Heart rate recovery is an important predictor of outcomes in patients with connective tissue disease-associated pulmonary hypertension

Low-frequency ultrasound for pulmonary hypertension therapy

BACKGROUND

Currently, there are no reliable clinical tools that allow non-invasive therapeutic support for patients with pulmonary arterial hypertension. This study aims to propose a low-frequency ultrasound device for pulmonary hypertension therapy and to demonstrate its potential.

METHODS

A novel low-frequency ultrasound transducer has been developed. Due to its structural properties, it is excited by higher vibrational modes, which generate a signal capable of deeply penetrating biological tissues. A methodology for the artificial induction of pulmonary hypertension in sheep and for the assessment of lung physiological parameters such as blood oxygen concentration, pulse rate, and pulmonary blood pressure has been proposed.

RESULTS

The results showed that exposure of the lungs to low-frequency ultrasound changed physiological parameters such as blood oxygen concentration, pulse rate and blood pressure. These parameters are most closely related to indicators of pulmonary hypertension (PH). The ultrasound exposure increased blood oxygen concentration over a 7-min period, while pulse rate and pulmonary blood pressure decreased over the same period. In anaesthetised sheep exposed to low-frequency ultrasound, a 10% increase in SpO2, a 10% decrease in pulse rate and an approximate 13% decrease in blood pressure were observed within 7 min.

CONCLUSIONS

The research findings demonstrate the therapeutic efficiency of low-frequency ultrasound on hypertensive lungs, while also revealing insights into the physiological aspects of gas exchange within the pulmonary system.

Does arterial oxygenation during exercise add prognostic value in pulmonary arterial hypertension?

BACKGROUND

The 6-min walking distance (6MWD) is often used to assess prognosis in pulmonary arterial hypertension (PAH) patients. Whether or not changes in arterial oxygen saturation (SpO₂) during exercise add prognostic value to the 6MWD in these patients is unclear. The objective of this study was to investigate if SpO₂ changes during exercise adds prognostic value to the 6MWD in PAH patients.

METHODS

Ambispective study that includes 137 patients with PAH: 38 idiopathic/heritable (i/h PAH), 42 with connective tissue disease (CTD-PAH), 34 with porto-pulmonary hypertension (PoPH), 21 with HIV-associated PAH and 2 with pulmonary venous occlusive disease (PVOD). Patients were characterized and, treated according to international recommendations, and were followed-up for 5 years. To integrate SpO₂ changes during exercise, we calculated the desaturation distance ratio (DDR) either in its original form (from a maximal theoretical value of 100%) or the actual resting SpO₂ value of the patient (new DDR) as well as the distance saturation product (DSP).

RESULTS

(1) during follow-up, 40 patients died (29.2%); (2) results confirmed the prognostic value of the 6MWD (AUC 0.913 [IQR 0.868-0.958]; p < 0.0001), original DDR (AUC 0.923 [0.881-0.966]; p < 0.001), New DDR (AUC 0.917 [0.872-0.961], p < 0.001), and DSP (AUC 0.914 [0.869-0.959], p < 0.001); and, (3) neither the original or new DDR or DSP added significant prognostic value to 6MWD in these patients.

CONCLUSIONS

Consideration of three different composite indices of arterial oxygenation changes during exercise does not add prognostic value to that of the 6MWD in patients with PAH.

Effect of pulmonary rehabilitation on heart rate recovery in adult individuals with asthma or chronic obstructive pulmonary disease

Introduction: Heart rate recovery (HRR) after exercise is a marker of disease severity and prognosis in cardiovascular and respiratory disorders. More than 30% of adult individuals with asthma may show a slow HRR. Pulmonary rehabilitation improves exercise capacity in individuals with asthma or chronic obstructive pulmonary disease (COPD).

Aim: The study aimed to evaluate the effect of pulmonary rehabilitation on HRR in individuals with asthma as compared to those with COPD.

Methods: Retrospective analysis of HRR one minute after the six-minute walking test (6MWT) was performed before and after an exercise training program. The COPD Assessment Test (CAT), Barthel Index-Dyspnea (BI-D), Medical Research Council (MRC) score for dyspnea, and the Five-Times-Sit-to-Stand test (5STS) were also assessed as secondary outcome measures.

