Respiratory Function and Cardiac Dyspnea

¹ Research Associate, Ontario Heart Foundation

The purpose of this study was to find those pulmonary function abnormalities which might be common to cardiac dyspnea irrespective of its etiology.

Ventilation, lung volumes, gas mixing, diffusing capacity and mechanics of breathing were measured in 58 patients with acquired or congenital heart disease. When compared with a normal series, the patients with slight cardiac dyspnea showed statistically a low forced vital capacity, low total lung capacity, a prolonged 90 per cent desaturation time, a low compliance and high work of breathing both at rest and on hyperventilation. Patients with moderate cardiac dyspnea had in addition hyperventilation at rest. Patients with severe cardiac dyspnea had, in addition to the above abnormalities of function, a lower than normal functional residual capacity and maximum breathing capacity, a decreased alveolar capillary permeability and an increased non-elastic resistance.

No test distinguished the patients with slight dyspnea from those with moderate dyspnea. The group with severe cardiac dyspnea differed significantly from the slight and moderate dyspnea groups in showing a lower total lung capacity and maximum voluntary ventilation, a more prolonged 90 per cent desaturation time, a lower compliance and a higher non-elastic resistance.

Reduction in lung volume correlated best with decreased pulmonary elasticity. The forced vital capacity and maximum voluntary ventilation were often within normal limits, even in severely dyspneic patients.

No significant relationship could be shown between diffusing capacity and the mechanics of breathing. Work of breathing correlated poorly with the degree of dyspnea.

Individual patients with severe dyspnea showed a greater number of coexisting abnormalities of pulmonary function than those with slight and moderate dyspnea.