Measurement Of Gas Volume Research Articles

Assessment of prematurely born children at follow-up using a tidal breathing parameter

Prematurely born children frequently have respiratory problems at follow-up. A non-invasive and easily performed lung function test would greatly facilitate their evaluation and appropriate treatment. We have, therefore, assessed whether the shape of the tidal breathing expiratory flow curve would give useful information in such a population. One hundred and twenty traces were randomly selected from plethysmographic measurements of thoracic gas volume and airway resistance made during a follow-up study of a prematurely born population. The children had a median gestational age of 29 (range 23-35, interquartile range 27-31) weeks and postnatal age at the time of measurement of 11 (range 6-24, interquartile range 7-13) months. From the flow and volume signals, the mean time to reach peak tidal expiratory flow as a proportion of the total expiratory time was determined for each child. The median differed significantly between children who, in the neonatal period, had or had not required mechanical ventilation and had or had not had an increased inspired oxygen requirement (p < 0.01), and who were or were not symptomatic at follow-up (p < 0.001). Logistic regression analysis demonstrated that a low ratio was independently associated with symptom status. These results suggest that assessment of a tidal breathing parameter during follow-up of prematurely born children may be useful. As can be measured without sedation, relatively quickly and with simple equipment, potentially large study populations could be investigated, and this technique should now be evaluated in a non-sedated group of young prematurely born children. Keywords: prematurity, lung function measurement, tidal breathing parameters

The effect of head-space pressure on gas production profiles

In vitro gas production techniques are becoming increasingly popular as tools to investigate the food quality for ruminant and monogastric herbivores. They are attractive due to their ability to measure the kinetics of digestion associated with the gut microbial fermentation of foodstuffs. It is therefore important to know and understand what factors affect the volume of gas produced, particularly as they relate to repeatability within or between laboratories. In studies involving gas pressure and volume measurement, the chemical composition of the culture medium, the nature of the microbial population and the type and amount of substrate available for fermentation all have a significant influence on gas accumulation. In this study, the manual pressure transducer technique (PTT) of Theodorou et al. (1994) was used to investigate the effect of head-space pressure on the resultant gas production profiles.

Measurement of the specific airway resistance by plethysmography in young children accompanied by an adult.

The purpose of this study was to evaluate a procedure for measurement of specific airway resistance (sRaw) by whole body plethysmography in young awake children accompanied by an adult. sRaw was measured by a single-step procedure, omitting the measurement of the thoracic gas volume. The frequency dependency of sRaw was investigated and the accuracy of simulating body temperature, atmospheric pressure and saturation with water vapour (BTPS) conditions by electronic compensation was assessed. One hundred and thirty one children with asthma were studied. In 57 children (mean (SD) age 5.6 (1.8) yrs) who performed measurements with and without an accompanying adult, the mean value of sRaw was 1.45 (0.36) and 1.44 (0.38) kPa x s, respectively, with a mean difference of 0.008 (0.152) kPa x s, and mean within-subject coefficients of variations (CV) of 8% and 10%, respectively. In 52 children (mean age 3.3 (0.8) yrs), for whom measurements made only in the presence of an accompanying adult, the CV was 8.5%. No measurements could be obtained in 22 children (17%) (mean age 2.8 (0.5) yrs). Measurements exhibited a significant frequency dependency, and electronic BTPS compensation substantially overestimated SRaw. In conclusion, the use of electronic compensation for simulating body temperature, atmospheric pressure and saturation with water vapour introduces a bias that affects the accuracy of the estimate of specific airway resistance. Nevertheless, plethysmographic measurements with and without an accompanying adult yielded comparable and equally repeatable estimates of specific airway resistance. The single-step plethysmographic procedure with an accompanying adult is a clinically useful method for evaluating airway function in children too young to perform plethysmographic measurements alone.

