Normal values for single exhalation diffusing capacity and pulmonary capillary blood flow in sitting, supine positions, and during mild exercise

The Pulmonary Vasculature

The pulmonary circulation is a low-pressure, low-resistance circuit whose primary function is to deliver deoxygenated blood to, and oxygenated blood from, the pulmonary capillary bed enabling gas exchange. The distribution of pulmonary blood flow is regulated by several factors including effects of vascular branching structure, large-scale forces related to gravity, and finer scale factors related to local control. Hypoxic pulmonary vasoconstriction is one such important regulatory mechanism. In the face of local hypoxia, vascular smooth muscle constriction of precapillary arterioles increases local resistance by up to 250%. This has the effect of diverting blood toward better oxygenated regions of the lung and optimizing ventilation-perfusion matching. However, in the face of global hypoxia, the net effect is an increase in pulmonary arterial pressure and vascular resistance. Pulmonary vascular resistance describes the flow-resistive properties of the pulmonary circulation and arises from both precapillary and postcapillary resistances. The pulmonary circulation is also distensible in response to an increase in transmural pressure and this distention, in addition to recruitment, moderates pulmonary arterial pressure and vascular resistance. This article reviews the physiology of the pulmonary vasculature and briefly discusses how this physiology is altered by common circumstances.

Diurnal variation in DLCO and non-standardized study procedures may cause a false positive safety signal in clinical trials

Diffusing capacity for carbon monoxide (DLCO) was measured in a phase I single ascending dose study after inhalation of AZD8154 or placebo in healthy participants at baseline (DLCO_Baseline) and follow-up (DLCO_Follow-up) 6 days after dosing. Initially, DLCO_Follow-up timepoint was 2 h earlier than the DLCO_Baseline timepoint and clinically significant decreases in DLCO_Follow-up (absolute change up to 19% from baseline and DLCO_%predicted values less than 70) were observed then. The observed reduction in DLCO_Follow-up was confirmed as a false positive finding after alignment of DLCO timings. As a consequence, when DLCO is used in clinical studies, measurements should be strictly standardized in relation to time of the day.

The supine position improves but does not normalize the blunted pulmonary capillary blood volume response to exercise in mild COPD

Patients with mild chronic obstructive pulmonary disease (COPD) demonstrate resting pulmonary vascular dysfunction as well as a blunted pulmonary diffusing capacity (DLCO) and pulmonary capillary blood volume (V_C) response to exercise. The transition from the upright to supine position increases central blood volume and perfusion pressure, which may overcome microvascular dysfunction in an otherwise intact alveolar-capillary interface. The present study examined whether the supine position normalized DLCO and V_C responses to exercise in mild COPD. Sixteen mild COPD participants and 13 age-, gender-, and height-matched controls completed DLCO maneuvers at rest and during exercise in the upright and supine position. The multiple FIO2-DLCO method was used to determine DLCO, V_C, and membrane diffusion capacity (D_M). All three variables were adjusted for alveolar volume (DLCOAdj, V_CAdj, and D_MAdj). The supine position reduced alveolar volume similarly in both groups, but oxygen consumption and cardiac output were unaffected. DLCOAdj, D_MAdj, and V_CAdj were all lower in COPD. These same variables all increased with upright and supine exercise in both groups. DLCOAdj was unaffected by the supine position. V_CAdj increased in the supine position similarly in both groups. D_MAdj was reduced in the supine position in both groups. While the supine position increased exercise V_CAdj in COPD, the increase was of similar magnitude to healthy controls; therefore, exercise V_C remained blunted in COPD. The persistent reduction in exercise DLCO and V_C when supine suggests that pulmonary vascular destruction is a contributing factor to the blunted DLCO and V_C response to exercise in mild COPD.NEW & NOTEWORTHY Patients with mild chronic obstructive pulmonary disease demonstrate a combination of reversible pulmonary microvascular dysfunction and irreversible pulmonary microvascular destruction.

Surfactant proteins changes after acute hemodynamic improvement in patients with advanced chronic heart failure treated with Levosimendan

Alveolar-capillary membrane evaluated by carbon monoxide diffusion (DLCO) plays an important role in heart failure (HF). Surfactant Proteins (SPs) have also been suggested as a worthwhile marker. In HF, Levosimendan improves pulmonary hemodynamics and reduces lung fluids but associated SPs and DLCO changes are unknown. Sixty-five advanced HF patients underwent spirometry, cardiopulmonary exercise test (CPET) and SPs determination before and after Levosimendan. Levosimendan caused natriuretic peptide-B (BNP) reduction, peakVO₂ increase and VE/VCO₂ slope reduction. Spirometry improved but DLCO did not. SP-A, SP-D and immature SP-B reduced (73.7 ± 25.3 vs. 66.3 ± 22.7 ng/mL*, 247 ± 121 vs. 223 ± 110 ng/mL*, 39.4 ± 18.7 vs. 34.4 ± 17.9AU*, respectively); while mature SP-B increased (424 ± 218 vs. 461 ± 243 ng/mL, * = p < 0.001). Spirometry, BNP and CPET changes suggest hemodynamic improvement and lung fluid reduction. SP-A, SP-D and immature SP-B reduction indicates a reduction of inflammatory stress; conversely mature SP-B increase suggests alveolar cell function restoration. In conclusion, acute lung fluid reduction is associated with SPs but not DLCO changes. SPs are fast responders to alveolar-capillary membrane condition changes.

Influence of resting lung diffusion on exercise capacity in patients with COPD

Background

Lung diffusing capacity for carbon monoxide (DLCO) gives an overall assessment of functional lung surface area for gas exchange and can be assessed using various methods. DLCO is an important factor in exercise intolerance in patients with chronic obstructive pulmonary disease (COPD). We investigated if the intra-breath (IBDLCO) method may give a more sensitive measure of available gas exchange surface area than the more typical single breath (SBDLCO) method and if COPD subjects with the largest resting DLCO relative to pulmonary blood flow (Qc) would have a more preserved exercise capacity.

