Nitric oxide diffusing capacity and alveolar microvascular recruitment in sarcoidosis

Week to week variability of pulmonary capillary blood volume and alveolar membrane diffusing capacity in patients with heart failure

BACKGROUND

Alveolar-capillary membrane diffusing capacity for carbon monoxide (DMCO) and pulmonary capillary volume (Vcap) can be estimated by the multi-step Roughton and Foster (RF, original method from 1957) or the single-step NO-CO double diffusion technique (developed in the 1980s). The latter method implies inherent assumptions. We sought to determine which combination of the alveolar membrane diffusing capacity for nitric oxide (DMNO) to DMCO ratio, an specific conductance of the blood for NO (θ_NO) and CO (θ_CO) gave the lowest week-to-week variability in patients with heart failure.

METHODS

44 heart failure patients underwent DMCO and Vcap measurements on three occasions over a ten-week period using both RF and double dilution NO-CO techniques.

RESULTS

When using the double diffusing method and applying θ_NO = infinity, the smallest week-to-week coefficient of variation for DMCO was 10 %. Conversely, the RF method derived DMCO had a much greater week-to-week variability (2x higher coefficient of variation) than the DMCO derived via the NO-CO double dilution technique. The DMCO derived from the double diffusion technique most closely matched the DMCO from the RF method when θ_NO = infinity and DMCO = DLNO/2.42. The Vcap measured week-to-week was unreliable regardless of the method or constants used.

CONCLUSIONS

In heart failure patients, the week-to-week DMCO variability was lowest when using the single-step NO-CO technique. DMCO obtained from double diffusion most closely matched the RF DMCO when DMCO/2.42 and θ_NO = infinity. Vcap estimation was unreliable with either method.

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.

Value of lung diffusing capacity for nitric oxide in systemic sclerosis

A decreased lung diffusing capacity for carbon monoxide (DL_CO ) in systemic sclerosis (SSc) is considered to reflect losses of alveolar membrane diffusive conductance for CO (DM_CO ), due to interstitial lung disease, and/or pulmonary capillary blood volume (V_C ), due to vasculopathy. However, standard DL_CO does not allow separate DM_CO from V_C . Lung diffusing capacity for nitric oxide (DL_NO ) is considered to be more sensitive to decrement of alveolar membrane diffusive conductance than DL_CO . Standard DL_CO and DL_NO were compared in 96 SSc subjects with or without lung restriction. Data showed that DL_NO was reduced in 22% of subjects with normal lung volumes and DL_CO , whereas DL_CO was normal in 30% of those with decreased DL_NO . In 30 subjects with available computed tomography of the chest, both DL_CO and DL_NO were negatively correlated with the extent of pulmonary fibrosis. However, DL_NO but not DL_CO was always reduced in subjects with ≥ 5% fibrosis, and also decreased in some subjects with < 5% fibrosis. DM_CO and V_C partitioning and Doppler ultrasound-determined systolic pulmonary artery pressure could not explain individual differences in DL_CO and DL_NO . DL_NO may be of clinical value in SSc because it is more sensitive to DM_CO loss than standard DL_CO , even in nonrestricted subjects without fibrosis, whereas DL_CO partitioning into its subcomponents does not provide information on whether diffusion limitation is primarily due to vascular or interstitial lung disease in individual subjects. Moreover, decreased DL_CO in the absence of lung restriction does not allow to suspect pulmonary arterial hypertension without fibrosis.

Lung Diffusing Capacities (DL ) for Nitric Oxide (NO) and Carbon Monoxide (CO): The Evolving Story

Nitric oxide and carbon monoxide diffusing capacities (D_LNO and D_LCO ) obey Fick's First Law of Diffusion and the basic principles of chemical kinetic theory. NO gas transfer is dominated by membrane diffusion (D_M ), whereas CO transfer is limited by diffusion plus chemical reaction within the red cell. Marie Krogh, who pioneered the single-breath measurement of D_LCO in 1915, believed that the combination of CO with red cell hemoglobin (Hb) was instantaneous. Roughton and colleagues subsequently showed, in vitro, that the reaction rate was finite, and prolonged in the presence of high P O 2 . Roughton and Forster (R-F) proposed that the resistance to transfer (1/D_L ) was the sum of the membrane resistance (1/D_M ) and (1/θVc), the red cell resistance (θ being the CO or NO conductance for blood uptake and Vc the capillary volume). From this R-F equation, D_M for CO and Vc can be solved with simultaneous NO and CO inhalation. At near maximum exercise, D_MCO and Vc for normal subjects were 88% and 79%, respectively, of morphometric values. The validity of these calculations depends on the values chosen for θ for CO and NO, and on the diffusivity of NO versus CO. Recent mathematical modeling suggests that θ for NO is "effectively" infinite because NO reacts only with Hb in the outer 0.1 μM of the red cell. An "infinite θ_NO " recalculation reduced D_MCO to 53% and increased Vc to 95% of morphometric values. © 2020 American Physiological Society. Compr Physiol 10:73-97, 2020.

Systemic Oxygen Transport with Rest, Exercise, and Hypoxia: A Comparison of Humans, Rats, and Mice

The objective of this article is to compare and contrast the known characteristics of the systemic O₂ transport of humans, rats, and mice at rest and during exercise in normoxia and hypoxia. This analysis should help understand when rodent O₂ transport findings can-and cannot-be applied to human responses to similar conditions. The O₂ -transport system was analyzed as composed of four linked conductances: ventilation, alveolo-capillary diffusion, circulatory convection, and tissue capillary-cell diffusion. While the mechanisms of O₂ transport are similar in the three species, the quantitative differences are naturally large. There are abundant data on total O₂ consumption and on ventilatory and pulmonary diffusive conductances under resting conditions in the three species; however, there is much less available information on pulmonary gas exchange, circulatory O₂ convection, and tissue O₂ diffusion in mice. The scarcity of data largely derives from the difficulty of obtaining blood samples in these small animals and highlights the need for additional research in this area. In spite of the large quantitative differences in absolute and mass-specific O₂ flux, available evidence indicates that resting alveolar and arterial and venous blood PO₂ values under normoxia are similar in the three species. Additionally, at least in rats, alveolar and arterial blood PO₂ under hypoxia and exercise remain closer to the resting values than those observed in humans. This is achieved by a greater ventilatory response, coupled with a closer value of arterial to alveolar PO₂ , suggesting a greater efficacy of gas exchange in the rats. © 2018 American Physiological Society. Compr Physiol 8:1537-1573, 2018.

