A systematic review of transition studies of pulmonary arterial hypertension specific medications

Transition from Intravenous Epoprostenol to Treprostinil Due to Intolerable Side Effects in Patients With Pulmonary Arterial Hypertension

Intravenous epoprostenol improves exercise capacity and survival in patients with pulmonary arterial hypertension (PAH); however, it has side effects. Reviewing the side effects associated with epoprostenol and treprostinil is essential for improving the long-term treatment strategies for PAH. This retrospective review included patients with PAH who transitioned from intravenous epoprostenol to intravenous treprostinil owing to intolerable side effects, including high cardiac output symptoms, ascites, and thrombocytopenia. Of the 85 patients who received epoprostenol at our hospital between 2013 and 2021, 16 (11 women), with a median age of 33 (range 26 to 40) years (including 12 with idiopathic PAH, 3 with hereditary PAH, and 1 with connective tissue disease pulmonary hypertension), had to switch from intravenous epoprostenol to treprostinil owing to the side effects. After transitioning, epoprostenol-associated intolerable side effects, such as high cardiac output symptoms, ascites, and thrombocytopenia, were ameliorated. In conclusion, for patients with PAH who have intolerable side effects from epoprostenol and have difficulty in continuing treatment, switching from epoprostenol to treprostinil may be an option. Switching treatment leads to better adherence and improved long-term prostacyclin therapy.

Aggressive Afterload Lowering to Improve the Right Ventricle: A New Target for Medical Therapy in Pulmonary Arterial Hypertension?

Despite numerous therapeutic advances in pulmonary arterial hypertension, patients continue to suffer high morbidity and mortality, particularly considering a median age of 50 years. This article explores whether early, robust reduction of right ventricular afterload would facilitate substantial improvement in right ventricular function and thus whether afterload reduction should be a treatment goal for pulmonary arterial hypertension. The earliest clinical studies of prostanoid treatment in pulmonary arterial hypertension demonstrated an important link between lowering mean pulmonary arterial pressure (or pulmonary vascular resistance) and improved survival. Subsequent studies of oral monotherapy or sequential combination therapy demonstrated smaller reductions in mean pulmonary arterial pressure and pulmonary vascular resistance. More recently, retrospective reports of initial aggressive prostanoid treatment or initial combination oral and parenteral therapy have shown marked afterload reduction along with significant improvements in right ventricular function. Some data suggest that reaching threshold levels for pressure or resistance (components of right ventricular afterload) may be key to interrupting the self-perpetuating injury of pulmonary vascular disease in pulmonary arterial hypertension and could translate into improved long-term clinical outcomes. Based on these clues, the authors postulate that improved clinical outcomes might be achieved by targeting significant afterload reduction with initial oral combination therapy and early parenteral prostanoids.

Strategies for optimizing intravenous prostacyclin-analog therapy in patients with pulmonary arterial hypertension

INTRODUCTION

Intravenous prostacyclin-analogs (PCA, e.g. epoprostenol, treprostinil, iloprost) have become an essential part in the therapy of patients with pulmonary hypertension (PH), mainly pulmonary arterial hypertension (PAH). They show considerable differences in pharmacology. A combination therapy including intravenous drugs is regarded as the 'gold standard' in most of PAH patients.

AREAS COVERED

This review discusses and summarizes the studies and concepts on which this therapy is based. To date, intravenous prostacyclin-analogs are mainly administered when standard therapy fails to improve patients to low-risk status. However, preliminary data from uncontrolled studies suggest that an 'upfront triple' therapy including intravenous or subcutaneous prostacyclin-analogs could be preferable in selected patients.

EXPERT OPINION

Various IV PCA have been evaluated in the treatment of patients with PAH. Today, combination therapy is the 'gold standard' for the majority of patients. Intravenous PCA is recommended from functional class III onwards. Timing of its initiation is still a point of discussion. An escalation of therapy to IV or SC PCA is always necessary if a low-risk status cannot be achieved with other targeted therapies. Preliminary data suggest that selected patients could benefit from an 'upfront triple' therapy. Controlled studies on which such recommendation could be based are lacking.

