title: Particle effects on heart-rate regulation in senescent mice.
abstract: Because epidemiology studies consistently identify the elderly at risk for air pollution-related morbidity and mortality, we developed a model of senescent-dependent susceptibility based on indices of physiological aging. In the current study, we hypothesized that heart-rate regulation during particulate matter (PM) exposure differs with senescence-dependent susceptibility owing to variation in autonomic nervous control. Heart rate (HR) and heart-rate variability (HRV) parameters were measured from 162 samples of 2-min electrocardiograph (ECG) recordings in age-matched healthy (n = 5) and terminally senescent (n = 3) AKR mice during 3-h exposures to filtered-air (FA, day 1) and carbon black (CB, day 4; <200 microg/m(3)). On day 1, HR was significantly (p <.01) depressed during FA in terminally senescent mice. By day 4, HR was further slowed significantly (p <.01) due to the effects of CB exposure for 3 days. The combined effects of terminal senescence and CB exposure acted to depress HR to an average (+/-SEM) 445 +/- 40 bpm, or approximately 80 bpm lower compared to healthy HR responses. The change in rMSSD, an HRV parameter corresponding to relative influences of parasympathetic tone on HR, was significantly (p <.01) greater on day 1 and day 4 in terminally senescent mice compared to healthy mice. In contrast, the LF/HF ratio, an HRV parameter derived from spectral analysis indicating relative changes in cardiac sympathetic tone, was significantly (p <.01) depressed in terminally senescent mice on day 1. By day 4, significant increases in LF/HF were evident in healthy mice during CB exposure, suggesting that HR regulation was associated with an increase in sympathetic tone. Alternatively, terminally senescent mice appeared to modulate a lower HR without change in LF/HF ratio during CB exposure, suggesting an absence of sympathetic tone. In conclusion, older healthy mice increase cardiac sympathetic tone during PM exposure while terminally senescent mice show a greater PM-induced parasympathetic tone in regulating HR. The significance of the current results suggest that PM-induced HR regulatory changes may ultimately depend on the degree of physiological aging.
authors.affiliation: Department of Environmental Health Sciences, Johns Hopkins University, Bloomberg School of Public Health, Baltimore, Maryland, 21205 USA. drclarke@welchlink.jhu.edu
authors.forename: Clarke G
authors.initials: CG
authors.lastname: Tankersley
authors.forename: Matthew
authors.initials: M
authors.lastname: Campen
authors.forename: Alexis
authors.initials: A
authors.lastname: Bierman
authors.forename: Susan E
authors.initials: SE
authors.lastname: Flanders
authors.forename: Karl W
authors.initials: KW
authors.lastname: Broman
authors.forename: Richard
authors.initials: R
authors.lastname: Rabold
mesh_terms: D000375:Aging; D000393:Air Pollutants / Q000633:toxicity*; D000818:Animals; D001835:Body Weight; D002244:Carbon / Q000633:toxicity*; D004562:Electrocardiography; D006339:Heart Rate / Q000187:drug effects*; D051379:Mice; D008806:Mice, Inbred AKR; D010316:Particle Size; D013997:Time Factors
chemical_list: D000393:Air Pollutants; D002244:Carbon