Inhomogeneities of ventilation and the diffusing capacity to perfusion in various chronic lung diseases

Diabetic Pneumopathy- A Novel Diabetes-associated Complication: Pathophysiology, the Underlying Mechanism and Combination Medication

BACKGROUND

The "diabetic lung" has been identified as a possible target organ in diabetes, with abnormalities in ventilation control, bronchomotor tone, lung volume, pulmonary diffusing capacity, and neuroadrenergic bronchial innervation.

OBJECTIVE

This review summarizes studies related to diabetic pneumopathy, pathophysiology and a number of pulmonary disorders including type 1 and type 2 diabetes.

METHODS

Electronic searches were conducted on databases such as Pub Med, Wiley Online Library (WOL), Scopus, Elsevier, ScienceDirect, and Google Scholar using standard keywords "diabetes," "diabetes Pneumopathy," "Pathophysiology," "Lung diseases," "lung infection" for review articles published between 1978 to 2023 very few previous review articles based their focus on diabetic pneumopathy and its pathophysiology.

RESULTS

Globally, the incidence of diabetes mellitus has been rising. It is a chronic, progressive metabolic disease. The "diabetic lung" may serve as a model of accelerated ageing since diabetics' rate of respiratory function deterioration is two to three-times higher than that of normal, non-smoking people.

CONCLUSION

Diabetes-induced pulmonary dysfunction has not gained the attention it deserves due to a lack of proven causality and changes in cellular properties. The mechanism underlying a particular lung illness can still only be partially activated by diabetes but there is evidence that hyperglycemia is linked to pulmonary fibrosis in diabetic people.

[Adaptation to altitude in respiratory diseases]

The frequency of high-altitude sojourns (for work, leisure, air travel or during car/train journeys) justifies the question of their tolerance, especially in people with pre-existing respiratory disease. Reduced barometric pressure and abrupt variations in temperature and inhaled air density may be responsible for modifications affecting the respiratory system and, in fine, oxygenation. These modifications may compromise altitude tolerance, further worsen respiratory dysfunction and render physical exercise more difficult. In obstructive lung disease, altitude is associated with gas exchange impairment, increased ventilation at rest and during exercise and heightened pulmonary artery pressure through hypoxic vasoconstriction, all of which may worsen dyspnea and increase the risk of altitude intolerance (acute mountain sickness, AMS). The most severe patients require rigorous evaluation, and hypoxic testing can be proposed. People with mild to moderate intermittent asthma can plan high altitude sojourns, provided that they remain under control at night and during exercise, and follow an adequate action plan in case of exacerbation. Respiratory disease patients with pulmonary artery hypertension (PAH) and chemoreflex control abnormalities need to be identified as at risk of altitude intolerance.

Endoscopic lung volume reduction with endobronchial valves in very low D LCO patients: results from the German Registry - Lungenemphysemregister e.V

Background

Endoscopic lung volume reduction (ELVR) with valves has been suggested to be the key strategy for patients with severe emphysema and concomitant low diffusing capacity of the lung for carbon monoxide (D_LCO). However, robust evidence is still missing. We therefore aim to compare clinical outcomes in relation to D_LCO for patients treated with ELVR.

Methods

We assessed D_LCO at baseline and 3 months follow-up and compared pre- and postprocedural pulmonary function test, quality of life, exercise capacity and adverse events. This is a retrospective subanalysis of prospectively collected data from the German Lung Emphysema Registry.

Results

In total, 121 patients treated with ELVR were analysed. Thirty-four patients with a D_LCO ≤20% and 87 patients with a D_LCO >20% showed similar baseline characteristics. After ELVR, there was a decrease of residual volume (both p<0.001 to baseline) in both groups, and both demonstrated better quality of life (p<0.01 to baseline). Forced expiratory volume in 1 s (FEV₁) improved significantly only in patients with a D_LCO >20% (p<0.001 to baseline). Exercise capacity remained almost unchanged in both groups (p=0.3). The most frequent complication for both groups was a pneumothorax (D_LCO ≤20%: 17.6% versus D_LCO >20%: 16.1%; p=0.728). However, there were no significant differences in other adverse events between both groups.

Conclusions

ELVR improves lung function as well as quality of life in patients with D_LCO >20% and D_LCO ≤20%. Adverse events did not differ between groups. Therefore, ELVR should be considered as a treatment option, even in patients with a very low D_LCO.

