Measurement of absolute lung volumes by imaging techniques

A reference equation for lung volume on computed tomography in Japanese middle-aged and elderly adults

BACKGROUND

Effective use of lung volume data measured on computed tomography (CT) requires reference values for specific populations. This study examined whether an equation previously generated for multiple ethnic groups in the United States, including Asians predominantly composed of Chinese people, in the Multi-Ethnic Study of Atherosclerosis (MESA) could be used for Japanese people and, if necessary, to optimize this equation. Moreover, the equation was used to characterize patients with chronic obstructive pulmonary disease (COPD) and lung hyperexpansion.

METHODS

This study included a lung cancer screening CT cohort of asymptomatic never smokers aged ≥40 years from two institutions (n = 364 and 419) to validate and optimize the MESA equation and a COPD cohort (n = 199) to test its applicability.

RESULTS

In all asymptomatic never smokers, the variance explained by the predicted values (R2) based on the original MESA equation was 0.60. The original equation was optimized to minimize the root mean squared error (RMSE) by adjusting the scaling factor but not the age, sex, height, or body mass index terms of the equation. The RMSE changed from 714 ml in the original equation to 637 ml in the optimized equation. In the COPD cohort, lung hyperexpansion, defined based on the 95th percentile of the ratio of measured lung volume to predicted lung volume in never smokers (122 %), was observed in 60 (30 %) patients and was associated with centrilobular emphysema and air trapping on inspiratory/expiratory CT.

CONCLUSIONS

The MESA equation was optimized for Japanese middle-aged and elderly adults.

Deep Learning for Estimating Lung Capacity on Chest Radiographs Predicts Survival in Idiopathic Pulmonary Fibrosis

Background Total lung capacity (TLC) has been estimated with use of chest radiographs based on time-consuming methods, such as planimetric techniques and manual measurements. Purpose To develop a deep learning-based, multidimensional model capable of estimating TLC from chest radiographs and demographic variables and validate its technical performance and clinical utility with use of multicenter retrospective data sets. Materials and Methods A deep learning model was pretrained with use of 50 000 consecutive chest CT scans performed between January 2015 and June 2017. The model was fine-tuned on 3523 pairs of posteroanterior chest radiographs and plethysmographic TLC measurements from consecutive patients who underwent pulmonary function testing on the same day. The model was tested with multicenter retrospective data sets from two tertiary care centers and one community hospital, including (a) an external test set 1 (n = 207) and external test set 2 (n = 216) for technical performance and (b) patients with idiopathic pulmonary fibrosis (n = 217) for clinical utility. Technical performance was evaluated with use of various agreement measures, and clinical utility was assessed in terms of the prognostic value for overall survival with use of multivariable Cox regression. Results The mean absolute difference and within-subject SD between observed and estimated TLC were 0.69 L and 0.73 L, respectively, in the external test set 1 (161 men; median age, 70 years [IQR: 61-76 years]) and 0.52 L and 0.53 L in the external test set 2 (113 men; median age, 63 years [IQR: 51-70 years]). In patients with idiopathic pulmonary fibrosis (145 men; median age, 67 years [IQR: 61-73 years]), greater estimated TLC percentage was associated with lower mortality risk (adjusted hazard ratio, 0.97 per percent; 95% CI: 0.95, 0.98; P < .001). Conclusion A fully automatic, deep learning-based model estimated total lung capacity from chest radiographs, and the model predicted survival in idiopathic pulmonary fibrosis. © RSNA, 2022 Online supplemental material is available for this article. See also the editorial by Sorkness in this issue.

Prediction of forced vital capacity with dynamic chest radiography in interstitial lung disease

PURPOSE

The pulmonary function test (PFT) has played an essential role in diagnosing and managing interstitial lung disease (ILD) but has its contraindications and difficult conditions to perform. Therefore, the present study aimed to evaluate dynamic chest radiography (DCR) ability to predict forced vital capacity (FVC) and other PFT parameters of ILD patients.

METHOD

The prospective observational study included 97 patients who underwent DCR at Tenri Hospital (Tenri, Japan) between June 2019 and April 2020. Twenty-five patients with stable disease status underwent DCR twice to evaluate test-retest reliability using the intraclass correlation coefficient. From the lung field areas measured by DCR, lung volumes at maximum inspiration (V.ins) and expiration (V.exp) were estimated. Correlation coefficients between the measured values of DCR and PFT parameters were calculated. Multilinear models for predicting FVC and other PFT parameters were developed.

