Regression simulation of the dependence of forced expiratory tracheal noises duration on human respiratory system biomechanical parameters

BACKGROUND: Estimating the duration of forced exhalation tracheal noises shows promise for recognizing bronchial obstruction. OBJECTIVE: Experimental simulation of an influence of biomechanical parameters on the duration of normal forced exhalation tracheal noises. METHOD AND MATERIALS: Thirty-two healthy non-smoking men aged 16-22 years were examined. The duration of noises, the parameters of computer spirometry, and the maximum static expiratory pressure are recorded. These data were analyzed by means of multiple linear regression simulation for logarithms of the elements of the proportionality relation obtained with the use of a one-component biomechanical model of forced exhalation and a linearized approximation of flow-volume curve. RESULTS: Dependence between duration of the forced expiratory noises recorded on human trachea and the product of forced volume capacity (in power of 1.05 +/- 0.27), maximum static expiratory pressure (in power of 0.46 +/- 0.23), equivalent expiratory resistance in the stage of functional expiratory stenosis (in power of 0.72 +/- 0.15 in healthy is an estimate of the equivalent expiratory resistance of human bronchial tree in the functional expiratory stenosis phase, whereas in patients with bronchial obstruction it is supposed to take into account an excess of noise generation time compared with the time predicted from normal individual value of this resistance.     

Estimation of tracheal sound intensity during forced expiration

The tracheal sounds during forced expiration were studied using the mathematical model of forced expiration. It has been shown that separated flow in the region of dynamic constriction of the trachea during forced expiration may cause the generation of tracheal sounds.     

Dynamics of the duration of tracheal forced expiratory noises during long-term isolation in the Mars-500 experiment

The dynamics of the duration of tracheal forced expiratory noises in a group of volunteers were studied before, during, and after a 520-day confinement. The duration did not change in most volunteers. Two volunteers exhibited significant changes in the duration of tracheal sounds and some spirometric parameters. The increase in the duration of tracheal forced expiratory noises and the decrease in spirometric parameters reveal ventilation impairment of the obstructive type. Analysis of the duration of tracheal forced expiratory noise dynamics during prolonged confinement has proven to be a sensitive technique to test ventilation function changes.     

Acoustic biomechanical relationships of human forced exhalation in bronchial obstruction

A statistically significant bidirectional influence of the incidence and degree of bronchial obstruction on the acoustic parameters of forced expiration and the spirometry/body plethysmography indicators of lung function has been revealed by means of nonparametric analysis of variance in a sample of 218 subjects. It has been shown that the acoustic band pass times and energies of forced expiratory tracheal noises coordinate with both tidal resistance and residual volume.     

Measuring peak expiratory flow in general practice: comparison of mini Wright peak flow meter and turbine spirometer.

OBJECTIVE--To compare measurements of the peak expiratory flow rate taken by the mini Wright peak flow meter and the turbine spirometer. DESIGN--Pragmatic study with randomised order of use of recording instruments. Phase 1 compared a peak expiratory flow type expiration recorded by the mini Wright peak flow meter with an expiration to forced vital capacity recorded by the turbine spirometer. Phase 2 compared peak expiratory flow type expirations recorded by both meters. Reproducibility was assessed separately. SETTING--Routine surgeries at Aldermoor Health Centre, Southampton. SUBJECTS--212 Patients aged 4 to 78 presenting with asthma or obstructive airways disease. Each patient contributed only once to each phase (105 in phase 1, 107 in phase 2), but some entered both phases on separate occasions. Reproducibility was tested on a further 31 patients. MAIN OUTCOME MEASURE--95% Limits of agreement between measurements on the two meters. RESULTS--208 (98%) Of the readings taken by the mini Wright meter were higher than the corresponding readings taken by the turbine spirometer, but the 95% limits of agreement (mean difference (2 SD] were wide (1 to 173 l/min). Differences due to errors in reproducibility were not sufficient to predict this level of disagreement. Analysis by age, sex, order of use, and the type of expiration did not detect any significant differences. CONCLUSIONS--The two methods of measuring peak expiratory flow rate were not comparable. The mini Wright meter is likely to remain the preferred instrument in general practice.     

