1. Adams, Jenny L. PhD

Article Content


Cardiovascular autonomic tone, assessed as heart rate variability (HRV), is reduced following an acute myocardial infarction (MI). Low HRV is associated with a high mortality risk in MI patients. Short-term readings under experimental conditions show increased sympathetic activity with concomitant lowered parasympathetic activity reduces total HRV, primarily in the breathing-related component. It is hypothesized that heart rate increases with inhalation and decreases with exhalation, and that paced breathing enhances respiratory sinus arrhythmia (RSA), increasing HRV.



To determine whether participation in a controlled breathing program increases HRV following MI and/or coronary artery bypass graft surgery (CABG).



From 2001-2005, 44 patients, age 46-65 years, who had an MI and/or undergone CABG 1-8 weeks previously and were referred to the Cardiac Rehabilitation Program at Baylor Heart and Vascular Hospital [Dallas, TX], were randomized to usual cardiac rehabilitation or cardiac rehabilitation with controlled breathing (6 breaths/min for 10 minutes twice daily during the 8-week treatment period). Weekly measurements of RSA, total power, and SDNN were taken using Biocom Technologies Heart Rhythm Scanner and Tracker software. Data were analyzed via mixed models using SAS version 9.2.



No significant changes between groups were seen in SDNN (P-value =.3984), baseline RSA (P-value =.6556), or total power (P-value =.6184).



Results suggest participation in the controlled breathing program offered no additional benefit in increasing HRV following MI or CABG. However, 84% of study patients were on heart rate lowering medications, which may have masked changes in HRV. An additional question raised is whether the expected cardiovascular improvements (e.g., decreased resting and sub-maximal blood pressure, heart rate and stroke volume) that typically result from aerobic training may be inhibited due to use of heart rate lowering medications and, therefore, improvements in these patients may simply be occurring at the skeletal muscle level.