A simplified measurement of respiratory resistance by forced oscillation

Physiologic and histopathologic effects of targeted lung denervation in an animal model

Parasympathetic efferent innervation of the lung is the primary source of lung acetylcholine. Inhaled long-acting anticholinergics improve lung function and symptoms in patients with chronic obstructive pulmonary disease. Targeted lung denervation (TLD), a bronchoscopic procedure intended to disrupt pulmonary parasympathetic inputs, is an experimental treatment for chronic obstructive pulmonary disease. The physiologic and histologic effects of TLD have not previously been assessed. Eleven sheep and two dogs underwent circumferential ablation of the main bronchi with simultaneous balloon surface cooling using a lung denervation system (Nuvaira, Inc., Minneapolis, MN). Changes in pulmonary air flow resistance were monitored before and following TLD. Four animals were assessed for the presence or abolishment of the sensory axon-mediated Hering-Breuer reflex before and following TLD. Six sheep were histologically evaluated 30 days post-TLD for the extent of lung denervation (axonal staining) and effect on peribronchial structures near the treatment site. No adverse clinical effects were seen in any treated animals. TLD produced a ~30% reduction in pulmonary resistance and abolished the sensory-mediated Hering-Breuer reflex. Axonal staining was consistently decreased 60% at 30 days after TLD. All treated airways exhibited 100% epithelial integrity. Damage to other peribronchial structures was minimal. Tissue 1 cm proximal and distal to the treatment was normal, and the esophagus and periesophageal vagus nerve branches were unaffected. TLD treatment effectively denervates the lung while protecting the bronchial epithelium and minimizing effects on peribronchial structures.

NEW & NOTEWORTHY The feasibility of targeted lung denervation, a new minimally invasive therapy for obstructive lung disease, has been demonstrated in humans with preliminary clinical studies demonstrating improvement in symptoms, pulmonary function, and exercise capacity in patients with chronic obstructive pulmonary disease. This preclinical animal study demonstrates the ability of targeted lung denervation to disrupt vagal inputs to the lung and details its physiologic and histopathologic effects.

The case for impulse oscillometry in the management of asthma in children and adults

OBJECTIVE

To provide a clinical rationale for including impulse oscillometry (IOS) as a part of standard office-based asthma assessment.

DATA SOURCES

PubMed and Google search, limited to English language and human disease, with the keywords IOS and asthma.

STUDY SELECTIONS

Articles included in this review were based on the expert opinion and previous publications by the authors.

RESULTS

In children, IOS was more useful than spirometry in identifying asthma and uncontrolled asthma and predicting loss of control and exacerbations. IOS predicts young children at risk for loss of lung function with age and the potential for early intervention to prevent further sequelae. In adults, peripheral airway impairment detected by IOS or spirometry (ie, forced expiratory flow between 25% and 75%) commonly occurs across severity, and each measure may be complementary in predicting loss of control even with normal forced expiratory volume in 1 second. Extrafine inhaled corticosteroids with or without long-acting β-agonists proved superior to standard particle aerosols in improving IOS-detected peripheral airway obstruction. Our data also suggest that currently available commercial reference values for lung resistance at 5 Hz and lung reactance at 5 Hz are applicable across diverse populations, but further studies are needed.

CONCLUSION

The findings of this review suggest that IOS can add value to traditional clinical and spirometric assessment and thus improve management of asthma in children and adults, as well as have the potential to detect early dysfunction of the peripheral airways, which may result in better outcomes.

Oscillation mechanics of the respiratory system

The mechanical impedance of the respiratory system defines the pressure profile required to drive a unit of oscillatory flow into the lungs. Impedance is a function of oscillation frequency, and is measured using the forced oscillation technique. Digital signal processing methods, most notably the Fourier transform, are used to calculate impedance from measured oscillatory pressures and flows. Impedance is a complex function of frequency, having both real and imaginary parts that vary with frequency in ways that can be used empirically to distinguish normal lung function from a variety of different pathologies. The most useful diagnostic information is gained when anatomically based mathematical models are fit to measurements of impedance. The simplest such model consists of a single flow-resistive conduit connecting to a single elastic compartment. Models of greater complexity may have two or more compartments, and provide more accurate fits to impedance measurements over a variety of different frequency ranges. The model that currently enjoys the widest application in studies of animal models of lung disease consists of a single airway serving an alveolar compartment comprising tissue with a constant-phase impedance. This model has been shown to fit very accurately to a wide range of impedance data, yet contains only four free parameters, and as such is highly parsimonious. The measurement of impedance in human patients is also now rapidly gaining acceptance, and promises to provide a more comprehensible assessment of lung function than parameters derived from conventional spirometry.

Propofol and in vivo oxidative stress: effects of preservative

Reactive oxygen species are associated with tissue inflammation and injury. Our laboratory has demonstrated that ethane, a stable product of lipid peroxidation, in exhaled breath can be used to measure total body oxidative stress. An ischemia-reperfusion model of lung injury in sheep has been studied in which pulmonary and bronchial lung perfusion could be interrupted and restored. The goal of this study was to investigate whether two commercial formulations of propofol and the individual components of the commercial formulations attenuated the oxidative stress produced in this model. Breath ethane and breath carbon monoxide were measured as biomarkers of oxidative stress that occur at reperfusion of ischemic tissue. Data were analyzed by a standard least-squares-fit model. One of the formulations for propofol, which contained the preservative ethylenediaminetetraacetic acid (EDTA), was found to decrease the overall level of oxidative stress in sheep. Furthermore, while several models of severe lung injury demonstrate additional production of reactive oxygen species, our model of ischemia/reperfusion of lung tissue did not.

