Changes In Airway Caliber Research Articles

Effect of nasal continuous positive airway pressure in uncontrolled nocturnal asthmatic patients with obstructive sleep apnea syndrome

The mechanisms of nocturnal asthma are intimately related to circadian rhythms, which influence inflammatory cells and mediators, hormone levels and cholinergic tone. Nocturnal airway narrowing in asthma is sometimes associated with sleep disorders, such as obstructive sleep apnea syndrome (OSAS). The aims of this study were to evaluate the association of nocturnal asthma and OSAS, and investigate the influence of continuous positive airway pressure (CPAP) therapy to improve nighttime symptoms in asthmatic patients with OSAS. Forty-three asthmatic patients who had nocturnal symptoms in spite of the optimal medical treatment according to the Global Initiative for Asthma guidelines and associated with snoring were studied. Pulmonary function tests (PFTs), asthma nighttime symptom scores, and polysomnography were performed on all patients. We treated the patients with an apnea-hypopnea index (AHI) 15 (moderate-severe OSAS) (n=16) with CPAP during 2 months. After 2 months, PFT, asthma nighttime symptom scores were reperformed. There was no significant difference in PFT values before and after CPAP treatment in OSAS patients. Asthma nighttime symptom scores were improved significantly (P<0.05) after CPAP treatment. In conclusion, in some patients with nocturnal asthma, OSAS may be responsible disease for nocturnal symptoms. In this condition, CPAP improves nocturnal symptoms without amelioration in PFT abnormalities.

Radiation-induced narrowing of the tracheobronchial tree: An in-depth 3D analysis

Radiation-induced narrowing of the tracheobronchial tree: An in-depth 3D analysis

Improved bronchodilator effect of deep inhalation after allergen avoidance in asthmatic children

Background In healthy adults and children, deep inhalation (DI) is able to reverse induced bronchoconstriction. This ability is impaired in asthma, but the reasons are still to be elucidated. Objectives This study investigated whether the bronchodilator effect of DI during methacholine-induced bronchoconstriction can be improved by allergen avoidance in asthmatic children, and its relationship with airway inflammation. Methods The effect of DI on methacholine-induced bronchoconstriction was studied at the beginning and the end of a 3-month allergen avoidance period at high altitude in 14 allergic asthmatic children who had severe asthma attacks. Changes in airway caliber were inferred from the respiratory resistance (Rrs) measured by a forced oscillation technique. Results were related to the percentage of eosinophils in induced sputum and compared with those obtained in 9 age-matched nonasthmatic children. Results In asthmatic subjects, DI had no significant effect on methacholine-induced increase in Rrs before ( P = .62) but significantly reversed it after ( P < .01) allergen avoidance. However, the ability of DI to reverse a methacholine-induced increase in Rrs tended to remain less in asthmatic than nonasthmatic children even after allergen avoidance ( P = .05). In the asthmatic children, the percentage of eosinophils in induced sputum was decreased at the end of the allergen avoidance period ( P < .001), without any significant correlation between sputum eosinophils and airway responsiveness to methacholine or effect of DI. Conclusion A short period of allergen avoidance may improve the ability of DI to reverse induced bronchoconstriction in some asthmatic children. This effect is associated, yet not correlated, with a reduction in airway inflammation.

Spirometry and peak expiratory flow in the primary care management of COPD

Spirometry is essential for the diagnosis of chronic obstructive pulmonary disease (COPD). In patients with COPD the decline in lung function is usually so slow that spirometry is unlikely to provide significantly new information more than every 1-2 years. However, it is useful to have an objective measure of lung function in the assessment of acute exacerbations of COPD and in the assessment of treatments. Peak expiratory flow (PEF) has been dismissed by national and international guidelines as an inappropriate test for the assessment of the impact of COPD, but with poor evidence in support of this position. This seems short-sighted since PEF is a reliable and reproducible test and could contribute to the management of COPD in the short term and in support of spirometry. As a result of infection or in response to treatment there may be changes in airway calibre in COPD which could be captured in the consultation by PEF. In a primary care setting spirometry is too time consuming and complex to be provided in the context of normal acute consulting. Furthermore there is no evidence that spirometry provides more information than PEF in the day-to-day management of a patient already diagnosed with COPD using forced expiratory volume in the first second/forced vital capacity (FEV1/FVC). Primary care teams should ensure that their patients have adequate access to high quality spirometry. This can be provided in primary care or in local centres or in hospitals depending on the interest, motivation and resources of primary care teams. In support of spirometry general practitioners (GPs) should then consider using PEF in the day-to-day management of COPD.

