peak swelling occurs 5 d postexercise. Maximal strength and the ability to fully flex the arm show the greatest decrements immediately after exercise with a linear restoration of these functions over the next 10 d. Blood creatine kinase (CK) levels increase precipitously at 2 d after exercise which is also the time when spontaneous muscle shortening is most pronounced. Whether the similarity in the time courses of some of these responses implies that they are caused by similar factors remains to be determined. Performance of one bout of eccentric exercise produces an adaptation such that the muscle is more resistant to damage from a subsequent bout of exercise. The length of the adaptation differs among the measures such that when the exercise regimens are separated by 6 wk, all measures show a reduction in response on the second, compared with the first, bout. After 10 wk, only CK and muscle shortening show a reduction in response. After 6 months only the CK response is reduced. A combination of cellular factors and neurological factors may be involved in the adaptation process.

Adaptation, Physiological↗
PubMed1992

Time course of serum protein changes after strenuous exercise of the forearm flexors.

The time course of changes in serum proteins and other blood constituents after eccentric exercise of the forearm flexors by six nonweight-trained female subjects (age, 19.7 +/- 1.9 years) was investigated. Eccentric muscle actions are those in which the muscle lengthens as it exerts force, as when a person lowers a weight. Serum levels of creatine kinase, lactate dehydrogenase, aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, gamma-glutamyl transpeptidase, myoglobin, as well as urea nitrogen, uric acid, creatinine, calcium, and phosphorus were examined before and for 6 days after exercise. Creatine kinase increased dramatically (peak value ranged from 6740 to 24,200 U/L) and aspartate aminotransferase, lactate dehydrogenase, alanine aminotransferase, and myoglobin followed the same time course as creatine kinase, but their peak values were lower. These proteins did not increase significantly until 48 hours after exercise and reached peak values 3 to 5 days after exercise. Alkaline phosphatase, gamma-glutamyl transpeptidase, uric acid, urea nitrogen, creatinine, calcium, and phosphorus showed no change. There is either a delay in muscle protein release by damaged muscle fibers, or the proteins are unable to leave the interstitial area for the 24 to 48 hour period after exercise. Because of the long delay, care should be taken when blood protein levels are interpreted in persons who have exercised strenuously (even if only for a short period of intense effort) several days before any diagnostic tests are performed.

Adolescent↗
PubMed1991

Muscle protein changes following eccentric exercise in humans.

This study characterized changes in the protein composition of human muscle tissue after eccentric exercise. Four subjects performed 70 maximum eccentric, isokinetic actions of the forearm flexors with one arm. The other arm served as control. A biopsy of the biceps muscle of each arm was taken 2 days after exercise when muscles were very sore (mean = 8.0; 1 = normal; 10 = very, very sore), and muscle damage was documented by a mean decrease of 0.2 radians in the relaxed elbow angle. Proteins from the biopsy tissue were solubilized in a high ionic strength buffer containing several proteolytic inhibitors. Protein concentrations of the extracts were determined and identical amounts loaded onto sodium dodecyl sulfate (SDS) polyacrylamide gels (7.5, 12.5, and 17.5%). Densitometric analysis of the Coomassie brilliant blue stained gels revealed alterations in the amounts of three protein bands in the exercised tissue relative to the control. These changes were in the linear portion of the graph of absorbance versus protein amount. Wilcoxon's signed rank test showed the first two of the following bands to increase significantly in amount (P less than 0.062). The average percentage changes [mean (SEM)] for these bands were 63 (21), 39 (5), and 82 (35). The corresponding molecular weights determined from known standards were 76300 (860), 33200 (310), and 12000 (80) daltons, respectively. These changes imply that the increased synthesis, decreased degradation, or some combination thereof, of these three proteins may be necessary for the repair or regeneration response to exercise-induced muscle damage.

Arm↗
PubMed1991

Time course of muscle adaptation after high force eccentric exercise.