Reference equations for pulmonary diffusing capacity of carbon monoxide and nitric oxide in adult Caucasians

The aim of this study was to determine reference equations for the combined measurement of diffusing capacity of the lung for carbon monoxide (CO) and nitric oxide (NO) (DLCONO). In addition, we wanted to appeal for consensus regarding methodology of the measurement including calculation of diffusing capacity of the alveolo-capillary membrane (Dm) and pulmonary capillary volume (Vc).

DLCONO was measured in 282 healthy individuals aged 18–97 years using the single-breath technique and a breath-hold time of 5 s (true apnoea period). The following values were used: 1) specific conductance of nitric oxide (θNO)=4.5 mLNO·mLblood−1·min−1·mmHg−1; 2) ratio of diffusing capacity of the membrane for NO and CO (DmNO/DmCO)=1.97; and 3) 1/red cell CO conductance (1/θCO)=(1.30+0.0041·mean capillary oxygen pressure)·(14.6/Hb concentration in g·dL−1).

Reference equations were established for the outcomes of DLCONO, including DLCO and DLNO and the calculated values Dm and Vc. Independent variables were age, sex, height and age squared.

By providing new reference equations and by appealing for consensus regarding the methodology, we hope to provide a basis for future studies and clinical use of this novel and interesting method.

Simultaneous measurement of pulmonary diffusing capacity for carbon monoxide and nitric oxide

In Europe and America, the newly-developed, simultaneous measurement of diffusing capacity for CO (D_LCO) and NO (D_LNO) has replaced the classic D_LCO measurement for detecting the pathophysiological abnormalities in the acinar regions. However, simultaneous measurement of D_LCO and D_LNO is currently not used by Japanese physicians. To encourage the use of D_LNO in Japan, the authors reviewed aspects of simultaneously-estimated D_LCO and D_LNO from previously published manuscripts. The simultaneous D_LCO-D_LNO technique identifies the alveolocapillary membrane-related diffusing capacity (membrane component, D_M) and the blood volume in pulmonary microcirculation (V_C); V_C is the principal factor constituting the blood component of diffusing capacity (D_B,D_B=θ·V_C where θ is the specific gas conductance for CO or NO in the blood). As the association velocity of NO with hemoglobin (Hb) is fast and the affinity of NO with Hb is high in comparison with those of CO, θ_NO can be taken as an invariable simply determined by diffusion limitation inside the erythrocyte. This means that θ_NO is independent of the partial pressure of oxygen (PO₂). However, θ_CO involves the limitations by diffusion and chemical reaction elicited by the erythrocyte, resulting in θ_CO to be a PO₂-dependent variable. Furthermore, D_LCO is determined primarily by D_B (∼77%), while D_LNO is determined equally by D_M (∼55%) and D_B (∼45%). This suggests that D_LCO is more sensitive for detecting microvascular diseases, while D_LNO can equally identify alveolocapillary membrane and microcirculatory abnormalities.

The measurement of DLNO and DLCO: A manufacturer's perspective

The simultaneous measurement of the lung transfer factor for carbon monoxide (DLCO) and nitric oxide (DLNO) is now available as a powerful method for studying the alveolar-capillary gas exchange. However, application of the DLNO-CO technique in daily settings is still limited by some technical drawbacks. This paper provides a manufacturer's overview of the measuring principles, technical challenges and current available solutions for implementing the DLNO-CO measurement in to a marketed device. This includes the recent developments in technology for NO sensors, latest findings on NO uptake and new statistical methods.

Standardisation and application of the single-breath determination of nitric oxide uptake in the lung

Diffusing capacity of the lung for nitric oxide (D_LNO), otherwise known as the transfer factor, was first measured in 1983. This document standardises the technique and application of single-breath D_LNO This panel agrees that 1) pulmonary function systems should allow for mixing and measurement of both nitric oxide (NO) and carbon monoxide (CO) gases directly from an inspiratory reservoir just before use, with expired concentrations measured from an alveolar "collection" or continuously sampled via rapid gas analysers; 2) breath-hold time should be 10 s with chemiluminescence NO analysers, or 4-6 s to accommodate the smaller detection range of the NO electrochemical cell; 3) inspired NO and oxygen concentrations should be 40-60 ppm and close to 21%, respectively; 4) the alveolar oxygen tension (P_AO2 ) should be measured by sampling the expired gas; 5) a finite specific conductance in the blood for NO (θNO) should be assumed as 4.5 mL·min^-1·mmHg^-1·mL^-1 of blood; 6) the equation for 1/θCO should be (0.0062·P_AO2 +1.16)·(ideal haemoglobin/measured haemoglobin) based on breath-holding P_AO2 and adjusted to an average haemoglobin concentration (male 14.6 g·dL^-1, female 13.4 g·dL^-1); 7) a membrane diffusing capacity ratio (D_MNO/D_MCO) should be 1.97, based on tissue diffusivity.

Lung Structure and the Intrinsic Challenges of Gas Exchange

Structural and functional complexities of the mammalian lung evolved to meet a unique set of challenges, namely, the provision of efficient delivery of inspired air to all lung units within a confined thoracic space, to build a large gas exchange surface associated with minimal barrier thickness and a microvascular network to accommodate the entire right ventricular cardiac output while withstanding cyclic mechanical stresses that increase several folds from rest to exercise. Intricate regulatory mechanisms at every level ensure that the dynamic capacities of ventilation, perfusion, diffusion, and chemical binding to hemoglobin are commensurate with usual metabolic demands and periodic extreme needs for activity and survival. This article reviews the structural design of mammalian and human lung, its functional challenges, limitations, and potential for adaptation. We discuss (i) the evolutionary origin of alveolar lungs and its advantages and compromises, (ii) structural determinants of alveolar gas exchange, including architecture of conducting bronchovascular trees that converge in gas exchange units, (iii) the challenges of matching ventilation, perfusion, and diffusion and tissue-erythrocyte and thoracopulmonary interactions. The notion of erythrocytes as an integral component of the gas exchanger is emphasized. We further discuss the signals, sources, and limits of structural plasticity of the lung in alveolar hypoxia and following a loss of lung units, and the promise and caveats of interventions aimed at augmenting endogenous adaptive responses. Our objective is to understand how individual components are matched at multiple levels to optimize organ function in the face of physiological demands or pathological constraints.

