The interaction of the lung and chest wall in dogs

The deformation of the lung by the chest wall was observed on radiographs of the ribs and interspaces and on morphologic preparations of samples cut from the frozen thorax. The effect of these deformities on the distribution of ventilation and regional lung volume of the underlying lung was determined using Xenon 133. We found that ribs and interspaces deform the lung surface with different radii of curvature, suggesting local differences in pleural pressure and that traction on the thoracic limb caused deformities in the underlying interspaces which were similar to those produced by 20 cm H2O mouth pressure. Xenon 133 showed that these changes in pressure had no effect on the regional volume or on ventilation distribution in the underlying lung. We conclude that changes in pleural pressure produced by localized deformities exert their effect close to the deformity and that the underlying lung responds to the average pressure exerted over a much larger area of the pleural surface.     

Respiratory mechanics in normal hamsters

Lung volumes and quasi-static deflation volume-pressure relationships were measured in male golden hamsters anesthetized with pentobarbital. Volume was measured with a pressure plethysmograph, and pleural pressure was estimated by the use of a water-filled esophageal catheter. Mean body weight +/- SE was 122.3 +/-3.0 g, mean lung weight was 0.74 +/- 0.2 g or about 0.6% of body weight. Mean lung volume at 25 cmH2O transpulmonary pressure (TLC25) was 7.2 +/- 0.14 ml, 9.78 +/- 0.17 ml/g lung weight or 5.92 +/- 0.06 ml/100 g body weight. Mean functional residual capacity was 2.4 +/- 0.06 ml or 33.3% of TLC25. Mean vital capacity was 5.2 +/- 0.13 ml. Mean quasi-static compliance of lung was 0.63 +/- 0.03 ml/cmH2O. Chord compliance of chest wall between lung volumes of 1 and 4 ml above RV was 3.39 +/- 0.53 ml/cmH2O. At FRC, the chest wall recoiled inward, so that pleural pressure was positive (1.4 +/- 0.13 cmH2O) and the lung was resisting further collapse. The slope of the lung's deflation volume-pressure curve changed at FRC, ERV was small (0.36 +/- 0.03 ml), and RV was determined by complete airway closure. Thus the mechanisms determining FRC are unusual and include an influence of airway closure.     

Respiratory mechanics in patients with tense cirrhotic ascites

Lung volumes are decreased by tense ascites and increase after large volume paracentesis (LVP). The overall effect of ascites and LVP on the respiratory function is poorly understood. We studied eight cirrhotic patients with tense ascites before and after LVP. Inspiratory muscle force (maximal transdiaphragmatic pressure (Pdi,max), and the lowest pleural pressure (Pp1,min)) was assessed while the patients were seated. Rib cage and abdominal volume displacements, as well as pleural and gastric pressures were measured during quiet breathing while the patients were supine. Pdi,max and Ppl,min were normal and did not change after LVP (from 84.2+/-19.7 to 85.2+/-17.0 cmH2O and from 68.3+/-19.7 to 74+/-15.9 cmH2O, respectively). The abdominal contribution to the generation of tidal volume was greater than that of the rib cage (79 vs 21%), a pattern which did not change after LVP (73 and 27%). Before LVP, tidal swings both of pleural pressure (Ppl,sw) and transdiaphragmatic pressure (Pdi,sw) were large (15.3+/-4.3 and 18.5+/-3.9 cmH2O, respectively) and the load on inspiratory muscles was increased as a consequence of elevated dynamic elastance of the lung (El,dyn) (11.4+/-2.6 cmH2O x L(-1)) and ("intrinsic") positive end-expiratory pressure (PEEPi) (4.3+/-3.5 cmH2O). LVP reduced the load on the inspiratory muscles, as shown by the significant decrease in Ppl,sw (10.6+/-2.0 cmH2O), Pdi,sw (12.8+/-3.0 cmH2O), El,dyn (10.0+/-2.0 cmH2O x L(-1)) and PEEPi (1.1+/-1.3 cmH2O). The amount of fluid removed was closely related to changes in Ppl,sw and PEEPi. We conclude that the strength of the inspiratory muscles is normal or reduced in seated cirrhotic patients. In the supine position, tense ascites results in an increase in lung elastic load and development of positive end-expiratory pressure, with a consequent overload and increased activation of inspiratory muscles. Large volume paracentesis decreases overloading and activation, but does not change the strength of the inspiratory muscles.     

