Altered Heart Rate Variability in Spontaneously Hypertensive Rats Is Associated with Specific Particulate Matter Components in Detroit, Michigan

Article excerpt

BACKGROUND: Exposure co fine particulate matter [aerodynamic diameter [less than or equal to] 2.5 [micro]m ([PM.sub.2.5])] is linked to adverse cardiopulmonary health effects; however, the responsible constituents are not well defined.

OBJECTIVE: We used a rat model to investigate linkages between cardiac effects of concentrated ambient particle (CAP) constituents and source factors using a unique, highly time-resolved data set.

METHODS: Spontaneously hypertensive rats inhaled Detroit Michigan, CAPs during summer or winter (2005-2006) for 13 consecutive days. Electrocardiogram data were recorded continuously, and heart rate (HR) and heart rate variability (HRV) metrics were derived. Extensive CAP characterization, including use of a Semicontinuous Elements in Aerosol Sampler (SEAS), was performed, and positive matrix factorization was applied to investigate source factors.

RESULTS: Mean CAP exposure concentrations were 518 [micro]g/[m.sup.3] and 357 [micro]g/[m.sup.3] in the summer and winter, respectively. Significant reductions in the standard deviation of the normal-to-normal intervals (SDNN) in the summer were strongly associated with cement/lime, iron/steel, and gasoline/diesel factors, whereas associations with the sludge factor and components were less consistent. In winter, increases in HR were associated with a refinery factor and its components. CAP-associated HR decreases in winter were linked to sludge incineration, cement/lime, and coal/secondary sulfate factors and most of their associated components. Specific relationships for increased root mean square of the standard deviation of successive normal-to-normal intervals (RMSSD) in winter were difficult to determine because of lack of consistency between factors and associated constituents.

CONCLUSIONS: Our results indicate that specific modulation of cardiac function in Detroit was most strongly linked to local industrial sources. Findings also highlight the need to consider both factor analytical results and component-specific results when interpreting findings.

KEY WORDS: air pollution, cardiac function, heart rate variability, particulate matter, toxicology. Environ Health Perspect 119:474-480 (2011). doi:10.1289/ehp.1002831 [Online 15 December 2010]

Numerous epidemiological and toxicological studies have reported associations between ambient fine particulate matter [aerodynamic diameter [less than or equal to] 2.5 [micro]m ([PM.sub.2.5])] and adverse cardiovascular events (e.g., Chen et al. 2010; Lanki et al. 2006). A number of these studies have documented changes in heart rate variability (HRV) (e.g., Schwartz et al. 2006). However, [PM.sub.2.5] is a complex mixture of both organic and inorganic materials, and the specific components responsible for these changes are unclear. The use of ambient particle concentrators, coupled with repeated measures and extensive exposure characterization, has facilitated identification of causative PM components. Investigators have reported linkages with water-soluble metals and organic compounds (Kodavanti et al. 2005), silicon (Si) and organic carbon (OC) (Batalha et al. 2002), vanadium (V) and bromine (Saldiva et al. 2002), and other trace elements (Gurgueira et al. 2002). Other investigators have employed factor analytical and other source apportionment methodologies co try to identify the sources of PM influencing toxicological outcomes (e.g., Chen et al. 2010); however, to date, these methods have been move widely employed in epidemiological studies (e.g., Sarnat et al. 2008).

The development of semicontinuous monitoring methodologies for elemental analysis has facilitated the identification of PM components linked with health effects. In particular, these methods allow the collection of highly time-resolved exposure measurements to correspond to continuous cardiac function data in animals. The Semicontinuous Elements in Aerosol Sampler (SEAS) (Kidwell and Ondov 2001, 2004) uses high-resolution inductively coupled plasma-mass spectrometry (ICP-MS) to perform every-30-min multielemental analysis of [PM. …