Feasibility of continuous bronchoscopy during exercise in the assessment of large airway movement in healthy subjects.

Excessive dynamic airway collapse (EDAC) is a recognized cause of exertional dyspnea arising due to invagination of the trachea and/or main bronchi. EDAC is typically assessed by evaluating large airway movement with forced expiratory maneuvers. This differs from the respiratory response to exercise hyperpnea. We aimed to evaluate large airway movement during physical activity, with continuous bronchoscopy during exercise (CBE), in healthy subjects and compare findings with resting bronchoscopic maneuvers and imaging techniques. Twenty-eight individuals were recruited to complete two visits including treadmill-based CBE, to voluntary exhaustion, and cine magnetic resonance imaging (MRI) with forced expiratory maneuvers at rest. Twenty-five subjects [aged 29 (26-33) yr, 52% female] completed the study (n = 2 withdrew before bronchoscopy, and one was unable to tolerate insertion of bronchoscope). The majority (76%) achieved a peak heart rate of >90% predicted during CBE. The procedure was prematurely terminated in five subjects (n = 3; elevated blood pressure and n = 2; minor oxygen desaturation). The CBE assessment enabled adequate tracheal visualization in all cases. Excessive dynamic airway collapse (tracheal collapse ≥50%) was identified in 16 subjects (64%) on MRI, and in six (24%) individuals during resting bronchoscopy, but in no cases with CBE. No serious adverse events were reported, but minor adverse events were evident. The CBE procedure permits visualization of large airway movement during physical activity. In healthy subjects, there was no evidence of EDAC during strenuous exercise, despite evidence during forced maneuvers on imaging, thus challenging conventional approaches to diagnosis.NEW & NOTEWORTHY This study demonstrates that large airway movement can be visualized with bronchoscopy undertaken during vigorous exercise. This approach does not require sedation and permits characterization of the behavior of the large airways and the tendency toward collapse during upright, ambulatory exercise. In healthy individuals, the response pattern of the large airways during exercise appears to differ markedly from the pattern of airway closure witnessed during forced expiratory maneuvers, assessed via imaging.

A new approach to improve the hemodynamic assessment of cardiac function independent of respiratory influence.

Cardiovascular and respiratory systems are anatomically and functionally linked; inspiration produces negative intrathoracic pressures that act on the heart and alter cardiac function. Inspiratory pressures increase with heart failure and can exceed the magnitude of ventricular pressure during diastole. Accordingly, respiratory pressures may be a confounding factor to assessing cardiac function. While the interaction between respiration and the heart is well characterized, the extent to which systolic and diastolic indices are affected by inspiration is unknown. Our objective was to understand how inspiratory pressure affects the hemodynamic assessment of cardiac function. To do this, we developed custom software to assess and separate indices of systolic and diastolic function into inspiratory, early expiratory, and late expiratory phases of respiration. We then compared cardiac parameters during normal breathing and with various respiratory loads. Variations in inspiratory pressure had a small impact on systolic pressure and function. Conversely, diastolic pressure strongly correlated with negative inspiratory pressure. Cardiac pressures were less affected by respiration during expiration; late expiration was the most stable respiratory phase. In conclusion, inspiration is a large confounding influence on diastolic pressure, but minimally affects systolic pressure. Performing cardiac hemodynamic analysis by accounting for respiratory phase yields more accuracy and analytic confidence to the assessment of diastolic function.

Fluoroscopic and radiographic assessment of variations in tracheal height during inspiration and expiration in healthy adult small-breed dogs.

