A sigmoidal fit for pressure-volume curves of idiopathic pulmonary fibrosis patients on mechanical ventilation: clinical implications

OBJECTIVE

Respiratory pressure-volume curves fitted to exponential equations have been used to assess disease severity and prognosis in spontaneously breathing patients with idiopathic pulmonary fibrosis. Sigmoidal equations have been used to fit pressure-volume curves for mechanically ventilated patients but not for idiopathic pulmonary fibrosis patients. We compared a sigmoidal model and an exponential model to fit pressure-volume curves from mechanically ventilated patients with idiopathic pulmonary fibrosis.

METHODS

Six idiopathic pulmonary fibrosis patients and five controls underwent inflation pressure-volume curves using the constant-flow technique during general anesthesia prior to open lung biopsy or thymectomy. We identified the lower and upper inflection points and fit the curves with an exponential equation, V = A-B.e-k.P, and a sigmoid equation, V = a+b/(1+e-(P-c)/d).

RESULTS

The mean lower inflection point for idiopathic pulmonary fibrosis patients was significantly higher (10.5 ± 5.7 cm H2O) than that of controls (3.6 ± 2.4 cm H₂O). The sigmoidal equation fit the pressure-volume curves of the fibrotic and control patients well, but the exponential equation fit the data well only when points below 50% of the inspiratory capacity were excluded.

CONCLUSION

The elevated lower inflection point and the sigmoidal shape of the pressure-volume curves suggest that respiratory system compliance is decreased close to end-expiratory lung volume in idiopathic pulmonary fibrosis patients under general anesthesia and mechanical ventilation. The sigmoidal fit was superior to the exponential fit for inflation pressure-volume curves of anesthetized patients with idiopathic pulmonary fibrosis and could be useful for guiding mechanical ventilation during general anesthesia in this condition.

The influence of breathing mechanics on the development of the slow component of O2 uptake

We examined the influence of operational lung volumes and mean inspiratory flow on the amplitude of the slow component of O₂uptake (V(O)₂(SC) ) during constant-load cycling performed below and above the respiratory compensation threshold (RCT) in young (24±1yr), healthy individuals (n=10). Subjects demonstrated a significantly greater rise in expiratory reserve volume (ERV) and mean inspiratory flow over the V(O)₂(SC) period during exercise performed above compared with below the RCT (P<0.05). Inspiratory reserve volume (IRV) was, on average, smaller for trials performed above relative to below the RCT (P<0.05). The difference in the magnitudes of change in ERV and mean inspiratory flow, but not IRV, were positively correlated with the increase in V(O)₂(SC) amplitude between work rates (R(2)=0.86, P<0.01). These findings suggest that dynamic hyperinflation and mean inspiratory flow (by increasing inspiratory resistive work) contribute to the development of the V(O)₂(SC') , particularly when exercise is performed above the RCT.

Comparison of hyperpolarized (3)He MRI rat lung volume measurement with micro-computed tomography

In this study, the upper-limit volume (gas plus partial tissue volume) as well as absolute volume (gas only) of lungs measured with hyperpolarized (3)He-MR imaging is compared with that determined by micro-computed tomography (CT) under similar ventilation conditions in normal rats. Five Brown Norway rats (210-259 g) were ventilated with O(2), alternately with (3)He, using a computer-controlled ventilator, and 3D density-weighted images of the lungs were acquired during a breath hold after six wash-in breaths of (3)He. The rats were then transferred to a micro-CT scanner, and a similar experimental setup was used to obtain images of the lungs during a breath hold of air with an airway pressure equal to that of the MR imaging breath hold. The upper-limit and absolute volumes obtained from (3)He-MR and micro-CT methods were not significantly different (p > 0.05). The good agreement between the lung volumes measured with the two imaging methods suggests that (3)He-MR imaging can be used for quantitative analysis of lung volume changes in longitudinal studies without the exposure to the ionizing radiation which accompanies micro-CT imaging.