RESULTS

Intraclass correlation coefficients between first and second measurements of V.ins and V.exp were 0.94 (95% CI: 0.89-0.97, p < 0.001) and 0.88 (95% CI: 0.78-0.94, p < 0.001), respectively. The correlation coefficient between V.ins and FVC was 0.86 (95% CI: 0.79-0.90, p < 0.001). A multilinear model for predicting FVC was developed using V.ins, V.exp, age, sex, and body mass index as predictor variables, wherein the adjusted coefficient of determination was 0.814.

CONCLUSIONS

Lung volumes measured by DCR correlated with the lung function of ILD patients. Prediction models with high predictive power and internal validity were developed, suggesting that DCR can predict FVC and other PFT parameters of ILD patients.

Quantifying lung and diaphragm morphology using radiographs in normative pediatric subjects, and predicting CT-derived lung volume

OBJECTIVE

To quantify the effect of age on two-dimensional (2D) radiographic lung and diaphragm morphology and determine if 2D radiographic lung measurements can be used to estimate computer tomography (CT)-derived lung volume in normative pediatric subjects.

MATERIALS AND METHODS

Digitally reconstructed radiographs (DRRs) were created using retrospective chest CT scans from 77 pediatric male and female subjects aged birth to 19 years. 2D lung and diaphragm measurements were made on the DRRs using custom MATLAB code, and Spearman correlations and exponential regression equations were used to relate 2D measurements with age. In addition, 3D lung volumes were segmented using CT scans, and power regression equations were fitted to predict each lung's CT-derived volume from 2D lung measurements. The coefficient of determination (R² ) and standard error of the estimate (SEE) were used to assess the precision of the predictive equations with p < .05 indicating statistical significance.

RESULTS

All 2D radiographic lung and diaphragm measurements showed statistically significant positive correlations with age (p < .01), including lung major axis (Spearman rho ≥  0.90). Precise estimations of CT-derived lung volumes can be made using 2D lung measurements (R²  ≥ 0.95), including lung major axis (R²  ≥ 0.97).

INTERPRETATIONS

The reported pediatric age-specific reference data on 2D lung and diaphragm morphology and growth rates could be clinically used to identify lung and diaphragm pathologies during chest X-ray evaluations. The simple, precise, and clinically adaptable radiographic method for estimating CT-derived lung volumes may be used when pulmonary function tests are not readily available or difficult to perform.

Projected lung areas using dynamic X-ray (DXR)

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The right projected lung area (PLA) was significantly larger than left one.

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PLA had correlation with height, weight, BMI, vital capacity (VC), and forced expiratory volume in one second (FEV₁).

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Multivariate analysis showed that body mass index (BMI), sex and VC were considered independent correlation factors, respectively.

Background

Dynamic X-ray (DXR) provides images of multiple phases of breath with less radiation exposure than CT. The exact images at end-inspiratory or end-expiratory phases can be chosen accurately.

Purpose

To investigate the correlation of the projected lung area (PLA) by dynamic chest X-ray with pulmonary functions.

Material and Methods

One hundred sixty-two healthy volunteers who received medical check-ups for health screening were included in this study. All subjects underwent DXR in both posteroanterior (PA) and lateral views and pulmonary function tests on the same day. All the volunteers took several tidal breaths before one forced breath as instructed. The outlines of lungs were contoured manually on the workstation with reference to the motion of diaphragm and the graph of pixel values. The PLAs were calculated automatically, and correlations with pulmonary functions and demographic data were analyzed statistically.

Results

The PLAs have correlation with physical characteristics, including height, weight and BMI, and pulmonary functions such as vital capacity (VC) and forced expiratory volume in one second (FEV₁). VC and FEV₁ revealed moderate correlation with the PLAs of PA view in forced inspiratory phase (VC: right, r = 0.65; left, r = 0.69. FEV1: right, r = 0.54; left, r = 0.59). Multivariate analysis showed that body mass index (BMI), sex and VC were considered independent correlation factors, respectively.

Conclusion

PLA showed statistically significant correlation with pulmonary functions. Our results indicate DXR has a possibility to serve as an alternate method for pulmonary function tests in subjects requiring contact inhibition including patients with suspected or confirmed covid-19.

