title: Effects of age on intrinsic heart rate, heart rate variability, and AV conduction in healthy humans.
abstract: Heart rate, heart rate variability, and atrioventricular (AV) conduction were studied in 20 young (30 +/- 5 yr) and 19 older (69 +/- 7 yr) healthy men and women before and after single and double autonomic blockade (randomized order: atropine, 0.04 mg/kg i.v.; propranolol, 0.2 mg/kg i.v.). Basal R-R intervals did not differ, but older age increased P-R intervals (177 +/- 24 vs. 149 +/- 17 ms, P < 0.001) and decreased SD of R-R (43 +/- 17 vs. 70 +/- 18 ms, P = 0.001) and heart rate spectral content (area under the power vs. frequency curve from 0.04 to 0.32 Hz: 3.01 +/- 2.1 vs. 7.82 +/- 4.8 beats/min2, P < 0.009), as well as postural responses (R-R decreases of 107 +/- 80 vs. 250 +/- 72 ms, P < 0.002). Atropine decreased R-R intervals, SD of R-R, and high-frequency (0.24-0.32 Hz) spectral content less in elderly subjects compared with younger subjects. Propranolol increased R-R and P-R intervals equally in old and young and abolished low-frequency (0.04-0.12 Hz) increases with standing (P < 0.0008). After double blockade, R-R, P-R, and paced AV intervals were longer in old subjects. Mean values were as follows: R-R intervals, 859 +/- 176 vs. 677 +/- 106 ms, P < 0.001; P-R intervals, 179 +/- 23 vs. 149 +/- 17 ms, P = 0.0002; paced P-R intervals (500 ms), 251 +/- 39 vs. 215 +/- 47 ms; and AV block cycle length, 413 +/- 51 vs. 385 +/- 69 ms (multivariate analysis of variance, P < 0.03). After double autonomic blockade, heart rate variability was nearly eliminated in young and old (reduced > 98%, P < 0.0001). We conclude that age differences in heart rate variability can be explained by autonomic influences, but heart rate and AV conduction differences exist independently of beta-adrenergic and/or parasympathetic influences.
authors.affiliation: Department of Medicine, University of California, San Francisco 94143, USA.
authors.forename: N
authors.initials: N
authors.lastname: Craft
authors.forename: J B
authors.initials: JB
authors.lastname: Schwartz
mesh_terms: D000328:Adult; D000375:Aging / Q000502:physiology*; D001283:Atrioventricular Node / Q000187:drug effects / Q000502:physiology*; D001285:Atropine / Q000494:pharmacology; D001340:Autonomic Nerve Block; D002304:Cardiac Pacing, Artificial; D004562:Electrocardiography; D004594:Electrophysiology; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D008297:Male; D008875:Middle Aged; D011433:Propranolol / Q000494:pharmacology; D012016:Reference Values
chemical_list: D001285:Atropine; D011433:Propranolol