Deadspace estimation from CO2 versus molar mass measurements in infants

BACKGROUND

Estimation of respiratory deadspace is often based on the CO2 expirogram, however presence of the CO2 sensor increases equipment deadspace, which in turn influences breathing pattern and calculation of lung volume. In addition, it is necessary to correct for the delay between the sensor and flow signals. We propose a new method for estimation of effective deadspace using the molar mass (MM) signal from an ultrasonic flowmeter device, which does not require delay correction. We hypothesize that this estimation is correlated with that calculated from the CO2 signal using the Fowler method.

METHODS

Breath-by-breath CO2, MM and flow measurements were made in a group of 77 term-born healthy infants. Fowler deadspace (Vd,Fowler) was calculated after correcting for the flow-dependent delay in the CO2 signal. Deadspace estimated from the MM signal (Vd,MM) was defined as the volume passing through the flowhead between start of expiration and the 10% rise point in MM.

RESULTS

Correlation (r = 0.456, P < 0.0001) was found between Vd,MM and Vd,Fowler averaged over all measurements, with a mean difference of -1.4% (95% CI -4.1 to 1.3%). Vd,MM ranged from 6.6 to 11.4 ml between subjects, while Vd,Fowler ranged from 5.9 to 12.0 ml. Mean intra-measurement CV over 5-10 breaths was 7.8 +/- 5.6% for Vd,MM and 7.8 +/- 3.7% for Vd,Fowler. Mean intra-subject CV was 6.0 +/- 4.5% for Vd,MM and 8.3 +/- 5.9% for Vd,Fowler. Correcting for the CO2 signal delay resulted in a 12% difference (P = 0.022) in Vd,Fowler. Vd,MM could be obtained more frequently than Vd,Fowler in infants with CLD, with a high variability.

CONCLUSIONS

Use of the MM signal provides a feasible estimate of Fowler deadspace without introducing additional equipment deadspace. The simple calculation without need for delay correction makes individual adjustment for deadspace in FRC measurements possible. This is especially important given the relative large range of deadspace seen in this homogeneous group of infants.

End-expiratory and tidal volumes measured in conscious mice using single projection x-ray images

The evaluation of airway resistance (R(aw)) in conscious mice requires both end-expiratory (V(e)) and tidal volumes (V(t)) (Lai-Fook SJ and Lai YL. J Appl Physiol 98: 2204-2218, 2005). In anesthetized BALB/c mice we measured lung area (A(L)) from ventral-to-dorsal x-ray images taken at FRC (V(e)) and after air inflation with 0.25 and 0.50 ml (DeltaV(L)). Total lung volume (V(L)) described by equation: V(L) = DeltaV(L) + V(FRC) = KA(L)(1.5) assumed uniform (isotropic) inflation. Total V(FRC) averaged 0.55 ml, consisting of 0.10 ml tissue, 0.21 ml blood and 0.24 ml air. K averaged 1.84. In conscious mice in a sealed box, we measured the peak-to-peak box pressure excursions (DeltaP(b)) and x-rays during several cycles. K was used to convert measured A(L)(1.5) to V(L) values. We calculated V(e) and V(t) from the plot of V(L) vs. cos(alpha - phi). Phase angle alpha was the minimum point of the P(b) cycle to the x-ray exposure. Phase difference between the P(b) and V(L) cycles (phi) was measured from DeltaP(b) values using both room- and body-temperature humidified box air. A similar analysis was used after aerosol exposures to bronchoconstrictor methacholine (Mch), except that phi depended also on increased R(aw). In conscious mice, V(e) (0.24 ml) doubled after Mch (50-125 mg/ml) aerosol exposure with constant V(t), frequency (f), DeltaP(b), and R(aw). In anesthetized mice, in addition to an increased V(e), repeated 100 mg/ml Mch exposures increased both DeltaP(b) and R(aw) and decreased f to apnea in 10 min. Thus conscious mice adapted to Mch by limiting R(aw), while anesthesia resulted in airway closure followed by diaphragm fatigue and failure.

