Longitudinal variability in airway responsiveness in a population-based sample of children and young adults. Intrinsic and extrinsic contributing factors

Phenotype definition, age, and gender in the genetics of asthma and atopy

When studying genetics of complex diseases it is important to have a clearly described and objective phenotype. When drawing conclusions in association studies, age and gender of the population should be considered. Until we know what causes phenotypic differences between males and females and between children and adults, we should try to study longitudinal cohorts with phenotype assessment at different time points and stratify our analyses for gender. To acquire sufficient power for these types of analyses, international collaboration may be the only way to elucidate the intricate, gene-environmental interactions in atopy and asthma in an age- and gender-dependent manor.

Airway hyperresponsiveness to methacholine at age 6 to 8 years in nonasthmatic patients is not related to increased health-care utilization for asthma in the ensuing 5 years: a longitudinal study of a birth cohort

BACKGROUND

Children with heightened airway responsiveness have a greater tendency to develop asthma symptoms. Many existing studies describing this relationship have relied on self-reported symptoms that may be prone to recall bias. In addition, few studies have examined the relationship of airway hyperresponsiveness (AHR) to indicators of asthma severity such as health-care utilization.

OBJECTIVE

To determine whether a positive response to methacholine challenge in children without current or physician-diagnosed asthma at age 6 to 8 years is predictive of the subsequent onset of asthma requiring medical evaluation or treatment in the ensuing 5 years.

METHODS

Data were obtained from subjects in a population-based birth cohort (n = 835) enrolled from 1987 to 1989, who were members of a large medical group practice component of a health maintenance organization (HMO). We analyzed a subset of subjects (n = 245) who had completed a methacholine challenge at age 6 to 8 years, had no current or physician-diagnosed asthma, and were still served by the same medical group. These children were followed up from the time of methacholine challenge until HMO disenrollment or through June 2001 (ages 11 to 13 years), whichever came first. Pharmacy claims data and diagnostic codes from physician-patient encounters were evaluated for incident asthma. Incident cases of clinical asthma were defined as any child with two outpatient visits or one hospitalization, one emergency department encounter associated with an asthma diagnostic code (ie, 493.XX), or any child filling prescriptions for two bronchodilators or one antiinflammatory asthma medicine. Methacholine responsiveness was interpreted using American Thoracic Society criteria.

RESULTS

Asthma incidence did not differ based on methacholine challenge results for children with normal, borderline, and mild AHR. No child in the study demonstrated moderate-to-severe AHR.

CONCLUSION

Our data suggest that AHR with a borderline or weakly positive result in a methacholine challenge in children 6 to 8 years old without current or physician-diagnosed asthma is not related to increased health-care utilization for asthma in the ensuing 5 years.

Determinants of maximally attained level of pulmonary function

This study investigated the determinants of sex-specific maximally attained levels of FEV(1), VC, and the ratio of FEV(1) to VC. Subjects were between the ages of 15 and 35 years (1,818 males and 1,732 females), participating in the Vlagtwedde/Vlaardingen study in The Netherlands. The subjects were followed (3-year intervals) with questionnaire, spirometry, peripheral blood eosinophil counts, and testing for airway responsiveness to histamine. Skin tests were performed only at study onset. Regression splines were used to assess the effects of these variables on levels of FEV(1), VC, and the ratio of FEV(1) to VC, with adjustment for age, height, and area of residence. Current (-44 ml/pack/day) and cumulative (-85 ml/10 packs/year) cigarette smoking were significant predictors of reduced maximal level of FEV(1) in males but not in females. The presence of respiratory symptoms (-114 ml in males, -106 ml in females), increased eosinophils (-128 ml [males], -53 ml [females]), and increased airway responsiveness (-225 ml [males], -213 ml [females]) were all significant predictors of reduced level of FEV(1). To the degree that these factors diminished plateau phase pulmonary function, they may be important predictors of chronic obstructive pulmonary disease in later life.

