P721Shear stress induced unfolding of von willebrand factor may be involved in the premature development of myocardial infarction

Background

Normally, von Willebrand factor (vWF) becomes highly reactive with platelets upon unfolding into a fibrillar conformation at critical shear rate (more than 5000 s–1), that may occur in stenotic arteries. At shear rates below critical value (1200–1300 s–1), which occur in intact coronary arteries, normally there is no conformational rearrangement of vWF. Pathologic unfolding of vWF at shear rates below critical value may increase a risk of the development of coronary thrombosis. There is little information on the role of shear stress induced conformational rearrangement of vWF in the development of myocardial infarction in young individuals.

Purpose

To investigate vWF-dependent platelet adhesion of patients with premature myocardial infarction at shear rates below critical value (1200–1300 s–1).

Methods

Using a microfluidic system, we measured platelet adhesion to a fibrinogen-coated optical surface at shear rates of 1200–1300 s–1 during 10 minutes. We assessed platelet-rich plasma of 8 male persons 40–52 years old, who had previous myocardial infarction at the age of 34–39. The control group comprised 6 healthy male volunteers 30–55 years old. We compared the intensity of scattered laser light measured in volts (V) at 10th minute. To study vWF-dependent platelet adhesion, we blocked GPIb receptor with monoclonal antibody to inhibit platelet interaction with vWF. To compare the intensity of vWF-dependent platelet adhesion with normally occurring adhesion to fibrinogen, we blocked GPIIb/IIIa receptor with monoclonal antibody.

Results

The inhibition of GPIb vWF-receptor decreased platelet adhesion to fibrinogen surface at shear rates of 1200–1300 s–1 by 17.8±4.7% in healthy volunteers and by 92±2.8% in persons with premature myocardial infarction (p<0.05). Inhibition of GPIIb/IIIa receptor decreased platelet adhesion by 91.5±3.8% in healthy volunteers and by 97.3±3.2% in persons with premature myocardial infarction.

Conclusion

Pathologic unfolding of vWF at shear rates below critical value may be involved in the development of premature myocardial infarction.

Acknowledgement/Funding

This work was supported by the grant of the Russian Science Foundation (project #16-15-10098)

Kinetics of a solid-state laser with polarizable saturable absorber

In this work we present a numerical study of a three-level laser containing a polarizable saturable absorber inside the cavity. This model allows us to study the kinetics of solid-state lasers in a general form. The stability of Q-switching regime is analyzed by means of numerical solution of rate equations; and main results of our analysis let us suggest that under certain conditions, the laser may pass from unstable relaxation oscillations to a stable CW operation by changing the mutual orientation of the absorber and polarizer, or by choosing the pump level.