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Biomedical subjects

A R Morton

Publications and source records attributed to A R Morton.

At least 91 records · Page 5Linked to original sources
PubMed1987

Entrainment of respiratory frequency to exercise rhythm during hypoxia.

Breathing frequency (f) is often reported as having an integer-multiple relationship to limb movement (entrainment) during rhythmic exercise. To investigate the strength of this coupling while running under hypoxic conditions, two male Caucasians and four male Nepalese porters were tested in the Annapurna region of the Himalayas at altitudes of 915, 2,135, 3,200, 4,420, and 5,030 m. In an additional study in a laboratory at sea level, three male and four female subjects inspired various O2-N2 mixtures [fraction of inspired O2 (FIO2) = 20.93, 17.39, 14.40, 11.81%] that were administered in a single-blind randomized fashion during a treadmill run (40% FIO2 maximum O2 consumption). Breathing and gait signals were stored on FM tape and later processed on a PDP 11/73 computer. The subharmonic relationships between these signals were determined from Fourier analysis (power spectrum), and the coincidence of coupling occurrence was statistically modeled. Entrainment decreased linearly during increasing hypoxia (P less than 0.01). Moreover, a significant linear increase in f occurred during hypoxia (P less than 0.05), whereas stride frequency and metabolic rate remained constant, suggesting that hypoxic-induced increases in f decreased the degree of entrainment.

Adult↗
PubMed1987

Maximal exercise cardiorespiratory responses of men and women during acute exposure to hypoxia.

Three male and four female subjects were acutely exposed to normoxic and hypoxic gas mixtures (FIO2 = 17.39%, 14.40%, 11.81%) in a single-blind randomized fashion during four treadmill runs to volitional exhaustion. Maximal scores for oxygen consumption (VO2), carbon dioxide production and heart rate decreased linearly (p less than 0.01) with increasing hypoxia. Conversely, maximal scores for ventilation, ventilatory equivalent (VE/VO2) and R increased linearly (p less than 0.01) with decreasing FIO2. During hypoxia, no significant differences in work time or respiratory compensation threshold were evident. However, female subjects had significantly higher (p less than 0.05) VE/VO2 scores and showed a relative decrease in VO2max that was significantly less (p less than 0.01) than male subjects. It was concluded that young highly active females, when compared to males of similar age and relative condition, have a stronger adaptive response to acute hypoxia during a maximal treadmill run.

Acute Disease↗
PubMed1986

The entrainment of ventilation frequency to exercise rhythm.

To investigate whether ventilation frequency could be entrained to a sub-harmonic of the exercise rhythm, 19 experimentally naive male volunteers were tested during steady state bicycle ergometry and arm cranking under conditions of constant applied workload. Each exercise was performed at two separate ventilatory loads, one within the linear range and the other in the curvilinear range of ventilatory response to exercise. A preferred exercise rhythm was initially adopted (4 min.) followed by forced incremented and decremented rhythm changes each lasting 3 min during a 12 min exercise period. Ventilation, pedal pulse train and heart rate were sampled at 17 Hz on a PDP 11/23 computer. Ratios of limb frequency to dominant respiratory frequency were determined following Fourier analysis of these signals. Data that lay within +/- 0.05 of an integer and half-integer ratio were accepted as indices of entrainment, provided that the observed entrained scores were statistically significant. Ventilation frequency showed a clear, but intermittent tendency to entrain with limb frequency. This tendency was greater during bicycle ergometry, possibly as a consequence of task familiarisation, although both exercise entrainments were independent of workload. No difference between preferred versus varied exercise rhythm was evident, but more entrainment (p less than 0.01) was observed during a decremental change in exercise rhythm. These responses do not appear to support an appreciable role for limb-based afferents in the control of entrainment. The results of this study provide evidence that exercise rhythm has some regulatory role in the control of breathing during moderate rhythmical laboratory-based exercise ergometry.

Adult↗
PubMed1986

Changes in selected cardiorespiratory responses to exercise and in body composition following a 12-week aerobic dance programme.

Cardiorespiratory and body composition changes were evaluated in 25 sedentary females, aged 18 to 30 years, following 12 weeks of aerobic dance training (3 days a week, 45 min a session). Fifteen subjects, from the same population, comprised a control group: they maintained their normal activity and dietary habits over the course of the study. Analysis of variance of the values for selected cardiorespiratory responses revealed that the aerobic dance programme produced training effects in the experimental group. These training effects were indicated by significant improvements in O2 pulse, VE, heart rate and perceived exertion during submaximal exercise. Significant improvements were also noted in VO2 max, maximal O2 pulse, VE max, maximal heart rate and maximal running time on the treadmill. Additionally, increases in lean body mass and body density, together with decreases in percentage body fat and the sum of four skinfold thicknesses were found to be significant for the experimental group. No significant improvements in any of these variables were found for the control group. It was concluded that this 12-week aerobic dance programme was successful in promoting beneficial changes in cardiorespiratory fitness and body composition.

Adolescent↗
PubMed1986

The anatomical and physiological characteristics of pre-adolescent males and females.

Two hundred and two pre-adolescent subjects aged 7-12 years were examined on a battery of anatomical and physiological tests. The total sample comprised non-competitive children, and those involved in training for swimming or tennis. A series of analyses of variance were applied to the data to determine whether any differences existed between preadolescent males and females. No significant interaction between age, sex and sporting involvement was found which indicated sex differences to be independent of age and training group. The results revealed that males were superior to females in physical exercise capacity, PWC170, forced vital capacity, and hand grip strength. Males also demonstrated a lesser proportion of body fat than females but were more mesomorphic. No significant differences existed in any of the other tests.