Normal lung attenuation distribution and lung volume on computed tomography in a Chinese population

Backgroud and objectives: Although lung attenuation distribution and lung volume on computed tomography (CT) have been widely used in evaluating COPD and interstitial lung disease, there are only a few studies regarding the normal range of these indices, especially in Chinese subjects. We aimed to describe the normal range of lung attenuation distribution and lung volume based on CT.

Methods: Subjects with normal lung function and basically normal chest CT findings (derivation group) at Ruijin Hospital, Shanghai (from January 2010 to June 2014) were included according to inclusion and exclusion criteria. The range of the percentage of lung volume occupied by low attenuation areas (LAA%), percentile of the histogram of attenuation values (Perc n), and total lung volume were analyzed. Relationships of these measures with demographic variables were evaluated. Participants who underwent chest CT examination for disease screening and had basically normal CT findings served as an external validation group.

Results: The number of subjects in the derivation group and external validation groups were 564 and 1,787, respectively. Mean total lung volumes were 4,468±1,271 mL and 4,668±1,192 mL, and median LAA%(-950 HU) was 0.19 (0.03–0.43) and 0.17 (0.01–0.41), in the derivation and external validation groups, respectively. Reference equations for lung volume and attenuation distribution (LAA% using -1,000–210 HU, Perc 1 to Perc 98) were generated: Lung volume (mL) = -1.015 *10^4+605.3*Sex (1= male, 0= female)+92.61*Height (cm) –12.99*Weight (kg) ±1766; LAA% (-950 HU)=[0.2027+0.05926*Sex (1= male, 0= female) –4.111*10^-3*Weight (kg) +4.924*10^-3*Height (cm) +8.504*10^-4*Age]^7.341–0.05; Upper limit of normal range: [0.2027+0.05926*Sex-4.111*10^-3*Weight+4.924*10^-3*Height+8.504*10^-4*Age+0.1993]^7.341–0.05.

Conclusion: This large population-based retrospective study demonstrated the normal range of LAA%, Perc n, and total lung volume measured on CT scans among subjects with normal lung function and CT findings. Reference equations are provided.

Prediction of anatomical lung volume using planimetric measurements on chest radiographs

BACKGROUND

The anatomical lung volume is conventionally measured by computed tomography (CT). However, chest radiographs could be considered as an alternative method with low cost and low radiation.

PURPOSE

To predict the anatomical lung volume using planimetric measurements of chest radiographs.

MATERIAL AND METHODS

In total, 119 participants (M:F ratio = 66:53; age, 53.7 ± 9.6 years) who underwent chest CT for lung cancer screening were enrolled. The lung volume on CT was measured as a reference for the anatomical lung volume. To eliminate the bias from the degree of inspiration, virtual chest radiographs (posterior-anterior view and lateral view) were generated from the CT images using the thick multiplanar technique, and the lung area (cm(2)) was measured in the right (P), left (Q), and lateral (R) lungs according to the planimetric method. A regression equation predicting the anatomical lung volume from the planimetric measurements was generated. The correlation between the measured and estimated lung volumes was evaluated. The percentage error rate (%) was calculated and the equation was validated internally and externally.

RESULTS

The equation predicting the anatomical lung volume (mL) was 9.6*S-1367, where the summed lung area (S) was defined as (P + Q + R). The measured and estimated lung volumes were highly correlated (R = 0.941, P < 0.001). The absolute error rate was 5.7 ± 4.9%. The root mean square error of the equation was 290.2. The root mean square errors on internal and external validation were 300.4 and 267.0.

CONCLUSION

The anatomical lung volume may be feasibly and accurately predicted from planimetric measurements of chest radiographs.

New predictive equation for lung volume using chest computed tomography for size matching in lung transplantation

PURPOSE

Lung size matching is important in lung transplantation (LT). With advances in computed tomography (CT) technology, multidetector row CT can accurately measure the thoracic cage and lung volumes. The objective of this study was to generate a new regression equation using demographic data based on the measured CT lung volume in a healthy population to predict the CT lung volume of the donor in LT size matching.

MATERIALS AND METHODS

The medical records of healthy subjects who underwent chest CT scans to screen for lung cancer were retrospectively reviewed. CT lung volume was semi-automatically measured using a threshold-based auto-segmentation technique. New regression equations for CT lung volume were generated by multiple linear regression analysis using demographic data including height (H, cm), weight (W, kg), and age (A, years). The percentage error rate (%) of the equations were calculated as ([Estimated CT lung volume--Measured CT lung volume]/Measured CT lung volume × 100). A percentage error rate within ± 20% was considered acceptable.

