[Changes in autonomic cardiovascular control in biological aging--studies using orthostatic provocation and analysis of heart rate profiles in long-term ECG]

Abstract

We compared the reactions of heart rate in long-term ECG as well as the heart rates and the blood pressures in orthostatic provocation tests using pharmacological blockades in 14 young human subjects aged 19 to 33 years (mean age = 22 +/- 2.2 years) with those of 16 healthy subjects between 67 and 89 years (m = 74 +/- 9.4 years). The blockades were carried out (following the schedule of Jose) first with only propranolol (0.2 mg/kg BW), then propranolol plus atropine (0.04 mg/kg BW), and, finally, only atropine was applied. For the interpretation of the frequency profiles in the long-term ECG prestudies were carried out with dogs, whose high vegetative tension provided us with essential knowledge about the specific type of the autonomous stimulation underlying the respective frequency reaction. Comparing the profiles between old and young human subjects the complete loss of instant reactions in the elderly can be stated. Variations of the heart rate result only from the modulation of the sympathetic stimulation. The "intrinsic heart rate (IHR)" after propranolol plus atropine is still below resting heart rate in the elderly, whereas IHR exceeded the resting heart rate in the younger subjects by nearly 50%. Thus, the basically initial vegetative situation is that, in the younger subjects, their resting heart rates are reached by a permanent parasympathetic slow-down of the IHR, whereas the elderly have to accelerate their slow IHR by permanent sympathetic stimulation in order to reach their "resting" heart rates. The orthostatic provocation tests with the respective blockades prove an age-dependent decrease in the sympathetic system and in the parasympathetic control. A down-regulation of the beta-receptors as a consequence of the permanent sympathetic drive is probable.