title: Effects of aging and coronary artery disease on sympathetic neural recruitment strategies during end-inspiratory and end-expiratory apnea.
abstract: In response to acute physiological stress, the sympathetic nervous system modifies neural outflow through increased firing frequency of lower-threshold axons, recruitment of latent subpopulations of higher-threshold axons, and/or acute modifications of synaptic delays. Aging and coronary artery disease (CAD) often modify efferent muscle sympathetic nerve activity (MSNA). Therefore, we investigated whether CAD (n = 14; 61 ± 10 yr) and/or healthy aging without CAD (OH; n = 14; 59 ± 9 yr) modified these recruitment strategies that normally are observed in young healthy (YH; n = 14; 25 ± 3 yr) individuals. MSNA (microneurography) was measured at baseline and during maximal voluntary end-inspiratory (EI) and end-expiratory (EE) apneas. Action potential (AP) patterns were studied using a novel AP analysis technique. AP frequency increased in all groups during both EI- and EE-apnea (all P < 0.05). The mean AP content per integrated burst increased during EI- and EE-apnea in YH (EI: Δ6 ± 4 APs/burst; EE: Δ10 ± 6 APs/burst; both P < 0.01) and OH (EI: Δ3 ± 3 APs/burst; EE: Δ4 ± 5 APs/burst; both P < 0.01), but not in CAD (EI: Δ1 ± 3 APs/burst; EE: Δ2 ± 3 APs/burst; both P = NS). When APs were binned into "clusters" according to peak-to-peak amplitude, total clusters increased during EI- and EE-apnea in YH (EI: Δ5 ± 2; EE: Δ6 ± 4; both P < 0.01), during EI-apnea only in OH (EI: Δ1 ± 2; P < 0.01; EE: Δ1 ± 2; P = NS), and neither apnea in CAD (EI: Δ -2 ± 2; EE: Δ -1 ± 2; both P = NS). In all groups, the AP cluster size-latency profile was shifted downwards for every corresponding cluster during EI- and EE-apnea (all P < 0.01). As such, inherent dysregulation exists within the central features of apnea-related sympathetic outflow in aging and CAD.
authors.affiliation: School of Kinesiology, Western University, London, Ontario, Canada.
authors.forename: Mark B
authors.initials: MB
authors.lastname: Badrov
authors.affiliation: School of Kinesiology, Western University, London, Ontario, Canada; Department of Kinesiology, University of Toledo, Toledo, Ohio.
authors.forename: Sophie
authors.initials: S
authors.lastname: Lalande
authors.affiliation: School of Kinesiology, Western University, London, Ontario, Canada.
authors.forename: T Dylan
authors.initials: TD
authors.lastname: Olver
authors.affiliation: Cardiac Rehabilitation and Secondary Prevention Program of St. Joseph's Health Care London, London, Ontario, Canada; Department of Medicine (Cardiology) and Program of Experimental Medicine, Western University, London, Ontario, Canada; and.
authors.forename: Neville
authors.initials: N
authors.lastname: Suskin
authors.affiliation: School of Kinesiology, Western University, London, Ontario, Canada; Department of Physiology and Pharmacology, Western University, London, Ontario, Canada kshoemak@uwo.ca.
authors.forename: J Kevin
authors.initials: JK
authors.lastname: Shoemaker
mesh_terms: D000200:Action Potentials; D000328:Adult; D000367:Age Factors; D000368:Aged; D000375:Aging / Q000502:physiology*; D001049:Apnea / Q000503:physiopathology*; D062186:Arterial Pressure; D001794:Blood Pressure; D062485:Breath Holding; D002302:Cardiac Output; D016022:Case-Control Studies; D003324:Coronary Artery Disease / Q000503:physiopathology*; D004525:Efferent Pathways / Q000503:physiopathology; D045853:Exhalation; D005260:Female; D006801:Humans; D001239:Inhalation; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000294:innervation; D010991:Plethysmography; D013318:Stroke Volume; D013564:Sympathetic Nervous System / Q000503:physiopathology*; D014655:Vascular Resistance; D055815:Young Adult
keywords: aging; apnea; coronary artery disease; sympathetic nervous system; sympathetic neural recruitment patterns