Methods

Informed consent, hemoglobin, spirometry, SBDLCO, IBDLCO, and Qc during IBDLCO were performed in moderate to severe COPD patients, followed by progressive cycle ergometry to exhaustion with measures of oxygen saturation (SaO₂) and expired gases.

Results

Thirty two subjects (47% female, age 66 ± 9 yrs., BMI 30.4 ± 6.3 kg/m², smoking hx 35 ± 29 pkyrs, 2.3 ± 0.8 on the 0-4 GOLD classification scale) participated. The majority used multiple inhaled medications and 20% were on oral steroids. Averages were: FEV₁/FVC 58 ± 10%Pred, peak VO₂ 11.4 ± 3.1 ml/kg/min, and IBDLCO 72% of the SBDLCO (r = 0.88, SB vs IB methods). Using univariate regression, both the SB and IBDLCO (% predicted but not absolute) were predictive of VO₂peak in ml/kg/min; SBDLCO/Qc (r = 0.63, p < 0.001) was the best predictor of VO₂peak; maximal expiratory flows over the mid to lower lung volumes were the most significantly predictive spirometric measure (r = 0.49, p < 0.01). However, in multivariate models only BMI added additional predictive value to the SBDLCO/Qc for predicting aerobic capacity (r = 0.73). Adjusting for current smoking status and gender did not significantly change the primary results.

Conclusion

In patients with moderate to severe COPD, preservation of lung gas exchange surface area as assessed using the resting SBDLCO/Qc appears to be a better predictor of exercise capacity than more classic measures of lung mechanics.

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.

Plasma immature form of surfactant protein type B correlates with prognosis in patients with chronic heart failure. A pilot single-center prospective study

BACKGROUND

Gas exchange abnormalities are part of the heart failure (HF) syndrome and growing interest raised on possible biomarkers of alveolar-capillary unit damage. The present pilot single-center study sought to investigate the prognostic values of circulating surfactant protein type B (SP-B) in a cohort of systolic HF patients.

METHODS

One hundred and fifty-one HF stable outpatients and 37 healthy subjects underwent a full clinical assessment, including pulmonary function and lung diffusion for carbon monoxide (DLco), maximal cardiopulmonary exercise test and measurements for both circulating immature and mature forms of SP-B. Study end-points were hospitalization due to HF worsening and cardiovascular mortality.

RESULTS

Immature SP-B, but not the mature form, was significantly higher in HF patients than in controls and was independently related to DLco, peak oxygen uptake and ventilatory efficiency. During the follow-up (median: 995 days; interquartile range: 739-1247 days), 97 patients experimented at least one HF hospitalization and 9 died for cardiovascular causes. At univariate analysis immature SP-B levels were significantly related to both cardiovascular death (p=0.033) and HF hospitalization (p<0.001). At multivariate analysis, immature SP-B levels remained independently associated to HF hospitalization (hazard ratio: 2.304; 95% confidence interval 1.858-3.019; p<0.001).

CONCLUSIONS

Present data confirm a strong relationship between circulating immature SP-B levels, gas exchange abnormalities and exercise limitations in stable HF as well as they are consistent with the use of immature SP-B in HF clinical risk assessment. Larger prospective studies are needed to confirm its prognostic role as well as to evaluate whether immature SP-B plasma concentration varies in response to specific treatment.

Levosimendan improves exercise performance in patients with advanced chronic heart failure

AIMS

Cardiopulmonary exercise test (CPET) provides parameters such as peak VO₂ and ventilation/CO₂ production (VE/VCO₂) slope, which are strong prognostic predictors in patients with stable advanced chronic heart failure (ADHF). The study aim was to evaluate the effects of the inodilator levosimendan on CPET in patients with ADHF under stable clinical conditions.

METHODS AND RESULTS

We enrolled patients with ADHF (peak VO₂ < 12 mL/min/kg) in a double-blind, placebo-controlled protocol. Patients were randomly assigned to i.v. infusion of placebo (500 mL 5% glucose; n = 19) or levosimendan (in 500 mL 5% glucose; n = 23). Before and 24 h after the end of the infusion, patients underwent determination of New York Heart Association class, B-type natriuretic peptide (BNP), haemoglobin, serum creatinine, and blood urea nitrogen levels, as well as CPET, standard spirometry, and alveolar capillary gas diffusion. BNP showed no change with placebo (1042 ± 811 to 1043 ± 867 pg/mL), but it was decreased with levosimendan (1163 ± 897 to 509 ± 543 pg/mL, P < 0.001). No changes were observed for haemoglobin, creatinine, and blood urea nitrogen in either group. With levosimendan, a minor improvement was observed in spirometry measurements, but not in alveolar capillary gas diffusion. Peak VO₂ showed a small, non-significant increase with placebo (9.5 ± 1.7 to 10.0 ± 2.1 mL/kg/min, P = 0.12), and a greater increase with levosimendan (9.8 ± 1.7 to 11.0 ± 1.9 mL/kg/min, P < 0.005). The VE/VCO₂ slope showed no change (44.0 ± 11 vs. 43.4 ± 10.3, P = 0.44), and a decrease (41.9 ± 10 vs. 36.6 ± 6.4, P < 0.001) in the placebo and in the levosimendan group, respectively.

CONCLUSION

Levosimendan treatment significantly improves peak VO₂ and reduces VE/VCO₂ slope and BNP in patients with ADHF.

Surfactant-derived proteins as markers of alveolar membrane damage in heart failure

Background

In heart failure (HF) alveolar-capillary membrane is abnormal. Surfactant-derived proteins (SPs) and plasma receptor for advanced-glycation-end-products (RAGE) have been proposed as lung damage markers.

Methods

Eighty-nine chronic HF and 17 healthy subjects were evaluated by echocardiography, blood parameters, carbon monoxide lung diffusion (DLCO) and cardiopulmonary exercise test. We measured immature SP-B, mature SP-B, SP-A, SP-D and RAGE plasma levels.

