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Biomedical subjects

S Godfrey

Publications and source records attributed to S Godfrey.

At least 127 records · Page 7Linked to original sources
PubMed1987

Exercise intensity determines and climatic conditions modify the severity of exercise-induced asthma.

Recent studies have shown some evidence that exercise-induced asthma (EIA) may not be entirely explained by respiratory heat loss (RHL). We investigated the interrelationship between heat exchange, exercise intensity and EIA. In order to differentiate between the effects of RHL and exercise intensity, we arranged for tests to be performed with the same RHL, but with different intensities of exercise and inspired air conditions. Each of 8 asthmatic children exercised twice in random order for 6 min on a cycle ergometer. One test consisted of exercise performed at a greater level of effort while breathing room air, mean (+/- SE) air conditions being 25.0 +/- 0.4 degrees C and 15.7 +/- 0.2 mg H2O/L. The other test was performed at a lesser level of effort while breathing cold (0.0 +/- 0.5 degrees C) and dry air (O mg H2O/L). The mean ratio of minute ventilations in the 2 exercise tests was 1.78 +/- 0.03, but the RHL was similar in both tests. The EIA after the exercise at the greater level was more severe than after the lesser level, the percent fall in FEV2 from baseline being 36 +/- 7% and 21 +/- 5%, respectively (p less than 0.025). We conclude that the exercise level has a major role in determining the severity of EIA and that climatic conditions act as modifying factors.

Adolescent↗
PubMed1987

Functional residual capacity in healthy preschool children lying supine.

Functional residual capacity (FRC) was measured by the closed-circuit helium dilution method in 41 supine healthy children 1 month to 8 yr of age. In 20 children, the measurement was carried out while they were awake, and in the others, who were less cooperative, testing was done during ketamine anesthesia before elective surgery. There was no significant difference in the FRC values between these groups, and they were subsequently analyzed as a single group. For males and females separately and combined, FRC correlated significantly with height, age, and weight, both with linear and nonlinear regression analyses. No significant difference between the sexes was found. The best correlation of FRC was with height; the linear equation being FRC (ml) = -457.3 + 8.8 X height (cm) (r2 = 0.662), and the nonlinear equation being FRC (ml) = 0.0052 X [height (cm)]2.44 (r2 = 0.827).

Child↗
PubMed1986

Increased bronchial responsiveness to exercise and histamine after allergen challenge in children with asthma.

Nonspecific bronchial reactivity to exercise and histamine was measured in nine children with asthma before and within nine days after allergen inhalation. All patients developed an immediate fall in FEV1 of greater than or equal to 16% after allergen inhalation, and five children also developed a definite late asthmatic response with a fall in peak expiratory flow of greater than or equal to 14% after 3 to 8 hours. Mean postexercise fall in FEV1 (delta FEV1) of the whole group was significantly greater after allergen challenge compared with that of control subjects (29 +/- 6% and 16 +/- 4%; p = 0.013). There was no change in refractoriness to repeated exercise after allergen challenge. The mean provocation concentration of histamine causing a decrease in FEV1 of 20% of the whole group was less after allergen challenge compared with that of control subjects (0.47 +/- 0.18 and 0.62 +/- 0.13), but this was not statistically significant (p = 0.19). Of the five children with late allergen reactions, all demonstrated increased histamine sensitivity, and all four children who developed definite exercise-induced asthma also demonstrated increased sensitivity to exercise. Of the four children without late allergen reactions, none demonstrated increase histamine sensitivity, but two of the three children with definite exercise-induced asthma demonstrated increased sensitivity to exercise. It may be that sensitivity to exercise is more easily affected by nonspecific reactivity than sensitivity to histamine. It is concluded that increased bronchial responsiveness to both exercise and histamine occur after allergen provocation in patients with asthma.

Adolescent↗
PubMed1986

Airway resistance measurements throughout the respiratory cycle in infants.

Using a constant-volume infant whole-body plethysmograph containing a heated rebreathing bag, we have been able to measure airway resistance (Raw) throughout the respiratory cycle using a computer-based technique. Data from the plethysmograph transducers are sampled at 60 Hz for the calculations and Raw is calculated at each point sampled during the breath, with appropriate corrections for absolute lung volume. It was found that in most cases Raw varied less with respect to tidal volume than to tidal flow. Various patterns of Raw change in relation to tidal volume were found. These included an elevated but relatively constant resistance, a progressively rising expiratory resistance, and in 3 infants with laryngomalacia, a progressively rising inspiratory resistance. It was also found that the dynamic performance of the rebreathing bag was such that considerable errors would occur if apparatus resistance was assumed to be constant and so the actual apparatus resistance at each point was subtracted from the total resistance to give Raw. In conclusion, Raw is not constant throughout the respiratory cycle in infants and the pattern of change conveys additional information.

