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Graduation date: 1982

The evidence for an increase in resting vagal tone to explain the lower heart rate of endurance athletes remains controversial. This study used spectral analysis of heart rate (HRV) and blood pressure (BPV) variability to examine the vagal and sympathovagal influences on the sinus node in 12 endurance-trained athletes (A) and 10 age and sex-matched control subjects (C) (age: 26(1.2) yrs; VO2max: A: 68.2(2.1) vs C: 41.4(2.0) ml/kg/min; p $<$ 0.05). Continuous ECG and BP recordings were obtained during supine rest, sitting, controlled respiration (12 breaths/min), standing, exercise at heart rates of 100 and 130 beats/min, and after 5 and 15 minutes of seated recovery. No differences were observed between A and C in the vagal or high frequency (HF) components (48.0(4.0) vs 44.2(6.9) nu), in the low frequency (LF) components (55.8(6.9) vs 52.0(4.0) nu), or in the LF/HF ratios (1.72(0.4) vs 1.22(0.2)) of the HRV spectral components at rest or other experimental conditions, despite the lower resting heart rates of the A (53.1(1.8) vs 65.1(2.1) beats/min; p $<$ 0.05). Standing and exercise decreased the HF components and increased the LF/HF ratios similarily in both the A and C, controlled respiration induced similar rises in the HF component of HRV. Despite a significantly higher systolic BP in athletes, no difference was observed between A and C in the HF or LF components of either systolic or diastolic BPV. Exercise induced an increase in the HF component of BPV which was associated with the rise in breathing frequency. These results indicate a similar sinoatrial sympathovagal balance in A and C suggesting that training-induced bradycardia could result from an adaptation in the intrinsic sinoatrial properties. Also, endurance training does not appear to influence the beat-to-beat BPV.

Thesis (Ph. D.)--University of Hawaii at Manoa, 1982. / Bibliography: leaves 260-277. / Microfiche. / xiv, 277 leaves, bound ill. 29 cm

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Typescript. / Bibliography: leaves 132-142. / xii, 142 l illus