Low-density areas on high-resolution computed tomograms in chronic pediatric asthma

OBJECTIVE

In children with chronic persistent asthma, we evaluated whether the presence of increased residual volume (RV) after anti-inflammatory treatment correlates with the detection of low-density areas on high-resolution computed tomography (HRCT), similar to those in emphysema.

METHODS

Children with a confirmed diagnosis of asthma (n = 32) were enrolled in a prospective study. All patients had reduction of airflow in the peripheral airways, increased RV, and increased serum eosinophil cationic protein (ECP) values indicating airway inflammation. All the children were treated with salmeterol (50 microg twice daily) and fluticasone (250 microg twice daily) for a 3-month period.

RESULTS

At the end of treatment, peripheral eosinophil counts, serum ECP, forced expiratory volume in 1 second (FEV(1)), mean forced expiratory flow during the middle half of forced vital capacity (FEF(25-75)), RV, and total lung capacity values improved in all the patients. HRCT was normal in 22 children (68.8%); in the remaining 10 subjects, low-density areas were found despite normalization of FEV(1), FEF(25-75), and significant reduction in ECP. A significant correlation was found between persistence of RV values >150% predicted and the presence of low-density areas on HRCT (r = 0.84, P <.0001).

CONCLUSIONS

Structural changes similar to emphysema are also present in asthmatic children. Our findings suggest that the persistence of increased RV may be used to identify subjects with low-density areas on HRCT.

Development of bronchial hyperresponsiveness during childhood

Bronchial hyperresponsiveness (BHR) produces the characteristic pathological abnormalities seen in asthma and clearly plays a central role in the pathophysiology of asthma. The presence of BHR has been demonstrated in infants with asthma, as has the possibility of BHR persisting through the childhood period. The level of BHR may not only reflect the state of the airways, as a marker of airway dysfunction, but may also predict the persistent prognosis of the disease. Thus, measurement of BHR may provide important information about the symptoms and lung function in children with asthma. In view of multiple pathophysiological mechanisms, BHR does not seem to have a single cause. Many potential confounding variables, such as age, gender and genetic status, and some environmental factors, such as allergens, infections, and pollutants, could be responsible for the establishment of childhood BHR. There may be differences between the mechanisms that induce transient BHR and the mechanisms that induce persistent BHR. Also, there may be differences between the causes that induce BHR in the infantile period and the causes that maintain persistent BHR during childhood asthma. There is also disagreement as to the most suitable method to measure BHR in children, especially in infants. The assessment of BHR in young children has not been uniformly successful, and measurements of BHR changes over the childhood period (are associated with a number of problems. To resolve these problems, there may be two ways to study childhood BHR. One is to use age-matched specific techniques to clarify the precise BHR in each age group; the other is to use simple techniques that can be performed over the childhood period on a large number of subjects. In studies of infantile respirator, dysfunction the ultimate goal is to establish a simple, noninvasive method by which measurements of respiratory function may be obtained in infants. Further investigations and acceptable methods will be needed to clarify, the mechanisms involved in the establishment of asthma throughout the childhood period.

Factors related to methacholine airway responsiveness in children

Studies of airway responsiveness (AR) have typically used similar dose schedules of methacholine for adults and children despite large ranges in subject size. Reported declines in AR with increasing age in children could be due to maturational changes or to proportionately smaller doses of methacholine in taller (older) children. Other investigators have related both height and various measures of lung function to AR. We examined data related to AR in 471 children, aged 6 to 8 yr, from a birth cohort. Each child underwent spirometry followed by sequential challenge with five doses of methacholine, ranging from 0.025 to 25 mg/ml, given with a dosimeter. Continuous slope and end FEV(1)-change indexes of responsiveness were computed. Using stepwise regression modeling, we found no significant association between AR and either height or age after entering a variable reflecting asthma or wheezing. In contrast, we found that baseline measures of FVC, FEV(1)/FVC, and FEF(25-75%) were significantly related to AR after controlling for other variables (p = 0.001). However, when all three of the latter measures were added to models, FEF(25-75%) was most closely related to AR. We conclude that after control for other variables, FEF(25-75%) and FVC, but not height, are significantly related to methacholine responsiveness in children.