Tracking lung tissue motion and expansion/compression with inverse consistent image registration and spirometry

Breathing motion is one of the major limiting factors for reducing dose and irradiation of normal tissue for conventional conformal radiotherapy. This paper describes a relationship between tracking lung motion using spirometry data and image registration of consecutive CT image volumes collected from a multislice CT scanner over multiple breathing periods. Temporal CT sequences from 5 individuals were analyzed in this study. The couch was moved from 11 to 14 different positions to image the entire lung. At each couch position, 15 image volumes were collected over approximately 3 breathing periods. It is assumed that the expansion and contraction of lung tissue can be modeled as an elastic material. Furthermore, it is assumed that the deformation of the lung is small over one-fifth of a breathing period and therefore the motion of the lung can be adequately modeled using a small deformation linear elastic model. The small deformation inverse consistent linear elastic image registration algorithm is therefore well suited for this problem and was used to register consecutive image scans. The pointwise expansion and compression of lung tissue was measured by computing the Jacobian of the transformations used to register the images. The logarithm of the Jacobian was computed so that expansion and compression of the lung were scaled equally. The log-Jacobian was computed at each voxel in the volume to produce a map of the local expansion and compression of the lung during the breathing period. These log-Jacobian images demonstrate that the lung does not expand uniformly during the breathing period, but rather expands and contracts locally at different rates during inhalation and exhalation. The log-Jacobian numbers were averaged over a cross section of the lung to produce an estimate of the average expansion or compression from one time point to the next and compared to the air flow rate measured by spirometry. In four out of five individuals, the average log-Jacobian value and the air flow rate correlated well (R2 = 0.858 on average for the entire lung). The correlation for the fifth individual was not as good (R2 = 0.377 on average for the entire lung) and can be explained by the small variation in tidal volume for this individual. The correlation of the average log-Jacobian value and the air flow rate for images near the diaphragm correlated well in all five individuals (R2 = 0.943 on average). These preliminary results indicate a strong correlation between the expansion/compression of the lung measured by image registration and the air flow rate measured by spirometry. Predicting the location, motion, and compression/expansion of the tumor and normal tissue using image registration and spirometry could have many important benefits for radiotherapy treatment. These benefits include reducing radiation dose to normal tissue, maximizing dose to the tumor, improving patient care, reducing treatment cost, and increasing patient throughput.

Helium–oxygen ventilation in the presence of expiratory flow-limitation: A model study

A comparison between air and heliox (80% helium-20% oxygen) ventilation was performed using a mathematical, non-linear dynamic, morphometric model of the respiratory system. Different obstructive conditions, all causing expiratory flow limitation (EFL), were simulated during mechanical ventilation to evaluate and interpret the effects of heliox on tidal EFL and dynamic hyperinflation. Relative to air ventilation, intrinsic positive end-expiratory pressure did not change with heliox if the obstruction was limited to the peripheral airways, i.e. beyond the seventh generation. When central airways were also involved, heliox reduced dynamic hyperinflation (DH) if the flow-limiting segment remained in the fourth to seventh airway generation during the whole expiration, but produced only minor effects if, depending on the contribution of peripheral to total apparent airway resistance, the flow-limiting segment moved eventually to the peripheral airways. In no case did heliox abolish EFL occurring with air ventilation, indicating that any increase in driving pressure would be without effect on DH. Hence, to the extent that chronic obstructive pulmonary disease (COPD) affects primarily the peripheral airways, and causes EFL through the same mechanisms operating in the model, heliox administration should not be expected to appreciably reduce DH in the majority of COPD patients who are flow-limited at rest.

Registration-derived estimates of local lung expansion as surrogates for regional ventilation

The main function of the respiratory system is gas exchange. Since many disease or injury conditions can cause biomechanical or material property changes that can alter lung function, there is a great interest in measuring regional lung ventilation. We describe a registration-based technique for estimating local lung expansion from multiple respiratory-gated CT images of the thorax. The degree of regional lung expansion is measured using the Jacobian of the registration displacement field. We compare lung expansion estimated across five pressure changes to a xenon CT based measure of specific ventilation, and have shown good agreement (linear regression, r2 = 0.89 during gas wash-in) in one animal.

