The effect of cisatracurium and rocuronium on lung function in anesthetized children.

BACKGROUND: Neuromuscular blocking drugs have been implicated in intraoperative bronchoconstrictive episodes. We examined the effects of clinically relevant doses of cisatracurium and rocuronium on the lung mechanics of pediatric subjects. We hypothesized that cisatracurium and rocuronium would have bronchoconstrictive effects. METHODS: We studied ASA physical status I and II pediatric subjects having elective dental or urological procedures, requiring general anesthesia with endotracheal intubations with either cisatracurium or rocuronium. Pulmonary function tests were performed before and after neuromuscular blocking drug dosing and again after albuterol administration. Using forced deflation and passive deflation techniques, forced vital capacity (FVC) and maximum expiratory flow rate at 10% (MEF10) of FVC were obtained. Fractional changes from the baseline were used to compare subjects. Changes in MEF10 of >30% were considered clinically significant. A Shapiro-Wilk test, paired t test, and Wilcoxon rank sum test were used to analyze the data. RESULTS: Twenty-five subjects (median age = 5.25 years; range = 9 months-9.9 years) were studied; 12 subjects received cisatracurium and 13 subjects received rocuronium. Data are shown as mean proportional change ± SD or, in the case of not normally distributed, median proportional change (first, third quartile) with P values. In the cisatracurium group, there were no differences between baseline and postneuromuscular blocker administration in the fractional change from the baselines of FVC (1.00 ± 0.04, P = 0.5), but there was a significant decrease in MEF10 (0.80 ± 0.18, P = 0.002). In the rocuronium group, there were small yet significant decreases of FVC (0.99 [first quartile 0.97, third quartile 1], P = 0.02) and significant decreases in MEF10 (0.78 ± 0.26, P = 0.008). After administration of albuterol in the cisatracurium group, FVC increased slightly but significantly from baseline values (1.02 ± 0.02, P = 0.005). MEF10 increased significantly beyond baseline values (1.24 ± 0.43, P =0.04). In the rocuronium group, there were also significant differences between baseline and postalbuterol administration from the baseline value of FVC (1.02 ± 0.02, P = 0.004) and MEF10 (1.23 ± 0.29, P = 0.01). CONCLUSIONS: At clinically relevant doses, both cisatracurium and rocuronium caused changes in lung function, indicating constriction of smaller airways. In general, these changes were mild and not clinically detectable. However, in the rocuronium group, 3 of 13 patients showed more noticeable decreases in MEF10 (≤50%), demonstrating the potential for significant broncho-bronchiolar constriction in susceptible patients.

Constancy of effort and variability of maximal expiratory flow rates.

In 14 normal subjects and in 13 patients with obstructive pulmonary diseases, we studied the variability within an individual of values for the maximal expiratory flow rate (Vmax) recorded simultaneously vs expired pulmonary volume (at the mouth) and vs thoracic volume (measured with a body plethysmograph). We found that the variance of Vmax within an individual at 25, 50, and 75 percent of the expired vital capacity did not differ statistically whether pulmonary volume was the expired or the thoracic gas volume. In ten healthy subjects on two occasions (at an interval of 12 days, on the average), we measured the peak expiratory flow rate and Vmax at different levels of inflation, with respect to either expired or thoracic volume. There was no statistical differences in Vmax between the first and the last day. A larger variability of Vmax measured vs expired volume implies a change in the expiratory effort from one forced expiration to another and a different degree of compression of intrathoracic air. Since this was not the case, we conclude that muscular effort during repeated forced expirations is similar. The good reproducibility of effort explains in great measure the good reproducibility of Vmax.

The effect of sleep loss on breathing in chronic obstructive pulmonary disease.

