Membrane diffusion- and capillary blood volume measurements are not useful as screening tools for pulmonary arterial hypertension in systemic sclerosis: a case control study

Patient-specific and gene-corrected induced pluripotent stem cell-derived endothelial cells elucidate single-cell phenotype of pulmonary veno-occlusive disease

Pulmonary veno-occlusive disease (PVOD) is a rare form of pulmonary hypertension characterized by the preferential remodeling of the pulmonary venules. Hereditary PVOD is caused by biallelic variants of the EIF2AK4 gene. Three PVOD patients who carried the compound heterozygous variants of EIF2AK4 and two healthy controls were recruited and induced pluripotent stem cells (iPSCs) were generated from human peripheral blood mononuclear cells (PBMCs). The EIF2AK4 c.2965C>T variant (PVOD#1), c.3460A>T variant (PVOD#2), and c.4832_4833insAAAG variant (PVOD#3) were corrected by CRISPR-Cas9 in PVOD-iPSCs to generate isogenic controls and gene-corrected-iPSCs (GC-iPSCs). PVOD-iPSC-endothelial cells (ECs) exhibited a decrease in GCN2 protein and mRNA expression when compared with control and GC-ECs. PVOD-ECs exhibited an abnormal EC phenotype featured by excessive proliferation and angiogenesis. The abnormal phenotype of PVOD-ECs was normalized by protein kinase B inhibitors AZD5363 and MK2206. These findings help elucidate the underlying molecular mechanism of PVOD in humans and to identify promising therapeutic drugs for treating the disease.

Value of lung diffusing capacity for nitric oxide in systemic sclerosis

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

Screening for pulmonary arterial hypertension in systemic sclerosis

Pulmonary arterial hypertension (PAH) is a dreaded complication of systemic sclerosis (SSc) that occurs in ∼10% of patients. Most individuals present with severe symptoms, significant functional impairment and severe haemodynamics at diagnosis, and survival after PAH diagnosis is poor. Therefore, early diagnosis through systematic screening of asymptomatic patients has the potential to identify PAH at an early stage. Current evidence suggests that early diagnosis and treatment of PAH in patients with SSc may lead to better clinical outcomes. Annual screening may include echocardiography, but this can miss some patients due to suboptimal visualisation or insufficient tricuspid regurgitation. Other options for screening include the DETECT algorithm or the use of a combination of pulmonary function testing (forced vital capacity/diffusing capacity of the lung for carbon monoxide ratio) and N-terminal-pro-brain natriuretic peptide levels. Symptomatic patients, those with an elevated tricuspid regurgitation velocity on echocardiogram with or without secondary echocardiographic features of PAH, and those who screen positive on the DETECT or other pulmonary function test algorithms should undergo right heart catheterisation. Exercise echocardiography or cardiopulmonary exercise testing, nailfold capillaroscopy and molecular biomarkers are promising but, as yet, unproven potential options. Future screening studies should employ systematic catheterisation to define the true predictive values for PAH.

Screening can detect PAH at an early stage of the disease, which permits earlier medical interventions and may improve outcomes in systemic sclerosis patients.bit.ly/2Q5akGu

Combined measurement of carbon monoxide and nitric oxide lung transfer does not improve the identification of pulmonary hypertension in systemic sclerosis

Screening is important to determine whether patients with systemic sclerosis (SSc) have pulmonary hypertension because earlier pulmonary hypertension treatment can improve survival in these patients. Although decreased transfer factor of the lung for carbon monoxide (TLCO) is currently considered the best pulmonary function test for screening for pulmonary hypertension in SSc, small series have suggested that partitioning TLCO into membrane conductance (diffusing capacity) for carbon monoxide (DMCO) and alveolar capillary blood volume (VC) through combined measurement of TLCO and transfer factor of the lung for nitric oxide (TLNO) is more effective to identify pulmonary hypertension in SSc patients compared with TLCO alone. Here, the objective was to determine whether combined TLCO–TLNO partitioned with recently refined equations could more accurately detect pulmonary hypertension than TLCO alone in SSc.

For that purpose, 572 unselected consecutive SSc patients were retrospectively recruited in seven French centres.

Pulmonary hypertension was diagnosed with right heart catheterisation in 58 patients. TLCO, TLNO and VC were all lower in SSc patients with pulmonary hypertension than in SSc patients without pulmonary hypertension. The area under the receiver operating characteristic curve for the presence of pulmonary hypertension was equivalent for TLCO (0.82, 95% CI 0.79–0.85) and TLNO (0.80, 95% CI 0.76–0.83), but lower for VC (0.75, 95% CI 0.71–0.78) and DMCO (0.66, 95% CI 0.62–0.70).

Compared with TLCO alone, combined TLCO–TLNO does not add capability to detect pulmonary hypertension in unselected SSc patients.