Endoscopic lung volume reduction with endobronchial valves can be safely performed in patients with a very low diffusing capacity of the lung (D_LCO). Clinical effectiveness is comparable to patients with higher D_LCO.https://bit.ly/3cOgDK1

Relative Regional Air Volume Change Maps at the Acinar Scale Reflect Variable Ventilation in Low Lung Attenuation of COPD patients

OBJECTIVES

The purpose of this study was to investigate regional air volume changes at the acinar scale of the lung in chronic obstructive pulmonary disease (COPD) patients using an image registration technique.

MATERIALS AND METHODS

Thirty-four emphysema patients and 24 subjects with normal chest CT and pulmonary function test (PFT) results were included in this retrospective study for which informed consent was waived by the institutional review board. After lung segmentation, a mass-preserving image registration technique was used to compute relative regional air volume changes (RRAVCs) between inspiration and expiration CT scans. After determining the appropriate thresholds of RRAVCs for low ventilation areas (LVAs), they were displayed and analyzed using color maps on the background inspiration CT image, and compared with the low attenuation area (LAA) map. Correlations between quantitative CT parameters and PFTs were assessed using Pearson's correlation test, and parameters were compared between emphysema and normal-CT patients using the Student's t-test.

RESULTS

LVA percentage with an RRAVC threshold of 0.5 (%LVA_0.5) showed the strongest correlations with FEV₁/FVC (r = -0.566), FEV₁ (r = -0.534), %LAA_-950insp (r = 0.712), and %LAA_-856exp (r = 0.775). %LVA_0.5 was significantly higher (P < 0.001) in COPD patients than normal subjects. Despite the identical appearance of emphysematous lesions on the LAA_-950insp map, the RRAVC map depicted a wide range of ventilation differences between these LAA clusters.

CONCLUSION

RRAVC-based %LVA_0.5 correlated well with FEV₁/FVC, FEV₁, %LAA_-950insp and %LAA_-856exp. RRAVC holds the potential for providing additional acinar scale functional information for emphysematous LAAs in inspiratory CT images, providing the basis for a novel set for emphysematous phenotypes.

Can DLNO/DLCO ratio offset prejudicial effects of functional heterogeneities in acinar regions?

OBJECTIVES

(1) To establish the general equation that describes relationship of DM_CO/Vc versus DL_NO/DL_CO under conditions with no functional heterogeneities. (2) To examine the effects of functional heterogeneities, including parallel and series (stratified) heterogeneities, on DL_NO/DL_CO.

RESULTS AND DISCUSSIONS

(1) Given that "true" θ_NO in pulmonary capillaries is represented by surface absorption-related θ_NO, relationship between DM_CO/Vc and DL_NO/DL_CO does not differ significantly from that obtained on premise of infinite θ_NO. DL_NO/DL_CO decided physiologically may mirror morphometric DM_CO/Vc actually working for gas exchange but not "total" morphometric ratio of DM_CO/Vc. (2) There are three parallel heterogeneities that affect diffusing capacity (D)-related parameters. Of them, only the heterogeneity of D/V_A, where V_A is alveolar volume, underestimates DL_CO and DL_NO. DL_NO/DL_CO does not alleviate negative impact of D/V_A heterogeneity, indicating that DM_CO/Vc estimated from DL_NO/DL_CO does not mirror "true" morphometric DM_CO/Vc in diseased lungs with D/V_A maldistribution. (3) Stratified heterogeneity underrates morphometric DM_CO, DM_NO, and DM_NO/DM_CO maximally by 1.4 %, 2.8 %, and 1.4 %, respectively, under conditions similar to single-breath D measurements, suggesting that effect of stratified heterogeneity on D measures is no longer needed to be considered in normal subjects but may be in patients having lung diseases with destructive lesions of acinar structures.

