The diffusion of gases through the lungs of man

Beyond Spirometry: Linking Wasted Ventilation to Exertional Dyspnea in the Initial Stages of COPD

Exertional dyspnea, a key complaint of patients with chronic obstructive pulmonary disease (COPD), ultimately reflects an increased inspiratory neural drive to breathe. In non-hypoxemic patients with largely preserved lung mechanics - as those in the initial stages of the disease - the heightened inspiratory neural drive is strongly associated with an exaggerated ventilatory response to metabolic demand. Several lines of evidence indicate that the so-called excess ventilation (high ventilation-CO2 output relationship) primarily reflects poor gas exchange efficiency, namely increased physiological dead space. Pulmonary function tests estimating the extension of the wasted ventilation and selected cardiopulmonary exercise testing variables can, therefore, shed unique light on the genesis of patients' out-of-proportion dyspnea. After a succinct overview of the basis of gas exchange efficiency in health and inefficiency in COPD, we discuss how wasted ventilation translates into exertional dyspnea in individual patients. We then outline what is currently known about the structural basis of wasted ventilation in "minor/trivial" COPD vis-à-vis the contribution of emphysema versus a potential impairment in lung perfusion across non-emphysematous lung. After summarizing some unanswered questions on the field, we propose that functional imaging be amalgamated with pulmonary function tests beyond spirometry to improve our understanding of this deeply neglected cause of exertional dyspnea. Advances in the field will depend on our ability to develop robust platforms for deeply phenotyping (structurally and functionally), the dyspneic patients showing unordinary high wasted ventilation despite relatively preserved FEV1.

Diffusing Capacity as a Predictor of Hospitalizations in a Clinical Cohort of Chronic Obstructive Pulmonary Disease

Rationale: Chronic obstructive pulmonary disease (COPD) hospitalizations are a major burden on patients. Diffusing capacity of the lung for carbon monoxide (DlCO) is a potential predictor that has not been studied in large cohorts. Objectives: This study used electronic health record data to evaluate whether clinically obtained DlCO predicts COPD hospitalizations. Methods: We performed time-to-event analyses of individuals with COPD and DlCO measurements from the Johns Hopkins COPD Precision Medicine Center of Excellence. Cox proportional hazard methods were used to model time from DlCO measurement to first COPD hospitalization and composite first hospitalization or death, adjusting for age, sex, race, body mass index, smoking status, forced expiratory volume in 1 second (FEV1), history of prior COPD hospitalization, and comorbidities. To identify the utility of including DlCO in risk models, area under the receiver operating curve (AUC) values were calculated for models with and without DlCO. Results were externally validated in a separate analogous cohort. Results: Of 2,793 participants, 368 (13%) had a COPD hospitalization within 3 years. In adjusted analyses, for every 10% decrease in DlCO% predicted, risk of COPD hospitalization increased by 10% (hazard ratio, 1.1; 95% confidence interval, 1.1-1.2; P < 0.001). Similar associations were observed for COPD hospitalizations or death. The model including demographics, comorbidities, FEV1, DlCO, and prior COPD hospitalizations performed well, with an AUC of 0.85 and an AUC of 0.84 in an external validation cohort. Conclusions: Diffusing capacity is a strong predictor of COPD hospitalizations in a clinical cohort of individuals with COPD, independent of airflow obstruction and prior hospitalizations. These findings support incorporation of DlCO in risk assessment of patients with COPD.

Referential equations for pulmonary diffusing capacity generated from the Japanese population using the Lambda, Mu, or Sigma method and their comparisons with prior referential equations

BACKGROUND

This study aimed to establish reference equations for single-breath lung carbon monoxide diffusing capacity (DLCO), alveolar volume (VA), and transfer coefficient of the lungs for carbon monoxide (KCO, sometimes written as DLCO/VA) in the Japanese population. A generalised additive model for location size and shape (GAMLSS) was used to build each equation.

METHODS

To collect pulmonary function data throughout a broad age range, we prospectively obtained pulmonary function data from healthy volunteers and retrospectively obtained data from patients with normal diffusing capacity aged 16-85 years.

RESULTS

In total, 702 tests were conducted. The validation group z-scores, except for DLCO in males, showed substantial discrepancies between the Global Lung Initiative (GLI) baseline prediction equations and the present study's prediction equations, indicating the need for a new reference value prediction approach. The root mean square errors of the DLCO, VA, and KCO reference values obtained from the present study's prediction equations were lower than those derived from the GLI and previous linear regression equations.

CONCLUSIONS

Reference values obtained in this study were more appropriate for our sample than those derived from the existing baseline prediction equations. This research's contribution is the development of a more precise prediction equation that can be used to establish a reference value range for pulmonary diffusing capacity.

ETHICS AND DISSEMINATION

This research does not include any dissemination plan (publications, data deposition and curation).

The added value of haemoglobin to height, age, and sex to predict DLCO in subjects with preserved exercise capacity

BACKGROUND

The single breath diffusion capacity for carbon monoxide (DLCO) captures several aspects of the role of the lung in meeting the metabolic demands of the body. The magnitude of the independent contributors to the DLCO is unknown. The aim of this study was to investigate the factors that independently contribute to the DLCO.

OBJECTIVES

The objective was to investigate the impact of height, age, sex and haemoglobin on DLCO, alveolar volume (VA) and carbon monoxide transfer coefficient (KCO).

METHODS

Study participants were pre-screened based on normal exercise capacity achieved during an incremental cardio-pulmonary exercise testing (CPET) using cycle ergometry at McMaster University Medical Center between 1988-2012. Participants who had an FEV1>80% predicted, with an FEV1/FVC ≥0.7 and who achieved a maximum power output ≥80% were selected for analysis. In total, 16,298 subjects [61% male, mean height 1.70m (range 1.26-2.07), age 49 yrs (10-94), weight 79 kg (23-190) had DLCO measured while demonstrating normal spirometry and exercise capacity.