How effort independent measures of respiratory resistance compare to the gold standard (FEV1)

Rationale The purpose of this investigation is to test and validate the Airway Perturbation Device (APD). The APD is a non-invasive, effort independent, hand held means of measuring respiratory resistance (RR). The RR measures will be compared to FEV1. Methods Fifty-six individuals (32F, 24M, ages 17-72) were asked to breathe normally into the APD during routine spirometry, methacholine challenge and bronchial reversal studies. Twenty-five had well defined asthma (>12% reversibility), 10 had COPD and 21 where non-asthmatic controls. Results The mean FEV1 % Pred. for the three groups are: Asthma: 77% (sd=14, 58-103%), COPD: 44% ( sd=15.7, 39-78%) Controls: 101% ( sd=9.6, 82-120%), The mean RR (Cm/H20) was: Asthma: 4.03 ( sd=0.90, 2.95-5.96), COPD: 3.44 ( sd=0.49, 2.88-4.50). Controls: 3.19 ( sd=0.62, 2.01-4.12). There was a significant relation between RR and FEV1 in the total group. (R=.347 p=.001). There was a highly significant relation between the change in RR and change in FEV1 after Albuterol (R=.836 p=.000) and at end point of methacholine challenge (R=.849 p=.000). Conclusions The APD device was easy to use, patient friendly and reproducible. Since changes in RR mirror the changes in FEV1 we believe the ADP could be useful diagnostic tool to measure changes in airway caliber. The APD device using passive breathing will be especially helpful in young children or in any persons where spirometry is difficult or impossible to perform.

Incidence of probable occupational asthma and changes in airway calibre and responsiveness in apprentice welders.

The majority of cross-sectional studies have shown a higher prevalence of ventilatory impairment in welders while only few longitudinal studies were able to detect chronic effects on spirometry or bronchial responsiveness. The aim of the study was to determine the incidence of probable occupational asthma (OA), bronchial obstruction and hyperresponsiveness among 286 students entering an apprenticeship programme in the welding profession. This epidemiological prospective cohort study consisted of a baseline assessment survey and two follow-up assessments. A respiratory symptom questionnaire was administered at each visit. Spirometry and methacholine bronchial challenge test results, conducted once prior to onset of exposure and later after an average of 15 months of apprenticeship, were available for 194 subjects. The incidence of probable OA was approximately 3% (6 of 194). The incidence of bronchial hyperresponsiveness, defined as a > or = 3.2-fold decrease in the provocative concentration causing a 20% fall in the forced expiratory volume in one second from baseline to the end of the study was 11.9%. A statistically significant difference was found between the baseline and end of study for the lung function values. In particular, the forced expiratory volume per cent predicted had significantly dropped by 8.4% on average. The significance of these early pulmonary function changes in relation to possible chronic effects of exposure to welding fumes and gases remains to be explored.

Relationship between cutaneous allergen response and airway allergen-induced eosinophilia.

Determinants of changes in airway caliber after allergen challenge include nonallergic airway responsiveness, immune response and dose of allergen given. However, determinants of the airway inflammatory response to allergens remain to be determined. To assess the relationship between skin reactivity to airborne allergens and lower airway eosinophilic response to allergen exposure in asthma and allergic rhinitis. Forty-two subjects with mild allergic asthma (mean age 24 years) and 14 nonasthmatic subjects with allergic rhinitis (mean age 25 years) had allergen skin prick tests and titration with the allergen chosen for subsequent challenge. On a second visit, 31 asthmatic subjects had a conventional challenge while 11 asthmatic subjects and all rhinitic subjects had a low-dose allergen challenge over four subsequent days. Induced sputum samples were obtained at 6 and 24 h after the conventional challenge and at days 2 and 4 of the low-dose challenge. In the asthmatic group, there was a weak correlation between wheal diameter induced by the concentration used for challenge and increase in eosinophils 6 h postconventional challenge (r = 0.372, P = 0.05), but no correlation was observed following the low-dose challenge. Rhinitic subjects showed a correlation between wheal diameter with the allergen dose used for bronchoprovocation and increase in eosinophils at day 2 of low dose (r = 0.608, P = 0.02). This study suggests that immediate immune responsiveness to allergen, assessed by the magnitude of the skin response, is a significant determinant of allergen-induced airway eosinophilia and can help to predict the airway inflammatory response.