Effects of inspiratory strength training on the detection of inspiratory loads

Pressure-threshold loads (DeltaPT) are inspiratory force-related loads, which contrast with resistive loads (DeltaR), are airflow-dependent loads. If detection of respiratory loads is a function of the background load, then pressure-threshold type inspiratory muscle strength training (IMST) would affect the detection of DeltaPT but have less effect on detection of DeltaR. DeltaR and DeltaPT detection and ventilatory responses were measured in healthy volunteers. IMST consisted of 4 sets of 6 breaths per day for 4 weeks, at 75% of maximal inspiratory pressure (MIP). MIP increased and a measure of inspiratory dirve, the mouth pressure generated in the initial 100 msec of an occluded inspiration (P(0.1)), decreased after IMST. IMST significantly increased MIP after 4 weeks of training. IMST did not change DeltaR detection threshold and DeltaR-breathing pattern. IMST decreased DeltaPT detection percent and DeltaPT-breathing pattern. Comparing DeltaR and DeltaPT at the same mouth pressure-generating level, the detection percent was different. We conclude that IMST affects the detection of DeltaPT, but not DeltaR. These results also suggest that mouth pressure is not the primary determinant of the inspiratory load detection. The significance of these results is that inspiratory pressure generating capacity can be increased by our pressure threshold training and this increase in respiratory muscle strength increases the ability of pulmonary patients to compensate for increased respiratory load and modulates the threshold for detection of changes in pulmonary mechanics.

Clinical applications of forced oscillation to assess peripheral airway function

Forced oscillation applies external pressures to the respiratory system to measure respiratory impedance. Impedance of larger central airways may be dissected from that of peripheral airways using multiple oscillation frequencies. Respiratory impedance is calculated by computer-assisted methods that yield separate resistive and reactive components. The reactive component includes respiratory system capacitative and inertive properties, which may be separately visualized for clinical purposes using resonance as a rough dividing line. Low oscillation frequencies comprise those below resonance, and relate most prominently to capacitative properties of peripheral airways. High oscillation frequencies comprise those greater than resonance, which relate most prominently to inertial properties of larger central airways. Measurements of resistance and reactance in patients with peripheral airway disease, before and after therapeutic intervention, manifest characteristic patterns of response in low frequency resistance and reactance measures that appear to be closely correlated with each other. In contrast, changes in large central airways manifest resistance change uniformly over low and high frequencies.

Validation of airflow perturbation device resistance measurements in excised sheep lungs

The airflow perturbation device (APD) is a recently redesigned instrument to measure resistance in the respiratory system. The APD is small and easy to use, gives rapid resistance measurements, and can easily separate inhalation from exhalation components. It also possesses some operational characteristics similar to forced oscillation (FO). Excised sheep lungs within a respiratory chamber were used to determine the effective resistance domain of the APD. Retrograde catheters were installed in the airways, alveolar capsules were used to measure alveolar pressures, and chamber pressure was used as pleural pressure. FO measurements were made to compare with the APD. The APD was found to give a resistance measurement about 1.7 to 1.9 times airway resistance. FO gave a resistance measurement 1.4 times airway resistance. Resistance values differed depending on analysis procedure and frequency of oscillation. Both devices were found to produce oscillations beyond the pleural surface of the lungs. It was concluded that the APD and FO measure similar respiratory resistances.

Blood flow distribution within the airway wall

Altered perfusion of the bronchial mucosal plexus relative to the adventitial plexus may contribute to geometric changes in the airway wall and lumen. We studied bronchial perfusion distribution in sheep by using fluorescent microspheres at baseline and during intrabronchial artery challenge with methacholine chloride (MCh; n = 7). Additionally, we measured airway resistance (Raw) during MCh with control or increased perfusion (n = 9). Raw with MCh was significantly greater for high than control flow. Microspheres in histological sections lodged predominantly in the mucosa (60%), and this was not altered by MCh. However, more microspheres lodged in airways >1-mm in diameter during MCh and increased perfusion than MCh and control flow. In airways < or =1 mm in diameter, fewer microspheres lodged during control than increased flow. If the number of microspheres represents regional agonist access to airway smooth muscle, then the differences observed in Raw can be explained by the distribution of agonist. During challenge, there was greater MCh delivery to larger airways during increased flow and less delivery to smaller airways during control flow. The results demonstrate the effects of axial perfusion distribution on Raw.

Clinical application of forced oscillation

This review summarizes current clinical use of the forced oscillation technique (FOT) for analysis of lung function. It presents an intuitive approach to FOT pattern recognition for interpretation of results in human subjects, and the view that FOT is now well established and, clinically, eminently useful in patients with airflow obstruction. The focus of this review is on findings that relate directly to clinical utility, with less emphasis on theoretical mechanisms. The major thrust for clinical application of FOT derives from a number of European clinical research centers. Farre and Navajas and their colleagues in Barcelona, Harf and the Lorinos and their coworkers in Paris, Peslin and Duvivier and their coworkers in Vandoeuvre-les-Nancy, Pride and coworkers in London, and Van de Woestijne, Clement, Demedts, Landser, Van Noord, and their colleagues in Leuven have essentially been responsible for clinical development of FOT over the past 25 years. Publishing space does not permit an exhaustive listing of the many contributions of these investigators, but it is intended that the present review will provide a useful infrastructure from which the reader may progress to other research citations as desired.

TNF-alpha induced bronchial vasoconstriction

The pro-inflammatory characteristics of tumor necrosis factor-alpha (TNF-alpha) have been extensively characterized in in vitro systems. Furthermore, this cytokine has been shown to play a pivotal role in airways inflammation in asthma. Since the airway vasculature also performs an essential function in inflammatory cell transit to the airways, experiments were performed to determine the effects of TNF-alpha on bronchial vascular resistance (BVR). In anesthetized, ventilated sheep, the bronchial artery (BA) was cannulated and perfused with autologous blood. BVR was defined as inflow pressure/flow and averaged 6.3 +/- 0.2 mmHg. ml(-1). min(-1) (+/-SE) for the 25 sheep studied. Recombinant human TNF-alpha (10 microg for 20 or 40 min) infused directly into the BA resulted in a significant decrease in BVR to 87% of baseline (P < 0.05). This vasodilation was followed by a reversal of tone by 120 min and a sustained increase in BVR to 126% of baseline (P < 0.05). Since others have shown TNF-alpha caused coronary vasoconstriction through endothelial release of endothelin-1 (ET-1), an ET-1 antagonist was used to block bronchial vasoconstriction. BQ-123, a selective ET(A) receptor antagonist, was delivered to the bronchial vasculature prior to TNF-alpha challenge. Attenuation of bronchial vasoconstriction was observed at 120 min (P < 0.03). Thus TNF-alpha causes bronchial vasoconstriction by the secondary release of ET-1. Although TNF-alpha exerts pro-inflammatory actions on most cells of the airways, vasoactive properties of this cytokine likely further contribute to the inflammatory status of the airways.