The degradability characteristics of fifty-four roughages and roughage neutral-detergent fibres as described by in vitro gas production and their relationship to voluntary feed intake

Fifty-four roughages of known voluntary dry-matter intakes (DMI; range 7.8-35.2 g/kg live weight per d) were examined in vitro in a gas production test. Samples (200 mg) of roughage and roughage neutral-detergent fibre (NDF) respectively were incubated in a mixed suspension of rumen contents for 96 h and the gas volumes recorded after 4, 6, 8, 12, 24, 30, 36, 48, 54, 60 and 96 h. The kinetics of gas production were derived from the volume recordings described by the exponential equation Y = A + B(l-e-ct) where A is the intercept and ideally reflects the fermentation of the soluble and readily available fraction of the feed, B describes the fermentation of the insoluble (but with time fermentable) fraction and c the fractional rate at which B is fermented per h; A + B describes total fermentation. In vitro true dry matter (TD) and NDF degradabilities (NDF-D) after 24 h incubation were also determined. Of the variation in DMI, 75% was accounted for by the in vitro gas production parameters A, B and c in stepwise multiple regressions; 82% of the variation in DMI was explained by the parameters (ANDF + BNDF) and cNDF as obtained from the incubation of roughage NDF. The rate constants (c) were less important than parameters related to the extent of gas production, accounting for only 6.5 (whole roughage) and 4.1% (NDF) of the variation in DMI. There was no statistical advantage in the use of the exponential model describing extent and rate of fermentation over some of the simple gas volume measurements: 75% of the variation in DMI was accounted for by in vitro gas production of whole roughage after 8 h of incubation. On average gas production from NDF measured from 24-96 h accounted for 81% of the variation in DMI. A combination of gas volume measurements after a short period of incubation (4-8 h) with a concomitant determination of NDF-D after many hours (> or = 24 h) can render NDF preparations and long incubation times redundant. A method is suggested to obtain two results for DMI prediction in one single incubation. Of the variation in DMI 80% was accounted for by the incubation of 500 mg whole roughage when incubation was terminated after 24 h and the residual undegraded substrate quantified.

Perinatal lung function and invasive antenatal procedures.

BACKGROUND: Second trimester amniocentesis has been associated with an excess of perinatal lung function abnormalities. Early amniocentesis might have a similar adverse effect, as could other invasive investigations carried out...

LDA-measurements in natural gas high-pressure pipelines for the testing of turbine gas meters

In industrial gas volume measurement, the reliable, precise and economically efficient determination of gas quantities by measurement is of utmost importance. Standby meter sections, Z-connection and permanent series connection of two gas meters of different designs are state of the art [Schmittner, D., The importance of the accuracy of measurement for industrial gas measurements. 3 R International, Vol. 30, No. 6–7, 1991, pp. 338–343 (in German)]. The permanent or temporary series connection for the comparison and test section makes expenses for a second complete measuring device necessary. An alternative at present is the dismounting of the gas meter and the check test in an appropriate high-pressure test facility. A test according to requirements, using a non-interacting measuring instrument which should be transportable, if possible, and usable with other gas meters can be a bridge between these two possibilities. To prove this, measurements with an LDA system were carried out in a natural gas high-pressure pipeline upstream of a turbine gas meter. After extensive profile and single-point measurements have been made it can be said that this test by the single-point method is feasible with an uncertainty of ≤ ± 0.5%, providing defined prerequisites are met.

Noninvasive quantification of regional myocardial metabolic rate for oxygen by use of 15O2 inhalation and positron emission tomography. Theory, error analysis, and application in humans.

A method has been developed to measure the regional myocardial metabolic rate of oxygen consumption (rMMRO2) and oxygen extraction fraction (rOEF) quantitatively and noninvasively in humans by use of 15O2 inhalation and positron emission tomography. This article describes the theory, an error analysis of the technique, and procedures of the method used in a human feasibility study. Inhaled 15O2 is transported to peripheral tissues, where it is converted to 15O-labeled water of metabolism, which exchanges with the relatively large extravascular tissue space. Quantification of this buildup of radioactivity allows the calculation of rMMRO2 and rOEF. However, a correction for the spillover of the pulmonary gas radioactivity signal into myocardial regions is required and has been made by use of a gas volume distribution estimated from the transmission scan. This was validated by comparative measurements using the inert gas [11C]CH4 in four greyhounds. Spillover of the cardiac chamber radioactivity has been corrected for with an inhaled [13O]CO (blood volume) scan. The underestimation of myocardial radioactivity due to wall motion and thickness has been corrected for by use of values of tissue fraction obtained from the flow measurement [15OKCO2 scan). Values of rOEF were similar (within 4%) whether obtained from gas volume measurements determined from the transmission or [11C]CH4 scan data. 15O2 scan information from six healthy volunteers showed a clear distribution of myocardial radioactivity after the vascular and pulmonary gas 15O background was subtracted. Subsequent compartmental analysis resulted in values for rOEF and rMMRO2 of 0.60 +/- 0.11 and 0.10 +/- 0.03 mL.min-1.g-1 in the human myocardium at rest. The results of this study are in good agreement with established values. This is the first known approach to allow the direct quantitative determination of rOEF and oxygen metabolism to be made noninvasively on a regional basis.