The repeated bout effect on changes in muscle damage indicators was examined in two groups of subjects following two bouts of 70 maximal eccentric actions of the forearm flexors. Fourteen college age female subjects were placed into two groups. The two bouts were separated by 6 weeks (n = 6), and 10 weeks (n = 8). The subjects performed the same amount of work for the bouts. The muscle damage indicators were isometric strength (STR), relaxed elbow joint angle (RANG), flexed elbow joint angle (FANG), perceived muscle soreness ratings (SOR), and plasma creatine kinase activity (CK). These measures were obtained pre-exercise and 5 days following each bout. The first bout showed significant changes in all measures over time for both groups (P less than 0.01). For the 6-week group, significantly smaller changes in RANG (P less than 0.01), SOR (P less than 0.05), and CK (P less than 0.01), as well as significantly faster recoveries (P less than 0.05) for STR and FANG were produced in the second bout. For the 10-week group, significantly smaller changes in RANG (P less than 0.05) and CK (P less than 0.01) were demonstrated by the second bout, but not significant difference was found for STR, FANG, and SOR between bouts 1 and 2. Changes in CK were still significantly smaller than that of the first bout when 6 subjects (3 subjects from each group) performed the same exercise 6 months after the second bout, but no difference in other measures.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Physiological↗
PubMed1991

Progress of patients with pulmonary atresia after systemic to pulmonary arterial shunts.

Between February 1980 and June 1987, 42 shunts were placed in 39 infants with pulmonary atresia: 33 were modified Blalock-Taussig shunts with polytetrafluoroethylene (PTFE) and 9 were classic Blalock-Taussig shunts. There were four hospital deaths not related to the shunts. The remaining 35 patients were followed up for 1.6 months to 6.3 years (mean, 24.7 +/- 18 months). Repeat cineangiocardiographic studies revealed stenosis or distortion of the pulmonary arteries related to the site of the shunt in 11/22 patients (50%) with PTFE shunts and in 1/6 (17%) with classic Blalock-Taussig shunts; the stenosis was severe in only 1 patient. Mean increase in the pulmonary arterial index in the group with classic Blalock-Taussig shunts was 117 +/- 52 mm2/m2 (not significant) and in the group with PTFE shunts, 158 +/- 21 mm2/m2 (p less than 0.001). Late shunt occlusion occurred in 1 patient 23 months postoperatively. Thereafter, shunt patency rate remained at 94% +/- 6%. At the end of 1 year 81% +/- 7% of patients were judged to have adequate palliation, but between 2 and 3 years, only 60% +/- 10%. Univariate analysis showed that after 2 years the ranking order for successful palliation was classic Blalock-Taussig, 5-mm PTFE, and 4-mm PTFE shunts, but differences did not achieve statistical significance.

Abnormalities, Multiple↗
PubMed1991

An injury model myopathy mimicking dystrophy: implications regarding the function of dystrophin.

The pathogenesis of dystrophin deficient myopathies remains unknown. Rat and human muscles subjected to severe injury following repeated eccentric muscle actions demonstrate histopathological alterations which mimic a dystrophic process. Immunofluorescent histochemical examination of these injured muscles demonstrates a separation of proteoglycans of the basal lamina from the muscle plasma membrane, the identical histopathological alteration observed in Duchenne muscular dystrophy. These findings are consistent with the hypothesis that dystrophin is essential for maintenance of the structural integrity of the sarcolemma.

Adult↗
PubMed1991

Minerals: exercise performance and supplementation in athletes.

