Inspiratory Muscle Weakness in Diastolic Dysfunction

Objectives: To test the hypothesis that patients with well-documented diastolic dysfunction (DD) in the setting of normal systolic function will have inspiratory muscle weakness when compared to normal control subjects, and will experience dyspnea and tachypnea during exercise.

Background: Respiratory muscle weakness has been described in patients with (systolic) congestive heart failure; however, whether or not patients with DD may present with the findings of congestive heart failure is not known.

Methods: We selected for study 14 patients with DD previously referred for cardiopulmonary evaluation whose diagnosis had been confirmed by data obtained at cardiac catheterization. Seven control subjects matched for age, sex, and weight were recruited from the hospital community. Subjects performed both basic pulmonary function tests and tests of muscle strength: handgrip strength (Hgr), and maximal subatmospheric static inspiratory muscle pressure (Pimax). Subjects then performed a graded exercise test on a bicycle ergometer. Minute ventilation, oxygen consumption, carbon dioxide production, and heart rate were monitored continuously. Echocardiography was performed three times: before exercise, at a selected submaximal exercise level (20% of a predicted maximal workload), and at maximal exercise. Subjects rated their degree of dyspnea using the Borg scale at the same three time intervals.

Results: Pimax was - 102 +/- 17 cm H(2)O in control subjects, and - 77 +/- 19 cm H(2)O in patients with DD (p = 0.013) [mean +/- SD]. Hgr was similar between the groups. At the selected submaximal exercise level, patients with DD rated dyspnea to be 2.6 +/- 2.2 Borg scale units (control subjects, 0.5 +/- 0.8 Borg scale units). Hey plots described a rapid, shallow breathing pattern in patients with DD during exercise. Patients with DD and control subjects achieved similar maximal work loads.

Conclusion: Patients with DD have diminished Pimax, adopt a rapid, shallow breathing pattern during exercise, and experience dyspnea at low work loads when compared to matched control subjects.