| Summary: | Passive head-up tilt testing with or without infusion of isoproterenol is used in the investigation and management of patients with syncope. Twenty-five healthy asymptomatic volunteers prospectively grouped according to age (young [28 ± 1.7 years]: n = 9; middle [51 ± 3.3 years]: n = 11; elderly [81 ± 2.4 years]: n = 5; mean ± SE) were studied during: (1) supine carotid sinus massage: (2) 60° head-up tilt alone; and (3) infusion of isoproterenol to raise the heart rate 20% above supine baseline, prior lo a 10-minute repeat tilt. Symptoms occurred in three subjects (12%) and only occurred with passive tilting alone. Two young subjects had syncope with sinus pauses greater than 10 seconds. One elderly subject developed atrial flutter. No subject had symptoms or hypotension during tilt plus isoproterenol or a pause greater than 3 seconds with carotid sinus massage. With passive tilt, mean heart rate increased by 16 ± 6 beats/min and 18 ± 7.8 beats/min in the young and middle aged subjects (P < 0.05), but only by 6 ± 5 beats/min in the elderly (P = NS, supine vs 60° in each group). With head-up tilt plus isoproterenol infusion, the mean heart rate elevation in response to tilt was 17 ± 9 beats/min, 8 ± 3 beats/min, and 12 ± 4 beats/min for the young, middle, and elderly subjects, respectively (P < 0.05, supine vs 60° in each group). Supine serum norepinephrine concentration values were 229 ± 33 pg/mL, 374 ± 107 pg/mL, and 409 ± 41 pg/mL (mean ± SE) in the young, middle aged, and elderly groups, respectively (P = 0.05. young vs elderly). With head-up till, these significantly rose in the three groups. With tilt, serum epinephrine tended to rise (P < 0.10) only in the young and middle aged groups. Serum dopamine did not significantly increase in response to tilt in any of the groups. These studies suggest that till testing protocols need lo he assessed against age and protocol matched controls.
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