Abstract In patients with chronic obstructive pulmonary disease (COPD) who exhibit reduced alveolar–capillary reserve, the combined assessment of pulmonary diffusing capacity for carbon monoxide and nitric oxide (DL,CO,NO) during exercise may pose difficulties, and the transition from upright to supine posture may offer a useful alternative. A total of 50 participants (35 with COPD and 15 healthy controls) underwent measurements of DL,CO,NO in the upright and supine postures. A subset (COPD: n = 12, controls: n = 12) also completed a 12‐week supervised high‐intensity interval training (HIIT) intervention. The reported DL,CO,NO metrics were diffusing capacity for nitric oxide and carbon monoxide (DL,NO and DL,CO,5s, respectively), alveolar–capillary membrane diffusing capacity (DM,CO), pulmonary capillary blood volume (VC), and alveolar volume (VA). The upright‐to‐supine change in neither DL,NO (P = 0.271), nor DM,CO (P = 0.068) nor VA (P = 0.934) differed between groups. In contrast, the upright‐to‐supine change in DL,CO5s was reduced in moderate and severe COPD compared with controls (control vs. moderate: median [IQR] 0.6 [0.3, 0.9] mmol/min/kPa, P < 0.001; control vs. severe: 0.9, [0.2, 1.5] mmol/min/kPa, P = 0.006), whereas it did not differ between controls and mild COPD (0.3 [−0.1, 0.7] mmol/min/kPa, P = 0.13). Similarly, the upright‐to‐supine VC change was reduced in moderate and severe COPD compared with healthy controls (control vs. moderate: 8.3 [3.9, 12.8] mL, P < 0.001; control vs. severe: 10.7 [1.2, 20.2] mL, P = 0.021), but not in mild COPD (5.3 [−0.2, 10.8] mL, P = 0.063). The HIIT intervention had no effect on these metrics. The blunted VC response to an upright‐to‐supine postural change in moderate‐to‐severe COPD is consistent with reduced alveolar–capillary reserve and may be useful when measurements during exercise are not possible.

Carpal tunnel syndrome (CTS) is the most common entrapment neuropathy and a frequent indication for hand surgery. Symptoms range from intermittent nocturnal paraesthesia to persistent sensory loss and thenar muscle weakness, often with functional impact and socioeconomic burden. Diagnosis is clinical, supported by neurophysiological exams. Mild CTS is usually managed conservatively, while surgical decompression provides the most effective and durable relief in moderate to severe cases. This review finds variation in diagnostic and treatment pathways highlighting the need for standardised care.

Abstract BackgroundDigital health offers opportunities for safe, equitable, and accessible care, and its integration into respiratory care is a strategic priority for the European Respiratory Society. However, sustainable implementation remains complex, and guidance for health care systems is limited. ObjectiveThis study aimed to undertake a scoping review of the published initiatives that have implemented digital respiratory technologies into real-world routine clinical practice over the past decade, identify the technologies used, implementation strategies used, the challenges and supports they encountered, and the lessons they reported for making care more equitable, strengthening patient-professional relationships, improving the patient journey, and reducing environmental impact. MethodsFollowing Arksey and O’Malley’s methodology, we searched ten databases (December 2013‐2023 [updated April 2025 and February 2026]): MEDLINE, Embase, CINAHL, PsycINFO, Cochrane Library, Web of Science, Scopus, IEEE Xplore, CABI Global Health, and WHO Medicus; and used key domains in the commonly used implementation frameworks such as the Consolidated Framework for Implementation Research (CFIR), Nonadaptation, Abandonment, and Challenges to the Scale-up, Spread, and Sustainability of Health and Care Technologies (NASSS), and the Reach, Effectiveness, Adoption, Implementation, and Maintenance (RE-AIM) framework to categorize results and understand methodologies used. As a scoping review, we mapped the available evidence, rather than synthesizing outcomes, appraising study quality, or estimating effectiveness. To broaden coverage and strengthen interpretation, we crowdsourced additional studies and sought feedback on our preliminary findings from a network of respiratory experts across 17 countries. ResultsOverall, 24,672 studies were identified; after deduplication, 14,811 were screened; 84 studies from 31 countries were included in the final review. The digital respiratory technologies comprised apps, platforms, chatbots, and smart devices. Reported technological functionalities encompassed remote consultation, clinician monitoring, video directly observed therapy, remote rehabilitation training, self-management support, education, monitoring medication adherence, and a school-based remote clinic. CFIR, RE-AIM, and the plan-do-study-act (PDSA) cycle were the most widely used frameworks. Successful implementation used simple technologies that fitted existing workflows and avoided additional workload. Co-development and trust-building with end-users influenced motivation and adoption, while leadership, team cohesion, and communication facilitated success. Barriers included insufficient resources, poor interoperability, lack of funding and reimbursement, and limited technical support. ConclusionsThis scoping review provides a cross-condition review of digital respiratory technologies implemented in routine clinical practice. Unlike previous disease-specific or experimental-focused reviews, our innovative approach used established implementation Theories, Models, and Frameworks (TMFs) to identify shared barriers and enablers across diverse populations and health care systems. We summarize key implementation domains in state-of-the-art digital respiratory care and identify major gaps related to health equity, patient–clinician trust, continuity of support, and environmental sustainability. These findings emphasize the value of using implementation TMFs for scaling effective, patient-centered digital respiratory care in real-world settings.