Self-adjusting nasal continuous positive airway pressure therapy based on measurement of impedance: A comparison of two different maximum pressure levels

STUDY OBJECTIVE

Automatic titration using the forced oscillation technique (FOT) has recently been developed for the treatment of obstructive sleep apnea syndrome (OSAS). So far, it is not known if therapy with automatic nasal continuous positive airway pressure (nCPAP) using a preset upper pressure limitation or a free range (which might lead to higher mean pressure) is preferable with regard to obstructive events, sleep stages, and pressure characteristics.

DESIGN

After diagnostic polysomnography, patients were randomly assigned to two settings with the self-adjusting nCPAP (APAP) device based on the FOT. In mode 1, the pressure variation ranged from 4 to 15.5 cm H(2)O, and in mode 2, the pressure variation ranged from 4 cm H(2)O to an individual upper pressure limit.

PATIENTS

Eleven men, aged 53.0 +/- 6.8 years with a body mass index of 32.4 +/- 5.1 kg/m(2) and an apnea-hypopnea index (AHI) of 31.6 +/- 26.6/h.

MEASUREMENTS AND RESULTS

Manually titrated pressure was at 9.3 +/- 2.1 cm H(2)O, the mean pressure in mode 1 was 5.4 +/- 1.0 cm H(2)O (p < 0.01), and the mean pressure in mode 2 was 5.1 +/- 0.7 cm H(2)O (p < 0.01). A reduction of respiratory events (baseline AHI, 31.6 +/- 26.6/h; AHI in mode 1, 3.4 +/- 4.5; AHI in mode 2, 5.0 +/- 7.2; each with p < 0.001) and an increase in the "rapid eye movement" stage of sleep (baseline, 13.0 +/- 5.5%; mode 1, 22.0 +/- 7.7 [p < 0. 05]; mode 2, 23.0 +/- 7.9 [p < 0.01]) were achieved. In mode 1, the mean pressure was below the manual pressure 91.7 +/- 9.3% of the time, and in mode 2, the mean pressure was below the manual pressure 90.4 +/- 6.3% of the time. The manual pressure was exceeded by 5.5 +/- 7.4% (mode 1) and by 5.2 +/- 3.1% (mode 2).

CONCLUSION

We conclude that nCPAP therapy based on the FOT permits the adequate treatment of OSAS with significantly lower pressure than manually titrated nCPAP therapy does. A presetting of an upper pressure limit has no advantage compared to free range.

Mouse models of airway responsiveness: physiological basis of observed outcomes and analysis of selected examples using these outcome indicators

The mouse is an ideal species for investigation at the interface of lung biology and lung function. As detailed in this review, there are well-developed methods for the quantitative study of lung function in mice. These methods can be applied to mice in both terminal and nonterminal experiments. Terminal experimental approaches provide more detailed physiological information, but nonterminal measurements provide adequate data for certain experiments. In this review, we provide two examples of how these models can be used to further understanding of the primary pathobiology of airway responsiveness in both the absence and the presence of induced airway inflammation. The first model is a dissection of chromosomal loci linked to the variance in airway responsiveness observed in the absence of any manipulation to induce airway inflammation. The second model explores the role of T-cell costimulatory signals in the induction of airway hyperresponsiveness. As the number of mice with targeted deletions of effector genes or insertion of informative transgenes grows, additional examples are likely to accrue.

Methacholine causes reflex bronchoconstriction

To determine whether methacholine causes vagally mediated reflex constriction of airway smooth muscle, we administered methacholine to sheep either via the bronchial artery or as an aerosol via tracheostomy into the lower airways. We then measured the contraction of an isolated, in situ segment of trachealis smooth muscle and determined the effect of vagotomy on the trachealis response. Administering methacholine to the subcarinal airways via the bronchial artery (0.5-10.0 microg/ml) caused dose-dependent bronchoconstriction and contraction of the tracheal segment. At the highest methacholine concentration delivered, trachealis smooth muscle tension increased an average of 186% over baseline. Aerosolized methacholine (5-7 breaths of 100 mg/ml) increased trachealis tension by 58% and airways resistance by 183%. As the bronchial circulation in the sheep does not supply the trachea, we postulated that the trachealis contraction was caused by a reflex response to methacholine in the lower airways. Bilateral vagotomy essentially eliminated the trachealis response and the airways resistance change after lower airways challenge (either via the bronchial artery or via aerosol) with methacholine. We conclude that 1) methacholine causes a substantial reflex contraction of airway smooth muscle and 2) the assumption may not be valid that a response to methacholine in humans or experimental animals represents solely the direct effect on smooth muscle.

Validation of impulse oscillometry in Friesian and Blue Belgian calves with respect to changes in extrathoracic upper airway resistance

Impulse oscillometry (IOS) was compared with conventional pulmonary function techniques (using oesophageal balloon and airflow measurements). Healthy Friesian (FR) and Blue Belgian (BB) calves were examined in different conditions of extrathoracic airway resistance (physiological and vertical head position). Higher resistance values were detected in BB calves compared with FR calves with both conventional and forced oscillation techniques in both head positions. Upper airway narrowing was characterised by increasing resistance values without changes in frequency dependence. Measuring input impedance in animals using a face mask, a considerable capacitive shunt of the upper airways (including the capacitive components of the mask) has to be taken into account. Even if the absolute value of this capacitive component is constant, its influence on the measurement results increases with growing frequency and with an increase in upper airway resistance. In conclusion, (1) impulse oscillometry is sensitive to upper airway resistance changes and (2) face mask capacitance is important and has frequency dependent effects on the respiratory impedance.