We have previously shown that one night of sleep deprivation results in significant deterioration of spirometric performance and ventilatory responsiveness to inhaled carbon dioxide in normal people. Since even a small decrease in pulmonary function may be clinically important in patients with chronic limitation of airflow, we undertook the present study to assess the effects of sleep loss on breathing in patients with chronic obstructive pulmonary disease (COPD). Criteria for inclusion in this study were a ratio of the forced expiratory volume in one second over the forced vital capacity (FEV1/FVC) of less than 60 percent, no hospital admission for pulmonary disease within two weeks of testing, stable (less than 30 percent variation) in tests of pulmonary function on two occasions within three months of testing, and no history of asthma. We studied 15 men (mean age, 57 +/- 3 years) on two consecutive mornings. Patients were studied with and without sleep deprivation in a randomized fashion. Patients were hospitalized for the study so that sleep deprivation, medications, smoking, and diet could be monitored and enforced. We found small but statistically significant falls in FEV1 (1.06 +/- 0.11 to 1.00 +/- 0.09 L; p less than 0.05) and in FVC (2.56 +/- 0.20 to 2.43 +/- 0.17 L; p less than 0.05) following sleep deprivation. Changes of similar magnitude which were not statistically significant occurred in maximal voluntary ventilation (MVV) and response to carbon dioxide. The arterial oxygen (PaO2) and carbon dioxide (PaCO2) tensions were not affected. Maximal expiratory pressure at the mouth increased slightly, but there was a fall in maximal inspiratory pressure (MIP) at the mouth. We conclude that sleep loss is associated with small but significant falls in FEV1 and FVC, as well as changes of similar magnitude in MVV, minute ventilation, and MIP in patients with severe COPD. Although the sleep loss which frequently accompanies exacerbations of COPD may be a slight additional stress of pulmonary reserve, a single night's loss of sleep in the patient with stable chronic airflow obstruction does not have major clinical consequences.

Comparison of maximal midexpiratory flow rate and forced expiratory flow at 50% of vital capacity in children.

BACKGROUND: The mid-portion of the maximal expiratory flow-volume (MEFV) curve is often described by values of the mean forced expired flow as lung volume decreases from 75% to 25% of vital capacity (ie, forced expiratory flow, midexpiratory phase [FEF(25-75)]). It is common practice to report also forced expired flow at 50% of vital capacity (FEF(50)). STUDY OBJECTIVE: To investigate whether FEF(50) and FEF(25-75) are highly correlated or whether the difference between them reflects a degree of airways obstruction. Also, we wanted to investigate the correlation between the two in cases of irregularly shaped MEFV curves (ie, "saw-toothing"). DESIGN: Analysis of the correlation between FEF(50) and FEF(25-75) in a single determination. We assessed the relationship between the FEF(50)/FEF(25-75) ratio and the degree of airways obstruction, as reflected by other traditional parameters such as FEV(1), FEV(1)/FVC ratio, and specific airway conductance (SGaw). PATIENTS: There were 1,350 forced expiratory maneuvers performed by children with a broad range of pulmonary abnormalities. RESULTS: FEF(50) correlated with FEF(25-75) as follows: FEF(50) (L/s) = 0.041 + 1.136*FEF(25-75)(L/s); r(2) = 0.956; standard error of the estimate = 0.013; p < 0.0001. The FEF(50)/FEF(25-75) ratio remained stable and did not correlate with FEV(1) (r = 0.12), FEV(1)/FVC ratio (r = 0.11), or SGaw (r = 0.02; difference not significant). The correlation between FEF(25-75) and FEF(50) was similar for both the smooth curve (r = 0.97) and the irregular curve (r = 0.96). CONCLUSIONS: Although not identical, FEF(25-75) and FEF(50) are highly correlated, and the ratio of the two is fairly constant. Therefore, the practice of reporting both of them is unnecessary. We suggest that it is reasonable to prefer FEF(50).

Influence of gender and inspiratory muscle training on the perception of dyspnea in patients with asthma.

BACKGROUND: Men and women respond differently to asthma. PATIENTS AND METHODS: Maximal inspiratory mouth pressure (P(Imax)), beta(2)-agonist consumption, and perception of dyspnea (POD) were measured in 22 women and 22 men with mild persistent-to-moderate asthma. Next, the women were randomized into two groups: those who received inspiratory muscle training and those who received sham training. The training ended when the P(Imax) of the training group was equal to that of the male subjects. POD was then measured once again. RESULTS: Baseline P(Imax) was significantly lower (p < 0.01) while POD and mean daily beta(2)-agonist consumption were significantly higher in the female subjects. P(Imax) reached the level of the male subjects at the end of the 20th week of training. The increase in the P(Imax) was associated with a statistically significant decrease in mean daily beta(2)-agonist use and in POD to a similar level as in male subjects. CONCLUSIONS: POD and mean daily beta(2)-agonist consumption in asthmatic women are significantly higher, and the P(Imax) significantly lower, than that of their male counterparts. When the P(Imax) of female subjects following training is equal to that in male subjects, the differences in POD and mean daily beta(2)-agonist consumption disappear.

Measurement of maximal static respiratory pressures at the mouth with different air leaks.