Markers of impaired growth of pulmonary function in children and adolescents

Our knowledge about the age-related growth of pulmonary function is incomplete. The purpose of this study was to describe the relation of various factors to the growth of pulmonary function in children and adolescents. A population sample comprising 408 children and adolescents (7-17 yr of age at enrollment) was reexamined after a 6-yr interval. Case history was obtained by interview and questionnaire. Pulmonary function, skin prick test reactivity to common allergens, and airway responsiveness (AR) were measured using standard techniques; airway hyperresponsiveness (AHR) was defined as a concentration of histamine causing a 20% decline in FEV1 < 8 mg/ml. The cross-sectional analyses of data from the two surveys showed that the presence of asthma (p < 0.02), atopy to house dust mite (HDM) (p = 0.03), and increasing degree of AR (p < 0.002) were associated with a lower level of FEV1 %pred. The longitudinal analysis revealed that asthma (p = 0.0001) and a lower level of FEV1 (p < 0.0001) at enrollment were associated with a lower level of FEV1 at follow-up. Further, an increase in the degree of AR (p = 0. 0001), new asthma (p = 0.0002), and new atopy to HDM (p = 0.03) also predicted a lower level of FEV1 at the end of the observation period. Confining the analysis to subjects without asthma and without evidence of AHR (n = 271) showed that both persistent (p = 0.04) and new (p = 0.03) atopy to HDM predicted a lower level of FEV1 at follow-up; compared with subjects with a negative skin reaction to HDM, those subjects who were sensitized to HDM had on average a 5%pred lower level of FEV1. The growth of FEV1 in children and adolescents appears to be impaired not only by symptomatic asthma but also by an increase in the degree of AR and atopy to HDM; sensitization to HDM appears to have a negative impact on the age-related growth in FEV1 even in nonasthmatic subjects without evidence of AHR.

Rate of 24-hour blood pressure decline and mortality after spontaneous intracerebral hemorrhage: a retrospective analysis with a random effects regression model

OBJECTIVE

To study the effect of decline in blood pressure on mortality in patients with spontaneous intracerebral hemorrhage (ICH).

DESIGN

Retrospective chart review.

SETTING

University-affiliated teaching hospital.

PATIENTS

Consecutive patients admitted with spontaneous ICH over a 3-year period.

MEASURES

Blood pressure recordings were obtained from the first 24 hrs. Patients (n = 105) with more than five blood pressure recordings and on average greater than one measurement per 2 hrs were included (mean measurements per patient = 20.3). Mean arterial pressure (MAP) recordings over the first 24 hrs after presentation were regressed on time for each patient. Each patient's MAP was calculated as a slope (change mm Hg/hr). We performed logistic regression analyses to determine the effect of MAP slope on mortality and functional outcome, adjusting for other predictive factors including Glasgow Coma Scale (GCS) score and hematoma volume. The effect of MAP slope on mortality was also evaluated in subsets of patients based on age, gender, initial GCS score, initial MAP, treatment status, hematoma volume, and presence of ventricular blood.

MAIN RESULTS

Mean slope of change in MAP was -2.0 mm Hg/hr (+/- 1.9, range -8.5 to +0.6). The slope of MAP (faster rate of decline) within the first 24 hrs was significantly associated with higher mortality (p =.04), independent of initial GCS score and hematoma volume. In subgroup analyses, MAP slope was significantly associated with mortality in men (p = .08), patients with hematoma volume <50 mm3 (p =.08), initial MAP < or = 146 mm Hg (p = .006), and those with initial GCS score > or = 10 (p= .07). MAP slope did not predict functional outcome among survivors.

CONCLUSIONS

A rapid decline in MAP within 24 hrs after presentation is independently associated with increased mortality in patients with ICH. A large, prospective, randomized trial is required to confirm these findings.