Carpal tunnel syndrome (CTS) is the most common entrapment neuropathy and a frequent indication for hand surgery. Symptoms range from intermittent nocturnal paraesthesia to persistent sensory loss and thenar muscle weakness, often with functional impact and socioeconomic burden. Diagnosis is clinical, supported by neurophysiological exams. Mild CTS is usually managed conservatively, while surgical decompression provides the most effective and durable relief in moderate to severe cases. This review finds variation in diagnostic and treatment pathways highlighting the need for standardised care.

Exertional dyspnoea is a debilitating symptom in chronic obstructive pulmonary disease (COPD) and often persists after the cessation of exercise. The underlying mechanisms are not fully understood, and a potential contributing factor that has not previously been investigated is alveolar-capillary membrane breaching with extravasation of fluid into the lungs. Sixteen individuals with COPD and 16 age- and sex-matched healthy controls were included. Alveolar-capillary membrane permeability was quantified using the pulmonary clearance index (PCI), calculated from scintigraphically determined alveolar clearance of 99mTc-labelled diethylenetriaminepentaacetic acid at rest and following an acute exercise bout performed at maximal exertion, as determined by a prior cardiopulmonary exercise test. In addition, lung tissue mass (LTM) was assessed using low-dose computed tomography, with rest-to-post-exercise changes interpreted as reflecting alterations in interstitial fluid accumulation. The mean change in PCI from rest-to-post-exercise was -0.01 [95% CI: -0.09, 0.06]%/min in the COPD group and -0.05 [95% CI: -0.12, 0.02]%/min in the healthy control group (Group × Time interaction, P = 0.446). The mean change in LTM from rest-to-post-exercise was 16.5 [95% CI: -7.0, 40.0]g/1.73 m2 in the COPD group and 35.2 [95% CI: 11.7, 58.7]g/1.73 m2 in the healthy control group (Group × Time interaction, P = 0.258). In conclusion, the present study found no evidence of alveolar-capillary membrane breaching following maximal exercise, neither in individuals with COPD nor in healthy matched controls.