The effect of two different circuit leaks on the measurement of maximal static inspiratory and expiratory pressures at the mouth (Pimax, Pemax) was assessed in 70 patients with respiratory disease. Patients were divided into three groups with similar anthropometric and spirometric characteristics. The first group (30 patients) had their Pmax measured with a leak of 2.0 mm internal diameter (ID) and 37 mm length (as proposed by T. Ringqvist) and repeated with a second leak of 1.0 mm ID and 15 mm length (as recommended by J. L. Clausen). The two measurements were done in random order. Measurements for the other two groups (20 patients each) were taken with one or another, the two leaks randomly alternated with no leak. Pimax measurements obtained with Ringqvist's leak were 17 percent (p less than 0.005) lower than those with Clausen's leak and 22 percent (p less than 0.005) lower than those with no leak. Pemax measurements performed with Ringqvist's leak in place were 11 percent (p less than 0.005) lower than those with Clausen's leak and 11 percent (p less than 0.005) lower than those obtained with no leak. The comparison between Clausen's leak and no leak showed no statistically significant difference. We conclude that whenever the effect of pressure generated in the mouth is to be avoided in the measurement of respiratory Pmax, a leak of the size proposed by Ringqvist is to be preferred.

Respiratory muscle strength and hemodynamics in chronic heart failure.

To examine whether respiratory muscle weakness is associated with cardiac function and/or exercise capacity in chronic heart failure (CHF), 23 patients with CHF were evaluated with respiratory muscle strength, pulmonary function tests, cardiac catheterization, and exercise test. The subjects were divided into three groups on their New York Heart Association (NYHA) functional class. Group A consisted of 13 patients with NYHA functional classification class 3 or 4, group B consisted of 10 patients with NYHA classification class 2, and group C consisted of 15 age-matched normal controls. Respiratory muscle strength was assessed with maximal static inspiratory mouth pressure at residual volume level and expiratory mouth pressure at total lung capacity level (PImax, PEmax, respectively). Pulmonary functions in patients with CHF showed almost normal. PImax in group A was significantly less than that in group B or C, although PImax in group B was not significantly different from that in group C. In the patients with CHF, PImax correlated positively with cardiac index and maximal oxygen consumption (r = 0.460 and r = 0.503, p < 0.05, respectively). These findings suggest that inspiratory muscle strength, which was impaired in patients with severe CHF, may be dependent on cardiac function and may be one of the limiting factors on impaired exercise capacity in the patients with CHF.

Positive effort dependence of maximal expiratory flow.

The maximal expiratory-flow volume (MEFV) curve in normal subjects is thought to be relatively effort independent over most of the vital capacity (VC). We studied seven normal males and found positive effort dependence of maximal expiratory flow between 50 and 80% VC in five of them, as demonstrated by standard isovolume pressure-flow (IVPF) curves. We then attempted to distinguish the effects of chest wall conformational changes from possible mechanisms intrinsic to the lungs as an explanation for positive effort dependence. IVPF curves were repeated in four of the subjects who had demonstrated positive effort dependence. Transpulmonary pressure was varied by introducing varied resistances at the mouth but effort, as defined by pleural pressure, was maintained constant. By this method, chest wall conformation at a given volume would be expected to remain the same despite changing transpulmonary pressures. When these four subjects were retested in this way, no increases in flow with increasing transpulmonary pressure were found. In further studies, voluntarily altering the chest wall pattern of emptying (as defined by respiratory inductive plethysmography) did however alter maximal expiratory flows, with transpulmonary pressure maintained constant. We conclude that maximal expiratory flow can increase with effort over a larger portion of the vital capacity than is commonly recognized, and this effort dependence may be the result of changes in central airway mechanical properties that occur in relation to changes in chest wall shape during forced expiration.

Airway pressure-volume curve estimated by flow interruption during forced expiration.

We attempted to estimate the pressure-volume characteristics of airways downstream from the choke point when the airflow was abruptly interrupted during forced expiration. The change of gas volume of the downstream segment after interruption could be estimated by multiplying the maximum flow (Vmax) immediately before interruption by the interruption time because the Vmax is maintained for a short period after airflow interruption at the mouth, as described in our previous report (J. Appl. Physiol. 66: 509-517, 1989). For the pressure of the downstream segment, we used the mouth pressure itself. Airway compliance, a slope of the pressure-volume curve, was measured in an airway model in eight normal subjects, in six patients with chronic obstructive pulmonary disease (COPD), and in one patient with tracheobronchopathia osteochondroplastica. Airway compliance was 0.96 ml/cmH2O in normal subjects and 2.49 ml/cmH2O in COPD patients. This difference of airway compliance was believed to be caused by the longitudinal expansion of the downstream segment and changes in the properties of the airway wall.