The single-breath diffusing capacity of CO and NO in healthy children of European descent

Rationale

The diffusing capacity (D_L) of the lung can be divided into two components: the diffusing capacity of the alveolar membrane (Dm) and the pulmonary capillary volume (Vc). D_L is traditionally measured using a single-breath method, involving inhalation of carbon monoxide, and a breath hold of 8–10 seconds (D_L,CO). This method does not easily allow calculation of Dm and Vc. An alternative single-breath method (D_L,CO,NO), involving simultaneous inhalation of carbon monoxide and nitric oxide, and traditionally a shorter breath hold, allows calculation of Dm and Vc and the D_L,NO/D_L,CO ratio in a single respiratory maneuver. The clinical utility of Dm, Vc, and D_L,NO/D_L,CO in the pediatric age range is currently unknown but also restricted by lack of reference values.

Objectives

The aim of this study was to establish reference ranges for the outcomes of D_L,CO,NO with a 5 second breath hold, including the calculated outcomes Dm, Vc, and the D_L,NO/D_L,CO ratio, as well as to establish reference values for the outcomes of the traditional D_L,CO method, with a 10 second breath hold in children.

Methods

D_L,CO,NO and D_L,CO were measured in healthy children, of European descent, aged 5–17 years using a Jaeger Masterscreen PFT. The data were analyzed using the Generalized Additive Models for Location Scale and Shape (GAMLSS) statistical method.

Measurements and Main Results

A total of 326 children were eligible for diffusing capacity measurements, resulting in 312 measurements of D_L,CO,NO and 297 of D_L,CO, respectively. Reference equations were established for the outcomes of D_L,CO,NO and D_L,CO, including the calculated values: Vc, Dm, and the D_L,NO/D_L,CO ratio.

Conclusion

These reference values are based on the largest sample of children to date and may provide a basis for future studies of their clinical utility in differentiating between alterations in the pulmonary circulation and changes in the alveolar membrane in pediatric patients.

Alveolar-capillary membrane diffusion measurement by nitric oxide inhalation in heart failure

BACKGROUND

In heart failure, lung diffusion is reduced, it correlates with prognosis and exercise capacity, and it is a therapy target.

DESIGN

Diffusion is measured as CO total diffusion (DL(CO)), which has two components: membrane diffusion (Dm) and capillary volume, the latter related to CO and O2 competition for hemoglobin. DL(CO) needs to be corrected for hemoglobin. Diffusion can also be measured with NO (DL(NO)), which has a very high affinity for hemoglobin, and thus, the resistance of hemoglobin being trivial, it directly represents Dm. Therefore, Dm is directly calculated from DL(NO) through a correction factor. DL(NO) has never been measured in heart failure. The study aims at determining, in heart failure, DL(NO), Dm correction factor, and whether Dm(NO) provides Dm estimates comparable to Dm(CO).

METHODS

We measured DL(CO), Dm(CO) by multi-maneuver Roughton-Forster method, and DL(CO) and DL(NO) by single-breath maneuver in 50 heart failure and 50 healthy subjects.

RESULTS

DL(CO) was 21.9 ± 4.8 ml/mmHg per min and 16.8 ± 5.1 in healthy subjects and heart failure subjects, respectively (p < 0.001). DL(NO) was 88.6 ± 20.5 ml/mmHg per min and 72.5 ± 22.3, respectively (p < 0.001). The correction factors to obtain Dm from DL(NO) were 2.68 (entire population), 2.63 (healthy subjects) and 2.75 (heart failure subjects). Dm(CO) and Dm(NO) were 34.7 ± 10.9 ml/mmHg per min and 33.8 ± 7.6 in healthy subjects and 25.9 ± 2.0 and 26.4 ± 8.1 in heart failure subjects.

CONCLUSIONS

DL(NO) and Dm(NO) measurements are feasible in heart failure. Dm(CO) and Dm(NO) provide comparable results. The correction factor to calculate Dm from DL(NO) in heart failure is 2.75, which is little different from the 2.63 value we observed in healthy subjects.

Noninvasive assessment of alveolar microvascular recruitment in conscious non-sedated rats

Recruitment of alveolar microvascular reserves, assessed from the relationship between pulmonary diffusing capacity (DLCO) and perfusion (Q˙c), is critical to the maintenance of arterial blood oxygenation. Leptin-resistant ZDF fatty diabetic (fa/fa) rats exhibit restricted cardiopulmonary physiology under anesthesia. To assess alveolar microvascular function in conscious, non-sedated, non-instrumented, and minimally restrained animals, we adapted a rebreathing technique to study fa/fa and control non-diabetic (+/+) rats (4-5 and 7-11mo old) at rest and during mild spontaneous activity. Measurements included O2 uptake, lung volume, Q˙c, DLCO, membrane diffusing capacity (DMCO), capillary blood volume (Vc) and septal tissue-blood volume. In older fa/fa than +/+ animals, DLCO and DMCO at a given Q˙c were lower; Vc was reduced in proportion to Q˙c. Results demonstrate the consequences of alveolar microangiopathy in the metabolic syndrome: lung volume restriction, reduced Q˙c, and elevated membrane resistance to diffusion. At a given Q˙c, DLCO is lower in rats and guinea pigs than dogs or humans, consistent with limited alveolar microvascular reserves in small animals.

Genetic variation of SCNN1A influences lung diffusing capacity in cystic fibrosis

INTRODUCTION

Epithelial Na channels (ENaCs) play a crucial role in ion and fluid regulation in the lung. In cystic fibrosis (CF), Na hyperabsorption results from ENaC overactivity, leading to airway dehydration. Previous work has demonstrated functional genetic variation of SCNN1A (the gene encoding the ENaC α-subunit), manifesting as an alanine (A) to threonine (T) substitution at amino acid 663, with the αT663 variant resulting in a more active channel.

METHODS

We assessed the influence of genetic variation of SCNN1A on the diffusing capacity of the lungs for carbon monoxide (DLCO) and nitric oxide (DLNO), together with alveolar-capillary membrane conductance (DM), pulmonary capillary blood volume, and alveolar volume (VA) at rest and during peak exercise in 18 patients with CF (10 homozygous for αA663 (AA group) and 8 with at least one T663 allele (AT/TT group)). Because of the more active channel, we hypothesized that the AT/TT group would show a greater increase in DLCO, DLNO, and DM with exercise because of exercise-mediated ENaC inhibition and subsequent attenuation of Na hyperabsorption.