Comprehensive integrated spirometry using raised volume passive and forced expirations and multiple-breath nitrogen washout in infants

With the rapid somatic growth and development in infants, simultaneous accurate measurements of lung volume and airway function are essential. Raised volume rapid thoracoabdominal compression (RTC) is widely used to generate forced expiration from an airway opening pressure of 30 cmH(2)O (V(30)). The (dynamic) functional residual capacity (FRC(dyn)) remains the lung volume most routinely measured. The aim of this study was to develop comprehensive integrated spirometry that included all subdivisions of lung volume at V(30) or total lung capacity (TLC(30)). Measurements were performed on 17 healthy infants aged 8.6-119.7 weeks. A commercial system for multiple-breath nitrogen washout (MBNW) to measure lung volumes and a custom made system to perform RTC were used in unison. A refined automated raised volume RTC and the following two novel single maneuvers with dual volume measurements were performed from V(30) during a brief post-hyperventilation apneic pause: (1) the passive expiratory flow was integrated to produce the inspiratory capacity (IC) and the static (passive) FRC (FRC(st)) was estimated by initiating MBNW after end-passive expiration; (2) RTC was initiated late during passive expiration, flow was integrated to produce the slow vital capacity ((j)SVC) and the residual volume (RV) was measured by initiating MBNW after end-expiration while the jacket (j) was inflated. Intrasubject FRC(dyn) and FRC(st) measurements overlapped (p=0.6420) but neither did with the RV (p<0.0001). Means (95% confidence interval) of FRC(dyn), IC, FRC(st), (j)SVC, RV, forced vital capacity and tidal volume were 21.2 (19.7-22.7), 36.7 (33.0-40.4), 21.2 (19.6-22.8), 40.7 (37.2-44.2), 18.1 (16.6-19.7), 40.7 (37.1-44.2) and 10.2 (9.6-10.7)ml/kg, respectively. Static lung volumes and capacities at V(30) and variables from the best forced expiratory flow-volume curve were dependent on age, body length and weight. In conclusion, we developed a comprehensive physiologically integrated approach for in-depth investigation of lung function at V(30) in infants.

A lung area estimation method for analysis of ventilation inhomogeneity based on electrical impedance tomography

PURPOSE

To evaluate a novel method for lung area estimation (LAE method) in electrical impedance tomography (EIT) images as a prerequisite of quantitative analysis of ventilation inhomogeneity.

METHODS

The LAE method mirrors the lung regions in the functional EIT (fEIT) image and subsequently subtracts the cardiac related areas. In this preliminary study, 51 mechanically ventilated patients were investigated, including 39~patients scheduled for thoracic surgery (test group); 10 patients scheduled for orthopedic surgery without pulmonary disease (control group) and 2 ICU patients undergoing chest computed tomography (CT) examination. EIT data was recorded in all groups. The results of the LAE method were compared to those obtained with the fEIT method and to CT images.

RESULTS

The lung area size determined with fEIT in control group is S(C,fEIT) = 361 +/- 35 (mean +/- SD) and in test group S(T,fEIT) = 299 +/- 61 (p< 0.01). The sizes estimated with the LAE method in control group S(C,LAE) = 353 +/- 27 and in test group S(T,LAE) = 353 +/- 61 (p=0.41). The result demonstrates that the novel LAE method improves the identification of lung region in EIT images, from which the analysis of ventilation distribution will benefit. The preliminary comparison with CT images exemplary indicates a closer match of the lung area shapes after the LAE than after the fEIT-based analysis.

CONCLUSION

The LAE method is a robust lung area determination method, suitable for patients with healthy or seriously injured lungs.

Abdominal compression increases upper airway collapsibility during sleep in obese male obstructive sleep apnea patients

STUDY OBJECTIVES

Abdominal obesity, particularly common in centrally obese males, may have a negative impact on upper airway (UA) function during sleep. For example, cranial displacement of the diaphragm with raised intra-abdominal pressure may reduce axial tension exerted on the UA by intrathoracic structures and increase UA collapsibility during sleep.

DESIGN

This study aimed to examine the effect of abdominal compression on UA function during sleep in obese male obstructive sleep apnea patients.

SETTING

Participants slept in a sound-insulated room with physiologic measurements controlled from an adjacent room.

