Table 1.
Vehicular emissions and heart rate variability changes
| Study | Subject exposure method | Characterization of HRV changes | BC levels |
|---|---|---|---|
| A. In vivo animal study | |||
| 1. Anselme et al. (2007) | Healthy and CHF rats exposed to diesel emissions | Immediate decrease in RMSSD in both CHF and healthy rats immediately after exposure, returning to baseline after 2.5 h | BC not measured |
| B. Human studies with accurate exposure | |||
| 1. Schwartz et al. (2005b) | Subjects lived adjacent to same urban road to which monitor was adjacent, less than 1 km distant | Monotonic decrease in SDNN with increase in BC exposure; significant BC associations in seven of eight tests (SDNN, RMSSD, PNN50, LF/HF, 1 and 24-h averages); no significant associations in eight tests for PM2.5 without BC (“non-traffic secondary particles”) | BC mean = 1.2 μg/m3 |
| 2. Adar et al. (2007) | Monitor followed subjects during activities, in residence at night | For change of one IQR, BC significantly associated with changes in all six measures of HRV, for both 5-min and 24-h means; sharply increased exposure to BC when subjects on buses associated with changes of similar magnitude in all six HRV measures (decreases in SDNN, PNN50 + 1, RMSSD, LF, and HF; increase in LF/HF), similar to Schwartz et al. (2005b) | BC mean not given; BC IQR for all periods was 330 ng/m3; for bus periods, IQR was 2911 ng/m3 |
| 3. Riediker et al. (2004b) | Presence of young patrol officers in vehicle for 9 h before tests | Significant increases in SDNN, PNN50 associated with “speed change” source factor, (braking and diesel emissions), but not “crustal,” “steel wear” or gasoline factors | BC not measured |
| 4. Ebelt et al. (2005) | Personal monitors in panel study in Vancouver | Estimated non-sulfate urban PM2.5 associated with decreased RMMSD, sulfate not associated | BC not measured |
| C. Human studies using central monitors not far from street level (horizontal exposure misclassification) | |||
| 1. Wheeler et al. (2006) | Central monitor for greater Atlanta area subjects | EC associated with SDNN changes in only one of four tests, NO2 in only 4 of 13 tests; authors discuss exposure error due to spatial variability of NO2, note “this greater exposure error is consistent with the fact that traffic, which varies spatially over short distances, is a significant source of outdoor NO2.” | EC mean = 1.6 μg/m3 |
| 2. Park et al. (2005) | Central monitor for subjects living within 40 km of monitor | BC associated with one of four measures of HRV changes; exposure discussed in context of PM2.5 (little exposure error) but not discussed for BC | BC mean = 0.92 μg/m3 |
| D. Studies using highly elevated central monitors (horizontal and vertical exposure misclassification) | |||
| 1. Luttmann-Gibson et al. (2006) | Central monitor elevated 400 feet above town where subjects lived, a mile from monitor | For IQR change in PM2.5 or sulfate, significant reductions in SDNN, RMSSD, HF, and LF (sulfate borderline for LF), no associations for BC; exposure error not discussed | BC mean = 1.0 μg/m3 |
SDNN standard deviation of normal-to-normal intervals, RMSSD square root of mean squared difference between adjacent normal-to-normal intervals, PNN50 percentage of adjacent normal-to-normal intervals differing by more than 50 ms, HF high-frequency power, LF low frequency power, LF/HF ratio LF to HF, RR risk ratio, OR odds ratio, IQR interquartile range increase, SD standard deviation