Questionnaires, spirometry and PEF monitoring in epidemiological studies on elderly respiratory patients.

Questionnaires are the most used subjective instrument of measurement in respiratory epidemiology. The standardisation of the questionnaires aims to limit bias by maximising validity and reliability, and comparability. Within the European Union project BIOMED1, a compendium of respiratory standard questionnaires (CORSQ) was developed for adults covering 18 topics from general information to early life events, through environmental risk factors and respiratory symptoms and diseases. Reliable spirometry data needs a rigorous quality control programme, as in the "Salute Respiratoria nell'Anziano" (Sa.R.A.) project, Italian for "Respiratory Health in the Elderly". Reproducibility rates were 95.8% for forced expiratory volume in one second (FEV1). Male sex and age were independent risk factors for a poorer reproducibility, as well as cognitive and physical impairment (shorter 6-min walking distance) and lower educational level for a poorer acceptability. Reference values for people aged 65-85 yrs have been produced; these results suggest that the effect of aging should be corrected for physical and mental disability. A revision of interpretative strategies included in current guidelines is needed. Peak expiratory flow monitoring has several methodological problems: reliability and sensitivity of the measurement in order to detect changes in airway calibre; compliance with long-term monitoring; choice of the best variability index; difference between asthmatic and nonasthmatic subjects; age-related differences. Despite these methodological problems, peak expiratory flow monitoring has been successfully used in the evaluation of the effects of air pollution in normal and asthmatic subjects, and in the elderly.

Tracking variations in airway caliber by using total respiratory vs. airway resistance in healthy and asthmatic subjects.

An index of airway caliber can be tracked in near-real time by measuring airway resistance (Raw) as indicated by lung resistance at 8 Hz. These measurements require the placing of an esophageal balloon. The objective of this study was to establish whether total respiratory system resistance (Rrs) could be used rather than Raw to track airway caliber, thereby not requiring an esophageal balloon. Rrs includes the resistance of the chest wall (Rcw). We used a recursive least squares approach to track Raw and Rrs at 8 Hz in seven healthy and seven asthmatic subjects during tidal breathing and a deep inspiration (DI). In both subject groups, Rrs was significantly higher than Raw during tidal breathing at baseline and postchallenge. However, at total lung capacity, Raw and Rrs became equivalent. Measured with this approach, Rcw appears volume dependent, having a magnitude of 0.5-1.0 cmH2O. l-1. s during tidal breathing and decreasing to zero at total lung capacity. When resistances are converted to an effective diameter, Rrs data overestimate the increase in diameter during a DI. Simulation studies suggest that the decrease in apparent Rcw during a DI is a consequence of airway opening flow underestimating chest wall flow at increased lung volume. We conclude that the volume dependence of Rcw can bias the presumed net change in airway caliber during tidal breathing and a DI but would not distort assessment of maximum airway dilation.

The role of adenosine as a novel bronchoprovocant in asthma.

There is evidence that bronchial hyperresponsiveness to inhaled adenosine may be a better marker of airway allergic inflammation than bronchial hyperresponsiveness to other spasmogens. Here the authors review the most recent development in this area of rapidly evolving clinical research, focusing on the putative role of adenosine as a useful bronchoprovocant in asthma. New studies have provided evidence that hyperresponsiveness to AMP strongly correlates with sputum, blood/bronchial tissue eosinophilia and exhaled nitric oxide, whereas hyperresponsiveness to methacholine is related to changes in forced expiratory volume in 1 s, thus reflecting changes in airway caliber and functional state. Other recent studies have emphasized that the state of atopy is critically important in the bronchial response to inhaled AMP. The early finding that in people with asthma treatment with inhaled glucocorticosteroids significantly reduces airway responsiveness to AMP, as compared with other spasmogens such as methacholine or bradykinin, has been confirmed by recent reports which have also outlined that this is an early phenomenon. Taken together these studies evidence that hyperresponsiveness to inhaled adenosine may be a better marker of airway allergic inflammation than hyperresponsiveness to other spasmogens. This peculiar property of adenosine suggests that bronchial provocation with inhaled adenosine could provide a reliable noninvasive tool for monitoring asthma activity/progression, and assessing the response to antiinflammatory treatments.