RESULTS

The DLCO increased exponentially with height, was 15% greater in males, increased with age yearly until 20, then decreased yearly after the age of 35, and was 6% higher per gram of haemoglobin (5.58*Height(m)1.69*1.15 in Males*(1-0.006*Age>35)*(1+0.01*Age<20) *(1+0.06*Hb gm/dl), (r = 0.76).

CONCLUSION

Height, age, sex, and haemoglobin all have independent influence on the DLCO in subjects with normal spirometry and preserved exercise capacity.

Inflammation associated with lung function abnormalities in COVID-19 survivors

BACKGROUND

Activation of inflammatory pathways promotes organ dysfunction in COVID-19. Currently, there are reports describing lung function abnormalities in COVID-19 survivors; however, the biological mechanisms remain unknown. The aim of this study was to analyze the association between serum biomarkers collected during and following hospitalization and pulmonary function in COVID-19 survivors.

METHODS

Patients recovering from severe COVID-19 were prospectively evaluated. Serum biomarkers were analyzed from admission to hospital, peak during hospitalization, and at the time of discharge. Pulmonary function was measured approximately 6 weeks after discharge.

RESULTS

100 patients (63% male) were included (age 48 years, SD ± 14) with 85% having at least one comorbidity. Patients with a restrictive spirometry pattern (n = 46) had greater inflammatory biomarkers compared to those with normal spirometry (n = 54) including peak Neutrophil-to-Lymphocyte ratio (NLR) value [9.3 (10.1) vs. 6.5 (6.6), median (IQR), p = 0.027] and NLR at hospital discharge [4.6 (2.9) vs. 3.2 (2.9) p = 0.005] and baseline C-reactive protein value [164.0 (147.0) vs. 106.5 (139.0) mg/dL, p = 0.083). Patients with an abnormal diffusing capacity (n = 35) had increased peak NLR [8.9 (5.9) vs. 5.6 (5.7) mg/L, p = 0.029]; baseline NLR [10.0 (19.0) vs. 4.0 (3.0) pg/ml, p = 0.002] and peak Troponin-T [10.0 (20.0) vs. 5.0 (5.0) pg/ml, p = 0.011] compared to patients with normal diffusing capacity (n = 42). Multivariable linear regression analysis identified predictors of restrictive spirometry and low diffusing capacity, but only accounted for a low degree of variance in pulmonary function outcome.

CONCLUSION

Overexpression of inflammatory biomarkers is associated with subsequent lung function abnormalities in patients recovered from severe COVID-19.

Probiotic-based nanoparticles for targeted microbiota modulation and immune restoration in bacterial pneumonia

While conventional bacterial pneumonia mainly centralizes avoidance of bacterial colonization, it remains unclear how to restore the host immunity for hyperactive immunocompetent primary and immunocompromised secondary bacterial pneumonia. Here, probiotic-based nanoparticles of OASCLR were formed by coating chitosan, hyaluronic acid and ononin on living Lactobacillus rhamnosus. OASCLR nanoparticles could effectively kill various clinic common pathogens and antibacterial efficiency was >99.97%. Importantly, OASCLR could modulate lung microbiota, increasing the overall richness and diversity of microbiota by decreasing pathogens and increasing probiotic and commensal bacteria. Additionally, OASCLR could target inflammatory macrophages by the interaction of OASCLR with the macrophage binding site of CD44 and alleviate overactive immune responses for hyperactive immunocompetent pneumonia. Surprisingly, OASCLR could break the state of the macrophage's poor phagocytic ability by upregulating the expression of the extracellular matrix assembly, immune activation and fibroblast activation in immunocompromised pneumonia. The macrophage's phagocytic ability was increased from 2.61% to 12.3%. Our work provides a potential strategy for hyperactive immunocompetent primary and immunocompromised secondary bacterial pneumonia.

Pulmonary diffusing capacity to nitric oxide and carbon monoxide during exercise and in the supine position: a test-retest reliability study

NEW FINDINGS

What is the central question in this study? How reliable is the combined measurement of the pulmonary diffusing capacity to carbon monoxide and nitric oxide (DLCO/NO ) during exercise and in the resting supine position, respectively? What is the main finding and its importance? The DLCO/NO technique is reliable with a very low day-to-day variability both during exercise and in the resting supine position, and may thus provide a useful physiological outcome that reflects the alveolar-capillary reserve in humans.

ABSTRACT

DLCO/NO , the combined single-breath measurement of the diffusing capacity to carbon monoxide (DLCO ) and nitric oxide (DLNO ) measured either during exercise or in the resting supine position may be a useful physiological measure of alveolar-capillary reserve. In the present study, we investigated the between-day test-retest reliability of DLCO/NO -based metrics. Twenty healthy volunteers (10 males, 10 females; mean age 25 (SD 2) years) were randomized to repeated DLCO/NO measurements during upright rest followed by either exercise (n = 11) or resting in the supine position (n = 9). The measurements were repeated within 7 days. The smallest real difference (SRD), defined as the 95% confidence limit of the standard error of measurement (SEM), the coefficient of variance (CV), and intraclass correlation coefficients were used to assess test-retest reliability. SRD for DLNO was higher during upright rest (5.4 (95% CI: 4.1, 7.5) mmol/(min kPa)) than during exercise (2.7 (95% CI: 2.0, 3.9) mmol/(min kPa)) and in the supine position (3.0 (95% CI: 2.1, 4.8) mmol/(min kPa)). SRD for DLCOc was similar between conditions. CV values for DLNO were slightly lower than for DLCOc both during exercise (1.5 (95% CI: 1.2, 1.7) vs. 3.8 (95% CI: 3.2, 4.3)%) and in the supine position (2.2 (95% CI: 1.8, 2.5) vs. 4.8 (95% CI: 3.8, 5.4)%). DLNO increased by 12.3 (95% CI: 11.1, 13.4) and DLCOc by 3.3 (95% CI: 2.9, 3.7) mmol/(min kPa) from upright rest to exercise. The DLCO/NO technique provides reliable indices of alveolar-capillary reserve, both during exercise and in the supine position.

