We investigated whether an exercise challenge protocol is suitable for measuring bronchial responsiveness in epidemiological studies of asthma in children, and determined its comparability with histamine challenge. The exercise challenge was 6 minutes of outdoor, free-range running at 85-90% of maximum heart rate, measured by heart rate monitor. Nose clips were worn. Distance run was measured to estimate oxygen consumption. Water content of the inspired air was < 10 mg H2O.l-1. Histamine challenge was by the rapid method. We used questionnaires to measure respiratory symptoms and skin prick tests to measure atopy. A total of 96 children aged 8-11 years were studied. Bronchial hyperresponsiveness (BHR) to exercise challenge was defined as a fall in forced expiratory volume in one second (FEV1) of 13% of greater. Eleven children had a positive response to exercise challenge and 11 to histamine challenge but 12 responded to one challenge and not to the other. The correlation coefficient between the two tests was 0.65 (p = 0.0001). Exercise challenge thus proved to be a practical epidemiological tool for objective measurements of bronchial responsiveness in children. In this sample, some children responded to one challenge and not to the other which suggests that the two challenges identify different abnormalities of the airways.

D Di if ff fe er re en nc ce es s i in n a ai ir rw wa ay y r re es sp po on ns si iv ve en ne es ss s b be et tw we ee en n c ch hi il ld dr re en n a an nd d a ad du ul lt ts s l li iv vi in ng g i in n t th he e s sa am me e e en nv vi ir ro on nm me en nt t: : a an n e ep pi id de em mi io ol lo og gi ic ca al l s st tu ud dy y i in n t tw wo o r re eg gi io on ns s o of f N Ne ew w S So ou ut th h W Wa al le es s In winter 1991 and 1992, we studied two large random samples of children living in two different regions; and, three months later, we conducted a study of adults who lived with enrolled children. A total of 805 children and 814 adults attended in Lismore, and 850 children and 711 adults in Wagga Wagga. Questionnaires were used to measure symptom history, histamine inhalation challenge to measure airway hyperresponsiveness (AHR) and skin-prick tests to measure allergy.There was a higher prevalence of asthma in children than in adults: recent wheeze was 1.5 times higher; asthma medication use was 1.5 times higher; diagnosed asthma was 1.6 times higher; and AHR was two times higher. Current asthma (AHR and recent wheeze) was 9.5-11.3% in children and 5.4-5.6% in adults. These differences were statistically significant. In both regions, airway responsiveness was more severe in children who were sensitized to common allergens than in similarly sensitized adults.These results suggests that airways can develop protective mechanisms with age, or that recent environmental changes in factors such as allergen levels, diet or treatment practices have led to immunological changes and to incresed airway responsiveness in this generation of children.

We assessed the validity, repeatability and practicality of a standardized exercise challenge protocol for measuring airway responsiveness in epidemiological studies of asthma in children aged 8-11 yrs. The construct validity of the exercise challenge was assessed by comparing response to exercise with other measures of asthma, i.e. wheeze frequency, diagnosed asthma, asthma medication use, atopy and urgent doctor visits (n = 802), and by comparison with response to histamine challenge (n = 201). Repeatability was assessed by comparison of responsiveness to two exercise challenges within 3 days (n = 113), and practicality was assessed by measurement of consent, compliance and throughput rates (n = 802). There was a significant relationship between frequency of wheeze attacks and % fall in forced expiratory volume in one second (FEV1) to exercise. The correlation (r) between % fall in FEV1 to exercise challenge and dose-response ratio to histamine challenge was 0.59. The repeatability of the exercise challenge was +/- 12% fall in FEV1. Consent and compliance rates for exercise challenge were 78 and 99%, respectively, and the mean throughput rate was 45 children per school day for a team of seven researchers. In conclusion, this exercise challenge was found to have good validity and to be reliable and practical. Thus, this challenge could be used as a standardized epidemiological tool to investigate the prevalence, aetiology and mechanisms of asthma.

Therapeutic objectives, during all phases of illness, were employed to minimize progression to respiratory insufficiency. When status asthmaticus developed, the methods of medical management, with year initiated in ( ), were considered and if necessary, utilized to prevent respiratory failure. The techniques used could not have been possible without the aid of a cooperative and intellectually'stimulating staff willing to comply with a rigid requirement for structured supervision of each level of care.The useful modifications in regimen were aggressive patient and current protocol surveillance (1956). increased theophylline dose (1959). blood gas monitoring (1963 In spite of the diuresis, measurements of dynamic skinfold thickness did not confirm mobilization of subcutaneous interstitial water. We conclude that FS has a potent diuretic effect in infants with HMD but it does not improve cardiorespiratory function acutely. This may be due to failure to mobilize pulmonary interstitial fluid in the time period tested. respiration, increases expiratory duration and i s vagal l y mediated. To explore whether a s i m i l a r response occurs i n humans, we studied respiratory timing i n 10 sleeping, heal thy term neonates on days 1.2 and 3, before and a f t e r a change i n lung volume accomplished by adding a continuous positive airway pressure(CPAP) o f 3 and 6 cm H 0. Using a mask and flowmeter with constant flow t o reduce dgadspace, we measured insptratory t i m e ( T i ) , expiratory time(Te) .total respiratory cycle duration ( T t o t ) , and t i d a l volume. Comparative movements o f upper and lower r i b cage were recorded v i a mercury s t r a i n gauges and transcutaneous(Tc) PO monitored v i a a skin electrode. Increasi n a luna volume cause8 a s i a n i f i c a n t prolongation o f Te% ( 1 6 0 x~e j~t o t l on a l l 3 davslmean data' i n table). As CPAP was from-47 t o Recent studies suggest that the lamellar bodies in lung tissue contain enzymes involved in the lecithin biosynthetic pathway. Phosphatidyl choline transferase (PCT), very possibly the ratelimiting enzyme in the lecithin biosynthetic pathway, has been described in fetal lung; however, the distinction has not been made between PCT activity in lamellar bodies and that in microsomes, a known site of lecithin biosynthesis. This study assessed lecithin biosynthesis by measuring the activity of PCT in these two subcellular fractions obtained from lung of New Zealand White rabbits of gestational age 25-31 days and postnatally to age 10 days. The lamellar and microsomal fractions were prepared by differential centrifugation, and their PCT activities were measured using the precursor. (14~)-~~~-choline. In both subcellular fractions, PCT activity reached an initial peak on the 28th day of gestation after which the activity dropped dramatically at term, followed by a gradual rise beginning between the 5th and 8th postnatal day. At the 28 day peak, lamellar body PCT activity was double that in the microsomal fraction. The dewnatration of high levels of P...