Results

Immature SP-B (arbitrary units), mature SP-A (ng/ml) and SP-D (ng/ml), but not mature SP-B (ng/ml) and RAGE (pg/ml) levels, were higher in HF than in controls [immature SP-B: 15.6 (13.1, 75^th–25^th interquartile range) Vs. 11.1 (6.4), p<0.01; SP-A, 29.6 (20.1) Vs. 18.3 (13.5), p = 0.01; SP-D: 125 (90) Vs. 78 (58), p<0.01]. Immature SP-B, SP-A, SP-D and RAGE values were related to DLCO, peak oxygen consumption, ventilatory efficiency, and brain natriuretic peptide (BNP), whereas plasma mature SP-B was not. The DLCO Vs. immature SP-B correlation was the strongest one. At multivariate analysis, RAGE was associated to age and creatinine, SP-A to DLCO and BNP, SP-D to BNP, mature SP-B to DLCO and creatinine, and immature SP-B only but strongly to DLCO.

Conclusions

Immature SP-B is the most reliable biological marker of alveolar-capillary membrane function in HF.

[Measurement of CO diffusion capacity (II): Standardization and quality criteria]

The diffusion capacity is the technique that measures the ability of the respiratory system for gas exchange, thus allowing a diagnosis of the malfunction of the alveolar-capillary unit. The most important parameter to assess is the CO diffusion capacity (DLCO). New methods are currently being used to measure the diffusion using nitric oxide (NO). There are other methods for measuring diffusion, although in this article the single breath technique is mainly referred to, as it is the most widely used and best standardized. Its complexity, its reference equations, differences in equipment, inter-patient variability and conditions in which the DLCO is performed, lead to a wide inter-laboratory variability, although its standardization makes this a more reliable and reproductive method. The practical aspects of the technique are analyzed, by specifying the recommendations to carry out a suitable procedure, the calibration routine, calculations and adjustments. Clinical applications are also discussed. An increase in the transfer of CO occurs in diseases in which there is an increased volume of blood in the pulmonary capillaries, such as in the polycythemia and pulmonary hemorrhage. There is a decrease in DLCO in patients with alveolar volume reduction or diffusion defects, either by altered alveolar-capillary membrane (interstitial diseases) or decreased volume of blood in the pulmonary capillaries (pulmonary embolism or primary pulmonary hypertension). Other causes of decreased or increased DLCO are also highlighted.

Diffusion capacity of carbon monoxide (DLCO) pre- and post-exercise in children in health and disease

RATIONALE

A decrease in diffusion capacity for carbon monoxide (DLCO) after exercise has been reported in healthy adults. There is limited information for post-exercise DLCO available in children either in health or in disease.

OBJECTIVES

To evaluate (1) reproducibility of DLCO measures in children, (2) differences in DLCO between elite athletic swimmers (AS), stable cystic fibrosis patients (CF), and healthy controls (Con) at rest; and (3) after a maximal treadmill exercise test.

METHODS

Participants performed spirometry and DLCO at baseline, a maximal treadmill exercise test and repeated DLCO measures for 2 hr after cessation of exercise.

RESULTS

The mean (SD) co-efficient of variation between baseline DLCO tests was 2.49% (1.86%). In girls, the mean baseline DLCO (ml/min/mmHg) was 18.61 (4.15) in CF, 22.32 (4.79) in controls and 27.18 (5.33) in AS. In boys: 23.68 (5.31) in CF, 28.09 (9.95) in controls and 37.75 (9.46) in AS. Baseline DLCO was significantly higher in AS than in CF patients (P < 0.01). In girls post-exercise, the greatest mean decrease in DLCO from baseline was -7.50% to -12.83% and in boys -6.92% to -17.71%. The decline in DLCO was less important in the athletes than the other groups (P < 0.05).

CONCLUSIONS

DLCO is highly repeatable in children. AS have an increased DLCO at rest compared to both children with CF and controls. There is a decline from baseline to post-exercise DLCO and while there are disease-specific differences, the general pattern of change in DLCO measures after exercise is similar in children to adults.

Diffusion capacity in children: what happens with exercise?

There is comparatively little data on diffusion capacity in children during exercise. With the advent of improved technology, there is an increasing interest in exercise testing of children in order to predict the evolution of lung disease. In addition to the standard measure of exercise capacity, the VO(2max), interest is evolving in the consequences of alterations in diffusion capacity which may be unmasked with exercise. This review will consider what is known about diffusion capacity with exercise in children with well documented lung disease in the form of cystic fibrosis, healthy controls and swimmers as elite athletes with the largest lung volumes.

Pulmonary gas exchange and acid-base balance during exercise

As the first step in the oxygen-transport chain, the lung has a critical task: optimizing the exchange of respiratory gases to maintain delivery of oxygen and the elimination of carbon dioxide. In healthy subjects, gas exchange, as evaluated by the alveolar-to-arterial PO2 difference (A-aDO2), worsens with incremental exercise, and typically reaches an A-aDO2 of approximately 25 mmHg at peak exercise. While there is great individual variability, A-aDO2 is generally largest at peak exercise in subjects with the highest peak oxygen consumption. Inert gas data has shown that the increase in A-aDO2 is explained by decreased ventilation-perfusion matching, and the development of a diffusion limitation for oxygen. Gas exchange data does not indicate the presence of right-to-left intrapulmonary shunt developing with exercise, despite recent data suggesting that large-diameter arteriovenous shunt vessels may be recruited with exercise. At the same time, multisystem mechanisms regulate systemic acid-base balance in integrative processes that involve gas exchange between tissues and the environment and simultaneous net changes in the concentrations of strong and weak ions within, and transfer between, extracellular and intracellular fluids. The physicochemical approach to acid-base balance is used to understand the contributions from independent acid-base variables to measured acid-base disturbances within contracting skeletal muscle, erythrocytes and noncontracting tissues. In muscle, the magnitude of the disturbance is proportional to the concentrations of dissociated weak acids, the rate at which acid equivalents (strong acid) accumulate and the rate at which strong base cations are added to or removed from muscle.