RESULTS

The AT/TT group had significantly lower pulmonary function, weight, and body mass index than the AA group. Both groups had similar peak workloads, relative peak oxygen consumptions, and cardiopulmonary responses to exercise. The AT/TT group demonstrated a greater increase in DLNO, DLNO/VA, and DM in response to exercise (% increases: DLNO = 18 ± 11 vs 41 ± 38; DLNO/VA = 14 ± 21 vs 40 ± 37; DM = 15 ± 11 vs 41 ± 38, AA vs AT/TT, respectively). There were no differences between groups in absolute diffusing capacity measures at peak exercise.

CONCLUSION

These results suggest that genetic variation of the α-subunit of ENaC differentially affects the diffusing capacity response to exercise in patients with CF.

Subclinical lung disease, macrocytosis, and premature graying in kindreds with telomerase (TERT) mutations

BACKGROUND

Mutations in the human gene encoding the protein component of telomerase (TERT) are the most common genetic defect in patients with familial idiopathic pulmonary fibrosis (IPF). The subclinical phenotypes of asymptomatic members of these families have not been evaluated with respect to TERT mutation status or telomere length.

METHODS

We measured a variety of pulmonary, blood, skin, and bone parameters for 20 subjects with heterozygous TERT mutations (carriers) and 20 family members who had not inherited a TERT mutation (noncarriers) to identify the spectrum of phenotypes associated with mutations in this gene. The two groups were matched for sex, age, and cigarette smoking. Three TERT mutation carriers had IPF (IPF carriers). The rest of the carriers were apparently healthy (asymptomatic carriers) and were compared with the noncarriers.

RESULTS

Asymptomatic carriers exhibited significantly lower diffusing capacity of lung for carbon monoxide (Dlco), impaired recruitment of Dlco with exercise, radiographic signs of lung fibrosis, and increased fractional lung tissue volume quantified by high-resolution chest CT scan than noncarriers. RBC and platelet counts were significantly lower, and the mean corpuscular volume and mean corpuscular hemoglobin concentration were significantly higher in carriers than in noncarriers. Carriers reported significantly earlier graying of hair than noncarriers. TERT mutation status is more accurately predicted by short telomere lengths than any of these measured phenotypes.

CONCLUSIONS

TERT mutation carriers exhibit early preclinical signs of lung fibrosis, bone marrow dysfunction, and premature graying. These clinical features and short telomere lengths characterize patients with germline TERT mutations.

Fatty diabetic lung: functional impairment in a model of metabolic syndrome

The Zucker diabetic fatty (ZDF fa/fa) rat with genetic leptin insensitivity develops obesity and Type 2 diabetes mellitus (T2DM) with age accompanied by hyperplastic changes in the distal lung (Am J Physiol Lung Cell Mol Physiol 298: L392-L403, 2010). To determine the functional consequences of structural changes, we developed a rebreathing (RB) technique to simultaneously measure lung volume, pulmonary blood flow, lung diffusing capacity (Dl(CO)), membrane diffusing capacity (Dm(CO)), pulmonary capillary blood volume (Vc), and septal tissue volume in anesthetized tracheostomized male ZDF fa/fa and matched lean (+/+) control animals at 4, 8, and 12 mo of age. Results obtained by RB technique were compared with that measured by a single-breath (SB) technique and to that expected in a wide range of species. In fa/fa animals compared with +/+, lung volumes and compliance were 13-35% lower at different ages, and the normal age-related increase in lung compliance was no longer evident. Mean pulmonary blood flow declined with age in fa/fa but not in +/+ animals. Dl(CO) measured at a given pulmonary blood flow was 20-43% lower at different ages due to reductions in both Dm(CO) and Vc. Septal tissue volume was also reduced in older fa/fa rats. We conclude that obese rats with T2DM develop significant restrictive pulmonary defects with diffusion impairment in a pattern similar to that previously reported in obese human subjects with T2DM. Functional impairment became exaggerated with age and duration of T2DM. In both fa/fa and +/+ animals, Dl(CO) measured by RB was systematically higher than by SB technique whereas lung volume was similar, a finding consistent with heterogeneous distribution of ventilation in the rat lung.

Pulmonary diffusion and aerobic capacity: is there a relation? Does obesity matter?

AIM

We sought to determine whether pulmonary diffusing capacity for nitric oxide (DLNO), carbon monoxide (DLCO) and pulmonary capillary blood volume (Vc) at rest predict peak aerobic capacity (VO2peak), and if so, to discern which measure predicts better.

METHODS

Thirty-five individuals with extreme obesity (body mass index or BMI = 50 +/- 8 kg m((-2)) and 26 fit, non-obese subjects (BMI = 23 +/- 2 kg m((-2)) participated. DLNO and DLCO at rest were first measured. Then, subjects performed a graded exercise test on a cycle ergometer to determine (VO2peak). Multivariate regression was used to assess relations in the data.

RESULTS

Findings indicate that (i) pulmonary diffusion at rest predicts (VO2peak) in the fit and obese when measured with DLNO, but only in the fit when measured with DLCO; (ii) the observed relation between pulmonary diffusion at rest and (VO2peak) is different in the fit and obese; (iii) DLNO explains (VO2peak) better than DLCO or Vc. The findings imply the following reference equations for DLNO: (VO2peak) (mL kg(-1) min(-1)) = 6.81 + 0.27 x DLNO for fit individuals; (VO2peak) (mL kg(-1) min(-1)) = 6.81 + 0.06 x DLNO, for obese individuals (in both groups, adjusted R(2 )=( )0.92; RMSE = 5.58).

CONCLUSION

Pulmonary diffusion at rest predicts (VO2peak), although a relation exists for obese subjects only when DLNO is used, and the magnitude of the relation depends on gender when either DLCO or Vc is used. We recommend DLNO as a measure of pulmonary diffusion, both for its ease of collection as well as its tighter relation with (VO2peak).

