Sensory consequences of critical inspiratory constraints during exercise in pulmonary arterial hypertension.

We aimed to assess detailed ventilatory and sensory responses to exercise contrasting subjects with and without PAH. 20 non-smoking patients with PAH (37.5 ± 12.1 ys; FEV1/FVC = 0.77 ± 0.04; mPAP by heart catheterization = 50.6 ± 18.1 mmHg) and 10 matched controls performed cycling cardiopulmonary exercise test with serial assessments of dyspnea, airway occlusion pressure during the first 0.1 s (P0.1) of tidal volume and inspiratory capacity (IC). Patients showed lower spirometric variables compared to controls. Dyspnea and ventilation (VE) were significantly higher in patients for a given work rate. Dyspnea persisted more intense in patients even when expressed as a function of VE. Lower IC at rest (in non-hyperinflators; n = 10) or exercise-induced reduction in IC (in hyperinflators) predisposed patients to achieve earlier and at lower workloads a critical inspiratory reserve volume (IRV). At this point, there was a sudden rise in P0.1 and dyspnea perception. Attainment of a critical IRV at premature workloads leads to neuromechanical dissociation with an abrupt increment in exertional dyspnea.

Low exertional inspiratory capacity is not related to dynamic inspiratory muscle weakness in heart failure.

Reduction in inspiratory capacity (IC) during exercise has been reported in chronic heart failure (CHF). Since inspiratory muscle dysfunction may be present to a variable degree, the assumption that IC reduction during exercise represents an increase in end-expiratory lung volume must be made with caution. This interpretation is flawed if patients develop dynamic inspiratory muscle strength reduction, i.e., progressively lower esophageal (Pes) pressures as the IC maneuvers are repeated. Sixteen CHF patients and 9 age-matched controls performed an incremental exercise test with serial IC and respiratory pressure measurements. Regardless whether IC decreased or not with exercise (N = 4 and N = 12, respectively), Pes,IC remained stable. This was confirmed by similar Pes,sniff immediately upon exercise cessation (p > .05). No association was found between changes in IC and related Pes from rest to peak exercise. Owing to the lack of dynamic inspiratory muscle weakness, non-invasive indexes of lung mechanics can be reliably obtained from exercise IC in CHF.