Lungs in heart failure

Lung function abnormalities both at rest and during exercise are frequently observed in patients with chronic heart failure, also in the absence of respiratory disease. Alterations of respiratory mechanics and of gas exchange capacity are strictly related to heart failure. Severe heart failure patients often show a restrictive respiratory pattern, secondary to heart enlargement and increased lung fluids, and impairment of alveolar-capillary gas diffusion, mainly due to an increased resistance to molecular diffusion across the alveolar capillary membrane. Reduced gas diffusion contributes to exercise intolerance and to a worse prognosis. Cardiopulmonary exercise test is considered the “gold standard” when studying the cardiovascular, pulmonary, and metabolic adaptations to exercise in cardiac patients. During exercise, hyperventilation and consequent reduction of ventilation efficiency are often observed in heart failure patients, resulting in an increased slope of ventilation/carbon dioxide (VE/VCO₂) relationship. Ventilatory efficiency is as strong prognostic and an important stratification marker. This paper describes the pulmonary abnormalities at rest and during exercise in the patients with heart failure, highlighting the principal diagnostic tools for evaluation of lungs function, the possible pharmacological interventions, and the parameters that could be useful in prognostic assessment of heart failure patients.

Reduced exercise tolerance and pulmonary capillary recruitment with remote secondhand smoke exposure

Rationale

Flight attendants who worked on commercial aircraft before the smoking ban in flights (pre-ban FAs) were exposed to high levels of secondhand smoke (SHS). We previously showed never-smoking pre-ban FAs to have reduced diffusing capacity (Dco) at rest.

Methods

To determine whether pre-ban FAs increase their Dco and pulmonary blood flow () during exercise, we administered a symptom-limited supine-posture progressively increasing cycle exercise test to determine the maximum work (watts) and oxygen uptake () achieved by FAs. After 30 min rest, we then measured Dco and at 20, 40, 60, and 80 percent of maximum observed work.

Results

The FAs with abnormal resting Dco achieved a lower level of maximum predicted work and compared to those with normal resting Dco (mean±SEM; 88.7±2.9 vs. 102.5±3.1%predicted ; p = 0.001). Exercise limitation was associated with the FAs' FEV₁ (r = 0.33; p = 0.003). The Dco increased less with exercise in those with abnormal resting Dco (mean±SEM: 1.36±0.16 vs. 1.90±0.16 ml/min/mmHg per 20% increase in predicted watts; p = 0.020), and amongst all FAs, the increase with exercise seemed to be incrementally lower in those with lower resting Dco. Exercise-induced increase in was not different in the two groups. However, the FAs with abnormal resting Dco had less augmentation of their Dco with increase in during exercise (mean±SEM: 0.93±0.06 vs. 1.47±0.09 ml/min/mmHg per L/min; p<0.0001). The Dco during exercise was inversely associated with years of exposure to SHS in those FAs with ≥10 years of pre-ban experience (r = −0.32; p = 0.032).

Conclusions

This cohort of never-smoking FAs with SHS exposure showed exercise limitation based on their resting Dco. Those with lower resting Dco had reduced pulmonary capillary recruitment. Exposure to SHS in the aircraft cabin seemed to be a predictor for lower Dco during exercise.

[Non-invasive study of pulmonary vascular recruitment during exercise]

The in vivo study of the pulmonary microcirculation, and its recruitment, is currently not common, although it may be of interest. The intrabreath analysis (IB) of the carbon monoxide (CO) and acetylene (C(2)H(2)) diffusion is used to study the transfer of CO (TLCO) and the pulmonary capillary blood flow (Qs), particularly during exercise. The evolution of the Qs during different stages of exercise has never been reported in healthy subjects. The authors measured the Qs and TL at rest and then during and after short bouts of exercise in 12 healthy subjects. The Qs increased from 5.6 L/min at rest to 13.8 L/min during exercise while the TLCO increased from 11 to 16.7 mmol/kPa/min. A linear relationship was found between the Qs and the TLCO, with Qs values close to those obtained with other techniques. The Qs returned to rest values more rapidly than the TLCO (probably because of the membrane factor). Pulmonary vascular recruitment can be easily studied in healthy subjects. This parameter may be important in the study in pulmonary vascular diseases.

Lung function with carvedilol and bisoprolol in chronic heart failure: is beta selectivity relevant?

BACKGROUND

Carvedilol is a beta-blocker with similar affinity for beta1- and beta2 receptors, while bisoprolol has higher beta1 affinity. The respiratory system is characterized by beta2-receptor prevalence. Airway beta receptors regulate bronchial tone and alveolar beta receptors regulate alveolar fluid re-absorption which influences gas diffusion.

AIMS

To compare the effects of carvedilol and bisoprolol on lung function in patients with chronic heart failure (CHF).

METHODS AND RESULTS

We performed a double-blind, cross-over study in 53 CHF patients. After 2 months of full dose treatment with either carvedilol or bisoprolol, we assessed lung function by salbutamol challenge, carbon monoxide lung diffusion (DLCO), including membrane conductance (DM), and gas exchange during exercise. FEV1 and FVC were similar; after salbutamol FEV1 was higher with bisoprolol (p<0.04). DLco was 82+/-21% of predicted with carvedilol and 90+/-20% with bisoprolol (p<0.01) due to DM changes. Peak VO2 was 17.8+/-4.5 mL/min/kg on bisoprolol and 17.0+/-4.6 on carvedilol, (p<0.05) with no differences in bronchial tone (same expiratory time) throughout exercise. Differences were greater in the 22 subjects with DLCO<80%.

CONCLUSION

Carvedilol and bisoprolol have different effects on DLCO and response to salbutamol. DLCO differences, being DM related, are due to changes in active membrane transport which is under alveolar beta2-receptor control. Peak VO2 was slightly higher with bisoprolol particularly in CHF patients with reduced DLCO.

Sildenafil improves the alveolar-capillary function in heart failure patients

BACKGROUND

Sildenafil is used for pulmonary hypertension treatment and its use is safe in chronic heart failure (HF) patients.

AIMS

To analyze the effects of sildenafil on lung mechanics, gas diffusion, exhaled nitric oxide (eNO) at rest and during exercise in chronic HF. We did so to evaluate if sildenafil prevents exercise-induced pulmonary edema formation.