Relationships of computed tomography-based small vessel indices of the lungs with ventilation heterogeneity and high transfer coefficients in non-smokers with asthma

Background: The mechanism of high transfer coefficients of the lungs for carbon monoxide (Kco) in non-smokers with asthma is explained by the redistribution of blood flow to the area with preserved ventilation, to match the ventilation perfusion. Objectives: To examine whether ventilation heterogeneity, assessed by pulmonary function tests, is associated with computed tomography (CT)-based vascular indices and Kco in patients with asthma. Methods: Participants were enrolled from the Hokkaido-based Investigative Cohort Analysis for Refractory Asthma (Hi-CARAT) study that included a prospective asthmatic cohort. Pulmonary function tests including Kco, using single breath methods; total lung capacity (TLC), using multiple breath methods; and CT, were performed on the same day. The ratio of the lung volume assessed using single breath methods (alveolar volume; V_A) to that using multiple breath methods (TLC) was calculated as an index of ventilation heterogeneity. The volume of the pulmonary small vessels <5 mm² in the whole lung (BV5 volume), and number of BV5 at a theoretical surface area of the lungs from the plural surface (BV5 number) were evaluated using chest CT images. Results: The low V_A/TLC group (the lowest quartile) had significantly lower BV5 number, BV5 volume, higher BV5 volume/BV5 number, and higher Kco compared to the high V_A/TLC group (the highest quartile) in 117 non-smokers, but not in 67 smokers. Multivariable analysis showed that low V_A/TLC was associated with low BV5 number, after adjusting for age, sex, weight, lung volume on CT, and CT emphysema index in non-smokers (not in smokers). Conclusion: Ventilation heterogeneity may be associated with low BV5 number and high Kco in non-smokers (not in smokers). Future studies need to determine the dynamic regional system in ventilation, perfusion, and diffusion in asthma.

Modeling of Red Blood Cells in Capillary Flow Using Fluid-Structure Interaction and Gas Diffusion

Red blood cell (RBC) distribution, RBC shape, and flow rate have all been shown to have an effect on the pulmonary diffusing capacity. Through this study, a gas diffusion model and the immersed finite element method were used to simulate the gas diffusion into deformable RBCs running in capillaries. It has been discovered that when RBCs are deformed, the CO flux across the membrane becomes nonuniform, resulting in a reduced capacity for diffusion. Additionally, when compared to RBCs that were dispersed evenly, our simulation showed that clustered RBCs had a significantly lower diffusion capability.

Molecular diameters of rarefied gases

Molecular diameters are an important property of gases for numerous scientific and technical disciplines. Different measurement techniques for these diameters exist, each delivering a characteristic value. Their reliability in describing the flow of rarefied gases, however, has not yet been discussed, especially the case for the transitional range between continuum and ballistic flow. Here, we present a method to describe gas flows in straight channels with arbitrary cross sections for the whole Knudsen range by using a superposition model based on molecular diameters. This model allows us to determine a transition diameter from flow measurement data that paves the way for generalized calculations of gas behaviour under rarefied conditions linking continuum and free molecular regime.

Natural Course of the Diffusing Capacity of the Lungs for Carbon Monoxide in COPD: Importance of Sex

BACKGROUND

The value of the single-breath diffusing capacity of the lungs for carbon monoxide (Dlco) relates to outcomes for patients with COPD. However, little is known about the natural course of Dlco over time, intersubject variability, and factors that may influence Dlco progression.

RESEARCH QUESTION

What is the natural course of Dlco in patients with COPD over time, and which other factors, including sex differences, could influence this progression?

STUDY DESIGN AND METHODS

We phenotyped 602 smokers (women, 33%), of whom 506 (84%) had COPD and 96 (16%) had no airflow limitation. Lung function, including Dlco, was monitored annually over 5 years. A random coefficients model was used to evaluate Dlco changes over time.

RESULTS

The mean (± SE) yearly decline in Dlco % in patients with COPD was 1.34% ± 0.015%/y. This was steeper compared with non-COPD control subjects (0.04% ± 0.032%/y; P = .004). Sixteen percent of the patients with COPD, vs 4.3% of the control subjects, had a statistically significant Dlco % slope annual decline (4.14%/y). At baseline, women with COPD had lower Dlco values (11.37% ± 2.27%; P < .001) in spite of a higher FEV₁ % than men. Compared with men, women with COPD had a steeper Dlco annual decline of 0.89% ± 0.42%/y (P = .039).

INTERPRETATION

Patients with COPD have an accelerated decline in Dlco compared with smokers without the disease. However, the decline is slow, and a testing interval of 3 to 4 years may be clinically informative. The lower and more rapid decline in Dlco values in women, compared with men, suggests a differential impact of sex in gas exchange function.

TRIAL REGISTRY

ClinicalTrials.gov; No.: NCT01122758; URL: www.clinicaltrials.gov.