Effects of edema on small airway narrowing

Numerous mediators of inflammation have been demonstrated to cause airway microvascular fluid and protein extravasation. That fluid extravasation results in airway wall edema leading to airway narrowing and enhanced reactivity has not been confirmed. In anesthetized, ventilated sheep (n = 30), airway vascular fluid extravasation was induced by infusing bradykinin (10(-6) M) through a cannulated, blood-perfused bronchial artery. Airway wall edema and luminal narrowing were determined morphometrically. Airway reactivity to methacholine (MCh; 10 microg/ml, intrabronchial artery) was determined by measuring conducting airway resistance (Raw) by forced oscillation. Raw measurements were made and lung lobes were excised and quick frozen before or after a 1-h bradykinin infusion. In 10 airways per lobe (range 0.2- to 2.0-mm relaxed diameter), wall area occupied 32 +/- 2% (SE) of the total normalized airway area (n = 9). Bradykinin infusion increased wall area to 42 +/- 5% (P = 0.02); luminal area decreased by <5%; and smooth muscle perimeter, a measure of smooth muscle constriction, was not altered (n = 5). Raw showed no change from baseline (1.4 +/- 0.4 cmH2O . l-1 . s) after bradykinin infusion (n = 10). During MCh challenge, Raw increased by 3.2 +/- 04 cmH2O . l-1 . s, and this change did not differ after administration of bradykinin. MCh challenge caused similar decreases in smooth muscle perimeter (10%) and luminal area (72 vs. 68%) before and after bradykinin infusion. However, the time constant of recovery of Raw from MCh constriction was increased from control (40 +/- 3 s) to 57 +/- 10 s after bradykinin infusion (P = 0.03). When lung lobes were excised at the same time after MCh challenge was terminated (n = 5), luminal area was greater before bradykinin infusion than after (86 vs. 78%; P = 0.007), as was smooth muscle perimeter. The results of this study demonstrate that airway wall edema limits relaxation after induced constriction rather than enhancing constriction.

Gender related differences in airway tone in children

The effects of gender, volume history, and inhaled atropine and isoproterenol on lung mechanics were assessed in 16 normal boys and 14 normal girls using lung volumes, flow-volume curves, and oscillatory resistances. Flows were measured from full and partial forced expiratory flow-volume curves. Six girls and 6 boys were studied before and after inhaled atropine, and 10 boys and 8 girls before and after inhaled isoproterenol. Girls demonstrated a significant increase in flows on full and partial curves with a deep inspiration [Vmax-partial 0.73 +/- 0.34 (SD) to Vmax-full 0.80 +/- 0.37 and 0.83 +/- 0.20 to 1.06 +/- 0.29 TLC/s in each group] and following inhalation of isoproterenol on the partial curves only (0.73 +/- 0.34 to 0.93 +/- 0.40 TLC/s). Boys showed a small but significant increase in Vmax with isoproterenol on full curves but not on partial curves. Following atropine, boys demonstrated a significant increase in Vmax on partial flow-volume curves (0.78 +/- 0.28 to 1.00 +/- 0.35 TLC/s) and a significant decrease in specific respiratory resistance (7.6 +/- 2.7 to 5.1 +/- 0.9 cmH2O/s), whereas girls had no such changes. These data suggest that boys have greater resting airway tone than girls and that this tone is less responsive to deep inspiration and isoproterenol independently, although a combination of isoproterenol and a deep inspiration will produce increased flows in boys. Atropine reduces airway tone predominantly in boys, suggesting that the increased resting airway tone in boys is partially mediated via the vagus nerve.

Respiratory effects of inhaled sulfuric acid on senior asthmatics and nonasthmatics

The objective of this study was two-fold: (1) to investigate the response of asthmatic subjects who were 60 to 75 y of age to inhaled sulfuric acid, and (2) to compare that response to findings from healthy subjects in the same age group. Nine subjects who had asthma and eight healthy subjects participated. Each subject was exposed to clean air, an inert ammonium sulfate aerosol, or 70 micrograms/m3 sulfuric acid during a 40-min exposure period composed of 30 min at rest and 10 min of light exercise on a treadmill. The sulfuric acid was delivered twice, one preceded by a lemonade drink to neutralize oral concentrations of ammonia. Exposures were separated by at least 1 wk. Oral ammonia levels and pulmonary function parameters (forced expiratory volume in one second, forced vital capacity, and total respiratory resistance) were measured before and after each exposure. None of the functional parameters in either group showed significant changes. However, total respiratory resistance changes from baseline after sulfuric acid exposure were significantly higher (+16%) in the asthmatic subjects, compared with the healthy subjects (-6%). These data suggest that older subjects are not at increased risk for adverse respiratory effects from inhalation of sulfuric acid by virtue of age alone, and older subjects with asthma are slightly more vulnerable than are their healthy peers.

Endogenous sensory neuropeptide release enhances nonspecific airway responsiveness in guinea pigs

To test whether endogenous sensory neuropeptide release results in airway hyperresponsiveness to exogenous bronchoconstrictor stimuli, male Camm-Hartley guinea pigs were exposed either to capsaicin aerosol for 10 min (CAP-AER) or to saline aerosol (SAL-AER) as a control condition. The following day, animals were anesthetized, tracheostomized, and beta-adrenergically blocked with propranolol, and their bronchoconstrictor responses to intravenously administered acetylcholine (ACh), neurokinin A (NKA), or capsaicin were measured. The bronchoconstriction induced by isocapnic dry gas hyperpnea also was assessed. Compared with the SAL-AER control group, the CAP-AER-treated animals exhibited augmented bronchoconstrictor responses to ACh and NKA. In contrast, the SAL-AER and CAP-AER groups had equivalent bronchoconstrictor responses to dry gas hyperpnea and to intravenously administered capsaicin. CAP-AER treatment caused neutrophilic airway inflammation, as reflected in increased numbers of neutrophils in bronchoalveolar lavage fluid obtained from CAP-AER-treated animals. Ablation of airway c-fiber neuron function (by chronic pretreatment with capsaicin prior to capsaicin aerosol inhalation) eliminated the ACh hyperresponsiveness observed in the CAP-AER-treated animals, demonstrating that sensory nerve products play a key role in the development of this nonspecific hyperresponsiveness. Our results demonstrate that sensory nerve stimulation with capsaicin aerosol leads to nonspecific bronchoconstrictor hyperresponsiveness and cellular airway inflammation, and thus disclose another potentially important role of sensory nerves in regulating airway function.(ABSTRACT TRUNCATED AT 250 WORDS)