RESULTS

A total of 141 men aged 27 to 55 years (mean, 46.7 ± 6.2 years) and 128 women aged 20 to 55 years (mean, 45.4 ± 7.2 years) were enrolled. The final regression equations for CT lung volume were (-5.890 + 0.067 H - 0.030 W + 0.020 A) in men and (-6.698 + 0.072 H - 0.024 W) in women. The mean absolute error rate was 10.9 ± 9.0% and 11.0 ± 8.5% in men and women, respectively. Percentage error rates were within ± 20% in 121 of 141 (85.8%) men and 113 of 128 (88.3%) women.

CONCLUSION

These equations could predict the CT lung volume of healthy subjects using demographic data. Using these equations, the predicted CT lung volume of donors could be matched to the measured CT lung volume of recipients in lung transplantation.

Automated lung volumetry from routine thoracic CT scans: how reliable is the result?

RATIONALE AND OBJECTIVES

Today, lung volumes can be easily calculated from chest computed tomography (CT) scans. Modern postprocessing workstations allow automated volume measurement of data sets acquired. However, there are challenges in the use of lung volume as an indicator of pulmonary disease when it is obtained from routine CT. Intra-individual variation and methodologic aspects have to be considered. Our goal was to assess the reliability of volumetric measurements in routine CT lung scans.

MATERIALS AND METHODS

Forty adult cancer patients whose lungs were unaffected by the disease underwent routine chest CT scans in 3-month intervals, resulting in a total number of 302 chest CT scans. Lung volume was calculated by automatic volumetry software. On average of 7.2 CT scans were successfully evaluable per patient (range 2-15). Intra-individual changes were assessed.

RESULTS

In the set of patients investigated, lung volume was approximately normally distributed, with a mean of 5283 cm(3) (standard deviation = 947 cm(3), skewness = -0.34, and curtosis = 0.16). Between different scans in one and the same patient the median intra-individual standard deviation in lung volume was 853 cm(3) (16% of the mean lung volume).

CONCLUSIONS

Automatic lung segmentation of routine chest CT scans allows a technically stable estimation of lung volume. However, substantial intra-individual variations have to be considered. A median intra-individual deviation of 16% in lung volume between different routine scans was found.

Clinical utility of computed tomographic lung volumes in patients with chronic obstructive pulmonary disease

BACKGROUND

Published data concerning the utility of computed tomography (CT)-based lung volumes are limited to correlation with lung function.

OBJECTIVES

The aim of this study was to evaluate the clinical utility of the CT expiratory-to-inspiratory lung volume ratio (CT Vratio) by assessing the relationship with clinically relevant outcomes.

METHODS

A total of 75 stable chronic obstructive pulmonary disease (COPD) patients having pulmonary function testing and volumetric CT at full inspiration and expiration were retrospectively evaluated. Inspiratory and expiratory CT lung volumes were measured using in-house software. Correlation of the CT Vratio with patient-centered outcomes, including the modified Medical Research Council (MMRC) dyspnea score, the 6-min walk distance (6MWD), the St. George's Respiratory Questionnaire (SGRQ) score, and multidimensional COPD severity indices, such as the BMI, airflow obstruction, dyspnea, and exercise capacity index (BODE) and age, dyspnea, and airflow obstruction (ADO), were analyzed.

RESULTS

The CT Vratio correlated significantly with BMI (r = -0.528, p < 0.001). The CT Vratio was also significantly associated with MMRC dyspnea (r = 0.387, p = 0.001), 6MWD (r = -0.459, p < 0.001), and SGRQ (r = 0.369, p = 0.001) scores. Finally, the CT Vratio had significant correlations with the BODE and ADO multidimensional COPD severity indices (r = 0.605, p < 0.001; r = 0.411, p < 0.001).

CONCLUSION

The CT Vratio had significant correlations with patient-centered outcomes and multidimensional COPD severity indices.

Post-mortem computed tomography ventilation; simulating breath holding

Whilst the literature continues to report on advances in the use of post-mortem computed tomography (PMCT), particularly in relation to post-mortem angiography, there are few papers published that address the diagnostic problems related to post-mortem changes in the lungs and ventilation. We present a development of previous methods to achieve ventilated PMCT (VPMCT). We successfully introduced a supraglottic airway in 17/18 cases without causing overt damage, despite rigor mortis. Using a clinical portable ventilator, we delivered continuous positive airway pressure to mimic clinical breath-hold inspiratory scans. This caused significant lung expansion and a reduction in lung density and visible normal post-mortem changes. All thoracic pathology identified at autopsy, including pneumonia, was diagnosed on VPMCT in this small series. This technique provides a rapid form of VPMCT, which can be used in both permanent and temporary mortuaries, allowing for the post-mortem radiological comparison of pre-ventilation and post-ventilation images mimicking expiratory and inspiratory phases. We believe that it will enhance the diagnostic ability of PMCT in relation to lung pathology.

