Frequency Dependence Of Dynamic Compliance Research Articles

The effect of body temperature on the dynamic respiratory system compliance–breathing frequency relationship in the rat

The mechanical inhomogeneity of the respiratory system is frequently investigated by measuring the frequency dependence of dynamic compliance, but no data are currently available describing the effects of body temperature variations. The aim of the present report was to study those effects in vivo. Peak airway pressure was measured during positive pressure ventilation in eight anesthetized rats while breathing frequency (but not tidal volume) was altered. Dynamic compliance was calculated as the tidal volume/peak airway pressure, and measurements were taken in basal conditions (mean rectal temperature 37.3 °C) as well as after total body warming (mean rectal temperature 39.7 °C). Due to parenchymal mechanical inhomogeneity and stress relaxation-linked effects, the normal rat respiratory system exhibited frequency dependence of dynamic lung compliance. Even moderate body temperature increments significantly reduced the decrements in dynamic compliance linked to breathing rate increments. The results were analyzed using Student's and Wilcoxon's tests, which yielded the same results (p < 0.05). Body temperature variations are known to influence respiratory mechanics. The frequency dependence of dynamic compliance was found, in the experiments described, to be temperature-dependent as temperature variations affected parenchymal mechanical inhomogeneity and stress relaxation. These results suggest that body temperature variations should be taken into consideration when the dynamic compliance-breathing frequency relationship is being examined during clinical assessment of inhomogeneity of lung parenchyma in patients.

Methyl Isocyanate Exposure

The Authors Reply: Drs Cullinan and Acquilla are correct in that a comparison of the findings of our study with those carried out on the Bhopal survivors would be inappropriate. The populations concerned are not comparable in that our subjects were exposed to much lower levels that would not lead to death or immediate serious impairment. Your correspondents ask us whether our population included only those who were still working. Our study subjects comprised a group of currently employed workers and also a group of retired workers who had undergone several examinations over the period of observation. Thus our study included both cross-sectional and longitudinal data. The cross-sectional data include only active workers, whilst the latter included both active and retired subjects; however, it was not possible to examine all of the retired workers. In our description of the subjects studied, we referred to a group of employees of a former owner of the facility who were retired or deceased. The retirees were a group of workers whose exposure was indirectly assessed by their former long-term supervisors. It will be noted that we were somewhat concerned about the accuracy of the assessments; nevertheless, the data available to us indicated that the vast majority of this group retired because of age rather than illness. For this reason, we doubt any serious survivor bias was present. Turning to the second question, namely, what they term "highly subjective exposure measurements," and ask whether they reflect short-term intensity exposures to MIC. Our paper described a significant number of workers who were seen at the clinic with acute symptoms, mainly eye and nasal irritations, which resulted from exposure to MIC. Some of these workers were seen during the time serial measurements of exposure were being made. The ventilatory capacity of these workers immediately after exposure was normal or virtually so, and when the examination was repeated later, there was no evidence of any airways obstruction. This information is contained in the last paragraph of the Results section, and we are somewhat surprised that it eluded your correspondents. In regard to Drs Cullinan and Acquilla's point relating to small airways disease, we are quite willing to accept that those exposed in the Bhopal disaster developed severe bronchiolitis. Nonetheless, we would point out that the detection of small airways diseases in the general population, many of whom smoke cigarettes (or Bidis in India), some of whom have asthma or are overweight, and who may also be exposed to many other irritant agents that affect the small airways, is fraught with difficulty. Thus it is necessary to exclude large airways disease first, ie, those subjects in whom small airways disease is sought must have a normal forced expiratory volume in one second(FEV1) and a normal forced vital capacity (FVC). In addition, they must have a normal compliance curve.1 Provided that both of these impairments are absent, one can try to persuade an asymptomatic subject to undergo one or another of a series of tests, some of which are unpleasant, most of which are time-consuming, and all of which are imprecise and lack the ability to predict the development of irreversible airways obstruction or respiratory disability.2 In this connection, we are referring to tests such as frequency dependence of dynamic compliance, closing volume, the performance of flow volume curves with helium and oxygen, the measurement of upstream airways resistance, lung elastic recoil, etc. We used these extensively some 25 or more years ago in a variety of occupationally exposed populations3-5 and found it difficult to decide the significance, if any, of our findings. Perhaps Drs Cullinan and Acquilla could advise us in this regard. This is not to deny that small airways disease can cause disability; it is a statement indicating how frustrating and futile it is to try to detect small airways disease in a working population by using tests that are imprecise and impractical. We would add that we enjoyed carrying out these studies, but we now realize that they were really a form of play therapy for potential respiratory physiologists. W. K. C. Morgan, MD Robert B. Reger, PhD Chest Diseases Unit; London Health Sciences Centre; London, Ontario, Canada