Verification of self-reported asthma and allergy in subjects and their family members volunteering for gene mapping studies

Studies which aim at mapping genes contributing to the development of asthma and atopy demand that hundreds of patients and their family members be assessed. In Finland, the Social Insurance Institution (SII) grants substantial reimbursement for medication to all patients who meet diagnostic criteria of asthma, which include a history of asthmatic symptoms and a measured reversibility of bronchial obstruction. To recruit a large number of asthma patients efficiently in a short period of time, we took advantage of the national reimbursement procedure and retrospectively collective data on patients' medical history and lung function test results at the time of diagnosis. First, we wanted to investigate if the reimbursements could be regarded as objective verification for self-reported asthma. Altogether 335 adult self-reported asthma patients were evaluated, 87% of them were verified as having chronic asthma. Reimbursement for medication showed a sensitivity of 95% and a specificity of 76% for verified asthma. Second, we were interested to see if self-reported nasal allergic symptoms or self-reported physician diagnosed allergic rhinitis were sensitive and specific measures of allergy. The self-reported allergic nasal symptoms had a poor specificity (31% in the proband group and 59% in the family members group) when compared to the allergy screening test (Phadiatop). The best verification for self-reported asthma was achieved by combining the information on self-reported disease, granted reimbursement by the SII and the medical records. For allergies, the specificity of self-reporting was far too low to be used alone, and a positive allergy screening test together with relevant symptoms was chosen as a marker of allergy.

Cotinine excretion as a predictor of peak flow variability

Environmental tobacco smoke (ETS) is suspected to be an important risk factor for bronchial hyperresponsiveness. In order to test the effect of ETS, we measured expiratory flow rates and urine cotinine excretion (UCE) within a narrow time window in two consecutive years. Maternal smoking habits and medical history were ascertained by standardized questionnaires. The percentage ratio of the amplitude over the mean (AVAM) of the diurnal peak flow rates of children (complete values from at least five consecutive days) was calculated as an indicator of bronchial responsiveness. The association of UCE and log10AVAM was analyzed by multiple linear regression. Complete data were available for a sample of 417 children. The median of UCE in children of parents who smoked (3.2 ng/mg and 2.9 ng/mg creatinine, Surveys 1 and 2, respectively) was higher than the median in children of nonsmoking parents (0 ng/mg in both surveys). With increasing UCE the log10AVAM rose in the first and second surveys, as well as in the longitudinal analysis (p = 0.003). This association, however, showed up only in boys (p = 0.0001) and not in girls (p = 0.31). Our data suggest that there is a need both for further analysis of the gender difference and for more support of strategies against passive smoking as far as children are concerned, since airway hyperresponsiveness is a risk factor for chronic airway impairment.

Longitudinal determinants of bronchial responsiveness to inhaled histamine

BACKGROUND AND STUDY OBJECTIVE

The point prevalence of bronchial hyperresponsiveness (BHR) is imperfectly associated with current asthma, possibly due to changes over time in bronchial responsiveness (BR). To evaluate cross-sectional and longitudinal determinants of BR, a population sample comprising 408 children and adolescents, aged 7 to 17 years at enrollment, was examined twice, 6 years apart.

METHODS

Case history was obtained by interview and questionnaire. BR to inhaled histamine, pulmonary function, and skin prick test reactivity were measured using standard techniques.

RESULTS

The point prevalence of BHR (the concentration of histamine causing a 20% decline in FEV1 <8 mg/mL) declined from childhood to early adulthood (25% and 6%, respectively; p<0.001); and similarly a decline in histamine dose-response slope was observed. At both surveys, prechallenge FEV1 percent predicted, asthma, and atopy, especially atopy to house dust mite (HDM), were important determinants for the degree of BR. After adjustment for prechallenge FEV1 percent predicted, no male-female difference was observed in degree of BR. Lower FEV1 percent predicted (p=0.003), asthma (p<0.001), higher degree of BR (p=0.003), and atopy to HDM (p=0.007) at enrollment predicted a higher degree of BR at the second survey (degree of BR at second survey adjusted for prechallenge FEV1). Furthermore, new asthma (p<0.001) and/or atopy to HDM (p=0.003) were associated with higher BR at the second survey. Confining the analysis to nonasthmatics showed that subjects with new or persistent atopy to HDM had significantly increased BR compared with nonatopic subjects; and, moreover, prechallenge FEV1 percent predicted was significantly correlated with BR.