Inhaled ultrasonically nebulized distilled water decreases exhaled nitric oxide in asthma.

Exhaled nitric oxide (eNO) is increasingly used as a marker of disease activity in asthma. Inhaled hypertonic saline has been shown to induce bronchoconstriction and to decrease eNO in asthmatic subjects, whereas the effects of hypotonic solutions on eNO in these patients have not been studied. To evaluate the effect of ultrasonically nebulized distilled water (UNDW), an indirect hypotonic stimulus, on eNO, 17 asthmatic patients were enrolled and eNO from lower airways was measured by chemiluminescence. UNDW significantly reduced FEV(1) >or= 20% in 9 subjects (UNDW+), but had no effect in eight patients (UNDW-). Baseline eNO concentration were found to be 51.3 +/- 11.1 ppb in UNDW+ and 32.9 +/- 7.5 ppb in UNDW- patients, respectively ( p = 0.199, NS). UNDW inhalation significantly decreased eNO (from 51.3 +/- 11.1 ppb to 31.0 +/- 7.1 ppb in UNDW+ ( p < 0.020, n = 9) and from 32.9 +/- 7.5 ppb to 26.2 +/- 7.3 ppb in UNDW- subjects ( p < 0.024, n = 8), respectively). eNO percentage reduction in UNDW+ patients was significantly higher compared with UNDW- subjects (-37 +/- 4% vs -23 +/- 3%, p = 0.021). There was no correlation between FEV(1) changes and eNO percentage decreases in both UNDW+ and UNDW- subjects. In UNDW+ patients, acute bronchodilation induced by salbutamol caused a recovery in both FEV(1) and eNO, though eNO levels remained lower than baseline values. We concluded that UNDW inhalation can significantly decrease eNO in asthmatic patients, either responders or nonresponders to this indirect osmotic challenge; the reduction in eNO levels was only partly dependent on acute changes in airway caliber.

Effects of Emphysema and Lung Volume Reduction Surgery on Transdiaphragmatic Pressure and Diaphragm Length

To determine the effect of emphysema and lung volume reduction surgery (LVRS) on diaphragm length (Ldi) and its capacity to generate transdiaphragmatic pressure (Pdi). Prospective clinical trial with a parallel group design. Laboratory investigations in normal volunteers recruited by advertisement and in emphysema outpatients being evaluated for elective LVRS. Thirteen normal subjects and 13 emphysema patients matched for age and sex. Six emphysema patients underwent LVRS. Ldi and maximal Pdi during static inspiratory efforts (PdiMax) were measured at three different lung volumes (LVs). Pdi during maximal bilateral phrenic nerve twitch stimulation (PdiTw) was measured at functional residual capacity (FRC). All measurements were repeated at 3, 6, and 12 months postoperatively. Ldi, PdiMax, and PdiTw were lower in emphysema patients than in normal subjects at their respective LVs. PdiMax and PdiTw at FRC returned within the normal range after LVRS in emphysema patients. The relationships between PdiMax and LV or Ldi were shifted respectively to higher LV and shorter Ldi in emphysema patients relative to normal subjects, both before and after LVRS. LVRS effected craniad displacement of the diaphragm but no change in rib cage dimensions. Improvements in dyspnea and quality of life after LVRS correlated with changes in LV and Ldi but not with changes in airway caliber. Adaptive mechanisms, consistent with sarcomere deletion, tend to restore diaphragm strength in emphysema patients at FRC, which are fully expressed after LVRS. Lung remodeling by LVRS may alter pleural surface pressure distribution, causing a sustained change in chest wall shape.