PARTICIPANTS

Fifteen obese (body mass index: 34.5 +/- 1.1 kg/m2) male obstructive sleep apnea patients (apnea-hypopnea index: 58.1 +/- 6.8 events/h) aged 50 +/- 2.6 years participated.

INTERVENTIONS

Gastric (PGA) and transdiaphragmatic pressures (P(DI)), UA closing pressure (UACP), UA airflow resistance (R(UA)), and changes in end-expiratory lung volume (EELV) were determined during stable stage 2 sleep with and without abdominal compression, achieved via inflation of a pneumatic cuff placed around the abdomen. UACP was assessed during brief mask occlusions.

MEASUREMENTS AND RESULTS

Abdominal compression significantly decreased EELV by 0.53 +/- 0.24 L (P=0.045) and increased PGA (16.2 +/- 0.8 versus 10.8 +/- 0.7 cm H2O, P < 0.001), P(DI) (11.7 +/- 0.9 versus 7.6 +/- 1.2 cm H2O, P < 0.001) and UACP (1.4 +/- 0.8 versus 0.9 +/- 0.9 cm H2O, P = 0.039) but not R(UA)(6.5 +/- 1.4 versus 6.9 +/- 1.4 cm H2O x L/s, P=0.585).

CONCLUSIONS

Abdominal compression negatively impacts on UA collapsibility during sleep and this effect may help explain strong associations between central obesity and obstructive sleep apnea.

Comparison of lung volume measurements by multiple-breath heptafluoropropane washout and computed tomography in small ventilated piglets

BACKGROUND

Knowledge of lung volume is essential for monitoring and optimizing mechanical ventilation. The aim of this study was to compare lung volume measurements by multiple-breath heptafluoropropane (HFP) washout (MBW) and by respiratory gated computed tomography (CT) in ventilated newborn piglets.

MATERIAL/METHODS

In 6 ventilated piglets (age: <12 h, median weight: 945 g) blood gases, respiratory mechanics, and lung volumes were measured in both the supine and prone positions. The measurements were performed in random order. Functional residual capacity (FRC) was measured simultaneously by HFP MBW (FRC(HFP)) using a new infrared mainstream sensor and by CT (FRC(CT)) at the end of inspiration and expiration (multi-slice Toshiba Aquilon 16, Otawara, Japan). Tidal volume (V(T)) was measured both by the Dräger Babylog 8000 ventilator (V(T BL)) and the volume difference of the CT scans (V(T CT)).

RESULTS

FRC(HFP) (25.2+/-8.5 ml) and FRC(CT) (24.9+/-7.6 ml) correlated strongly (r=0.97) without significant bias. Bland-Altman limits of agreement showed differences between the two methods that ranged from -19.7 to +19.5%. A similar strong correlation without statistically significant bias was found between V(T BL) (8.5+/-2.0 ml) and V(T CT) (9.0+/-2.4 ml) with r=0.91. The limits of agreement were -24.4 and +14.0%. Body position (prone vs. supine) had no significant effect on blood gases, respiratory mechanics, or lung volumes.

CONCLUSIONS

Lung volumes measured in small ventilated lungs by HFP washout and CT are highly correlated and independent of body position. However, the relatively large limits of agreement indicate differences in the two techniques.

The impact of iatrogenic gastroschisis on pulmonary maturation in the fetal rabbit models of congenital diaphragmatic hernia

PURPOSE

The aim of this study was to analyze the effect of iatrogenic gastroschisis on pulmonary hypoplasia in fetal rabbits with congenital diaphragmatic hernia (CDH).

MATERIALS AND METHODS

A total of 30 pregnant rabbits received fetal surgery on gestational day 23. A left diaphragmatic hernia was created in one end fetus (DH group) of each rabbit, and the other end fetus of the same rabbit received sham thoracotomy as control (CR group). Another 19 pregnant rabbits underwent partial resection of the diaphragm in both end fetuses on gestational day 23, and then artificial gastroschisis was performed on one end fetus (GS group) on gestational day 26, while the other end remained as control (CGS group). The fetuses were harvested on gestational day 30. The histological and morphometric evaluation of lungs and livers of the end fetuses in each group was conducted.