Massive gas embolism following lung inflation for thoracic tomodensitometry in a multiple trauma patient with lung contusions

We report a case of gas embolism into both right and left circulation in a polytrauma patient with lung contusions, revealed by thoracic CT scan showing the heart and aorta filled with gas. It followed a lung inflation with a O2/N2O mixture for about 30 seconds at a pressure of at least 40 cmH2O in order to obtain apnoea for CT scan and to recruit atelectatic territories. The presumed mechanism was the passage of the O2/N2O mixture during the lung inflation manoeuvre out of disrupted airways into torn pulmonary blood vessels and pushed back into the heart chambers. The patient recovered fully. Lung inflation manoeuvre to obtain a prolonged apnoea during CT scan examinations of thorax is contraindicated in case of thorax trauma, as it carries a risk of gas embolism.     

MR analysis of lung volume and thoracic dimensions in patients with emphysema before and after lung volume reduction surgery

OBJECTIVE: This study was performed to assess the accuracy of determining lung volume in patients with emphysema using MR imaging and then to investigate changes in thoracic dimensions after lung volume reduction surgery. SUBJECTS AND METHODS: Fast gradient-echo breath-hold MR imaging through the entire thorax at full inspiration and expiration was performed in 21 patients with severe emphysema and was performed again in nine of the patients who underwent surgery. Lung volumes were determined using a semiautomated computerized method of delineating the lungs and summing cross-sectional areas. These summed areas were compared with volumes measured on plethysmography and CT. Postoperative changes in thoracic structure were determined by measuring anteroposterior and transverse lung dimensions and lung height before and after surgery. RESULTS: The correlation coefficients and SEM for determining inspiratory lung volume were MR imaging versus plethysmography, r = .77, SEM = -12% (volume measured as less on MR imaging); CT versus plethysmography, r = .86, SEM = -13% (volume measured as less on CT); and MR imaging versus CT, r = .87, SEM = 4% (volume measured as greater on MR imaging). The correlation coefficients and SEM for determining expiratory volume on MR imaging versus plethysmography were r = .77, SEM = 6% (volume measured as greater on MR imaging). After surgery, decreases were found in all thoracic dimensions, and such decreases were greatest at expiration. CONCLUSION: MR measurements of lung volume are comparable with those of CT and differ from those of plethysmography. Changes in thoracic dimensions after lung volume reduction surgery are consistent with improved respiratory mechanics.     

Does airway pressure release ventilation alter lung function after acute lung injury?

