Air Quality Criteria for Lead Volume II of II - (NEPIS)(EPA) - US ...

AX6-167
Table AX6-5.4 (cont’d). Cardiovascular Effects of Lead on Children
Reference, Study
Location, and Period Study Description Pb Measurement Findings, Interpretation
United States (cont’d)
Gump et al. (2005)
U.S.-Oswego, NY
Dates of study not
given
Europe
Factor-Litvak et al.
(1996)
Europe-Kosovska
Mitrovica and Pristina,
Kosovo
~1992-1993
122 9.5-yr old children participated.
Multiple regression models of percent
changes in systolic and diastolic blood
pressure, heart rate, stroke volume,
cardiac output, and total peripheral
resistance due to acute stress were
adjusted by stepwise entry of up to
50 possible control variables with
quartile blood Pb forced in last. A linear
contrast was used to test dose-response
effects of quartile Pb. Linear Pb terms
were also used.
281 5.5-yr old children studied since
pregnancy participated. Multiple linear
regression models of systolic blood
pressure, adjusted for height, BMI,
gender, ethnic group, and birth order, and
diastolic blood pressure, adjusted for
waist circumference, ethnic group, and
birth order were constructed by stepwise
elimination from a larger pool of
potential confounding variables and
retained if they modified the linear blood
Pb coefficient by more the 10%.
Contemporary blood Pb
quartile:
1st quartile: 1.5-2.8 µg/dL
2nd quartile: 2.9-4.1 µg/dL
3rd quartile: 4.2-5.4 µg/dL
4th quartile: 5.5-13.1 µg/dL
Blood Pb arithmetic mean
(range):
22.7 µg/dL (5-55)
All ∃ represent percent change in outcome from nonstress to stress
condition for each change in 1 µg/dL blood Pb.
Systolic blood pressure: ∃ = !0.009 (95% CI: !0.74, 0.055)
Diastolic blood pressure: ∃ = 0.069 (95% CI: !0.001, 0.138)
Heart rate: ∃ = 0.013 (95% CI: !0.046, 0.072)
Stroke volume: ∃ = !0.069 (95% CI: !0.124, !0.015)
Cardiac output: ∃ = !0.056 (95% CI: !0.113, 0.001)
Total peripheral resistance: ∃ = 0.088 (95% CI: 0.024, 0.152)
Mean successive difference of cardiac interbeat interval:
∃ = !0.028 (95% CI: (!0.098, 0.042)
Despite low power to detect significant effects, blood pressure, cardiac
output, and total peripheral resistance change to stress were associated
with contemporary blood Pb. Stepwise modeling creates unique
models for each outcome. Some models had up to 12 control variables
plus Pb, an excessive number for only 122 subjects. Scatter plots of
regression with linear Pb and bar charts of response to quartile Pb
showed obvious non-linearity, though all Pb effects were modeled as
linear effects. Probability of contemporary exposure to mercury and
PCB’s was very high. No model diagnostic testing reported.
For each increase of 1 µg/dL of blood Pb:
Systolic blood pressure: ∃ = 0.054 (95% CI: !0.024, 0.13)
Diastolic blood pressure: ∃ = 0.042 (95% CI: !0.01, 0.090)
Despite low power to detect significant effects, there was a marginally
significant tendency for blood pressure to be positively associated with
blood Pb. Stepwise multiple regression may have capitalized on
chance results. The linear Pb term may have reduced the ability to
detect significant effects of Pb if the modeled relationship were
nonlinear. Log Pb was tested but not reported. A quadratic Pb term
was reported nonsignificant. No model diagnostics reported.