Four-year follow-up of effects of toluene diisocyanate exposure on the respiratory system in polyurethane foam manufacturing workers. I. Study design and results of the first cross-sectional observation

A 4-year cohort study was designed to assess the exposure-effect relationship of working in polyurethane foam (PF) manufacturing factories with exposure to toluene diisocyanate (TDI) and its effects on the respiratory system. This paper describes the results of the first cross-sectional observations. The study population included 90 male workers who had been working in PF factories for 0.5-25 years (mean 13.3 years) (PF workers) and 44 reference workers in the same factories. The mean exposure concentration of TDI calculated from 129 personal samples was 3.2 ppb. Peak exposure excursions above 20 ppb occurred in 16 of 129 samples. Pulmonary function and its change during the working day as assessed by examining the forced expiratory flow-volume curve, respiratory impedance, and airway resistance and specific airway conductance were not different in the PF workers from those in the reference workers. Chest X-radiographs did not show any noteworthy radiological changes. Prevalences of "phlegm in winter," "nasal stuffiness or discharge in winter," and "irritation of eye and throat mucous membranes" were significantly higher in the PF workers. The findings indicate that TDI exposure at levels around 3 ppb may not adversely affect the pulmonary function over many years of exposure of those who are not hypersensitive to TDI. The causal chemicals inducing some respiratory and irritative symptoms could not be specifically identified since the PF workers were exposed not only to TDI but also to other irritative agents in the PF manufacturing processes.

Response of young asthmatic patients to inhaled sulfuric acid

The intent of this study was to explore the effects of inhalation of [H+] defined here as acid airborne particles at near ambient concentrations on the pulmonary function of adolescent asthmatic subjects. During rest and exercise, 22 adolescent asthmatic subjects inhaled atmospheres containing either clean air or sulfuric acid particles (H2SO4) through a mouthpiece. The concentration of hydrogen ion at the mouthpiece ([H+]) ranged from 1.18 to 3.59 mumol/m3 (51 to 176 micrograms/m3 of H2SO4). The lower range of [H+] is near the peak values measured during the summer months in the eastern United States and Canada. Pulmonary function and oral ammonia levels were measured before and after exposure in all subjects. Significant group responses to [H+] were seen in FEV1 (p = 0.016) and FVC (p = 0.039) measured 2 to 3 min post-exposure. Also, the slopes of the change in pulmonary function versus [H+] were computed for each subject. The slopes of changes in FEV1 and Vmax50 and Vmax75 versus [H+] were related to the subject's response to a standard exercise treadmill test, specifically to the subject's percentage decrease in FEV1 after exercise challenge. Pulmonary function changes 20 min postexposure did not show a significant group response to [H+] exposure; however, the relationship between percentage FEV1 decrease after exercise and the individual slopes of Vmax50 and Vmax75 persisted for at least 20 min after exposure.

Acute pulmonary effects of nitrogen dioxide exposure during exercise in competitive athletes

The acute pulmonary responses of athletes after short-term exposure to ambient concentrations of NO2 during heavy exercise have been examined. Intercollegiate male athletes were screened for history of cardiac disease, respiratory disease, allergic conditions and extensive exposure to pollutants. After completion of serum IgE level determination, exercise tolerance test and methacholine challenge test with normal results, nine healthy subjects 18 to 23 years of age were exposed to filtered air and to 0.18 and 0.30 ppm NO2 for 30 min on different days while exercising on a treadmill. Pulmonary function parameters were measured before and after each exposure. In this study, no statistically significant changes were observed in FEV1, RT PEFR, and Vmax50% after exposure to 0.18 and 0.30 ppm NO2. For these selected healthy athletes, short-term exposure to ambient NO2 levels during heavy exercise does not affect adversely the pulmonary function.

Initial airway function is a risk factor for recurrent wheezing respiratory illnesses during the first three years of life. Group Health Medical Associates

We recently reported a significant relationship between lung function measured prior to any lower respiratory tract illness and subsequent wheezing illnesses during the first year of life (N Engl J Med 1988; 319:1112-7). Follow-up has continued for this group of infants during the second and third years of life. When compared with never wheezers, infants who wheezed during the first year of life and had at least one additional lower respiratory illness had 22% lower initial levels of an indirect index of airway conductance derived from the shape of tidal breathing curves (p less than or equal to 0.01), 22% lower respiratory conductance (p less than or equal to 0.05), 25% lower maximal flows at the end-expiratory point (p less than or equal to 0.01), and 10% lower functional residual capacity (p less than or equal to 0.05). Infants who wheezed only once during the first 3 yr of life or who started wheezing during the second year of life had normal tidal breathing curves but significantly lower maximal expiratory flows (p less than or equal to 0.05). Their functional residual capacity was also lower than that of never wheezers (p less than or equal to 0.05). We conclude that diminished initial airway function may be a predisposing factor for recurrent wheezing respiratory illnesses starting in the first year of life. Infants who will have only one wheezing respiratory illness or who will start wheezing after the first year of life seem to have lower levels for some but not for all lung function tests performed in this study.

