Laser-light scattering, a new method for continuous monitoring of platelet activation in circulating fluid

We evaluated a novel technique of laser-light scattering (LLS) to detect platelet-volume changes continuously, reflecting platelet aggregation in circulating fluid. Carotid arteries from 20 dogs were mounted in a dual perfusion chamber. Balloon angioplasty (BA) was performed and arteries perfused with platelet-rich plasma (PRP). A He-Ne laser beam was passed through cuvettes connected to tubing draining the arteries. From the angle of incidence, the average volume of aggregates was measured by the ratio of scattering light at 1 to 5 degrees, spread on the diode array of a multichannel analyzer. Platelet volume varied linearly with the scattered light ratio at 1 to 5 degrees (y = -24.2 + 27.6 x (y = particle size, mum(3); x = scattered light ratio at 1/5 degrees)). For comparison, we used an electronic particle counter (Coulter counter) to measure platelet volume. P-selectin expression was measured to confirm platelet activation. Comparing 10 uninjured and 10 BA-injured arteries, we found that platelet volume as measured with LLS increased from 21.6 +/- 4.1 to 52.1 +/- 12.5 mum(3) (P < .003); as measured with the Coulter counter, it increased from 29.9 +/- 2.4 to 62.3 +/- 7.0 μm(3) (P < .005). Six BA-injured arteries perfused with PRP and aspirin (0.2 mg/mL) were compared with six arteries treated with BA alone. The aspirin decreased platelet volume as measured with LLS from 56.2 +/- 11.8 to 40.2 +/- 12.7 mum(3) (P < .01); the Coulter counter revealed a decrease from 51.9 +/- 18.5 to 38.8 +/- 14.2 μm(3) (P < .001). Coulter counter and LLS results were correlated: r = 0.74, P < .05. The peak of P-selectin expression coincided with peak platelet volume. These data demonstrate that increases in circulating-platelet size stimulated by endovascular injury can be reliably and continuously monitored with the use of LLS.