Results: Slow HRR prevalence was significantly lower in individuals with asthma than with COPD (29.1 vs. 46.7%, respectively: p = 0.003). Post-program HRR did not change in more than 70% of individuals in either population and improved in 16% of both populations, whereas it actually worsened in 12 and 10% of individuals with asthma and COPD, respectively. The outcome measures significantly improved in both populations, irrespective of baseline HRR.

Conclusion: In individuals with asthma or COPD, exercise training does not significantly improve HRR.

Heart rate recovery in 1 minute after the 6-minute walk test predicts adverse outcomes in pulmonary arterial hypertension

Heart rate recovery in 1 minute (HRR1) after the end of the 6-minute walk test (6MWT) is a non-invasive method of determining autonomic dysfunction. This parameter remains largely unexplored in pulmonary arterial hypertension (PAH) registries. We aimed to define the cut-off value and accuracy for abnormal HRR1 after the 6MWT and to investigate the association between HRR1 and clinical worsening in patients with PAH. This composite outcome was defined as first occurrence of all-cause death OR hospitalization from any cause OR disease progression characterized by decreased ≥ 15% in six-minute walking distance from baseline AND start of new specific PAH treatment or persistent worsening of World Health Organization functional class (WHO-FC). We performed a prospective cohort study that included 102 consecutive patients with PAH confirmed by right heart catheterization that underwent an 6MWT upon the diagnosis, recruited from September 2004 to April 2020 and followed up until April 2021 or death. The median HRR1 was 18 beats (IQR: 10–22), 50 and 52 PAH patients with <18 beats and ≥18 beats, respectively. The best cut-off for HRR1 to discriminate clinical worsening was 17 beats, with area under the curve (AUC) of 0.704 (95%CI: 0.584–0.824). The internal validation model by bootstrap showed an AUC of 0.676 (95%CI: 0.566–0.786) and the most accurate value was obtained in the seventh year of follow-up (AUC = 0.711; 95%CI: 0.596–0.844). Patients with an HRR1 <18 beats at baseline had a median event-free time of 2.17 years (95%CI: 1.82 to 2.52) versus 4.75 years (95%CI: 1.43 to 8.07) from those with ≥18 beats. In conclusion, a HRR1 value of less than 18 beats may be a reliable indicator of poor prognosis in patients with PAH.

Heart-Rate Recovery at 1 Min After Exercise Predicts Response to Balloon Pulmonary Angioplasty in Patients With Inoperable Chronic Thromboembolic Pulmonary Hypertension

Background

Dysfunction of autonomic nervous system plays an important role in the development of pulmonary hypertension. The present study aimed to investigate the interaction between balloon pulmonary angioplasty (BPA) and cardiac autonomic function by using heart-rate recovery at 1 min (HRR1) after exercise as a surrogate marker.

Methods and Results

We retrospectively enrolled 89 consecutive patients with inoperable chronic thromboembolic pulmonary hypertension who underwent BPA from May, 2018 to Jan, 2021. According to hemodynamics at follow-up, patients were categorized as BPA responders if they met one or both of the following criteria: (1) mean pulmonary arterial pressure ≤ 30 mmHg and (2) a reduction of pulmonary vascular resistance ≥ 30%. Compared with baseline, HRR1 tended to increase within 7 days after the first BPA session, and this improvement persisted at follow-up. HRR1 at baseline and at follow-up were associated with well-validated markers of CTEPH severity, including N-terminal pro-brain natriuretic peptide, mean pulmonary arterial pressure and pulmonary vascular resistance. Furthermore, the change of HRR1 from baseline to follow-up was also associated with the change of those variables. After adjustment for confounders, baseline HRR1 was still a strong independent predictor of BPA outcome. Receiver operator characteristic curve analysis showed that the cutoff value for HRR1 in predicting BPA outcome was 19 beats.

Conclusions

BPA could significantly improve HRR1, suggesting the alleviation of sympathovagal imbalance. Easily available and non-invasive HRR1 seems to be a useful tool in predicting outcome of BPA and dynamically monitoring the efficacy of BPA.

Heart Rate Recovery at 1 Min after Exercise Is a Marker of Disease Severity and Prognosis in Chronic Thromboembolic Pulmonary Hypertension

BACKGROUND

Attenuated heart rate recovery at 1 min (HRR1) was demonstrated to correlate with poor prognosis in patients with pulmonary arterial hypertension, whereas its role in patients with chronic thromboembolic pulmonary hypertension (CTEPH) remains unclear.