Registration-based assessment of regional lung function via volumetric CT images of normal subjects vs. severe asthmatics

The purpose of this work was to explore the use of image registration-derived variables associated with computed tomographic (CT) imaging of the lung acquired at multiple volumes. As an evaluation of the utility of such an imaging approach, we explored two groups at the extremes of population ranging from normal subjects to severe asthmatics. A mass-preserving image registration technique was employed to match CT images at total lung capacity (TLC) and functional residual capacity (FRC) for assessment of regional air volume change and lung deformation between the two states. Fourteen normal subjects and thirty severe asthmatics were analyzed via image registration-derived metrics together with their pulmonary function test (PFT) and CT-based air-trapping. Relative to the normal group, the severely asthmatic group demonstrated reduced air volume change (consistent with air trapping) and more isotropic deformation in the basal lung regions while demonstrating increased air volume change associated with increased anisotropic deformation in the apical lung regions. These differences were found despite the fact that both PFT-derived TLC and FRC in the two groups were nearly 100% of predicted values. Data suggest that reduced basal-lung air volume change in severe asthmatics was compensated by increased apical-lung air volume change and that relative increase in apical-lung air volume change in severe asthmatics was accompanied by enhanced anisotropic deformation. These data suggest that CT-based deformation, assessed via inspiration vs. expiration scans, provides a tool for distinguishing differences in lung mechanics when applied to the extreme ends of a population range.

Clinical overview and treatment options for non-skeletal manifestations of mucopolysaccharidosis type IVA

Mucopolysaccharidosis type IVA (MPS IVA) or Morquio syndrome is a multisystem disorder caused by galactosamine-6-sulfatase deficiency. Skeletal manifestations, including short stature, skeletal dysplasia, cervical instability, and joint destruction, are known to be associated with this condition. Due to the severity of these skeletal manifestations, the non-skeletal manifestations are frequently overlooked despite their significant contribution to disease progression and impact on quality of life. This review provides detailed information regarding the non-skeletal manifestations and suggests long-term assessment guidelines. The visual, auditory, digestive, cardiovascular, and respiratory systems are addressed and overall quality of life as measured by endurance and other functional abilities is discussed. Impairments such as corneal clouding, astigmatism, glaucoma, hearing loss, hernias, hepatomegaly, dental abnormalities, cardiac valve thickening and regurgitation, obstructive sleep apnea, tracheomalacia, restrictive and obstructive respiratory compromise, and muscular weakness are discussed. Increased awareness of these non-skeletal features is needed to improve patient care.

Changes in lung volume and upper airway using MRI during application of nasal expiratory positive airway pressure in patients with sleep-disordered breathing

Nasal expiratory positive airway pressure (nEPAP) delivered with a disposable device (Provent, Ventus Medical) has been shown to improve sleep-disordered breathing (SDB) in some subjects. Possible mechanisms of action are 1) increased functional residual capacity (FRC), producing tracheal traction and reducing upper airway (UA) collapsibility, and 2) passive dilatation of the airway by the expiratory pressure, carrying over into inspiration. Using MRI, we estimated change in FRC and ventilation, as well as UA cross-sectional area (CSA), in awake patients breathing on and off the nEPAP device. Ten patients with SDB underwent nocturnal polysomnography and MRI with and without nEPAP. Simultaneous images of the lung and UA were obtained at 6 images/s. Image sequences were obtained during mouth and nose breathing with and without the nEPAP device. The nEPAP device produced an end-expiratory pressure of 4–17 cmH2O. End-tidal Pco2rose from 39.7 ± 5.3 to 47.1 ± 6.0 Torr ( P < 0.01). Lung volume changes were estimated from sagittal MRI of the right lung. Changes in UA CSA were calculated from transverse MRI at the level of the pharynx above the epiglottis. FRC determined by MRI was well correlated to FRC determined by N2washout ( r = 0.76, P = 0.03). nEPAP resulted in a consistent increase in FRC (46 ± 29%, P < 0.001) and decrease in ventilation (50 ± 15%, P < 0.001), with no change in respiratory frequency. UA CSA at end expiration showed a trend to increase. During wakefulness, nEPAP caused significant hyperinflation, consistent with an increase in tracheal traction and a decrease in UA collapsibility. Direct imaging effects on the UA were less consistent, but there was a trend to dilatation. Finally, we showed significant hypoventilation and rise in Pco2during use of the nEPAP device during wakefulness and sleep. Thus, at least three mechanisms of action have the potential to contribute to the therapeutic effect of nEPAP on SDB.