Analysis of expiratory pattern for monitoring bronchial obstruction in school-age children

This study was designed to assess the validity of the percent of volume expired at tidal peak flow (dV/Vt) as an indicator of bronchial obstruction in school-age children. We analyzed 126 dV/Vt ratios and compared them with spirometric and plethysmographic results measured in 24 healthy (14 males) and 60 asthmatic (41 males) children; 42 of them underwent measurements before and after bronchial challenge with histamine. The two groups differed in resistance, forced expiratory volume in 1 sec (FEV1), and forced expiratory flows, as percents of predicted (FEV1: 94.6 +/- 2.4% in controls vs 86.7 +/- 1.6% in asthmatics; P less than 0.001). They did not differ in peak expiratory flow (PEF), forced vital capacity, functional residual capacity, measured by body plethysmography, and in dV/Vt. The dV/Vt was found to correlate with FEV1 (r = 0.58, P less than 0.001), PEF (r = 0.57, P less than 0.001), and other lung function parameters. Forty-two of the asthmatic children performed a bronchoprovocation histamine test. The fall of dV/Vt after histamine was significantly correlated (r = 0.61, P less than 0.001) with the variation in FEV1 and other lung function parameters. We conclude that dV/Vt is a good indicator of bronchial obstruction, as useful in school-age children as in adults and infants, with no need for the subject's cooperation.

Prior exposure to ozone potentiates subsequent response to sulfur dioxide in adolescent asthmatic subjects

The objective of this study was to test whether prior exposure to a low concentration of ozone (120 ppb) would condition airways in asthmatic subjects to respond to a subthreshold concentration of sulfur dioxide (100 ppb). Eight male and five female subjects 12 to 18 yr of age participated. They all had allergic asthma and exercise-induced bronchospasm. Subjects were exposed to three test atmosphere sequences during intermittent moderate exercise (a 45-min exposure to one pollutant followed by a 15-min exposure to the second pollutant). The sequences were: air followed by 100 ppb SO2, 120 ppb O3 followed by 120 ppb O3, and 120 ppb O3 followed by 100 ppb SO2. The pulmonary function measurements assessed were FEV1, total respiratory resistance (RT), and maximal flow (Vmax50). Air-SO2 and O3-O3 exposures did not cause significant changes in pulmonary function. On the other hand, exposure to 100 ppb SO2 after a 45-min exposure to 120 ppb O3 caused a significant (8%) decrease in FEV1 (p = 0.046), a significant (19%) increase in RT (p = 0.048), and a significant (15%) decrease in Vmax50 (p = 0.008). It is concluded that prior O3 exposure increased bronchial hyperresponsiveness in these subjects such that they responded to an ordinarily subthreshold concentration of SO2. These data suggest that assessment of pulmonary changes to single pollutant challenges overlooks the interactive effects of common coexisting or sequentially occurring air pollutants.

Pulmonary effects of sulfur dioxide exposure and ipratropium bromide pretreatment in adults with nonallergic asthma

In this study we examined the potential short-term effect of sulfur dioxide (SO2) on total respiratory resistance and forced expiratory volume in patients with nonallergic asthma. A group of nine adult subjects with nonallergic asthma, 55 years of age or older, were exposed to SO2 at 0, 0.5, and 1.0 ppm for 20 minutes at rest followed by 10 minutes during light-moderate exercise. The measures of pulmonary function assessed were FEV1, specific total respiratory resistance (SRT), and maximal expiratory flow rates at 50% (Vmax50) and 75% (Vmax75) of expired vital capacity. Measurements were made before exposure to SO2 (baseline), postresting exposure, postexercising exposure, and at 30 minutes thereafter (recovery). Repeat measure analysis of variance revealed a statistically significant dose-response effect of SO2 inhalation on FEV1 (p = 0.008), SRT (p = 0.033), Vmax50 (p = 0.017), and Vmax75 (p = 0.048). Eight subjects had repeat exposure to SO2 at 1.0 ppm after treatment with either placebo or ipratropium bromide, 60 micrograms by metered-dose inhaler. Inpratropium bromide treatment, compared to placebo treatment, resulted in a statistically significant improvement in all baseline measures of pulmonary function: FEV1 (p = 0.017), SRT (p = 0.027), Vmax50 (p = 0.018), and Vmax75 (p = 0.035). However, this drug did not significantly alter the proportionate change in pulmonary function caused by SO2 inhalation in these subjects. These findings indicate that adults with nonallergic asthma are sensitive to short-term low-level SO2 exposure and that treatment with 60 micrograms of ipratropium bromide causes significant bronchodilation but does not protect, completely, these patients from the effect of SO2 inhalation.

The pulmonary effects of ozone and nitrogen dioxide alone and combined in healthy and asthmatic adolescent subjects

Separate exposures to 0.12 ppm ozone (O3) or 0.18 ppm nitrogen dioxide (NO2) have not demonstrated consistent changes in pulmonary function in adolescent subjects. However, in polluted urban air, O3 and NO2 occur in combination. Therefore, this project was designed to investigate the pulmonary effects of combined O3 and NO2 exposures during intermittent exercise in adolescent subjects. Twelve healthy and twelve well-characterized asthmatic adolescent subjects were exposed randomly to clean air or 0.12 ppm O3 and 0.30 ppm NO2 alone or in combination during 60 minutes of intermittent moderate exercise (32.5 1/min). The inhalation exposures were carried out while the subjects breathed on a rubber mouthpiece with nose clips in place. The following pulmonary functional values were measured before and after exposure: peak flow, total respiratory resistance, maximal flow at 50 and 75 percent of expired vital capacity, forced expiratory volume in one second and forced vital capacity (FVC). Statistical significance of pulmonary function changes was tested by analysis of covariance for repeated measures. After exposure to 0.12 ppm O3 a significant decrease was seen in maximal flow at 50% of FVC in asthmatic subjects. After exposure to 0.30 ppm NO2 a significant decrease was seen in FVC also in the asthmatic subjects. One possible explanation for these changes is the multiple comparison effect. No significant changes in any parameters were seen in the asthmatic subjects after the combined O3-NO2 exposure or in the healthy subjects after any of the exposures.