OBJECTIVES

The aim of this study was to investigate the correlations between HRR1 and functional status, echocardiography, hemodynamics, and prognosis of CTEPH.

METHODS

We retrospectively enrolled patients with CTEPH who underwent right heart catheterization and cardiopulmonary exercise test between June 2014 to October 2020 in Fuwai hospital. The primary outcome was clinical worsening. Linear regression was performed to assess the association between HRR1 and established markers of CTEPH severity. Receiver operating characteristic curve analysis was performed to determine the optimal cutoff of HRR1. Cox regression models were used to assess the association between HRR1 and clinical worsening.

RESULTS

A total of 211 patients with CTEPH were included in the study. After adjusting for confounders, HRR1 positively correlated with 6-min walk distance, mixed venous oxygen saturation, and peak oxygen consumption, and negatively correlated with NT-proBNP, pulmonary vascular resistance, and ventilatory equivalent of carbon dioxide. Compared with patients with HRR1 ≥16 beats, patients with HRR1 <16 beats had approximately a 3-fold risk of experiencing clinical worsening and the risk escalated with time.

CONCLUSION

HRR1 could reflect disease severity and was independently associated with prognosis in patients with CTEPH.

Identifying a Heart Rate Recovery Criterion After a 6-Minute Walk Test in COPD

BACKGROUND

Slow heart rate recovery (HRR) after exercise is associated with autonomic dysfunction and increased mortality. What HRR criterion at 1-minute after a 6-minute walk test (6MWT) best defines pulmonary impairment?.

STUDY DESIGN AND METHODS

A total of 5008 phase 2 COPDGene (NCT00608764) participants with smoking history were included. A total of 2127 had COPD and, of these, 385 were followed-up 5-years later. Lung surgery, transplant, bronchiectasis, atrial fibrillation, heart failure and pacemakers were exclusionary. HR was measured from pulse oximetry at end-walk and after 1-min seated recovery. A receiver operator characteristic (ROC) identified optimal HRR cut-off. Generalized linear regression determined HRR association with spirometry, chest CT, symptoms and exacerbations.

RESULTS

HRR after 6MWT (bt/min) was categorized in quintiles: ≤5 (23.0% of participants), 6-10 (20.7%), 11-15 (18.9%), 16-22 (18.5%) and ≥23 (18.9%). Compared to HRR≤5, HRR≥11 was associated with (p<0.001): lower pre-walk HR and 1-min post HR; greater end-walk HR; greater 6MWD; greater FEV1%pred; lower airway wall area and wall thickness. HRR was positively associated with FEV1%pred and negatively associated with airway wall thickness. An optimal HRR ≤10 bt/min yielded an area under the ROC curve of 0.62 (95% CI 0.58-0.66) for identifying FEV1<30%pred. HRR≥11 bt/min was the lowest HRR associated with consistently less impairment in 6MWT, spirometry and CT variables. In COPD, HRR≤10 bt/min was associated with (p<0.001): ≥2 exacerbations in the previous year (OR=1.76[1.33-2.34]); CAT≥10 (OR=1.42[1.18-1.71]); mMRC≥2 (OR=1.42[1.19-1.69]); GOLD 4 (OR=1.98[1.44-2.73]) and GOLD D (OR=1.51[1.18-1.95]). HRR≤10 bt/min was predicted COPD exacerbations at 5-year follow-up (RR=1.83[1.07-3.12], P=0.027).

CONCLUSION

HRR≤10 bt/min after 6MWT in COPD is associated with more severe expiratory flow limitation, airway wall thickening, worse dyspnoea and quality of life, and future exacerbations, suggesting that an abnormal HRR≤10 bt/min after a 6MWT may be used in a comprehensive assessment in COPD for risk of severity, symptoms and future exacerbations.

Management of Pulmonary Arterial Hypertension in Patients with Systemic Sclerosis

Systemic sclerosis (SSc) is a rare and complex immune-mediated connective tissue disease characterized by multi-organ fibrosis and dysfunction. Systemic sclerosis-associated pulmonary arterial hypertension (SSc-PAH) is a leading cause of death in this population. Pulmonary arterial hypertension (PAH) can coexist with other forms of pulmonary hypertension in SSc, including pulmonary hypertension related to left heart disease, interstitial lung disease, chronic thromboembolism and pulmonary venous occlusive disease, which further complicates diagnosis and management. Available pulmonary arterial hypertension therapies target the nitric oxide, endothelin and prostacyclin pathways. These therapies have been studied in SSc-PAH in addition to idiopathic PAH, often with different treatment responses. In this article, we discuss the management as well as the treatment options for patients with SSc-PAH.

