Inspiratory muscle function, dynamic hyperinflation and exertional dyspnoea in pulmonary arterial hypertension

Abstract

Despite a preserved forced expiratory volume in 1 s (FEV1)/vital capacity (VC), patients with idiopathic or heritable pulmonary arterial hypertension (PAH) may dynamically decrease their inspiratory capacity (IC) during cycle exercise (i.e. dynamic hyperinflation) [1][2][3] and this could increase exertional dyspnoea [1,3,4]. Little information is currently available about whether the reduced IC during cycle exercise is related to respiratory mechanics abnormalities or to impaired inspiratory muscle function (fatigue or weakness). The aim of this study was to evaluate the relationship between inspiratory muscle activity, dynamic changes in IC and the intensity of dyspnoea in PAH patients undergoing incremental symptom-limited cardiopulmonary cycle exercise test (CPET).We studied 10 consecutive lifelong nonsmoking clinically stable patients with idiopathic or heritable PAH [1], diagnosed according to the current evidence-based guidelines [5], with a normal body mass index, no spirometric evidence of obstructive ventilatory defect [6] and no other concomitant diseases [1]. Five patients (four female/one male, mean±SD age 45±6 years, FEV1/VC = 103±4% predicted) reduced their IC dynamic hyperinflation during exercise (hyperinflator group (PAH-H)), whereas 5 age-and sex-matched PAH (four female/one male; 41±14 years; FEV1/VC = 117±6% predicted) did not (non-hyperinflator group (PAH-NH)). The research was carried out in accordance with the principles outlined in the Helsinki Declaration. The subjects gave their informed consent to participate, and the study received the approval of the appropriate local review authority

Exertional dyspnoea in pulmonary arterial hypertension

“…It is not entirely clear what drives dyspnoea, with one study showing that Borg dyspnoea ratings were higher at lower absolute levels of ventilation than in healthy subjects [29]. This same study demonstrated, however, that 60% of patients with PAH had reduced expiratory flows at low lung volumes and that dynamic hyperinflation accounted for 50-60% of the variance of Borg dyspnoea ratings during cycle ergometry [29].…”

“…Unlike muscles, which may increase in strength/endurance with increased loading, there is mixed evidence of respiratory muscle weakness in pulmonary hypertension [12,29,31,32]. Although this does not lead to exercise limitation, it is conceivable, although unproven, that this may contribute to the sensation of dyspnoea.…”

“…Although the breathing pattern in PAH has been shown to be rapid and shallow [29], frank breathing pattern disorders, such as hyperventilation, may coexist with PAH, just as they may in other cardiorespiratory disorders. However, dyspnoea, as assessed by the Dyspnoea-12 questionnaire, shows stronger correlations with anxiety and depression scores than functional class or 6-min walking distance [5], highlighting the complex nature of dyspnoea and how it may be influenced by emotional and psychological health.…”

Compromised Cerebrovascular Regulation and Cerebral Oxygenation in Pulmonary Arterial Hypertension

“…The present study directly assessed central chemoreceptor sensitivity and demonstrates its increase in PAH as well. Dyspnea is traditionally associated with ventilatory abnormalities, characterized by higher ventilatory demand, dynamic hyperinflation, and a rapid, shallow breath frequency, especially in patients with severe PAH . When compared with HF, patients with PAH have similar exercise intolerance, but are more dyspneic in relation to reduced ventilatory efficiency .…”

What is the origin of dyspnoea in smokers without airway disease?

“…Similarly, patients with pulmonary hypertension, i.e. damage of the pulmonary vasculature, have decreased inspiratory capacity and increased dyspnoea on effort despite normal lung function [18].…”