Anatomical backgrounds on gas exchange parameters in the lung

Many problems regarding structure-function relationships have remained unsolved in the field of respiratory physiology. In the present review, we highlighted these uncertain issues from a variety of anatomical and physiological viewpoints. Model A of Weibel in which dichotomously branching airways are incorporated should be used for analyzing gas mixing in conducting and acinar airways. Acinus of Loeschcke is taken as an anatomical gas-exchange unit. Although it is difficult to define functional gas-exchange unit in a way entirely consistent with anatomical structures, acinus of Aschoff may serve as a functional gas-exchange unit in a first approximation. Based on anatomical and physiological perspectives, the multiple inert-gas elimination technique is thought to be highly effective for predicting ventilation-perfusion heterogeneity between acini of Aschoff under steady-state condition. Changes in effective alveolar P_O2, the most important parameter in classical gas-exchange theory, are coherent with those in mixed alveolar P_O2 decided from the multiple inert-gas elimination technique. Therefore, effective alveolar-arterial P_O2 difference is considered useful for assessing gas-exchange abnormalities in lung periphery. However, one should be aware that although alveolar-arterial P_O2 difference sensitively detects moderately low ventilation-perfusion regions causing hypoxemia, it is insensitive to abnormal gas exchange evoked by very low and high ventilation-perfusion regions. Pulmonary diffusing capacity for CO (D_LCO) and the value corrected for alveolar volume (V_AV), i.e., D_LCO/V_AV (K_CO), are thought to be crucial for diagnosing alveolar-wall damages. D_LCO-related parameters have higher sensitivity to detecting abnormalities in pulmonary microcirculation than those in the alveolocapillary membrane. We would like to recommend four categories derived from combining behaviors of D_LCO with those of K_CO for differential diagnosis on anatomically morbid states in alveolar walls: type-1 abnormality defined by decrease in both D_LCO and K_CO; type-2 abnormality by decrease in D_LCO but increase in K_CO; type-3 abnormality by decrease in D_LCO but restricted rise in K_CO; and type-4 abnormality by increase in both D_LCO and K_CO.

Multicenter study of quantitative computed tomography analysis using a computer-aided three-dimensional system in patients with idiopathic pulmonary fibrosis

PURPOSE

To evaluate the feasibility of automated quantitative analysis with a three-dimensional (3D) computer-aided system (i.e., Gaussian histogram normalized correlation, GHNC) of computed tomography (CT) images from different scanners.

MATERIALS AND METHODS

Each institution's review board approved the research protocol. Informed patient consent was not required. The participants in this multicenter prospective study were 80 patients (65 men, 15 women) with idiopathic pulmonary fibrosis. Their mean age was 70.6 years. Computed tomography (CT) images were obtained by four different scanners set at different exposures. We measured the extent of fibrosis using GHNC, and used Pearson's correlation analysis, Bland-Altman plots, and kappa analysis to directly compare the GHNC results with manual scoring by radiologists. Multiple linear regression analysis was performed to determine the association between the CT data and forced vital capacity (FVC).

RESULTS

For each scanner, the extent of fibrosis as determined by GHNC was significantly correlated with the radiologists' score. In multivariate analysis, the extent of fibrosis as determined by GHNC was significantly correlated with FVC (p < 0.001). There was no significant difference between the results obtained using different CT scanners.

CONCLUSION

Gaussian histogram normalized correlation was feasible, irrespective of the type of CT scanner used.

Calculating alveolar capillary conductance and pulmonary capillary blood volume: comparing the multiple- and single-inspired oxygen tension methods

Key elements for determining alveolar-capillary membrane conductance (Dm) and pulmonary capillary blood volume (Vc) from the lung diffusing capacity (Dl) for carbon monoxide (DlCO) or for nitric oxide (DlNO) are the reaction rate of carbon monoxide with hemoglobin (thetaCO) and the DmCO/DlNO relationship (alpha-ratio). Although a range of values have been reported, currently there is no consensus regarding these parameters. The study purpose was to define optimal parameters (thetaCO, alpha-ratio) that would experimentally substantiate calculations of Dm and Vc from the single-inspired O2 tension [inspired fraction of O2 (FiO2)] method relative to the multiple-FiO2 method. Eight healthy men were studied at rest and during moderate exercise (80-W cycle). Dm and Vc were determined by the multiple-FiO2 and single-FiO2 methods (rebreathe technique) and were tabulated by applying previously reported thetaCO equations (both methods) and by varying the alpha-ratio (single-FiO2 method) from 1.90 to 2.50. Values were then compared between methods throughout the examined alpha-ratios. Dm and Vc were critically dependent on the applied thetaCO equation. For the multiple-FiO2 method, Dm was highly variable between thetaCO equations (rest and exercise); the range of Vc was less widespread. For the single-FiO2 method, the thetaCO equation by Reeves and Park (1992) combined with an alpha-ratio between 2.08 and 2.26 gave values for Dm and Vc that most closely matched those from the multiple-FiO2 method and were also physiologically plausible compared with predicted values. We conclude that the parameters used to calculate Dm and Vc values from the single-FiO2 method (using DlCO and DlNO) can significantly influence results and should be evaluated within individual laboratories to obtain optimal values.