Viscoelasticity of the trachea and its effects on flow limitation.

To test the hypothesis that peak expiratory flow is determined by the wave-speed-limiting mechanism, we studied the time dependency of the trachea and its effects on flow limitation. For this purpose, we assessed the relationship between transmural pressure and cross-sectional area [the tube law (TL)] of six excised human tracheae under controlled conditions of static (no flow) and forced expiratory flow. We found that TLs of isolated human tracheae followed quite well the mathematical representation proposed by Shapiro (Shapiro AH. J Biomech Eng 99: 126-147, 1977) for elastic tubes. Furthermore, we found that the TL measured at the onset of forced expiratory flow was significantly stiffer than the static TL. As a result, the stiffer TL measured at the onset of forced expiratory flow predicted theoretical maximal expiratory flows far greater than those predicted by the more compliant static TL, which in all cases studied failed to explain peak expiratory flows measured at the onset of forced expiration. We conclude that the observed viscoelasticity of the tracheal walls can account for the measured differences between maximal and "supramaximal" expiratory flows seen at the onset of forced expiration.     

Lung hyperinflation in isolated dog lungs during high-frequency oscillation

To study the phenomenon of lung hyperinflation (LHI), i.e., an increase in lung volume without a concomitant rise in airway pressure, we measured lung volume changes in isolated dog lungs during high-frequency oscillation (HFO) with air, He, and SF6 and with mean tracheal pressure controlled at 2.5, 5.0, and 7.5 cmH2O. The tidal volume and frequency used were 1.5 ml/kg body wt and 20 Hz, respectively. LHI was observed during HFO in all cases except for a few trials with He. The degree of LHI was inversely related to mean tracheal pressure and varied directly with gas density. Maximum expiratory flow rate (Vmax) was measured during forced expiration induced by a vacuum source (-150 cmH2O) at the trachea. Vmax was consistently higher than the peak oscillatory flow rate (Vosc) during HFO, demonstrating that overall expiratory flow limitation did not cause LHI in isolated dog lungs. Asymmetry of inspiratory and expiratory impedances seems to be one cause of LHI, although other factors are involved.     

Correlation between Acoustic Characteristics of Forced Expiratory Tracheal Noises and Lung Function Parameters in Healthy Subjects and Patients with Obstructive Lung Diseases

The correlations between acoustic characteristics and lung function parameters measured by body plethysmography were revealed when analyzing the sample of 230 subjects consisting of subgroups of healthy subjects, subjects with risk factors, and patients with obstructive lung diseases. Multidirectional character of the correlations between acoustic characteristics of forced expiratory tracheal sounds and parameters measured by body plethysmography/spirometry was established in subgroups of healthy subjects, asthma patients with spirometrically confirmed and unconfirmed obstructive changes, and patients with chronic pulmonary disease.     

Properties of steady maximal expiratory flow within excised canine central airways

Using our transistor model of the lung during forced expiration (J. Appl. Physiol. 62: 2013-2025, 1987), we recently predicted that 1) axially arranged choke points can exist simultaneously during forced expiration with sufficient effort, and 2) overall maximal expiratory flow may be relatively insensitive to nonuniform airways obstruction because of flow interdependence between parallel upstream branches. We tested these hypotheses in excised central airways obtained from five canine lungs. Steady expiratory flow was induced by supplying constant upstream pressure (Pupstream = 0-16 cmH2O) to the bronchi of both lungs while lowering pressure at the tracheal airway opening (16 to -140 cmH2O). Intra-airway pressure profiles obtained during steady maximal expiratory flow disclosed a single choke point in the midtrachea when Pupstream was high (2-16 cmH2O). However, when Pupstream was low (0 cmH2O), two choke sites were evident: the tracheal site persisted, but another upstream choke point (main carina or both main bronchi) was added. Flow interdependence was studied by comparing maximal expiratory flow through each lung before and after introduction of a unilateral external resistance upstream of the bronchi of one lung. When this unilateral resistance was added, ipsilateral flow always fell, but changes in flow through the contralateral lung depended on the site of the most upstream choke. When a single choke existed in the trachea, addition of the external resistance increased contralateral flow by 38 +/- 28% (SD, P less than 0.003). In contrast, when the most upstream choke existed at the main carina or in the bronchi, addition of the external resistance had no effect on contralateral maximal expiratory flow.(ABSTRACT TRUNCATED AT 250 WORDS)     

