No abstract

The effects of rhythmic input on breath period (TT) under constant metabolic drive were assessed in 10 musically trained and 10 untrained subjects. They tapped to a metronome and then to four musical segments, each for 5 min. Ten of these subjects (5 from each group) also listened to the selections without tapping. TT, beat period (TB), and phase coupling (PC) were assessed during the last 20 breaths of each presentation. TT coefficient of variation decreased significantly (P less than 0.001) in all subjects (base line = 23%; listening = 15%; listening and tapping = 10%). Significant correlation between rhythm and TT, indicating relative entrainment, was found in half of the subjects (r greater than 0.45; P less than 0.01). Significant integer TT/TB ratio and PC, both indicating tight entrainment between rhythm and breathing, were observed in 12 subjects (though not consistently in each one). These data advance the following hypothesis: musical rhythm can be a zeitgeber (i.e., pacemaker), with its ability to entrain respiration dependent on the strength of its signal relative to spurious signals from the higher neural centers that introduce noise into the central pattern generator. Tapping reinforces the zeitgeber, increasing its signal-to-noise ratio and thereby promoting entrainment.

These findings indicate that HT improves mood state, suggesting that it may be a useful tool in reducing stress. Therefore, to the extent that stress contributes to coronary heart disease, these findings support the role of HT as an effective component of cardiac rehabilitation.

Background: Chronotropic incompetence (CI) is often seen in subjects with chronic congestive heart failure (CHF). The prevalence of CI, its mechanisms and association with beta-blocker use as well as exercise capacity have not been clearly defined. Methods and results: Cardiopulmonary exercise tolerance testing data for 278 consecutive patients with systolic CHF was analyzed. CI, defined as the inability to reach 80% of maximally predicted heart rate was present in 128 of 278 subjects (46%). The prevalence of CI was highest in those with most impaired exercise capacity (72, 48, and 24% for subjects with a VO 2 of b 14.0, 14.0-20.0, and N 20.0 ml/kg/min respectively; p = 0.001). While subjects with CI had lower peak exercise heart rate (114 vs. 152 bpm), and lower peak VO 2 (15.4 vs. 19.9 ml/kg/min), they were equally likely to be on chronic beta-blocker therapy (74% vs. 71%; p = 0.51).Heart rate and norepinephrine (NE) levels were measured during exercise in a separate cohort of 24 subjects with CHF. There was no difference in beta-blocker dose between subjects with and without CI, however, exercise induced NE release and Chronotropic Responsiveness Index, a measure of post-synaptic beta-receptor sensitivity to NE, were lower in subjects with CI (1687 ± 911 vs. 2593 ± 1451 pg/ml p = 0.08; CRI 12.7 ± 5.7 vs. 22.1 ± 4.7, p = 0.002). Conclusions: CI occurs in N 70% of subjects with advanced systolic CHF irrespective of beta-blocker use and is associated with a trend toward impaired NE release, post-synaptic beta-receptor desensitization and reduced exercise capacity.