Influence of oral beclomethasone dipropionate on early non-infectious pulmonary outcomes after allogeneic hematopoietic cell transplantation: results from two randomized trials

Early non-infectious pulmonary complications represent a significant cause of mortality after hematopoietic cell transplantation (HCT). We tested the hypothesis that oral beclomethasone dipropionate (BDP) is effective for preventing early non-infectious pulmonary complications after allogeneic HCT. We retrospectively reviewed the medical records of 120 patients, 60 in each treatment arm, to identify non-infectious and infectious pulmonary events and pulmonary function test results from all patients who participated in two randomized trials of oral BDP for treatment of acute gastrointestinal GVHD. 17-Beclomethasone monopropionate (17-BMP), the active metabolite of BDP, was evaluated in blood from the right atrium in four patients. Thirty-three of 42 (79%) placebo-treated patients experienced a decrease of the DL(CO) from pretransplant to day 80 after transplant, compared with 27 of 49 (55%) BDP-treated patients (P=0.02). In the first 200 days after randomization, there were no cases of non-infectious pulmonary complications in BDP-treated patients, vs four cases among placebo-treated patients (P=0.04). Levels of 17-BMP were detected in atrial blood at steady state. Delivery of a potent glucocorticoid such as 17-BMP to the pulmonary artery after oral dosing of BDP may be useful in modulating pulmonary inflammation and preventing the development of non-infectious pulmonary complications after allogeneic HCT.

Carbon monoxide diffusion capacity: how low can you go for hematopoietic cell transplantation eligibility?

Current guidelines suggest that patients with a pretransplantation diffusion capacity of the lung for carbon monoxide (DLCO) < or = 60% are not ideal candidates for hematopoietic cell transplantation (HCT); however, recent studies suggest this criterion may exclude patients who will benefit from the procedure. We conducted a study of all adult patients who underwent autologous or allogeneic HCT between 1990 and 2005, and had a DLCO < 60%, of predicted normal, to examine whether there is a lower limit for the DLCO threshold in the context of respiratory failure and nonrelapse mortality risk (NRM), and whether a comprehensive risk scoring system, such as the Pretransplant Assessment of Mortality (PAM) risk score, can more effectively risk stratify these patients with a very low pretransplantation DLCO. We found that among patients with a DLCO < or = 60% the risk of respiratory failure or NRM was not significantly different; however, the PAM score effectively risk-stratified these patients for NRM risk. There was a stepwise relationship between PAM score category and NRM risk; the highest PAM score category was associated with a 4.38-fold increase in risk (P < .001). These findings suggest that the pretransplantation DLCO should not be considered the sole eligibility criteria for allogeneic HCT.

Quantitative assessment of air trapping in chronic obstructive pulmonary disease using inspiratory and expiratory volumetric MDCT

OBJECTIVE

The purpose of our study was to determine the attenuation threshold value for the detection and quantification of air trapping using paired inspiratory and expiratory volumetric MDCT scans and to assess whether the densitometric parameter can be used for the quantification of airway dysfunction in chronic obstructive pulmonary disease (COPD) regardless of the degree of emphysema.

MATERIALS AND METHODS

This study included 36 patients with COPD who underwent 64-MDCT. The entire lung volume with attenuation between -500 and -1,024 H was segmented as whole lung. The lung volume with attenuation between -500 and -950 H was segmented as limited lung, while the lung volume of less than -950 H was segmented as emphysema and eliminated. The relative volumes for limited lung (relative volume(n-950)) with attenuation values below thresholds (n) ranging from -850 to -950 H, and relative volume for whole lung (relative volume(<n)) were obtained on inspiratory and expiratory CT. Then the differences of relative volumes after expiration in whole lung (relative volume change(<n)) and limited lung (relative volume change(n-950)) were calculated. Patients were classified into two groups according to mean relative volume less than -950 H. Correlations between densitometry parameters and pulmonary function tests (PFTs) reflecting airway dysfunction were evaluated.

RESULTS

The highest correlation with PFTs was observed at the upper threshold of -860 H. In the moderate to severe emphysema group (relative volume(<-950) > 15%), relative volume change(860-950) significantly correlated with the results of PFTs, whereas no significant correlations were seen between relative volume change(<-860) and PFTs. In the minimal or mild emphysema group (inspiratory relative volume(<-950) < 15%), all densitometric parameters correlated with PFTs.