[Physical activities and sports in asthmatic patients]. / L'attività fisica e sportiva nei soggetti asmatici.

Asthma patients are too often advised to refrain from sport. Enforced sedentariness, especially in children, leads to muscle hypotonia, reduced mechanical efficiency, paramorphisms, and adverse psychological consequences. Not all asthmatics develop airway spasm as a result of exercise. On the other hand, there are subjects whose bronchial hyper-reactivity is stimulated solely by muscular effort. The pathogenesis of exercise-induced bronchospasm is not fully understood. In any event, numerous studies have demonstrated the beneficial and even therapeutic effect of physical exercise and sport in cases of asthma. Provided they are practised with judgment and in accordance with a suitable programme, swimming, activities of an alternating aerobic and anaerobic type, cross-country skiing, gymnastics, and fencing are primarily indicated. Some asthmatics have also won Olympic medals. In the light of the studies carried out so far, it is strongly suggested that asthmatics be encouraged to take up sport suitable to their psychophysical characteristics, and not kept wrapped up in cotton wool.

The forced expiratory volume-time curve estimation using the electrocardiogram.

The feasibility of estimating the forced expiratory volume-time curve from the amplitude modulation of the electrocardiogram was studied using a numerical torso model and ECG signal processing. A two dimensional numerical model of the torso was solved for the maximum expiration and inspiration to study the changes in the surface potential as a result of changes in the lung volume. The numerical model showed that significant changes in the surface potential amplitude occur between maximum inspiration and maximum expiration and that this amplitude change in the left-right axis of the torso might be three times as large as in the front-back axis. In the experimental setup, ECG waveforms from the surface of the chest and the mouth air flow were simultaneously recorded from four male subjects during several forced vital capacity (FVC) maneuvers. The amplitude of the QRS complex was measured for different expired lung volumes and an estimation of the forced expiratory volume-time curve was obtained. The FVC and the FEV1 (forced expiratory volume after 1 s) spirometry indices were calculated for the two volume-time curves obtained from the electrocardiogram and from the spirometry measurements. The results differ between 0.1 and 0.8 1. These preliminary results are encouraging and might indicate that a relationship between the volume-time curve during FVC test and the electrocardiogram signals does exist. Further validation in a larger number of subjects and patients is needed before the technique can be applicable for clinical use.

Exposure to naphthalene-diisocyanate in a rubber plant: symptoms and lung function.

Twenty-three subjects exposed to naphthalene-diisocyanate (NDI, [mean air concentration 0.002-0.007 mg/m3]) were examined with regard to symptoms and pulmonary function. Irritation of the eyes, cough, and exertion dyspnea were more common in exposed subjects than in unexposed controls. Closing volume, as a percentage of vital capacity (CV%), was 6% higher than the reference value (P = .01) on Monday morning after 2 days with no exposure to NDI. The other lung function variables were normal. Two days of industrial exposure caused no further change in any lung function variable. The difference between measured and expected CV% increased with age in the exposed subjects. Five employees who had complained of severe symptoms during NDI exposure and who, therefore, had been transferred to other tasks with no exposure to NDI, displayed marked increases in CV% and a reduction in the forced vital capacity by an average of 0.6 L. Smokers and nonsmokers displayed similar lung function changes.

Respiratory effects of occupational exposure to an epoxy resin system.

A standardized respiratory questionnaire and pulmonary function tests were used to examine thirty-four employees of a snow-ski manufacturing plant, including twenty-five workers who were exposed to an epoxy resin system containing the amine hardener 3-dimethylamino propylamine (3-DMAPA). Maximum expiratory flow-volume curves were obtained on Monday and Thursday, before and after each shift, and FVC, FEV1.0, MEF50%, and MEF25% were caculated. Environmental measurements of the total amine levels were found to range from 0.41 to 1.38 ppm. The group with the greatest exposure (0.55-1.38 ppm) showed significant decreases in lung function over Monday and over the week. Although all employees in this group showed decreases in pulmonary function, acute changes were greater in present cigarette smokers and in subjects who reported respiratory symptoms upon exposure to the epoxy resin system. There was no evidence of permanent loss of lung function in subjects with either the highest or longest exposure.

Maximal expiratory flow-volume loop in a southern Indian college sportsmen.