Indications for lung transplant referral and listing

Lung transplantation is a valuable therapeutic option for many patients with severe lung disease who have exhausted other medical or surgical therapies. However, since lungs are not a manufacturable organ like artificial heart valves or left ventricular assist devices, and since they are a limited resource compared to number of patients requiring the organs, the Department of Health and Human Services set the Final Rule of organ allocation in 1998. This led to development and implementation of Lung Allocation Score (LAS) in 2005. The score broadly divides lung diseases into 4 diagnostic criteria with a coefficient factor given to each category. The score is based on the prognostic factors of each patient to determine the risk of mortality without a transplant combined with the probability of patient survival post-transplant. Most of the guidelines for "Indications for referral and listing in lung transplant" is based on consensus opinion as there is limited amount of robust data and trials about this topic. The International Society for Heart and Lung Transplant (ISHLT) has published three editions for candidate selection and listing. In this article, we have attempted to highlight the guidelines and incorporated other disease specific prognostic factors that are not captured in the LAS. Ultimately, there are other factors like geographic location, height, blood group, preformed antibodies, transplant center experience, past wait times and transplant rate, availability of organs, etc., which also play a role especially when considering listing a patient for lung transplant. We also highlighted a representative disease in each category and most criteria for that disease will apply to other diseases in that category. Finally, this article does not delve into the history and reasoning behind each guideline but is meant to provide a general overview of indications and contraindications applicable in the field of adult lung transplantation.

Value of heart rate recovery in female patients with pulmonary arterial hypertension due to systemic lupus erythematosus

OBJECTIVE

This study intended to explore the relation between heart rate recovery at 1 minutes (HRR1) during the recovery phase of cardiopulmonary exercise test (CPET) and exercise capacity in female systemic lupus erythematosus associated pulmonary arterial hypertension (SLE-PAH) patients.

METHODS

Twenty-one female SLE-PAH patients underwent right heart catheterization (RHC), pulmonary function test (PFT) and CPET. Forty-two healthy subjects matched with SLE-PAH patients in age, sex and BMI were recruited as a control group. The correlations between HRR1 with clinical and CPET parameters were performed.

RESULTS

Peak HR, ΔHR, HRR1, Peak HR-warm HR_1min , Peak HR-warm HR_2min and CR were significantly lower in SLE-PAH than in controls (P < .01). Increased incidence of CRI was seen in SLE-PAH. Except for the Peak P_ET O₂ , which was higher in controls, all other CPET parameters were lower in SLE-PAH. SLE-PAH patients with HRR1 ≥ 16 had longer 6MWD, lower NT-proBNP, better percent of predicted gas transfer index or diffusing capacity for carbon monoxide (DLco% pred) as well as better CO and CI. Peak HR, ΔHR, HRR1, Peak HR-warm HR_1min , Peak HR-warm HR_2min , CR, Peak Load, Peak VO₂ , Peak P_ET CO₂ , OUEP and OUES were lower and duration of exercise was shorter in patients with HRR1 < 16. HRR1 had positive correlation with 6MWD, DLco% pred, CO, CI and some key CPET parameters.

CONCLUSIONS

HRR1 is an easily obtained auxiliary parameter in SLE-PAH patients to reflect an altered autonomic tone. SLE-PAH patients with HRR1 < 16 have more severe hemodynamics, worse clinical findings and marked oxygen uptake inefficiency than those with HRR1 ≥ 16.

Pulmonary Manifestations of Systemic Sclerosis and Mixed Connective Tissue Disease

Systemic sclerosis (SSc) is a rare disease characterized by widespread collagen deposition resulting in fibrosis. Although skin involvement is the most common manifestation and also the one that determines the classification of disease, mortality in SSc is usually a result of respiratory compromise in the form of interstitial lung disease (ILD) or pulmonary hypertension (PH). Clinically significant ILD is seen in up to 40% of patients and PH in up to 20%. Treatment with either cyclophosphamide or mycophenolate has been shown to delay disease progression, whereas rituximab and lung transplantation are reserved for refractory cases.

