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The measurement of esophageal pressure allows for the calculation of several important and clinically useful parameters of respiratory mechanics. Esophageal pressure is often measured with balloon-tipped catheters. These catheters may be handmade from natural latex condoms and polyethylene tubing. Given the potential of natural latex to cause allergic reaction, it is important to determine whether esophageal catheter balloons can be fabricated, by hand, using nonlatex condoms as construction materials. To determine the static and dynamic response characteristics of esophageal balloon catheters handmade from latex and nonlatex materials, six esophageal catheter balloons were constructed from each of the following condom materials: natural latex, synthetic polyisoprene, and polyurethane (18 total). Static compliance and working volume range of each balloon catheter was obtained from their pressure-volume characteristics in water. The dynamic response of balloon catheters were measured via a pressure "step" test, from which a third-order underdamped transfer function was modeled. The dynamic ranges of balloon catheters were characterized by the frequencies corresponding to ±5% amplitude- and phase-distortion (fA5% and fφ5%). Balloon catheters handmade from polyurethane condoms displayed the smallest working volume range and lowest static balloon compliance. Despite this lower compliance, fA 5% and fφ5% were remarkably similar between all balloon materials. Our findings suggest that polyisoprene condoms are an ideal nonlatex construction material to use when fabricating esophageal catheter balloons by hand.

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Obesity is associated with important decrements in lung volumes. Despite this, ventilation remains normally or near normally distributed at least for moderate decrements in functional residual capacity (FRC). We tested the hypothesis that this is because maximum flow increases presumably as a result of an increased lung elastic recoil. Forced expiratory flows corrected for thoracic gas compression volume, lung volumes, and forced oscillation technique at 5-11-19 Hz were measured in 133 healthy subjects with a body mass index (BMI) ranging from 18 to 50 kg/m(2). Short-term temporal variability of ventilation heterogeneity was estimated from the interquartile range of the frequency distribution of the difference in inspiratory resistance between 5 and 19 Hz (R5-19_IQR). FRC % predicted negatively correlated with BMI (r = -0.72, P < 0.001) and with an increase in slope of either maximal (r = -0.34, P < 0.01) or partial flow-volume curves (r = -0.30, P < 0.01). Together with a slight decrease in residual volume, this suggests an increased lung elastic recoil. Regression analysis of R5-19_IQR against FRC % predicted and expiratory reserve volume (ERV) yielded significantly higher correlation coefficients by nonlinear than linear fitting models (r(2) = 0.40 vs. 0.30 for FRC % predicted and r(2) = 0.28 vs. 0.19 for ERV). In conclusion, temporal variability of ventilation heterogeneities increases in obesity only when FRC falls approximately below 65% of predicted or ERV below 0.6 liters. Above these thresholds distribution is quite well preserved presumably as a result of an increase in lung recoil.

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BACKGROUND: The nonspecific (NS) pulmonary function (PF) pattern refers to a PF test with a normal total lung capacity (TLC), normal FEV1/FVC ratio, and a low FEV1, a low FVC, or both. Currently, no information is available regarding the long-term stability of the NS pattern or variables that predict changes in subjects with an initial NS PF pattern. METHODS: From 1990 to 2005 we identified 1,284 subjects with an NS pattern on initial PF testing with one or more follow-up PF tests 6 months or more after the initial NS test result. Lung volumes, diffusing capacity, and spirometry data were analyzed. A multivariate, multinomial logistic regression model was used to study the association between different variables and the final PF pattern. RESULTS: Overall, 3,674 PF tests were performed in 1,284 subjects over a median follow-up period of 3 years. At last follow-up, 818/1,284 (64%) subjects continued to show the NS pattern, whereas 208/1,284 (16%) showed a restrictive pattern, 191/1,284 (15%) an obstructive pattern, 42/1,284 (3%) a normal pattern, and 25/1,284 (2%) a mixed pattern. The multinomial logistic regression analysis showed that increasing values for specific airway resistance and the difference between TLC and alveolar volume were predictors of a change to an obstructive pattern on follow-up. CONCLUSIONS: The NS pattern is a distinct and stable PF test pattern with roughly two-thirds of patients continuing to show this pattern on follow-up testing. Current interpretation guidelines erroneously label the NS pattern as representing obstruction and need to be changed to reflect these data.