Case report: Stepwise transition from subcutaneous treprostinil to epoprostenol in high-risk pulmonary arterial hypertension

BACKGROUND

Idiopathic pulmonary arterial hypertension is associated with high morbidity and mortality. In recent years, the use of targeted therapies has led to an improvement in prognosis. Prostacyclin analogues treprostinil and epoprostenol require continuous subcutaneous or intravenous infusion and are generally administered in a stepwise approach. However, there are no clear recommendations for transition in high-risk patients requiring high doses of prostacyclin analogues.

CASE SUMMARY

In this report, we describe the case of a 20-year-old woman under combined treatment with sildenafil, macitentan, and treprostinil who required transition from subcutaneous treprostinil therapy to intravenous epoprostenol due to erratic drug absorption and functional class progression. The transition was performed over 48 h in a stepwise approach reducing treprostinil dose 4 ng/kg/min every 3 h while increasing epoprostenol infusion 2 ng/kg/min until achieving a maintenance dose of 32 ng/kg/min. There were no side effects requiring changes in the infusion rate.

DISCUSSION

Patients with advanced pulmonary arterial hypertension may necessitate switching from subcutaneous treprostinil to epoprostenol. Although many protocols have been used to date, there are no guidelines to direct this process safely. This 48-h scheme based on the pharmacokinetic properties of each drug was successful and well-tolerated.

Optimization of specific therapy for pulmonary hypertension: the possibilities of riociguat

Pulmonary hypertension (PH) is a severe and often rapidly progressive disease with fatal outcome. Endothelial dysfunction in PH is associated with decreased nitric oxide production. After reviewing the mechanisms of action and the evidence base for specific therapy with phosphodiesterase 5 inhibitors (PDE-5) and soluble guanylate cyclase stimulators, a reseach review on switching from PDE-5 to riociguat is conducted. A potential advantage of riociguat is its independence from endogenous nitric oxide and from the other (besides PDE-5) isoenzymes of phosphodiesterases. The favorable efficacy profile of sildenafil has been proven for the main forms of pulmonary arterial hypertension, of riociguat for the main forms of pulmonary arterial hypertension and chronic thromboembolic PH. The clinical efficacy of replacing PDE-5 with riociguat has been demonstrated in uncontrolled trials and in the randomized controlled study REPLACE. The possibility of therapy optimization by switching from IFDE-5 to riociguat is fixed in the Russian (class and level of evidence B-3) and Eurasian (class and level of evidence IIb-B) clinical guidelines, as well as in the materials of the Cologne Expert Consensus. An additional argument for switching is the lower cost as compared to combination therapy in the Russian Federation. According to the Russian and Eurasian guidelines for PH and the Russian instructions for the use of riociguat, the drug should be taken at least 24 hours after sildenafil discontinuation.

Real-world experience of selexipag titration in pulmonary arterial hypertension

Selexipag is an oral selective prostacyclin-receptor agonist that was approved for use in patients with World Health Organisation (WHO) functional class II-III pulmonary arterial hypertension (PAH). Treatment with individualised doses of selexipag resulted in significant reductions in the composite end point of death or a complication related to PAH in the phase III GRIPHON (Prostacyclin [PGI2] Receptor Agonist In Pulmonary Arterial Hypertension) study. In order to better understand the real-world approach to selexipag titration and to establish the individualised maintenance regimens used in our centre, we performed this retrospective study of the first 20 patients prescribed selexipag. Baseline characteristics differed from the GRIPHON study, with more combination therapy and comorbidities at drug initiation. Maintenance doses were stratified as low-dose in 10% (n=2), medium-dose in 70% (n=14) and high-dose in 20% (n=4). This study highlights that selexipag can be safely initiated, titrated and transitioned in an outpatient setting to achieve an individualised dosing regimen.