The objective of this study was to document tidal variations in tracheal height during normal respiration in 19 healthy adult (> 1 y old) small-breed dogs (< 10 kg) using fluoroscopy and radiography. Each dog underwent tracheal fluoroscopic examination on inspiration and expiration while in a standing position (F-S) and in right lateral recumbency (F-RL), followed by radiographic projections obtained in right lateral recumbency. The percent variation in tracheal height during maximal inspiration and expiration was determined at 3 different locations [cervical region (CR), thoracic inlet (TI), and intrathoracic (IT) region]. When all imaging procedures and sites of measurement were considered, tracheal height varied during physiologic inspiration and expiration from 0% to 21.1%, with a mean of 4.5%. The mean percent variation in tracheal height was not significantly different among imaging modalities (F-S versus F-RL versus radiography) (P = 0.16) or measurement sites (CR versus TI versus IT) (P = 0.89). The body condition score (BCS) (P = 0.96), age (P = 0.95), and breed (P = 0.19) did not significantly influence the mean percent variation in tracheal height. The average variation in tracheal height during maximal physiological inspiration and expiration is small (< 6%) in most healthy adult small-breed dogs as assessed by fluoroscopy and radiography, although tracheal height may vary by as much as 21.1% in some healthy individuals. Inspiratory and expiratory radiographs acquired in right lateral recumbency provide an accurate assessment of tracheal height as an alternative to fluoroscopy.

L'objectif de la présente étude était de documenter les variations de la hauteur de la trachée durant la respiration normale chez 19 chiens adulte en santé (> 1 an) de petites races (< 10 kg) à l'aide de la fluoroscopie et de la radiographie. Chaque chien a été soumis à un examen fluoroscopique de la trachée lors de l'inspiration et de l'expiration alors qu'il était en position debout (F-S) et en décubitus latéral droit (F-RL), suivi d'images radiographiques obtenues en décubitus latéral droit. Le pourcentage de variation de la hauteur de la trachée durant l'inspiration et l'expiration maximales fut déterminé à trois endroits différents [région cervicale (CR), l'entrée thoracique (TI), et la région intrathoracique (IT)]. Lorsque toutes les procédures d'imagerie et les sites de mesure étaient considérés, la hauteur de la trachée variait durant l'inspiration et l'expiration physiologique de 0 % à 21,1 %, avec une moyenne de 4,5 %. Le pourcentage de variation moyen de la hauteur de la trachée n'était pas significativement différent parmi les différentes modalités d'imagerie (F-S versus F-RL versus radiographie) (P = 0,16) ou les sites de mesure (CR versus TI versus IT) (P = 0,89). Le score de condition corporelle (BCS) (P = 0,96), l'âge (P = 0,95), et la race (P = 0,19) n'influençaient pas significativement le pourcentage de variation moyen de la hauteur de la trachée. La variation moyenne de la hauteur de la trachée durant l'inspiration et l'expiration physiologique maximale est petite (< 6 %) chez la plupart des chiens adultes de petites races en santé telle qu'évalué par fluoroscopie et radiographie, bien que la hauteur de la trachée puisse varier jusqu'à 21,1 % chez certains individus en santé. Les radiographies à l'inspiration et à l'expiration obtenues en décubitus latéral droit fournissent une évaluation précise de la hauteur de la trachée comme alternative à la fluoroscopie.(Traduit par Docteur Serge Messier).

Assessment of the Airway Smooth Muscle Relaxant Effect of Drotaverine.

BACKGROUND: Drotaverine, a type 4 cyclic nucleotide phosphodiesterase (PDE4) inhibitor, blocks the degradation of 3',5'-cyclic adenosine monophosphate. However, published receptor binding data showed that drotaverin also binds to the L-type voltage-operated calcium channel (L-VOCC). Based on these molecular mechanisms of action, a direct and indirect (by blocking the constrictor response) relaxant effect on airway smooth muscle can be predicted, which has not yet been assessed. SUMMARY: Accordingly, drotaverine and reference agents were tested both on the histamine-, methacholine-, or KCl-induced contraction response and on precontracted guinea pig tracheal preparations. It was found that drotaverine not only relaxed the precontracted tracheal preparations but also decreased mediator-induced contraction. These effects of drotaverine were concentration dependent, with a significantly higher potency on the KCl-induced response, than on either the histamine or methacholine induced one. A similar result was noted for nifedipine. The PDE inhibitor, theophylline, also relaxed the precontracted preparations but was ineffective on the mediator-induced contraction in a physiologically relevant concentration range. Moreover, theophylline did not show selectivity and was the least potent relaxant among the 3 tested molecules. Key Message: These results show that drotaverine is a more potent airway smooth muscle relaxant molecule than theophylline. This enhanced potency on relaxation and inhibition of the constrictor response, at least partly, may be explained by the combined L-VOCC blocking and PDE inhibitory potential of drotaverine.