METHODS

We studied 22 chronic HF males. We measured after a single dose of placebo, sildenafil (25 mg) and sildenafil (100 mg), lung diffusion (DLCO), molecular diffusion (DM), pulmonary capillary volume (VC), eNO, all at rest and during exercise, standard pulmonary function, and maximal cardiopulmonary exercise.

RESULTS

At rest sildenafil improved pulmonary mechanics and DLCO from 23.1+/-6.3 ml/mmHg/min to 23.9+/-6.4 (25 mg, p<0.05) and to 25.3+/-6.7 100 mg, p<0.02). Sildenafil (100 mg) prevents edema formation (highest DM/VC during exercise). At rest eNO was low and not affected by tested drugs. With light exercise eNO was higher with sildenafil 100 mg. Peak VO(2) increased with sildenafil from 1376+/-331 ml/min to 1471+/-375 (25 mg, p<0.01) and 1524+/-461 (100 mg, p<0.02). Peak VO(2) increase was related to DLCO improvement.

CONCLUSION

In chronic HF sildenafil increases exercise performance, improves lung mechanics and gas diffusion and prevents exercise-induced pulmonary edema formation probably by restoring NO pathways.

Stroke volume response during exercise measured by acetylene uptake and MRI

The intra-breath technique to measure acetylene absorption offers the possibility to determine augmentation of the pulmonary blood flow per heart beat (Q(C)) as an estimate of the stroke volume response during exercise. However, this method has not been compared with a validated test until now. Therefore, the aim of this study was to compare Q(C) with stroke volume (SV(MRI)) determined by magnetic resonance imaging (MRI) at rest and during exercise in healthy subjects and patients. For this purpose, ten healthy subjects and ten patients with idiopathic pulmonary arterial hypertension (iPAH) with expected impaired stoke volume response during exercise were measured by both methods. Exercise-induced changes in Q(C) and SV(MRI) were correlated in healthy controls (r = 0.75, p < 0.05). Compared to healthy controls, Q(C) increased less during exercise in iPAH patients (11 +/- 17 ml versus 33 +/- 12 ml, p < 0.05). A similar difference in stroke volume response to exercise between the two groups was measured by MRI (-0.6 +/- 8 ml versus 23 +/- 12 ml, p < 0.05, respectively). Hence, intra-breath and MRI measurements showed similar differences in exercise-induced changes in stroke volume between controls and patients. From these results it can be concluded that the intra-breath measurement of acetylene absorption might be of value as a non-invasive tool to estimate stroke volume augmentation during exercise and can detect differences in stroke volume responses between iPAH patients and healthy subjects.

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.

Lateral Decubitus Position Generates Discomfort and Worsens Lung Function in Chronic Heart Failure

BACKGROUND

Lateral decubitus position is poorly tolerated by heart failure patients.

STUDY OBJECTIVES

To evaluated pulmonary function and lung diffusion in heart failure patients in the following five body positions: sitting, prone, supine, and left and right decubitus.

SETTING

Heart failure unit of a university hospital.

SUBJECTS

We studied 14 chronic heart failure patients in New York Heart Association class III and 14 healthy volunteers.

MEASUREMENTS AND RESULTS

After 15 min of a selected position, subjects were evaluated by a discomfort scale, ear oximetry, and pulmonary function, which included FEV1, FVC, vital capacity (VC), alveolar volume, and diffusing capacity of the lung for carbon monoxide (D(LCO)) with subcomponent membrane resistance (DM) and capillary volume. In healthy subjects, we observed a reduction of D(LCO) and capillary volume in both lateral decubiti. Some discomfort was documented in both lateral decubiti when selected positions were compared with the sitting position. In the sitting position, pulmonary function suggested slight restriction ([mean +/- SD] FVC, 89.8 +/- 22.3% predicted; FEV1, 84.7 +/- 16.9% predicted, VC, 88.6 +/- 21.5% predicted; and FEV1/VC, 74 +/- 7) with low D(LCO) (73 +/- 19% predicted). Compared with sitting, lung mechanics were unchanged in prone and supine positions; FEV1, FVC, and FEV1/VC were lower when patients were lying on their side, with unchanged alveolar volume and VC. D(LCO) was similar when comparing sitting, prone, and supine positions, and it was lower in lateral decubitus because of the lower capillary volume (vs sitting) and DM (vs prone and supine). Body position-related FVC and D(LCO) reduction were greatest in the largest hearts (deltaFVC and deltaD(LCO) vs left ventricle diastolic volume R = 0.524, p < 0.05 and R = 0.630, p < 0.02, respectively; deltaFVC and deltaD(LCO) vs cardiothoracic index R = 0.539, p < 0.05 and R = 0.685, p < 0.01, respectively).

CONCLUSIONS

In heart failure, lateral decubitus airway obstruction and lung diffusion impairment become greater as heart dimensions increase.

Spironolactone improves lung diffusion in chronic heart failure

AIMS

To evaluate whether anti-aldosteronic treatment influences lung diffusion (DLCO) in chronic heart failure (HF) patients. Spironolactone improves clinical conditions and prognosis in chronic HF and reduces connective tissue matrix turnover; DLCO abnormalities in chronic HF are related to increase in fibrosis and connective tissue derangement.

METHODS AND RESULTS

Thirty stable chronic HF patients, with reduced DLCO (<80% of predicted), were randomly assigned to active treatment (25 mg spironolactone daily) or placebo in addition to conventional anti-failure treatment. They were evaluated by quality of life questionnaire, laboratory investigations, cardiopulmonary exercise test, and pulmonary function test, which included DLCO and membrane diffusing capacity (DM). The evaluation was done before treatment and 6 months after. Quality of life score and standard pulmonary function tests were not significantly affected by spironolactone, while active treatment increased DLCO due to an increase of DM (DLCO: 18.3+/-3.9 vs. 19.9+/-5.5 mL/min/mmHg; DM: 28.1+/-7.7 vs. 33.3+/-8.6 mL/min/mmHg) and peak oxygen consumption (peak VO2 16.8+/-1.9 vs.18.6+/-2.2 mL/min/kg). Increments of DLCO and peak VO2 were linearly related (R=0.849, P<0.001).