Significant blood resistance to nitric oxide transfer in the lung

Lung diffusing capacity for nitric oxide (DLNO) is used to measure alveolar membrane conductance (DMNO), but disagreement remains as to whether DMNO=DLNO, and whether blood conductance (thetaNO)=infinity. Our previous in vitro and in vivo studies suggested that thetaNO<infinity. We now show in a membrane oxygenator model perfused with whole blood that addition of a cell-free bovine hemoglobin (Hb) glutamer-200 solution increased diffusing capacity of the circuit (D) for NO (DNO) by 39%, D for carbon monoxide (DCO) by 24%, and the ratio of DNO to DCO by 12% (all P<0.001). In three anesthetized dogs, DLNO and DLCO were measured by a rebreathing technique before and after three successive equal volume-exchange transfusions with bovine Hb glutamer-200 (10 ml/kg each, total exchange 30 ml/kg). At baseline, DLNO/DLCO=4.5. After exchange transfusion, DLNO rose 57+/-16% (mean+/-SD, P=0.02) and DLNO/DLCO=7.1, whereas DLCO remained unchanged. Thus, in vitro and in vivo data directly demonstrate a finite thetaNO. We conclude that the erythrocyte and/or its immediate environment imposes considerable resistance to alveolar-capillary NO uptake. DLNO is sensitive to dynamic hematological factors and is not a pure index of conductance of the alveolar tissue membrane. With successive exchange transfusion, the estimated in vivo thetaNO [5.1 ml NO.(ml blood.min.Torr)(-1)] approached 4.5 ml NO.(ml blood.min.Torr)(-1), which was derived from in vitro measurements by Carlsen and Comroe (J Gen Physiol 42: 83-107, 1958). Therefore, we suggest use of thetaNO=4.5 ml NO.(min.Torr.ml blood)(-1) for calculation of DM(NO) and pulmonary capillary blood volume from DLNO and DLCO.

CO and NO pulmonary diffusing capacity during pregnancy: Safety and diagnostic potential

This paper reviews the scientific evidence for the safety of carbon monoxide (CO) and nitric oxide (NO) inhalation to measure pulmonary diffusing capacity (DL(CO) and DL(NO)) in pregnant women and their fetuses. In eight earlier studies, 650 pregnant women had DL(CO) measurements performed at various times during pregnancy, with a minimum of two to four tests per session. Both pregnant subjects that were healthy and those with medical complications were tested. No study reported adverse maternal, fetal, or neonatal outcomes from the CO inhalation in association with measuring DL(CO). Eleven pregnant women, chiefly with pulmonary hypertension, and 1105 pre-term neonates, mostly with respiratory failure, were administered various dosages of NO (5-80ppm for 4 weeks continuously in pregnant women, and 1-20ppm for 15min to 3 weeks for the neonates). NO treatment was found to be an effective therapy for pregnant women with pulmonary hypertension. In neonates with respiratory failure and pulmonary hypertension, NO therapy improved oxygenation and survival and has been associated with only minor, transient adverse effects. In conclusion, maternal carboxyhemoglobin ([Hb(CO)]) levels can safely increase to 5% per testing session when the dose-exposure limit is 0.3% CO inhalation for <or=3min, and for NO, 80ppm for <or=3min. The risk of late fetal or neonatal death from increased Hb(CO) from diffusion testing is considerably less than the risk of death from all causes reported by the Centers for Disease Control, and is therefore considered "minimal risk".

Simulation system for a rebreathing technique to measure multiple cardiopulmonary function parameters

BACKGROUND

We developed a simple method for simulating a rebreathing maneuver to test the accuracy of the apparatus for simultaneous measurement of lung volume, diffusing capacity of the lung for carbon monoxide (Dlco), diffusing capacity of the lung for nitric oxide (Dlno), and pulmonary blood flow (Qc).

METHODS

A test gas mixture containing 0.3% methane, 0.3% CO, 0.8% acetylene, 30% O(2), and 40 ppm nitric oxide in balance of nitrogen was sequentially diluted with a rebreathing gas mixture containing 0.3% acetylene, 0.3% methane, and 21% O(2) in balance of nitrogen in order to simulate the in vivo end-tidal disappearance of the test gas mixture. Simulation of one rebreathing maneuver consisted of at least four serial dilution steps with a performance time of < 5 min. Using this technique, we estimated functional residual capacity, Qc, Dlco, and Dlno at various flow rates and dilution ratios (0.95 to 4.04 L, 3.54 to 6.83 L/min, 7.27 to 15.12 mL/min/mm Hg, and 6.51 to 12.00 mL/min/mm Hg, respectively) and verified simulation results against nominal values. The same apparatus also could simulate a single-breath procedure.

RESULTS

Compared to nominal values, errors in measured values by rebreathing and single-breath Dlco simulation remained < 5% and 7%, respectively. Slopes of the correlations were close to 1.0 (within +/- 5% and +/- 6.4% in rebreathing and single-breath Dlco simulation studies, respectively).

CONCLUSION

The results demonstrate the feasibility of this simulation method for standardizing the experimental measurements obtained by rebreathing and single-breath techniques. Incorporation of these simulation steps enhances the noninvasive assessment of cardiopulmonary function.

Predicting diffusive alveolar oxygen transfer from carbon monoxide-diffusing capacity in exercising foxhounds

Although lung diffusing capacity for carbon monoxide (DL(CO)) is a widely used test of diffusive O2 transfer, few studies have directly related DL(CO) to O2-diffusing capacity (DL(O2)); none has used the components of Dl(CO), i.e., conductance of alveolar membrane and capillary blood, to predict DL(O2) from rest to exercise. To understand the relationship between DL(CO) and DL(O2) at matched levels of cardiac output, we analyzed cumulative data from rest to heavy exercise in 43 adult dogs, with normal lungs or reduced lung capacity following lung resection, that were studied by two techniques. 1) A rebreathing (RB) technique was used to measure Dl(CO) and pulmonary blood flow at two O2 tensions, independent of O2 exchange. DL(CO) was partitioned into CO-diffusing capacity of alveolar membrane and pulmonary capillary blood volume using the Roughton-Forster equation and converted into an equivalent DL(O2), [DL(O2)(RB)]. 2) A multiple inert-gas elimination technique (MIGET) was used to measure ventilation-perfusion distributions, O2 and CO2 exchange under hypoxia, to derive DL(O2) [DL(O2)(MIGET)] by the Lilienthal-Riley technique and Bohr integration. For direct comparisons, DL(O2)(RB) was interpolated to the cardiac output measured by the Fick principle corresponding to DL(O2)(MIGET). The DL(O2)-to-DL(CO) ratio averaged 1.61. Correlation between DL(O2)(RB) and DL(O2)(MIGET) was similar in normal and post-resection groups. Overall, DL(O2)(MIGET) = 0.975 DL(O2)(RB); mean difference between the two techniques was under 5% for both animal groups. We conclude that, despite various uncertainties inherent in these two disparate methods, the Roughton-Forster equation adequately predicts diffusive O2 transfer from rest to heavy exercise in canines with normal, as well as reduced, lung capacities.

