Adaptive force sonorheometry for assessment of whole blood coagulation

Abstract

Background: Viscoelastic diagnostics that monitor the hemostatic function of whole blood (WB), such as thromboelastography, have been developed with demonstrated clinical utility. By measuring the cumulative effects of all components of hemostasis, viscoelastic diagnostics have circumvented many of the challenges associated with more common tests of blood coagulation.

Methods: We describe a new technology, called sonorheometry, that adaptively applies acoustic radiation force to assess coagulation function in WB. The repeatability (precision) of coagulation parameters was assessed using citrated WB samples. A reference range of coagulation parameters, along with corresponding measurements from prothrombin time (PT) and partial thromboplastin time (PTT), were obtained from WB samples of 20 healthy volunteers. In another study, sonorheometry monitored anticoagulation with heparin (0-5 IU/ml) and reversal from varied dosages of protamine (0-10 IU/ml) in heparinized WB (2 IU/ml).

Results: Sonorheometry exhibited low CVs for parameters: clot initiation time (TC1), <7%; clot stabilization time (TC2), <6.5%; and clotting angle (theta), <3.5%. Good correlation was observed between clotting times, TC1 and TC2, and PTT (r=0.65 and 0.74 respectively; n=18). Linearity to heparin dosage was observed with average linearity r>0.98 for all coagulation parameters. We observed maximum reversal of heparin anticoagulation at protamine to heparin ratios of 1.4:1 from TC1 (P=0.6) and 1.2:1 from theta (P=0.55).

Conclusions: Sonorheometry is a non-contact method for precise assessment of WB coagulation.

Fig. 1

(a) Depiction of the sonorheometry mechanism. An ultrasound transducer generates acoustic radiation force, which is incident upon a 1 ml sample of whole blood. Resulting displacements are evident as shifts in the returning echoes. (b) Diagram of the sonorheometry signature curve with coagulation parameters clot initiation time (TC₁), clot stabilization time (TC₂), and clotting angle (θ).

Fig. 2

PTT test results and sonorheometry measurements were obtained from citrated WB samples of 20 healthy subjects. Correlation values and linear regression analysis are shown for PTT versus sonorheometry parameters (a) clot initiation time, TC₁, and (b) clot stabilization time, TC₂. Lines indicate the least squares best-fit line through the data. Circles mark two subjects who were flagged by the Core Laboratory at the University of Virginia as having high PTT test results.

Fig. 3

Correlation values and linear regression analysis (n=5) are shown for (a) clotting angle ϴ (median ± IQR), (b) clot initiation time TC₁ (mean ± SD), (c) and clot stabilization time TC₂ (mean ± SD) versus heparin dosage.

Fig. 4

(a) Sonorheometry characteristic curves from a single volunteer are displayed for varied dosages of heparin and protamine: (I) Control; no protamine, no heparin (II) 1.4:1; 2.8 IU protamine, 2 IU heparin/ml blood (III) 1:1; 2 IU protamine, 2 IU heparin/ml blood (IV) 0:1; 0 IU protamine, 2 IU heparin/ml blood. (b) Clot initiation times, TC₁, and (c) clotting angle, θ, are illustrated versus protamine to heparin dosage ratios (n=5). At all protamine to heparin ratios, concentration of heparin is 2 IU/ml blood. Results are expressed as mean ± SD (TC₁; 4b) or median ± IQR (θ; 4c). Significance values (P values) were calculated for each protamine to heparin ratio in comparison to the control. *P<0.05 versus control using unpaired, 2-tailed t-test (TC₁; 4b) or Mann-Whitney U-test (θ; 4c).