Biomedical subjects

J Richard Coast

Publications and source records attributed to J Richard Coast.

5 recordsLinked to original sources

PubMed2005

Zidovudine-induced diaphragmatic contractile dysfunction: impact of an antioxidant diet.

OBJECTIVE: Zidovudine (AZT) is a primary drug therapy used to treat HIV-infected individuals. While AZT inhibits replication of HIV, it also induces a drug-specific myopathy resulting in altered muscle mitochondria, increased oxidative stress and muscle contractile dysfunction. The purpose of this study was to assess the impact of an antioxidant diet (high in vitamins C and E) on AZT-mediated diaphragmatic contractile dysfunction in rodents. METHODOLOGY: Adult, Sprague-Dawley rats were assigned to feeding groups: control (CON, n = 9), AZT-treatment (AZT, n = 8), antioxidant diet only (Anti-Ox, n = 6), and AZT + antioxidant diet (AZT + Anti, n = 9). Two costal diaphragm strips were removed from each animal (under surgical anaesthesia) and evaluated for force-frequency relationship, maximal specific tension, and fatigue resistance using an in vitro preparation. RESULTS: Results indicate significant reductions in normalized force production (20-200 Hz), including maximal specific tension, between AZT animals and all other groups. While AZT reduced diaphragm contractility, the addition of an antioxidant diet eliminated this decrease. CONCLUSION: These data suggest that an increase in oxidative stress mediated by AZT may contribute to AZT-induced muscle contractile dysfunction, and that antioxidant vitamin supplementation may help ameliorate this effect.

Animals↗

PubMed2004

The effect of chest wall restriction on exercise capacity.

OBJECTIVE: Subjects with restrictive pulmonary disease exhibit a decreased exercise capacity compared to non-diseased subjects, as do subjects in certain workplace situations, for example when wearing bullet-proof vests. The purpose of this study was to examine the effects of varying degrees of chest wall restrictive loading on exercise performance. We have designed and validated a chest wall restrictor that mimics the elastic loading occurring in some disease states and some occupational situations. METHODOLOGY: In this study, 18 subjects performed five graded maximal cycling tests while wearing the device at four different inflation pressures (0, 20, 40, and 60 mmHg). RESULTS: Maximal values of oxygen uptake (VO2max), minute ventilation (VImax), tidal volume (VT at max) and breathing frequency (fB at max) were monitored, as was the time to maximal exercise (TTM). VO2, VI, VT, and fB were also measured at three submaximal loads. The results showed that VO2max, VImax, TTM, and VT at max were significantly decreased, while fB at max was maintained. At submaximal loads, the ventilatory parameters VT, and fB were altered with load, but VI and VO2 were not affected by load. CONCLUSIONS: These results indicate that the wearing of this device decreases variables associated with maximal exercise, and that the decreases are related to the degree of chest wall restriction. Furthermore, submaximal exercise ventilation was minimally altered, with an increase in fB and a decrease in VT associated with increasing restrictive loads. Submaximal oxygen uptake was not affected by breathing restriction.

Adult↗

PubMed2004

Do gender differences in running performance disappear with distance?

It has been suggested that gender differences in running should disappear as distances increase, particularly past the marathon. This suggestion is primarily based on differences in fuel utilization, muscle damage following exercise, relative improvements in performance over the past decades, and on the analysis of marathon vs. ultramarathon performances of men and women. We reasoned that the best comparison of the potential of a human is by the use of world best times, which should be reasonable indicators of the effect of distance on relative performance of women and men. We compared current world best running performances at distances from 100 m to 200 km. Records as of December 2002 were obtained. T-tests analyzed speed differences between genders, and regression analysis tested the percent differences between men and women across distance. Speeds were different, with the average difference being 12.4% faster for men. There was a significant slope to the speed difference across distances in that longer distances were associated with greater differences. These results may be confounded by the reduced number of women in longer distance events. Furthermore, the proposed metabolic advantage for women because of increased fat metabolism may be masked by regular feeding during endurance races.

Adult↗

PubMed2002

Effect of ammonia on in vitro diaphragmatic contractility, fatigue and recovery.

BACKGROUND: Following strenuous exercise, in vivo diaphragmatic strength has been reported to decrease. This decrease has been suggested to result from an increase in metabolic by-products of intense exercise. OBJECTIVE: We tested the hypothesis that physiological NH(3) concentrations adversely affect diaphragmatic contractility, fatigability, and recovery. METHODS: Rat diaphragm strips were exposed to one of six experimental conditions (n = 6 per condition): Krebs-Ringer control solution, or the control solution with NH(3) added (in mM): 0.11, 2.5, 5.0, 10.0, or 14.0. Initial diaphragmatic contractility was assessed with the force-frequency response in the control solution. Following the first force-frequency response, the solution was replaced with one of the six solutions and a second force-frequency response was measured. Strips were then subjected to a short fatigue protocol and contractility was reassessed with a third force-frequency response. A longer fatigue protocol was then administered, followed by a 20-min recovery assessment period. RESULTS: Ammonia significantly (p < 0.05) reduced diaphragmatic contractility, but only at concentrations of 5 mM or greater. Additionally, ammonia did not alter the rate of fatigue. CONCLUSIONS: This study suggests that physiological NH(3) concentrations do not adversely affect in vitro diaphragmatic contractility, fatigue, or recovery. These data are not consistent with diaphragmatic fatigue associated with exercise induced by arterial concentrations of NH(3) seen in humans, although further testing in situ or in vivo is needed.

Ammonia↗

PubMed2002

Effect of recovery interval on multiple-bout sprint cycling performance after acute creatine supplementation.

The purpose of this study was to examine the effect of varying recovery intervals on multiple-bout, short-duration, high-intensity cycling efforts of adult men supplemented with creatine (Cr) or a placebo (Pl). Thirty subjects underwent 3 trials of a maximal cycling protocol (T(0), T(1), T(2)). T(0) included V(O)2 max testing and familiarization with the sprint cycling protocol. T(1) consisted of 8 15-second bouts of sprint cycling exercise. Subjects were randomly assigned to recovery interval groups (1 minute, 3 minutes, 6 minutes), and Cr or Pl groups (0.3 g x kg(-1) x d(-1)). Posttesting (T(2)) took place 7 days after T(1) and consisted of an identical protocol as during T(1). Changes in mean power (MP), peak power (PP), and fatigue index (FI) were compared between trials. MP was significantly increased in Cr 1-minute, Cr 3-minute, and Pl 6-minute groups (p < 0.05). Significant PP increases were demonstrated in Cr 1-minute and Pl 6-minute groups (p < 0.05), and FI significantly increased in Pl 1-minute group (p < 0.05). Results indicate that Cr supplementation is effective in improving recovery from repeated sprint cycling performances when the recovery interval is of a short (<6 minutes) duration.

Adult↗