RESULTS

In the DH group, the lungs were hypoplastic with a decrease in the total lung weight to body weight ratio, and remarkable thickening in alveolar septa. The lung vessels showed significantly thicker arterial walls when compared with those from control fetuses. The pathological finding in the CGS group was similar to that of the DH group. The thickness of the alveolar septa and of the pulmonary arterial walls showed no significant difference among the GS group, DH group and the CGS group. The ratio of liver weight to body weight increased notably in the GS group, DH group and CGS group compared with that in the CR group.

CONCLUSIONS

In the fetal rabbit models of CDH, pulmonary hypoplasia is the most significant pathological feature. Iatrogenic gastroschisis does not improve pulmonary maturation due to the active growth of the liver that herniates into the thoracic cavity.

Reference values for lung volumes in an Iranian population: introducing a new equation model

BACKGROUND

Measurement of lung volumes, especially residual volume and total lung capacity are essential for assessment of restrictive lung disorders. Information regarding normative prediction values for lung volumes as measured by body plethysmography is scarce, and plethysmographic parameters are believed to be poorly reproducible. In this study, we report a comprehensive set of predictive equations for static lung volumes from a general population sample of urban Iranians as measured by body plethysmography.

METHODS

Standardized measurements were carried out on 1487 healthy nonsmoking volunteers (845 men and 642 women), aged six to 85 years, living in Isfahan, Iran. Nonlinear multiple regression analysis was used to calculate prediction equations based on subjects' ages and heights for the subdivisions of lung volumes [total lung capacity, functional residual capacity, residual volume, and residual volume/total lung capacity (%)], separately for the two genders. The derived equations were used to calculate prediction values for the subjects. The two sets of predicted and measured values were compared by paired sample t-test.

RESULTS

Prediction equations based on a new nonlinear model, (alpha(1) x age + alpha(2) x age(n) + beta x height + c) which best fitted our data are presented. The measured and predicted values closely resemble and there is no significant difference between the two sets. Since increments in total lung capacity, functional residual capacity, and residual volume disclose air trapping within the lungs, their upper limits of normal are as important as the lower limits. So, we have presented both for the equations.

CONCLUSION

Despite the usual beliefs we found rather reproducible prediction equations with high coefficient of determination (r2) and low standard error of estimate (SEE) in Iranian population.

Quantification of single-breath underestimation of lung volume in emphysema

The extent to which a single breath measurement represents available gas dilutional as well as compressible thoracic volume in emphysema patients has not been quantified. We therefore measured single breath (TLCSB) and rebreathe helium dilution (TLCRB), and plethysmographic lung volume (TLCpleth), in fifty-five outpatients with clinical and radiographic emphysema, and in twenty-one normal controls. Among emphysema patients, TLCSB increasingly underestimated both TLCpleth and TLCRB as FEV1% predicted decreased (p for interaction=0.001 for both) by a mean of 1.7 l for TLCRB (p<0.001) and 2.2l for TLCpleth (p<0.001). In contrast, TLCRB underestimated TLCpleth by a mean of 0.5l (p<0.001) regardless of FEV1% (p for interaction=0.25). TLCSB, TLCRB, and TLCpleth showed strong agreement among normal subjects. We conclude that TLCSB underestimates available gas dilutional and compressible lung volume as physiologic emphysema severity increases. In contrast, TLCRB and TLCpleth show closer agreement which is unaffected by physiologic emphysema severity.

Nitrogen washout/washin, helium dilution and computed tomography in the assessment of end expiratory lung volume

INTRODUCTION

End expiratory lung volume (EELV) measurement in the clinical setting is routinely performed using the helium dilution technique. A ventilator that implements a simplified version of the nitrogen washout/washin technique is now available. We compared the EELV measured by spiral computed tomography (CT) taken as gold standard with the lung volume measured with the modified nitrogen washout/washin and with the helium dilution technique.