CONCLUSION

These data show a positive effect of spironolactone on gas diffusion and exercise capacity suggesting a novel mechanism by which anti-aldosteronic drugs improve HF clinical condition and prognosis.

Exercise-induced changes in exhaled nitric oxide in heart failure

BACKGROUND

In heart failure abnormalities of pulmonary function are frequently observed as shown by hyperpnea, reduced lung compliance, reduced alveolar-capillary gas diffusion, positive methacholine challenge and, during exercise, early expiratory flow limitation. Nitric oxide (NO) might be related to all the above abnormalities.

AIMS

We evaluated whether a correlation between exhaled NO (eNO) and lung function exists at rest and during exercise in heart failure.

METHODS

We studied 33 chronic heart failure patients and 11 healthy subjects with: (a) standard pulmonary function, (b) lung diffusion for carbon monoxide (DLco) including its subcomponents, capillary volume and membrane resistance and eNO both at rest and during light exercise, (c) maximal cycloergometer cardiopulmonary exercise test.

RESULTS

Forced expiratory volume in 1 s (FEV(1)) was reduced in heart failure patients (83+/-17% of predicted), as was DLco (75+/-18% of predicted) due to reduced membrane resistance (32.6+/-10.3 ml mmHg(-1) min(-1) vs. 39.9+/-6.9 in patients vs. controls, P<0.02). Exhaled NO was lower in patients vs. controls (9.7+/-5.4 ppm vs. 14.4+/-6.4, P<0.05) and was, during exercise, constant in patients and reduced in controls. No significant correlation was found between eNO and lung function. Vice-versa eNO changes during exercise were correlated with peak exercise oxygen consumption (r=0.560, P<0.001).

CONCLUSIONS

The hypothesis of a link between eNO and lung function in heart failure was not proved. The correlation between eNO changes during exercise and peak V(O(2)) might be due to hemoglobin oxygenation, which binds NO to hemoglobin.

Exercise response after rapid intravenous infusion of saline in healthy humans

Patients with chronic heart failure have an abnormal pattern of exercise ventilation (Ve), characterized by small tidal volumes (Vt), increased alveolar ventilation, and elevated physiological dead space (Vd/Vt). To investigate whether increased lung water in isolation could reproduce this pattern of exercise ventilation, 30 ml/kg of saline were rapidly infused into nine normal subjects, immediately before a symptom-limited incremental exercise test. Saline infusion significantly reduced forced vital capacity, 1-s forced expiratory volume, and alveolar volume (P < 0.01 for all). After saline, exercise ventilation assessed by the Ve/Vco(2) slope increased from 24.9 +/- 2.4 to 28.0 +/- 2.9 l/l, (P < 0.0002), associated with a small decrease in arterial Pco(2), but without changes in Vt, Vd/Vt, or alveolar-arterial O(2) difference. A reduction in maximal O(2) uptake of 175 +/- 184 ml/min (P < 0.02) was observed in the postsaline infusion exercise studies, associated with a consistent reduction in maximal exercise heart rate (8.1 +/- 5.9 beats/min, P < 0.01), but without a change in the O(2) pulse. Therefore, infusion of saline to normal subjects before exercise failed to reproduce either the increase in Vd/Vt or the smaller exercise Vt described in heart failure patients. The observed increase in Ve can be attributed to dilution acidosis from infusion of the bicarbonate-free fluid and/or to afferent signals from lung and exercising muscles. The reduction in maximal power output, maximal O(2) uptake, and heart rate after saline infusion may be linked to accumulation of edema fluid in exercising muscle, impairing the diffusion of O(2) to muscle mitochondria.

Exercise-Induced Pulmonary Edema in Heart Failure

Background— In heart failure (HF) patients, exercise may increase pulmonary capillary hydrostatic pressure and thereby generate pulmonary edema. If pulmonary edema developed, alveolar-capillary membrane conductance (D m ), measured immediately after exercise, would decrease. To test this hypothesis, we measured D m before and at 2 and 60 minutes after exercise.

Methods and Results— We studied 10 HF patients with exercise-induced periodic breathing, 10 with peak V̇ o 2 ≤15 mL · min −1 · kg −1 (severe HF), 10 with V̇ o 2 =15 to 20 mL · min −1 · kg −1 (moderate HF), and 10 normal subjects (control). Using the Roughton-Forster technique, we measured carbon monoxide diffusion capacity (DL co ) and its components, capillary blood volume (V c ) and D m , at rest and 2 and 60 minutes after exercise. At rest, DL co and D m were lowest in periodic breathing and highest in control subjects. D m decreased in periodic breathing, severe HF, and moderate HF (−7.83±3.98, −5.57±2.03, and −3.85±3.53 mL · min −1 · mm Hg −1 , respectively; P <0.01) at 2 minutes after exercise but not in control subjects. V c increased in all groups at 2 minutes and remained elevated at 60 minutes only in periodic breathing. D m /V c was decreased in periodic breathing, severe HF, and moderate HF at 2 minutes but not in control subjects. D m and D m /V c remained low at 60 minutes only in periodic breathing.

Conclusions— D m decreases after exercise in HF patients but not in control subjects, which suggests a decrease in conductance across the alveolar-capillary barrier, as with pulmonary edema. The reductions were most marked in HF patients with periodic breathing and less reduced in less severe HF.

Exhaled nitric oxide and exercise performance in heart failure

BACKGROUND

In heart failure abnormalities of pulmonary function are frequently observed particularly during exercise, which is characterized by hyperpnea, low tidal volume, early expiratory flow limitation and reduced lung compliance. Exhaled nitric oxide (NO) is increased in asthma. We evaluated whether a correlation between exhaled NO and lung mechanics exists during exercise in heart failure.

METHODS

We studied 33 chronic heart failure patients and 11 healthy subjects with: a) standard pulmonary function, b) lung diffusion for carbon monoxide (DLCO) including its subcomponents, capillary volume and membrane resistance and eNO both at rest and during light exercise, c) maximal cycloergometer cardiopulmonary exercise test.

