Thixotropy of rib cage respiratory muscles in normal subjects.
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In this study, we searched for signs of thixotropic behavior in human rib cage respiratory muscles. If rib cage respiratory muscles possess thixotropic properties similar to those seen in other skeletal muscles in animals and humans, we expect resting rib cage circumference would be temporarily changed after deep rib cage inflations or deflations and that these aftereffects would be particularly pronounced in trials that combine conditioning deep inflations or deflations with forceful isometric contractions of the respiratory muscles. We used induction plethysmography to obtain a continuous relative measure of rib cage circumference changes during quiet breathing in 12 healthy subjects. Rib cage position at the end of the expiratory phase (EEP) was used as an index of resting rib cage circumference. Comparisons were made between EEP values of five spontaneous breaths immediately before and after six types of conditioning maneuvers: deep inspiration (DI); deep expiration (DE); DI combined with forceful effort to inspire (FII) or expire (FEI); and DE combined with forceful effort to inspire (FIE) or expire (FEE), both with temporary airway occlusion. The aftereffects of the conditioning maneuvers on EEP values were consistent with the supposition that human respiratory muscles possess thixotropic properties. EEP values were significantly enhanced after all conditioning maneuvers involving DI, and the aftereffects were particularly pronounced in the FII and FEI trials. In contrast, EEP values were reduced after DE maneuvers. The aftereffects were statistically significant for the FEE and FIE, but not DE, trials. It is suggested that respiratory muscle thixotropy may contribute to the pulmonary hyperinflation seen in patients with chronic obstructive pulmonary disease. (+info)
Effect of expiratory resistive loading on the noninvasive tension-time index in COPD.
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Expiratory resistive loading (ERL) is used by chronic obstructive pulmonary disease (COPD) patients to improve respiratory function. We, therefore, used a noninvasive tension-time index of the inspiratory muscles (TT(mus) = I/PI(max) x TI/TT, where I is mean inspiratory pressure estimated from the mouth occlusion pressure, PI(max) is maximal inspiratory pressure, TI is inspiratory time, and TT is total respiratory cycle time) to better define the effect of ERL on COPD patients. To accomplish this, we measured airway pressures, mouth occlusion pressure, respiratory cycle flow rates, and functional residual capacity (FRC) in 14 COPD patients and 10 normal subjects with and without the application of ERL. TT(mus) was then calculated and found to drop in both COPD and normal subjects (P<0.05). The decline in TT(mus) in both groups resulted solely from a prolongation of expiratory time with ERL (P<0.001 for COPD, P<0.05 for normal subjects). In contrast to the COPD patients, normal subjects had an elevation in I and FRC, thus minimizing the decline in TT(mus). In conclusion, ERL reduces the potential for inspiratory muscle fatigue in COPD by reducing TI/TT without affecting FRC and I. (+info)
Respiratory dynamics during laughter.
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Lung and chest wall mechanics were studied during fits of laughter in 11 normal subjects. Laughing was naturally induced by showing clips of the funniest scenes from a movie by Roberto Benigni. Chest wall volume was measured by using a three-dimensional optoelectronic plethysmography and was partitioned into upper thorax, lower thorax, and abdominal compartments. Esophageal (Pes) and gastric (Pga) pressures were measured in seven subjects. All fits of laughter were characterized by a sudden occurrence of repetitive expiratory efforts at an average frequency of 4.6 +/- 1.1 Hz, which led to a final drop in functional residual capacity (FRC) by 1.55 +/- 0.40 liter (P < 0.001). All compartments similarly contributed to the decrease of lung volumes. The average duration of the fits of laughter was 3.7 +/- 2.2 s. Most of the events were associated with sudden increase in Pes well beyond the critical pressure necessary to generate maximum expiratory flow at a given lung volume. Pga increased more than Pes at the end of the expiratory efforts by an average of 27 +/- 7 cmH2O. Transdiaphragmatic pressure (Pdi) at FRC and at 10% and 20% control forced vital capacity below FRC was significantly higher than Pdi at the same absolute lung volumes during a relaxed maneuver at rest (P < 0.001). We conclude that fits of laughter consistently lead to sudden and substantial decrease in lung volume in all respiratory compartments and remarkable dynamic compression of the airways. Further mechanical stress would have applied to all the organs located in the thoracic cavity if the diaphragm had not actively prevented part of the increase in abdominal pressure from being transmitted to the chest wall cavity. (+info)
Plethysmographic measurements of lung volume and airway resistance. ERS/ATS Task Force on Standards for Infant Respiratory Function Testing. European Respiratory Society/ American Thoracic Society.
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Functional residual capacity (FRC) is the only static lung volume that can be measured routinely in infants. It is important for interpreting volume-dependent pulmonary mechanics such as airway resistance or forced expiratory flows, and for defining normal lung growth. Despite requiring complex equipment, the plethysmographic method for measuring FRC is very simple to apply and, unlike the gas dilution techniques, enables repeat measures of lung volume to be obtained within a few minutes. This method has the further advantage that with suitable adaptations to the equipment, simultaneous measurements of airway resistance can also be obtained. The aim of this paper is to provide recommendations pertaining to equipment requirements, study procedures and reporting of data for plethysmographic measurements in infants. Implementation of these recommendations should help to ensure that such measurements are as accurate as possible and that meaningful comparisons can be made between data collected in different centres or with different equipment. These guidelines cover numerous aspects including terminology and definitions, equipment, data acquisition and analysis and reporting of results and also highlight areas where further research is needed before consensus can be reached. (+info)
Spirometric performance in Belgian Blue calves: II. Analysis of environmental factors and estimation of genetic parameters.