A brief history of carbon monoxide and its therapeutic origins

It is estimated that 10% of carbon throughout the cosmos is in the form of carbon monoxide (CO). Earth's earliest prebiotic atmosphere included the trinity of gasotransmitters CO, nitric oxide (NO), and hydrogen sulfide (H₂S), for which all of life has co-evolved with. The history of CO can be loosely traced to mythological and prehistoric origins with rudimentary understanding emerging in the middle ages. Ancient literature is focused on CO's deadly toxicity which is understandable in the context of our primitive relationship with coal and fire. Scientific inquiry into CO appears to have emerged throughout the 1700s followed by chemical and toxicological profiling throughout the 1800s. Despite CO's ghastly reputation, several of the 18th and 19th century scientists suggested a therapeutic application of CO. Since 2000, the fundamental understanding of CO as a deadly nuisance has undergone a paradigm shift such that CO is now recognized as a neurotransmitter and viable pharmaceutical candidate. This review is intended to provide a brief history on the trace origins pertaining to endogenous formation and therapeutic application of CO.

Diffusing capacity in chronic obstructive pulmonary disease assessment: A meta-analysis

To achieve a multidimensional evaluation of chronic obstructive pulmonary disease (COPD) patients, the spirometry measures are supplemented by assessment of symptoms, risk of exacerbations, and CT imaging. However, the measurement of diffusing capacity of the lung for carbon monoxide (DLCO) is not included in most common used models of COPD assessment. Here, we conducted a meta-analysis to evaluate the role of DLCO in COPD assessment.The studies were identified by searching the terms "diffusing capacity" OR "diffusing capacity for carbon monoxide" or "DLCO" AND "COPD" AND "assessment" in Pubmed, Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, Embase, Scopus, and Web of Science databases. The mean difference of DLCO % predict was assessed in COPD patient with different severity (according to GOLD stage and GOLD group), between COPD patients with or without with frequent exacerbation, between survivors and non-survivors, between emphysema dominant and non-emphysema dominant COPD patients, and between COPD patients with or without pulmonary hypertension.43 studies were included in the meta-analysis. DLCO % predicted was significantly lower in COPD patients with more severe airflow limitation (stage II/IV), more symptoms (group B/D), and high exacerbation risk (group C/D). Lower DLCO % predicted was also found in exacerbation patients and non-survivors. Low DLCO % predicted was related to emphysema dominant phenotype, and COPD patients with PH.The current meta-analysis suggested that DLCO % predicted might be an important measurement for COPD patients in terms of severity, exacerbation risk, mortality, emphysema domination, and presence of pulmonary hypertension. As diffusion capacity reflects pulmonary ventilation and perfusion at the same time, the predictive value of DLCO or DLCO combined with other criteria worth further exploration.

Modeling of Gas Exchange in the Lungs

This overview presents the recent progress in our understanding of gas transfer by the lungs during the respiratory cycle and during breath holding. Different phenomena intervene in gas transfer, convection and diffusion in the gas, dissolution, diffusion across the alveolar-capillary membrane, diffusion across blood plasma, and finally diffusion and reaction with hemoglobin inside blood cells. The different gases, O₂ , CO, and NO, have very different reaction times with hemoglobin ranging from a few microseconds to tens of milliseconds. This is leading to different outcomes. For O₂ , the solutions to the coupled nonlinear gas and blood equations are obtained at the acinus level. They include the fact that the acinar internal ventilation is strongly heterogeneous due to the arborescent structure. Also, in the dynamic calculation, one takes care of the delay between the start of inhalation and arrival of fresh air in the acinus. This "dead" time is the dynamic equivalent of the dead space ventilation. The question of the dependence of Vo₂ on ventilation and perfusion takes a different form. The results show that Vo₂ is not only a function of the ventilation/perfusion ratio but also depends on the variables: acinar ventilation VE_ac and perfusion Q_ac . The ratio VE_ac /Q_ac roughly determines arterial O₂ saturation and arterial and alveolar O₂ partial pressure. The classic Roughton-Forster interpretation of DLCO (separation between independent membrane and blood resistance) was a mathematical conjecture. It was shown recently that this conjecture was violated. This article presents an alternative interpretation that uses time concepts instead of resistance. © 2021 American Physiological Society. Compr Physiol 11:1289-1314, 2021.

The effects of lung volume reduction treatment on diffusing capacity and gas exchange

Lung volume reduction (LVR) treatment in patients with severe emphysema has been shown to have a positive effect on hyperinflation, expiratory flow, exercise capacity and quality of life. However, the effects on diffusing capacity of the lungs and gas exchange are less clear. In this review, the possible mechanisms by which LVR treatment can affect diffusing capacity of the lung for carbon monoxide (D _LCO) and arterial gas parameters are discussed, the use of D _LCO in LVR treatment is evaluated and other diagnostic techniques reflecting diffusing capacity and regional ventilation (V')/perfusion (Q') mismatch are considered.A systematic review of the literature was performed for studies reporting on D _LCO and arterial blood gas parameters before and after LVR surgery or endoscopic LVR with endobronchial valves (EBV). D _LCO after these LVR treatments improved (40 studies, n=1855) and the mean absolute change from baseline in % predicted D _LCO was +5.7% (range -4.6% to +29%), with no real change in blood gas parameters. Improvement in V' inhomogeneity and V'/Q' mismatch are plausible explanations for the improvement in D _LCO after LVR treatment.

Pathophysiology of respiratory failure and physiology of gas exchange during ECMO

Lungs play a key role in sustaining cellular respiration by regulating the levels of oxygen and carbon dioxide in the blood. This is achieved by exchanging these gases between blood and ambient air across the alveolar capillary membrane by the process of diffusion. In the microstructure of the lung, gas exchange is compartmentalized and happens in millions of microscopic alveolar units. In situations of lung injury, this structural complexity is disrupted resulting in impaired gas exchange. Depending on the severity and the type of lung injury, different aspects of pulmonary physiology are affected. If the respiratory failure is refractory to ventilator support, extracorporeal membrane oxygenation (ECMO) can be utilized to support the gas exchange needs of the body. In ECMO, thin hollow fiber membranes made up of polymethylpentene act as blood-gas interface for diffusion. Decades of innovative engineering with membranes and their alignment with blood and gas flows has enabled modern oxygenators to achieve clinically and physiologically significant amount of gas exchange.