METHODS

Patients admitted to the general intensive care unit of Ospedale Maggiore Policlinico Mangiagalli Regina Elena requiring ventilatory support and, for clinical reasons, thoracic CT scanning were enrolled in this study. We performed two EELV measurements with the modified nitrogen washout/washin technique (increasing and decreasing inspired oxygen fraction (FiO2) by 10%), one EELV measurement with the helium dilution technique and a CT scan. All measurements were taken at 5 cmH2O airway pressure. Each CT scan slice was manually delineated and gas volume was computed with custom-made software.

RESULTS

Thirty patients were enrolled (age = 66 +/- 10 years, body mass index = 26 +/- 18 Kg/m2, male/female ratio = 21/9, partial arterial pressure of carbon dioxide (PaO2)/FiO2 = 190 +/- 71). The EELV measured with the modified nitrogen washout/washin technique showed a very good correlation (r2 = 0.89) with the data computed from the CT with a bias of 94 +/- 143 ml (15 +/- 18%, p = 0.001), within the limits of accuracy declared by the manufacturer (20%). The bias was shown to be highly reproducible, either decreasing or increasing the FiO2 being 117+/-170 and 70+/-160 ml (p = 0.27), respectively. The EELV measured with the helium dilution method showed a good correlation with the CT scan data (r2 = 0.91) with a negative bias of 136 +/- 133 ml, and appeared to be more correct at low lung volumes.

CONCLUSIONS

The EELV measurement with the helium dilution technique (at low volumes) and modified nitrogen washout/washin technique (at all lung volumes) correlates well with CT scanning and may be easily used in clinical practice.

TRIAL REGISTRATION

Current Controlled Trials NCT00405002.

A new automated method versus continuous positive airway pressure method for measuring pressure-volume curves in patients with acute lung injury

OBJECTIVE

To compare pressure-volume (P-V) curves obtained with the Galileo ventilator with those obtained with the CPAP method in patients with acute lung injury (ALI) or acute respiratory distress syndrome (ARDS).

DESIGN

Prospective, observational study.

SETTING

General critical care center.

PATIENTS AND PARTICIPANTS

Patients with ALI/ARDS and receiving mechanical ventilation.

INTERVENTIONS

Pressure-volume curves were obtained in random order with the CPAP technique and with the software PV Tool-2 (Galileo ventilator).

MEASUREMENTS AND RESULTS

In ten consecutive patients, airway pressure was measured by a pressure transducer and changes in lung volume were measured by respiratory inductive plethysmography. P-V curves were fitted to a sigmoidal equation with a mean R (2) of 0.994 +/- 0.003. Intraclass correlation coefficients were all >0.75 (P < 0.001 at all pressure levels). Lower (LIP) and upper inflection (UIP), and deflation maximum curvature (PMC) points calculated from the fitted variables showed a good correlation between methods with intraclass correlation coefficients of 0.98 (0.92, 0.99), 0.92 (0.69, 0.98), and 0.97 (0.86, 0.98), respectively (P < 0.001 in all cases). Bias and limits of agreement for LIP (0.51 +/- 0.95 cmH(2)O; -1.36 to 2.38 cmH(2)O), UIP (0.53 +/- 1.52 cmH(2)O; -2.44 to 3.50 cmH(2)O), and PMC (-0.62 +/- 0.89 cmH(2)O; -2.35 to 1.12 cmH(2)O) obtained with the two methods in the same patient were clinically acceptable. No adverse effects were observed.

CONCLUSION

The PV Tool-2 built into the Galileo ventilator is equivalent to the CPAP method for tracing static P-V curves of the respiratory system in critically ill patients receiving mechanical ventilation.

Prenatal prediction of survival in isolated diaphragmatic hernia using observed to expected total fetal lung volume determined by magnetic resonance imaging based on either gestational age or fetal body volume

OBJECTIVES

To compare the predictive value of the prenatal observed to expected (o/e) lung volume as measured by fetal magnetic resonance imaging (MRI), based on an algorithm using either the gestational age or fetal body volume (FBV), for neonatal survival of fetuses with isolated congenital diaphragmatic hernia (CDH).

