摘要
Purpose: It is thought that the mechanisms responsible for impaired chronotropic response to exercise are related to disturbance of cardi ovascular autonomic regulation such as the baroreflex. However, it is still uncl ear whether the baroreflex mechanisms modulate heart rate(HR) responses to exerc ise via vagal and/or sympathetic alteration. We therefore investigated the effec ts of baroreflex sensitivity (BRS) on the exercise HR response in the early phas e of vagal deactivation and in the later phase of sympathetic excitation via met abolic stimulation. Methods: Twenty-four patients(18 males and 6 females, age 5 9±9 years) with heart disease underwent symptom-limited treadmill exercise tes ting according to the Bruce protocol, and BRS was measured utilizing the phenyle phrine method. Subjects were grouped by their resting BRS value: 12 with normal BRS(≥6 ms/mm Hg) and 12 with depressed BRS(< 6ms/mm Hg). The HR response to exe rcise was assessed using two parameters: the increment in HR during exercise and the ratio of HR response to the metabolic reserve(chronotropic index). Results: (1) In the patients with depressed BRS, the HR responses within 1 min after the start of exercise and from 1 min to peak exercise were attenuated compared with those having a normal BRS (15±8vs. 24±8 bpm and 36±9vs. 47±15 bpm, respecti vely). (2) The chronotropic index in the patients with depressed BRS was lower t han in those with normal BRS(0.50±0.14 vs. 0.64±0.08). Conclusion: These findi ngs suggest that impaired BRS modulates both the parasympathetic influence in ea rly exercise and sympathetic effects in the later phase on HR response to exerci se.
Purpose: It is thought that the mechanisms responsible for impaired chronotropic response to exercise are related to disturbance of cardi ovascular autonomic regulation such as the baroreflex. However, it is still uncl ear whether the baroreflex mechanisms modulate heart rate(HR) responses to exerc ise via vagal and/or sympathetic alteration. We therefore investigated the effec ts of baroreflex sensitivity (BRS) on the exercise HR response in the early phas e of vagal deactivation and in the later phase of sympathetic excitation via met abolic stimulation. Methods: Twenty-four patients(18 males and 6 females, age 5 9±9 years) with heart disease underwent symptom-limited treadmill exercise tes ting according to the Bruce protocol, and BRS was measured utilizing the phenyle phrine method. Subjects were grouped by their resting BRS value: 12 with normal BRS(≥6 ms/mm Hg) and 12 with depressed BRS(< 6ms/mm Hg). The HR response to exe rcise was assessed using two parameters: the increment in HR during exercise and the ratio of HR response to the metabolic reserve(chronotropic index). Results: (1) In the patients with depressed BRS, the HR responses within 1 min after the start of exercise and from 1 min to peak exercise were attenuated compared with those having a normal BRS (15±8vs. 24±8 bpm and 36±9vs. 47±15 bpm, respecti vely). (2) The chronotropic index in the patients with depressed BRS was lower t han in those with normal BRS(0.50±0.14 vs. 0.64±0.08). Conclusion: These findi ngs suggest that impaired BRS modulates both the parasympathetic influence in ea rly exercise and sympathetic effects in the later phase on HR response to exerci se.