Diminished lung function as a predisposing factor for wheezing respiratory illness in infants

In a prospective study of 124 infants enrolled as newborns, we assessed the relation between initial lung function and the subsequent incidence of lower respiratory tract illness during the first year of life. The risk of having a wheezing illness was 3.7 times higher (95 percent confidence interval, 0.9 to 15.5; P = 0.06) among infants whose values for total respiratory conductance (the reciprocal of the resistance to air flow of the entire respiratory system) were in the lowest third, as compared with infants with values in the upper two thirds of the range of values for the group. Boys with initial values in the lowest third for an indirect index of airway conductance had a 10-fold increase (95 percent confidence interval, 2.2 to 44.2; P = 0.001) in the risk of having a wheezing illness. A 16-fold increase (95 percent confidence interval, 1.7 to 147.1; P = 0.002) in the risk of having a wheezing illness was found among girls whose initial values for lung volume at the end of tidal expiration were in the lowest third. We conclude that diminished lung function is a predisposing factor for the development of a first wheezing illness in infants.

The effects of ozone and nitrogen dioxide on pulmonary function in healthy and in asthmatic adolescents

The aim of this project was to investigate whether well-characterized asthmatic adolescent subjects were more sensitive to the inhaled effects of oxidant pollutants than were well-characterized healthy adolescent subjects. Ten healthy and 10 asthmatic subjects inhaled via a mouth-piece 0.12 or 0.18 ppm of ozone (O3) or nitrogen dioxide (NO2) or clean air for 30 min at rest followed by 10 min during moderate exercise (32.5 L/min) on a treadmill. The following pulmonary functional values were measured before and after exposure: peak flow, total respiratory resistance (RT), maximal flow at 50 and 75% of expired VC, and FEV1. After exercise exposure to 0.18 ppm O3, statistically significant increases were seen in RT in asthmatic and healthy adolescent subjects. No consistent changes were seen in either group after NO2 exposure. Also, no significant differences in response to oxidant pollutants between the 2 groups could be demonstrated. It was concluded that neither group was consistently sensitive to these pollutants.

Phasic changes in upper airway impedance

To identify within breath variations in the mechanical properties of the isolated upper airway, we examined changes in impedance spectra over the course of the respiratory cycle. Changes were evaluated with a modified forced oscillation technique applied to the isolated, sealed upper airways of nine anesthetized mongrel dogs. Upper airway impedance spectra were studied during sequential 350 msec epochs. We found spectral changes which were reproducible within the respiratory cycle. Impedance spectra revealed that during mid-inspiration at the point of peak upper airway muscle activity, the low frequency real part decreased and the imaginary part was less negative and less steep. During late inspiration and early expiration the impedance values returned to their end-expiratory values. The only significant change in parameter estimates from a three-parameter model indicated an increase in compliance. Since these changes correlated not only with tidal flow through the lower trachea and lung but also with upper airway muscle activation, we reasoned that changes in impedance could have resulted from an increase in upper airway size. Therefore, we used a sealed speaker system and, while the animal was apnoeic, evaluated impedance at two different airway pressures and the resultant volumes. The changes in impedance spectra with a volume increase were similar to those seen during spontaneous breathing efforts. We conclude that the mechanical properties of the upper airway change during the respiratory cycle and that these changes correlate with the respiratory activation of upper airway muscles. We suspect that these changes in input impedance could reflect a change in the size of the airway rather than a true increase in elasticity.

Respiratory resistance feedback in the treatment of bronchial asthma in adults

Two studies evaluated feedback of total respiratory resistance of the airways (TRR) as a treatment for adults with moderate to severe chronic bronchial asthma. Respiratory function tests and questionnaires were used to select the patients and to assess treatment effects. Study I provided eight biofeedback sessions in four weeks (each session containing four, 3-min training trials) plus three pre-treatment and three post-treatment sessions. Over the eight treatment sessions biofeedback failed to produce any significant improvements, although overall the nine patients showed lower mean initial TRR values at the three post-treatment sessions compared with the three pre-treatment sessions. Patients consistently showed improvement following bronchodilator administration at the end of every session. In study II, biofeedback was provided in one intensive session of 20, 2-min trials. While careful instruction about biofeedback was provided to subjects, and more post-treatment measures were included, no significant improvements were shown following biofeedback, but were shown following bronchodilator administration.

Within-breath changes of airway calibre in patients with airflow obstruction by continuous measurement of respiratory impedance

We bench-tested a commercially available instrument for measuring respiratory impedance (Siregnost FD5: Siemens) and found that resistance (R) and phase changes were accurately recorded in models. In a single human subject, total respiratory resistance (R(l)) was closely comparable to resistance measured by the Mead-Whittenberger technique. The derived continuous variable (R(os)) was similar to R at less than 4 cmH2O . litres-1 . sec, but underestimated R at higher values. Ros was highly correlated with airways resistance by body plethysmography (R(aw)), but with a low slope and high intercept (R(os) = 1.38 + 0.59 R(aw): r = 0.89). Because of turbulence, both in model larynxes and in normal subjects, R(os) tends to rise with increases in flow in either direction. R(os) also tends to fall as lung volume rises, and vice versa, reflecting cyclic changes in airway calibre. We devised indices of expiratory narrowing of airways from the maximum flow-volume loop, and the plethysmographic alveolar pressure-flow loop, and compared them with the slope of the relation between R(os) and lung volume during tidal breathing, in nine normal subjects and 16 patients with airflow obstruction. Twelve of the 16 patients, all with abnormal flow-volume loops, had high R(os)-volume slopes, demonstrating excessive expiratory narrowing even during tidal breathing. We found no patients with normal inspiratory R(os) together with an abnormal R(os)-volume slope. Thus unstressed inspiratory calibre was never dissociated from airways narrowing on expiration.