Duration of tracheal sound recorded during forced expiration: From a model to establishing standards

Analysis of the duration of tracheal sound recorded during forced expiration (TSFE) was performed to detect bronchial conductance disorders and to develop a method for establishing individually tailored standards. A standard individual duration of the TSFE served as an estimate of the relevant expiratory resistance of the bronchial tree in healthy subjects and showed the extent to which sound duration exceeded that predicted from the normal individual resistance in flow-limited subjects.     

Dynamic characteristics of the external respiratory function in young male residents of the north during the annual cycle

The following aspects were studied during the annual cycle in young men (aged 19.0 ± 0.9 years) living in northern European Russia (62°N): the peak and instantaneous volumetric flow rates (PVFR and IVFR, respectively) at the moments of expiration of 25, 50, and 75% of the forced vital capacity of the lungs (FVC); the average volumetric expiratory flow rate in the process of expiration from 25 to 75% of FVC; the respiratory rate; and the time of attainment of PVFR and FVC. The pulmonary function parameters were determined using an SPM-01-R-D microprocessor spirograph. It was found that only the velocity characteristics of the external respiratory function significantly (the F test) changed in young men during the annual cycle; the time functions were not significantly different. A greater variation in the velocity parameters of the external respiratory function was found during the annual cycle compared to those for the inhabitants of temperate latitudes, which is indicative of adaptive reactions of the external respiratory function and a slightly restricted bronchial patency at the level of mediumand, especially, small-caliber bronchi. The PVFR and IVFR at the moments of expiration of 25, 50, and 75% of FVC and the average volumetric expiratory flow rate in the 25–75% range of the FVC in the male residents of the North are higher during the cold season and lower in the warm season.     

External respiration function of young male residents of northern Europe during the annual cycle

In young men (19.0 ± 0.9 years of age), the following parameters were studied during the annual cycle: the tidal and minute lung volumes, vital and forced vital capacities of the lungs, expiratory and inspiratory reserve volumes, 0.5-and 1-s forced expiratory volumes, and Tiffenau index. Young men working under the conditions of the North (62°N) proved to have deeper breathing; the minute volume and vital capacity of their lungs were increased. Analysis of the lung volume during the annual cycle demonstrated changes in most parameters studied (except the expiratory reserve volume and Tiffenau index). The maximum values of the lung volumes were recorded in the cold time of the year (from November to April), whereas the minimum values were observed in the warm time (from May to September).     

Smooth muscle dynamics and maximal expiratory flow in asthma.

A computational model for maximal expiratory flow in constricted lungs is presented. The model was constructed by combining a previous computational model for maximal expiratory flow in normal lungs and a previous mathematical model for smooth muscle dynamics. Maximal expiratory flow-volume curves were computed for different levels of smooth muscle activation. The computed maximal expiratory flow-volume curves agree with data in the literature on flow in constricted nonasthmatic subjects. In the model, muscle force during expiration depends on the balance between the decrease in force that accompanies muscle shortening and the recovery of force that occurs during the time course of expiration, and the computed increase in residual volume (RV) depends on the magnitude of force recovery. The model was also used to calculate RV for a vital capacity maneuver with a slow rate of expiration, and RV was found to be further increased for this maneuver. We propose that the measurement of RV for a vital capacity maneuver with a slow rate of expiration would provide a more sensitive test of smooth muscle activation than the measurement of maximal expiratory flow.     