Body plethysmographic measurement of thoracic gas volume without panting against a shutter

When a subject breathes through a pneumotachograph in a body box, the measured value of specific airway resistance (sRaw1) is equal to the product of thoracic gas volume (TGV) and the sum of the airway resistance (Raw) and the instrument resistance (Rins). If an additional resistance (Radd) is put in the breathing path, the measured specific, airway resistance (sRaw2) exceeds sRaw1 by the product of TGV and Radd and can be used for determining TGV. With the use of a device increasing Rins by a known amount (Radd) during normal breathing, sRaw1 and sRaw2 were measured in 3 normal subjects, 16 asthmatic patients, 2 patients with chronic obstructive pulmonary disease, and 1 patient with restrictive lung disease from the slopes of the x-y plots of airflow vs. box signals obtained before and after adding Radd. TGV was calculated by dividing (sRaw2-sRaw1) bu Radd. We also determined subjects' TGV by the panting method of A. B. DuBois, S. Y. Botelho, G. N. Bedell, and J. H. Comroe, Jr. (J. Clin. Invest. 35: 322-326, 1956) and functional residual capacity by the helium-dilution method. The results of the new method were quite reproducible (coefficient of variation = 5.6) and equivalent to those obtained by the other two methods.

Tidal breathing parameters in the first week of life and subsequent cough and wheeze.

Assessment of tidal breathing parameters may be a useful method of predicting respiratory problems in early childhood. Low values of TPTEF/TE (the ratio of the proportion of time to reach peak tidal expiratory flow to total expiratory time) outside the neonatal period have been significantly related to respiratory tract illness with wheezing in boys in the first year of life. TPTEF/TE measurements in the perinatal period were evaluated in nonsedated infants and the predictive value of this early measurement for subsequent respiratory morbidity during infancy was assessed. Flow during tidal breathing was measured while the infant slept quietly in a plethysmograph using a Fleisch pneumotachograph inserted into an infant face mask. Recruitment continued until traces from 60 infants with 10 consecutive flow curves without artefacts were obtained. In addition, plethysmographic measurements of airway resistance (Raw) and thoracic gas volume (TGV) were measured and specific conductance (sGaw) calculated. Parents recorded their infant's cough and wheeze during the first 12 months of life. Sixty five measurements were made in 60 infants with a mean age of two days and gestational age of 40 weeks. Two observers separately calculated TPTEF/TE ratios on 25 traces randomly selected from the pool of 60. The mean difference between the two observers was -0.004 (limits of agreement 0.048 to -0.056). Thirteen infants became symptomatic (wheeze, with or without cough); their median TPTEF/TE ratio (0.349) was significantly lower than the rest of the cohort (median 0.412) and they also had significantly higher Raw and lower sGaw. The positive predictive value of a low TPTEF/TE ratio, however, was only 41%. These results suggest that the use of this test in the prediction of future respiratory disease in an individual is limited.

Lung function from infancy to school age in cystic fibrosis.

The aim was to investigate pulmonary mechanics in patients with cystic fibrosis during infancy and again in early childhood to see whether infant tests predicted status at school age. Plethysmographic measurements of thoracic gas volume and airways resistance were made in 29 patients at 6 months and again at 5 years 10 months. Maximum flow at functional residual capacity was measured during infancy for comparison with maximum expiratory flow rates during childhood. While many patients had normal measurements during infancy, pulmonary function had deteriorated by school age. Thoracic gas volume at school age was significantly related to the values in infancy, but other measurements made during childhood were independent of infant values. The relations between measurements in infancy and early childhood described here provide a background against which the role of external factors on pulmonary function in young children with cystic fibrosis can be investigated.