Understanding the contribution of native tracheobronchial structure to lung function: CT assessment of airway morphology in never smokers.

BACKGROUND: Computed tomographic (CT) airway lumen narrowing is associated with lower lung function. Although volumetric CT measures of airways (wall volume [WV] and lumen volume [LV]) compared to cross sectional measures can more accurately reflect bronchial morphology, data of their use in never smokers is scarce. We hypothesize that native tracheobronchial tree morphology as assessed by volumetric CT metrics play a significant role in determining lung function in normal subjects. We aimed to assess the relationships between airway size, the projected branching generation number (BGN) to reach airways of <2mm lumen diameter -the site for airflow obstruction in smokers- and measures of lung function including forced expiratory volume in 1 second (FEV1) and forced expiratory flow between 25% and 75% of vital capacity (FEF 25-75). METHODS: We assessed WV and LV of segmental and subsegmental airways from six bronchial paths as well as lung volume on CT scans from 106 never smokers. We calculated the lumen area ratio of the subsegmental to segmental airways and estimated the projected BGN to reach a <2mm-lumen-diameter airway assuming a dichotomized tracheobronchial tree model. Regression analysis was used to assess the relationships between airway size, BGN, FEF 25-75, and FEV1. RESULTS: We found that in models adjusted for demographics, LV and WV of segmental and subsegmental airways were directly related to FEV1 (P <0.05 for all the models). In adjusted models for age, sex, race, LV and lung volume or height, the projected BGN was directly associated with FEF 25-75 and FEV1 (P = 0.001) where subjects with lower FEV1 had fewer calculated branch generations between the subsegmental bronchus and small airways. There was no association between airway lumen area ratio and lung volume. CONCLUSION: We conclude that in never smokers, those with smaller central airways had lower airflow and those with lower airflow had less parallel airway pathways independent of lung size. These findings suggest that variability in the structure of the tracheobronchial tree may influence the risk of developing clinically relevant smoking related airway obstruction.

Assessment of time-frequency representation techniques for thoracic sounds analysis.

A step forward in the knowledge about the underlying physiological phenomena of thoracic sounds requires a reliable estimate of their time-frequency behavior that overcomes the disadvantages of the conventional spectrogram. A more detailed time-frequency representation could lead to a better feature extraction for diseases classification and stratification purposes, among others. In this respect, the aim of this study was to look for an omnibus technique to obtain the time-frequency representation (TFR) of thoracic sounds by comparing generic goodness-of-fit criteria in different simulated thoracic sounds scenarios. The performance of ten TFRs for heart, normal tracheal and adventitious lung sounds was assessed using time-frequency patterns obtained by mathematical functions of the thoracic sounds. To find the best TFR performance measures, such as the 2D local (ρ(mean)) and global (ρ) central correlation, the normalized root-mean-square error (NRMSE), the cross-correlation coefficient (ρ(IF)) and the time-frequency resolution (res(TF)) were used. Simulation results pointed out that the Hilbert-Huang spectrum (HHS) had a superior performance as compared with other techniques and then, it can be considered as a reliable TFR for thoracic sounds. Furthermore, the goodness of HHS was assessed using noisy simulated signals. Additionally, HHS was applied to first and second heart sounds taken from a young healthy male subject, to tracheal sound from a middle-age healthy male subject, and to abnormal lung sounds acquired from a male patient with diffuse interstitial pneumonia. It is expected that the results of this research could be used to obtain a better signature of thoracic sounds for pattern recognition purpose, among other tasks.