[Physiological function of the lung; fundamentals on inspiratory capacity]

Inspiratory capacity (IC) is recently highlighted in the clinical field of chronic obstructive pulmonary disease (COPD). Generally, IC is positively associated with exercise capacity and survival prognosis. Since chest surgery generally results in restive change in vital capacity, the decrease in IC potentially causes dysfunction of exercise capacity and dyspnea on exertion, which frequently results in disuse syndrome and deterioration in the quality of life. Although IC seems to be less appreciated, it has more important clinical implementation in terms of exercise capacity and dyspnea than one second forced expiratory volume (FEV1.0). In this aspect, surgical strategies to prevent unnecessary decrease in IC should be cared. Also, appropriate treatments such as chest physiotherapy or exercise training are needed to increase IC for the post-operative patients.

Two methods of setting positive end-expiratory pressure in acute lung injury: an experimental computed tomography volumetric study

This study was conducted to observe effects of two methods of setting positive end-expiratory pressure (PEEP) based on the pressure-volume (PV) curve. After lung injury was induced by oleic acid in six mongrel adult dogs, the inflation PV curve was traced and the lower inflection point (LIP) was measured. The 'PEEP(INF)' was defined as LIP+2 cmH(2)O. After recruitment maneuver to move the lung physiology to the deflation limb of PV curve, decremental PEEP was applied. The lowest level of PEEP that did not result in a significant drop in PaO(2) was defined as the 'PEEP(DEF)'. Arterial blood gases, lung mechanics, hemodynamics, and lung volumes (measured on computed tomography during end-expiratory pause) were measured at PEEP of 0 cmH(2)O, PEEP(INF) and PEEP(DEF) sequentially. The median PEEP(INF) was 13.4 cm H(2)O (interquartile range, 12.5-14.3) and median PEEP(DEF) was 12.0 cm H(2)O (10.0-16.5) (p=0.813). PEEP(DEF) was associated with significantly higher PaO(2) and lung volumes, and significantly lower shunt fraction and cardiac index when compared to PEEP(INF) (p<0.05). Setting the PEEP based on the deflation limb of the PV curve was useful in improving oxygenation and lung volumes in a canine lung injury model.

Pressure-controlled versus volume-controlled ventilation during one-lung ventilation for thoracic surgery

BACKGROUND

Pressure-controlled ventilation (PCV) has been suggested as a tool to improve oxygenation during one-lung ventilation (OLV) for patients undergoing thoracic surgery. In this study we investigated whether PCV results in improved arterial oxygenation compared with volume-controlled ventilation (VCV) during OLV.

METHODS

Fifty-eight patients with good preoperative pulmonary function scheduled for thoracic surgery were prospectively randomized into two groups. Those in group A underwent OLV initially with VCV for 30 min followed by PCV for a similar period of time. Those in group B underwent OLV initially with PCV for 30 min followed by VCV for a similar duration. Airway pressures and arterial blood gases were obtained during OLV at the end of each ventilatory mode.

RESULTS

There were no differences during OLV in arterial oxygenation between VCV (Pao2, 206.1 +/- 62.4 mm Hg) and PCV (Pao2, 202.1 +/- 56.4 mm Hg; P = 0.534). Peak airway pressure was lower with PCV than with VCV (24.43 +/- 3.42 cm H2O vs. 34.16 +/- 5.21 cm H2O; P < 0.001).

CONCLUSIONS

The use of PCV during OLV does not lead to improved oxygenation during OLV compared with VCV for patients with good preoperative pulmonary function, but PCV did lead to lower peak airway pressures. Further study is needed for patients with severe obstructive or restrictive pulmonary disease.

Fetal lung volume: three-dimensional ultrasonography compared with magnetic resonance imaging

OBJECTIVES

An accurate and reliable method for measuring fetal lung volumes would be helpful in predicting the outcome in cases with suspected impaired lung growth. Recent studies show that it is possible to obtain fetal lung volume estimations with magnetic resonance imaging (MRI) and three-dimensional (3D) ultrasonography. The purpose of this study was to assess the agreement of lung volumes measured with 3D ultrasonography and MRI in uncomplicated pregnancies.

METHODS

This was a prospective study in which MRI and 3D ultrasonography examinations were conducted on the same day to measure the fetal lung volumes of 10 women with uncomplicated pregnancies. Intraclass correlation was used to evaluate the agreement between fetal lung volume measurements obtained by MRI and 3D ultrasonography. A proportionate Bland-Altman plot was constructed.

