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Biomedical subjects

R L Hughson

Publications and source records attributed to R L Hughson.

172 records · Page 10Linked to original sources
PubMed1981

Effect of oral propranolol on the anerobic threshold and maximum exercise performance in normal man.

The effect of propranolol on the anaerobic threshold was studied in six healthy male volunteers. The subjects exercised on a cycle ergometer in a progressive exercise test to exhaustion with propranolol or no drug. Power output was increased by 30 W ever 2 min. Propranolol caused a significant reduction of heart rate by 20-45 beats per minute at all power outputs. In light and moderate exercise, no differences in oxygen uptake, ventilation, or blood lactate were observed in the propranolol and no-drug tests. The anaerobic threshold was not different between the no-drug (2.32 +/- 0.19 L O2/min, mean +/J- SD) and the propranolol (2.83 +/- 0.27 L O2/min) test; however, the heart rate at the anaerobic threshold was significantly lower in the propranolol (143 +/- 13 beats per minute) than the no-drug (187 +/- 9 beats per minute) tests. Above the anaerobic threshold, oxygen uptake was similar at a given power output but it reached a lower peak value (p less than 0.02) in the propranolol (3.16 +/- 0.16 L O2/min) versus the no-drug (3.64 +/- 0.39 L O2/min) tests. It was concluded that propranolol caused no change in anaerobic threshold in this specific progressive exercise protocol. The results suggest that a training intensity for endurance exercise bases on the anaerobic threshold does not need to be modified for subjects on propranolol medication.

Adult↗
PubMed1980

Heat injuries in Canadian mass participation runs.

In two Canadian runs with a total of approximately 2900 participants 26 people collapsed with heat injury and were taken to hospital. All were relatively young (13 to 38 years old). A retrospective survey showed that all were novices to 10-km races and that many had collapsed even though they had consumed fluids before and during the run. A review of etiologic factors suggested that the extremes in the Canadian climate, which preclude heat acclimatization in the spring and early summer, may be an important influence on the incidence of heat injury.

Adolescent↗
PubMed1980

Ventilatory CO2 response in endurance-trained rats.

A CO2 rebreathing technique was used to assess possible changes in the ventilatory response to CO2 in rats following a 14-week swim training program. Over the final 9 weeks, the rats swam 1 hr per day with a weight of 2.5% of the body weight attached to the tail. Ventilation was measured by a barometric method in awake, restrained rats in a total body plethysmography at CO2 concentrations of 0, 2, 4, 6, and 8%, with an initial O2 concentration of approximately 100%. Ventilation increased in the trained rats with increasing CO2 from 775ml . min-1 . kg-1 at 0% CO2 to 1,387 ml . min-1 . kg-1 at 8% CO2. This increase was a consequence of a 34% increase in tidal volume and a 32% increase in breathing frequency. In comparison with a group of sedentary control rats, there was a significantly higher ventilation and tidal volume at 0% CO2; however, this difference disappeared with increasing levels of CO2. A significantly lower resting heart rate was observed in the exercised (296 +/- 44 beats . min-1, mean +/- SD) compared to the sedentary control rats 380 +/- 42). It was concluded that, while the normal training response of resting bradycardia was observed following this duration and intensity of training, endurance swimming had no significant effect on the ventilatory response to CO2 in the rat.

Animals↗
PubMed1980

Open-circuit gas exchange analysis in the non-steady-state.

The serial measurement of oxygen uptake (VO2) of four subjects was calculated during the transition from rest to constant-load cycle ergometer work using an open-circuit gas exchange analysis system. In calculating VO2, the mixed expired gas concentrations were matched with the ventilatory volume by various delay factors. A delay factor equivalent to the passing of 20 L of expired ventilation through the mixing chamber yielded results which were most similar to the VO2 obtained by a computerized breath-by-breath analysis. Previous checks of the response of the system to changes in calibrating gas mixtures had indicated that it was necessary to pass approximately 20-25 L of gas through the system before a plateau response was observed. This volume remained relatively constant, independent of flow rate. It is proposed that an understanding of the response characteristics of an open circuit system will enable the accurate calculation of VO2 over short time intervals in the non-steady-state.

Adult↗
PubMed1977

Oral and intravenous propranolol during exercise.

The intrinsic sinoatrial (SA) rate at rest and during exercise was measured in 5 normal male subjects after prolonged oral and acute intravenous administration of propranolol and atropine. At rest, the intrinsic SA rate was similar after both oral and intravenous propranolol. At the higher levels of power output on a cycle ergometer, cardiac rate was slower after oral than after intravenous propranolol. When the intravenous study was repeated with the use of an additional dose of propranolol, cardiac rate was lower at comparable levels of power output, but not as low as that after oral propanolol. Differences in responses were interpreted as reflecting varying degrees of beta blockade, the most complete being that after prolonged oral propranolol administration of 320 mg daily. The intravenous dose of propranolol usually used to obtain the "pharmacologically isolated heart" at rest is too small to induce full beta blockade in exercise.

Administration, Oral↗
PubMed1977

Reduction of intrinsic sinoatrial frequency and norepinephrine response of the exercised rat.

Physical training is associated with a reduction of intrinsic sinoatrial activity; the present study examined the role of the parasympathetic nervous system in this reduction. Six groups of rats were studied for 10 weeks: inactive control; treadmill exercised; parasympathetic receptor blockade with atropine; exercise plus atropine; parasympathetic receptor stimulation with carbachol; and exercise plus carbachol. In vivo ISF (cardiac frequency 20 min after injection of propranolol and atropine) was measured at 3-week intervals. At the end of 10 weeks the right atrium was excised, in vitro measurements were made of ISF, and chronotropic dose-response curves to acetylcholine and norepinephrine were established. In vivo, ISF was reduced with time, the greatest reduction being found in the exercise plus atropine group; the treadmill-exercised and the atropine-treated groups also had a greater reduction than the control group. In vitro, no differences were observed in acetylcholine responses. The maximum norepinephrine chronotropic response was reduced in the treadmill-exercised and the exercise plus atropine groups. The maximum norepinephrine-induced frequency correlated with the in vitro ISF (r = 0.75). Thus, ISF was reduced with training, but this effect was independent of parasympathetic activity. The properties of the sinoatrial node which set ISF also influenced the maximum norepinephrine response.

Acetylcholine↗
PubMed1975

The inotropic and chronotropic responses of the guinea pig and dog myocardium to isoprenaline and salbutamol.

The relative effects of isoprenaline and salbutamol on the inotropic and chronotropic responses of the denervated myocardium of the chloralose anesthetized dog and of the isolated guinea pig atrium, and the inotropic response of the isolated dog papillary muscle were studied. Both the in vivo dog heart and the in vitro guinea pig atrium displayed a similar relative response pattern to isoprenaline and salbutamol with regard to their inotropic and chronotropic responses. However, a comparison of the relative inotropic responses of the dog heart in vivo and in vitro showed that in vitro, salbutamol has a much lower affinity and efficacy for the adrenergic receptors than isoprenaline.

Albuterol↗