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Genetic parameters and environmental effects for spirometric variables (SV) in calves were estimated using 734 Belgian Blue calves (15 to 297 d of age), sired by 20 AI bulls. For each calf, the following SV were measured: 1) the average ventilation (l/min) recorded during the 15 s of maximal ventilatory changes induced by lobeline administration (0.25 mg/kg, i.v.) (15-s MV(L)); 2) the vital capacity, and the maximal peak expiratory and inspiratory flows recorded after lobeline administration; and 3) the ventilatory reserve (15-s MV(L) - ventilation at rest). Analysis of environmental factors showed age of calf, herd, sex, and vaccination status had significant effects on SV. A sire model and a multiple-trait derivative-free REML procedure were used to estimate genetic parameters for SV, body weight, and muscling score. Heritabilities for SV ranged from 0.28 +/- 0.11 to 0.44 +/- 0.16. Genetic correlations among SV varied from 0.76 to 0.98 and environmental correlations from 0.69 to 0.80. Genetic correlations of SV with body weight (0.25 to 0.56) and with muscling score (0.21 to 0.76) were positive, as were environmental correlations of SV with body weight (0.44 to 0.70) and muscling score (0.09 to 0.25). These results suggest that selection may improve SV without impairing other traits of economic importance. (+info)
The Bronchitis Randomized On NAC Cost-Utility Study (BRONCUS): hypothesis and design. BRONCUS-trial Committee.
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Chronic obstructive pulmonary disease (COPD) is an irreversible disorder characterized by airflow obstruction and a progressive decline in forced expiratory volume in one second (FEV1). At present, no treatment except quitting smoking appears to affect the progression of the disease. Oxidative stress has been implicated in its pathogenesis. The Bronchitis Randomized on NAC Cost-Utility Study (BRONCUS) is a phase III, randomized, double-blind, placebo-controlled, parallel group, multicentre study designed to assess the effectiveness of the antioxidant agent N-acetylcysteine (NAC) in altering the decline in FEV1, exacerbation rate, and quality of life in patients with moderate to severe COPD. In addition, cost-utility of the treatment will be estimated. Patients will be followed for 3 yrs and evaluated every 3 months. The necessary sample size to demonstrate an effect on the decline in FEV1 of 20 mL x yr(-1) was estimated to be 478 patients. Five hundred and twenty-three patients with moderate to severe COPD were recruited from 10 European countries from June 1, 1997-December 31, 1999. They were 63+/-8 yrs old and consisted of 243 (46%) current smokers and 280 (54%) exsmokers. Patients had on the average 4.9+/-1.6 exacerbations during the last 2 yrs. Postbronchodilator FEVI averaged 57+/-9% and the reversibility after 400 microg of Salbutamol averaged 4+/-4% predicted. The final results of the trial will be available in about 2 yrs. The study will provide objective data on the effects of N-acetylcysteine on outcome variables in chronic obstructive pulmonary disease. (+info)
The bias flow nitrogen washout technique for measuring the functional residual capacity in infants. ERS/ATS Task Force on Standards for Infant Respiratory Function Testing.
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The functional residual capacity (FRC) is the most commonly measured static lung volume in infants. It is important for interpreting volume-dependent pulmonary mechanics, e.g. airway resistance, and defining normal lung growth. The bias flow nitrogen washout technique is widely used for measuring FRC because the dead space and circuit resistance are low, making it suitable for small or sick infants. Moreover, data acquisition and calculation are easily programmed for a personal computer. The aim of this paper is to provide recommendations pertaining to equipment requirements, study procedures and reporting of data for functional residual capacity measurements. While measuring the functional residual capacity is regarded as physiologically and clinically important, the accuracy of the measurement is undoubtedly equally important. Hence, the paper also emphasizes factors influencing the accuracy of functional residual capacity measurements independent of equipment requirements. These recommendations represent the "State of the Art" in 2000. (+info)
Gravity effects on regional lung ventilation determined by functional EIT during parabolic flights.
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Gravity-dependent changes of regional lung function were studied during normogravity, hypergravity, and microgravity induced by parabolic flights. Seven healthy subjects were followed in the right lateral and supine postures during tidal breathing, forced vital capacity, and slow expiratory vital capacity maneuvers. Regional 1) lung ventilation, 2) lung volumes, and 3) lung emptying behavior were studied in a transverse thoracic plane by functional electrical impedance tomography (EIT). The results showed gravity-dependent changes of regional lung ventilation parameters. A significant effect of gravity on regional functional residual capacity with a rapid lung volume redistribution during the gravity transition phases was established. The most homogeneous functional residual capacity distribution was found at microgravity. During vital capacity and forced vital capacity in the right lateral posture, the decrease in lung volume on expiration was larger in the right lung region at all gravity phases. During tidal breathing, the differences in ventilation magnitudes between the right and left lung regions were not significant in either posture or gravity phase. A significant nonlinearity of lung emptying was determined at normogravity and hypergravity. The pattern of lung emptying was homogeneous during microgravity. (+info)