Impaired cardiac autonomic response in lung transplant patients: A retrospective cohort study

BACKGROUND

Cardiac autonomic dysfunction (AD) is associated with adverse prognosis in lung disease; however, its implications in lung transplantation have not been previously described. This study evaluated the prevalence of AD in lung transplant (LTx) candidates, its determinants, prognostic implications, and prevalence post-transplant.

METHODS

Retrospective one-year study of 103 LTx candidates with AD assessed using heart rate (HR) from the six-minute walk test (6MWT). Impaired chronotropic response index (CRI) was defined as <80% age-adjusted HR during 6MWT. Abnormal HR recovery (HRR) was categorized as reduction in HR ≤ 12 beats/minute after the first minute of 6MWT cessation.

RESULTS

Abnormal CRI and HRR were observed in 94% and 76% of patients, respectively. A lower CRI was associated with obstructive lung disease and lower estimated aerobic capacity. CRI was independently associated with 6MW distance [12 m per 10% CRI, P = 0.03], but not with post-transplant cardiovascular events, hospital stay, or one-year mortality. At 3 months post-transplant, no improvement was observed in CRI (99%, n = 66/67, P = 0.25) or HRR (88%, n = 36/41, P = 0.12).

CONCLUSION

Cardiac AD was prevalent in LTx candidates and recipients, with chronotropic incompetence a modest contributor to exercise intolerance pretransplant. Further study may help determine whether direct autonomic measures such as HR variability may be more prognostic of LTx outcomes.

Contribution of pulmonary function tests (PFTs) to the diagnosis and follow up of connective tissue diseases

Introduction

Connective Tissue Diseases (CTDs) are systemic autoimmune conditions characterized by frequent lung involvement. This usually takes the form of Interstitial Lung Disease (ILD), but Obstructive Lung Disease (OLD) and Pulmonary Artery Hypertension (PAH) can also occur. Lung involvement is often severe, representing the first cause of death in CTD. The aim of this study is to highlight the role of Pulmonary Function Tests (PFTs) in the diagnosis and follow up of CTD patients.

Main body

Rheumatoid Arthritis (RA) showed mainly an ILD with a Usual Interstitial Pneumonia (UIP) pattern in High-Resolution Chest Tomography (HRCT). PFTs are able to highlight a RA-ILD before its clinical onset and to drive follow up of patients with Forced Vital Capacity (FVC) and Carbon Monoxide Diffusing Capacity (DL_CO). In the course of Scleroderma Spectrum Disorders (SSDs) and Idiopathic Inflammatory Myopathies (IIMs), DL_CO appears to be more sensitive than FVC in highlighting an ILD, but it can be compromised by the presence of PAH. A restrictive respiratory pattern can be present in IIMs and Systemic Lupus Erythematosus due to the inflammatory involvement of respiratory muscles, the presence of fatigue or diaphragm distress.

Conclusions

The lung should be carefully studied during CTDs. PFTs can represent an important prognostic tool for diagnosis and follow up of RA-ILD, but, on their own, lack sufficient specificity or sensitivity to describe lung involvement in SSDs and IIMs. Several composite indexes potentially able to describe the evolution of lung damage and response to treatment in SSDs are under investigation. Considering the potential severity of these conditions, an HRCT jointly with PFTs should be performed in all new diagnoses of SSDs and IIMs. Moreover, follow up PFTs should be interpreted in the light of the risk factor for respiratory disease related to each disease.

The prognostic value of heart rate recovery in patients with coronary artery disease: A systematic review and meta-analysis

BACKGROUND

Routine outpatient care of patients with coronary artery disease (CAD) lacks a simple measure of physical fitness and risk of mortality. Heart rate recovery (HRR) is noninvasive and easily obtainable in outpatient settings. Prior studies have suggested that delayed postexercise HRR in the first minutes is associated with mortality in several types of populations. However, a comprehensive overview of the prognostic value of delayed HRR for time to mortality specifically in CAD patients is not available. The purpose of the current meta-analysis is to evaluate the prognostic value of delayed HRR in CAD patients.

METHODS

We conducted a systematic search in OVID MEDLINE and OVID EMBASE to identify studies reporting on HRR and risk of incident cardiovascular events or mortality in CAD patients. Hazard ratios for delayed versus nondelayed HRR were pooled using random-effects meta-analysis.

