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Biomedical subjects

R Dowdeswell

Publications and source records attributed to R Dowdeswell.

6 recordsLinked to original sources
PubMed1999

Assessment of reliability of lung function screening programs or longitudinal studies.

The aim was to determine reliability of lung function measurements performed according to recommendations of the American Thoracic Society (ATS) at a screening program in a large South African gold mine and to determine the usefulness of the reliability coefficient G for monitoring the reliability of lung function measurements in a mass screening program. The reliability coefficient G estimates the amount of random error of measurement, relative to the total variation in a measurement. The coefficient G was calculated as a correlation coefficient between two consecutive lung function tests performed within 6 mo, over a period of 43 mo on 3,378 miners. There was significant temporal variability in the reliability. For FEV(1), the coefficient G showed increased variability over the first 5 mo and stabilized at a value of 0.93 for the next 23 mo, after which it systematically declined over the next 15 mo. We estimated that in a large screening program, an optimal sample size of around 900 miners, examined randomly throughout the year, on a yearly basis, would provide a sufficient sample to examine monthly or quarterly fluctuation in the reliability. The value of the reliability coefficient G did not change when the time between two consecutive tests increased up to 15 mo. In conclusion, monitoring of lung function reliability in a screening program by the reliability coefficient G should improve data quality, and provide a measure on which the confidence in a decision-making process could be based when examining temporal changes in lung function for individual subjects.

Adult↗
PubMed1996

Health effects of passive smoking in adolescent children.

OBJECTIVE AND DESIGN: To study the effects of passive smoking on health in adolescent schoolchildren by questionnaire, spirometry and laboratory investigations. SETTING: Two schools in the Vanderbijlpark area. PARTICIPANTS: Seven hundred and twenty-six high-school children of average age 16 years. OUTCOME MEASURES: Lung function, serological abnormality or historical (i.e. questionnaire) evidence of ill health. RESULTS: The prevalence of respiratory illness before and after 2 years, respiratory symptoms, earache over the past year, low birth weight and learning difficulties were found to be significantly increased in the children exposed to parenteral smoke in the home, especially those exposed to maternal smoking. Spirometric and laboratory parameters, however, were not affected by passive smoking.

Adolescent↗
PubMed1993

Exercise, regardless of induced bronchoconstriction or inspired air conditions, does not alter airway reactivity.

The effects of exercise on asthmatic airway caliber are well recognized. Only a few studies, however, evaluated the effects of prior exercise on asthmatic airway reactivity. Eight asthmatic children (ages 10 to 16 years; mean, 12) performed histamine inhalation tests on three occasions assigned in random order: (1) control; (2) 40 to 60 min after exercise (6 min ergometer cycling) done while breathing cold dry (CD) air (temperature = -13 degrees C, relative humidity = 0 percent); and (3) 40 to 60 min after exercise done while breathing warm humid (WH) air (temperature = 33 degrees C, relative humidity = 100 percent). While there was a marked exercise-induced bronchoconstriction (EIB) in the CD test with a postexercise fall in FEV1 of 39.2 +/- 8 percent (mean +/- SEM), there was no EIB in the WH test (4.6 +/- 2 percent). There was no difference, however, in the geometric mean histamine concentration required to produce a 20 percent fall in FEV1 (PC20) among the CD, WH, and control tests (0.52 mg/ml, 0.60 mg/ml, and 0.55 mg/ml, respectively). Airway reactivity in asthmatic children is not influenced by a prior exercise challenge, independent of the conditions of the inspired air during the exercise. Moreover, exercise per se, regardless of development of EIB, does not change the reactivity.

Adolescent↗
PubMed1985

Reflex heart rate control in asthma. Evidence of parasympathetic overactivity.

The bronchial hyperreactivity characteristic of asthma may be related to enhanced parasympathetic nervous activity. We postulated that an abnormality in the autonomic control of airway caliber might be reflected by a parallel change in the reflex control of heart rate. We examined the heart-rate variations induced by deep breathing (respiratory sinus arrhythmia), the Valsalva maneuver, and standing up from the recumbent position in asthmatic subjects and nonasthmatic control subjects. The asthmatic patients had evidence of enhanced parasympathetic neural drive to the sinoatrial node, as manifested by a significantly greater magnitude of respiratory sinus arrhythmia, than the controls (p less than 0.0005). We were unable to induce a similar change in normal subjects by resistance breathing. A statistical analysis suggested the presence of a relationship between the magnitude of respiratory sinus arrhythmia and the degree of bronchial hyperreactivity in a group of asthmatic patients. Our results support the hypothesis that enhanced parasympathetic activity is an important factor in the pathogenesis of bronchial asthma.

Adult↗
PubMed1978

A comparative assessment of carbuterol, fenoterol and hexoprenaline in allergic asthma.

Carbuterol tablets (2,0 mg) were compared with the tablets of fenoterol (2,5 mg) and hexoprenaline (1 mg). The three drugs were shown to be equally effective for a period of 4 hours, but carbuterol and fenoterol exerted a statistically significant bronchodilating action for 7 and 8 hours respectively, while the action of hexoprenaline lasted for 4 hours in the majority of patients. The aerosols of carbuterol (200 mg) and fenoterol (400 mg) appeared to be similar in inhibiting exercise-induced asthma, whereas hexoprenaline (200 mg) did not appear to be as effective.

Adolescent↗