The acoustic reflection method for the assessment of paediatric upper airways.

The acoustic reflection method (ARM) is based on the analysis of the reflection of an acoustic wave in the airway, allowing the calculation of its longitudinal cross-sectional area profile and airway resistance. The ARM represents a simple, quick and totally non invasive tool for the investigation of the upper airways, requiring minimal cooperation, which makes this technique particularly suitable for children. Normal values of the minimal cross sectional area of the upper airways in children have been recently published. The ARM has shown its utility in the investigation of the nasal cavity in healthy and diseased children and of the upper airways in children with various diseases such as mucopolysaccharidosis and cystic fibrosis. This simple, rapid, and inexpensive technique seems promising for the non-invasive investigation of the whole upper airway during wakefulness in children, both in health and disease, and may constitute a complementary or alternative method to explore and follow children with anomalies of the upper airways.

Assessment of airway hyperresponsiveness in murine tracheal rings.

Isolated tracheal rings have often been used to directly measure the contractile output of airway smooth muscle (ASM). Here, we describe the method for excising murine tracheas, mounting tracheal rings in organ baths, and measuring the isometric forces generated by the ASM when stimulated by drug additions or electric field stimulation. The apparatus for the setup and the pathways responsible for stimulation are detailed. Examples of the responses and analyses of two types of ASM stimulation are illustrated: (1) the carbachol concentration-response curve and (2) the frequency-response curve elicited by electric field stimulation.

Objective assessment of tracheoesophageal and esophageal speech using acoustic analysis of voice.

The aim of this study was to analyze the voice quality of alaryngeal tracheoesophageal and esophageal speech, and to determine which of them is more similar to laryngeal voice production, and thus more acceptable as a rehabilitation method of laryngectomized persons. Objective voice evaluation was performed on a sample of 20 totally laryngectomized subjects of both sexes, average age 61.3 years. Subjects were divided into two groups: 10 (50%) respondents with built tracheoesophageal prosthesis and 10 (50%) who acquired esophageal speech. Testing included 6 variables: 5 parameters of acoustic analysis of voice and one parameter of aerodynamic measurements. The obtained data was statistically analyzed by analysis of variance. Analysis of the data showed a statistically significant difference between the two groups in the terms of intensity, fundamental frequency and maximum phonation time of vowel at a significance level of 5% and confidence interval of 95%. A statistically significant difference was not found between the values of jitter, shimmer, and harmonic-to-noise ratio between tracheoesophageal and esophageal voice. There is no ideal method of rehabilitation and every one of them requires an individual approach to the patient, but the results shows the advantages of rehabilitation by means of installing voice prosthesis.

Reproducibility of forced expiratory tracheal collapse: assessment with MDCT in healthy volunteers.