Exhaled nitric oxide after inhalation of isotonic and hypotonic solutions in healthy subjects

Airway nitric oxide (NO) homoeostasis is influenced by chemical and mechanical stimuli in humans; airway epithelium, which is an important site of NO production, is sensitive to osmotic challenge. The effect of inhaled hypotonic solutions on exhaled NO (eNO) is not known. In this study we evaluated the effect of ultrasonically nebulized distilled water (UNDW), a hypotonic indirect stimulus, on eNO levels. A total of 10 non-smoking healthy subjects were enrolled in the study. eNO was detected by chemiluminescence, and specific airway conductance (sGaw) was measured by plethysmography. Bronchial challenges with UNDW and with an isotonic solution were performed according to a double-blind experimental design. Baseline levels of eNO were 28.1±14.7p.p.b. UNDW did not cause any significant change in sGaw (from 0.190±0.029 to 0.181±0.036cmH2Oċs-1). With respect to baseline values, the eNO concentration decreased significantly after inhalation of 8 or 16ml of UNDW (from 26.0±13.1 to 17.2±8.5 and 16.6±7.7p.p.b. respectively; P &lt; 0.001, n = 10). After bronchial challenge with UNDW, eNO was significantly reduced in comparison with after inhalation of the isotonic solution. In five subjects, pretreatment with NG-nitro-l-arginine methyl ester (l-NAME), an inhibitor NO synthesis, decreased NO levels from 21.7±8.5 to 10.0±3.3p.p.b. Subsequent inhalation of 16ml of UNDW did not cause any further decrease in NO levels (10.1±3.7p.p.b.; not significant compared with l-NAME). We conclude that inhalation of aqueous solutions decreases eNO levels in healthy subjects, and that this effect is not associated with any significant change in airway calibre. The UNDW-induced decrease in eNO is not enhanced by pretreatment with the NO synthase inhibitor l-NAME, suggesting that inhaled solutions may interfere with the airway NO pathway in humans.

Exhaled nitric oxide after inhalation of isotonic and hypotonic solutions in healthy subjects

Airway nitric oxide (NO) homoeostasis is influenced by chemical and mechanical stimuli in humans; airway epithelium, which is an important site of NO production, is sensitive to osmotic challenge. The effect of inhaled hypotonic solutions on exhaled NO (eNO) is not known. In this study we evaluated the effect of ultrasonically nebulized distilled water (UNDW), a hypotonic indirect stimulus, on eNO levels. A total of 10 non-smoking healthy subjects were enrolled in the study. eNO was detected by chemiluminescence, and specific airway conductance (sGaw) was measured by plethysmography. Bronchial challenges with UNDW and with an isotonic solution were performed according to a double-blind experimental design. Baseline levels of eNO were 28.1+/-14.7 p.p.b. UNDW did not cause any significant change in sGaw (from 0.190+/-0.029 to 0.181+/-0.036 cm H(2)O x s(-1)). With respect to baseline values, the eNO concentration decreased significantly after inhalation of 8 or 16 ml of UNDW (from 26.0+/-13.1 to 17.2+/-8.5 and 16.6+/-7.7 p.p.b. respectively; P<0.001, n=10). After bronchial challenge with UNDW, eNO was significantly reduced in comparison with after inhalation of the isotonic solution. In five subjects, pretreatment with N(G)-nitro-L-arginine methyl ester (L-NAME), an inhibitor NO synthesis, decreased NO levels from 21.7+/-8.5 to 10.0+/-3.3 p.p.b. Subsequent inhalation of 16 ml of UNDW did not cause any further decrease in NO levels (10.1+/-3.7 p.p.b.; not significant compared with L-NAME). We conclude that inhalation of aqueous solutions decreases eNO levels in healthy subjects, and that this effect is not associated with any significant change in airway calibre. The UNDW-induced decrease in eNO is not enhanced by pretreatment with the NO synthase inhibitor L-NAME, suggesting that inhaled solutions may interfere with the airway NO pathway in humans.