RESULTS

The intraclass correlation coefficient between MRI and 3D ultrasonography measurements for the right lung was 0.92 (95% CI 0.71-0.98) and for the left lung was 0.95 (95% CI 0.82-0.99). The proportionate limits of agreement between the methods were for the right lung -32.57% to 20.03% and for the left lung -21.26% to 17.13%.

CONCLUSIONS

There is good agreement between lung volumes measured by MRI and those measured by 3D ultrasonography.

Application of an optical flow method to inspiratory and expiratory lung MDCT to assess regional air trapping: a feasibility study

OBJECTIVE

We describe the application of an optical flow method to inspiratory and expiratory high-resolution volumetric lung MDCT for the assessment of regional air trapping.

CONCLUSION

Qualitative and quantitative assessment of regional air trapping is feasible using an optical flow method to align volumetric MDCT data sets.

Reliability and validity of the lung volume measurement made by the BOD POD body composition system

The BOD POD Body Composition System uses air-displacement plethysmography to measure body volume. To correct the body volume measurement for the subject's lung volume, the BOD POD utilizes pulmonary plethysmography to measure functional residual capacity (FRC) at mid-exhalation as that is the subject's lung volume during the body volume measurement. Normally, FRC is measured at end-exhalation. The BOD POD FRC measurement can be corrected to an end-exhalation volume by subtracting approximately one-half of the measured tidal volume. Our purpose was to determine the reliability and validity of the BOD POD FRC measurement at end-exhalation. Ninety-two healthy adults (half female) underwent duplicate FRC measurements by the BOD POD and one FRC measurement by a traditional gas dilution technique. The latter method was used as the reference method for the validity component of the study. The order of the FRC measurements by the two methods was randomized. The test-retest correlation coefficients for the duplicate BOD POD FRC measurements for the male and female subjects were 0.966 and 0.948, respectively. The mean differences between the BOD POD FRC trial #1 measurement and gas dilution FRC measurement for the male and female subjects were -32 and -23 ml, respectively. Neither difference was statistically significant. The correlation coefficients for these two measurements in the male and female subjects were 0.925 and 0.917, respectively. Based on these results, we conclude that the BOD POD FRC measurement in healthy males and females is both reliable and valid.

Comparative study of four sigmoid models of pressure-volume curve in acute lung injury

Background

The pressure-volume curve of the respiratory system is a tool to monitor and set mechanical ventilation in acute lung injury. Mathematical models of the static pressure-volume curve of the respiratory system have been proposed to overcome the inter- and intra-observer variability derived from eye-fitting. However, different models have not been compared.

Methods

The goodness-of-fit and the values of derived parameters (upper asymptote, maximum compliance and points of maximum curvature) in four sigmoid models were compared, using pressure-volume data from 30 mechanically ventilated patients during the early phase of acute lung injury.

Results

All models showed an excellent goodness-of-fit (R² always above 0.92). There were significant differences between the models in the parameters derived from the inspiratory limb, but not in those derived from the expiratory limb of the curve. The within-case standard deviations of the pressures at the points of maximum curvature ranged from 2.33 to 6.08 cmH₂O.

Conclusion

There are substantial variabilities in relevant parameters obtained from the four different models of the static pressure-volume curve of the respiratory system.

Factors of thoracic cage deformity that affect pulmonary function in adolescent idiopathic thoracic scoliosis

STUDY DESIGN

This clinical study examined the association between pulmonary function and thoracic cage deformities in scoliosis.

OBJECTIVE

To determine the factors in spinal and thoracic cage deformities that affect pulmonary function in scoliosis.

SUMMARY OF BACKGROUND DATA

Pulmonary function in scoliosis has generally been evaluated in terms of lateral spinal curvature. No previous report has evaluated changes in pulmonary function taking into consideration measurements reflecting not only spinal curvature but also thoracic cage deformities, although scoliosis is a three-dimensional deformity.

METHODS

A total of 109 patients (mean age, 14.2 years) with adolescent idiopathic right thoracic scoliosis (mean lateral spinal curvature, 37.7 degrees) had full assessment of pulmonary function and a radiographic evaluation from radiographs of the whole spine, Moiré topography, and thoracic computed tomography.

