Tensiometrical and Rheological Parameters of The Blood Serum of Patients Operated on The Heart

The aim of this study was to establish patterns of changes in surface tension and
dilatational viscoelasticity of serum of patients operated on for the heart under
cardiopulmonary bypass during intra- and intraoperative periods.


Introduction
Timely diagnosis of patients with Coronary Heart Disease (CHD) and acquired valvular pathology leads to decreasing of adverse pathological processes numbers, in particular, atherosclerotic lesions of the main arteries, related to the manifestations of multifocal atherosclerosis. A significant part of such patients showed a high level of proatherogenic lipids in serum [1], which are surfaceactive substances (surfactants). Modern metabolic technologies make it possible to directly determine the molecular markers of various diseases, as, for example, this was done in [2]. However, a detailed chemical blood analysis is a complex and expensive process, while measuring of surface tension and dilatational viscoelasticity is the integral characteristic of blood and other fluids [3,4]. This approach led to a significant activity of researchers in relation to interphase (adsorption and rheological) characteristics of serum and plasma upon various pathologies [5][6][7][8]. The hemodynamic parameters, composition and properties of blood in micro vessels determine not only the behavior of its flow, but also the forces that control the transfer of water and substances through the capillary endothelium [9]. One of the important factors that significantly effectson the capillary hydrostatic pressure and the fluid balance between the microvascular bed and the tissue is blood viscosity and its rheological characteristics.
A significant amount of data has been accumulated as yet, showing the important role of changes in the rheological properties of blood both under normal and pathological processes in the human body [10]. Optimization of blood flow in the extreme conditions serves as an adaptive reaction that increases the reserve capabilities of the circulatory system and the organism as a whole.
On the other hand, increasing of blood viscosity and its rheological properties upon pathology leads to a deterioration in its transport capabilities, the appearance of tissue hypoxia, metabolic changes, which to a certain extent determines the prognosis and nature of the course of the underlying disease [11]. The blood contains various high and low molecular weight surfactants, the concentrations of which vary significantly with various pathologies [12], which manifests in a change in their rheological characteristics. However, data on such changes in patients operated on for the heart under Cardiopulmonary Bypass (CPB) are practically absent. Thus, the aim of this study was to establish patterns of changes in surface tension and dilatational viscoelasticity of serum of patients operated on for the heart under cardiopulmonary bypass during intra-and intraoperative periods.

Experimental Part
Experimental studies of surface tension and dilatational viscoelasticity using drop and bubble form methods were performed using PAT-1 and PAT-2 tensiometers (SINTERFACE Technologies, Berlin, Germany). The technique is described in detail earlier [13].
A drop of blood serum was formed on a vertical capillary with the channel diameter of 1 mm and the external diameter of 3mm. The capillary end face has an internal diameter of 2.96mm. That is, the walls of the end face of the capillary are thin, which eliminates the influence of the contact angle on the shape and size of the droplet.  carried out by the program included in PAT-2, using the Fourier transform and the model described in [14]. Dilatational module E is presented in [15][16][17] as a complex indicator that includes real and imaginary components: where the real part of E r is the elastic modulus, E i is the imaginary part by which the dilatation viscosity is determined. Expression (2) can be transformed into equations for the viscoelastic modulus |E| and phase angle φ : It can be noted that the results using the drop shape method may differ from rheological parameters for a flat surface. For a flat surface with the diffusion mechanism of adsorption of a surfactant, both components of the module are given by the equations [15,16]: The parameter Equations (4) can be written in another form: Here E is the viscoelastic modulus, and ϕ is the phase angle between stress (disturbance) ( dγ ) and deformation (dA). For a spherical drop with radius R during adsorption from the bulk volume of the drop on its surface, JoosP. obtained the equation: It is important to note that for the volume of drops and oscillation frequencies used in this work, the results of calculations according to equation (6)  The analysis was performed using licensed software packages STATISTICA 5.11, Microsoft EXCEL 6.0, and Med Stat [18].

Results and Discussion
In the Figure 1 the curves of the dynamic surface tension of blood serum for a healthy volunteer and a patient with coronary artery disease were showed. It can be seen that the curve for the patient lies much lower, and equilibrium is achieved in 1500-2000 sec. Therefore, drops area oscillations (rheological studies) were performed at a time of more than 2000 s (Figure 1). (Table 1) shows the results of studies of blood serum before, during and after surgery. Six parameters are presented: γ100 s -dynamic surface tension at an adsorption time of 100 seconds, equilibrium surface tension -γ∞ (adsorption time 2500 seconds), viscoelastic modulus, and phase angle ϕ at frequencies of 0.1 and 0.01 Hz. The indicated tensiometric and rheological parameters in a number of studies [9][10][11][12] were recognized as the most informative. One can see that almost all parameters for patients (except for the phase angle at a frequency of 0.1) significantly differ from parameters for healthy people. Both dynamic γ at 100 s and equilibrium γ in patients are 5-6 mN/m less than in healthy ones. This indicates a significant increase in the content of surfactants in the blood of patients. In addition to measuring the tensiometric and rheological parameters for all studied populations, a biochemical analysis of the following blood serum components was performed: glucose, total protein, albumin, urea ( Table 2).   9) 45,5±1,3 Note: 1. * -Statistical significance of differences with respect to the control group at the level of p<0.05.

2.
◊ -statistical significance of the differences with respect to the preoperative period p <0.05. Note: 1. * -Statistical significance of differences with respect to the control group at the level of p<0.05.

2.
◊ -Statistical significance of the differences with respect to the preoperative period p <0.05.