Transition from Bosentan to Ambrisentan in Pulmonary Arterial Hypertension: A Single-Center Prospective Study

Background

Pulmonary hypertension patients experienced a high financial burden due to the high cost of drug therapy, high incidence of comorbidities and hospitalizations. Endothelin receptor antagonists (ERAs) in PAH treatment showed a high cost. While ambrisentan has been covered by medical insurance of a local government of China, there has been a drug transition from bosentan to ambrisentan in treating PAH patients. We evaluated the safety, efficacy and tolerability of ambrisentan after drug transition.

Methods

Liver and renal functions were inspected at baseline, month 1, 3 and 6. NT-proBNP, echocardiographic variables, WHO functional class (WHO-FC), 6-minute walking distance (6MWD) were measured in the baseline and month 6 to evaluate the safety and efficacy. Quality of life (QOL) scale was used in the baseline and month 6 to investigate the tolerability and quality of life of PAH patients.

Results

Among 224 PAH patients, 49 stable PAH patients meet the inclusion criteria were enrolled, among which three patients discontinued during the study. Our results showed no difference in 6-minute walking distance (6MWD) of PAH patients from baseline and month 6. The liver and renal function, N-terminal pro-brain natriuretic peptide (NT-proBNP), WHO functional class (WHO-FC) showed no difference either. For echocardiography parameters, the left ventricular end-diastolic dimension (LVEDD) of month 6 decreased. Other parameters were no significant difference from the baseline. There was no difference in the QOL scale between baseline and month 6.

Conclusion

Our results suggested that it is safe and tolerable for stable PAH patients to transition from bosentan to ambrisentan without influencing hematologic parameters or heart function.

A multicenter retrospective study of patients with pulmonary hypertension transitioned from inhaled to oral treprostinil

Oral treprostinil has recently been shown to delay disease progression in patients with pulmonary arterial hypertension in a long-term outcomes study. The potential advantages of an oral formulation have resulted in patients transitioning from inhaled to oral treprostinil. The current study reports a retrospective analysis of patients who transitioned from treatment with inhaled to oral treprostinil. A multicenter retrospective chart review was conducted for 29 patients with pulmonary hypertension that transitioned from inhaled to oral treprostinil. Data were collected from inhaled treprostinil initiation and patients were followed until discontinuation of oral treprostinil or the end of the observation period. Persistence was calculated using Kaplan–Meier estimates. Prior to transition to oral treprostinil, patients had received inhaled treprostinil for a median of 643 (IQR: 322–991) days and 52% of patients were New York Heart Association/World Health Organization Functional Class III. For patients that cross-titrated between formulations, the median time to complete the cross titration was 24 (IQR: 1–57) days. At 16- and 24-weeks post-transition, oral treprostinil persistence was 86 and 76%, respectively. Persistence was 59% at 52 weeks post-transition. Clinical stability for the majority of patients at first follow-up post-transition was suggested based on available New York Heart Association/World Health Organization Functional Classification. Transitions from inhaled to oral treprostinil appeared safe and tolerable in the short-term. Additional prospective studies are needed to fully evaluate the safety and efficacy of transitions from inhaled to oral treprostinil.

Intravenous prostacyclin-analogue therapy in pulmonary arterial hypertension - A review of the past, present and future

Therapy with intravenous prostacyclin analogues in patients with pulmonary arterial hypertension (PAH) has been established for decades and is an integral component of the current guidelines for the treatment of pulmonary hypertension. Initially, these drugs were infused by external pump systems via tunnelled right atrial catheters with the need for cooling and frequent exchange of drug reservoirs. Associated complications included, among others, catheter-related infections. More recently, fully implantable pump systems have been developed with drug reservoirs that are filled transcutaneously, allowing intervals between refills of several weeks. This technique results in a low rate of infections. Epoprostenol, iloprost and treprostinil have all been used intravenously in PAH, but titration, dosing and dose escalation in long-term therapy are not standardized. Intravenous prostacyclin analogues are still under-used, despite available data suggesting that early and broad application of these therapies as part of risk-oriented, guideline-directed combination therapy for patients with PAH may lead to a survival benefit. This review provides a detailed overview of the drugs, infusion systems and dosing strategies used for intravenous therapy in patients with PAH.