Anthropometry↗
PubMed1986

The effect of running training on exercise-induced asthma.

A running training program had no effect upon the severity of exercise-induced asthma, however, it appeared as if the children benefitted not only from a decrease in the frequency and duration of asthma in daily life, but also by improvement in self-confidence and ability to participate in group activities.

Adolescent↗
PubMed1985

The effects of cigarette smoking on maximal oxygen consumption and selected physiological responses of elite team sportsmen.

The acute and chronic effects of cigarette smoking on selected physiological responses were determined in seven well-trained non-smokers and seven well-trained habitual smokers. Non-smokers and smokers did not differ significantly with respect to maximal oxygen consumption (VO2max). The acute effect of smoking two cigarettes immediately prior to a graded exercise stress test on a treadmill ergometer did not significantly alter the VO2max of either group. However, the time taken for non-smokers to reach exhaustion decreased significantly (F = 5.381, P less than 0.05) by a mean of 0.64 min. Smokers recorded lower scores for forced vital capacity (FVC) and forced expiratory volume in the 1st s exhalation (FEV1) than non-smokers. Only the mean FVC of smokers recorded 5 min post-exercise was significantly altered by pre-exercise smoking. No differences were found between the resting heart rates (HR) of non-smokers and smokers. Smoking two cigarettes significantly (F = 44.720, P less than 0.01) increased the mean resting HR of smokers and non-smokers by 15.8 beats X min-1 and 15.6 beats X min-1 respectively. No alteration to the exercise HR of either group was found under smoking conditions of the VO2max tests.

Adult↗
PubMed1985

Absence of refractoriness in asthmatic subjects after exercise with warm, humid inspirate.

Twelve asthmatic adults each completed two six minute treadmill runs separated by an interval of 20 minutes. Running speed was constant for each subject, and inspired air temperature averaged 5.5 degrees C (SD 1.5 degree) for both tests. Total minute ventilation and total respiratory heat loss showed no significant difference between the two runs. Forced expiratory volume in one second (FEV1) was measured before exercise and at five minute intervals throughout the recovery periods, during which subjects breathed room air at an average temperature of 17.8 degrees C (1.8 degree). Reduction in FEV1 from pre-exercise readings averaged 39.3% (13.3%) for the first run and 11.5% (7.3%) for the second. On another day the subjects underwent an identical procedure except that the first exercise period was performed with the saturated inspirate at 37.3 degrees C (1.7 degree). This run produced a mean FEV1 reduction of only 3.1% (7.3%). The ensuing run, during which the inspiratory temperature averaged 6.0 degrees C (2.0 degrees), led to a mean fall in FEV1 of 37.3% (17.3%). This was not significantly different from the value recorded for the first of the paired runs with cool air. We therefore have been unable to confirm that exercise with warm humid inspirate may induce refractoriness to exercise induced asthma. Our data are compatible with the theory that refractoriness may be due to depletion of mediators during an initial exercise induced asthma attack.

Asthma↗
PubMed1984

Histamine reactivity during the refractory period after exercise induced asthma.

An episode of exercise induced asthma will usually be followed by a period during which further exercise will not induce asthma. Postulated mechanisms include persistence of catecholamines released during exercise, development of tolerance to released mediators, and mediator depletion. To investigate the underlying mechanism further eight asthmatic men underwent three experimental protocols as follows: two treadmill runs of eight minutes; two incremental challenges with histamine inhalation; and a treadmill run of eight minutes followed by an incremental challenge with histamine inhalation. In each case the two challenges began 40 minutes apart. Patients performed the paired exercise trial first. Refractoriness to bronchoconstriction was shown in the repeated exercise studies but did not occur with repeated histamine challenge. The geometric mean histamine concentrations required to produce a 20% fall in forced expiratory volume in one second (FEV1) were 1.53 mg/ml and 0.93 mg/ml for the first and second challenges respectively (NS) and 1.4 mg/ml (NS) for the histamine challenge after exercise. It is concluded that refractoriness to exercise induced asthma is not explained by the development of smooth muscle tolerance to repeated histamine exposure or by the persistence of catecholamines released during exercise. The data are consistent with the theory of mediator depletion as the cause of refractoriness.

Adult↗
PubMed1984

A reinterpretation of the effect of temperature and water content of the inspired air in exercise-induced asthma.

To compare the importance of water loss with heat loss in the mechanism of exercise-induced asthma (EIA), we conditioned the air inspired during exercise to the same water content (Wi) while changing its temperature (Ti), and vice versa. We calculated separately the amount of heat and water required to bring the inspired air to alveolar conditions. Ten asthmatics ran for 8 min on 4 occasions in an environmental chamber. The air was conditioned to a Ti of 9 to 10 degrees C or 35 degrees C, with a Wi of 9 to 10 mg H2OL-1. The airway response to exercise was not significantly different when Ti varied by 25 degrees C, but the amount of water required to saturate the inspired air remained the same. However, the amount of heat required was significantly greater with cooler air (p less than 0.005). We conclude that it is the osmotic and not the cooling effects induced by the vaporization of water that is the more important factor determining EIA.

Adolescent↗