IMAGING FOR THE SNORING AND SLEEP APNEA PATIENT

Upper airway imaging techniques have significantly advanced the understanding of the pathogenesis of obstructive sleep apnea and the biomechanical mechanisms by which therapeutic interventions for this disorder exert their effects. Both static and dynamic imaging studies have been used to examine the structure and function of the upper airway during wakefulness and sleep. These studies have highlighted the importance of the lateral pharyngeal walls in addition to the tongue and soft palate in modulating changes in upper airway caliber. Upper airway imaging has also been used to understand the changes in upper airway anatomy associated with weight loss, mandibular repositioning devices, and upper airway surgery. At present, upper airway imaging should be considered in patients undergoing upper airway surgery and possibly in patients being evaluated for oral appliances. MR imaging and nasopharyngoscopy are the imaging modalities of choice in patients undergoing a UPPP. Cephalometrics should be considered in patients being treated with mandibular repositioning devices. Upper airway imaging has provided an important framework to examine the pathogenesis of airway closure, and these investigations may, in time, lead to more effective treatment options for patients with sleep apnea.

The use of a mobile computed tomography scanner in the pediatric intensive care unit to evaluate airway stenting and lung volumes with varying levels of positive end-expiratory pressure.

Presentation of a case report describing the use of a mobile computed tomography (CT) scanner in the pediatric intensive care unit (PICU) to radiographically evaluate tracheobronchial stenting and lung volumes while using different levels of positive end-expiratory pressure (PEEP) and positioning in a critically ill infant. Case report of a single patient. Pediatric intensive care unit in a University Hospital. A 6-month-old premature infant with bronchopulmonary dysplasia, tracheobronchomalacia, and progressive respiratory failure. CT scans of the chest were performed by using a mobile CT scanner in the PICU. Serial CT scans were performed at PEEP levels of 5, 10, 15, and 20 cm H(2)O in both the supine and prone position. Scheduled medical care and standard monitoring were continued during the course of the CT scans. Identical anatomic levels demonstrating the trachea, bronchi, and lung parenchyma were compared while different levels of PEEP and supine or prone positioning were used. From these comparisons, the level of PEEP in which lung volumes were optimized was radiographically determined. No significant changes in large airway caliber were observed. There was no difference noted between prone and supine positioning. CT scans were completed with minimal disruption to the patient's care. Mobile CT scanners can be used in the PICU for the diagnostic evaluation of critically ill children. This option allows for the continuation of medical therapies and monitoring in the intensive care setting while avoiding the potential complications of transporting a critically ill child to the radiology department. The use of mobile CT scanners may disrupt PICU routine and is more expensive than use of fixed CT scanners. Mobile CT scanners may be useful in radiographically determining the optimal level of PEEP in infants with tracheobronchomalacia and bronchopulmonary dysplasia.

Interrupter resistance in preschool children: measurement characteristics and reference values.

There is a need for quick, reliable, and noninvasive lung function tests to assess airway obstruction in preschool children both for pediatric pulmonary care as well as for research purposes. We studied feasibility, reproducibility, and validity of measurements of the respiratory system using the interrupter technique (interrupter resistance [Rint]) and obtained reference values in children from a general population, 2 to 7 yr of age. Accuracy was studied by comparisons of Rint with plethysmographic airway resistance (Raw) in 20 patients (7 to 14 yr) with mild to severe chronic airways obstruction and was satisfactory in patients with FEV(1) > 60% predicted. The technique proved sensitive enough to detect changes in airway caliber within a small group of 12 children who developed mild respiratory tract infections. Among children from a general population, subgroups with mild respiratory symptoms or mild respiratory disease had higher mean Rint values. Airway obstruction was better detected using expiratory rather than inspiratory interruptions, both programmed at peak tidal ventilatory flow. Reproducibility within subjects was satisfactory (intraclass correlation 0.82 and 0.79). The same applied to interobserver agreement (intraclass correlation 0.98). The interrupter technique proves to be a reliable and practical test of airway function, suitable for clinical and epidemiologic studies in preschool children.

Modulation of airway caliber by deep inhalation in children.

