Impact of right ventricular work and pulmonary arterial compliance on peak exercise oxygen uptake in idiopathic pulmonary arterial hypertension

BACKGROUND

Pulmonary arterial hypertension (PAH) is associated with increased right ventricular (RV) afterload, RV dysfunction and decreased peak oxygen uptake (pVO₂). However, the pulmonary hemodynamic mechanisms measured by exercise right heart catheterization (RHC) that contribute to reduced pVO₂ in idiopathic PAH (IPAH) are not completely characterized. Therefore, we sought to evaluate the exercise RHC determinants of pVO₂ in patients with IPAH.

METHODS

519 consecutive patients with suspected and/or confirmed pulmonary hypertension were prospectively screened to identify 20 patients with IPAH. All IPAH patients were prospectively evaluated with resting and exercise RHC and cardiopulmonary exercise testing.

RESULTS

85% of the patients were female; the median age was 34[29-42] years old. At peak exercise, mean pulmonary arterial (PA) pressure was 76 ± 17 mmHg, PA wedge pressure was 14 ± 5 mmHg, cardiac output (CO) was 5.7 ± 1.9 L/min, pulmonary vascular resistance was 959 ± 401 dynes/s/cm⁵ and PA compliance was 0.9[0.6-1.2] ml/mmHg. On univariate analysis, pVO2 positively correlated to peak CO, peak cardiac index, peak stroke volume index, peak RV stroke work index (RVSWI) and peak oxygen saturation. There was a negative correlation between pVO₂ and Δ (rest to peak change) PA compliance. In age-adjusted multivariate model, peak RVSWI (Coefficient = 0.15, Beta = 0.63, 95% CI [0.07-0.22], p < 0.01) and ΔPA compliance (Coefficient = -2.51, Beta = -0.43, 95% CI [-4.34-(-0.68)], p = 0.01) had the best performance predicting pVO₂ (R² = 0.66).

CONCLUSIONS

In conclusion, a load dependent measurement of RV function (RVSWI) and the pulsatile component of RV afterload (ΔPA compliance) significantly influence pVO₂ in IPAH, further highlighting the pivotal role of hemodynamic coupling to IPAH exercise capacity.

Clinical usefulness of end-tidal CO2 profiles during incremental exercise in patients with chronic thromboembolic pulmonary hypertension

INTRODUCTION

Great ventilation to carbon dioxide output (ΔV˙E/ΔV˙CO₂) and reduced end-tidal partial pressures for CO₂ (PetCO₂) during incremental exercise are hallmarks of chronic thromboembolic pulmonary hypertension (CTEPH) and idiopathic pulmonary arterial hypertension (IPAH). However, CTEPH is more likely to involve proximal arteries, which may lead to poorer right ventricle-pulmonary vascular coupling and worse gas exchange abnormalities. Therefore, abnormal PetCO₂ profiles during exercise may be more prominent in patients with CTEPH and could be helpful to indicate disease severity.

METHODS

Seventy patients with CTEPH and 34 with IPAH underwent right heart catheterization and cardiopulmonary exercise testing. According to PetCO₂ pattern during exercise, patients were classified as having an increase or stabilization in PetCO₂ up to the gas exchange threshold (GET), an abrupt decrease in the rest-exercise transition or a progressive and slow decrease throughout exercise. A subgroup of patients with CTEPH underwent a constant work rate exercise test to obtain arterial blood samples during steady-state exercise.

RESULTS

Multivariate logistic regression analyses showed that progressive decreases in PetCO₂ and SpO₂ were better discriminative parameters than ΔV˙E/ΔV˙CO₂ to distinguish CTEPH from IPAH. This pattern of PetCO₂ was associated with worse functional impairment and greater reduction in PaCO₂ during exercise.

CONCLUSION

Compared to patients with IPAH, patients with CTEPH present more impaired gas exchange during exercise, and PetCO₂ abnormalities may be used to identify more clinically and hemodynamically severe cases.

A haemodynamic study of pulmonary hypertension in chronic hypersensitivity pneumonitis

Chronic hypersensitivity pneumonitis is a common fibrotic interstitial lung disease. The prevalence of pulmonary hypertension diagnosed by right heart catheterisation and its cardiopulmonary function findings in patients with chronic hypersensitivity pneumonitis are unknown. Consecutive symptomatic patients with chronic hypersensitivity pneumonitis were prospectively evaluated. All patients were submitted to right heart catheterisation, pulmonary function testing, a 6-min walk test, echocardiography, blood gas determination and N-terminal pro-brain natriuretic peptide analyses. Nonhypoxaemic patients also underwent incremental cardiopulmonary exercise testing. 50 patients underwent right heart catheterisation; 25 (50%) of these had pulmonary hypertension and 22 (44%) had a pre-capillary haemodynamic pattern. The patients with pre-capillary pulmonary hypertension had lower forced vital capacity (mean ± sd 50 ± 17% versus 69 ± 22% predicted, p<0.01), carbon monoxide diffusing capacity (37 ± 12% versus 47 ± 14% predicted, p<0.01), arterial oxygen tension (median (interquartile range) 59.0 (47.8-69.3) versus 73.0 (62.2-78.5) mmHg, p<0.01) and saturation after the 6-min walk test (78 ± 8% versus 86 ± 7%, p<0.01). In pre-capillary pulmonary hypertension, oxygen uptake was also lower at the anaerobic threshold (41 ± 11% versus 50 ± 8% predicted, p=0.04) and at peak exercise (12.8 ± 1.6 versus 15.0 ± 2.5 mL · kg(-1) · min(-1), p=0.02). Pre-capillary pulmonary hypertension is common in symptomatic chronic hypersensitivity pneumonitis and is related to interstitial lung disease severity. Additionally, pulmonary hypertension is more prevalent in hypoxaemic patients with impaired lung function and exercise capacity.

Usefulness of pulmonary capillary wedge pressure as a correlate of left ventricular filling pressures in pulmonary arterial hypertension

BACKGROUND

Pulmonary arterial hypertension (PAH) is characterized by a pulmonary capillary wedge pressure (PCWP) of ≤15 mm Hg, given a normal left ventricular filling pressure (LVFP). However, recent studies have shown that, in PAH patients, diagnosis based on PCWP can erroneously classify a significant number of patients compared with diagnosis based on left ventricular end-diastolic pressure (LVEDP). Therefore, we sought to compare the diagnostic accuracy of end-expiratory PCWP and LVEDP measurements in patients suspected of having pulmonary hypertension (PH).

METHODS

We reviewed the hemodynamic data from 122 patients suspected of having PH who underwent simultaneous right- and left-side heart catheterizations at a PH referral center from 2006 to 2011.

RESULTS

PH was diagnosed in 105 patients, 79% of whom (n = 83) showed a pre-capillary pattern according to the LVEDP measurement. Ninety percent of patients with PCWP ≤15 mm Hg were correctly classified as having pre-capillary PH. However, 39% of patients with a PCWP >15 mm Hg had LVEDP ≤15 mm Hg and would have been erroneously diagnosed with pulmonary venous hypertension based on their PCWP measurements alone. The sensitivity and specificity was 0.89 and 0.64, respectively. A Bland-Altman analysis of the PCWP and LVEDP measurements revealed a mean bias of 0.3 mm Hg with 95% limits of agreement of -7.2 to 7.8 mm Hg.

CONCLUSIONS

A PCWP ≤15 mm Hg was found to be a reliable indicator of normal LVFP in pre-capillary PH patients. When measured properly and analyzed in the clinical context, PCWP is a valuable tool for accurate diagnosis of PAH.