CONCLUSION

The densitometric parameter of relative volume change calculated on paired inspiratory and expiratory MDCT using the threshold of -860 H in limited lung correlated closely with airway dysfunction in COPD regardless of the degree of emphysema.

Diffusing Capacity for Nitric Oxide and Carbon Monoxide in Patients With Diffuse Parenchymal Lung Disease and Pulmonary Arterial Hypertension

BACKGROUND

The passage of carbon monoxide (CO) through the alveolocapillary membrane and into the plasma and intraerythrocytic compartments determines the diffusing capacity of the lung for CO (DLCO) as defined by the Roughton and Forster equation. On the other hand, the single-breath diffusing capacity of the lung for nitric oxide (DLNO) is thought to represent the true membrane diffusing capacity because of its very high affinity for hemoglobin (Hb) and its independence from pulmonary capillary blood volume. Therefore, the DLNO/DLCO ratio can be used to differentiate between thickened alveolocapillary membranes (both DLNO and DLCO are decreased, and the DLNO/DLCO ratio is normal) and decreased perfusion of ventilated alveoli (the DLNO less decreased than the DLCO; therefore, the DLNO/DLCO ratio is high) in patients with pulmonary disease.

STUDY DESIGN

We measured the combined values of DLCO and DLNO in 41 patients with diffuse parenchymal lung disease (DPLD), 26 patients with pulmonary arterial hypertension (PAH), and 71 healthy subjects.

RESULTS

The DLCO (corrected to the standard Hb value) was lowered in the DPLD group (64% of predicted) and in the PAH group (64% of predicted), and was normal in the control group (105% of predicted). The DLNO/DLCO ratio in patients with PAH (4.98) was significantly higher than that in patients with DPLD (4.56) and in healthy subjects (4.36).

CONCLUSION

The DLNO/DLCO ratio is significantly higher in patients with PAH than in healthy subjects, although this ratio cannot be applied as a screening test to discriminate between patients with DPLD and PAH as the overlap between these groups is too large.

Validation of a two-compartment model of ventilation/perfusion distribution

Ventilation (V (A)) to perfusion (Q ) heterogeneity (V (A)/Q ) analyses by a two-compartment lung model (2C), utilizing routine gas exchange measurements and a computer solution to account for O(2) and CO(2) measurements, were compared with multiple inert gas elimination technique (MIGET) analyses and a multi-compartment (MC) model. The 2C and MC estimates of V (A)/Q mismatch were obtained in 10 healthy subjects, 43 patients having chronic obstructive pulmonary disease (COPD) and in 14 dog experiments where hemodynamics and acid-base status were manipulated with gas mixtures, fluid loading and tilt-table stressors. MIGET comparisons with 2C were made on 6 patients and 32 measurements in healthy subjects before and after exercise at normoxia and altitude hypoxia. Statistically significant correlations for logarithmic standard deviations of V (A)/Q distributions (SD(V (A)/Q )) were obtained for all 2C comparisons, with similar values between 2C and both other methods in the 1.1-1.5 range, compatible with mild to moderate COPD. 2C tended to overestimate MC and MIGET values at low and underestimate them at high SD(V (A)/Q ) values. SD(V (A)/Q ) weighted by Q agreed better with MC and MIGET estimates in the normal range, whereas SD(V (A)/Q ) weighted by V (A) was closer to MC at higher values because the V (A)-weighted SD(V (A)/Q ) is related to blood-to-gas PCO(2) differences that are elevated in disease, thereby allowing better discrimination. The 2C model accurately described functional V (A)/Q characteristics in 26 normal and bronchoconstricted dogs during non-steady state rebreathing and could be used to quantify the effect of reduced O(2) diffusing capacity in diseased lungs. These comparisons indicate that 2C adequately describes V (A)/Q mismatch and can be useful in clinical or experimental situations where other techniques are not feasible.