Forced expiratory tracheal noise time in young men in health and in bronchial obstruction

A group of 270 young men aged 16–25 years including healthy nonsmokers, healthy smokers, and bronchial asthma patients with and without spirometry-confirmed bronchial obstruction was tested. The forced expiratory noise time recorded on the trachea in a frequency band of 200–2000 Hz, the spirometry indices, and the anthropometric parameters were measured. It was shown that the forced expiratory tracheal noise time and its ratios to the squared chest circumference, to the body mass, and to the height reflected bronchial resistance and are promising indices for diagnosing bronchial obstruction.     

Anesthesia equipment

A randomized clinical crossover trial was carried out to compare the use in the home, during 1-week periods, of two commercially available chamber devices (the Aerochamber and the Spacer) and a standard metered-dose inhaler (MDI) in 24 patients with reversible bronchospasm and satisfactory inhaler technique. Measurements of peak flow, forced expiratory volume in 1 second (FEV1), forced vital capacity (FVC), ratio of FEV1 to FVC and forced midexpiratory flow rate were made immediately before and 15 minutes after inhalation of terbutaline sulfate. No difference was noted in results of spirometry, peak flow readings or side effects between the devices. The results of spirometry were better during the trial than immediately before it (p less than 0.01). The mean score for inhaler technique was significantly lower at follow-up than during the trial (p less than 0.001). The results suggest that in this population there is no advantage to using either a chamber device rather than an MDI or one chamber device rather than the other.     

Trachea and lung dimensions in nonsmoking twins: morphological and functional studies

To compare genetic and environmental factors that determine lung function and dimensions, chest radiographs and pulmonary function were measured in 17 pairs of nonsmoking twin adolescent boys (12 monozygotic pairs and 5 dizygotic pairs). Genetic factors dominated in tracheal width and lung dimensions (height, width, and apicofissural and fissurodiaphragmatic distances) at residual volume. Genetic factors also affected forced vital capacity, functional residual capacity, forced expiratory volume in 1 s, maximum expiratory flow at 25% vital capacity, and maximum flow at 50% vital capacity-to-forced vital capacity ratio. Peak expiratory flow correlated with tracheal width at residual volume. Age correlated with lung dimensions (width and depth) but not with tracheal width. These results indicate that genetic factors determine the dimensions and function of central airways, peripheral airways, and lung parenchyma in adolescent males. The effects of genetic factors on some functional measurements (airway resistance, closing volume-to-vital capacity ratio, and phase III in single-breath N2 washout) may be masked because of poor reproducibility of the tests.     

Model of forced expiratory flows and airway geometry in infants.

Early measurements of autopsied lungs from infants, children, and adults suggested that the ratio of peripheral to central airway resistance was higher in infants than older children and adults. Recent measurements of forced expiration suggest that infants have high flows relative to lung volume. We employed a computational model of forced expiratory flow along with physiological and anatomic data to evaluate whether the infant lung is a uniformly scaled-down version of the adult lung. First, we uniformly scaled an existing computational model of adult forced expiration to estimate forced expiratory flows (FEF) and density dependence for an 18-mo-old infant. The values obtained for FEF and density dependence were significantly lower than those reported for healthy 18-mo-old infants. Next, we modified the model for the infant lung to reproduce standard indexes of expiratory flow [forced expiratory volume in 0.5 s (FEV(0.5)), FEFs after exhalation of 50 and 75% forced vital capacity, FEF between 25 and 75% expired volume] for this age group. The airway sizes obtained for the infant lung model that produced accurate physiological measurements were similar to anatomic data available for this age and larger than those in the scaled model. Our findings indicate that the airways in the infant lung model differ from those in the scaled model, i.e., middle and peripheral airway sizes are larger than result from uniform downscaling of the adult lung model. We show that the infant lung model can be made to reproduce individual flow-volume curves by adjusting lumen area generation by generation.     