Pulmonary diffusing capacity for nitric oxide during exercise in morbid obesity

Morbidly obese individuals may have altered pulmonary diffusion during exercise. The purpose of this study was to examine pulmonary diffusing capacity for nitric oxide (DLNO) and carbon monoxide (DLCO) during exercise in these subjects. Ten morbidly obese subjects (age = 38 +/- 9 years, BMI = 47 +/- 7 kg/m(2), peak oxygen consumption or VO(2peak) = 2.4 +/- 0.4 l/min) and nine nonobese controls (age = 41 +/- 9 years, BMI = 23 +/- 2 kg/m(2), VO(2peak) = 2.6 +/- 0.9 l/min) participated in two sessions: the first measured resting O(2) and VO(2peak) for determination of wattage equating to 40, 75, and 90% oxygen uptake reserve (VO(2)R). The second session measured pulmonary diffusion from single-breath maneuvers of 5 s each, as well as heart rate (HR) and VO(2) over three workloads. DLNO, DLCO, and pulmonary capillary blood volume were larger in obese compared to nonobese groups (P <or= 0.06) only when expressed relative to alveolar volume (VA). The slope between VO(2) and all measures of pulmonary diffusion, whether or not expressed to VA, were not different between groups (P > 0.10). The morbidly obese have increased pulmonary diffusion per unit increase in VA compared with nonobese controls which may be due to a lower rise in VA per unit increase in VO(2) in the obese during exercise.

Diminished alveolar microvascular reserves in type 2 diabetes reflect systemic microangiopathy

OBJECTIVE

Alveolar microvascular function is moderately impaired in type 1 diabetes, as manifested by restriction of lung volume and diffusing capacity (DL(CO)). We examined whether similar impairment develops in type 2 diabetes and defined the physiologic sources of impairment as well as the relationships to glycemia and systemic microangiopathy.

RESEARCH DESIGN AND METHODS

A cross-sectional study was conducted at a university-affiliated diabetes treatment center and outpatient diabetes clinic, involving 69 nonsmoking type 2 diabetic patients without overt cardiopulmonary disease. Lung volume, pulmonary blood flow (Q), DL(CO), membrane diffusing capacity (measured from nitric oxide uptake [DL(NO)]), and pulmonary capillary blood volume (V(C)) were determined at rest and exercise for comparison with those in 45 healthy nonsmokers as well as with normal reference values.

RESULTS

In type 2 diabetic patients, peak levels of oxygen uptake, Q and DL(CO), DL(NO), and V(C) at exercise were 10-25% lower compared with those in control subjects. In nonobese patients (BMI <30 kg/m(2)), reductions in DL(CO), DL(NO), and V(C) were fully explained by the lower lung volume and peak Q, but these factors did not fully explain the impairment in obese patients (BMI >30 kg/m(2)). The slope of the increase in V(C) with respect to Q was reduced approximately 20% in patients regardless of BMI, consistent with impaired alveolar-capillary recruitment. Functional impairment was directly related to A1C level, retinopathy, neuropathy, and microalbuminuria in a sex-specific manner.

CONCLUSIONS

Alveolar microvascular reserves are reduced in type 2 diabetes, reflecting restriction of lung volume, alveolar perfusion, and capillary recruitment. This reduction correlates with glycemic control and extrapulmonary microangiopathy and is aggravated by obesity.

Partitioned exhaled nitric oxide to non-invasively assess asthma

Asthma is a chronic inflammatory disease of the lungs, characterized by airway hyperresponsiveness. Chronic repetitive bouts of acute inflammation lead to airway wall remodeling and possibly the sequelae of fixed airflow obstruction. Nitric oxide (NO) is a reactive molecule synthesized by NO synthases (NOS). NOS are expressed by cells within the airway wall and functionally, two NOS isoforms exist: constitutive and inducible. In asthma, the inducible isoform is over expressed, leading to increased production of NO, which diffuses into the airway lumen, where it can be detected in the exhaled breath. The exhaled NO signal can be partitioned into airway and alveolar components by measuring exhaled NO at multiple flows and applying mathematical models of pulmonary NO dynamics. The airway NO flux and alveolar NO concentration can be elevated in adults and children with asthma and have been correlated with markers of airway inflammation and airflow obstruction in cross-sectional studies. Longitudinal studies which specifically address the clinical potential of partitioning exhaled NO for diagnosis, managing therapy, and predicting exacerbation are needed.

Assessing recruitment of lung diffusing capacity in exercising guinea pigs with a rebreathing technique

Noninvasive techniques for assessing cardiopulmonary function in small animals are limited. We previously developed a rebreathing technique for measuring lung volume, pulmonary blood flow, diffusing capacity for carbon monoxide (Dl(CO)) and its components, membrane diffusing capacity (Dm(CO)) and pulmonary capillary blood volume (Vc), and septal volume, in conscious nonsedated guinea pigs at rest. Now we have extended this technique to study guinea pigs during voluntary treadmill exercise with a sealed respiratory mask attached to a body vest and a test gas mixture containing 0.5% SF(6) or Ne, 0.3% CO, and 0.8% C(2)H(2) in 40% or 98% O(2). From rest to exercise, O(2) uptake increased from 12.7 to 25.5 ml x min(-1) x kg(-1) while pulmonary blood flow increased from 123 to 239 ml/kg. The measured Dl(CO), Dm(CO), and Vc increased linearly with respect to pulmonary blood flow as expected from alveolar microvascular recruitment; body mass-specific relationships were consistent with those in healthy human subjects and dogs studied with a similar technique. The results show that 1) cardiopulmonary interactions from rest to exercise can be measured noninvasively in guinea pigs, 2) guinea pigs exhibit patterns of exercise response and alveolar microvascular recruitment similar to those of larger species, and 3) the rebreathing technique is widely applicable to human ( approximately 70 kg), dog (20-30 kg), and guinea pig (1-1.5 kg). In theory, this technique can be extended to even smaller animals provided that species-specific technical hurdles can be overcome.

Lung diffusing capacity for nitric oxide and carbon monoxide: dependence on breath-hold time

BACKGROUND

The combined measurement of diffusing capacity of the lung for nitric oxide (Dlno) and diffusing capacity of the lung for carbon monoxide (Dlco) is a simple, noninvasive tool, but methodologic factors might influence results and reproducibility. We thus quantified the influence of breath-hold time on Dlco and Dlno in subjects with or without airway disease.