RATIONALE AND OBJECTIVES: To assess the reproducibility of multidetector-row computed tomography (MDCT)-measured forced expiratory tracheal collapse in healthy volunteers. METHODS AND MATERIALS: Fourteen healthy, nonsmoking volunteers (6 males, 8 females, mean age 48.7 +/- 13.8 years) underwent repeat imaging 1 year after baseline imaging of tracheal dynamics employing the same scanner and technique (64-MDCT, 40 mAs, 120 kVp, and 0.625 mm detector collimation) with spirometric monitoring of total lung capacity and forced exhalation. Cross-sectional area (CSA) of the trachea was measured 1 cm above the aortic arch at end-inspiration and dynamic expiration, and percentage (%) expiratory reduction in tracheal lumen was calculated. Measurements were compared between baseline (Yr1) and repeat imaging (Yr2) using correlation coefficients and Bland-Altman plots. RESULTS: Mean end-inspiratory CSA was 255.3 +/- 56 mm(2) at Yr1 and 255.1 +/- 52 mm(2) at Yr2; mean dynamic expiratory CSA was 125.6 +/- 60 mm(2) at Yr1 and 132.1 +/- 58 mm(2) at Yr2; and mean % expiratory reduction was 51.7 +/- 18% at Yr1 and 48.7 +/- 19% at Yr2. Mean differences between Yr1 and Yr2 values were 0.2 mm(2) for end-inspiratory CSA, 6.5 mm(2) for dynamic expiratory CSA, and 3.0% for percentage expiratory reduction. There was excellent correlation between the Yr1 and Yr2 measures of end-inspiratory CSA (r(2) = 0.97, P < .001), dynamic expiratory CSA (r(2) = 0.89, P < .001), and % expiratory reduction (r(2) = 0.86, P < .001). CONCLUSION: MDCT measurements of forced expiratory tracheal collapse in healthy volunteers are highly reproducible over time.

Assessment of tracheal temperature and humidity in laryngectomized individuals and the influence of a heat and moisture exchanger on tracheal climate.

BACKGROUND: The beneficial function of heat and moisture exchangers (HMEs) is undisputed, but knowledge of their effects on intra-airway temperature and humidity is scarce. The aim of this study was to evaluate the clinical applicability of a new airway climate explorer (ACE) and to assess the HME's influence on tracheal climate. METHODS: Intratracheal temperature and humidity were measured with and without HME in 10 laryngectomized patients. RESULTS: An HME causes the intratracheal mean humidity minima to increase with 3.2 mg H(2)O/L (95% CI: 1.5-4.8 mg H(2)O/L; p <.001), from 21.4 to 24.6 mg H(2)O/L, and the mean temperature minima to decrease with 1.6 degrees C (95% CI: 0.9-2.4 degrees C; p <.001) from 28.5 degrees C to 26.9 degrees C. Relative humidity values suggest that the tested HME keeps inspired air (nearly) fully saturated during the full course of inspiration. CONCLUSION: Assessment of intratracheal temperature and humidity, and evaluation of HME effectiveness is feasible with the ACE. The tested HME significantly increases the intratracheal humidity, but decreases the intratracheal temperature. Relative humidity calculations suggest that increasing the thermal capacity of this rehabilitation device can further increase the heat and moisture exchange efficiency.

In vivo assessment of safety and mechanisms underlying in vitro relaxation induced by Mikania laevigata Schultz Bip. ex Baker in the rat trachea.

Mikania laevigata, popularly known in Brazil as "guaco", is largely used in folk medicine against respiratory diseases. However, neither the assessment of the toxicity of "guaco" syrup (GS, used by humans) nor its efficacy or mechanisms of action has been properly investigated. Using in vitro procedures, we showed that the hydroalcoholic extract (HE) from Mikania laevigata induces a concentration-dependent relaxation of rat trachea which does not depend on epithelium-derived substances but involves changes in the cellular mobilization of calcium, perhaps due to a direct effect on membrane potassium channels. In addition, we assessed both oral and intraperitoneal acute toxicity, as well as the oral subchronic and chronic toxicity of GS containing controlled amounts of coumarin, the main biological marker of Mikania laevigata preparations used in humans. The calculated LD(50) of GS after intraperitoneal administration was 0.904 g/kg in mice (both sexes) and 0.967 and 0.548 g/kg in male and female rats, respectively. However, the LD(50) values of GS by the oral route were calculated to be up to 10 g/kg, in both male and female mice and rats. Repeated dose 28- or 90-day oral treatment with GS (75, 150 and 300 mg/kg) did not produce any disturbances in the hematological or biochemical parameters of either male or female rats, nor did it provide evidence of toxicity in the hepatic, renal or pancreatic systems. Besides the mechanistic findings, our results provide evidence of the safety of Mikania laevigata in rodents, even after subchronic and chronic administration, at least in relation to the evaluated parameters.