BACKGROUND: During airway pressure release ventilation (APRV), tidal ventilation occurs between the increased lung volume established by the application of continuous positive airway pressure (CPAP) and the relaxation volume of the respiratory system. Concern has been expressed that release of CPAP may cause unstable alveoli to collapse and not reinflate when airway pressure is restored. OBJECTIVE: To compare pulmonary mechanics and oxygenation in animals with acute lung injury during CPAP with and without APRV. DESIGN: Experimental, subject-controlled, randomized crossover investigation. SETTING: Anesthesiology research laboratory, University of South Florida College of Medicine Health Sciences Center. SUBJECTS: Ten pigs of either sex. INTERVENTIONS: Acute lung injury was induced with an intravenous infusion of oleic acid (72 micrograms/kg) followed by randomly alternated 60-min trials of CPAP with and without APRV. Continuous positive airway pressure was titrated to produce an arterial oxyhemoglobin saturation of at least 95% (FIO2 = 0.21). Airway pressure release ventilation was arbitrarily cycled to atmospheric pressure 10 times per minute with a release time titrated to coincide with attainment of respiratory system relaxation volume. MEASUREMENTS: Cardiac output, arterial and mixed venous pH, blood gas tensions, hemoglobin concentration and oxyhemoglobin saturation, central venous pressure, pulmonary and systemic artery pressures, pulmonary artery occlusion pressure, airway gas flow, airway pressure, and pleural pressure were measured. Tidal volume (VT), dynamic lung compliance, intrapulmonary venous admixture, pulmonary vascular resistance, systemic vascular resistance, oxygen delivery, oxygen consumption, and oxygen extraction ratio were calculated. MAIN RESULTS: Central venous infusion of oleic acid reduced PaO2 from 94 +/- 4 mm Hg to 52 +/- 9 mm Hg (mean +/- 1 SD) (p < 0.001) and dynamic lung compliance from 40 +/- 6 mL/cm H2O to 20 +/- 6 mL/cm H2O (p = 0.002) and increased venous admixture from 13 +/- 3% to 32 +/- 7% (p < 0.001) in ten swine weighing 33.3 +/- 4.1 kg while they were spontaneously breathing room air. After induction of lung injury, the swine received CPAP (14.7 +/- 3.3 cm H2O) with or without APRV at 10 breaths per minute with a release time of 1.1 +/- 0.2 s. Although mean transpulmonary pressure was significantly greater during CPAP (11.7 +/- 3.3 cm H2O) vs APRV (9.4 +/- 3.8 cm H2O) (p < 0.001), there were no differences in hemodynamic variables. PaCO2 was decreased and pHa was increased during APRV vs CPAP (p = 0.003 and p = 0.005). PaO2 declined from 83 +/- 4 mm Hg to 79 +/- 4 mm Hg (p = 0.004) during APRV, but arterial oxyhemoglobin saturation (96.6 +/- 1.4% vs 96.9 +/- 1.3%) did not. Intrapulmonary venous admixture (9 +/- 3% vs 11 +/- 5%) and oxygen delivery (469 +/- 67 mL/min vs 479 +/- 66 mL/min) were not altered. After treatment periods and removal of CPAP for 60 min, PaO2 and intrapulmonary venous admixture returned to baseline values. DISCUSSION: Intrapulmonary venous admixture, arterial oxyhemoglobin saturation, and oxygen delivery were maintained by APRV at levels induced by CPAP despite the presence of unstable alveoli. Decrease in PaO2 was caused by increase in pHa and decrease in PaCO2, not by deterioration of pulmonary function. We conclude that periodic decrease of airway pressure created by APRV does not cause significant deterioration in oxygenation or lung mechanics.     

Doppler grid surface scanning applications for pulmonary subsurface parenchymal perfusion assessment

Subsurface perfusion to lung parenchyma underlying the pleura is difficult to assess in live ventilated animals. The purpose of this study was to assess applicability of a newly developed laser Doppler grid scanning imaging technology that measures perfusion of pleural subsurface lung regions in intact normal and abnormal animal lungs. Eighty-six Doppler grid perfusion measurements were performed in five New Zealand White Rabbits (3-5 kg); four with unilateral bullous lung disease, one normal control. Left upper lobe lung surface was exposed to 10 1-sec spot Nd:YAG exposures (70 W/cm2). One week following laser exposure, all rabbits underwent sequential bilateral open thoracotomy. Unaffected left lower lobes in these animals and all four lobes of a previously untreated rabbit were used as controls. Pleural subsurface perfusion measurements were recorded over a contiguous 900-pixel square surface grid using quantitative noncontact laser Doppler imaging during open thoracotomy procedures. Scans were obtained in a normal volume ventilation mode, at 30 cm of inspiratory hold airway pressure, and postinflation. A perfusion-pressure response curve was obtained in normal lung at 10-, 20-, and 30-cm static airway pressure. Post mortem measurements were used as 0 flow controls. Normal lung tissue was found to have relatively high pleural subsurface perfusion (1362 +/- 328 corrected units on a scale of 0-4095). Areas of atelectasis had decreased perfusion (659 +/- 512 U., 48.4 +/- 12.5% compared to normal lung, p < 0.02), but returned to normal levels after inflation of the lung (1253 +/- 363 U., p = 0.21 compared to normal). Pleural subsurface perfusion decreased uniformly and progressively as lung inflation pressure increased (p < 0.0001). Perfusion increased immediately to supranormal values following release of high inspiratory inflation pressure holds (1603 +/- 626 U., 117 +/- 18% compared to normal lung, p = 0.03). Bullae had markedly decreased perfusion (541 +/- 68 U.) that was not further reduced by increased inflation pressures. Noncontact laser Doppler grid perfusion imaging appears to provide a new tool for measuring pleural subsurface perfusion over a large area of lung surface in clinical experimental settings. Results are rapid, reproducible, and consistent. Sampling errors inherent in current point sampling Doppler flow techniques are reduced by the multiple contiguous measurements. We have used this technique to demonstrate inspiratory pressure-related reduction in pleural subsurface perfusion in normal lung, reversible decreased perfusion in atelectatic regions, and reduced perfusion in bullous and laser-treated lung regions.     