There is limited knowledge on diffusing capacity in scoliosis patients. It remains to be determined if impaired pulmonary diffusing capacity is mostly influenced by reduced alveolar-capillary membrane diffusing capacity (DM, CO), reduced pulmonary capillary blood volume (VC) or both. This study aims to report findings from dual test gas pulmonary diffusing capacity for carbon monoxide and nitric oxide (DL, CO, NO) with quantification of pulmonary diffusing capacity for carbon monoxide corrected for haemoglobin with a five s breath-hold (DL, COc, 5s) and nitric oxide with a five s breath-hold (DL, NO, 5s), DM, CO and VC. The study included 57 patients with idiopathic scoliosis seen at our department from 1972 to 1983, all of whom underwent radiological assessment and measurement of DL, CO, NO during examination 40 years after diagnosis. One-way ANOVA was performed for between-group differences and Pearson's correlation coefficient was used to assess correlations between DL, CO, NO metrics and Cobb angle. No significant between-group differences based on disease severity were detected. Thirty-nine percent of the patients were presented with either reduced DL, COc, 5s or reduced DL, NO, 5s represented as Z-scores below -1.65. No significant correlations between Cobb angle and Z-scores for DL, COc, 5s, DL, NO, 5s, DM, CO and VC according to height measurements were found. When using arm span instead, a weak negative correlation between DL, COc, 5s and Cobb angle (r = -0.29; P = 0.04) was detected. In conclusion, approximately 39% of patients with idiopathic scoliosis had either reduced DL, COc, 5s or reduced DL, NO, 5s 40 years after diagnosis with varying contributions from VC or DM, CO.

Introduction: Postural changes are known to have a significant influence on lung function and gas exchange due to the gravitational influence on the lungs, as postural changes alter the lungs’ orientation relative to gravity. Previously, assessing lung function in more challenging postures was difficult due to limitations of available equipment. However, with the development of handheld equipment, it is now possible to investigate lung function in different postures. Therefore, this study aimed to investigate the effects of postural changes, including supine and quadruped postures, as well as handstands, on airway resistance and pulmonary diffusing capacity. Methods: Twelve healthy young participants underwent measurements of impulse oscillometry and pulmonary diffusing capacity with carbon monoxide corrected for haemoglobin (DL,COc) during upright standing, as well as in the supine, quadruped, and handstand postures. Results: Total airway resistance increased from upright standing to supine (p < 0.001) and handstand (p < 0.001), and small airway resistance increased from upright standing to handstand (p = 0.019). DL,COc increased from upright standing to supine (p < 0.001), quadruped (p = 0.028) and handstand (p < 0.001), whereas DL,COc were lower in quadruped posture compared to supine (p = 0.007) and handstand (p = 0.022), with no difference between supine and handstand (p = 0.17). Conclusion: Both supine posture and handstand increase airway resistance compared to upright standing, whereas supine and quadruped postures, as well as handstand, increase pulmonary diffusing capacity similarly. Funding: The Centre for Physical Activity Research (CFAS) is supported by TrygFonden (grants ID 101390, ID 20045, ID 125132, and ID 177225). Trial registration: None.

High-intensity interval training (HIIT) has shown to improve exercise capacity, symptom burden, and quality of life in patients with chronic obstructive pulmonary disease (COPD), but it remains to be investigated if HIIT can counteract limb muscle dysfunction. Therefore, we examined the impact of a 12-wk supervised HIIT protocol on muscle oxygen conductance. Eight patients with mild-to-moderate COPD and eight age-, sex-, and BMI-matched controls underwent a 12-wk HIIT intervention. Leg blood flow ([Formula: see text]) and arterio-venous blood samples were collected at rest and during active single-leg knee-extensor exercise (KEE) at unloaded (0 W) and 20% of peak workload (WLpeak) to estimate leg muscle oxygen conductance pre- and post-HIIT. In pre-HIIT, [Formula: see text] was similar between groups during unloaded KEE (P = 0.108) but lower at 20% WLpeak in the COPD group, compared with the control group. [Formula: see text] responses were higher during unloaded KEE (28%, P = 0.012) and 20% WLpeak (40%, P < 0.001) post-HIIT in the COPD group, whereas no change occurred in the control group. Flow-adjusted skeletal muscle O2 conductance was higher in the COPD pre-HIIT group but only increased in the control group. Thus, there was no difference in diffusive or convective capacity between groups post-HIIT at submaximal KEE. COPD assessment score decreased by 2.8 [1;4] (P = 0.003) in the COPD group and V̇o2peak increased in both groups (COPD 192 mL O2/min, P = 0.032, control 257 mL O2/min, P = 0.004) with no time/group interaction. A 12-wk HIIT intervention may improve peripheral exercise capacity in COPD by increasing the vasodilatory function in working muscle while concurrently improving whole-body exercise capacity and symptom burden.NEW & NOTEWORTHY Individuals with COPD exhibit lower blood flow to the exercising leg muscles, which may be considered part of the limb muscle dysfunction associated with the disease. A 12-wk high-intensity interval training (HIIT) program increased leg blood flow in patients with COPD during single-leg knee extensor exercise achieved by improving the vasodilatory response. HIIT also improved maximal oxygen uptake and exercise capacity while reducing symptom burden.