RESULTS

Forced expiratory volume in 1 second (FEV1) was reduced in heart failure patients (83 +/- 17% of predicted) as was DLCO (75 +/- 18% of predicted) due to reduced membrane resistance (32.6 +/- 10.3 ml/mmHg/min vs. 39.9 +/- 6.9 in patients vs. controls, p < 0.02). eNO was lower in patients vs. controls (9.7 +/- 5.4 ppm vs. 14.4 +/- 6.4, p < 0.05) and was, during exercise, constant in patients and reduced in controls. No significant correlation was found between eNO and lung function. Vice-versa eNO changes during exercise were correlated with peak exercise oxygen consumption (r = 0.560, p < 0.001).

CONCLUSIONS

The hypothesis of a link between eNO and lung function in heart failure was not proved. The correlation between eNO changes during exercise and peak VO2 might be due to hemoglobin oxygenation which binds NO to hemoglobin.

Does lung diffusion impairment affect exercise capacity in patients with heart failure?

OBJECTIVE

To determine whether there is a relation between impairment of lung diffusion and reduced exercise capacity in chronic heart failure.

DESIGN

40 patients with heart failure in stable clinical condition and 40 controls participated in the study. All subjects underwent standard pulmonary function tests plus measurements of resting lung diffusion (carbon monoxide transfer, TLCO), pulmonary capillary volume (VC), and membrane resistance (DM), and maximal cardiopulmonary exercise testing. In 20 patients and controls, the following investigations were also done: (1) resting and constant work rate TLCO; (2) maximal cardiopulmonary exercise testing with inspiratory O2 fractions of 0.21 and 0.16; and (3) rest and peak exercise blood gases. The other subjects underwent TLCO, DM, and VC measurements during constant work rate exercise.

RESULTS

In normoxia, exercise induced reductions of haemoglobin O2 saturation never occurred. With hypoxia, peak exercise uptake (peak O2) decreased from (mean (SD)) 1285 (395) to 1081 (396) ml/min (p < 0.01) in patients, and from 1861 (563) to 1771 (457) ml/min (p < 0.05) in controls. Resting TLCO correlated with peak O2 in heart failure (normoxia < hypoxia). In heart failure patients and normal subjects, TLCO and peak O2 correlated with O2 arterial content at rest and during peak exercise in both normoxia and hypoxia. TLCO, VC, and DM increased during exercise. The increase in TLCO was greater in patients who had a smaller reduction of exercise capacity with hypoxia. Alveolar-arterial O2 gradient at peak correlated with exercise capacity in heart failure during normoxia and, to a greater extent, during hypoxia.

CONCLUSIONS

Lung diffusion impairment is related to exercise capacity in heart failure.

Differential changes of lung diffusing capacity and tissue volume in hypergravity

In normal gravity, lung diffusing capacity (DL(CO)) and lung tissue volume (LTV; including pulmonary capillary blood volume) change in concert, for example, during shifts between upright and supine. Accordingly, DL(CO) and LTV might be expected to decrease together in sitting subjects in hypergravity due to peripheral pooling of blood and reduced central blood volume. Nine sitting subjects in a human centrifuge were exposed to one, two, and three times increased gravity in the head-to-feet direction (G(z+)) and rebreathed a gas containing trace amounts of acetylene and carbon monoxide. DL(CO) was 25.2 +/- 2.6, 20.0 +/- 2.1, and 16.7 +/- 1.7 ml. min(-1). mbar(-1) (means +/- SE) at 1, 2, and 3 G(z+), respectively (ANOVA P < 0.001). Corresponding values for LTV increased from 541 +/- 34 to 677 +/- 43, and 756 +/- 71 ml (P < 0.001) at 2 and 3 G(z+). Results are compatible with sequestration of blood in the dependent part of the pulmonary circulation just as in the systemic counterpart. DL(CO,) which under normoxic conditions is mainly determined by its membrane component, decreased despite an increased pulmonary capillary blood volume, most likely as a consequence of a less homogenous distribution of alveolar volume with respect to pulmonary capillary blood volume.

Intrabreath diffusing capacity of the lung in healthy individuals at rest and during exercise

BACKGROUND

Traditional approaches to measuring the diffusing capacity of the lung for carbon monoxide (DLCO) treat the lung as a single, well-mixed compartment and produce a single value for DLCO to represent an average diffusing capacity of the lung (DL). Because DL distribution in the lung is inhomogeneous, and changes in the DL in diseased lungs may be regional, measuring regional DL, especially during exercise, may be more sensitive in detecting pulmonary vascular diseases.

OBJECTIVES

To characterize regional changes in DL in healthy individuals from rest to exercise, and to provide normal references for future studies in pulmonary vascular disorders.

METHODS

We reanalyzed DLCO and phase III CH(4) slopes that were obtained during a slow, single exhalation at rest and during exercise in our extended database of 105 healthy individuals. DLCO profiles between 20% and 80% of exhaled vital capacity (VC) (ie, the intrabreath DLCO) were analyzed by calculating the average DLCO measured at midlung volume (ie, 30 to 45% of exhaled VC [DLCOMLV]) and by fitting the whole curve with a third-order polynomial equation.

RESULTS

DLCO decreased nonlinearly by approximately 30%, from 20 to 80% of exhaled VC at rest. DLCO during exercise was greater than that at rest, and the increase was similar at all lung volumes. The CH(4) slopes at rest and during exercise were similar. Prediction equations based on regressions on age, sex, and height were computed for resting and exercise DLCOMLV and the phase III CH(4) slope (an index of ventilation distribution).

CONCLUSIONS

Capillary recruitment/dilation during exercise in healthy individuals is a uniform process throughout the lungs. Our analyses provide a database for a noninvasive method that can incorporate exercise to evaluate the volume-dependent distribution of DLCO in lung diseases.