Pulmonary and ventilatory responses to pregnancy, immersion, and exercise

To examine the effects of pregnancy, immersion, and exercise during immersion on pulmonary function and ventilation, 12 women were studied at 15, 25, and 35 wk of pregnancy and 8-10 wk postpartum. Pulmonary function and ventilation were measured under three experimental conditions: after 20 min of rest on land (LR), after 20 min of rest during immersion to the level of the xiphoid (IR), and after 20 min of exercise during immersion at 60% of predicted maximal capacity (IE). Forced vital capacity remained relatively constant, except for a decrease at 15 wk, for the duration of pregnancy. Expiratory reserve volume decreased with a change in the pregnancy status and with the duration of pregnancy. However, the forced vital capacity was maintained by an increase in the inspiratory capacity during pregnancy. Forced expiratory volume for 1 s, expressed as percent of forced vital capacity, did not differ significantly between conditions or as a result of pregnancy. Forced vital capacity was lower during the IR trial compared with LR and IE trials. The decreased forced vital capacity of the IR trials was mediated by a decrease in the expiratory reserve volume. Whereas the inspiratory capacity increased during IR and IE compared with LR, the increase was not large enough to offset the decrease in the expiratory reserve volume. Resting immersion resulted in a significant decrease in maximal voluntary ventilation as did pregnancy. Pregnancy resulted in significant increases in minute ventilation (VE), which were related to increases in the O2 consumption.(ABSTRACT TRUNCATED AT 250 WORDS)     

Novel method for measuring effects of gas compression on expiratory flow

During forced vital capacity maneuvers in subjects with expiratory flow limitation, lung volume decreases during expiration both by air flowing out of the lung (i.e., exhaled volume) and by compression of gas within the thorax. As a result, a flow-volume loop generated by using exhaled volume is not representative of the actual flow-volume relationship. We present a novel method to take into account the effects of gas compression on flow and volume in the first second of a forced expiratory maneuver (FEV(1)). In addition to oral and esophageal pressures, we measured flow and volume simultaneously using a volume-displacement plethysmograph and a pneumotachograph in normal subjects and patients with expiratory flow limitation. Expiratory flow vs. plethysmograph volume signals was used to generate a flow-volume loop. Specialized software was developed to estimate FEV(1) corrected for gas compression (NFEV(1)). We measured reproducibility of NFEV(1) in repeated maneuvers within the same session and over a 6-mo interval in patients with chronic obstructive pulmonary disease. Our results demonstrate that NFEV(1) significantly correlated with FEV(1), peak expiratory flow, lung expiratory resistance, and total lung capacity. During intrasession, maneuvers with the highest and lowest FEV(1) showed significant statistical difference in mean FEV(1) (P < 0.005), whereas NFEV(1) from the same maneuvers were not significantly different from each other (P > 0.05). Furthermore, variability of NFEV(1) measurements over 6 mo was <5%. We concluded that our method reliably measures the effect of gas compression on expiratory flow.     

Deep breaths, methacholine, and airway narrowing in healthy and mild asthmatic subjects.

Deep breaths taken before inhalation of methacholine attenuate the decrease in forced expiratory volume in 1 s and forced vital capacity in healthy but not in asthmatic subjects. We investigated whether this difference also exists by using measurements not preceded by full inflation, i.e., airway conductance, functional residual capacity, as well as flow and residual volume from partial forced expiration. We found that five deep breaths preceding a single dose of methacholine 1) transiently attenuated the decrements in forced expiratory volume in 1 s and forced vital capacity in healthy (n = 8) but not in mild asthmatic (n = 10) subjects and 2) increased the areas under the curve of changes in parameters not preceded by a full inflation over 40 min, during which further deep breaths were prohibited, without significant difference between healthy (n = 6) and mild asthmatic (n = 16) subjects. In conclusion, a series of deep breaths preceding methacholine inhalation significantly enhances bronchoconstrictor response similarly in mild asthmatic and healthy subjects but facilitates bronchodilatation on further full inflation in the latter.