Reference Values for Pulmonary Single-Breath Diffusing Capacity - Results of the "Study of Health in Pomerania"

OBJECTIVES

 The assessment of pulmonary single-breath diffusing capacity is a frequently performed diagnostic procedure and considered as an important tool in medical surveillance examinations of pulmonary diseases.The aim of this study was to establish reference equations for pulmonary single-breath diffusing capacity parameters in a representative adult-population across a wide age range and to compare the normative values from this sample with previous ones.

METHODS

 Diffusing capacity measurement was carried out in 3566 participants (1811 males) of a cross-sectional, population-based survey ("Study of Health in Pomerania - SHIP").

RESULTS

 Individuals with cardiopulmonary disorders and current smoking habits were excluded, resulting in 1786 healthy individuals (923 males), aged 20 - 84 years. Prediction equations for both sexes were established by quantile regression analyses, taking into consideration the influence of age, height, weight and former smoking.

CONCLUSION

 The study provides a novel set of prediction equations for pulmonary single-breath diffusing capacity in an adult Caucasian population. The results are comparable to previously reported equations, underline their importance and draw attention to the need for up-to-date reference equations that adequately take into account both the subjects' origin, age, anthropometric characteristics and the equipment used.

Diffusing Capacity Is an Independent Predictor of Outcomes in Pulmonary Hypertension Associated With COPD

BACKGROUND

Patients with COPD who experience pulmonary hypertension (PH) have worse mortality than those with COPD alone. Predictors of poor outcomes in COPD-PH are not well-described. Diffusing capacity of the lung (Dlco) assesses the integrity of the alveolar-capillary interface and thus may be a useful prognostic tool among those with COPD-PH.

RESEARCH QUESTION

Using a single center registry, we sought to evaluate Dlco as a predictor of mortality in a cohort of patients with COPD-PH.

STUDY DESIGN AND METHODS

This retrospective cohort study analyzed 71 COPD-PH patients from the Johns Hopkins Pulmonary Hypertension Registry with right-sided heart catheterization (RHC)-proven PH and pulmonary function testing data within one year of diagnostic RHC. Transplant-free survival was calculated from index RHC. Adjusted transplant-free survival was modelled using Cox proportional hazard methods; age, pulmonary vascular resistance, FEV1, oxygen use, and N-terminal pro-brain natriuretic peptide were included as covariates.

RESULTS

Overall unadjusted transplant-free 1-, 3-, and 5-year survivals were 87%, 60%, and 51%, respectively. Survival was associated with reduced Dlco across the observed range of pulmonary artery pressures and pulmonary vascular resistance. Severe Dlco impairment was associated with poorer survival (log-rank χ2 13.07) (P < .001); adjusting for covariates, for every percent predicted decrease in Dlco, mortality rates increased by 4% (hazard ratio, 1.04; 95% CI, 1.01-1.07).

INTERPRETATION

Among patients with COPD-PH, severe gas transfer impairment is associated with higher mortality, even with adjustment for airflow obstruction and hemodynamics, which suggests that Dlco may be a useful prognostic marker in this population. Future studies are needed to further investigate the association between Dlco and morbidity and to determine the utility of Dlco as a biomarker for disease risk and severity in COPD-PH.

ERS International Congress, Madrid, 2019: highlights from the Allied Respiratory Professionals' Assembly

This article provides an overview of outstanding sessions that were (co)organised by the Allied Respiratory Professionals' Assembly during the European Respiratory Society International Congress 2019 in Madrid, Spain. Session content was mainly targeted at allied respiratory professionals such as respiratory physiologists, respiratory physiotherapists and respiratory nurses, and is summarised in this document. Short take-home messages related to pulmonary function testing highlight the importance of quality control. Furthermore, novel findings regarding the assessment of functional status call attention to bodily factors that can affect functional status. Regarding pulmonary rehabilitation, data were presented about the use of equipment and type of exercise training in COPD and lung cancer. Recent developments in physical activity-related research give insight in enablers of physical activity after hospital admission. The importance of integrated respiratory care was also highlighted, with the occupational therapist, nurse, and nutritional and psychological counsellor playing a pivotal role, which relates directly to research in the field of respiratory nursing that formulates the need for more nursing led-interventions in the future. To conclude, this review provides readers with valuable insight into some of the emerging and future areas affecting clinical practice of allied healthcare professionals.

A highlights review of selected presentations from #ERSCongress 2019 by @ERS_Assembly9http://bit.ly/2VNFgAj

Incorporating Lung Diffusing Capacity for Carbon Monoxide in Clinical Decision Making in Chest Medicine

Lung diffusing capacity for carbon monoxide (Dlco) remains the only noninvasive pulmonary function test to provide an integrated picture of gas exchange efficiency in human lungs. Due to its critical dependence on the accessible "alveolar" volume (Va), there remains substantial misunderstanding on the interpretation of Dlco and the diffusion coefficient (Dlco/Va ratio, Kco). This article presents the physiologic and methodologic foundations of Dlco measurement. A clinically friendly approach for Dlco interpretation that takes those caveats into consideration is outlined. The clinical scenarios in which Dlco can effectively assist the chest physician are discussed and illustrative clinical cases are presented.

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.