Small airway involvement in mixed connective tissue disease.

We studied pulmonary functions in 17 female patients with mixed connective tissue disease (MCTD) to detect early pulmonary involvement in this disease; in 8 of the 17 patients follow-up studies were also performed at 1.2- to 5.9-year intervals. In the first pulmonary function tests, decreases in vital capacity (VC) and diffusing capacity (DLCO) were observed in 6 (35%) and 8 (47%) patients, respectively. The ratio of forced expiratory volume in one second to VC was normal in all the patients, but pulmonary resistance and static compliance were abnormal in 6 (35%) and 10 (59%) patients, respectively. However, frequency dependence of dynamic compliance was found in all 16 patients tested. Moreover, 4 (24%) of the 17 patients had normal DLCO and DLCO-to-alveolar volume ratio (DLCO/VA). Reductions in DLCO and DLCO/VA were significantly correlated with the disease duration. These results suggest that small airway obstruction is an early and frequent indication of functional pulmonary impairment, and that impairment of alveolar gas exchange is progressive in patients with MCTD.

非喫煙慢性副鼻腔炎患者の末梢気道病変の検討

Coexistence of chronic sinusitis and chronic inflammatory lesions on the bronchi has long been recognized and the term of sinobronchial syndrome (SBS) has been used.However, it has not been clear whether chronic sinusitis precedes to the development of bronchial diseases. In the present study, detailed pulmonary function tests were performed subjecting 28 cases of chronic sinusitis without any smoking history. In all patients, lung volumes, forced expiratory volume in one second, diffusing capacity, respiratory resistance and blood gas analysis were within normal ranges.About 10% of patients revealed the peripheral airway dysfunction indicated by the results of flow volume curves with air and HeO2 closing volume, frequency dependence of dynamic compliance and upstream resistance. Airway responsiveness to inhaled methacholine was also examined by means of Astograph and seven patients revealed hyperresponsiveness. Statistical analysis indicated that the degree of the peripheral airway dysfunction tended to associate with the degree of airway hyperresponsiveness.These results may indicate that chronic sinusitis is not the preceding pathological condition for the development of inflammatory lesions in bronchi and that airway hyperresponsiveness may play an important role to produce the bronchial diseases in patients of SBS.

Direct-writing recorder of the frequency dependence of dynamic compliance analyzed from one cycle of breathing and pulmonary resistance: effect of fenoterol on asthmatic subjects.

We developed a new method of direct-writing recording of the frequency dependence of dynamic compliance analysed from one cycle of breathing and pulmonary resistance. Both pulmonary resistance (RL) and frequency dependence of dynamic compliance (Cdyn.f) are calculated by Fourier-series analysis of flow and transpulmonary pressure in a single cycle of breathing. RL was obtained from fundamental harmonics. Cdyn.f was calculated from 1st and 2nd harmonics and estimated by the ratio of Cdyn at 0.5 Hz to Cdyn at zero frequency, C0.5/C0. We used fenoterol aerosol which contained 0.2 mg of fenoterol with one puff of aerosol. Two puffs of fenoterol aerosol were used in each subject and followed changes of RL, C0 and C0.5 as long as 30 min. After fenoterol inhalation RL decreased considerably and C0.5/C0 cont [C0.5/(control C0)] increased. With time, while RL was kept stable, C0.5/C0 cont increased further. We suggest that fenoterol has a potent effect on the small airways which is enhanced with time.