Spirometrically controlled quantitative CT for assessing diffuse parenchymal lung disease

OBJECTIVE: Assessment of lung attenuation by CT reflects changes in the air-to-tissue ratio of the lung. We have analyzed the interdependence of intrathoracic gas volume, lung morphology, and functional disorder by high resolution CT (HRCT) to assess quantitative disease threshold in obstructive and restrictive diffuse lung disease. MATERIALS AND METHODS: Pulmonary HRCT was performed on 24 healthy volunteers, 11 patients with chronic obstructive pulmonary disease (COPD), and 16 patients with idiopathic lung fibrosis (IPF). HRCT measurement was standardized by taking three scans at the carina +/- 5 cm and by defining inspiration levels by percent vital capacity (VC) via spirometrically gating to the scanner. RESULTS: The mean lung density at 50% VC (DL50) for healthy subjects was -819 +/- 3.8 (mean +/- SEM) HU. In contrast, COPD DL50 was lower, averaging -861 +/- 6.4 HU, and the IPF DL50 was considerably higher (-731 +/- 17.7 HU), both significantly different (p < 0.001) compared with the control group. The accuracy of quantitative HRCT at different inspiration levels was evaluated by scanning the basal layer at 20, 50, and 80% VC. The control values were -747 +/- 5.6, -816 +/- 3.6, and -855 +/- 3.0 HU, respectively, which were significantly higher (p < 0.001) than those seen in COPD patients at 20 and 50% VC. Again, the IPF patients exhibited increased lung density (p < 0.001) at all inspiratory levels. Discrimination power was best among all cohorts at 20 and 50% VC. Position-dependent artifacts on lung density were quantified by the anteroposterior density gradient (APG). Irrespective of the underlying disease, APG at 50 and 80% VC was similar, but was up to twofold higher at 20% VC, indicating that quantitative estimates near RV may misrepresent mean lung density. CONCLUSION: Our data indicate that quantitative HRCT measurements should be performed not near full inspiration or expiration, but at an intermediate degree of lung inflation, e.g., 50% VC, for reasons of accuracy, intra- and intersubjective comparability, and feasibility. We conclude quantitative HRCT to be a sensitive tool for the evaluation of diffuse parenchymal lung disease.     

Lung fluid dynamics in awake newborn lambs

We measured steady-state lung lymph flow, lymph protein flow, and simultaneous pulmonary vascular pressures in 12 1-wk-old unanesthetized lambs and compared these measurements to those of previous studies, performed under similar conditions, on nine awake adult sheep. The purpose of these experiments was to compare newborn and adult sheep with respect to transvascular filtration of fluid and microvascular permeability to plasma proteins. We prepared the lambs surgically to isolate and collect lung lymph and measure average pulmonary arterial and left atrial pressures, allowing at least 2 days for the lambs to recover from surgery before studies began. Lambs had higher pulmonary arterial and left atrial pressures, lower lymph and plasma protein concentrations, and 57% more lymph flow per gram of dry bloodless lung than sheep; the difference in protein flow between lambs and sheep was not significant. Protein concentration in lymph relative to that in plasma was significantly lower in lambs than in sheep; but the ratio of albumin concentration to globulin concentration in both lymph and plasma was almost identical in the two groups of animals. Extravascular lung water per gram of dry bloodless lung was greater in lambs (4.82+/-0.11 g) than in sheep (4.45+/-0.08 g), but there was no histologic evidence of pulmonary edema in either group of animals. These findings suggest that lambs have more transvascular filtration of fluid per unit lung mass than sheep, but that microvascular sites for protein exchange do not differ appreciably in lambs and sheep. To test this conclusion, we measured steady-state lymph flow in three lambs before and after raising pulmonary microvascular pressure by rapid intravenous infusion of saline. Lymph flow increased as a function of the net transvascular driving pressure (hydraulic pressure gradient-protein osmotic pressure gradient). This response was almost identical to that of four sheep with pulmonary microvascular pressure augmented by inflation of a balloon in the left atrium. In eight lambs we measured the time for intravenously injected (125)I-albumin to equilibrate in lymph at half the specific activity of plasma: the protein tag equilibrated faster than in sheep. This difference could be explained partly by the higher pulmonary arterial and left atrial pressures of lambs than sheep, and possibly by the presence of more microvascular sites for protein exchange relative to the volume of distribution of protein in the lung of the younger animals.     

