title: Similar orthostatic defense in active, healthy young adult and late middle-aged men.
abstract: Orthostatic defense is commonly validated with a 60 degrees to 80 degrees head-up tilt test, addressing the step response rather than the response to permanent orthostatis. During the initial phase of tilt, neural factors predominate, while later, the slower humoral factors fade in. It has been demonstrated that, during adaptation of the circulatory system to the standing conditions, overshoot and undershoot occur. These oscillations hamper straight-forward interpretation of a tilt test, and may contribute to the inconclusiveness of current studies regarding the aging of orthostatic defense. Gradual, progressive, orthostatic load testing seems a valuable alternative. We used a novel, incremental, head-up tilt protocol (0 degrees to 80 degrees, 13 increments) to impose graded orthostatic stress on 46 healthy young adult men (mean age +/- SD 25 +/- 3 years), and on 16 healthy late middle-aged men (60 +/- 4 years), while recording the electrocardiogram and the blood pressure. A first-order estimate of the heart rate range associated with the sympathovagal transition was made by combined analysis of heart rate and heart rate variability trends. We observed similar responses in heart rate, heart rate variability, and blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D001341:Autonomic Nervous System / Q000502:physiology; D001794:Blood Pressure / Q000502:physiology; D006321:Heart / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D018667:Tilt-Table Test / Q000379:methods*