Effect of bronchoconstrictive aerosols on pulmonary gas trapping in the A/J mouse

We exposed conscious A/J mice to several challenge aerosols and measured gas trapped within excised lungs by quantitating their buoyancy in saline (Archimedes' principle). The temporal stability of the excised lung gas volume (ELGV) measurement was also examined. ELGV increased in a dose proportional manner with increasing concentrations of methacholine and reached a maximum of 338 ± 33% above vehicle-exposed controls. The A/J mice were 100 times more responsive to aerosol methacholine compared to hyporesponsive C3H/HeJ mice. Aerosol challenges of U-46619, a thromboxane A 2 mimetic, and serotonin resulted in a 40% and 135% increase in ELGV's versus their controls, respectively. ELGV's were not increased after aerosols of leukotriene C 4, histamine, substance P, N-formyl-methionyl-leucyl-phenylalanine and platelet activating factor. Both normal (filtered air-exposed) and hyperinflated (methacholine-exposed) excised lungs lost about 10% of their initial volume by 30 min and 40–65% of initial volume by 4 h. Occlusion of the trachea in either group did not affect the total gas lost, suggesting that the majority of the gas loss was via transpleural diffusion. We conclude that determination of ELGV in mice, when performed soon after challenge testing, is a simple, rapid and reliable estimate of airway obstruction.

The simplified version of Boyle's Law leads to errors in the measurement of thoracic gas volume.

When using Boyle's Law for thoracic gas volume (Vtg) measurement, it is generally assumed that the alveolar pressure (Palv) does not differ from barometric pressure (Pbar) at the start of rarefaction and compression and that the product of the change in volume and pressure (delta P x delta V) is negligibly small. In a gentle panting maneuver in which the difference between Palv and Pbar is small, errors introduced by these assumptions are likely to be small; however, this is not the case when Vtg is measured using a single vigorous inspiratory effort. Discrepancies in the Vtg between the "complex" version of Boyle's Law, which does not ignore delta P x delta V and accounts for large swings in Palv, and the "simplified" version, during both a panting maneuver and a single inspiratory effort were calculated for normal control subjects and patients with cystic fibrosis or asthma. Defining the Vtg from the complete version as "correct," the errors introduced by the simplified version ranged from -3 to +3% for the panting maneuver whereas they ranged from 2 to 9% for the inspiratory maneuver. Using the simplified equation, the Vtg for the inspiratory maneuver was 0.135 +/- 0.237 L greater (p < 0.02) than for the panting maneuver. This discrepancy disappeared when the complete equation was used. While the errors introduced by the use of the simplified version of Boyle's Law are small, they are systematic and unnecessary.

Ethnic origin and lung function of infants born prematurely.

Ethnic origin has an important influence on the lung function of adults and young children but its effect during infancy, particularly following premature delivery, is unclear. The results from infants of pure Afro-Caribbean (subjects) and pure Caucasian (controls) descent, all of whom were born prematurely (median gestational age 28 weeks), were compared. Fifty subjects were each retrospectively matched with a control for gestational age, sex, and requirement for neonatal ventilation. Lung function measurements were performed at similar postnatal ages in each pair. The median postnatal ages of the two groups at the time of study was seven and eight months, respectively. Lung function was assessed by measurement of functional residual capacity (FRC) by a helium gas dilution technique and plethysmographic measurement of thoracic gas volume (TGV) and airways resistance (Raw), from which specific conductance (sGaw) was calculated. No differences were found between the subjects and controls regarding FRC or TGV, but Raw was higher and sGaw lower in the subjects. The mean Raw of the subjects was 50.3 cm H2O/1/s and of the controls was 44.1 cm H2O/1/s (95% confidence intervals of the difference 1.5 to 10.9). Prematurely born infants of Afro-Caribbean origin have more severe lung function abnormalities at approximately 7-8 months of age than those of Caucasian origin. This merits further investigation.

Methods for Measurement of Gas Volume of Fruits and Vegetables

Theory is presented for a differential mass-volume technique to measure non-destructively gas volume (Vg) changes, based only on the initial and final masses and volumes of an organ. Volume was measured using Archimedes' principle, but a non-invasive image analysis procedure could be an improvement. A reduction in Vg during the ripening of `Kada' tomato (Lycopersicon esculentum Mill) fruits, and irreversible Vg changes of 0.02, 0.29, 0.66, 1.2, and 1.3 ml for mature-green fruits compressed by 0, 2.5, 5.0, 7.5. and 10 mm for 5 minutes indicates the potential of this procedure. The method was compared with other methodologies using sweetpotato (Ipomea batatas L.) root segments subjected to vacuum water infiltration. The results were similar to the pycnometric method. The gasometric method underestimated Vg for roots in which the intercellular air volumes where blocked by the water used for infiltration, and large overestimation occurred with the traditional infiltration technique without correction for water absorption. Absolute Vg values were also estimated by semi-pycnometry (defined as the difference between the organ volume measured by water immersion and the organ volume without Vg measured with a pycnometer, after its maceration and elimination of gas bubbles with vacuum). Semi-pycnometry applied to tomato and bell pepper (Capsicum annuum L.) fruits, where the use of tissue segments limits the pycnometric method, and in sweetpotatoes, where the gasometric method overestimates Vg, generated results that were consistently similar to the differential mass-volume method.