This study investigates the change in diffusing capacity from rest to submaximal exercise in patients with mild to severe chronic obstructive pulmonary disease (COPD) compared with a healthy, age- and sex matched control group, and investigates if the diffusing capacity can be altered by high-intensity interval training (HIIT). Thirty-five patients with COPD and 15 healthy age- and sex matched controls were included. Pulmonary diffusing capacity was measured using the combined single-breath method using carbon monoxide and nitric oxide (DL,CO,NO), which were measured at rest and during 60% of peak workload (WLpeak) to estimate the alveolar-capillary reserve (change from rest to exercise). A subgroup of 12 patients with COPD and 12 control participants completed a 12-wk supervised HIIT intervention with measurements of DL,CO,NO, computed tomography-based lung tissue mass, and single-photon emission computed tomography to assess the pulmonary perfusion distribution pre and post the HIIT intervention. The alveolar-capillary reserve was reduced in patients with COPD in a severity-dependent manner compared with the healthy control group and this was unaltered following the HIIT intervention, despite an increase in exercise capacity. HIIT did not increase lung tissue mass, nor did it improve the pulmonary perfusion distribution during exercise in either group. Alveolar-capillary reserve is reduced in a severity-dependent manner in COPD, and a 12-wk supervised HIIT intervention did not induce any changes in either the alveolar-capillary reserve or lung tissue mass, suggesting that the concomitant increase in exercise capacity is likely due to extrapulmonary adaptations. (Clinical Trial Registration IDs: NCT05552833 and NCT05583396)NEW & NOTEWORTHY Using the combined measurement of the diffusing capacity for carbon monoxide and nitric oxide, we found that the increase in diffusing capacity during submaximal exercise, that is, the alveolar-capillary reserve, was reduced in patients with COPD in a severity-dependent manner. A 12-wk supervised high-intensity training intervention increased exercise capacity but without any changes in alveolar-capillary reserve or lung tissue mass, supporting that the increase in exercise capacity is not caused by pulmonary adaptations.

BACKGROUND:Heart failure with reduced ejection fraction (HFrEF) and metabolic dysfunction-associated steatotic liver disease (MASLD) are both associated with liver fibrosis. HFrEF patients may develop liver fibrosis due to hepatic congestion, MASLD, or a combination of both. The Fibrosis-4 (FIB-4) score calculated using age, aspartate aminotransferase, alanine aminotransferase, and platelet count, serves as a screening tool for advanced liver fibrosis. This study examines the association between the FIB-4 score and all-cause mortality, cardiovascular mortality, and major adverse liver outcomes (MALO) in patients with HFrEF. METHOD AND RESULTS:This study included 4523 HFrEF patients from the Danish Heart Failure Registry. Based on FIB-4 score, 25.5 % were low-risk, 45.7 % were indeterminate-risk, and 28.8 % were high-risk for advanced liver fibrosis. After five years, the cumulative incidence of all-cause mortality was 43 % for the high-risk group, 36 % for the indeterminate-risk group, and 23 % for the low-risk group. The indeterminate-risk and high-risk group had an increased hazard ratio (HR) for all-cause mortality (HR 1.33, 95 % confidence interval [CI] 1.16-1.52; HR 1.51, 95 % CI 1.31-1.74) compared to the low-risk group. Similarly, HRs were elevated for cardiovascular mortality (HR 1.61, 95 % CI 1.27-2.05; HR 2.14, 95 % CI 1.67-2.74) and MALO (HR 1.77, 95 % CI 1.01-3.31; HR 2.54, 95 % CI 1.43-4.52). CONCLUSION:A high FIB-4 score in patients with HFrEF is associated with increased mortality and MALO.