Exercise hyperpnea in chronic heart failure: relationships to lung stiffness and expiratory flow limitation

The changes in breathing pattern and lung mechanics in response to incremental exercise were compared in 14 subjects with chronic heart failure and 15 normal subjects. In chronic heart failure subjects, exercise hyperpnea was achieved by increasing breathing frequency more than tidal volume. The rate of increase in breathing frequency with carbon dioxide output was inversely correlated (r = -0.61, P < 0.05) with dynamic lung compliance measured at rest, but not with static lung compliance either at rest or at maximum exercise. Although decrease in expiratory flow reserve near functional residual capacity in chronic heart failure occurred earlier with exercise than in the normal subjects (P < 0.01), it was not correlated with changes in breathing pattern or occurrence of tachypnea. Tachypnea was achieved in chronic heart failure subjects with an increase in duty cycle because of a greater than normal decrease in expiratory time with exercise. We conclude that in chronic heart failure preexisting increase in lung stiffness plays a significant role in causing tachypnea during exercise. The results of the present study do not support the hypothesis that dynamic compression of the airways downstream from the flow-limiting segment occurring during exercise contributes to hyperpnea.

Single-breath carbon monoxide diffusing capacity

Measurement of DL(CO) remains a clinically useful way to assess transfer of gases across the lung. It is important, however, to be vigilant in controlling the sources of variation and to be aware of those that remain when interpreting the measured values.

Modulation of alveolar-capillary sodium handling as a mechanism of protection of gas transfer by enalapril, and not by losartan, in chronic heart failure

OBJECTIVES

We sought to compare the protective efficacy of enalapril and losartan on lung diffusion in chronic heart failure (CHF).

BACKGROUND

In CHF, hydrostatic overload causes disruption of the alveolar-capillary membrane and depression of carbon monoxide diffusion (DCO); enalapril improves DCO through mechanisms still undefined; and saline infusion in the pulmonary circulation worsens DCO, putatively because of an upregulated sodium transport to the alveolar interstitium. We investigated whether enalapril modulates sodium handling and whether losartan shares the same properties.

METHODS

In 29 patients with CHF, DCO, its membrane diffusion subcomponent (DM) and right atrial and pulmonary wedge pressures were monitored during saline infusion, in the control condition, during enalapril therapy (20 mg/day) for two weeks and after crossover to losartan (50 mg/day) for two weeks (first 20 patients), or after the combination of enalapril with aspirin (325 mg/day) for one week (last 9 patients).

RESULTS

Saline, 150 ml, lowered DCO (-7.9%; p < 0.01) and DM (-9.9%; p < 0.01) without hydrostatic variations. Responses to 750 ml of saline were qualitatively similar. After treatment with enalapril, baseline DCO (p < 0.01) and DM (p < 0.01) were augmented; after sodium loading, the percent reductions of DCO (p < 0.01) and DM (p < 0.01) were comparable to those before it, resulting in higher absolute values. This suggests that the greater the gas conductance improvement with enalapril, the lower the impedance with saline. Losartan was ineffective on gas transfer at rest and under salt challenge. Aspirin counteracted the benefits of enalapril.

CONCLUSIONS

In CHF, enalapril protects lung diffusion, possibly through a prostaglandin-mediated modulation of sodium overfiltration to the alveolar interstitium; losartan does not share this ability.

Changes in transfer factor of the lung in response to bronchodilatation

Measurement of the transfer factor for carbon monoxide (TLCO) is a widely used clinical lung function test. Although it is frequently applied in patients with bronchial obstruction, there is little information on the effects of bronchodilatation on the test. We therefore measured TLCO in 40 patients before and after inhalation of terbutaline. TLCO was measured with the single-breath technique in 20 patients and with the intra-breath technique in 20 patients. TLCO was also measured in 20 healthy subjects with the single-breath technique. Forced expiratory volume (FEV1) increased from 2.9 +/- 1. 1 to 3.2 +/- 1.2 l in patients with bronchial obstruction in response to terbutaline inhalation. TLCO increased from 8.2 +/- 2.6 to 8.6 +/- 2.7 mmol min-1 kPa-1 (P< 0.001) and alveolar volume (VA) from 5.74 +/- 1.21 to 5.90 +/- 1.21 l (P<0.001). There was no difference between the single-breath and the intra-breath techniques. There was little change in FEV1 in the healthy subjects in response to terbutaline. TLCO increased from 10.2 +/- 2.1 to 10.5 +/- 2.2 mmol min-1 kPa-1 (P< 0.01), but there was no change in VA. The increase in TLCO in patients may partly be explained by improved distribution of the inhaled gas. In healthy subjects, terbutaline may increase pulmonary capillary volume. We conclude that bronchodilatation results in a small increase in TLCO in patients with light to moderate bronchoconstriction as well as in healthy subjects. The effect is small and should in most cases be simple to account for in the interpretation of pulmonary function tests, provided the patient's treatment is known.

Reduced gas transfer at rest and during exercise in school-age survivors of bronchopulmonary dysplasia

School-age children who survive bronchopulmonary dysplasia (BPD) may have a permanent reduction in alveolar surface area that could limit gas transfer both at rest and during exercise. To test this hypothesis, 10 survivors of BPD, 10 children born prematurely without BPD, and 10 healthy children born at term, 6 to 9 yr of age, underwent treadmill exercise studies. During a three-phase protocol we measured intrabreath acetylene (C2H2) and carbon monoxide (CO) transfer, pulmonary function, and SaO2. Both at rest and during exercise, C2H2 transfer corrected for body surface area was lower in survivors of BPD than it was in children born prematurely without BPD or children born at term. With exercise the transfer of both gases increased sharply over resting values in children born prematurely and at term. In survivors of BPD C2H2 transfer with exercise did increase, but not as much as it did in control subjects, and corrected CO transfer did not change at all. In survivors of BPD and children born prematurely, FEV1 fell during recovery from exercise, but this did not correlate with C2H2 transfer or DL(CO)/VA. Thus, soluble gas transfer at rest and during acute exercise is reduced in children who survive BPD. This is likely explained either by long-term derangements in lung structure or residual right ventricular dysfunction affecting cardiac output.