Effects of ventilation and pleural effusion on measurements of airway thermal volume and blood flow in dog lungs

We studied the effects of ventilation and pleural effusion on measurements of airway thermal volume (ATV) and pulmonary blood flow (PBF) by using the airway gas thermometry method of V. B. Serikov, M. S. Rumm, K. Kambara, M. I. Bootomo, A. R. Osmack, and N. C. Staub (J. Appl. Physiol. 72: 944-953, 1992) in 39 anesthetized dogs with or without lung edema or pleural effusion. To examine the differential effects of increased-pressure and increased-permeability lung edema on accuracy and sensitivity of ATV and PBF, two models of lung edema were induced by intravenous infusion of a Dextran 70 solution and alloxan monohydrate, respectively. Dogs were hyperventilated for 3 min by using a wide range of minute ventilation (VE) to produce two steady-state conditions of airway temperature. Higher levels of VE increased an estimated amount of ATV. The ATV produced by hyperventilation at VE values of 559, 158, and 72 ml.min-1.kg-1 was consistent with the gravimetric total lung mass, the blood-free wet lung weight, and the extravascular lung water volume, respectively. The coefficient of lung thermal conductivity, a practical index of the rate of heat conduction through tissue from lung vessels, was related to the ratio of the decrease in expired air temperature to VE, and estimated PBF was consistent with the thermodilution cardiac output. Pleural effusion had little effect on measurements of ATV and PBF. However, ATV and PBF showed increased variation in dogs with dextran-induced lung edema.     

The critical role of interleukin 4 but not interferon gamma in the pathogenesis of colitis in T-cell receptor alpha mutant mice

PURPOSE: To compare keratocyte density determined by using confocal microscopy with keratocyte density determined in the same corneas by histology. METHODS: Digital en face images of central corneas were recorded three times by using confocal microscopy in vivo in six New Zealand White rabbits. Bright objects (keratocyte nuclei) in the images were automatically identified by using a custom algorithm to estimate total and regional stromal keratocyte densities. The corneas were then excised, fixed, and sectioned in a sagittal plane for histology. Keratocyte nuclei were manually counted from digitized images of 50 histologic sections per cornea. Total and regional keratocyte densities were estimated from the histologic sections by using stereologic methods based on nuclei per unit area, mean nuclear diameter, and section thickness. Histologic cell densities were corrected for tissue shrinkage. RESULTS: By confocal microscopy, total keratocyte density was 39,000 +/- 1,200 cells/mm3 (mean +/- SE; n = 6); cell density was 47,100 +/- 1,300 cells/mm3 in the anterior stroma and decreased to 27,900 +/- 2,700 cells/mm3 in the posterior stroma (P = 0.004). Analysis of the three separate confocal images of each cornea produced repeatable total cell densities (mean coefficient of variation = 0.035). By histology, total keratocyte density was 37,800 +/- 1,100 cells/mm3, not significantly different from that estimated by confocal microscopy (P = 0.43); anterior cell density was 48,300 +/- 900 cells/mm3 and decreased to 29,400 +/- 900 cells/mm3 posteriorly (P < 0.001). CONCLUSIONS: Rabbit keratocyte density estimated by automated analysis of confocal microscopy images in vivo is repeatable and agrees with keratocyte density estimated from histologic sections.     

