Mechanisms of Inhaled Fine Particulate Air Pollution-induced Arterial Blood Pressure Changes

BACKGROUND: Epidemiologic studies suggest a positive association between fine particulate matter and arterial blood pressure, but the results have been inconsistent. OBJECTIVES: We investigated the effect of ambient particles on systemic hemodynamics during a 5-hr exposure to concentrated ambient air particles (CAPs) or filtered air (FA) in conscious canines. METHODS: Thirteen dogs were repeatedly exposed via permanent tracheostomy to CAPs (358.1 +/- 306.7 mu g/m(3), mean +/- SD) or FA in a crossover protocol (55 CAPs days, 63 FA days). Femoral artery blood pressure was monitored continuously via implanted telemetry devices. We measured baroreceptor reflex sensitivity before and after exposure in a subset of these experiments (n = 10 dogs, 19 CAP's days, 20 FA days). In additional experiments, we administered alpha-adrenergic blockade before exposure (n = 8 dogs, 16 CAPs days, 15 FA days). Blood pressure, heart rate, rate-pressure product, and baroreceptor reflex sensitivity responses were compared using linear mixed-effects models. RESULTS: CAN exposure increased systolic blood pressure (2.7 +/- 1.0 mmHg, p = 0.006), diastolic blood pressure (4.1 +/- 0.8 mmHg; p < 0.001), mean arterial pressure (3.7 +/- 0.8 mmHg; p < 0.001), heart rate (1.6 +/- 0.5 bpm; p < 0.001), and rate-pressure product (539 +/- 110 bpm x mmHg; p < 0.001), and decreased pulse pressure (-1.7 +/- 0.7 mmHg, p = 0.02). These changes were accompanied by a 20 +/- 6 msec/mmHg (p = 0.005) increase in baroreceptor reflex sensitivity after CAPs versus FA. After alpha-adrenergic blockade, responses to CAPs and FA no longer differed significantly. CONCLUSIONS: Controlled exposure to ambient particles elevates arterial blood pressure. Increased peripheral vascular resistance may mediate these changes, whereas increased baroreceptor reflex sensitivity may compensate for particle-induced alterations in blood pressure.