Airway function in stage I and stage II pulmonary sarcoidosis.

Airway function was studied in 39 patients with stage I sarcoidosis and in 20 patients with stage II sarcoidosis. All of our patients were nonsmokers. Characteristic functional changes of restrictive lung disease was observed in 4 patients with stage II sarcoidosis. Specific airway conductance and % FEV1 were abnormal in 3 patients with stage II sarcoidosis. Abnormal small airway function was demonstrated in several patients with stage I and stage II sarcoidosis, always by multiple tests. Frequency dependence of dynamic compliance was demonstrated in 40% of stage I and 50% of stage II sarcoidosis. Maximal flow (Vmax50, Vmax25) was decreased respectively in 36 and 30% of patients of stage I sarcoidosis and in 56 and 62% of patients with stage II sarcoidosis. The ratio of closing volume to vital capacity was increased above corrected predictions in 30% of stage I and 44% of stage II sarcoidosis. delta Vmax25 decreased and Visov/VC (%) increased in more than 50% of patients. Upstream airway resistance was abnormally increased in 50% of patients with stage I and in 73% with stage II sarcoidosis. These results suggest that small airway dysfunction is common in early sarcoidosis without restrictive defect.

Computer measurement of dynamic compliance: technique and reproducibility in man.

A computer program was developed to calculate the frequency dependence of dynamic compliance (Cdyn) using continuous data analysis. Cdyn was measured repeatedly in eight normal human subjects over a 2-yr period. Comparison with Cdyn results measured manually showed that the computer program improved 10-fold the ratio of variance within subjects to between subjects of the compliance at specific frequencies, but there was only slight improvement in indices of the slope of the frequency dependence of compliance. We suggest that the absolute compliance at specific frequencies merits further consideration as a pathophysiological measurement and that, if the frequency dependence of compliance continues to be used, standardization of its calculation should be applied and the wide normal range should be more widely appreciated. Measurements of Cdyn in subjects breathing 80% helium-20% oxygen confirm that inertia is insignificant when breathing with tidal volumes of less than 500 ml and frequency of less than 1.5 Hz.

Frequency dependence of dynamic compliance analyzed from one cycle of breathing.

An analytical method for testing frequency dependence of dynamic compliance (Cdyn) from a Fourier-series analysis of flow and transpulmonary pressure in a single cycle of breathing was described and compared to the conventional method in an electrical model, in excised dog lobes and in human subjects. In the electrical model, the frequency dependence of Cdyn in the Fourier method corresponded exactly with the theoretical frequency dependence of Cdyn. A frequency dependence of Cdyn was evaluated by a ratio of Cdyn at 1 Hz to Cdyn at zero frequency, C1Hz/CoHz, from the regression line between Cdyn and the frequency in excised dog lobes and human subjects. In healthy nonsmokers, C1Hz/CoHz was significantly smaller in the Fourier method than in the conventional method. The discrepancy of frequency dependence of Cdyn between the two methods was thought to be possibly due to the effects of the nonsinusoidal breathing pattern on the conventional method, and due to the effects of a volume-dependent compliance on the Fourier method.

Assessment of alpha-1-antitrypsin deficiency heterozygosity as a risk factor in the etiology of emphysema. Physiological comparison of adult normal and heterozygous protease inhibitor phenotype subjects from a random population.

For plethysmographic studies of lung mechanics and measurement of pulmonary diffusing capacity, 62 subjects were drawn from a randomly selected population sample. Data obtained from the 24 subjects of heterozygous phenotype for alpha-1-antitrypsin deficiency (PiMZ) were compared by age group with data from 38 normal (PiM) subjects matched for sex, age, and smoking history. Comparison of mean values by age group for lung volumes, diffusing capacity, lung elastic recoil, maximum expiratory flow, and the occurrence of frequency dependence of dynamic compliance revealed no differences between phenotype groups. There was no evidence of an accelerated effect of aging among PiMZ subjects when compared with normal counterparts nor was there evidence of an increased effect of smoking. From these data it appears that the PiMZ phenotype per se is not a risk factor in the development of emphysema.