A Case Report of a Patient With Pulmonary Arterial Hypertension Transitioned From Inhaled Iloprost to Selexipag

Pulmonary arterial hypertension (PAH) is a progressive disease characterized by elevated pulmonary vascular resistance that can lead to right ventricular failure and death. The use of medications that affect the prostacyclin pathway is an important treatment strategy in PAH. Inhaled iloprost is a prostacyclin analogue, and selexipag is an oral, non-prostanoid, prostacyclin IP receptor agonist. Data are limited on transitioning patients from inhaled iloprost to selexipag. In this case report, we describe the successful transition of a 57-year-old female with heritable PAH from inhaled iloprost to selexipag over 8 weeks in an out-patient setting. After initiation of selexipag, the patient's inhaled iloprost dose was gradually reduced and eventually discontinued. The patient tolerated the transition well with stable symptoms, 6-minute walk distance, and pulmonary hemodynamics. Additional studies are needed to better define the comparative efficacy and safety of inhaled iloprost and selexipag.

Transitions between infused and oral prostacyclin pathway agents in pulmonary arterial hypertension: key considerations

Prostacyclin pathway agents are a critical treatment for patients with pulmonary arterial hypertension. Seven prostacyclin pathway agents are available, including agents administered by parenteral infusion, by inhalation, and orally. Pulmonary arterial hypertension patients are now transitioned from one prostacyclin pathway agent to another with increasing frequency. Such transitions require careful downtitration and uptitration to avoid decompensation from rapid withdrawal and to achieve a patient's optimal dose based on efficacy and tolerability. Clinical guidance is especially lacking for transitions involving the newer, oral prostacyclin pathway agents; specifically, selexipag and oral treprostinil. We present three case reports of patients with pulmonary arterial hypertension who underwent one or more transition between parenteral and oral prostacyclin pathway agents, including some transitions that were successful and some that were not. These cases illustrate key considerations, such as titration protocols, patient selection, side effect management, and pharmacokinetics.

Balloon atrial septostomy and transition of subcutaneous to intravenous prostacyclin infusion for rescuing advanced right heart failure in idiopathic pulmonary arterial hypertension: a case report

Background

Intravenous (IV) prostacyclin analogues infusion and balloon atrial septostomy (BAS) are two important treatment options for managing advanced right heart failure in patients with idiopathic pulmonary arterial hypertension (IPAH). References and protocols are rare for dose titrations and transitions between subcutaneous and IV prostacyclin in functional Class IV IPAH patients. Balloon atrial septostomy is rarely done in very few expert centres.

Case summary

A young female with IPAH who had received maximal medication including subcutaneous prostacyclin analogues injection was admitted due to advanced right heart failure. She received ascites drainage twice. Later, we directly switched the administration route of prostacyclin from subcutaneous to IV at a ratio of 1:1 instantly. Such rapid conversion led her into a state of profound hypotension and drowsy consciousness, which was resolved after escalating IV inotropics and reducing prostacyclin dosage. Five days later, she received BAS under the guidance of intracardiac echocardiography. Her urine output increased and dyspnoea improved gradually. Six months later, clinical worsening happened again with increase of ascites and dyspnoea. She underwent 2nd and 3rd session of graded BAS with relief of symptoms again. She received permanent transition to IV prostacyclin analogues infusions via a peripherally inserted central catheter after three sessions of BAS.

Discussion

Balloon atrial septostomy is effective in stabilizing the critical right heart failure in IPAH patients but should be intended as a bridge to lung transplant procedure. Transition from subcutaneous to IV prostacyclin is helpful but needs to be titrated in proper aliquots and time intervals to avoid abrupt haemodynamic changes.

