Abstract
Background: Several determinants of exercise intolerance in patients with precapillary pulmonary hypertension (PH) due to pulmonary arterial hypertension and/or chronic thromboembolic PH (CTEPH) have been suggested, including diaphragm dysfunction. However, these have rarely been evaluated in a multimodal manner. Methods: Forty-three patients with PH (age 58 ± 17 years, 30% male) and 43 age- and gender-matched controls (age 54 ± 13 years, 30% male) underwent diaphragm function (excursion and thickening) assessment by ultrasound, standard spirometry, arterial blood gas analysis, echocardiographic assessment of pulmonary artery pressure (PAP), assay of amino-terminal pro-brain natriuretic peptide (NT-proBNP) levels, and cardiac magnetic resonance (CMR) imaging to evaluate right ventricular systolic ejection fraction (RVEF). Exercise capacity was determined using the 6-min walk distance (6MWD). Results: Excursion velocity during a sniff maneuver (SniffV, 4.5 ± 1.7 vs. 6.8 ± 2.3 cm/s, P<0.01) and diaphragm thickening ratio (DTR, 1.7 ± 0.5 vs. 2.8 ± 0.8, P<0.01) were significantly lower in PH patients versus controls. PH patients with worse exercise tolerance (6MWD <377 vs. ≥377 m) were characterized by worse SniffV, worse DTR, and higher NT-pro-BNP levels as well as by lower arterial carbon dioxide levels and RVEF, which were all univariate predictors of exercise limitation. On multivariate analysis, the only independent predictors of exercise limitation were RVEF (r = 0.47, P=0.001) and NT-proBNP (r = −0.27, P=0.047). Conclusion: Patients with PH showed diaphragm dysfunction, especially as exercise intolerance progressed. However, diaphragm dysfunction does not independently contribute to exercise intolerance, beyond what can be explained from right heart failure.
Highlights
Pulmonary arterial hypertension (PAH) and chronic thromboembolic pulmonary hypertension (CTEPH) as forms of precapillary pulmonary hypertension (PH) are associated with significant exercise intolerance, but the exact mechanisms leading to exercise limitation are multifactorial and still not well understood [1,2,3,4,5,6].License 4.0 (CC BY).In precapillary PH, and in PAH and chronic thromboembolic PH (CTEPH) in particular, increased pressure in the pulmonary arteries overloads the right ventricle (RV), causing hypertrophy and failure [5]
Lower values of inspiratory muscle strength as assessed by transdiaphragmatic pressure following magnetic stimulation of the phrenic nerve roots were shown to relate to exercise intolerance in patients with precapillary PH [8]. While this showed that inspiratory muscle dysfunction parallels the development of exercise intolerance in PH, it is not yet known whether the diaphragm contribution to exercise intolerance is independent of RV systolic dysfunction in precapillary PH. This prospective study was conducted in patients with precapillary PH and age- and sex-matched controls to evaluate whether diaphragm function, assessed by diaphragm ultrasound, [10] contributes to exercise intolerance, evaluated by the 6-min walking test, over and above impaired right ventricular pump function, as assessed by cardiac magnetic resonance (CMR) imaging
The present study confirmed that diaphragm impairment is a very common finding in patients with precapillary PH
Summary
Pulmonary arterial hypertension (PAH) and chronic thromboembolic pulmonary hypertension (CTEPH) as forms of precapillary pulmonary hypertension (PH) are associated with significant exercise intolerance, but the exact mechanisms leading to exercise limitation are multifactorial and still not well understood [1,2,3,4,5,6].License 4.0 (CC BY).In precapillary PH, and in PAH and CTEPH in particular, increased pressure in the pulmonary arteries overloads the right ventricle (RV), causing hypertrophy and failure [5]. Lower values of inspiratory muscle strength as assessed by transdiaphragmatic pressure following magnetic stimulation of the phrenic nerve roots were shown to relate to exercise intolerance in patients with precapillary PH [8]. While this showed that inspiratory muscle dysfunction parallels the development of exercise intolerance in PH, it is not yet known whether the diaphragm contribution to exercise intolerance is independent of RV systolic dysfunction in precapillary PH. Several determinants of exercise intolerance in patients with precapillary pulmonary hypertension (PH) due to pulmonary arterial hypertension and/or chronic thromboembolic PH (CTEPH) have been suggested, including diaphragm dysfunction These have rarely been evaluated in a multimodal manner. Diaphragm dysfunction does not independently contribute to exercise intolerance, beyond what can be explained from right heart failure
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