To elucidate whether deep inhalation (DI) modulates changes in airway caliber in childhood, we measured the effect of DI on respiratory impedance before and after inhaled methacholine or salbutamol in 4- to 7-yr-old children (n = 15) suffering from recurrent wheezing. In all children, the real part of impedance between 12 and 16 Hz (Re[Z](12-16)) increased after methacholine from 5.6 +/- 1.2 to 8.2 +/- 1.6 cmH(2)O. l(-1). s (P < 0.001) and resonance frequency from 18 +/- 3 to 25 +/- 5 Hz (P < 0.001). These changes were partially reversed by DI: Re[Z](12-16) decreased to 7.2 +/- 1.2 cmH(2)O. l(-1). s (P < 0.01) and resonance frequency to 19 +/- 5 Hz (P < 0.001). In nine children, on a separate occasion, Re[Z](12-16) decreased after salbutamol from 8.3 +/- 1.9 to 5.1 +/- 0.9 cmH(2)O. l(-1). s (P < 0.001) and resonance frequency from 21 +/- 6 to 15 +/- 3 Hz (P < 0.05). The decrease of Re[Z](12-16) was partially reversed by DI (to 6.2 +/- 1.4 cmH(2)O. l(-1). s, P < 0. 01), but resonance frequency did not change significantly (P = 0.75). We conclude that in 4- to 7-yr-old children pharmacologically induced changes in airway caliber are modulated by DI. These findings suggest that airway-to-parenchyma interdependence is operative in this age range.

HRCT imaging of airway responsiveness: effects of anesthetics.

The noninvasive imaging method, high resolution computed tomography (HRCT), has been developed in animal models and applied to humans with obstructive lung disease for assessing regional and individual airway responsiveness. The ability to directly view airway responses during provocations such as tracheal intubation in an asthmatic could greatly enhance our understanding and treatment of airway hyperresponsiveness. HRCT uses increased kilovoltage peak (kVp) and milliamperage (mAs) settings, thin slices, high spacial frequency reconstruction algorithms, and small fields of view to resolve structures as small as 200 microm. Therefore, airways as small as 1-2 mm in diameter can be viewed and measured. HRCT is a more sensitive technique for resolving airway caliber changes than clinical or research methods of pulmonary function tests. HRCT allows direct in vivo measurement of airway responsiveness to pharmacological and physiological stress that induces bronchoconstriction or bronchodilation. Using HRCT, we are able to measure airway dilation at baseline airway tone with inhalation anesthetics, differentiate the bronchodilating properties of inhalational agents in airways with tone, assess bronchodilating agents commonly used as premedications prior to anesthesia, and measure airway heterogeneity at baseline tone and their response to a variety of stimuli. This ability of HRCT to measure airway caliber and response heterogeneity in vivo noninvasively will dramatically improve our understanding of pulmonary physiology in general and the effects of anesthetics on the airways specifically.

Changes in exhaled carbon monoxide and nitric oxide levels following allergen challenge in patients with asthma.

Carbon monoxide is a product of haem degradation by haem oxygenase (HO), activated by inflammatory cytokines and oxidants. This study examined whether allergen challenge can increase exhaled CO levels, as a reflection of HO activation. Exhaled CO and nitric oxide, an expired gas also thought to reflect cytokine-induced airway inflammation, were measured in 15 atopic steroid-naive nonsmoking patients with asthma (13 males, aged 30+/-2 yrs) before and for up to 20 h after allergen challenge. Baseline CO (4.4+/-0.3 parts per million (ppm)) and NO (20.6+/-1.2 parts per billion (ppb)) levels were elevated in asthmatic as compared with nonsmoking normal volunteers (n = 37, 2.1+/-0.2 ppm and 7.0+/-0.1 ppb, respectively, p<0.05). In 10 patients with a dual response in the forced expiratory volume in one second (FEV1) there was a maximal increase in exhaled CO at 1 h (343+/-7.1%) and at 6 h (69+/-12%, p<0.01), followed by a maximal fall in FEV1 (28+/-9%, p<0.05) at 9 h, whereas the maximal NO increase was observed at 10 h (50.2+/-11.8%). The maximal increase in exhaled CO in single response patients (n = 5) was 30+/-2% during the early asthmatic reaction and 46.3+/-9.2% between 4 and 10 h, followed by a fall in FEV1 (9+/-3%, p>0.05) at 9 h, whereas exhaled NO was not significantly changed. In five patients exhaled CO was not attenuated by inhalation of increasing concentrations of histamine causing a 20% fall in FEV1 (PC20) or its subsequent relief by beta2-agonists. In conclusion, exhaled carbon monoxide is increased during the early and late asthmatic reactions independently of the change in airway calibre, while exhaled nitric oxide is increased only during the late reaction and follows the increase in carbon monoxide and fall in the forced expiratory volume in one second in time.