[Magnetic resonance imaging of respiratory movement and lung function]

Lung function measurements are the domain of spirometry or plethysmography. These methods have proven their value in clinical practice, nevertheless, being global measurements the functional indices only describe the sum of all functional units of the lung. Impairment of only a single component of the respiratory pump or of a small part of lung parenchyma can be compensated by unaffected lung tissue. Dynamic imaging can help to detect such local changes and lead to earlier adapted therapy. Magnetic resonance imaging (MRI) seems to be perfect for this application as it is not hampered by image distortion as is projection radiography and it does not expose the patient to potentially harmful radiation like computed tomography. Unfortunately, lung parenchyma is not easy to image using MRI due to its low signal intensity. For this reason first applications of MRI in lung function measurements concentrated on the movement of the thoracic wall and the diaphragm. Recent technical advances in MRI however might allow measurements of regional dynamics of the lungs.

Chest X-rays in COPD screening: are they worthwhile?

The BTS/NICE COPD guideline recommends a chest X-ray at initial COPD evaluation; this is a grade D recommendation based on expert opinion. We have investigated which pathologies other than COPD are detected by chest X-ray and how they alter management. Dundee smokers aged 40 or over and receiving bronchodilators are assessed for COPD by their practice nurse and offered a chest X-ray if there is no record of a chest X-ray within the previous three years. We retrospectively analysed the chest X-ray reports and case records of these patients. The chest X-ray report was structured with 7 specific questions, most importantly "Are there any features of other disease likely to be causing dyspnoea?" and "Are there any features to suggest lung cancer?" Management of patients with chest X-ray findings suggesting other disease causing dyspnoea or lung cancer was assessed by questionnaire and case record study. Five hundred forty-six consecutive chest X-ray reports were analysed. Fourteen percent of all chest X-rays detected potentially treatable dyspnoea causing disease; where management following receipt of X-ray reports was audited, 84% were thought to help. Eleven lung cancers were detected, 3 had stage 1 disease. Considerable benign and malignant pathology is detected by chest X-ray performed at initial COPD assessment. Clinical management is changed in the majority with a potentially treatable abnormality. This evidence suggests that the NICE guideline to perform chest X-ray at initial COPD evaluation should be elevated from a grade D to grade C recommendation.

Proton magnetic resonance imaging for assessment of lung function and respiratory dynamics

Since many pulmonary diseases present with a variable regional involvement, modalities for assessment of regional lung function gained increasing attention over the last years. Together with lung perfusion and gas exchange, ventilation, as a result of the interaction of the respiratory pump and the lungs, is an indispensable component of lung function. So far, this complex mechanism is still mainly assessed indirectly and globally. A differentiation between the individual determining factors of ventilation would be crucial for precise diagnostics and adequate treatment. By dynamic imaging of the respiratory pump, the mechanical components of ventilation can be assessed regionally. Amongst imaging modalities applicable to this topic, magnetic resonance imaging (MRI), as a tool not relying on ionising radiation, is the most attractive. Recent advances in MRI technology have made it possible to assess diaphragmatic and chest wall motion, static and dynamic lung volumes, as well as regional lung function. Even though existing studies show large heterogeneity in design and applied methods, it becomes evident that MRI is capable to visualise pulmonary function as well as diaphragmatic and thoracic wall movement, providing new insights into lung physiology. Partly contradictory results and conclusions are most likely caused by technical limitations, limited number of studies and small sample size. Existing studies mainly evaluate possible imaging techniques and concentrate on normal physiology. The few studies in patients with lung cancer and emphysema already give a promising outlook for these techniques from which an increasing impact on improved and quantitative disease characterization as well as better patient management can be expected.

