Relationship between exercise induced dyspnea and functional capacity with doppler-derived diastolic function’

BACKGROUND: Dyspnea is the frequent cause of exercise intolerance and physical inactivity among patients referred for exercise tolerance test. Diastolic dysfunction has shown significant correlation with exercise capacity and exercise induced dyspnea. To find out the frequency of diastolic dysfunction (DD) and the relationships between impaired exercise capacity and exercise induced dyspnea with DD by Doppler-derived indices among patients referred for stress test in a tertiary care hospital of Karachi. METHODS: For this study 135 consecutive patients who were referred for stress test at our non-invasive lab were screened for eligibility. Patients with valvular pathology, atrial fibrillation (AF) and coronary artery disease (CAD) were excluded. Stress test was performed on treadmill using Bruce protocol. Assessment of diastolic function as determined by trans-mitral flow velocity pattern was carried at baseline and at peak exercise. We evaluated impaired exercise capacity and exercise induced dyspnea using validated Borg Scale among study subjects. RESULTS: Study subjects 88% were males, mean age was 46 ± 16 years, BMI 27 ± 5 kg/m2, prevalence of diabetes mellitus (DM) 15%, hypertension 28% and smoking 21%. Exercise induced DD occurred among 44.6%. Patients with exercise induced DD had lower exercise capacity (9.2 vs. 10.2 METS; p = 0.04) and higher Borg Scale (5.2 vs. 4.0; p < 0.001). DD at baseline was present in 25(26%) of patients so they were excluded from the study. Five patients develop ischemia during stress test so were also excluded. So final analysis was done on 105 patients. Among patients without DD at baseline, there was significant vicariate linear inverse correlation between post exercise E/A ratio and Borg scale (r = −0.23; p = 0.02) and exercise capacity was assessed by exercise duration and MET (r-0.825; p = 0.04). Multivariate regression analysis revealed post exercise E/A ratio as an independent determinant of severity of exercise induced dyspnea and impaired exercise tolerance. CONCLUSION: DD is significantly associated with impaired functional capacity and dyspnea among patients referred for exercise tolerance test.