This paper examines whether mineral supplements are necessary for athletes, and whether these supplements will enhance performance. Macrominerals (calcium, magnesium, and phosphorus) and trace minerals (zinc, copper, selenium, chromium, and iron) are described. Calcium supplements are important for the health of bones. Athletes tend to have enhanced calcium status as assessed by bone mineral density, with the notable exception of female amenorrhoeic athletes. Magnesium status is adequate for most athletes, and there is no evidence that magnesium supplements can enhance performance. Phosphorus status is adequate for athletes. Phosphorus supplementation over an extended period of time can result in lowered blood calcium, however, some studies have shown that acute 'phosphate loading' will enhance performance. Athletes may have a zinc deficiency induced by poor diet and loss of zinc in sweat and urine. Limited data exist on the relationship of performance and zinc status. Widespread deficiencies in copper have not been documented, and there are no data to suggest that copper supplementation will enhance performance. There is no reason to suspect a selenium deficiency in athletes. The relationship between selenium status and performance has not been established, but selenium may play a role as an antioxidant. Because of the low intakes of chromium for the general population, there is a possibility that athletes may be deficient. Exercise may create a loss in chromium because of increased excretion into the urine. Many athletes, particularly female, are iron depleted, but true iron deficiencies are rare. Iron depletion does not affect exercise performance but iron deficiency anaemia does. Iron supplements have not been shown to enhance performance except where iron deficiency anaemia exists. In conclusion, poor diets are perhaps the main reason for any mineral deficiencies found in athletes, although in certain cases exercise could contribute to the deficiency. Mineral supplementation may be important to ensure good health, but few studies have definitively documented any beneficial effect of mineral supplementation on performance.

Exercise↗
PubMed1991

Envelope expansion methods for speech enhancement.

The last decade has seen increasing interest in techniques for the enhancement of digital speech signals. Significant gains have been made in terms of signal-to-noise ratio (SNR) and quality, but few techniques have produced improvements in intelligibility. A method for speech enhancement based on nonlinear expansion of the spectral envelope is presented. The expansion is consistent with both the long-term spectrum of the speech and with the probability that speech is present in a given sample. Objective SNR measures are used to compare this algorithm with the well-known spectral subtraction method, with an alternative expansion scheme, and with limiting SNRs resulting from perfect recovery of the amplitude spectrum. For the purpose of intelligibility assessments, a simplified version of the algorithm has been implemented on a Texas Instruments TMS320-C25 system. Listening trials with this real-time system, conducted using a modified rhyme test, have produced small, but consistent, improvements in articulation scores.

Acoustics↗
PubMed1991

Nutritional ergogenic aids: chromium, exercise, and muscle mass.

Athletes who want to develop muscle mass have sought various ways to reach this goal. We are all too familiar with the abuse of anabolic steroids and growth hormone. Given the concern for such abuses, athletes and coaches are seeking new and safer means to achieve the same end. Within the last couple of years, advertisements for chromium supplements have been prominently displayed in body-building and strength-training magazines. These supplements are purported to be a safe alternative to anabolic steroids and are said to promote an increase in muscle mass. This brief review will focus on the theoretical basis for believing that chromium supplements will increase muscle mass, and on the current research regarding the relationship of chromium and exercise.

Chromium↗
PubMed1991

Effects of coenzyme Q10 supplementation on exercise performance, VO2max, and lipid peroxidation in trained cyclists.

The effects of dietary supplementation with Coenzyme Q10 (CoQ10), a reputed performance enhancer and antioxidant, on physiological and biochemical parameters were examined. Ten male bicycle racers performed graded cycle ergometry both before and after being given 100 mg per day CoQ10 or placebo for 8 weeks. Analysis of variance showed a significant difference between groups for postsupplementation serum CoQ10. Although both groups demonstrated training related improvements in all physiological parameters over the course of the study, there were no significant differences between the two groups (p > .05). Both groups showed a 21% increase in serum MDA (an index of lipid peroxidation) after the presupplementation exercise test. After 8 weeks this increase was only 5%, and again was identical for both groups. Supplementation with CoQ10 has no measurable effect on cycling performance, VO2max, submaximal physiological parameters, or lipid peroxidation. However, chronic intense training seems to result in marked attenuation of exercise-induced lipid peroxidation.

Adult↗
PubMed1990

Kawasaki disease in Auckland, 1979-1988.

Records of 34 children diagnosed as having Kawasaki disease in the Auckland region from 1979 to 1988 inclusive were reviewed. Diagnostic and associated features were similar to those reported from North America and Japan. The incidence (average 5.1 per year per 100,000 less than 5 years of age) was similar to that reported in Europe and North America amongst nonorientals and was similar in Polynesians and nonPolynesians. Coronary artery abnormalities were found in five cases (15%), and two cases, both of whom presented before five months of age, died. Those with abnormal coronary arteries had fever for a significantly longer period than those with normal coronary arteries.

Child, Preschool↗