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Measurements of dynamic force-length behavior of maximally activated strips of smooth muscle during oscillatory length changes show that force decreases well below the isometric force during the shortening phase of the oscillation. The magnitude of the decrease depends on the rate of shortening; for slower shortening, the decrease is smaller and force is larger. Modeling of expiratory flow, based on these data, predicts that vital capacity in constricted lungs depends on the rate of expiration. In maximally constricted lungs, forced vital capacity (FVC) is predicted to be 16% smaller than control, and vital capacity for a very slow expiration (SVC), 31% less than control. These predictions were tested by measuring FVC and SVC in constricted normal subjects. In the first group of 9 subjects, four maneuvers were made following the delivery of two doses of methacholine in the order: SVC, FVC, FVC, SVC. In a second group of 11 subjects, two maneuvers were performed at each dose in the order: FVC, SVC. At the highest dose of methacholine, FVC for both trials in group 1 and for the one trial in group 2 were all approximately 13% less than control, a slightly smaller decrease than predicted. SVC for the 1st trial in group 1 was 27% less than control, also slightly smaller than predicted. The difference between FVC and SVC for this trial, 13%, was close to the predicted difference of 15%. However, SVC for the 2nd trial in group 1 (preceded by 3 vital capacity maneuvers) and for group 2 (preceded by 1) were no different from FVC. We conclude that vital capacity in constricted lungs depends on the dynamic force-length properties of smooth muscle and that the history dependence of the dynamic properties of smooth muscle is more complicated than has been inferred from oscillatory force-length behavior.

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We investigated whether obesity is associated with airway hyperresponsiveness in otherwise healthy humans and, if so, whether this correlates with a restrictive lung function pattern or a decreased number of sighs at rest and/or during walking. Lung function was studied before and after inhaling methacholine (MCh) in 41 healthy subjects with body mass index ranging from 20 to 56. Breathing pattern was assessed during a 60-min rest period and a 30-min walk. The dose of MCh that produced a 50% decrease in the maximum expiratory flow measured in a body plethysmograph (PD50MCh) was inversely correlated with body mass index (r2=0.32, P<0.001) and waist circumference (r2=0.25, P<0.001). Significant correlations with body mass index were also found with the maximum changes in respiratory resistance (r2=0.19, P<0.001) and reactance (r2=0.40, P<0.001) measured at 5 Hz. PD50MCh was also positively correlated with functional residual capacity (r2=0.56, P<0.001) and total lung capacity (r2=0.59, P<0.001) in men, but not in women. Neither PD50MCh nor body mass index correlated with number of sighs, average tidal volume, ventilation, or breathing frequency. In this study, airway hyperresponsiveness was significantly associated with obesity in otherwise healthy subjects. In obese men, but not in women, airway hyperresponsiveness was associated with the decreases in lung volumes.

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BACKGROUND: Little is known about a fairly frequent abnormal pattern of pulmonary function test results: reduced FEV(1) and FVC with a normal FEV(1)/FVC and normal total lung capacity. We term this a nonspecific pattern (NSP). We sought to identify medical conditions having this pattern and to explore mechanisms producing it. METHODS: From a database of 80,929 test results, the NSP was found in 7,702 subjects from whom was drawn a random sample of 100 subjects. Medical records and all available tests were examined. RESULTS: Airway hyperresponsiveness (AHR) and obesity were common. Two groups of subjects were identified. Group A consisted of 68 subjects with evidence of airway disease, including AHR and chronic lung disease. A volume derecruitment model was proposed to explain their NSP. Group B consisted of 32 subjects with no evidence of airway disease. Restricted expansion of the thorax or lung may explain the NSP in most of these subjects. Forty subjects had repeated tests, and in only 17 were the test results consistently nonspecific. CONCLUSIONS: In a random sample of 100 subjects with the NSP, the probable underlying cause of the pattern in 68 subjects was airway disease. In most of the remaining 32 subjects, restricted expansion of the thorax or lung may be implicated.

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We examined the effects of chest wall strapping (CWS) on the response to inhaled methacholine (MCh) and the effects of deep inspiration (DI). Eight subjects were studied on 1 day with MCh inhaled without CWS (CTRL), 1 day with MCh inhaled during CWS (CWSon/on), and 1 day with MCh inhaled during temporary removal of CWS (CWSoff/on). On the CWSon/on day, MCh caused greater increases in pulmonary resistance, upstream resistance, dynamic elastance, residual volume, and greater decreases in maximal expiratory flow than on the CTRL day. On the CWSoff/on day, the changes in these parameters with MCh were not different from the CTRL day. Six of the subjects were again studied using the same protocol on CTRL and CWSon/on days, except that, on a third day, MCh was given after applying the CWS, but the measurements before and after the inhalation were made without CWS (CWSon/off). The latter sequence was associated with more severe airflow obstruction than during CTRL, but less than with CWSon/on. The bronchodilator effects of a DI were blunted when CWS was applied during measurements (CWSon/on and CWSoff/on) but not after it was removed (CWSon/off). We conclude that CWS is capable of increasing airway responsiveness only when it is applied during the inhalation of the constrictor agent. We speculate that breathing at low lung volumes induced by CWS enhances airway narrowing because the airway smooth muscle is adapted at a length at which the contractile apparatus is able to generate a force greater than normal.

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