Two-year observation of pulmonary function in workers exposed to low concentrations of toluene diisocyanate

Pulmonary effects were investigated in 106 toluene diisocyanate (TDI)-exposed workers and 39 referents in 64 exposed workers and 21 referents on the 2-year follow-up study in 1982. Means of individual, time-weighted average (TWA) exposure concentrations measured by personal monitors were approximately 0.001 ppm in each year. Short-term exposure at 0.02 ppm or over was observed in 9.3% of the collected samples in 1980 and 1.9% in 1982. Pulmonary function was assessed by measurements of maximum expiratory flow-volume curve and respiratory impedance. No differences were observed in the means of the pulmonary functions and their individual daily changes between the TDI workers and the referents. Significant intra-individual, two-year decreases were observed in some pulmonary function parameters in both groups, but when the effect of aging was adjusted, the decreases disappeared. Prevalences of respiratory symptoms in the TDI workers were not significantly higher than those in the referents, except for irritating complaints of the eyes and throat probably due to peak exposure to TDI and/or co-existing irritants. Eight of the TDI workers had episodes of acute asthmatic reactions shortly after having begun their TDI jobs and most parameters in their maximum expiratory flow were significantly less than the predicted values, though exposure concentrations when the episodes occurred could not be defined. From these results, it was suggested that TDI exposure at the levels of 0.001 ppm may not induce adverse pulmonary effects when the workers are not hypersusceptive to TDI.

Computation of respiratory impedance from forced sinusoidal oscillations during breathing

Computation of impedances from forced oscillation data during breathing can yield results which reflect not only changes in respiratory mechanics, but artifacts related to the signal analysis. A method has been developed, employing sinusoidal forcing, to determine intra-breath variations of respiratory impedance. The measured pressure and flow waveforms are each the sum of a slowly varying constituent associated with breathing, and a high-frequency oscillatory constituent, whose amplitude and phase vary with time. The signal constituents were separated with a moving-average filter. Characteristic amplitudes and phases of the oscillatory constituents over a short time interval (window) were determined by correlating the constituents with sine waves of the same frequency. Continuous estimates of the time-varying impedance were obtained by moving the window over the data. Two procedures were developed to examine the accuracy of impedances computed with this technique: (1) the analysis of fixed-amplitude sinusoids superimposed on a breathing pattern; and (2) the analysis of a known, time-varying impedance. The effects of forcing frequency, window size, breathing frequency, and the position within the respiratory cycle on the computed impedances were examined. For quiet breathing, the technique can yield impedances which are accurate to within 5% in magnitude, and 5 degrees in phase angle at all instants within the breath. An efficient algorithm was developed for implementing the technique on a computer.

Effect of the antitussive glaucine on bronchomotor tone in man

In view of the observation that the antitussive agent glaucine prevents histamine-induced bronchoconstriction in guinea pigs we investigated this agent for a possible peripheral action in man, using a new method for measuring changes in bronchomotor tone. The forced airflow oscillation method was used to determine respiratory resistance (Rrs) over a range of lung volumes (VL) in seven healthy supine subjects. Computer analysis of the hyperbolic relationship between Rrs and VL was used to determine the asymptotic resistance and yield estimates of lower airways conductance (Glaw). Specific lower airways conductance (sGlaw) was expressed as the slope of the linear plot of Glaw against VL and is a sensitive index of bronchomotor tone. After baseline measurements of sGlaw subjects received placebo or 60 mg glaucine orally according to a double-blind crossover protocol. Histamine, 500 micrograms, was inhaled 45 minutes later. Measurements of sGlaw were repeated every 10 minutes for two hours. Although there was a trend towards bronchodilatation after glaucine administration (sGlaw = 130% of baseline) there was no significant difference from the effect of placebo (sGlaw = 89% of baseline). After inhalation of histamine sGlaw fell to 26% of baseline after both glaucine and placebo (p less than 0.01). In a further study three subjects received glaucine and placebo according to an identical protocol except that the histamine was omitted. Again the increase in sGlaw failed to achieve significance. Glaucine does not affect the bronchoconstrictor response to histamine in man and there is no convincing evidence of an effect on resting bronchomotor tone.

Estimation of respiratory impedance and source pressure using a Thévenin equivalent circuit model

The objective of this paper is to present a new technique which can provide both active respiration source pressure and lung impedance in a single noninvasive test. The method is based upon a Thévenin equivalent circuit model of respiratory mechanics. Using this model, the equivalent source pressure and source impedance can be computed from the measured changes of respiratory pressures and flows in two consecutive cycles before and after addition of purely resistive loads to the mouth. In maximal breathing the source parameters were reproducible in six normal human subjects. The total respiratory resistance during maximal breathing had an average value of 3.46 cmH2O l-1 s-1, and the total dynamic compliance had an average value of 0.078 l cmH2O-1. The airway resistances measured using a plethysmographic method were within the range of 45-65% of the estimated total respiratory resistances. These two resistances were related with a correlation coefficient of 0.98. An average value of the magnitudes of the fundamental components of the source pressure was 6.73 cmH2O during maximal breathing and 2.09 cmH2O during spontaneous breathing.

Reflex effects of aerosolized histamine on phrenic nerve activity

Studies were conducted in anesthetized, paralyzed dogs on the effect of aerosolized histamine on phrenic nerve activity. The paralyzed dogs were ventilated in phase with their recorded phrenic nerve activity at a constant inspiratory flow-rate, using a cycle-triggered ventilator. Phrenic nerve activity was measured before and during administration of aerosolized histamine while the inspiratory flow-rate and arterial blood gases were kept constant. In addition, before and after histamine, phrenic nerve activity was recorded for single bursts during which the ventilator was switched off. The effects of histamine on respiratory resistance were prevented by prior administration of isoproterenol and atropine. Although no changes occurred in respiratory resistance, histamine increased the instantaneous magnitude of phrenic nerve activity. The effect was evident early in the inspiratory period and was found even when the lungs were not inflated. Inflation of the lungs excited phrenic nerve activity; this effect increased after histamine. All of these actions of histamine were abolished by vagotomy. We conclude that histamine increased phrenic nerve activity during inspiration by a vagal reflex.