Flow volume loops using computerised pulmonary function testing equipment were analysed in twenty sportsmen of Loyola College, Madras. There was no significant difference in mean P.E.F.R. (P greater than 0.2) and VE 25% (P greater than 0.2) in sportsmen, compared to Indian or American normals. On the other hand, the mean VE 50% (P less than 0.05) and VE 75% (P less than 0.001) were significantly higher in sportsmen compared to Indian values, but was similar to those reported in American normals (P greater than 0.1). Inspiratory flow rates were similar to those reported in Indians. Our results show that there is an increase in maximal expiratory flow rates at lower lung volumes in Southern Indian College Sportsmen compared to Indian normals.

[Maximal ventilatory pressure through the mouth in adults: normal values and explanatory variables]. / Les pressions ventilatoires maximales à la bouche chez l'adulte: valeurs normales et variables explicatives.

Mouth pressure measured during maximal inspiratory or expiratory efforts depends on the force exerted by ventilatory muscles. Normal values and anthropometric factors accounting for maximal inspiratory and expiratory pressures (MIP, MEP) are not fully agreed upon to date. We measured MIP and MEP in 253 normal subjects (135 females and 118 males, age 15-59 years) using a digital transducer (163 Sibelmed). All subjects had normal forced vital capacity (FVC) and one second forced expiratory volume (FEV1). Sex, age, height and weight were recorded for all subjects and were entered as independent variables in computation of linear multiple regressions with MEP or MIP the dependent variables. MEP and MIP were greater in males than in females (p less than 0.01) with MIP lower than MEP in both sexes (p less than 0.01). In both males and females, FVC and FEV1 depend on age and height (p less than 0.01). In the entire group, we found a correlation of MIP in females and MEP in males with age (p less than 0.01) and of both MIP and MEP in females with weight (p less than 0.01). However, in subjects aged 20-59 years, there was no significant dependence of MIP and MEP on age, and when the weight of subjects was normal (n = 170), MIP and MEP were independent of weight. We conclude that in adults aged 20-59 years and with normal weight, maximal ventilatory pressures depend solely on sex. In this subgroup mean (+/- SD) values of MEP and MIP were 111 +/- 25 cmH2O and 79 +/- 19 cmH2O respectively in females and 192 +/- 42 cmH2O and 117 +/- 25 cmH2O in males.

[Preliminary study on determination methods of respiratory muscle functions].

Attention has been paid to the research of respiratory muscle functions recently. In this paper some lung function indices concerning respiratory muscle functions, such as maximal inspiratory and expiratory pressure at mouth, inspiratory and expiratory tolerance time, transdiaphragmatic pressure and maximal transdiaphragmatic pressure and diaphragmatic electromyogram etc, were determined in 24 healthy young men and the normal values were obtained. They were important in the study of respiratory muscle functions in hard physical labours, especially in divers, pilots and sportsmen etc. These indices were also useful for evaluating convalescent therapy chronic lung diseases, respiratory muscles training programs or the drug effects on respiratory muscle fatigue etc.

A importância da medida da força muscular respiratória na prática da pneumologia / The importance of measurement of respiratory muscle strenght in pulmonology practice

A medida da força dos músculos respiratórios é um exame não invasivo, simples, de baixo custo e útil naprática clínica. Dentre os métodos utilizados para mensuração da força muscular respiratória, destaca-se, a medida das pressões respiratórias máximas em nível da boca: PImáx e PEmáx. A Pressão inspiratória máxima (PImáx) reflete a força dos músculos inspiratórios e do diafragma; enquanto a pressão expiratória máxima (PEmáx) reflete a força dos músculos abdominais e expiratórios. As indicações comuns na prática clínica incluem: a confirmação da disfunção muscular respiratória em doenças neuromusculares; diagnóstico diferencial de dispneia, tosse ineficaz; espirometria com distúrbio ventilatório restritivo sem causa aparente; avaliação de resposta à fisioterapia e à reabilitação pulmonar; avaliação pré-operatória da função dos músculos ventilatórios e da possibilidade de desmame da ventilação mecânica; e, avaliação do risco de mortalidade e hospitalizações em pacientes com DPOC e insuficiência cardíaca.Esta revisão teve como objetivo apresentar a importância da aplicação do teste da força muscular respiratória na prática da pneumologia. Descreveremos a técnica e a interpretação dos resultados.