Pattern of diffusion disturbance related to clinical diagnosis: The K(CO) has no diagnostic value next to the DL(CO)

AIM OF THE STUDY

The diffusion capacity of the lung for carbon monoxide (DL(CO)) is an important tool in the diagnosis and follow-up of patients with pulmonary diseases. In case of a decreased DL(CO) the K(CO), defined as DL(CO)/V(A) (V(A) is alveolar volume), can differentiate between normal alveolocapillary membrane (normal K(CO)) and abnormal alveolocapillary membrane (low K(CO)). The latter category consists of decreased surface of the membrane, increased thickness or decreased perfusion of ventilated alveoli. The V(A)/TLC (TLC is total lung capacity determined by whole body plethysmography) can partially differentiate between these categories. The aim of this study was to investigate the diagnostic value of the specific diffusion disturbances, which can be constructed by combining the DL(CO), K(CO) and V(A)/TLC.

METHODS

In 460 patients the diagnosis made by clinicians were fitted into five diagnostic categories: asthma, chronic obstructive pulmonary disease (COPD), treatment effects of haematologic malignancies, heart failure and diffuse parenchymal lung diseases (DPLD). These categories were linked to the pattern of diffusion disturbance.

RESULTS

Almost all patients with asthma have a normal DL(CO), most patients in the other groups do not have the expected pattern of diffusion disturbance, especially in the group with DPLD a bad match is observed.

CONCLUSION

In this study the pattern of diffusion disturbance is of limited use in establishing a diagnosis. The use of the K(CO) next to the DL(CO) has no additional diagnostic value. Regional ventilation-perfusion inequality probably forms an important underlying mechanism of decreased DL(CO).

Pretransplant lung function, respiratory failure, and mortality after stem cell transplantation

RATIONALE

The role of pulmonary function before stem cell transplant as a potential risk factor for the development of early post-transplant respiratory failure and mortality is controversial.

METHODS

We conducted a retrospective analysis of the pretransplant pulmonary function of 2,852 patients who received their transplant between 1990 and 2001.

MEASUREMENTS

Pretransplant FEV(1), FVC, total lung capacity (TLC), diffusing capacity of carbon monoxide (DL(CO)), and the alveolar-arterial oxygen tension difference P(A-a)O(2) were measured and assessed for association with development of early respiratory failure and mortality in Cox proportional hazard logistic models.

MAIN RESULTS

In multivariate analyses, progressive decrease of all lung function parameters was associated with a stepwise increase in risk of developing early respiratory failure and mortality when assessed in independent models. On the basis of a significant correlation between FEV(1) and FVC (r = 0.81), FEV(1) and TLC (r = 0.61), and FVC and TLC (r = 0.80), and a lack of correlation between FEV(1) and DL(CO), we developed a pretransplant lung function score based on pretransplant FEV(1) and DL(CO) to determine the extent of pulmonary compromise before transplant. Multivariate analysis indicated that higher pretransplant lung function scores are associated with a significant increased risk for developing early respiratory failure (category II hazard ratio [HR], 1.4; category III HR, 2.2; category IV HR, 3.1; p < 0.001) and death (category II HR, 1.2; category III HR, 2.2; category IV HR, 2.7; p < 0.005).

CONCLUSIONS

These results suggest that not only does compromised pretransplant lung function contribute to the risk for development of early respiratory failure and mortality but this risk may be estimated before transplant by grading the extent of FEV(1) and DL(CO) compromise.

Pulmonary function testing prior to hematopoietic stem cell transplantation

The pretransplant pulmonary function test plays an important role in the management of noninfectious pulmonary complications after hematopoietic stem cell transplantation (HCT). Although these tests are widely used as standard preoperative assessments in the nontransplant population, common conditions associated with the HCT patient requires that particular attention be given to interpretation of pulmonary function testing (PFT) results, such as comparison of serial pulmonary function tests and evaluation of the diffusion capacity. Although their utility in helping to predict the likelihood of developing post transplant pulmonary complications and mortality is not well established, current data indicate that pretransplant PFTs are important as a reference for the interpretation of post transplant PFTs and for identifying patients at high risk for developing pulmonary complications and/or mortality after HCT. Future studies of pretransplant pulmonary function should consider the advances in HCT, so that pretransplant PFTs will become a useful tool in pretransplant risk assessment and help the transplant oncologist to determine the most appropriate conditioning regimen for a patient with compromised lung function.