BACKGROUND:Patients who have undergone double lung transplantation (DLTx) are at increased risk of pulmonary thromboembolism (PTE). Although the presence of clinically overt PTE can adversely affect short-term mortality, the prognostic impact of asymptomatic (silent) PTE detected by routine imaging after DLTx is unclear. This study aimed to determine whether PTE identified by routine ventilation-perfusion single-photon emission computed tomography (V̇-Q̇ SPECT) 12 weeks post-DLTx is associated with subsequent all-cause and graft-related mortality. METHODS:Single-center retrospective cohort study evaluating 130 DLTx recipients who underwent routine V̇-Q̇ SPECT imaging 12 weeks posttransplant between 2012 and 2017. V̇-Q̇ SPECT scans were assessed for perfusion and ventilation defects indicative of PTE. The association between PTE and mortality outcomes was analyzed using multivariable Cox regression, Kaplan-Meier survival curves, and cumulative incidence functions. RESULTS:PTE was identified in 24.6% (n = 32) of the patients 12 weeks post-DLTx. After 3 months of follow-up, there was no detectable difference in lung function between patients with and without PTE. Moreover, the presence of PTE was not associated with increased hazard ratios for all-cause mortality (HR = 0.72; 95% CI: 0.37-1.41; p = 0.34) or graft-specific mortality (HR = 0.95; 95% CI: 0.42-2.16; p = 0.91). CONCLUSIONS:PTE is a frequent finding on routine V̇-Q̇ SPECT 12 weeks post-DLTx that does not inform risk of all-cause or graft-related mortality. These findings suggest that an incidentally detected PTE in asymptomatic patients may not necessitate changes in clinical management for asymptomatic DLTx patients.

Background Iron deficiency (ID) is common in patients with atrial fibrillation/flutter (AF), but its prognostic implications and optimal diagnostic criteria, particularly in those with and without heart failure (HF), remain unclear. This study assessed the associations between different ID definitions and clinical outcomes in patients with AF. Methods This Danish nationwide cohort study included 10 834 patients with AF who underwent iron studies between 2008 and 2019, stratified by HF status. ID was defined using four criteria: European Society of Cardiology (ESC) guidelines, ferritin <100 ng/mL, transferrin saturation (TSAT) <20% and serum iron ≤13 µmol/L. Associations between ID definitions and all-cause mortality, cardiovascular mortality and all-cause hospitalisation were evaluated using Cox regression models, adjusted for confounders. Results Prevalence of ID varied substantially across definitions, ranging from 36.2% to 62.7%. Over a median follow-up of 31 months, TSAT <20% was associated with increased all-cause and cardiovascular mortality in both HF (HR 1.25, 95% CI 1.14 to 1.37 and HR 1.31, 95% CI 1.14 to 1.49, respectively) and patients without HF (HR 1.39, 95% CI 1.18 to 1.64 and HR 1.54, 95% CI 1.18 to 2.00, respectively). Similarly, serum iron ≤13 µmol/L was associated with higher all-cause and cardiovascular mortality in HF (HR 1.44, 95% CI 1.31 to 1.58 and HR 1.42, 95% CI 1.24 to 1.63, respectively) and patients without HF (HR 1.67, 95% CI 1.41 to 1.97 and HR 1.46, 95% CI 1.13 to 1.89, respectively). ID defined by ESC guidelines or ferritin <100 ng/mL was not associated with mortality in either group but was linked to higher all-cause hospitalisation in patients with HF (HR 1.15, 95% CI 1.08 to 1.23 and HR 1.16, 95% CI 1.09 to 1.23, respectively). Conclusions ID defined by TSAT <20% or serum iron ≤13 µmol/L is associated with increased mortality in patients with AF, irrespective of HF status, highlighting these criteria as clinically relevant for risk stratification.