Role of luminal volume changes in the increase in pulmonary blood flow at birth in sheep

The mechanism by which pulmonary blood flow increases and pulmonary vascular resistance decreases after birth is not fully understood. The aim of this study was to simulate the decrease in lung volume caused by the onset of air-breathing at birth and determine whether it can duplicate the changes in pulmonary blood flow and vascular resistance that occur at this time. In chronically catheterized fetal sheep near term (145 days of gestation), fetal pulmonary arterial blood flow was measured, using coloured microspheres, before and after fetal lung liquid volumes were reduced from 52.2 +/- 2.7 to 21.2 +/- 1.6 ml kg-1. During the 30 min period following the reduction in lung liquid volume, the pulmonary-to-systemic arterial pressure difference decreased from 6.8 +/- 1.2 mmHg (pulmonary > systemic) to 1.6 +/- 0.5 mmHg. Reducing the volume of fetal lung liquid increased pulmonary blood flow from 59.1 +/- 10.5 to 204.2 +/- 40.4 ml min-1 (100 g tissue)-1 and reduced pulmonary vascular resistance from 0.53 +/- 0.20 to 0.14 +/- 0.04 mmHg min ml-1 (100 g tissue)-1. We conclude that a reduction in fetal lung liquid volume, which simulates the reduction in lung volume that occurs at birth, causes a 3- to 4-fold increase in pulmonary blood flow and a reduction in pulmonary vascular resistance of a similar magnitude. Thus, the reduction in lung volume associated with the lung changing from a liquid- to an air-filled organ, may partly account for the increase in pulmonary blood flow and decrease in pulmonary vascular resistance at birth.     

Lung density for assessment of hydration status in hemodialysis patients using the computed tomographic densitometry technique

The density of the lung reflects the total mass of fluid, air, and dry lung tissue per unit volume of the lung. Lung density can be measured by evaluation of attenuation of an electron beam with computed tomography (CT). This technique has been shown to be sufficiently reliable and sensitive to distinguish normal from abnormal lung water. The aim of this study was to find out whether lung density properly reflects the hydration status in hemodialysis patients in comparison with other standard methods. Fourteen hemodialysis patients, with an ultrafiltration ranging from 0.3 to 4.5 liters per session, underwent CT measurements of lung density, ultrasonographic measurements of the diameter of the inferior vena cava after quiet expiration (IVCe) and quiet inspiration (IVCi), and measurements of the hematocrit and plasma levels of the biochemical hydration markers cyclic guanosine monophosphate (cGMP) and atrial natriuretic peptide (ANP). These measurements were performed before and 3.5 to 4 hours after termination of dialysis. Quantitative estimates of lung density were obtained within pixels with CT numbers ranging between -1000 and -100 Hounsfield Units (HU), and compared with normal data from 18 normal controls. In normal controls, the lung density ranged from -800 to -730 HU. In hemodialysis patients, lung density was significantly higher than normal before dialysis (-678 +/- 96 HU, P < 0.01) and significantly decreased after dialysis (-706 +/- 92 HU, P < 0.05), indicating a decrease in fluid content of the lung. The density was normalized in 5 patients. A significant correlation was found between lung density and IVCe both before and after dialysis (r = 0.8, P < 0.01 for both). Change in density was significantly correlated to amount of ultrafiltration (r = 0.67, P < 0.01) and percent change in blood volume (r = 0.63, P < 0.05), indicating that lung density is greatly affected by changes in the extracellular fluid volume, mainly the intravascular volume. In conclusion, lung water reflects the hydration status in hemodialysis patients and can be monitored by measuring the lung density by CT. Accordingly, normalization of lung density can help to achieve a proper dry weight in these patients.     

Actions of nitric oxide on renal epithelial transport

A 55-year-old male who had a remote history of occupational asbestos exposure consulted us because of chest pain. Chest X-ray revealed diffuse pleural thickening and pleural effusion on the right. A diagnosis of malignant mesothelioma, biphasic type was made by needle pleural biopsy. Fourteen months later, the patient died of brain metastasis. At autopsy, malignant mesothelioma of the pleura with metastasis to the brain and bilateral adrenal glands was observed. Brain metastases proven by autopsy are rare in cases of malignant mesothelioma. The ferruginous body count in the lung tissue was 16 per gram of wet weight.     

