Difference in exercise heart rate, oxygen uptake and ratings of perceived exertion relationships in male post myocardial infarction patients with and without beta blockade therapy

The purpose of the study was to examine the relationships between heart rate (HR), oxygen uptake (V·O₂) and ratings of perceived exertion (RPE) in post myocardial infarction patients (PMIP). This will enable prediction equations to be established for V·O₂and percentage peak V·O₂. Two groups were examined so it was possible to establish whether these relationships were different between those using and not using beta blockade drugs. Thirty-six male recent PMIP performed a graded exercise test (modified Bruce protocol) during which time HR, V·O₂and RPE were recorded at intervals of 30 seconds, 30 seconds and 3 minutes respectively. The subjects were sub-divided into a group on a drug regime including beta blockers (blockade;n = 17; aged 61.5±6.3 years) and a control group using no drugs likely to affect HR (non-blockade;n = 19; aged 62.1±6.0 years). The results showed that although HR related to V·O₂with an r = 0.71, P<0.01 for blockade, and an r = 0.68, P< 0.01 for non-blockade, a significant difference (P< 0.01) existed between groups for the intercept of the regression lines. The relationship between RPE and HR had a similar trend. If HR was replaced by RPE to predict V·O₂, the correlation coefficients increased and also the difference between groups in the intercept disappeared. The multiple regression equations were V·O₂= 0.14 HR + 1.30 RPE-4.37 (r =0.80 , P< 0.01) for blockade, and V·O₂= 0.16 HR + 1.31 RPE-10.80 (r = 0.77,P < 0.01) for non-blockade. The multiple regression improved the linear regression based on HR alone by 14% for blockade and 13% for non-blockade. The same improvements based on RPE alone were by 8% for both blockade and non-blockade.