BACKGROUND:Cardiopulmonary exercise testing (CPET) is usually considered the gold standard for assessing maximal oxygen consumption (V̇O2max), a health and performance marker in patients with chronic obstructive pulmonary disease (COPD). Despite the widespread application of CPET, the absolute and relative test-retest reliability of CPET-derived metrics remains unexamined. OBJECTIVE:To examine and compare test-retest reliability of CPET derived metrics in individuals with COPD and healthy matched controls. METHODS:12 individuals with COPD and 12 healthy age- and sex-matched controls were included in this case-control study. Each participant completed two CPET on a bicycle ergometer on two different days. Absolute reliability was reported as smallest real difference (SRD) and relative reliability as coefficient of variance (CV) and intraclass correlation coefficients (ICC). MAIN RESULTS:SRD for peak oxygen uptake was 451.6 (267.4;1006.4) mL/min and CV was 7.8 (4.7;11.0)% in patients with COPD, whereas SRD was 244.2 (151.4;491.5) mL/min and CV was 3.0 (1.8;4.2)% in healthy controls but with no significant between group difference for SRD. CV values for all CPET derived metrics were found to be below 10%. Apart from peak workload achieved and peak minute ventilation, SRD and CV were significantly higher in COPD than in controls for all other CPET-derived metrics. CONCLUSION:This study provides test-retest reliability estimates of the most widely used CPET derived metrics in individuals with COPD and healthy matched controls. Test-retest reliability for most metrics derived from CPET were found to be lower in individuals with COPD when compared to healthy controls.

BACKGROUND:Sodium-glucose cotransporter-2 inhibitors (SGLT2i) increase haemoglobin and haematocrit levels, potentially causing secondary erythrocytosis-defined as a haemoglobin level above 16.5 g/dL in men and 16.0 g/dL in women-which is associated with an elevated thromboembolic risk. This study investigated the incidence of erythrocytosis and its association with thromboembolic events in patients with heart failure with reduced ejection fraction (HFrEF) treated with SGLT2i. METHODS:In this nationwide cohort study, we included 3138 patients with new-onset HFrEF who initiated SGLT2i treatment after diagnosis, and 3138 propensity score-matched untreated controls. Haemoglobin was measured at baseline and six-month follow-up. Erythrocytosis incidence at follow-up was assessed using Poisson regression. Cox models were used to evaluate the association between erythrocytosis and one-year risk of fatal and non-fatal thromboembolic events (myocardial infarction, stroke, pulmonary embolism, or deep venous thrombosis), stratified by SGLT2i treatment. RESULTS:Erythrocytosis developed in 207 patients (3.3%). Incidence was higher among SGLT2i-treated patients (109.5 vs. 26.8 per 1000 person-years), with an adjusted incidence rate ratio of 4.10 (95% CI 2.95-5.83). No significant association was observed between erythrocytosis and one-year thromboembolic risk in the total population (HR: 0.85 95% CI 0.44-1.65), even when stratified by SGLT2i-treated (HR: 0.81 95% CI 0.38-1.74) and untreated patients (HR: 0.75, 95% CI 0.19-3.05) (interaction P = 0.77). CONCLUSION:Although erythrocytosis incidence was higher in SGLT2i-treated HFrEF patients, it was not associated with an increased one-year thromboembolic risk.