Pulmonary infection with Mycobacterium avium-intracellulare leads to air trapping distal to the small airways

To clarify the structure and function of the airways in Mycobacterium avium-intracellulare (MAI) infection, we performed pulmonary function tests and high-resolution computed tomography (HRCT) of the thorax in female patients 61 +/- 9 yr of age (n = 12) with pulmonary MAI infection without predisposing lung disease and compared their data with those of normal female volunteers 54 +/- 8 yr of age (n = 9). We calculated the E/I ratio, i.e., the average ratio of HRCT number at full expiration to that at full inspiration, as an index for the evaluation of air trapping distal to the small airways. Patients showed significant increases in residual volume and slope of phase III (DeltaN2) of the single-breath nitrogen test, and significant decreases in flow at 50 and 25% of FVC, suggesting hyperinflation and obstruction of the small airways. HRCT of patients revealed the small nodules and ectasis of bronchioles and small bronchi located mainly in segments (S) S2, S3, S4, and S5. The E/I ratio was significantly elevated in patients, and especially higher in the upper lung field than in the lower lung field, suggesting air trapping distal to the small airways. The difference of E/I ratio between the upper and lower field is probably related to the segmental distribution of CT abnormalities. These findings suggest that MAI infection can lead to air trapping distal to the small airways.     

Ultrasonography of the thorax (excluding the heart)

Until recently, ultrasonography has had a subordinate role in the evaluation of the thorax in both small animals and humans, most likely due to the inability of sound to penetrate air-filled lung. When pathologic processes such as pleural effusion and lung consolidation provide an acoustic window to the thorax, however, thoracic ultrasonography becomes feasible. As this article illustrates, ultrasonography may be effectively employed in the diagnosis and management of various thoracic wall, pleural, mediastinal, pulmonary, and diaphragmatic diseases by providing valuable information not obtainable with routine radiography and enabling percutaneous aspiration or tissue core biopsy of lesions.     

Changes in regional lung mechanics and ventilation distribution after unilateral pulmonary artery occlusion

Regional pneumoconstriction induced by alveolar hypocapnia is an important homeostatic mechanism for optimization of ventilation-perfusion matching. We used positron imaging of 13NN-equilibrated lungs to measure the distribution of regional tidal volume (VT), lung volume (VL), and lung impedance (Z) before and after left (L) pulmonary artery occlusion (PAO) in eight anesthetized, open-chest dogs. Measurements were made during eucapnic sinusoidal ventilation at 0.2 Hz with 4-cmH2O positive end expiratory pressure. Right (R) and L lung impedances (ZR and ZL) were determined from carinal pressure and positron imaging of dynamic regional VL. LPAO caused an increase in magnitude of ZL relative to magnitude of ZR, resulting in a shift in VT away from the PAO side, with a L/R magnitude of Z ratio changing from 1.20 +/- 0.07 (mean +/- SE) to 2.79 +/- 0.85 after LPAO (P < 0.05). Although mean L lung VL decreased slightly, the VL normalized parameters specific admittance and specific compliance both significantly decreased with PAO. Lung recoil pressure at 50% total lung capacity also increased after PAO. We conclude that PAO results in an increase in regional lung Z that shifts ventilation away from the affected area at normal breathing frequencies and that this effect is not due to a change in VL but reflects mechanical constriction at the tissue level.     

The effects of nephrectomy on the developing fetus

Bilateral renal pathologies such as renal agenesis and renal dysplasia and lower urinary tract obstruction have been reported to result in pulmonary hypoplasia. Although oligohydramnios and resultant thoracic compression was suggested to be the cause of pulmonary hypoplasia, the exact mechanism is still unknown. Additionally the effect of absence of renal tissue on the development of the fetus has not been previously studied in detail. Therefore an experimental study was planned to investigate the effects of fetal nephrectomy on development. The fetuses from 27 New Zealand white rabbits were studied on the 23rd day of gestation. Right ovarian-end fetuses underwent bilateral nephrectomy or sham operations. Rabbits underwent hysterectomy on gestational day 30, and live fetuses were studied. Fetal body, lung, heart and liver weights, and lung, heart and thorax volumes were determined, organ weight/body weight ratios were calculated. Additionally, lungs were evaluated by histological examination. Although fetal nephrectomy resulted in decreased body weight (BW), lung, heart, liver weights and heart weight/BW ratio (p < 0.05), lung weight/BW and liver weight/BW ratios did not differ. Additionally, heart and thorax volumes were significantly decreased in the nephrectomy group (p < 0.05). However lung volume and thorax volume/BW ratio did not differ between groups. The histological evaluation of lungs revealed exfoliated cells but normal lung development. Bilateral fetal nephrectomy results in small-for-gestational age (SGA) status during birth without affecting the development of organic systems. Since SGA status may be associated with decreased placentofetal blood flow, bilateral nephrectomy may act through decreasing placentofetal blood flow and/or through the lack of kidney-related growth factors.     