RESULTS

Multiple regression analysis (stepwise method) was performed at each vertebral level from T3-T12 to identify the factor that most strongly affects %VC. The correlation coefficient was highest at T9 and next highest at T8, with values of 0.641 (r2 = 0.411, P < 0.0001) and 0.625 (r2 = 0.390, P < 0.0001), respectively. At T9, multiple regression analysis showed that the sagittal diameter of the thoracic cage and the total lung area were identified as factors that most strongly affect %VC. Similarly, the sagittal diameter of the thoracic cage and the rotation angle to the sagittal plane were identified at T8.

CONCLUSIONS

The factors that reduced %VC were the sagittal diameter of the thoracic cage, total lung area and vertebral rotation at the T8 and T9 levels.

[Optoelectronic plethysmography -- a new technic to measure changes of chest wall volume]

Optoelectronic plethysmography (OEP) is a new, noninvasive diagnostic tool that allows to measure changes of chest wall volume and its three compartments. Mathematical basis of the method, elements of the system and possibilities of combining OEP with other recording techniques used in pneumonology were discussed in details. OEP applications, results of the latest investigations and development perspectives were briefly presented.

Major differences in the pulmonary circulation between birds and mammals

The lungs of domestic chickens were perfused with blood or dextran/saline and the pulmonary artery pressure (P(a)) and venous pressure (P(v)) were varied in relation to air capillary pressure (P(A)). In Zone 3 conditions, pulmonary vascular resistance (PVR) was virtually unchanged with increases in either P(a) or P(v). This is very different behavior from mammals where the same interventions greatly reduce PVR. In Zone 2 conditions blood flow was essentially independent of P(v) as in mammalian lungs but all the capillaries appeared to be open, apparently incompatible with a Starling resistor mechanism. In Zone 1 the capillaries were open even when P(A) exceeded P(a) by over 30 cm H(2)O which is very different behavior from that of the mammalian lung. We conclude that the air capillaries that surround the blood capillaries provide rigid support in both compression and expansion of the vessels. The work suggests a pathogenesis for pulmonary hypertension syndrome in chickens which costs the broiler industry $1 billion per year.

Fetal Body Volume: Use at MR Imaging to Quantify Relative Lung Volume in Fetuses Suspected of Having Pulmonary Hypoplasia

PURPOSE

To retrospectively determine an algorithm based on fetal body volume (FBV) by using magnetic resonance (MR) imaging to calculate relative lung volume in fetuses with normally developed lungs and prospectively assess the use of this algorithm in predicting pulmonary hypoplasia in the late second and early third trimesters for fetuses at risk for pulmonary hypoplasia.

MATERIALS AND METHODS

Oral informed consent was obtained for the prospective component of this ethics committee-approved study. MR imaging lung volumetry was performed in 36 fetuses with normally developed lungs between 18 and 39 weeks gestational age by using T2-weighted single-shot fast spin-echo imaging in fetal transverse and sagittal planes. Findings were then correlated with biometric variables and gestational age. The best-performing algorithm was applied to 37 fetuses (between 18 and 29 weeks gestational age) at risk for pulmonary hypoplasia to determine observed-expected lung volume ratio. This group was stratified according to pregnancy management, and observed-expected ratios were correlated with outcome. In fetuses with isolated congenital diaphragmatic hernia (CDH) (n = 19), observed-expected ratio was correlated with lung-head ratio, neonatal survival in pregnancies managed expectantly (n = 13), and/or lung-body weight ratio at necropsy (n = 9). For that purpose, linear regression correlation was used with the Pearson correlation coefficient; P < .05 was considered to indicate a significant difference.

RESULTS

Total fetal lung volume correlated best with total FBV (r = 0.96, P < .05). Observed-expected ratio based on FBV correlated with lung-head ratio in patients with CDH (r = 0.71, P < .001) and with lung-body weight ratio at necropsy (r = 0.68, P < .05) and could be used to help predict neonatal survival.

CONCLUSION

FBV measured with MR imaging can be used as a single parameter in an algorithm and showed closest correlation with normal total fetal lung volume. In the transition from second to third trimester, this algorithm enabled calculation of the observed-expected ratio and prediction of outcome in fetuses at risk for pulmonary hypoplasia.