The effect of dopamine on pulmonary diffusing capacity and capillary blood volume responses to exercise in young healthy humans

NEW FINDINGS

What is the Central question? Does dopamine, a pulmonary vascular vasodilator, contribute to the regulation of pulmonary diffusing capacity and capillary blood volume responses to exercise and exercise tolerance? What are the main findings and their importance? Dopamine appears not to be important for regulating pulmonary diffusing capacity or pulmonary capillary blood volume during exercise in healthy participants. Dopamine blockade trials demonstrated that endogenous dopamine is important for maintaining exercise tolerance; however, exogenous dopamine does not improve exercise tolerance.

ABSTRACT

Pulmonary capillary blood volume (V_c ) and diffusing membrane capacity (D_m ) expansion are important contributors to the increased pulmonary diffusing capacity (DL_CO ) observed during upright exercise. Dopamine is a pulmonary vascular vasodilator, and recent studies suggest that it may play a role in V_c regulation through changes in pulmonary vascular tone. The purpose of this study was to examine the effect of exogenous dopamine and dopamine receptor-2 (D₂ -receptor) blockade on DL_CO , V_c and D_m at baseline and during cycle exercise, as well as time-to-exhaustion at 85% of V ̇ O 2 peak . We hypothesized that dopamine would increase DL_CO , V_c , D_m and time-to-exhaustion, while D₂ -receptor blockade would have the opposite effect. We recruited 14 young, healthy, recreationally active subjects ( V ̇ O 2 peak 45.8 ± 6.6 ml kg^-1  min^-1 ). DL_CO , V_c and D_m were determined at baseline and during exercise at 60% and 85% of V ̇ O 2 peak under the following randomly assigned and double blinded conditions: (1) intravenous saline and placebo pill, (2) intravenous dopamine (2 µg kg^-1  min^-1 ) and placebo pill, and (3) intravenous saline and D₂ -receptor antagonist (20 mg oral metoclopramide). Exogenous dopamine and dopamine blockade had no effect on DL_CO , V_c and D_m responses at baseline or during exercise. Dopamine blockade reduced time-to-exhaustion by 47% (P = 0.04), but intravenous dopamine did not improve time-to-exhaustion. While dopamine modulation did not affect DL_CO , V_c or D_m , the reduction in time-to-exhaustion with D₂ -receptor blockade suggests that endogenous dopamine is important for exercise tolerance.

[Rebreathing method for measuring CO transfer factor in children]

INTRODUCTION

The reference technique to measure the diffusing capacity of the lung for carbon monoxide (DLco) is the single-breath method (sb). For patients unable to perform this method, the rebreathing method (rb) can be used. However, the clinical relevance of DLCOrb has not been evaluated. The aim of this study was to assess the feasibility of the rb method in children seen in a clinical setting and its relationships with sb method.

SUBJECTS AND METHOD

We prospectively included children referred for 1) a suspected or confirmed interstitial lung disease (ILD group) (DLCOsb and DLCOrb measurements) ; 2) controlled asthma with normal lung function (DLCOrb measurements to derive DLCOrb/KCOrb expected values). DLCOrb was computed from the decrease in CO and Helium concentrations during tidal breathing in a rebreathing bag.

RESULTS

Data on DLCOrb measurements were available for 53 (91%) children in the ILD group and 48 (91%) control children (mean (range) 11.5 (4.3-18.2) and 9.5 (4-17) years ; respectively). In the ILD group, high or moderate correlations were found between raw DLCOrb and DLCOsb values (rhô=0.82 ; P<0.0001) and between KCOrb and KCOsb (rhô=0.62 ; P<0.0001), respectively. Results expressed as percentage predicted were moderately correlated (rhô=0.55 ; P=0.0003 for DLCO ; rhô=0.51 ; P=0.001 for KCO).

CONCLUSION

DLCOrb is easy to perform in children and gives values that are highly correlated to DCLOsb. Our preliminary results are in favour of a possible clinical use after further validation.

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.

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.

Transfer coefficients better reflect emphysematous changes than carbon monoxide diffusing capacity in obstructive lung diseases

The overlap between asthma and chronic obstructive pulmonary disease (COPD) has attracted the interest of pulmonary physicians; thus, measurement of carbon monoxide diffusion capacity (DLco) and/or transfer coefficients (Kco, DLco/V_A) may become valuable in clinical settings. How these parameters behave in chronic obstructive lung diseases is poorly understood. We predicted that Kco might more accurately reflect emphysematous changes in the lungs than DLco. We examined DLco and Kco in nonsmokers and smokers with asthma and investigated their relationships with forced expiratory volume in 1 s (%FEV₁) by group. We then selected nonsmokers (As-NS) and smokers with asthma (As-Sm) in both groups and those with COPD while controlling for the degree of airflow limitation across groups. Emphysema volumes [%lung attenuation volume (%LAV)] and percentage of cross-sectional area of small pulmonary vessels <5 mm² (%CSA_<5) were measured by computed tomography. In As-NS, %Kco was significantly higher when FEV₁% was reduced, but such a correlation was not seen in As-Sm. %Kco successfully differentiated among the three groups when airflow limitation levels were matched. However, %DLc, was significantly reduced only in patients with COPD. Both %LAV and %CSA_<5 were better correlated with %Kco than with %DLco. There was discordance between %DL_CO and %Kco in As-Sm, which was not seen in As-NS. Overall, %Kco better reflects emphysematous changes in obstructive lung diseases than %DLco. NEW & NOTEWORTHY Despite differing behaviors of %Kco and %DLco in several diseases, the characteristics of these parameters have not been fully examined in smokers with asthma. Here, we demonstrated that %Kco is a more sensitive parameter of pathophysiology, better reflecting emphysematous changes in chronic obstructive lung diseases overall, compared with %DLco. Thus, more precise interpretations of %DLco and %Kco may provide clues for understanding the pathophysiology of obstructive lung diseases.