RESULTS

Four studies were included, comprising 2,428 CAD patients. The study quality of the included studies was rated moderate (n = 2) to high (n = 2). Delayed HRR was defined by ≤12 to ≤21 beat/min in the recovery period. During follow-up (range 2.0-9.8 years), 151 patients died (6.2% [range 2.5%-19.5%]). Only data on mortality could be pooled. Heterogeneity was limited (I² = 32%; P = .23); pooled unadjusted hazard ratio for mortality, based on 3 studies, was 5.8 (95% CI 3.2-10.4).

CONCLUSIONS

In CAD patients, delayed HRR is significantly associated with all-cause mortality. As exercise testing is performed routinely in CAD patients, HRR can be considered in monitoring exercise; still, further research must investigate the addition of HRR in current risk scores.

Six-Minute Walk Test as a Predictor of Diagnosis, Disease Severity, and Clinical Outcomes in Scleroderma-Associated Pulmonary Hypertension: The DIBOSA Study

BACKGROUND

Pulmonary hypertension (PH) is a common complication of scleroderma (SSc) and is a leading cause of morbidity and mortality.

OBJECTIVES

To explore the utility of the 6MWT in the prediction of SSc-PH and to assess its prognostic implications.

METHODS

A retrospective review of SSc patients from 2003 to 2013, with 6MWT and echocardiogram (n = 286), was conducted. Presence of PH was defined by right heart catheterization. Patients were randomized into development and validation cohorts. Using regression techniques, we developed a scoring system to predict the presence of SSc-PH and tested it in our validation cohort. Trends of mortality and disease severity were studied for incremental scores.

RESULTS

The DIBOSA scoring system includes DIstance walked in 6 min, BOrg dyspnea index, and SAturation of oxygen at 6 min. The DIBOSA score in the development cohort ranged from 0 to 3, resulting in an area of 0.858 (P < 0.0001) under the ROC curve. A score of 0 had a NPV of 100% and a score of 3 had a PPV of 86.58%. The validation cohort had an area under the ROC curve of 0.842. The DIBOSA score correlated with both pulmonary artery pressures and mortality. The 3-year survival rates for DIBOSA scores of 0, 1, 2, and 3 were 100, 100, 87.67, and 66.67%, respectively (HR = 3.92, P < 0.0001).

CONCLUSIONS

DIBOSA score is a sensitive tool for the prediction of SSc-PH. The DIBOSA score is a direct predictor of mortality in SSc-PH and strongly correlates with pulmonary pressures. 6MWT can be used to predict clinical outcomes in SSc-PH.

Incremental shuttle walk test distance and autonomic dysfunction predict survival in pulmonary arterial hypertension

BACKGROUND

To ensure effective monitoring of pulmonary arterial hypertension (PAH), a simple, reliable assessment of exercise capacity applicable over a range of disease severity is needed. The aim of this study was to assess the ability of the incremental shuttle walk test (ISWT) to correlate with disease severity, measure sensitivity to change, and predict survival in PAH.

METHODS

We enrolled 418 treatment-naïve patients with PAH with baseline ISWT within 3 months of cardiac catheterization. Clinical validity and prognostic value of ISWT distance were assessed at baseline and 1 year.

RESULTS

ISWT distance was found to correlate at baseline with World Health Organization functional class, Borg score, and hemodynamics without a ceiling effect (all p < 0.001). Walking distance at baseline and after treatment predicted survival; the area under the receiver operating characteristic curve for ability of ISWT distance to predict mortality was 0.655 (95% confidence interval 0.553-0.757; p = 0.004) at baseline and 0.737 (95% confidence interval 0.643-0.827; p < 0.001) at 1 year after initiation of treatment. Change in ISWT distance also predicted survival (p = 0.04). Heart rate (HR) and systolic blood pressure (SBP) parameters reflecting autonomic response to exercise (highest HR, change in HR, HR recovery at 1 minute >18 beats/min, highest SBP, change in SBP, and 3-minute SBP ratio) were significant predictors of survival (all p < 0.05).

CONCLUSIONS

In patients with PAH, the ISWT is simple to perform, allows assessment of maximal exercise capacity, is sensitive to treatment effect, predicts outcome, and has no ceiling effect. Also, measures of autonomic function made post-exercise predict survival in PAH.