Abstract
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 microg/m3, 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 CAPs 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: CAPs 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.