Transition protocol from subcutaneous treprostinil to intravenous epoprostenol in deteriorating patients with pulmonary arterial hypertension

BACKGROUND

Despite advantages in the treatment options of pulmonary arterial hypertension, continuous parenteral prostanoid administration, although often complicated by serious side effects, remains the treatment of choice for patients with advanced disease. The need of transitioning from one parenteral prostanoid agent to the other is often faced in the daily clinical practise. Up to today, there is no established transition protocol from subcutaneous treprostinil to intravenous epoprostenol.

METHODS

A staggered approach to subcutaneous treprostinil down-titration with simultaneous epoprostenol up-titration is described. Subcutaneous treprostinil is down-titrated by 5 ng/kg/min every 5 h while intravenous epoprostenol is up-titrated by 2 ng/kg/min every 2 h.

RESULTS

The designed protocol was implemented in 4 patients with pulmonary arterial hypertension (3 women, median age 70.5 (range 38-79) years). Median starting subcutaneous treprostinil dose was 44.5 (range 37-100) ng/kg/min and median treprostinil down-titration time was 32.5 (range 25-85) hours. The median maximal epoprostenol dose was 36 (range 28-90) ng/kg/min, achieved in 36 (range 30-90) hours. Only mild prostanoid-related side effects were reported.

CONCLUSIONS

The proposed staggered transition protocol from subcutaneous treprostinil to intravenous epoprostenol was safe in a limited number of patients with pulmonary arterial hypertension.

Combination Therapy in Pulmonary Arterial Hypertension: Gleaning a Practical Approach from the Randomized Trials

In the past decade, combination therapy in pulmonary arterial hypertension (PAH) has evolved from something PAH practitioners felt almost compelled to do, notwithstanding the absence of data, to a strategy proven by well-conducted randomized clinical trials. Whereas in the past, PAH treatment was limited to parenteral epoprostenol; today multiple drugs administrable either parenterally, inhaled, or orally have expanded the options for treating PAH patients. The SERIPHIN, AMBITION, and GRIPHON trials and emerging findings in FREEDOM-EV confirm the validity of a combined-therapy approach. Data from these trials in which either combined therapy was planned or an agent was added to background therapy have demonstrated significant reduction in the progression of disease and are on the cusp of demonstrating survival benefit. Combination therapy may be started simultaneously in some cases, but in many cases a stepped approach to initiating a second, or third, agent is better tolerated. Trials of all the specific combinations of drugs may not be possible, but a continuing trend toward treating PAH with multiple agents is likely. Currently, Food and Drug Administration-approved agents are predominantly pulmonary vasodilators acting through different pathways, with minimal impact on progression of the proliferative pulmonary arteriopathy that is the key pathologic finding in PAH. It is to be hoped that treatment strategies that result in halting progression and substantial reversal of pulmonary arteriolar obstruction will soon be discovered and available.

Risk stratification and medical therapy of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) remains a severe clinical condition despite the availability over the past 15 years of multiple drugs interfering with the endothelin, nitric oxide and prostacyclin pathways. The recent progress observed in medical therapy of PAH is not, therefore, related to the discovery of new pathways, but to the development of new strategies for combination therapy and on escalation of treatments based on systematic assessment of clinical response. The current treatment strategy is based on the severity of the newly diagnosed PAH patient as assessed by a multiparametric risk stratification approach. Clinical, exercise, right ventricular function and haemodynamic parameters are combined to define a low-, intermediate- or high-risk status according to the expected 1-year mortality. The current treatment algorithm provides the most appropriate initial strategy, including monotherapy, or double or triple combination therapy. Further treatment escalation is required in case low-risk status is not achieved in planned follow-up assessments. Lung transplantation may be required in most advanced cases on maximal medical therapy.

