Doppler Ultrasound Determination of the Distribution of Human Cardiac Output: Effects of Age and Physical Stresses

Due to its high spatial, temporal, and dynamic resolution, noninvasive Doppler ultrasound can be used to determine the distribution of phasic cardiac output in humans. The effects of ageing and various common physical stresses on combined human major central and regional blood flows have not been reported. We tested the hypothesis that there are no significant age-related differences in steady-state human central and regional hemodynamics during leg exercise, hypoxia, eating, and standing. We used noninvasive, image-guided Doppler flowmetry (~7% linearity, ~11% accuracy) to measure absolute values and percent changes (%C) in phasic blood flows in the following major arteries: ascending aorta (CO, cardiac output), common carotid (CQ, brain), subclavian (SQ, arm), renal (RQ, kidney), superior mesenteric (MQ, gut), and common femoral (FQ, leg). Mean arm cuff blood pressure (BP), heart rate (HR), stroke volume (SV), and total peripheral resistance (PR) were also determined. We studied 16 young (Y, 24/3years, 8 males) and 16 elderly (E, 73/2years, 7 males) healthy, lean adults during separate experiments of: 50% submaximal leg exercise; 12% oxygen breathing; ~700 calorie meal; and 70° upright tilt. Exercise results (X/SD) are given as Y(%C) then E(%C) where (+) represents p<0.05 vs resting, fasting control: HR: 78/8+,66/7+; BP: 6/5,8/6; SV: - 15/5+,21/4+; CO: 96/11+,87/9+; PR: -83/13+,- 76/10+; CQ: 16/8+,14/6+; SQ: -6/8,-12/8; MQ: -21/11+,-15/11; RQ: -14/8/-12/7; FQ: 919/88+,898/74 Importantly, there were no significant (p<0.05) age-related differences in the percentage changes in any of these hemodynamic variables. Similar results were found during hypoxia, eating, and standing. We conclude that although physical stresses significantly (p<0.05) affects various central and regional hemodynamics, there are no significant age-related differences in these variables between healthy, successfully aged, 20 and 70 year old cohorts. These data suggest that given an appropriate genetic template and behavior free of significant trauma and disease states, cardiovascular control mechanisms and the distributions of cardiac output dur- ing common, daily, physical stresses are maintained with age through 70 years of life.