Cuffed tracheal tubes in children: past, present and future.

This article reviews recent developments and core topics in the use and design of pediatric cuffed tracheal tubes. A concept for an appropriate pediatric cuffed tracheal tube is introduced. The main points in this concept are evidence-based tracheal tube size recommendation, continuous cuff pressure monitoring and a pediatric tracheal tube with an anatomically-based intubation depth mark and a short distally placed high-volume-low pressure cuff made from an ultra-thin polyurethane membrane with markedly improved tracheal sealing performance. The main points in proper handling of cuffed tracheal tubes in children are highlighted. Finally, an outlook on future developments in the design of pediatric cuffed tracheal tubes and an overview of tasks to be performed in evaluating them is given.

Theoretical assessment of unsteady aerodynamic effects in phonation.

This paper ranks the importance of unsteady aerodynamic mechanisms in glottal flow. Particular emphasis is given to separation point motion, acceleration of glottal airflow by vocal fold motion, and viscous blockage. How nondimensional parameters such as the Reynolds, Strouhal, and Womersley numbers help in this ranking is also addressed. An equation of motion is derived which includes terms explicitly describing the effects of interest, assuming (1) a symmetrical glottis, (2) zero pressure recovery downstream of the vocal folds, and (3) a quasisteady glottal jet. Estimating the order of magnitude of the terms in this equation, it is shown that the flow is characterized by two temporal regimes: (1) a flow initiation/shutoff regime where local unsteady acceleration and wall motion dominate, and (2) a "quasisteady" regime where the flow is dominated by convective acceleration. In the latter case, separation point motion and viscous blockage are shown to be out of phase with motion of the vocal folds, thereby impacting the shape of the glottal volume flow waveform. The analysis suggests that glottal flow may be considered quasisteady only insofar as traditional assumptions concerning glottal jet behavior can be confirmed.

Low molecular weight quaternised chitosan (11): in vitro assessment of absorption enhancing properties.

N-Trimethyl chitosan chloride (TMC; high molecular weight) and N-trimethyl chitosan oligosaccharide (TMO; low molecular weight) with different degrees of quaternisation were synthesised and evaluated for their absorption enhancing properties across mucosal epithelia. These quaternised chitosan derivatives (0.0625% w/v-0.5% w/v) showed a significant decrease in the transepithelial electrical resistance (TEER) of cultured rabbit tracheal epithelial cell monolayers as compared to the control. The degree of quaternisation and concentration of the compounds influenced the extent of the reduction in TEER. Higher degrees of quaternisation and an increase in the concentration of the compound were associated with a more pronounced reduction in the TEER. The TMO derivatives seemed to be more effective in lowering the TEER of tracheal cell monolayers as compared to the TMC polymers. Ciliary beat frequency (CBF) is the main defence mechanism of the respiratory tract and is therefore a useful parameter in evaluating the toxicity of nasally administered drugs and additives. The effect of the synthesised chitosan derivatives on the CBF of human nasal epithelial cells at pH 7.4 was determined by a method based on an analogue contrast enhancement technique. The TMO oligomers exhibited lower inhibition of the CBF of human nasal epithelial cells compared to that of the TMC polymers. It was proposed that this reduced effect on the CBF is due to the lower viscosity and molecular weight of TMO. However, no acute toxicity was found with any of the synthesised chitosan derivatives by means of the CBF tests conducted in this study.

Assessment of a new method to distinguish esophageal from tracheal intubation by measuring the endotracheal cuff pressure in a porcine model.