A new ventilation inhomogeneity index from multiple breath indicator gas washout tests in mechanically ventilated patients

OBJECTIVES: a) To determine the validity of a new method to analyze indicator gas washout tests on mechanically ventilated patients. This method takes into account the difference between the end-expiratory gas fraction and the mean gas fraction in the lung and provides the end-expiratory lung volume and a new index of ventilation inhomogeneity called volumes regression index. b) To determine the validity of this index as a predictor of chronic obstructive pulmonary disease. c) To compare this index with the moment ratio index and Becklake index. DESIGN: Prospective study of diagnostic test. Criterium standards: Closed-circuit indicator gas dilution technique and Tiffeneau index. SETTING: Surgical intensive care unit of a university hospital. PATIENTS: A total of 38 mechanically ventilated postoperative patients, divided into two groups: the obstructive group (n = 21) and the nonobstructive group (n = 17), based on their preoperative lung function. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: a) The mean coefficient of variation of all lung volume measurements in a group of nine healthy volunteers was 5%, and the difference between this technique and the closed-circuit helium dilution measurements was -2 +/- 5%. In patients, the mean coefficient of variation of the lung volume measurements was 3.5%. The volumes regression index was measured as 0.02 +/- 0.04 in a dummy lung, 0.37 +/- 0.08 in the healthy volunteers, 0.64 +/- 0.23 in the nonobstructive patients, and 1.1 +/- 0.3 in the obstructive patients. The volumes regression index provided a better correlation (r2 = .46) with preoperatively determined Tiffeneau index than the Becklake index (r2 = .11) or the moment ratio index (r2 = .18). CONCLUSION: The proposed technique provides a means for accurate measurement of the end-expiratory lung volume and the amount of ventilation inhomogeneity in mechanically ventilated intensive care unit patients.     

Pressure-controlled, inverse ratio ventilation that avoids air trapping in the adult respiratory distress syndrome

OBJECTIVES: To investigate physiologic and outcome data in patients switched from volume-cycled conventional ratio ventilation to pressure-controlled inverse ratio ventilation that did not produce air trapping and intrinsic positive end-expiratory pressure (PEEP). SETTING: Medical intensive care unit. DESIGN: Retrospective analysis of crossover data and outcome. PATIENTS: Fourteen patients with the adult respiratory distress syndrome who were receiving mechanical ventilation with volume-cycled, conventional ratio ventilation followed by pressure-controlled, inverse ratio ventilation. INTERVENTIONS: Our approach to pressure-controlled, inverse ratio ventilation was to use tidal volumes and applied PEEP values comparable to those volumes and values used on volume-cycled, conventional ratio ventilation, use inspiratory times to increase mean airway pressure instead of additional applied PEEP, and avoid air trapping (intrinsic PEEP). MEASUREMENTS AND MAIN RESULTS: With this approach, there was a reduction in peak airway pressure from 53 +/- 8.5 (SD) to 40 +/- 5.9 cm H2O (p < .01), and an increase in mean airway pressure from 20 +/- 3.9 to 30 +/- 5.2 cm H2O (p < .01). Tidal volume, mean inflation pressure, and compliance did not change. Oxygenation (PaO2) improved from 57 +/- 11.3 torr (7.6 +/- 1.5 kPa) to 94 +/- 40.2 torr (12.5 +/- 5.4 kPa) (p = .01) but the oxygenation index (mean airway pressure x FIO2 x 100/PaO2) did not change significantly (25.9 +/- 10.3 to 27.2 +/- 12.2). There was no significant change in PaCO2 or pH even though delivered minute ventilation decreased from 17.4 +/- 4.3 to 14.8 +/- 5.8 L/min (p = .02). Cardiac index slightly decreased, but hemodynamic values were otherwise stable. Only three of the 14 study patients survived. CONCLUSIONS: These data demonstrate that oxygenation is primarily a function of mean airway pressure, and that longer inspiratory times can be used as an alternative to applied PEEP to increase this oxygenation. If no air trapping develops, lung inflation pressures and delivered volumes remain constant with this approach. Because the technique was used only in patients refractory to conventional techniques, the poor outcome is not surprising.