CARDIAC OUTPUTS OF POST-MYOCARDIAL INFARCTION PATIENTS DURING SWIMMING AND CYCLING

Abstract

The cardiovascular response of post myocardial-infarction (MI) patients and inactive normal subjects was compared at submaximum and maximum intensities of tethered swimming and upright cycling. At any given O2 uptake (.ovrhdot.VO2), the inactive normals had similar cardiac outputs (.ovrhdot.Q) and heart rates (HR) during swimming and cycling, but the post-MI patients had lower .ovrhdot.Q and higher HR during swimming compared to cycling. The maximum responses of inactive normals were not significantly different during swimming and cycling, but during swimming the post-MI patients had a 21% lower .ovrhdot.VO2. The lower .ovrhdot.VO2 swimming was due to a lower .ovrhdot.Q. While swimming at any exercise rate including maximum, the stroke volume (Vs) of the post-MI patients did not increase above resting Vs seated. Any increase in .ovrhdot.Q during swimming was apparently due solely to increases in HR. Since the HR of the post-MI patients were not significantly different during maximum effort swimming and cycling, the intensity of swimming can be safely prescribed from the maximum HR achieved cycling.