Evaluation of Chest Motion and Volumetry During the Breathing Cycle by Dynamic MRI in Healthy Subjects

RATIONALE AND OBJECTIVES

To investigate diaphragm and chest wall motion during the whole breathing cycle using magnetic resonance imaging (MRI) and a volumetric model in correlation with spirometry.

MATERIALS AND METHODS

Breathing cycles of 15 healthy volunteers were examined using a trueFISP sequence (5 slices in 3 planes, 3 images per second). Time-distance curves were calculated and correlated to spirometry. A model for vital capacity (VC), continuous time-dependent vital capacity (tVC), and investigating the influence of horizontal and vertical parameters on tVC was introduced.

RESULTS

Time-distance curves of the breathing cycle using MRI correlated highly significant with spirometry (P < 0.0001). VC calculated by the model was similar to VC measured in spirometry (5.00 L vs. 5.15 L). tVC correlated highly significantly with spirometry (P < 0.0001). Vertical parameters had a more profound influence on tVC change than horizontal parameters.

CONCLUSIONS

Dynamic MRI is a simple noninvasive method to evaluate local chest wall motion and respiratory mechanics. It widens the repertoire of tools for lung examination with a high temporal resolution.

Lung volume in mechanically ventilated patients: measurement by simplified helium dilution compared to quantitative CT scan

OBJECTIVE

We describe a simplified helium dilution technique to measure end-expiratory lung volume (EELV) in mechanically ventilated patients. We assessed both its accuracy in comparison with quantitative computerized tomography (CT) and its precision.

DESIGN AND SETTING

Prospective human study.

PATIENTS

Twenty-one mechanically ventilated ALI/ARDS patients.

INTERVENTIONS

All patients underwent a spiral CT scan of the thorax during an end-expiratory occlusion. From the CT scan we computed the gas volume of the lungs (EELVCT). Within a few minutes, a rebreathing bag, containing a known amount of helium, was connected to the endotracheal tube, and the gas mixture diluted in the patient's lungs by delivering at least ten large tidal volumes. From the final helium concentration, EELV could be calculated by a standard formula (EELVHe).

MEASUREMENT AND RESULTS

The results obtained by the two techniques showed a good correlation (EELVHe=208+0.858xEELV(CT), r=0.941; P<0.001). Bias between the two techniques was 32.5+/-202.8 ml (95% limits of agreement were -373 ml and +438 ml), with a mean absolute difference of 15%. The amount of pathological tissue did not affect the difference between the two techniques, while the amount of hyperinflated tissue did. Bias between two repeated helium EELV measurements was -24+/-83 ml (95% limits of agreement were -191 ml and +141 ml), with a mean absolute difference of 6.3%.

CONCLUSIONS

The proposed helium dilution technique is simple and reproducible. The negligible bias and the acceptable level of agreement support its use as a practical alternative to CT for measuring EELV in mechanically ventilated ARDS patients.

A spirometry-based algorithm to direct lung function testing in the pulmonary function laboratory

OBJECTIVE

To design a spirometry-based algorithm to predict pulmonary restrictive impairment and reduce the number of patients undergoing unnecessary lung volume testing.

DESIGN

Two prospective studies of 259 consecutive patients and 265 consecutive patients used to derive and validate the algorithm, respectively.

SETTING

A pulmonary function laboratory of a tertiary care hospital.

PATIENTS

Consecutive adults referred to the laboratory for lung volume measurements and spirometry.

MEASUREMENTS

The sensitivity of the algorithm for predicting pulmonary restriction and the cost savings associated with its use.

RESULTS

Total lung capacity correlated strongly with FVC (r = 0.66) and showed an inverse correlation with the FEV(1)/FVC ratio (r = - 0.41). According to the algorithm, only patients with an FVC < 85% of predicted and an FEV(1)/FVC ratio >or= 55% required lung volume measurements following spirometry. The algorithm had a high sensitivity for predicting restriction and a high negative predictive value (NPV) for excluding restriction (sensitivity, 96%; NPV, 98%). The diagnostic properties of the algorithm were reproducible in the validation study. Application of the algorithm would eliminate the need for lung volume testing in 48 to 49% of patients referred to the pulmonary function test (PFT) laboratory, reducing costs by 33%.

CONCLUSIONS

A spirometry-based algorithm accurately excludes pulmonary restriction and reduces unnecessary lung volume testing in the PFT laboratory almost in half.