Frequency dependence of dynamic compliance in papin-induced experimental emphysema (author's transl)

Frequency dependence of dynamic compliance in papin-induced experimental emphysema (author's transl)

Peripheral airways as a determinant of ventilatory function in the human lung.

We have investigated the morphological differences responsible for the variability in two tests of pulmonary function, maximal expiratory flow rates (MEF) and the frequency dependence of dynamic compliance (CDYN ratio). Functional measurements were obtained from 53 normal and minimally diseased postmortem human lungs. Morphological measurements performed on these same lungs included airway diameter at three levels in the bronchial tree, the amount of bronchial gland mass, and the alveolar surface to volume ratio. Multiple regression analysis suggests that the diameter of the peripheral conduction airways (membranous bronchioles) is the major morphological determinant for both MEF and the CDYN ratio in lungs at any particular age. Age-dependent changes in both functional tests were associated primarily with differences in the alveolar surface to volume ratio. Minimal emphysema and a lesion associated with cigarette smoking, respiratory bronchiolitis, have no demonstrable effect on either MEF or the CDYN ratio. These studies provide further evidence that the peripheral conducting airways are a major determinant of ventilatory function in the normal human lung.

Airway function in sarcoidosis

Airway function was studied in 18 patients with sarcoidosis, aged 18 to 49 years. Eleven of the patients were smokers. All patients had the characteristic functional changes of restrictive lung disease: decreased lung volumes and single breath diffusing capacity, and increased static transpulmonary pressures. Abnormal airway function was demonstrated in every patient by at least one test, and nearly always by multiple tests. Specific airway conductance was abnormally low in two patients. The ratio of the 1 second forced expiratory volume to the forced vital capacity was decreased in six patients. Frequency dependence of dynamic compliance was demonstrated in eight patients. The ratio of closing volume to vital capacity was increased above age-corrected predictions in all but two patients. Upstream airway resistance was abnormally increased in 16 of the patients. These results suggest that airway dysfunction is not uncommon in sarcoidosis.

Effect of gas density on dynamic pulmonary compliance.

We measured dynamic pulmonary compliance (Cdyn( in nine asymptomatic young men breathing gases of different density. When corrected for gas inertia, Cdyn was significantly lower during dense gas breathing (sulfur hexafluoride) than during air breathing. At higher breathing frequencies (60-90 breaths/min), Cdyn was greater on helium than on air. Static compliance was not different while breathing the three gas mixtures. These results may be explained by a density dependence of airways resistance in parallel lung units which contribute to frequency dependence of dynamic compliance. We conclude that most frequency-dependent behavior occurs among intraregional lung units subtended from airways between segmental bronchi and peripheral airways.

Exertional dyspnea and cough as preludes to acute attacks of bronchial asthma.

Although wheezing is believed to be a cardinal manifestation of asthma, some patients with this disorder may not present with wheezing, but rather with either exertional dyspnea or cough. In 14 such patients with dyspnea, there was peripheral airway dysfunction with markedly elevated residual volumes, frequency dependence of dynamic compliance and depressed flow rates in the middle-vital-capacity range, whereas specific conductance and one-second forced expiratory volumes were normal. Circumstantial evidence suggests that mucosal edema or mucous secretions may have been responsible. In seven patients with cough, studies revealed a more severe obstructive pattern that appeared to be the result of increased large-airway resistance, and the patients' response to isoproterenol indicated that contraction of bronchial smooth muscle may have been principally responsible. Thus, intermittent episodes of cough or breathlessness may represent variant aspects of asthmatic attacks.

Frequency dependence of dynamic compliance--effects of smoking on the small airway

Frequency dependence of dynamic compliance--effects of smoking on the small airway

Ventilatory mechanics in patients with bronchiectasis starting in childhood.