Airway Resistance↗
PubMed1986

Can thoracic gas volume be measured in infants with airways obstruction?

Thoracic gas volume (Vtg) was measured in a whole-body, infant plethysmograph in 46 infants with recurrent wheezing after bronchiolitis, 25 infants with cystic fibrosis, and 6 infants without overt lung disease during the first 13 months of life. When related to weight or length, 56.5% of the bronchiolitic infants had low Vtg values, which were more than 2 SD below their predicted normal. The Vtg of the other groups was normal or above. The bronchiolitic infants with Vtg values in the normal range had more severe airways obstruction and it is probable that their Vtg values were also underestimated. Investigation of possible sources of technical or experimental error failed to reveal any explanation for the low Vtg in the bronchiolitic infants. In 5 infants, Vtg determined plethysmographically was correlated linearly to functional residual capacity determined by helium dilution, although Vtg values were greater in all. The administration of albuterol or treatment with steroids failed to make significant changes in Vtg in the bronchiolitic infants. It is suggested that there is a physiologic basis for the presumed underestimation of Vtg in wheezy infants after bronchiolitis, either because of uneven alveolar pressure changes within the chest leading to the effective exclusion of a portion of the lung volume or because there are some alveolar units with very low compliance that change little in volume during respiratory efforts against an occlusion. These results call into question the validity of the plethysmographic measurement of Vtg or airway resistance in these infants. If the error in Vtg is due to uneven alveolar pressure changes, it is suggested that the calculated specific airway conductance is probably correct.

Airway Obstruction↗
PubMed1986

Nemaline myopathy as a cause of sleep hypoventilation.

Two siblings, a 14.5-year-old boy and his 11.5-year-old sister, with congenital nemaline myopathy presented with severe respiratory failure and, in the case of the older patient, with cor pulmonale and systemic hypertension. The children were treated initially by continuous mechanical ventilation, but after a few weeks they only required ventilation at night. At the start of treatment, both were found to have a decreased ventilatory response to CO2 which apparently improved during 4 to 5 years of follow-up treatment. It has not been possible to wean them from nocturnal mechanical ventilation, but during the daytime they attend school and function almost normally. It is postulated that respiratory failure in nemaline myopathy may not be related to the severity of the muscle weakness but may result from a disturbance of the feedback required for normal control of breathing.

Adolescent↗
PubMed1986

Controversies in the pathogenesis of exercise-induced asthma.

Exercise-induced asthma is considered in terms of the stimulus, the intermediary pathway and the response. Various controversies about each of these components are discussed. The stimulus may be cooling of the airways, loss of water or neither of these, and there is evidence for and against the identity of exercise- and hyperventilation-induced asthma. The intermediary pathway seems certain to involve the release of chemical mediators, although other neurogenic mechanisms have been proposed. Since the response is far from uniform, it may well be that different pathways are involved in different subjects. The effector mechanism appears to be bronchospasm, but recent evidence has suggested that an inflammatory response may be involved in a late reaction to exercise. The variability of exercise-induced asthma may well be due to variations in intrinsic bronchial reactivity resulting from allergenic stimulation.

Asthma↗
PubMed1985

Clinical, physiologic, and psychologic comparison of treatment by cromolyn or theophylline in childhood asthma.

Treatment of chronic perennial childhood asthma with cromolyn sodium (CS) or long-acting theophylline (LAT) was compared in 13 children by a double-blind, cross-over trial in which each drug was administered for 4 wk. LAT was administered twice daily in individual doses to elicit adequate blood levels (mean 14.0 +/- 1.6 SEM, micrograms per milliliters). Powdered CS was administered by inhalation in a dose of 20 mg four times daily. The patients were followed by means of a daily symptom and drug consumption diary and twice daily peak flow measurements. A series of psychologic studies were performed in the third week of each month. Exercise and histamine bronchial provocation tests were performed at the end of each month. There were no significant differences between the month in which CS was taken and the month in which LAT was taken in terms of diary scores, peak flow rates, additional drug consumption, or in bronchial reactivity to exercise or histamine at the end of each month. The results of psychologic tests reflecting visual-spatial planning were significantly better for the four children receiving CS with lower IQ scores (87 to 105) but not for the nine children with higher IQ scores (111 to 134). The possibility that the psychologic performance of children with lower intelligence may be adversely affected by theophylline requires further evaluation.

Adolescent↗