OBJECTIVES: With the knowledge of differences in anatomic structures between the trachea and the esophagus, the authors conducted an animal study to evaluate the usefulness of endotracheal cuff pressure in distinguishing endotracheal and esophageal intubations. METHODS: Six swine were anesthetized and endotracheally intubated with 7.5-mm cuffed endotracheal tubes. The intubations were confirmed by fiber-optic bronchoscopy. Each pilot balloon was connected to a 10-mL syringe and a manometer via a three-way stopcock. The cuff pressures were measured for each 1-mL incremental filling of air (1-10 mL). After removal of the endotracheal tubes, each swine was then intubated with the same endotracheal tubes into its esophagus. The cuff pressures of the esophageal intubation were measured with the same procedure. The cuff pressures and the pressure-volume relationships in both intubations were compared. RESULTS: The cuff pressure increased significantly in the esophageal intubation in comparison with the endotracheal intubation in all the comparisons from 1 mL to 10 mL (p = 0.028 for all Wilcoxon signed-rank tests). The slope of the pressure-volume curve of the cuff pressure was also significantly higher in the esophageal intubation during the inflation of the cuff on average (0.047 vs. 0.032 cm H2O/mL; p = 0.001), particularly in the first 5 mL of air inflation. CONCLUSIONS: The cuff pressure in the esophageal intubation was significantly higher than that in the endotracheal intubation under the same inflated volume from 1 to 10 mL. This may provide the basis for an adjunctive, simple, rapid, and reliable method to verify endotracheal intubation.

Respiratory lumenal change of the pharynx and trachea in normal subjects and COPD patients: assessment by cine-MRI.

The purpose of this study was to use cine-MRI during continuous respiration to measure the respiratory lumenal diameter change in the pharynx and at an upper tracheal level. Fifteen non-smokers and 23 chronic obstructive pulmonary disease (COPD) patients with smoking history (median 50 pack-years) were included. Cine-MRI with seven frames/s was performed during continuous respiration. Minimal and maximal cross-sectional lumenal diameters within the pharynx and the upper tracheal lumen area were measured. The median diameter change in the pharynx (tracheal area) was 70% (1.4 cm(2)) in volunteers and 76% (1.7 cm(2)) in smokers (P=0.98, P=0.04). Tracheal lumenal collapse was a median of 43% in volunteers and 64% in smokers (P=0.011). No clear disease-related difference of the pharynx-lumen was found. The maximal cross-sectional area of the upper trachea lumen as well as the respiratory collapse was larger in COPD patients than in normal subjects. This information is important for the modelling of ventilation and prediction of drug deposition, which are influenced by the airway diameter.

Preload changes by positive pressure ventilation can be used for assessment of left ventricular systolic function.

BACKGROUND: Assessment of preload independent left ventricular function with conductance volumetry is traditionally accomplished by inflating a balloon in the inferior caval vein. Our aim was to investigate if a similar change in preload could be achieved by positive pressure ventilation with large tidal volume. METHODS: Conductance volumetry generating left ventricular pressure-volume loops was used in seven pentobarbital-anesthetized pigs. Changes in preload recruitable stroke work were studied, comparing the effects of inferior vena cava occlusion (IVCO) or large tidal volume (LTV). Cardiodepression was induced by halothane anesthesia and halothane + phenylephrine, and stimulation by epinephrine infusion. RESULTS: Although the decreasis in left ventricular end diastolic volume was slightly less with LTV (16.5 +/- 1.7 ml, mean +/- SEM) than with IVCO (22.4 +/- 1.7 ml) (P < 0.0001) the PRSW-slopes showed a high degree of correlation (r=0.80, P < 0.0001). Although peak tracheal pressures increased significantly to 27.8 +/- 0.9 mmHg during LTV, esophageal pressures (used as an indicator of pericardial pressure) were unchanged. CONCLUSIONS: Positive pressure ventilation with LTV is similar to IVCO in creating transient changes in preload, necessary for assessment of left ventricular systolic function. This observation was valid also during drug-induced cardiac depression and stimulation. The preload recruitable stroke work used for this validation was shown to be a reliable and stable method.