METHODS

Simultaneous single-breath measurements of Dlco and Dlno were performed in 10 patients with cystic fibrosis (CF) [mean +/- SD age, 33 +/- 9 years; FEV(1), 69 +/- 28% of predicted] and 10 healthy subjects (age, 31 +/- 9 years; FEV(1), 108 +/- 8% of predicted), using the Masterscreen PFT (Viasys/Jaeger; Höchberg, Germany), with 45 ppm of inspired nitric oxide (NO), and breath-hold times of 4 s, 6 s, 8 s, and 10 s. The last two of three consecutive measurements were used for analysis.

RESULTS

In healthy subjects but not patients with CF, Dlno, and Dlco differed significantly (p < 0.05 each) between breath-hold times. Differences primarily occurred at 4 s and 10 s, while at 6 s and 8 s alveolar volume (VA), Dlno, Dlco, and Dlno/Dlco were similar. Variability of consecutive measurements (either three or the last two measurements) did not depend on breath-hold time. At 8 s, mean variabilities of Dlno and Dlco in healthy subjects were 4.9% and 2.5%, respectively, and 4.2% and 3.2% at 6 s. At 8 s, mean variabilities of Dlno and Dlco in CF patients were 4.4% and 1.9%, and 7.4% and 3.3% at 6 s.

CONCLUSIONS

Single-breath determinations of dlno and dlco showed no difference between breath-hold times of 6 s and 8 s in subjects with or without airway obstruction, and reproducibility was acceptable. Standardization of breath-hold time for Dlno measurements seems important for clinical and research comparisons.

Short-term variability of nitric oxide diffusing capacity and its components

When monitoring nitric oxide diffusing capacity (DL(NO)) in patients, it is necessary to distinguish natural biological variation from a real change in alveolar-membrane conductance. The short-term variability of single-breath DL(NO) has not been established. The aim was to determine the short-term variability DL(NO) in healthy subjects. Twelve healthy subjects performed single-breath hold diffusing capacity tests at rest over a 2-month period (eight separate sessions with 8+/-3 days between each session). Each subject inhaled 41+/-4 ppm NO and a standard diffusion mixture. DL(NO), which is a multiple of the membrane diffusing capacity for carbon monoxide (Dm(CO)), as well as carbon monoxide diffusing capacity (DL(CO)) and pulmonary capillary blood volume (V(c)) remained unaltered over the 2-month period (P>0.05). Reproducibility (calculated as 2.77 multiplied by the within-subject standard deviation) over eight sessions was 20, 5 and 8 mL min(-1)mmHg(-1) for DL(NO), DL(CO) and Dm(CO), respectively, and 19 mL for V(c) (when Dm(CO)=DL(NO)/2.42). DL(NO), DL(CO), Dm(CO) and V(c) remain unchanged over a period of 2 months. Since the inter-session variability is 20, 5 and 8 mL min(-1)mmHg(-1) for DL(NO), DL(CO) and Dm(CO), and 19 mL for V(c), a meaningful change should equal or exceed those values. While there is a small chance that week-to-week variation can also be partly due to mild pathophysiological changes, any differences that are below the reproducibility values are likely to be natural biological variation or technical variation of the equipment, rather than true physiological change.

Diffusing capacity for nitric oxide: Reference values and dependence on alveolar volume

Nitric oxide (NO) has a much stronger affinity for hemoglobin than carbon monoxide (CO); therefore, the DL(NO) (diffusing capacity for NO) is less influenced by changes in capillary blood volume than the DL(CO) (diffusing capacity for CO), and represents the true membrane diffusing capacity. We measured the combined single breath DL(NO)/DL(CO) in 124 healthy subjects, and generated reference equations for the DL(NO) and K(NO). In a subset of 21 subjects the measurements were performed on different inspiratory levels. The reference equation for DL(NO) in females is 53.47*H(height)0.077*A(age)-48.28(RSD5.22) and for males 59.84*H-0.25*A-44.20(RSD6.39). Reference equations for K(NO) in females is -2.03*H-0.025*A+11.52(RSD0.48) and for males -0.15*H-0.045*A+9.47(RSD0.65). The K(CO) (DL(CO)/V(A)) increases when V(A) (alveolar volume) decreases, probably due to an increase of blood volume per unit lung volume. The DL(NO) was much stronger related to the V(A), the K(NO) was almost independent of V(A). Because of the relative independence of the K(NO) on V(A), the K(NO) appears to be a much better index for the diffusion capacity per unit lung volume (transfer coefficient) than the K(CO).

A CHI3L1 gene polymorphism is associated with serum levels of YKL-40, a novel sarcoidosis marker

BACKGROUND

YKL-40, a chitinase-like cartilage glycoprotein, has recently shown its potential as a marker for sarcoidosis.

METHODS

This study aimed to assess whether YKL-40 at presentation may predict the course of sarcoidosis over a 4-year follow-up period and to investigate whether polymorphisms in the chitinase 3-like 1 (CHI3L1) gene might influence serum YKL-40 levels in sarcoidosis patients (n=63) and controls (n=333).

RESULTS

Patients had significantly higher (mean, 95% CI) serum YKL-40 levels (181.3 ng/ml, 50.7-648.1) compared to controls (36.6 ng/ml, p<0.0001. Serum YKL-40 was elevated in 79% of the patients and was inversely correlated with DLco at presentation (r(2)=-0.27, p=0.03), but not after 2-4 years of follow-up (r(2)=-0.16, p=0.27). Serum YKL-40 levels in controls were dependent on the CHI3L1 -329 G/A polymorphism (mean, 95% CI): GG (n=213) 48.3 ng/ml, 41.7-56.0; GA (n=101) 31.2 ng/ml, 26.6-36.3; AA (n=17) 17.8 ng/ml, 13.6-23.4, p<0.0001. In patients, this effect was not observed.

CONCLUSIONS

YKL-40 may be used as a sarcoidosis disease marker, but it is unsuitable as a marker to predict the course of the disease. The CHI3L1 -329 G/A polymorphism contributes to inter-individual variations of YKL-40 levels, but does not influence sarcoidosis disease susceptibility or severity.