METHODS

We included 53 fetuses with a prenatal diagnosis of isolated CDH, 26 without and 27 with prenatal tracheal occlusion, who were assessed by fetal MRI, liveborn after 32 weeks, and in whom follow-up until discharge from the neonatal care unit was available. Measurements of lung volumes were expressed as a percentage of the appropriate mean (o/e total fetal lung volume (TFLV) x 100) either for gestational age or for FBV. Measurements of FBV were expressed as a percentage of the appropriate mean (o/e FBV x 100) for gestation. Fetuses with prenatal intervention were all assessed > or = 24 h after balloon removal. Regression analysis was used to examine the effect on postnatal survival of either o/e TFLV based on gestational age or based on FBV, gestation at delivery, side of CDH, intrathoracic position of the liver and prenatal intervention. Receiver-operating characteristics (ROC) curves were constructed for the prediction of survival by o/e TFLV based on gestational age and o/e TFLV based on FBV, for all fetuses, as well as for those with o/e FBV between 90 and 110% and those with values beyond that range. A power calculation for the number of fetuses needed to show a difference between the ROC curves was performed.

RESULTS

Regression analysis demonstrated that o/e TFLV based on gestational age and on FBV were the only independent predictors of postnatal survival. The area under the ROC curve for prediction of postnatal survival from the o/e TFLV based on gestational age was 0.811, and for that based on FBV it was 0.868 (P < 0.001 for both). For fetuses with o/e FBV between 90 and 110%, and those with values < 90% and > 110%, the area for measurements based on gestational age was 0.895 and 0.733, respectively; when based on FBV it was 0.906 and 0.833 (P < 0.01 for all). A minimum of 273 patients would be needed to provide a probability of 90% of detecting a difference between the areas under both ROC curves.

CONCLUSIONS

In fetuses with isolated CDH, lung volume as measured by fetal MRI was significantly correlated with survival. Prediction tended to be better by o/e TFLV based on FBV rather than gestational age. The difference in the prediction of survival between o/e TFLV based on FBV or gestational age was dependent on fetal biometry.

[Application of electrical impedance equipment in evaluating local lung volume during different PEEP ventilation and at different respiratory rate]

OBJECTIVE

To evaluate the applicability of electrical impedance equipment in assessing local lung volume during different PEEP ventilation and at different respiratory rate in neonatal piglets.

METHODS

Electrical impedance measurements (EIM) were performed on 6 healthy newborn piglets (age 4 +/- 1 d, weight 1.66 +/- 0.31 kg) using 8 electrodes distributed to 4 quadrants of the lung (left, right, upper, lower). Tidal impedance and functional residual impedance changes during PEEP levels of 2, 4, 6 and 8 cm H2O and frequencies ranging from 0.5 to 15 Hz were investigated.

RESULTS

The sum of regional tidal impedance obtained from four quadrants, significantly reflected tidal volume (VT) measured by a pneumotachograph during both frequency and PEEP changed (r2 = 0.98). A decrease of PEEP 4 to 2 cm H2O caused a significant increase in total tidal impedance (TTI) as well as in VT (P < 0.01 and P < 0.05); whereas an increase in frequency from 0.5 to 15 Hz was associated with a significant decrease in both TTI and VT (P < 0.05 and P < 0.01). Increased frequency had a balancing effect on air distribution, whereas higher PEEP did not result in more homogeneous ventilation. Minimal impedance values (FRI) (surrogate variable for FRC) showed that total FRI significantly decreased with increasing PEEP level.

CONCLUSIONS

EIM demonstrated good applicability to assess changes in thoracic gas volume. It is highly suggested that this method could be considered and further studied as a non-invasive bedside method to monitor continuously regional lung ventilation of neonates under any mode of mechanical ventilation.

Quantification of intrathoracic liver herniation by magnetic resonance imaging and prediction of postnatal survival in fetuses with congenital diaphragmatic hernia

OBJECTIVE

To quantify the degree of intrathoracic liver herniation by magnetic resonance imaging (MRI) and evaluate its effect on postnatal survival in fetuses with isolated congenital diaphragmatic hernia (CDH).