Quantification of bleomycin-induced murine lung damage in vivo with micro-computed tomography

RATIONALE AND OBJECTIVES

We explored noninvasive, in vivo cone-beam microcomputed tomography (micro-CT) to visualize and quantify fibrotic and inflammatory damage over the entire lung volume of mice.

MATERIALS AND METHODS

We used bleomycin to induce pulmonary damage in vivo and compared the results from micro-CT with histologic measurements. Ten C57BL/6 mice were given 5 U/kg bleomycin intratracheally. Seven surviving mice were scanned with micro-CT before administration of bleomycin, and again before sacrifice. The resulting images were analyzed for lung volume measurements. After the final scan, all lungs were examined histologically and pulmonary damage was quantified. Damaged lung tissue regions were matched between micro-CT images and histologic sections for each mouse.

RESULTS

The percent lung damage calculated from micro-CT and histology were correlated (r(2) = 0.49, r = 0.64 with P = 0.12), and the means of their respective distributions were not different (P > 0.05).

CONCLUSION

This study shows that micro-CT is a promising alternative to predicting lung damage caused by bleomycin. CT image volumes of the thorax allow for global tissue sampling, which may be useful when following nonuniform lung damage that can occur from intratracheal administration of bleomycin.

Comparison between total lung capacity and residual volume values obtained by pletysmography and single breath methods with methane

We analyzed pulmonary function tests of twenty asthmatic patients from Gaffrée e Guinle University Hospital, classified according to Brazilian Guidelines for Asthma (2002), similar to GINA, into mild persistent or moderate (9) or severe (11) asthma. We obtained parameters from spirometry, plethysmograph (PL) and single breath technique for diffusion capacity (SB), with methane. Total lung capacity and residual volume were called TLC(PL) and RV(PL) when measured by pletysmography and TLC(SB) and RV(SB) when determined by single breath test. There were 13 women and 7 men with mean age of 47.6 years. The pulmonary dysfunction degree to FEV1/FVC was 58.8% with CI95=53.9 to 63.6. The mean values in litres for TLC(PL) (5.94) and RV(PL) (2.55) were significantly higher than for TLC(SB) (4.73) and RV(SB) (1.66). Multiple regression equations were determined for TLC(PL) e RV(PL) using only single breath values, TLC(SB) or RV(SB), and spirographic para- meters, with significant regression coefficients. However, the inclusion of spirometric parameters, except for FVC, did not improve the predicted capacity for the equations. Considering only the TLC(SB), r(2)=0.79, the equation is: TLC(PL)=(TLC(SB) *1.025)+1.088, with EPE=0.64. The regression for RV(PL), r(2) =0.23, is: RV(PL)=(RV(SB) *0.9268)+1.012. The results obtained after bronchodilation with 400 mcg of salbutamol did not improve the regression. We concluded that the SB technique did not obtain the same results as pletysmography for TLC and RV, but for TLC this difference can be predicted.

Fetal lung volume in congenital diaphragmatic hernia

In a retrospective study of 22 neonates with congenital diaphragmatic hernia, fetal lung volume (FLV) measured by magnetic resonance imaging was associated with survival; the best FLV ratio cut-off to predict mortality was 30% of expected FLV. This study supports a correlation between FLV and the chances of survival.

Do Changes in Lung Function Predict High-Altitude Pulmonary Edema at an Early Stage?

PURPOSE

Ascent to high altitude is associated with alterations in lung function. The mechanisms of these changes and whether they reflect early stages of high-altitude pulmonary edema (HAPE) has been debated. Therefore, we investigated the time course of pulmonary function in relation to hemodynamics and clinical symptoms in mountaineers ascending rapidly to high altitude.

METHODS

In 26 unacclimatized subjects we assessed spirometry, single-breath nitrogen washout, diffusing capacity (DLCO), and Doppler echocardiography in Zurich, 490 m, after climbing within 24 h to Monte Rosa, 4559 m, and after one night at 4559 m.