Connective tissue disease-associated pulmonary arterial hypertension

Although rare in its idiopathic form, pulmonary arterial hypertension (PAH) is not uncommon in association with various associated medical conditions, most notably connective tissue disease (CTD). In particular, it develops in approximately 10% of patients with systemic sclerosis and so these patients are increasingly screened to enable early detection. The response of patients with systemic sclerosis to PAH-specific therapy appears to be worse than in other forms of PAH. Survival in systemic sclerosis-associated PAH is inferior to that observed in idiopathic PAH. Potential reasons for this include differences in age, the nature of the underlying pulmonary vasculopathy and the ability of the right ventricle to cope with increased afterload between patients with systemic sclerosis-associated PAH and idiopathic PAH, while coexisting cardiac and pulmonary disease is common in systemic sclerosis-associated PAH. Other forms of connective tissue-associated PAH have been less well studied, however PAH associated with systemic lupus erythematosus (SLE) has a better prognosis than systemic sclerosis-associated PAH and likely responds to immunosuppression.

[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.

Relevance of partitioning DLCO to detect pulmonary hypertension in systemic sclerosis

We investigated whether partitioning DLCO into membrane conductance for CO (DmCO) and pulmonary capillary blood volume (Vcap) was helpful in suspecting precapillary pulmonary (arterial) hypertension (P(A)H) in systemic sclerosis (SSc) patients with or without interstitial lung disease (ILD). We included 63 SSc patients with isolated PAH (n=6), isolated ILD (n=19), association of both (n=12) or without PAH and ILD (n=26). Partitioning of DLCO was performed by the combined DLNO/DLCO method. DLCO, DmCO and Vcap were equally reduced in patients with isolated PAH and patients with isolated ILD but Vcap/alveolar volume (VA) ratio was significantly lower in the isolated PAH group. In patients without ILD, DLCO, DmCO, Vcap and Vcap/VA ratio were reduced in patients with isolated PAH when compared to patients without PAH and both Vcap/VA and DLCO had the highest AUC to detect PAH. In patients with ILD, Vcap had the highest AUC and performed better than DLCO to detect PH in this subgroup. In conclusion, Vcap/VA was lower in PAH than in ILD in SSC whereas DLCO was not different. Vcap/VA ratio and DLCO had similar high performance to detect PAH in patients without ILD. Vcap had better AUC than DLCO, DmCO and FVC/DLCO ratio to detect PH in SSC patients with ILD. These results suggest that partitioning of DLCO might be of interest to detect P(A)H in SSC patients with or without ILD.

Impaired carbon monoxide diffusing capacity as a marker of limited systemic sclerosis

BACKGROUND

As impairment of diffusing capacity for carbon monoxide (DLCO) likely reflects underlying pulmonary vasculopathy in limited systemic sclerosis (lSSc), we examined whether DLCO could help to distinguish secondary from idiopathic Raynaud's phenomenon (iRP).

METHODS

We compared pulmonary function test (PFT) results in 145 lSSc patients and 24 age- and sex-matched iRP patients. RP duration at time of PFT was similar in the two groups.

RESULTS

DLCO values were low (<80% of predicted) in 106 (73%) of the 145 lSSc patients, and in 69 (71%) of the 97 patients with early lSSc. Interstitial lung disease (ILD) was found in 10% of lSSc patients. DLCO was significantly lower in lSSc than in iRP (72±15% versus 89±9%, p<0.0001). When evaluated, alveolar capillary membrane conductance (Dm) was markedly lower in lSSc patients without ILD than in iRP patients (45±12% versus 71±2.5%, p=0.003), although capillary blood volume was not different. DLCO was low in 3 iRP patients (12.5%). The sensitivity and specificity of low DLCO values for early lSSc diagnosis in patients with Raynaud's phenomenon were 71% and 87.5%, respectively. Sensitivity was similar to that of anti-centromere-antibodies (75%) and nailfold capillary abnormalities (81%). A DLCO cutoff of <70% had a sensitivity and specificity of 41% and 100%, respectively. In multivariable analysis, age and low DLCO were the only independent predictors of death; the hazard ratio for DLCO ≤50% was 7.9 (95% CI 2.3-26, p=0.0007).

CONCLUSION

Isolated DLCO impairment is significantly more frequent in patients with lSSc than in patients with idiopathic iRP. DLCO measurement could be a useful diagnostic tool for lSSc.

Early detection of pulmonary vascular disease in pulmonary arterial hypertension: time to move forward

Pulmonary arterial hypertension (PAH) can be a rapidly progressive disorder and is associated with high rate of mortality, despite medical intervention. With the availability of effective therapy, early disease detection is an important strategic objective to improve treatment outcomes. Resting echocardiography is currently the recommended screening modality for high-risk population groups. However, it is clear that derangements in resting haemodynamics (and symptoms) are late sequelae of the pathobiological processes that begin in the distal pulmonary arteries. Exercise stress may unmask early pulmonary vascular dysfunction but the definition, clinical significance, and natural history of 'exercise PAH' remain undefined. We will review the currently available and potential future strategies aimed at early disease detection, and propose that ultimately the way forward is to detect disease at a stage prior to the rise in resting pulmonary artery pressure.