Pharmacokinetics and Pharmacodynamics of β&lt;sub&gt;2&lt;/sub&gt;-Agonists (in the Light of Fenoterol)

As an example of beta 2-agonists fenoterol was used in this study on 27 patients with chronic obstructive airways diseases (COAD). After refraining from any kind of bronchodilator during 12 h the patients were given the drug in a crossover design in three groups. Using aerosol inhalation, intravenous route and nasal instillation we measured the response of airway resistance, intrathoracic gas volume and fenoterol plasma concentrations. The plethysmographic measurement of airways resistance (Rt) and intrathoracic gas volume showed comparable results of bronchodilation (at different dosages) for each of the routes. Even the onset of action was nearly the same with all the different routes. The amount of bronchodilatation was in the range of 59% of the initial Rt values. The duration of bronchodilatation was much longer after metered dose inhalers (MDI) inhalation ( > 4 h) than after intravenous routes. The duration after nasal administration was in between. The infusion maintains its effect only as long as the infusion is given. The bronchodilation response induced by fenoterol reaches the same values with different routes of administration and depends on the amount of decrease of airway obstruction. The highest plasma concentrations were reached with the intravenous boluses. Immediately after injection the concentration decreased rapidly. The maximum plasma concentrations after MDI were around 20% of that after the intravenous route for the same bronchodilatation. The heart rate is a function of the plasma concentration. At low concentrations such as after aerosol inhalation of 200 micrograms the influence on the heart rate is not significant. After aerosol inhalation the effect at the receptor can be calculated to be > 7 times stronger than seen from any plasma concentration after intravenous administration. It is assumed that there are structures near the beta 2-bronchodilator receptor which are responsible for the long-lasting effect that is observed only after aerosol inhalation. These depot structures cannot be reached from the plasma in concentrations needed under in vivo conditions. Loss of these structures shortens the duration of the bronchodilator effect. In respect to effect/side effect relationship, more frequent administration of smaller doses may be the best method for administering beta 2-agonists as aerosols in patients with COAD. For many patients with severe forms of this disease, individual optimal dosage with MDI has to be defined following repeated measurements of the airway obstruction so as to achieve the best possible bronchodilatation.

Does a family history of atopy influence lung function at follow‐up of infants born prematurely?

The aim of this study was to assess whether a family history of atopy influenced lung function at follow-up of infants born prematurely. Analysis was made of thoracic gas volume and airways resistance measurements performed at 1 year of age in 86 infants born at a median gestational age of 29 weeks. These measurements had been made during a prospective follow-up study. The 30 infants with a family history of atopy were found to have a higher airways resistance (median 35 cmH2O/l/s) than the 56 infants without such a family history (median 30 cmH2O/l/s) (p < 0.05). However, when the results from 18 infants with a family history of atopy were compared with 18 controls who were matched for requirement for neonatal ventilation, parental smoking and were within at least 1 week of gestational age, no significant difference in airways resistance was found between the two groups. Multiple regression analysis demonstrated that gestational age and birth weight explained the apparent relationship between a family history of atopy and an elevated airways resistance at follow-up.

Lung volume measurements in wheezy infants: comparison of plethysmography and gas dilution

The accuracy both of plethysmographic measurements of thoracic gas volume (TGV) and determinations of functional residual capacity (FRC) by gas dilution techniques in infants with obstructive lung disease is subject to continued dispute. We studied 25 wheezy infants and compared TGV derived from end-expiratory airway occlusions (TGVEE), corrected TGV after end-inspiratory airway occlusions (TGVEI), and FRC determined by nitrogen wash-out (FRCN2). Group mean TGVEE and TGVEI differed significantly (25.8 +/- 8.4 versus 24.6 +/- 7.1 ml.kg-1). TGVEE and FRCN2 did not differ significantly. TGVEE and TGVEI, as well as TGVEE and FRCN2, and TGVEI and FRCN2 data, respectively, showed lack of agreement. Based on 95% confidence intervals, calculated from TGVEE data, 14 of the 25 infants showed a significantly higher TGVEI than TGVEE; only one patient had a significantly lower TGVEI. Compared to FRCN1 data, TGVEE and TGVEI measurements yielded lower values in at least one third of our patients. The present study illustrates, that there is no gold standard for the measurement of lung volume in infants with airway obstruction.