CONCLUSIONS

BR declines from childhood to early adulthood, possibly reflecting the increase in airway caliber. The level of FEV1 and atopy, especially to HDM, are important determinants for changes over time in level of BR, also in nonasthmatic subjects.

Increased variability in bronchial responsiveness in aluminum potroom workers with work-related asthma-like symptoms

In a longitudinal study, we studied the variability in bronchial responsiveness (BR) to methacholine in aluminum potroom workers suffering from work-related asthma-like symptoms (WASTH) and in symptom-free workers. In the index group, 26 men suffering from WASTH were selected from a cross-sectional survey. The reference group comprised 45 symptom-free men recruited from the enrollment of new employees. Bronchial responsiveness was expressed as the dose-response slope (DRS) of the line through origin and the last data point. The standard deviation of the log-transformed DRS was positively associated with symptom score (P = .012) and the mean BR (P < .001). Our results indicate that the severity of respiratory symptoms in aluminum potroom workers with WASTH reflects the variability in BR.

Relationship between atopy and frequent bronchial response to exercise in school children

The natural history of a bronchial response to exercise (BRE) was studied in a cohort of primary-school children, who were followed over a 2-year period. In 1,094 children, three free-running tests were performed in 1-year intervals. Children who responded in one of the tests were designated as "infrequent" responders (20.5%), whereas those responding at two or all three occasions were designated as "frequent" responders (7.4%). A frequent positive BRE was closely associated with atopy (defined as skin test positivity to 1 of 7 common aeroallergens) and respiratory symptom status. Compared to atopics without respiratory symptoms, an increased risk for a frequent positive BRE was seen for atopic children who were symptomatic during the whole study period [odds ratio (OR) 25.4; confidence interval (CI) 6.9-94.0], who had gained symptoms (OR, 11.0; CI, 2.8-43.2) or who had symptoms at the beginning of the study but had lost them during follow-up (OR, 4.6; CI, 1.0-20.6). A sensitization to dust mites (OR, 8.0; CI, 4.3-15.0) but not to animal dander (OR, 2.3; CI, 1.0-5.2) or pollen (OR, 0.7; CI, 0.3-1.6) was significantly related to a frequent positive BRE. Our findings support the notion that while "children grow out of asthma," they might maintain their bronchial hyperresponsiveness. Regarding specific sensitization, mite allergy seems to play the predominant role.

Longitudinal measurement of airway hyperresponsiveness in selected subjects with persisting pulmonary symptoms

The relationship between airway hyperresponsiveness and pulmonary symptoms was examined longitudinally in 52 subjects. Subjects were part of a larger study, the Natural History of Asthma, and had repeated measures of airway hyperresponsiveness using methacholine. Atopy was determined using skin tests and serum IgE levels. The subjects completed a standardized respiratory questionnaire. Each subject reported respiratory and pulmonary symptoms at either their initial or follow-up visit. The subjects did not, however, have a physician-confirmed diagnosis of asthma. Subjects were divided into groups according to the current status of their respiratory symptoms. The four groups included subjects who were initially normal but developed respiratory symptoms at follow-up; subjects who had symptoms at all visits; subjects with respiratory symptoms at their initial visit but who had no symptoms at follow-up; and subjects who had respiratory symptoms prior to their initial visit and who did not have a recurrence during follow-up. There was no statistical difference in airway hyperresponsiveness, IgE, or skin test scores at the initial visits. Subjects who had airway responsiveness were significantly more atopic than subjects who did not have airway responsiveness. Subjects were classified as "consistently positive," "variable," or "consistently negative" responders according to the pattern of methacholine-induced airway hyperresponsiveness. Overall, among the four groups, 33% were consistently positive at all visits, 43% were variable, and 22% were consistently negative. Airway hyperresponsiveness was statistically associated with atopy, but not necessarily associated with questionnaire-based respiratory symptomatology. These factors need to be considered in epidemiological studies of asthma utilizing respiratory questionnaires.