Nitric oxide diffusing capacity and alveolar microvascular recruitment in sarcoidosis

We measured diffusing capacities for carbon monoxide (DLCO) and nitric oxide, lung volume, and cardiac output by a rebreathing technique at two alveolar O2 tensions (PAO2) at rest and exercise. Membrane diffusing capacity for CO (DMCO) and VC were estimated from DLCO by the Roughton-Forster (RF) method and also from simultaneous lung diffusing capacity for NO and DLCO measured at one O2 tension (modified RF method). Estimates by these methods agreed closely in normal subjects (Tamhane et al., Chest 2001;120:1850-1856). Using these methods, we studied patients with stages II-III pulmonary sarcoidosis to determine (1) whether the modified RF method accurately estimates DMCO and VC in parenchymal disease and (2) whether sarcoidosis alters recruitment of diffusing capacity with respect to cardiac output. In patients, DMCO and VC estimated by the two methods agreed closely. DMCO was disproportionately reduced relative to VC at any given cardiac output, and the slope of the relationship between DLCO and cardiac output was moderately, though significantly, below normal. We conclude that in sarcoidosis (1) the modified RF method provides comparable estimates of DMCO and VC as the standard RF method and (2) the limitation to diffusive gas transport resides primarily in the membrane barrier, although recruitment of microvascular reserves is also modestly impaired.

Estimate of pulmonary diffusing capacity for oxygen during exercise in humans from routine O2 and CO2 measurements

A method to estimate pulmonary diffusing capacity for O(2) (D(LO2)) during exercise based on routine O(2) and CO(2) transport variables is presented. It is based on the fitting of a mathematical model to gas exchange data. The model includes heterogeneity (described as two exchanging compartments), diffusion limitation and right-to-left shunt. Mass conservation equations and Bohr integration were solved to calculate partial pressures in each compartment. Diffusion was distributed with perfusion. Two-compartment ventilation and perfusion distributions were estimated at rest during conditions of negligible diffusion limitation. These distributions were used during hypoxic and normoxic exercise to obtain the D(LO2) from the model computations (D(LO2)2C) compatible with experimental data. Three normals, four sarcoid patients and four patients after lung resection were studied. An independent technique for carbon monoxide was used to provide experimental estimates of DLo2 (D(LO2)EXP, rebreathing technique for sarcoid patients and single breath for lung resection). D(LO2)2C was highly correlated with D(LO2)EXP (r2 = 0.95, P<0.001) and the slope of the regression line was not statistically different from 1. The mean (D(LO2)EXP - D(LO2)2C) difference was -1.0 +/- 7.4 ml min-1 mmHg-1. The results suggest that use of a refined analytical procedure allows for assessment of D(LO2) from routine O(2) and CO(2) measurements comparable with those obtained from independent carbon monoxide techniques. The method may be an alternative for estimates of D(LO2) during exercise.

Relationship between lung function, ventilation-perfusion inequality and extent of emphysema as assessed by high-resolution computed tomography

The development of the high-resolution computed tomography (HRCT) has improved the ability to detect and quantify emphysema in various groups of patients with chronic airflow obstruction (COPD). Significant correlations have previously been found between indices of air flow obstruction, hyperinflation, reduced diffusing capacity for carbon monoxide (DLCO), and the extent of emphysema (emph.%) assessed by HRCT. However, the relationship between emph.% and ventilation-perfusion (V(A)/Q) inequality in COPD is unknown. Twenty COPD patients with a mean forced expiratory volume in 1 s (FEV1) of 38.2 (+/- 15.5)% in percent of predicted value (%P), a mean PaO2 value of 9.6 (+/- 1.3) kPa, and a mean diffusing capacity of 43.6 (+/- 23.0)%P, were subjected to measurements by the multiple elimination inert gas technique (MIGET). The extent of emphysema was determined by HRCT at both full inspiration, emph.I(%) and at full expiration, emph.E(%), with a cut-off limit of -910 Hounsfield Units (HU) using the "Density Mask" method. The ventilation directed towards high V(A)/Q areas was 73 (+/- 10.2)% and the mean ventilation (V-mean) was elevated about three times compared to normal. The mean emph.(I)% and emph.(E) was 45.6 (+/- 16.9) and 32.7 (+/- 190)%, respectively. Significant correlations were shown between the emphysema extent and several lung function parameters, but no correlation was found between the emphysema extent and the V(A)/Q relationships or the blood gas values. Reduced DLCO%P correlated with less high V(A)/Q ventilation (r=0.73, P < 0.05) for the subgroup of COPD patients with DLCO(%P) less than 50% (n=12).

CONCLUSIONS

In COPD patients, suffering from moderate to severe emphysema without severe blood gas impairment, no correlation was shown between the extent of emphysema, as assessed by HRCT, and the severity of ventilation-perfusion inequality. A substantial collateral ventilation in severe emphysema may be a mechanism that prevents a deterioration in V(A)/Q relationships and in blood gas levels.