Measurement of thoracic gas volume in patients born prematurely: Should occlusion be made at end‐inspiration or end‐expiration?

It has been suggested that in infants born at term thoracic gas volume (TGV) may be more accurately estimated in a plethysmograph if end-inspiratory (TGVl) rather than end-expiratory (TGVE) occlusions are used. The aim of this study was to assess whether the timing of occlusion affected TGV results in patients born very prematurely. Fifteen children with a median gestational age of 28 weeks (range 23-34) and postnatal age of 10 months (range 6-24) were studied. Measurements of TGV and airway resistance (R(aw)) were made in a whole body plethysmograph after sedation with chloral hydrate. End-expiratory and end-inspiratory occlusions were performed randomly in each subject. Overall, TGVl was significantly lower than TGVE (median, TGVl 233 mL; range, 130-498. Median TGVE 250 mL; range, 132-604; P < 0.05; 95% confidence intervals for the difference, 4-50 mL). In 13 infants, TGVl was lower than TGVE; the remaining two patients did not differ significantly from the rest of the group and neither had neonatal chronic lung disease. In only five infants did TGVl lie below the 95% confidence intervals of TGVE, however, two-way analysis of variance with replicated measurements showed a significant difference between TGVE and TGVl (P < 0.05). The median R(aw) was 55 cmH2O/L/s (range, 36-71). A significant positive correlation was found between R(aw) and TGVE-TGVl (r2 = 0.5, P < 0.01). We conclude that in children born very prematurely and with high R(aw) occlusion at end-expiration rather than end-inspiration yields higher TGV results at follow-up.

180 LUNG VOLUMES AND LUNG MECHANICS IN NEONATES AND INFANTS WITH CONGENITAL DIAPHRAGMATIC HERNIA (CDH)

Neonates with CDH are exceptionally vulnerable to complications of artificial ventilation such as pneumothorax and bronchopulmonary dysplasia (BPD) because of their reduced lung volumes, demonstrable by measurement of functional residual capacity (FRC) and thoracic gas volume (TGV). Methods: Serial lung function tests were performed in three infants with CDH, including single occlusion tests, nitrogen washout measurement of FRC (SensorMedics 2600, USA), and determination of TGV (Jaeger Baby-Bodyplethysmograph). Results: Two neonates with right-sided CDH showed appropriate increase of initially low respiratory system compliance, FRC, and TGV shortly after operation. The remaining infant had left-sided CDH and developed severe BPD accompanied by extremely low compliance and FRC, and elevated resistance and TGV values. Conclusions: Serial measurement of both FRC and TGV permits early detection of lung overinflation in infants with CDH threatened by BPD. Our results are consistent with reports indicating a better prognosis for right-sided CDH in regard of lung function. *) supported by BMFT-project “Risikoneugeborenes”

Epidural Anesthesia and Intrathoracic Blood Volume

To investigate how epidural anesthesia changes intrathoracic gas volume, high epidural anesthesia was administered to five pentobarbital-anesthetized dogs lying supine, and the total intrathoracic volume at end-expiration was measured with a high-speed three-dimensional x-ray scanner. The amount of gas in the lungs at end-expiration [the functional residual capacity (FRC)] was measured with a nitrogen washout technique, and the intrathoracic tissue volume, including the intrathoracic blood volume, was calculated as the difference between intrathoracic volume at end-expiration and FRC. High epidural anesthesia with the local anesthetic etidocaine to a T-1 myotomal level significantly (P < 0.05) increased intrathoracic volume at end-expiration [76 +/- 35 mL (M +/- SD)] by significantly increasing both intrathoracic tissue volume (33 +/- 15 mL) and FRC (43 +/- 26 mL). Increases in intrathoracic tissue volume were probably caused by increases in intrathoracic blood volume. We conclude that increases in FRC caused by epidural anesthesia in anesthetized dogs lying supine may be minimized by a concurrent increase in intrathoracic blood volume. These results suggest that measurements of thoracic gas volume alone may be insufficient to describe chest wall responses to epidural anesthesia.