METHODS

Forty fetuses that were expectantly managed and that were delivered after 32 weeks' gestation were included in this study. On axial T2 weighted MR images the degree of intrathoracic liver herniation was measured by volumetry, using the xyphoid process and thoracic apex as landmarks. The ratio of the volume of the liver that was herniated into the thoracic cavity to the volume of the thoracic cavity was calculated (LiTR). All the fetuses also underwent lung volumetry, and the ratio of the observed/expected total fetal lung volume (o/e TFLV) was calculated. Regression analysis was used to investigate the effect on survival of side of occurrence of CDH, o/e TFLV, LiTR and gestational age at delivery. Receiver-operating characteristics (ROC) curves were constructed to examine the prediction of survival by o/e TFLV or LiTR alone and o/e TFLV and LiTR together.

RESULTS

Univariate regression analysis demonstrated that significant predictors of survival were o/e TFLV and LiTR. Multiple regression analysis demonstrated that o/e TFLV and LiTR provided independent prediction of survival. The area under the ROC curve (AUC) for the prediction of postnatal survival from o/e TFLV alone was 0.846 (P < 0.001; SE = 0.062) and the AUC from LiTR alone was 0.875 (P = 0.001; SE = 0.072). The AUC for the prediction of postnatal survival from o/e TFLV and LiTR combined was 0.912 (P < 0.001; SE = 0.045), however it was not statistically significantly different from that of o/e TFLV alone.

CONCLUSION

In expectantly managed CDH fetuses, assessment of LiTR using MRI provided prediction of postnatal survival independently from o/e TFLV.

Three-dimensional sonographic measurement of contralateral lung volume in fetuses with isolated congenital diaphragmatic hernia

PURPOSE

To use 3-dimensional sonography (3DUS) to measure contralateral lung volume and evaluate the potential of this measurement to predict neonatal outcome in isolated congenital diaphragmatic hernia (CDH).

METHODS

Between January 2002 and December 2004, the contralateral lung volumes of 39 fetuses with isolated CDH were measured via 3DUS using rotational multiplanar imaging. The observed/expected contralateral fetal lung volume ratios (o/e-ContFLVR) were compared with the lung/head ratio (LHR), observed/expected total fetal lung volume ratio (o/e-TotFLVR), and postnatal outcome.

RESULTS

Contralateral lung volumes are less reduced than total lung volumes in CDH. The bias and precision of 3DUS in estimating contralateral lung volumes were 0.99 cm(3) and 1.11 cm(3), respectively, with absolute limits of agreement ranging from -1.19 cm(3) to +3.17 cm(3). The o/e-ContFLVR was significantly lower in neonatal death cases (median, 0.49 cm(3); range, 0.22-0.99 cm(3)) than in survival cases (median, 0.58 cm(3); range, 0.42-0.92 cm(3) [p < 0.01]). Overall accuracy of the o/e-ContFLVR, o/e-TotFLVR, and LHR in predicting neonatal death were 67.7% (21/31), 80.7% (25/31), and 77.4% (24/31), respectively.

CONCLUSION

Although o/e-ContFLVR can be precisely measured with 3DUS and can be used to predict neonatal death in CDH, it is less accurate than LHR and o/e-TotFLVR for that purpose.

Lung function made easy: assessing lung size

Spirometry is available in most GP surgeries and provides an invaluable tool for assessing respiratory function in chronic obstructive pulmonary disease (COPD) and asthma. Spirometry alone may not provide the clinician with an accurate assessment of lung disease as it misses two important measurements of lung volume. By measuring Residual Volume (RV) and Total Lung Capacity (TLC) it is possible to determine true restrictive or hyperinflated disease processes. Helium dilution, body plethysmography and nitrogen washout are three different methods which may be used to measure lung volume. These tests are normally only provided in the acute setting. Comparing values of RV and TLC to predicted values makes it possible to grade the severity of disease far more accurately than spirometry. Four case studies of asthma, obesity, COPD and pulmonary fibrosis clearly demonstrate anomalies that may arise when interpreting lung disease from spirometry compared to the interpretation made with additional lung volume data.