<b>Landau, L. I., Phelan, P. D., and Williams, H. E. (1974).</b><i>Thorax</i>, <b>29</b>, 304-312. <b>Ventilatory mechanics in patients with bronchiectasis starting in childhood.</b> The mechanics of ventilation have been studied in 69 children and young adults with bronchiectasis since childhood. Many were well with little disability and although symptoms had ameliorated in the second decade cough and sputum still persisted. This study suggests that many patients had generalized small airway disease, as demonstrated by abnormal maximum expiratory flow volume curves together with increased lung volumes and frequency dependence of dynamic compliance. A group of patients was found in whom compliant airways in the bronchiectatic segment may have been contributing to `slow space9 emptying and air trapping. Postoperative function in those treated surgically related to the extent of persisting disease rather than to the resection itself. In the absence of persisting disease there were no significant changes in lung volumes or elastic recoil after resection of one or two lobes in childhood.

Physiological approaches to detection of small airway disease

Recent developments in the field of lung mechanics relating to the problem of obstructive airway disease and its detection are reviewed. The importance of studying the behavior of the intrapulmonary airways during the compressed as well as the noncompressed state is stressed. The role of premature “airway closure,” in contributing to the abnormalities of gas exchange associated with disease in the small peripheral airways is discussed. The possibility is explored that some alternative methods for detecting small airway disease other than frequency dependence of dynamic compliance may be developed. Some physiological approaches to studying the behavior of small peripheral airways in human subjects during life are presented.

Small airway disease in asymptomatic asthmatic adolescents.

To determine the frequency of persistent obstruction of the small airways in adolescents with asthma during asymptomatic periods, frequency dependence of dynamic compliance was measured in 15 adolescents. The subjects, selected from 500 children participating in a long-term epidemiologic study of asthma, had normal respiratory resistance and lung volume. They came from the mild to moderate end of the spectrum of asthma in childhood, because all children in the epidemiologic study with severe asthma had abnormal respiratory function tests. Eight of the 15 adolescents had frequency dependence of dynamic compliance; its presence did not correlate with the number of episodes of overt wheezing or the time lapse from the most recent episode. Frequency dependence of compliance in 5 of the 7 subjects was abolished after an inhalation of isoproterenol. The study indicated that small airway obstruction persisted in some adolescents with mild to moderate asthma during asymptomatic periods, but its presence could not...

Flow dependence of the intrapulmonary distribution of inspired boluses of 133 Xe in smokers and non-smokers.

1. Starting at 50% vital capacity, boluses of 133Xe were inhaled either at very low or maximal flow rates, the inspiration terminating at total lung capacity (TLC). Flow-dependent changes in bolus distribution were examined by measuring regional radioctivity and computing regional time-constants, and also by recording alveolar plateaux during the subsequent vital capacity expiration. Regional residual volumes, as a fraction of regional total lung capacities, were also calculated. Three groups of subjects were studied: young non-smokers, young cigarette smokers, and older non-smokers. 2. All three groups gave similar results in terms of regional time-constants though there was less variation in the results for young non-smokers. 3. Regional residual volumes also gave similar results in all groups although again there was less variation in young non-smokers. In young smokers, residual volumes in some regions depended on the flow rate used in their measurement, which indicated intraregional inhomogeneity of function. 4. In young non-smokers alveolar plateaux after slow and fast bolus inspirations differed little; this was not the case either in older subjects or in smokers. The increased flow-dependence of the alveolar plateau is analogous with the increased frequency-dependence of dynamic compliance and probably indicates obstruction of small peripheral airways.

Lung function studies in young apparently health cigarette smokers versus non-smokers

Spirometric and plethysmographic measurements combined with investigations of lung PV-characteristics by means of oesophageal catheters were carried out in both 20 young healthy smokers and 20 non-smokers. The mean age of all probands was 29 years. The following results were obtained: (1) Spirometric data andairway resistance were normal in all subjects. Viscous work of breathing, however, was significantly elevated in cigarette smokers. (2) The static elastic recoil pressures of all subjects fell within the normal limits given by Turner in 1968. (3) Significance of long-termed cigarette smoking was demonstrated by a rise of static compliance and a pronounced frequency dependence of dynamic compliance. Respiratory findings present in cigarette smokers are related to peripheral airway changes. In addition, smoke-specific lesions may be due to disturbances of alveolar surfactant.