Long-term variability of bronchial responsiveness to histamine in a random population sample of adults

Long-term variability of bronchial responsiveness has been studied in a random population sample of adults. During a follow-up period of 18 yr, 2,216 subjects contributed 5,012 observations to the analyses. Each subject could have as many as seven observations. Bronchial responsiveness was assessed with a histamine challenge test. The threshold value was defined as the concentration of histamine that caused a decrease in FEV1 of 10% of more (PC10). After a 3-yr interval, a change of the threshold value with two or more doubling concentrations occurred in 21% of the subjects. This proportion increased to 43% if the time between two measurements increased to 18 yr. Of all subjects with multiple observations, 41% were always nonresponders (PC10 > or = 32 mg/ml), 11% were always responders (PC10 < or = 16 mg/ml), and 48% changed responder status. Of the subjects with greater than three observations, 65% changed responder status. Regression analyses, stratified by symptom status, sex, and smoking habit, were used to estimate intraclass correlation coefficients (ICC) as a measure of variability of responsiveness. On average, ICC values were low (0.40), also indicating considerable variability. With adjustment for FEV1, age, area of residence, and eosinophil count, the ICC values decreased slightly. This indicated that with adjustment, the total variability decreased more than the within-subject variability. ICC values did not differ significantly between asymptomatic and symptomatic subjects. Analyses of responsiveness as a binary variable revealed similar results.

Evaluation of cold air challenge data in a population sample using a model of bronchial hyperreactivity and disposition to bronchial obstruction

To explore the role of bronchial hyperreactivity and obstruction after cold air challenge, data from a cross-sectional study of more than 7,000 10-year-old children were used. Current knowledge of hyperreactivity is primarily based on pharmacological provocation tests with variable prechallenge flow rates and their decrease relative to baseline. Using forced expiratory volume (FEV) in 1 sec values before and after cold air challenge, however, it is possible to define a subsample of children with predominant hyperreactivity and a subsample with predominant obstruction after challenge. The prevalence of respiratory symptoms and the diagnoses in the two subsamples were compared. The analysis showed that children with bronchial obstruction have nearly the same frequency of respiratory symptoms as those with bronchial hyperreactivity. A combined model of bronchial obstruction and hyperreactivity was, therefore, more predictive of symptoms than a model of hyperreactivity alone.

Relationship between viral antibodies and bronchial hyperresponsiveness in 495 unselected children and adolescents

The purpose of this study was to investigate whether recent and previous subclinical viral respiratory infection can explain the presence of increased bronchial responsiveness to histamine. We studied a randomly selected population of 495 children and adolescents, aged 7-16 years, from Copenhagen. If the subjects had had symptoms of respiratory infection recently, the examination was postponed for at least 6 weeks. Bronchial hyperresponsiveness (BHR) to inhaled histamine was found in 79 (16%) of the subjects, of whom 28 had asthma. Forty-eight subjects (10%) had increased levels of serum IgM antibodies against either parainfluenza, influenza, adenovirus, or respiratory syncytial virus (RSV), reflecting a recently acquired infection. No association between BHR and antibodies against respiratory viruses was found, as 7 (8.9%) of the 79 subjects with BHR and 41 (9.9%) of the 416 subjects without BHR had viral antibodies. Furthermore, no association between degree of bronchial responsiveness and viral antibodies was found. Moreover, 251 individuals (51%) had signs of earlier RSV infection, i.e. IgG antibodies against RSV. No relationship was found between age of the subjects and the presence of antibodies against either respiratory viruses in general or IgG-RSV. No relationship was found between the presence of antibodies against RSV and BHR; furthermore, evidence of earlier RSV infection was unrelated to the level of lung function and degree of bronchial responsiveness. We conclude that increased bronchial responsiveness in asymptomatic, unselected schoolchildren and adolescents is not likely to be caused by recent or previous viral respiratory infections.