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.

Pulmonary Diffusion Capacity for Carbon Monoxide (DLCO) in Indonesian Patients with End-stage Renal Disease

OBJECTIVES

End-stage renal disease affects all systems in human including the respiratory system. This study aimed to discover the lung diffusion capacity of carbon monoxide (DLCO) in chronic hemodialysis patients and to establish its relation to several demographic and clinical factors as well as spirometry parameters.

MATERIAL AND METHODS

This was a cross-sectional study among chronic hemodialysis patients aged .18 years, clinically stable in the last four weeks, without prior history of lung and cardiac disorder. Spirometry and DLCO examination were performed in the span of 24 hours after hemodialysis.

OUTCOMES

There were 40 subjects analyzed. Majority of them were males (67.5%), non-smokers (55%), with a median age of 51 years, a mean body mass index of 22.6±3.9 kg/m2, a hemoglobin level of 9.5±1.3 g/dL, a median dialysis adequacy of 1.62 and a hemodialysis duration of 31.5 months. Hypertension was the most common underlying disease. About 20% of subjects had varying degrees of dyspnea. Prevalence of DLCO reduction was 52.5% with mild to moderate degree. Restrictive spirometry pattern was evident in 47.5% of subjects and obstructive pattern in 5%. There was a significant relation between DLCO reduction with smoking history (OR 4.52 [95% CI 1.04-19.6]) and also with restrictive disorder [OR 5.5 (95% CI 1.29-23.8)]. We suspected a lung parenchymal disorder as the cause of lung restriction and diffusion inhibition.

CONCLUSIONS

Reduction of lung diffusion capacity in chronic dialysis patients is common, although not accompanied by dyspnea. Risk factors for DLCO reduction are smoking history and restrictive disorder in spirometry.

Diffusion Reaction of Carbon Monoxide in the Human Lung

The capture of CO, a standard lung function test, results from diffusion-reaction processes of CO with hemoglobin inside red blood cells (RBCs). In its current understanding, suggested by Roughton and Forster in 1957, the capture is represented by two independent resistances in series, one for diffusion from the gas to the RBC periphery, the second for internal diffusion reaction. Numerical studies in 3D model structures described here contradict the independence hypothesis. This results from two different theoretical reasons: (i) The RBC peripheries are not equi-concentrations; (ii) diffusion times in series are not additive.

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.

2017 ERS/ATS standards for single-breath carbon monoxide uptake in the lung

This document provides an update to the European Respiratory Society (ERS)/American Thoracic Society (ATS) technical standards for single-breath carbon monoxide uptake in the lung that was last updated in 2005. Although both D_LCO (diffusing capacity) and T_LCO (transfer factor) are valid terms to describe the uptake of carbon monoxide in the lung, the term D_LCO is used in this document. A joint taskforce appointed by the ERS and ATS reviewed the recent literature on the measurement of D_LCO and surveyed the current technical capabilities of instrumentation being manufactured around the world. The recommendations in this document represent the consensus of the taskforce members in regard to the evidence available for various aspects of D_LCO measurement. Furthermore, it reflects the expert opinion of the taskforce members on areas in which peer-reviewed evidence was either not available or was incomplete. The major changes in these technical standards relate to D_LCO measurement with systems using rapidly responding gas analysers for carbon monoxide and the tracer gas, which are now the most common type of D_LCO instrumentation being manufactured. Technical improvements and the increased capability afforded by these new systems permit enhanced measurement of D_LCO and the opportunity to include other optional measures of lung function.

The blood transfer conductance for nitric oxide: Infinite vs. finite θNO

Whether the specific blood transfer conductance for nitric oxide (NO) with hemoglobin (θ_NO) is finite or infinite is controversial but important in the calculation of alveolar capillary membrane conductance (Dm_CO) and pulmonary capillary blood volume (V_C) from values of lung diffusing capacity for carbon monoxide (DLCO) and nitric oxide (DLNO). In this review, we discuss the background associated with θ_NO, explore the resulting values of Dm_CO and V_C when applying either assumption, and investigate the mathematical underpinnings of Dm_CO and V_C calculations. In general, both assumptions yield reasonable rest and exercise Dm_CO and V_C values. However, the finite θ_NO assumption demonstrates increasing V_C, but not Dm_CO, with submaximal exercise. At relatively high, but physiologic, DLNO/DLCO ratios both assumptions can result in asymptotic behavior for V_C values, and under the finite θ_NO assumption, Dm_CO values. In conclusion, we feel that the assumptions associated with a finite θ_NO require further in vivo validation against an established method before widespread research and clinical use.

A new method for measuring lung deposition efficiency of airborne nanoparticles in a single breath

Assessment of respiratory tract deposition of nanoparticles is a key link to understanding their health impacts. An instrument was developed to measure respiratory tract deposition of nanoparticles in a single breath. Monodisperse nanoparticles are generated, inhaled and sampled from a determined volumetric lung depth after a controlled residence time in the lung. The instrument was characterized for sensitivity to inter-subject variability, particle size (22, 50, 75 and 100 nm) and breath-holding time (3–20 s) in a group of seven healthy subjects. The measured particle recovery had an inter-subject variability 26–50 times larger than the measurement uncertainty and the results for various particle sizes and breath-holding times were in accordance with the theory for Brownian diffusion and values calculated from the Multiple-Path Particle Dosimetry model. The recovery was found to be determined by residence time and particle size, while respiratory flow-rate had minor importance in the studied range 1–10 L/s. The instrument will be used to investigate deposition of nanoparticles in patients with respiratory disease. The fast and precise measurement allows for both diagnostic applications, where the disease may be identified based on particle recovery, and for studies with controlled delivery of aerosol-based nanomedicine to specific regions of the lungs.