The measurement of respiratory muscle strength is a noninvasive test, simple, inexpensive and useful in clinical practice. Among the used methods to measure the respiratory muscle strength, the determination ofmaximal respiratory pressures in terms of mouth: MIP and MEP have been showed most important. The MaximumInspiratory Pressure (MIP) reflects the strength of the inspiratory muscles and the diaphragm; while the MaximumExpiratory Pressure (MEP) reflects the strength of the abdominal and expiratory muscles. The common indications in clinical practice include: confirmation of respiratory muscle dysfunction in neuromuscular diseases; differential diagnosis of dyspnea, ineffective cough or restrictive lung disease without apparent cause; response evaluation to physical therapy and pulmonary rehabilitation; preoperative evaluation of thefunction of respiratory muscles and the possibility of ventilation weaning ; and mortality and hospitalization riskassessment in patients with COPD and heart failure. This review aims to present the importance of the application of respiratory muscle strength test in the practice of pulmonology. Furthermore, this review also describes the technique and interpretation of results.

Influence of increased gas density and external resistance on maximum expiratory flow.

The effect of external resistance on the relationship of expiratory air flow and intrathoracic and mouth pressure on subjects breathing gas of increased density was investigated. Five subjects breathing air performed multiple maximum forced expiratory maneuvers through orifices of various sizes at 1, 4, and 7 ATA in a standard double-lock compression chamber. Measurements of flow and pleural, mouthpiece, and transpulmonary pressures were made, and flow-volume and pressure-volume curves were constructed and analyzed at 75, 50, 35, and 25% of vital capacity. At each lung volume, maximum flow could be maintained until a certain orifice size was reached. This "limiting orifice" was 7.5--10 mm in diameter and did not change with lung volume or density. Under the conditions studied, this finding leads to the conclusion that the flow-limiting segment of the lungs behaved as a rigid orifice less than 10 mm in diameter. Orifices slightly larger than the limiting orifice increased pleural pressure, as expected, but transpulmonary pressure decreased while the flow remained stable, which indicates that airway compression may be lessened by increased intra-airway pressure.

Expired air temperature at the mouth during a maximal forced expiratory manoeuvre.

We have studied the temperature of expired air during a maximal forced expiratory manoeuvre, because this has not previously been fully investigated and it will influence how flow and volume recording devices should be calibrated and used. Temperature was recorded with a fine thermocouple, the response time of which was determined at various gas velocities and for which a correction was made. Recordings during maximal forced expiratory manoeuvres were made on 12 normal subjects and 12 subjects with chronic airflow limitation. The thermocouple was placed in the mouthpiece, so that it was at the level of the lips during a blow. In the normal subjects, the effect of differing inhalation protocols was also determined. In the normal subjects, the mean temperature was 33.6 degrees C at peak expiratory flow (PEF), and 34.4 degrees C at 75% forced vital capacity (FVC), but fell to 33.4 degrees C at FVC. In the subjects with chronic airflow limitation, the temperature was constant at 35.0 degrees C from PEF up to 50% FVC, being significantly higher than in the normals, and fell to 33.5 degrees C at FVC. Expired air temperature up to 50% FVC was significantly negatively correlated with absolute PEF, forced expiratory volume in one second (FEV1) and FVC. In the normals, a slow inhalation through the nose raised the expired temperature by almost 1 degree C throughout the blow, whereas inhaling air at 6 degrees C did not affect expired air temperature. The expired air temperature can vary by up to 3 degrees C between individual subjects, and it is influenced by the route of inhalation and the inspired volume.(ABSTRACT TRUNCATED AT 250 WORDS)

Importance of airway closure in limiting maximal expiration in normal man.

To elucidate the importance of airway closure in limiting maximum expiration, two complementary plethysmographic techniques have been used to estimate the volume of and pressure within the trapped thoracic gas. Three young (19-23 yr) and three older (43-66 yr) subjects were studied. The first study defined the curve of possible pressure-volume relationships for the trapped gas; the second study attempted to estimate the volume of trapped gas. In the first study the subject in a Mead plethysmograph expired through a pneumotachograph and back into the box. A reduction in box volume greater than that caused by drying and cooling of expired gas implies gas compression due mainly to airway closure. In the second study a known volume of air was withdrawn from the mouth at full expiration and changes in box volume and mouth pressure were recorded. The apparent volume in pressure communication with the mouth (Vpc) was calculated using Boyle's law. In the young subjects we did not detect thoracic gas compression although there was evidence of trapped gas (RV-Vpc greater than 0). In the older subjects there was a larger volume of trapped gas that was compressed to pressures of more than 22 cmH2O. Airway closure appears to limit maximal expiration in older subjects.