Comparison of loss in lung volume with open versus in-line catheter endotracheal suctioning

OBJECTIVE

Disconnecting the endotracheal tube from the ventilator causes significant loss in lung volume, which is further exacerbated by suctioning. In-line catheter suction systems have putative benefits over open catheter suction by maintaining positive pressure, thereby minimizing hypoxemia and hemodynamic instability. However, there is a theoretical risk of generating large negative airway pressures and auto-cycling of the ventilator with in-line catheter suction systems. We studied the effects on lung volume with both these techniques.

DESIGN

Open, randomized, crossover, clinical trial.

SETTING

Pediatric critical care unit.

PATIENTS

Fourteen paralyzed patients, age 6 days to 13 yrs.

INTERVENTIONS

Each patient, acting as his or her own control, was suctioned with an in-line catheter suction system and open catheter suction. Each suction maneuver was standardized. Changes in lung volume were measured by inductance plethysmography. Heart rate, blood pressure, and oxygen saturation were continuously monitored.

MEASUREMENTS AND MAIN RESULTS

Total lung volume loss was greater with open catheter suction compared with in-line catheter suction systems (p = .008). The most significant amount of lung volume loss associated with open catheter suction appears to be related to ventilator disconnection, rather than actual suctioning. Patients with decreased pulmonary compliance (< 0.8 mL/cm H2O/kg) demonstrated a greater loss in lung volume, both absolute and relative, as a result of ventilator disconnection (p = .038 and .006, respectively). Patients suctioned with open catheter suction desaturated to a greater extent than patients suctioned with in-line catheter suction (p = .026). There was evidence of ventilator triggering during the actual suction maneuver in all patients during in-line catheter suctions.

CONCLUSIONS

The most significant loss in lung volume during suctioning occurs primarily during ventilator disconnection. Hence, open catheter suction results in greater lung volume loss when compared with in-line catheter suction. We suggest that in-line catheter suction is preferable, especially in patients with significant lung disease and who require high positive end-expiratory pressures, to avoid alveolar derecruitment and exacerbating hypoxemia during endotracheal tube suctioning.

Monitoring early inflammation in CF. Infant pulmonary function testing

Infant pulmonary function tests (iPFTs) have primarily been used as research tools to further define physiologic pulmonary abnormalities in infants and young children with cystic fibrosis (CF). Methodologies used to measure pulmonary function in infants are described, with particular relevance to CF. A comprehensive review of studies and findings in CF infants using iPFTs is presented. Further goals in improving methodologies and in defining pulmonary disease in CF are presented.

Measuring lung function in infancy

Although the earliest reliable lung function tests in infants were performed as long as 40 years ago, there has only recently been a growth in this area, as simpler methods and better equipment and IT resources have been developed. Exciting information is accumulating about the normal physiology and pathology of the infant lung. Many basic questions are still unanswered and the ability to perform these tests remains confined to a few specialized centres. To co-ordinate the development of ILFT and establish standardization in a number of areas including measurement conditions, equipment specifications, methodology protocols and data analysis, international collaboration is necessary between the teams working in this field (Table 5). Collaborative groups are currently addressing these issues and are also developing recommendations regarding the design of randomized clinical trials, multi-centre studies and research agendas. Infant lung function testing remains primarily a research tool. Our aim should be not only to refine and develop the techniques of physiological measurement but to apply ILFT to the objective study of respiratory illness in infants in the clinical setting so as to aid in the prevention and treatment of these common, debilitating and costly diseases.

Diaphragm and chest wall: assessment of the inspiratory pump with MR imaging-preliminary observations

Magnetic resonance (MR) imaging of the thorax with three-dimensional (3D) reconstruction and functional quantification was evaluated as a tool for structure-function evaluation of chest-wall mechanics. Good agreement was found between the corresponding spirometric and MR imaging values of lung volumes. Fast MR imaging of the thorax with 3D reconstruction should improve the ability to evaluate the inspiratory pump in clinical and research investigations.

Measuring pulmonary function in infancy

In recent years there has been a growing interest in the measurement of pulmonary function in infants for both clinical and research purposes. Such measurements remain limited by the complexity of the equipment as well as by the technical and physiological challenges of testing infants and neonates. Despite these problems, assessment of respiratory function in early life provides exciting information about the post-natal growth and development of lungs in health and disease. The aim of this paper is to discuss the physiological, technical and ethical problems surrounding these procedures, as well as reviewing the current methods of testing pulmonary function in the very young. Consideration is given to the developments needed if infant pulmonary function tests are to realise fully, their potential as research and clinical tools.