Time-based understanding of DLCO and DLNO

Capture of CO and NO by blood requires molecules to travel by diffusion from alveolar gas to haemoglobin molecules inside RBCs and then to react. One can attach to these processes two times, a time for diffusion and a time for reaction. This reaction time is known from chemical kinetics and, therefore, constitutes a unique physical clock. This paper presents a time-based bottom-up theory that yields a simple expression for DLCO and DLNO that produces quantitative predictions which compare successfully with experiments. Specifically, when this new approach is applied to DLCO experiments, it can be used to determine the value of the characteristic diffusion time, and the value of capillary volume (Vc). The new theory also provides a simple explanation for still unexplained correlations such as the observed proportionality between the so-called membrane conductance DM and Vc of Roughton and Forster's interpretation. This new theory indicates that DLCO should be proportional to the haematocrit as found in several experiments.

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.

History of respiratory gas exchange

As early as the 6th century B.C. the Greeks speculated on a substance pneuma that meant breath or soul, and they argued that this was essential for life. An important figure in the 2nd century A.D. was Galen whose school developed an elaborate cardiopulmonary system that influenced scientific thinking for 1400 years. A key concept was that blood was mixed with pneuma from the lung in the left ventricle thus forming vital spirit. It was also believed that blood flowed from the right to the left ventricle of the heart through pores in the interventricular septum but this view was challenged first by the Arab physician Ibn al-Nafis in the 13th century and later by Michael Servetus in the 16th century. The 17th century saw an enormous burgeoning of knowledge about the respiratory gases. First Torricelli explained the origin of atmospheric pressure, and then a group of physiologists in Oxford clarified the properties of inspired gas that were necessary for life. This culminated in the work of Lavoisier who first clearly elucidated the nature of the respiratory gases, oxygen, carbon dioxide and nitrogen. At that time it was thought that oxygen was consumed in the lung itself, and the fact that the actual metabolism took place in peripheral tissues proved to be a very elusive concept. It was not until the late 19th century that the issue was finally settled by Pflüger. In the early 20th century there was a colorful controversy about whether oxygen was secreted by the lung. During and shortly after World War II, momentous strides were made on the understanding of pulmonary gas exchange, particularly the role of ventilation-perfusion inequality. A critical development in the 1960s was the introduction of blood gas electrodes, and these have transformed the management of patients with severe lung disease.

[Pulmonary CO/NO transfer: physiological basis, technical aspects and clinical impact]

Diseases affecting the alveolar-capillary membrane or the capillary blood vessels can impair pulmonary gas exchanges and lung diffusion. The single-breath transfer factor of the lung for carbon monoxide (TL,CO) is the classical technique for measuring gas transfer from the alveolus to the pulmonary capillary blood. Pulmonary gas exchanges can also be explored by the transfer factor of the lung for nitric oxide (TL,NO). TL,NO represents a better index for the diffusing capacity of the alveolar-capillary membrane whereas TL,CO is more influenced by red blood cell resistance. Membrane diffusing capacity (DM) and pulmonary capillary blood volume (Vc) derivated from TL,CO and TL,NO by the Roughton-Forster equation can give additional insights into pulmonary pathologies. The clinical impact of the CO/NO transfer has still to be precised even if this measurement seems to provide an alternative way of investigating the alveolar membrane and the blood reacting with the gas.

Joseph Barcroft's studies of high-altitude physiology

Joseph Barcroft (1872-1947) was an eminent British physiologist who made contributions to many areas. Some of his studies at high altitude and related topics are reviewed here. In a remarkable experiment he spent 6 days in a small sealed room while the oxygen concentration of the air gradually fell, simulating an ascent to an altitude of nearly 5,500 m. The study was prompted by earlier reports by J. S. Haldane that the lung secreted oxygen at high altitude. Barcroft tested this by having blood removed from an exposed radial artery during both rest and exercise. No evidence for oxygen secretion was found, and the combination of 6 days incarceration and the loss of an artery was heroic. To obtain more data, Barcroft organized an expedition to Cerro de Pasco, Peru, altitude 4,300 m, that included investigators from both Cambridge, UK and Harvard. Again oxygen secretion was ruled out. The protocol included neuropsychometric measurements, and Barcroft famously concluded that all dwellers at high altitude are persons of impaired physical and mental powers, an assertion that has been hotly debated. Another colorful experiment in a low-pressure chamber involved reducing the pressure below that at the summit of Mt. Everest but giving the subjects 100% oxygen to breathe while exercising as a climber would on Everest. The conclusion was that it would be possible to reach the summit while breathing 100% oxygen. Barcroft was exceptional for his self-experimentation under hazardous conditions.

Clinical applications of lung function tests: a revisit

The development and clinical application of lung function tests have a long history, and the various components of lung function tests provide very important tools for the clinical evaluation of respiratory health and disease. Spirometry, measurement of the diffusion factor, bronchial provocation tests and forced oscillation techniques have found diverse clinical applications in the diagnosis and monitoring of respiratory diseases, such as chronic obstructive pulmonary disease, interstitial lung diseases and asthma. However, there are some practical issues to be resolved, including the establishment of reference values for individual test parameters and the roles of these tests in preoperative risk assessment and pulmonary rehabilitation. Novel measurements, including negative expiratory pressure, the fraction of exhaled nitric oxide and analysis of exhaled breath condensate, may provide new insights into physiological abnormalities or airway inflammation in respiratory diseases, but their clinical applications need to be further evaluated. The clinical application of lung function tests continues to face challenges, which may be overcome by further improvement of conventional techniques for lung function testing and further specification of new testing techniques.