Doppler ultrasound can be used to evaluate leg blood flow (Q̇leg), especially of interest when investigating peripheral vascular limitations in patients with chronic obstructive pulmonary disease (COPD). However, the within-session repeatability, a subdomain of test-retest reliability, of this method remains unknown. This study aimed to provide within-session repeatability estimates of Doppler ultrasound-based Q̇leg at rest and during single-leg knee-extensor exercise (KEE) in patients with COPD, and to compare these estimates to matched healthy controls. In this case-controlled study, 16 participants with COPD were matched based on sex and age with 16 healthy controls. All participants underwent measurement of Q̇leg using Doppler ultrasound in a KEE setup at various intensities with the same measurement being performed again separated by 10 s. Smallest real difference (SRD) was lowest at rest in both groups and increased during exercise, reaching values ranging from 164 to 231 mL in COPD and 122-180 mL in the control group. The coefficient of variance (CV) was highest at rest and decreased during exercise to values ranging from 4.0% to 5.0% in COPD and 2.6%-3.2% in the control group. The CV was significantly lower in the control group during 0 watt and exercise at 20% of max watt, but apart from that, no reliability estimates were different between groups. To conclude, Doppler ultrasound showed nearly equal within-session repeatability when evaluating Q̇leg in COPD patients and healthy individuals with a CV not exceeding 5% during exercise for both groups.

Beak fractures represent a rare subtype of calcaneal fractures with potential risk of soft tissue complications due to compromised local perfusion. Early diagnosis and timely intervention are crucial to prevent necrosis, infection, and soft tissue defects. This case report describes a 71-year-old male with a beak fracture and delayed intervention with reoccurring soft tissue defects. Given the rarity of the condition, atypical presentation and need for urgent intervention, this emphasizes the importance of awareness of beak fractures of the calcaneus.

The combined single-breath measurement of the diffusing capacity of carbon monoxide (DL,CO) and nitric oxide (DL,NO) is a useful technique to measure pulmonary alveolar-capillary reserve in both healthy and patient populations. The measurement provides an estimate of the participant's ability to recruit and distend pulmonary capillaries. The method has recently been reported to exhibit a high test-retest reliability in healthy volunteers during exercise of light to moderate intensity. Of note, this technique permits up to 12 repeated maneuvers and only requires a single breath with a relatively short breath-hold time of 5 s. Representative data are provided showing the gradual changes in DL,NO and DL,CO from rest to exercise at increasing intensities of up to 60% of maximal workload. The measurement of diffusing capacity and evaluation of alveolar-capillary reserve is a useful tool to evaluate the lung's ability to respond to exercise both in the healthy population as well as in patient populations such as those with chronic lung disease.

In patients with chronic obstructive pulmonary disease (COPD), pulmonary vascular dysfunction and destruction are observable before the onset of detectable emphysema, but it is unknown whether this is associated with central hypovolemia. We investigated if patients with COPD have reduced pulmonary blood volume (PBV) evaluated by 82Rb-positron emission tomography (PET) at rest and during adenosine-induced hyperemia. This single-center retrospective cohort study assessed 6,301 82Rb-PET myocardial perfusion imaging (MPI) examinations performed over a 6-yr period. We compared 77 patients with COPD with 44 healthy kidney donors (controls). Cardiac output ([Formula: see text]) and mean 82Rb bolus transit time (MBTT) were used to calculate PBV. [Formula: see text] was similar at rest (COPD: 3,649 ± 120 mL vs. control: 3,891 ± 160 mL, P = 0.368) but lower in patients with COPD compared with controls during adenosine infusion (COPD: 5,432 ± 124 mL vs. control: 6,185 ± 161 mL, P < 0.050). MBTT was shorter in patients with COPD compared with controls at rest (COPD: 8.7 ± 0.28 s vs. control: 11.4 ± 0.37 s, P < 0.001) and during adenosine infusion (COPD: 9.2 ± 0.28 s vs. control: 10.2 ± 0.37 s, P < 0.014). PBV was lower in patients with COPD, even after adjustment for body surface area, sex, and age at rest [COPD: 530 (29) mL vs. 708 (38) mL, P < 0.001] and during adenosine infusion [COPD: 826 (29) mL vs. 1,044 (38) mL, P < 0.001]. In conclusion, patients with COPD show evidence of central hypovolemia, but it remains to be determined whether this has any diagnostic or prognostic impact.NEW & NOTEWORTHY The present study demonstrated that patients with chronic obstructive pulmonary disease (COPD) exhibit central hypovolemia compared with healthy controls. Pulmonary blood volume may thus be a relevant physiological and/or clinical outcome measure in future COPD studies.