Outpatient inhaled nitric oxide in a patient with idiopathic pulmonary fibrosis: a bridge to lung transplantation

Inhaled nitric oxide (INO) has been shown to improve oxygenation and decrease intrapulmonary shunt and pulmonary hypertension in various lung diseases. In this study we report a patient with end-stage idiopathic pulmonary fibrosis and pulmonary hypertension who received INO after coronary artery bypass surgery, with significant improvement in arterial oxygenation and pulmonary arterial pressure. Using a pulsing delivery system, the patient continued to receive outpatient INO for 30 months while waiting for lung transplantation. Exercise study and two-dimensional echocardiogram, after 3 months of inhaled NO, demonstrated continued benefits of INO for improvement of arterial oxygenation, pulmonary arterial pressure and exercise tolerance.

Effects of hypercapnia and hypocapnia on [Ca2+]i mobilization in human pulmonary artery endothelial cells

The hydrogen ion is an important factor in the alteration of vascular tone in pulmonary circulation. Endothelial cells modulate vascular tone by producing vasoactive substances such as prostacyclin (PGI2) through a process depending on intracellular Ca2+ concentration ([Ca2+]i). We studied the influence of CO2-related pH changes on [Ca2+]i and PGI2 production in human pulmonary artery endothelial cells (HPAECs). Hypercapnic acidosis appreciably increased [Ca2+]i from 112 +/- 24 to 157 +/- 38 nmol/l. Intracellular acidification at a normal extracellular pH increased [Ca2+]i comparable to that observed during hypercapnic acidosis. The hypercapnia-induced increase in [Ca2+]i was unchanged by the removal of Ca2+ from the extracellular medium or by the depletion of thapsigargin-sensitive intracellular Ca2+ stores. Hypercapnic acidosis may thus release Ca2+ from pH-sensitive but thapsigargin-insensitive intracellular Ca2+ stores. Hypocapnic alkalosis caused a fivefold increase in [Ca2+]i compared with hypercapnic acidosis. Intracellular alkalinization at a normal extracellular pH did not affect [Ca2+]i. The hypocapnia-evoked increase in [Ca2+]i was decreased from 242 +/- 56 to 50 +/- 32 nmol/l by the removal of extracellular Ca2+. The main mechanism affecting the hypocapnia-dependent [Ca2+]i increase was thought to be the augmented influx of extracellular Ca2+ mediated by extracellular alkalosis. Hypercapnic acidosis caused little change in PGI2 production, but hypocapnic alkalosis increased it markedly. In conclusion, both hypercapnic acidosis and hypocapnic alkalosis increase [Ca2+]i in HPAECs, but the mechanisms and pathophysiological significance of these increases may differ qualitatively.

Longitudinal follow-up study of smoking-induced lung density changes by high-resolution computed tomography

To evaluate the ability of high-resolution computed tomography (HRCT) to detect longitudinal changes in structural abnormalities caused by smoking, HRCT and pulmonary function tests were used to examine nonsmokers, current smokers, and past smokers annually for 5 yr. Inspiratory HRCT was taken for the upper, middle, and lower lung fields, while expiratory images were obtained for the upper and lower lung fields only. We estimated the three quantitative CT parameters including MLD (mean CT value), HIST (CT value with the most frequent appearance), and %LAA (relative area of low attenuation with CT values less than -912 HU). Most of the pulmonary function tests, excepting FEV(1), did not change annually, whereas many of the inspiratory HRCT parameters did. In nonsmokers, only %LAA in the middle or lower lung fields exhibited an annual increase. In current smokers, %LAA in the upper lung field was augmented, while inspiratory MLD or HIST in the middle or lower lung field became more positive. In past smokers, %LAA in any lung field examined increased. The annual change in %LAA in the upper lung field was larger for past smokers than nonsmokers, with little difference between past and current smokers. Expiratory CT parameters showed few annual changes in all groups. In conclusion, (1) aging increases airspace abnormalities, mainly in the lower lung field; (2) although continuous smoking worsens airspace abnormalities mainly in the upper portion of the lung, this trend does not seem to slow down even after smoking cessation; and (3) inspiratory HRCT images are superior to expiratory images for longitudinal estimation of structural abnormalities caused by aging and smoking.