Deciphering the nitric oxide to carbon monoxide lung transfer ratio: physiological implications

Using simultaneous nitric oxide and carbon monoxide lung transfer measurements (T(LNO) and T(LCO)), the membrane transfer capacity (D(m)) and capillary lung volume (V(c)) as well as the dimensionless ratio T(LNO)/T(LCO) can be calculated. The significance of this ratio is yet unclear. Theoretically, the T(LNO)/T(LCO) ratio should be inversely related to the product of both lung alveolar capillary membrane (mu) and blood sheet thicknesses (K). NO and CO transfers were measured in healthy subjects in various conditions likely to be associated with changes in K and/or mu. Experimentally, deflation of the lung from 7.4 to 4.8 l decreased the T(LNO)/T(LCO) ratio from 4.9 to 4.2 (n=25) which was consistent mainly with a thickening of the blood sheet. Compared with continuous negative pressure breathing, continuous positive pressure breathing increased this ratio suggesting a thinning of the capillary sheet. It was also observed with 12 healthy subjects that slight haemodilution that may thicken the blood sheet decreased the T(LNO)/T(LCO) ratio from 4.85 to 4.52. In conclusion, the T(LNO)/T(LCO) ratio is related to the thickness of the alveolar blood barrier. This ratio provides novel information for the analysis of the diffusion properties.

Membrane conductance in trained and untrained subjects using either steady state or single breath measurements of NO transfer

The aim of this work was to define the relationship between membrane conductance for NO (Dm) and physical activity by using either the steady state NO transfer (T(LNO)SS) or the single breath method (T(LNO)SB), making the hypothesis that NO transfer is only limited by the membrane. Alterations in T(LNO)SS with lung volume during tidal ventilation were measured in six subjects at rest and during steady exercise at 30, 60, and 80% of maximal aerobic power (MAP). A fast responding chemoluminescent NO analyser was used. Two calculation methods were used by sampling NO: (1) at mid-tidal volume, (2) in the middle of the alveolar plateau. T(LNO)SB at rest and maximal oxygen consumption (V(.-)O(2)max) were also measured in 18 other subjects. At rest T(LNO)SS with method 2 was 192% of the value given by method 1. T(LNO)SS with method 1 increased by 50% with 80% MAP as it did not change with method 2. Method 2 seemed inaccurate. T(LNO)SB at rest, which is closely related to Dm, was correlated to age and V(.-)O(2)max, T(LNO)SB=182-1.2 age+24.3 V(.-)O(2) max(l min(-1)) (p<0.01, r(2)=0.72). The T(LNO)SS and T(LNO)SB versus lung volume relationships suggest an influence of the breathing pattern on Dm. Dm can be estimated either by these two NO transfer methods, however the use of the T(LNO)SS method is highly sensitive to the alveolar sampling level. Dm increase during exercise is a function of MAP. Dm at rest decreases with age as it increases with MAP.

Intrabreath analysis of carbon monoxide uptake during exercise in patients at risk for lung injury

The single exhalation analysis of carbon monoxide, acetylene, and methane allows the determination of intrabreath (regional) DL, pulmonary capillary blood flow and ventilation inhomogeneities during rest and exercise. We reasoned that this technique might be more sensitive in detecting regional pulmonary capillary abnormalities than resting single breath DL (DL(sb)). We selected a group of breast cancer patients in high-dose chemotherapy (HDCT) protocols who were at risk for pulmonary injury. We grouped the patients into pre-HDCT and post-HDCT, and used resting DL(sb) to further categorize the latter into those with and without pulmonary injury. We found that exercise DL increases were blunted in post-HDCT patients with low resting DL(sb). More importantly, even in post-HDCT patients with normal resting DL(sb), exercise DL response was reduced in the slowest emptying lung units along with evidence for ventilation inhomogeneities (increased methane slope). We conclude that exercise assessments of DL at low lung volumes and gas mixing properties may be sensitive indicators of lung injury.

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.

The diabetic lung: relevance of alveolar microangiopathy for the use of inhaled insulin

The alveolar-capillary network receives the entire cardiac output and constitutes the largest microvascular organ in the body, making it highly susceptible to systemic microangiopathy. Owing to its large reserves, symptoms and disability develop later in the lung than in smaller microvasculature such as the kidney or retina despite a comparable severity of anatomic involvement. Hence, pulmonary impairment in diabetes mellitus is under-recognized. Nonetheless, respiratory autonomic neuropathy and structural derangement of the thorax and lung parenchyma develop in many asymptomatic diabetic patients; the pathophysiology parallels that in other target organs. Even subclinical loss of alveolar microvascular reserves can be quantified noninvasively from lung diffusing capacity and its components (membrane diffusing capacity and alveolar-capillary blood volume) measured at a given cardiac output at rest or during exercise. The alveolar diffusion-perfusion relation tracks the recruitment of microvascular reserves in a manner independent of physical fitness. This article addresses the importance and pathophysiologic basis of diabetic pulmonary involvement, the assessment of diabetic alveolar microangiopathy, and the relevance of this understanding for the emerging use of inhaled insulin.

Lung diffusion capacity for nitric oxide and carbon monoxide is impaired similarly following short-term graded exercise

Study aimed to determine whether short-term graded exercise affects single-breath lung diffusion capacity for nitric oxide (DLNO) and carbon monoxide (DLCO) similarly, and whether the DLNO/DLCO ratios during rest are altered post-exercise compared to pre-exercise. Eleven healthy subjects (age=29+/-6 years; weight=76.6+/-13.2 kg; height=177.9+/-13.2 cm; and maximal oxygen uptake or V(.-)(O(2max) = 52.7 +/- 9.3 ml kg(-1) min(-1))performed simultaneous single-breath DLNO and DLCO measurements at rest (inspired NO concentration=43.2+/-4.1 ppm, inspired CO concentration=0.30%) 15 min before and 2h after a graded exercise test to exhaustion (exercise duration=593+/-135 s). Resting DLNO and DLCO was similarly reduced 2h post-exercise (DLNO=-7.8+/-3.5%, DLCO=-10.3+/-6.9%, and P<0.05) due to reductions in pulmonary capillary blood volume (-11.3+/-9.0%, P<0.05) and membrane diffusing capacity for CO (-7.8+/-3.5%; P<0.05). The change in DLCO was reflected by the change in DLNO post-exercise such that 68% of the variance in the change in DLCO was accounted for by the variance in the change in DLNO (P<0.05). The DLNO/DLCO ratio was not altered post-exercise (5.87+/-0.37) compared to pre-exercise (5.70+/-0.34). We conclude that the decrease in single-breath DLNO and DLCO from pre- to post-exercise is similar, the magnitude of the change in DLCO closely reflects that of the change in DLNO, and single-breath DLNO/DLCO ratios are independent of the timing of measurement suggesting that using NO and CO transfer gases are valid in looking at short-term changes in lung diffusional conductance.