Sex differences in heart rate variability: a longitudinal study in international elite cross-country skiers.

PURPOSE: Exercise-related sudden cardiac deaths (SCD) occur with a striking male predominance. A higher sympathetic tone in men has been suggested as risk factor for SCD. Elite athletes have the highest risk for exercise-related SCD. We aimed to analyze the autonomic nervous system of elite cross-country skiers from Norway, Russia and Switzerland in supine position and after orthostatic challenge in various training periods (TP). METHOD: Measurements of heart rate variability (HRV) were performed on a weekly basis over 1 year using an orthostatic challenge test with controlled breathing. Main outcome parameters were the high-frequency power in supine position (HFsupine) as marker of cardiac parasympathetic activity and the low-frequency/high-frequency power ratio after orthostatic challenge (LF/HFstand) as marker of cardiac sympathetic activation. Training intensity and duration were recorded daily and expressed as training strain. The training year was divided into three TPs. An average of weekly HRV measurements was calculated for each TP. RESULT: Female (n = 19, VO2max 62.0 ± 4.6 ml kg(-1) min(-1), age 25.8 ± 4.3 years) and male (n = 16, VO2max 74.3 ± 6.3 ml kg(-1) min(-1), age 24.4 ± 4.2 years) athletes were included. Training strain was comparable between sexes (all p > 0.05) and changed between TPs (all p < 0.05) while no HRV parameters changed over time. There were no sex differences in HFsupine while the LF/HFstand was significantly higher in male athletes in all TPs. CONCLUSION: For a comparable amount of training, male athletes showed constantly higher markers of sympathetic activity after a provocation maneuver. This may explain part of the male predominance in sports-related SCD.

Optical tweezers study of red blood cell aggregation and disaggregation in plasma and protein solutions.

Kinetics of optical tweezers (OT)-induced spontaneous aggregation and disaggregation of red blood cells (RBCs) were studied at the level of cell doublets to assess RBC interaction mechanics. Measurements were performed under in vitro conditions in plasma and fibrinogen and fibrinogen + albumin solutions. The RBC spontaneous aggregation kinetics was found to exhibit different behavior depending on the cell environment. In contrast, the RBC disaggregation kinetics was similar in all solutions qualitatively and quantitatively, demonstrating a significant contribution of the studied proteins to the process. The impact of the study on assessing RBC interaction mechanics and the protein contribution to the reversible RBC aggregation process is discussed.

Direct measurements of magnetic interaction-induced cross-correlations of two microparticles in Brownian motion.

The effect of magnetic interactions on the Brownian motion of two magnetic microparticles is investigated. The cross-correlations of the thermal fluctuations of the two magnetic microbeads are directly measured using double-trap optical tweezers. It is experimentally demonstrated that the cross-correlation function is governed by the gradient of the magnetic force between the microparticles. The magnetic forces are measured with femtonewton precision, and the magnetic dipole moments of individual microparticles are determined within an accuracy on the order of fA-m(2).

An effect of glycoprotein IIb/IIIa inhibitors on the kinetics of red blood cells aggregation.

The reversible aggregation of red blood cells (RBCs) continues to be of the basic science and clinical interest. Recently it has been reported about a specific binding between fibrinogen and unknown erythrocyte glycoprotein receptors. The aim of this study was to investigate whether the red blood cell aggregation (RBCA) include the cell-cell interaction using the membrane receptors that bind such ligands as fibrinogen or fibronectin. To test this hypothesis the RBCs were incubated with monafram - the drug of the monoclonal antibodies against glycoprotein (GP) IIb/IIIa, with the GPIIb-IIIa receptor antagonist tirofiban, epifibatide and with the fibrinogen inhibiting peptide. It has been found that the RBC incubation with monafram resulted in a marked RBCA decrease mainly in persons with high level of aggregation. Another research session has shown that RBC incubation with fibronectin was accompanied by a significant RBCA rise. The monafram addition to red cell incubation medium resulted in a significant RBCA lowering. The cell incubation with tirofiban and epifibatide issued in RBCA decrease. The similar results were obtained when RBCs were incubated with the fibrinogen inhibiting peptide. Although monafram, tirofiban, eptifibatide and the fibrinogen inhibiting peptide were related to fibrinogen function they didn't inhibit RBCA completely. Therefore, under moderate and low red blood cell aggregation the cell binding is probably related to nonspecific mode. It seems evident that the specific and nonspecific modes of red blood cell aggregate formation could co-exist. Additional theoretical and experimental investigations in this area are needed.

Cellular viscoelasticity probed by active rheology in optical tweezers.

A novel approach to probe viscoelastic properties of cells based on double trap optical tweezers is reported. Frequency dependence of the tangent of phase difference in the movement of the opposite erythrocyte edges while one of the edges is forced to oscillate by optical tweezers appeared to be highly dependent on the rigidity of the cellular membrane. Effective viscoelastic parameters characterizing red blood cells with different stiffnesses (normal and glutaraldehyde-fixed) are determined. It is shown that the photo-induced effects caused by laser trapping at the power level used in the experiments are negligible giving the possibility to use the offered technique for dynamic monitoring of soft materials viscoelastic properties.

Normal and system lupus erythematosus red blood cell interactions studied by double trap optical tweezers: direct measurements of aggregation forces.

Direct measurements of aggregation forces in piconewton range between two red blood cells in pair rouleau are performed under physiological conditions using double trap optical tweezers. Aggregation and disaggregation properties of healthy and pathologic (system lupus erythematosis) blood samples are analyzed. Strong difference in aggregation speed and behavior is revealed using the offered method which is proposed to be a promising tool for SLE monitoring at single cell level.