Risk stratification and medical therapy of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) remains a severe clinical condition despite the availability over the past 15 years of multiple drugs interfering with the endothelin, nitric oxide and prostacyclin pathways. The recent progress observed in medical therapy of PAH is not, therefore, related to the discovery of new pathways, but to the development of new strategies for combination therapy and on escalation of treatments based on systematic assessment of clinical response. The current treatment strategy is based on the severity of the newly diagnosed PAH patient as assessed by a multiparametric risk stratification approach. Clinical, exercise, right ventricular function and haemodynamic parameters are combined to define a low-, intermediate- or high-risk status according to the expected 1-year mortality. The current treatment algorithm provides the most appropriate initial strategy, including monotherapy, or double or triple combination therapy. Further treatment escalation is required in case low-risk status is not achieved in planned follow-up assessments. Lung transplantation may be required in most advanced cases on maximal medical therapy.

Chronic Right Heart Failure: Expanding Prevalence and Challenges in Outpatient Management

Right heart failure is caused by right heart dysfunction resulting in suboptimal stroke volume to supply the pulmonary circulation. Therapeutic developments mean that patients with acute right heart failure survive to hospital discharge and live with chronic right heart failure. Chronic right heart failure management aims to reduce afterload, optimize preload, and support contractility, with the best evidence available in vascular targeted therapy for pulmonary arterial hypertension. However, the management of chronic right heart failure relies on adapting therapies for left ventricular heart failure to the right. We review right heart failure management in the ambulatory setting and its challenges.

Safety and tolerability of transition from inhaled treprostinil to oral selexipag in pulmonary arterial hypertension: Results from the TRANSIT-1 study

BACKGROUND

A long-term trial showed that the oral prostacyclin (PGl₂) receptor (IP) agonist, selexipag, delayed disease progression in patients with pulmonary arterial hypertension (PAH). Transition to selexipag in patients treated with more burdensome inhaled therapies that target the prostacyclin pathway may be considered by patients and physicians. The Phase 3b, prospective, open-label TRANSIT-1 (Tolerability and Safety of the Transition From Inhaled Treprostinil to Oral Selexipag in Patients With Pulmonary Arterial Hypertension) study evaluated the safety and tolerability of transition from inhaled treprostinil to oral selexipag.

METHODS

Patients receiving non-prostanoid oral PAH therapy and inhaled treprostinil at stable doses, in World Health Organization Functional Class II/III, with 6-minute walk distance ≥ 300 meters were enrolled. The 16-week main treatment period included downtitration of inhaled treprostinil over 8 weeks and parallel uptitration of selexipag over 12 weeks. Sustained treatment transition at Week 16 was defined as (1) receiving selexipag at Week 16; (2) no selexipag interruption(s) totaling ≥ 8 days; and (3) no inhaled treprostinil or other prostanoids after Week 8. Clinical parameters and patient-reported treatment satisfaction outcomes were assessed at Week 16.

RESULTS

All 34 enrolled patients completed the study. At Week 16, 32 patients (94.1%) had stopped inhaled treprostinil and were receiving selexipag. Twenty-eight patients (82.4%) met all criteria for sustained treatment transition. During the study, 3 patients discontinued selexipag due to adverse events. Overall, most adverse events were typical of prostanoid therapies and started during the uptitration phase. In general, patients remained clinically stable throughout treatment and reported improved convenience.

CONCLUSIONS

Transition to oral selexipag from inhaled treprostinil in PAH patients was successful and well tolerated in most patients, and associated with greater convenience.

CLINICAL TRIAL NUMBER

NCT02471183.

Right ventricular afterload predicts long-term transition from parenteral to oral treprostinil in pulmonary arterial hypertension