Predictors of individual differences in acute response to ozone exposure

The purpose of this study was to identify personal characteristics that predict individual differences in acute FEV1 response to ozone exposure. Response and predictor data were collected on 290 white male volunteers 18 to 32 yr of age who were each exposed to one of six concentrations of ozone between 0.0 and 0.40 part per million. The sample was divided into an exploratory sample of 96 and a confirmatory sample of 194 subjects. Exploratory analysis indicated that ozone, age, and several other variables explained a significant proportion of the variance in response. In the confirmatory sample, only age and ozone concentration predicted FEV1 decrement. For the combined sample ozone explained 31% of the variance, with age accounting for an additional 4%. The model predicted a decreasing response with increasing age for all nonzero ozone concentrations. For exposure to 0.40 ppm, the model predicts decrements in FEV1 of 1.07 and 0.47 L for 18- and 30-yr-old subjects, respectively. We concluded that for white male subjects age was a significant predictor of response, with older subjects being less responsive to ozone. Furthermore, we demonstrated that exploratory analysis without control of type I statistical error rates may result in apparent findings that cannot be replicated.

Development of lung function in relation to increased degree of bronchial responsiveness

To study the relationship between development of lung function and bronchial responsiveness, we examined 106 subjects recruited from a random sample of 527 subjects, aged 8-18 years, from Copenhagen. Lung function and bronchial responsiveness to inhaled histamine were measured at two occasions, in 1986 and 1988. The participating subjects (n = 106) were divided into three groups: (a) 20 asthmatics with bronchial hyperresponsiveness (BHR), (b) 42 nonasthmatic subjects with BHR in 1986, and (c) 44 controls without BHR. In 1986, FEV1 expressed as percentage of predicted value, was found to be similar in the three groups (91%, 94%, and 99%, respectively). The increase in height during the observation period was found to be 5, 6, and 6 cm, respectively, in the three groups. However, at the second examination, in 1988, FEV1 was found to be significantly reduced in both asthmatics (87%) and nonasthmatic subjects (85%) compared with the controls (103%). In 1988, 16 asthmatics (80%) and 24 (57%) nonasthmatic subjects were found to have BHR, whereas none of the controls were found to have BHR. A multiple regression analysis was used to determine the correlation between change in FEV1 and potential factors of importance. The change in FEV1 was highly correlated with the presence of BHR in 1986, however, no correlation was found between change in FEV1 and change in bronchial responsiveness. In conclusion, nonasthmatic subjects with former BHR showed signs of airflow obstruction and less increase in lung function during growth irrespective of the change in level of bronchial responsiveness, which may suggest a risk for subsequent development of obstructive lung disease.

Measurement of sleep-related breathing disturbances in epidemiologic studies. Assessment of the validity and reproducibility of a portable monitoring device

The feasibility and reliability of measuring sleep-related breathing disorders with a portable monitor (PM) were assessed in a heterogeneous population, consisting of 31 patients recruited from a sleep laboratory and pulmonary disease clinic, 16 participants in a genetic-epidemiologic study of sleep apnea, and four volunteers with no specific sleep complaints. The validity of measurements made by the PM was assessed with comparisons of respiratory parameters made with the PM to those determined with in-hospital polysomnography (PSG) (25 studies). Reproducibility was assessed in 29 subjects who underwent in-home monitoring on two occasions. There was a high level of agreement between the number of respiratory events (apneas or hypopneas) per hour of estimated sleep (respiratory disturbance index, RDI) recorded with the PM and PSG and log-transformed (r = 0.96). Using a RDI of greater than or equal to 10 to define "abnormality," 20 of the 21 subjects who would have been classified as abnormal with PSG were classified similarly with use of the PM. A similar high level of agreement was demonstrated for the log-transformed RDI determined with replicate in-home studies (r = 0.94). No evidence of a "first-night effect" for the RDI was suggested in studies performed with the PM; ie, RDI was 18.4 +/- 27.7 and 17.4 +/- 25.7 (mean +/- SD) for first and second night studies, respectively (p = 0.21). A second compared with an initial study with the PM would have resulted in reclassification of abnormality based on an RDI of greater than or equal to 10 in one subject. These findings suggest that measurement of the RDI with in-home monitoring provides a valid and highly reproducible index for assessment of sleep-related respiratory disturbances for use in epidemiologic studies of general populations.