Assessment of the alveolar volume when sampling exhaled gas at different expired volumes in the single breath diffusion test

BACKGROUND

Alveolar volume measured according to the American Thoracic Society-European Respiratory Society (ATS-ERS) guidelines during the single breath diffusion test can be underestimated when there is maldistribution of ventilation. Therefore, the alveolar volume calculated by taking into account the ATS-ERS guidelines was compared to the alveolar volume measured from sequentiallly collected samples of the expired volume in two groups of individuals: COPD patients and healthy individuals. The aim of this study was to investigate the effects of the maldistribution of ventilation on the real estimate of alveolar volume and to evaluate some indicators suggestive of the presence of maldistribution of ventilation.

METHODS

Thirty healthy individuals and fifty patients with moderate-severe COPD were studied. The alveolar volume was measured either according to the ATS-ERS guidelines or considering the whole expired volume subdivided into five quintiles. An index reflecting the non-uniformity of the distribution of ventilation was then derived (DeltaVA/VE).

RESULTS

Significant differences were found when comparing the two measurements and the alveolar volume by quintiles appeared to have increased progressively towards residual volume in healthy individuals and much more in COPD patients. Therefore, DeltaVA/VE resulted in an abnormal increase in COPD.

CONCLUSION

The results of our study suggest that the alveolar volume during the single breath diffusion test should be measured through the collection of a sample of expired volume which could be more representative of the overall gas composition, especially in the presence of uneven distribution of ventilation. Further studies aimed at clarifying the final effects of this way of calculating the alveolar volume on the measure of DLCO are needed. DeltaVA/VE is an index that can help assess the severity of inhomogeneity in COPD patients.

Mechanics of airway and alveolar collapse in human breath-hold diving

A computational model of the human respiratory tract was developed to study airway and alveolar compression and re-expansion during deep breath-hold dives. The model incorporates the chest wall, supraglottic airway, trachea, branched airway tree, and elastic alveoli assigned time-dependent surfactant properties. Total lung collapse with degassing of all alveoli is predicted to occur around 235 m, much deeper than estimates for aquatic mammals. Hysteresis of the pressure-volume loop increases with maximum diving depth due to progressive alveolar collapse. Reopening of alveoli occurs stochastically as airway pressure overcomes adhesive and compressive forces on ascent. Surface area for gas exchange vanishes at collapse depth, implying that the risk of decompression sickness should reach a plateau beyond this depth. Pulmonary capillary transmural stresses cannot increase after local alveolar collapse. Consolidation of lung parenchyma might provide protection from capillary injury or leakage caused by vascular engorgement due to outward chest wall recoil at extreme depths.

How useful is the lung-to-head ratio in predicting outcome in the fetus with congenital diaphragmatic hernia? A systematic review and meta-analysis

OBJECTIVE

Fetal surgery to improve lung growth comprises tracheal occlusion in selected 'high-risk' fetuses with congenital diaphragmatic hernia (CDH). Sonographically measured fetal lung-to-head ratio (LHR) is utilized to recruit candidates for fetal surgery. This study provides a meta-analysis of the evidence regarding the prognostic use of lung-to-head ratio measurements in fetal CDH.

METHODS

MEDLINE, SCOPUS and ISI PROCEEDINGS databases were searched for MeSH terms: lung, head, hernia and ratio. References in retrieved studies were also searched. Studies were categorized as follows: Phase I studies measured normal fetal LHR; Phase II studies compared fetal LHR in CDH survivors and non-survivors (if LHR informed therapy decisions or LHR was not measured during the window for intervention (< 32 weeks' gestation), studies were excluded); Phase III studies used LHR to guide selection for fetal surgery (non-randomized trials were excluded); Phase IV studies measured CDH survival before and after LHR application in clinical practice.

RESULTS

The one Phase I study showed that LHR varied substantially with gestation and technique. No complete studies met the selection criteria for Phase II: meta-analysis of subgroups revealed similar LHR in CDH survivors and non-survivors. A single Phase III study revealed no benefit for LHR-directed fetal surgery. No Phase IV studies were identified.

CONCLUSION

The prognostic use of LHR in fetal CDH entered clinical practice prior to publication of robust normal data and is not supported by current evidence. Application of a structured approach to any 'new' prognostic test could improve its validity and clinical application.