Despite the increasing trends, reports on long-term follow-up are limited on transitioning from parenteral to oral treprostinil therapy in patients with pulmonary arterial hypertension (PAH). We investigated both the effectiveness of parenteral to oral treprostinil transition and the characteristics associated with transition failure over a duration of two years. The study included 37 Group I functional class I and II patients with PAH on combination therapy. Patients were excluded if cardiac index ≤2.2 L/min/m², right atrial pressure ≥11 mmHg, or 6-min walk distance ≤250 m. Patients were categorized as successful (_STransition) or unsuccessful (_UTransition) transition based on clinical stability, or a parenteral comparator (_CParenteral) if they remained on parenteral therapy (no transition). All patients underwent two right heart catheterizations, one at enrollment and a second post transition. Of 24 total transition patients, 46% were classified as _UTransition. _UTransition occurred on average 577 days post transition. Both _UTransition and _STransition had similar hemodynamics at diagnosis and treprostinil dose before and after transition. Before transition, the pulmonary vascular resistance (PVR) was significantly higher in the _UTransition (6.7 ± 2 WU) vs. _STransition group (3.5 ± 1.5 WU). At follow-up catheterization, the _UTransition group demonstrated further increases in PVR, greater than the _CParenteral group, without recovery despite “rescue” therapy in the _UTransition group. A pre-transition PVR of 4.16 WU discriminated the _UTransition from the _STransition group. While a subset of PAH patients on combination therapy may be safely transitioned from parenteral to oral treprostinil, caution should be exercised in patients with elevated baseline PVR to avoid irreversible destabilization.

Measuring pulmonary arterial compliance: mission impossible? Insights from a novel in vivo continuous-flow based experimental model

Arterial compliance (C) is related to the elasticity, size, and geometrical distribution of arteries. Compliance is a determinant of the load that impedes ventricular ejection. Measuring compliance is difficult, particularly in the pulmonary circulation in which resistive and compliant vessels overlap. Comparing different methods for quantification of compliance to a method that involves a continuous flow might help to identify the optimal method. Pulmonary arterial compliance was computed in six pigs based on the stroke volume to pulse pressure ratio, diastolic decay exponential fitting, area method, and the pulse pressure method (PPM). Compliance measurements were compared to those obtained under continuous flow conditions through a right ventricular bypass (Heartware Inc., Miami Lakes, FL, USA). Compliance was computed for various flows using diastolic decay exponential fitting after an abrupt interruption of the pump. Under the continuous flow conditions, resistance (R) was a decreasing function of the flow, and the fitting to P = e^-t/RC yielded a pulmonary time constant (RC) of 2.06 s ( ± 0.48). Compliance was an increasing function of flow. Steady flow inter-method comparisons of compliance under pulsatile flow conditions showed large discrepancies and values (7.23 ± 4.47 mL/mmHg) which were lower than those obtained under continuous flow conditions (10.19 ± 1 0.31 mL/mmHg). Best agreement with steady flow measurements is obtained with the diastolic decay method. Resistance and compliance are both flow-dependent and are inversely related in the pulmonary circulation. The dynamic nature of the pulsatile flow may induce a non-uniformly distributed compliance, with an influence on the methods of measurement.

Pulmonary hypertension in patients with interstitial lung disease

Interstitial lung diseases (ILDs) comprise a broad and heterogeneous group of more than two hundred diseases with common functional characteristics. Their diagnosis and management require a multidisciplinary approach. This multidisciplinary approach involves the assessment of comorbid conditions including pulmonary hypertension (PH) that exerts a dramatic impact on survival. The current World Health Organization (WHO) classification of PH encompasses many of the interstitial lung diseases into WHO Group 3, while sarcoidosis, Pulmonary Langerhans Cell Histiocytosis and lymphangioleiomyomatosis are placed into WHO Group 5 as diseases with unclear or multifactorial mechanisms. Connective tissue diseases could span any of the 5 WHO groups based on the primary phenotype into which they manifest. Interestingly, several challenging phenotypes present with features that overlap between two or more WHO PH groups. Currently, PH-specific treatment is recommended only for patients classified into WHO Group 1 PH. The lack of specific treatment for other groups, including PH in the setting of ILD, reflects the poor outcomes of these patients. Thus, identification of the optimal strategy for ILD patients with PH remains an amenable need. This review article provides a brief overview of biomarkers indicative of vascular remodeling in interstitial lung disease, summarizes the current state of knowledge regarding patients with PH and ILD and highlights future perspectives that remain to be addressed.