RESULTS

Mean (+/- SD) FVC fell from 103 +/- 9% predicted in Zurich to 96 +/- 10% predicted at 4559 m, FEV1/FVC increased from 0.82 +/- 0.06 to 0.84 +/- 0.08, and closing volume increased from 0.35 +/- 0.14 to 0.44 +/- 0.11 L above residual volume (P < 0.05, all changes). On the following day at 4559 m, closing volume remained elevated in 9 of 21 subjects who had a lower DLCO but similar pulmonary artery systolic pressures compared with the remaining 12 subjects (40 +/- 8 vs 43 +/- 7 mm Hg, P = NS). None of the subjects had overt HAPE.

CONCLUSION

We conclude that changes in pulmonary function after rapid ascent to high altitude were consistent with interstitial fluid accumulation, but they were not related to changes in pulmonary artery pressure. Individual lung function responses to high-altitude exposure varied largely and did not predict subsequent HAPE.

Plethysmographic estimation of thoracic gas volume in apneic mice

Electrical stimulation of intercostal muscles was employed to measure thoracic gas volume (TGV) during airway occlusion in the absence of respiratory effort at different levels of lung inflation. In 15 tracheostomized and mechanically ventilated CBA/Ca mice, the value of TGV obtained from the spontaneous breathing effort available in the early phase of the experiments (TGVsp) was compared with those resulting from muscle stimulation (TGVst) at transrespiratory pressures of 0, 10, and 20 cmH2O. A very strong correlation ( r2 = 0.97) was found, although with a systematically (∼16%) higher estimation of TGVst relative to TGVsp, attributable to the different durations of the stimulated (∼50 ms) and spontaneous (∼200 ms) contractions. Measurements of TGVst before and after injections of 0.2, 0.4, and 0.6 ml of nitrogen into the lungs in six mice resulted in good agreement between the change in TGVst and the injected volume ( r2 = 0.98). In four mice, TGVsp and TGVst were compared at end expiration with air or a helium-oxygen mixture to confirm the validity of isothermal compression in the alveolar gas. The TGVst values measured at zero transrespiratory pressure in all CBA/Ca mice [0.29 ± 0.05 (SD) ml] and in C57BL/6 ( N = 6; 0.34 ± 0.08 ml) and BALB/c ( N = 6; 0.28 ± 0.06 ml) mice were in agreement with functional residual capacity values from previous studies in which different techniques were used. This method is particularly useful when TGV is to be determined in the absence of breathing activity, when it must be known at any level of lung inflation or under non-steady-state conditions, such as during pharmaceutical interventions.

Fetal Lung Volume Measurements: Determination with MR Imaging—Effect of Various Factors

PURPOSE

To retrospectively determine the effect of gestational age (GA), imaging plane, section thickness, and inter- and intraobserver variability on fetal lung volume (FLV) measurements obtained with magnetic resonance (MR) imaging in a cohort of fetuses without thoracic abnormalities.

MATERIALS AND METHODS

Institutional review board approval was obtained. Informed consent for this retrospective cohort study was waived, and the conduct of this study was HIPAA compliant. FLV was measured in 30 fetuses (GA, 17-36 weeks) referred for MR imaging for indications other than pulmonary abnormalities. Measurements were made on single-shot fast spin-echo images by tracing free-form regions of interest on individual consecutive sections in the transverse, sagittal, and coronal planes. Measurements were performed twice by two observers independently. Correlations between FLV and GA, imaging plane, and section thickness were assessed, as were intra- and interobserver variability. Time to perform FLV was assessed in a subset of fetuses.

RESULTS

Total FLV ranged from 2 to 110 mL. Mixed-effects regression model showed significant quadratic trend in FLV with increasing GA, with comparable strength of correlation (r = 0.89-0.91) in the three imaging planes of measurement. Intraobserver agreement was good in all three planes (r = 0.65-0.83) and was highest in the transverse plane. Interobserver agreement was good in all three planes (r = 0.68-0.76). FLV showed no significant dependence on section thickness (P = .23) or imaging plane (P = .82). Mean time to obtain FLV measurements ranged from 48 seconds at GA of 21 weeks to 77 seconds at GA of 29-30 weeks.

CONCLUSION

GA-based FLV measurements obtained with MR images are independent of section thickness and imaging plane and can be performed with good inter- and intraobserver agreement in less than 2 minutes.