Concentrated ambient particles alter myocardial blood flow during acute ischemia in conscious canines

Abstract

Background: Experimental and observational studies have demonstrated that short-term exposure to ambient particulate matter (PM) exacerbates myocardial ischemia.

Objectives: We conducted this study to investigate the effects of concentrated ambient particles (CAPs) on myocardial blood flow during myocardial ischemia in chronically instrumented conscious canines.

Methods: Eleven canines were instrumented with a balloon occluder around the left anterior descending coronary artery and catheters for determination of myocardial blood flow using fluorescent microspheres. Telemetric electrocardiographic and blood pressure monitoring was available for four of these animals. After recovery, we exposed animals by inhalation to 5 hr of either filtered air or CAPs (mean concentration+/-SD, 349.0+/-282.6 microg/m3) in a crossover protocol. We determined myocardial blood flow during a 5-min coronary artery occlusion immediately after each exposure. Data were analyzed using mixed models for repeated measures. The primary analysis was based on four canines that completed the protocol.

Results: CAPs exposure decreased total myocardial blood flow during coronary artery occlusion by 0.12 mL/min/g (p<0.001) and was accompanied by a 13% (p<0.001) increase in coronary vascular resistance. Rate-pressure product, an index of myocardial oxygen demand, did not differ by exposure (p=0.90). CAPs effects on myocardial blood flow were significantly more pronounced in myocardium within or near the ischemic zone versus more remote myocardium (p interaction<0.001).

Conclusions: These results suggest that PM exacerbates myocardial ischemia by increased coronary vascular resistance and decreased myocardial perfusion. Further studies are needed to elucidate the mechanism of these effects.

Keywords: coronary vasoconstriction; microspheres; myocardial blood flow; myocardial ischemia; particulate air pollution.

Figure 1

Exposure protocol for assessing the effects of CAPs on myocardial blood flow during coronary artery occlusion. After recovery from surgery, dogs were randomized to one of two exposure sequences. Myocardial blood flow was determined with fluorescent microspheres at baseline (no exposure, no coronary artery occlusion) and during a 5-min coronary artery occlusion immediately after 5 hr exposure to either CAPs or filtered air. Exposures in the same animal were separated by a minimum of 1 week.

Figure 2

Transverse sections through the ventricles showing myocardial blood flow in one animal at baseline (left), during coronary artery occlusion immediately after 5 hr exposure to filtered air (center), and during coronary artery occlusion immediately after 5 hr exposure to CAPs (right). At baseline, myocardial blood flow is uniform except for a minor flow deficit at the location of hydraulic balloon occluder implantation. During coronary artery occlusion after exposure to filtered air, myocardial blood flow was diminished in the anterolateral left ventricular myocardium. During coronary artery occlusion after exposure to CAPs, myocardial blood flow to the same region was further diminished.

Figure 3

Total myocardial blood flow at baseline and during coronary artery occlusion after a 5 hr exposure to either filtered air or CAPs. Bars represent model-estimated mean ± SE from four dogs exposed to CAPs on 7 days and filtered air on 9 days.

Figure 4

Myocardial blood flow in tissue not in the ischemic zone compared with tissue within or near the ischemic zone during coronary artery occlusion immediately after 5 hr exposure to either filtered air or CAPs. Bars represent model-estimated mean ± SE from four dogs exposed to CAPs on 7 days and filtered air on 9 days.