Since the original publications by Martini et al. (Dtsch. Arch. Klin. Med. 169: 212-222, 1930) and Fahraeus and Lindqvist (Am. J. Physiol. 96: 562-568, 1931), it has been known that the relative apparent viscosity of blood in tube flow depends on tube diameter. Quantitative descriptions of this effect and of the dependence of blood viscosity on hematocrit in the different diameter tubes are required for the development of hydrodynamic models of blood flow through the microcirculation. The present study provides a comprehensive data base for the description of relative apparent blood viscosity as a function of tube diameter and hematocrit. Data available from the literature are compiled, and new experimental data obtained in a capillary viscometer are presented. The combined data base comprises measurements at high shear rates (u > or = 50 s-1) in tubes with diameters ranging from 3.3 to 1,978 microns at hematocrits of up to 0.9. If corrected for differences in suspending medium viscosity and temperature, the data show remarkable agreement. Empirical fitting equations predicting relative apparent blood viscosity from tube diameter and hematocrit are presented. A pronounced change in the hematocrit dependence of relative viscosity is observed in a range of tube diameters in which viscosity is minimal. While a linear hematocrit-viscosity relationship is found in tubes of < or = 6 microns, an overproportional increase of viscosity with hematocrit prevails in tubes of > or = 9 microns. This is interpreted to reflect the hematocrit-dependent transition from single- to multifile arrangement of cells in flow.

Athletes who wish to resume high-level activities after an injury to the anterior cruciate ligament (ACL) are often advised to undergo surgical reconstruction. Nevertheless, ACL reconstruction (ACLR) does not equate to normal function of the knee or reduced risk of subsequent injuries. In fact, recent evidence has shown that only around half of post-ACLR patients can expect to return to competitive level of sports. A rising concern is the high rate of second ACL injuries, particularly in young athletes, with up to 20% of those returning to sport in the first year from surgery experiencing a second ACL rupture. Aside from the increased risk of second injury, patients after ACLR have an increased risk of developing early onset of osteoarthritis. Given the recent findings, it is imperative that rehabilitation after ACLR is scrutinized so the second injury preventative strategies can be optimized. Unfortunately, current ACLR rehabilitation programs may not be optimally effective in addressing deficits related to the initial injury and the subsequent surgical intervention. Motor learning to (re-)acquire motor skills and neuroplastic capacities are not sufficiently incorporated during traditional rehabilitation, attesting to the high re-injury rates. The purpose of this article is to present novel clinically integrated motor learning principles to support neuroplasticity that can improve patient functional performance and reduce the risk of second ACL injury. The following key concepts to enhance rehabilitation and prepare the patient for re-integration to sports after an ACL injury that is as safe as possible are presented: (1) external focus of attention, (2) implicit learning, (3) differential learning, (4) self-controlled learning and contextual interference. The novel motor learning principles presented in this manuscript may optimize future rehabilitation programs to reduce second ACL injury risk and early development of osteoarthritis by targeting changes in neural networks.

In general, the small number of haemorrheological studies concerning acute changes in long term exercise reveals remarkable small effects, given the substantial changes of pertinent cardiorespiratory parameters. To a large extent, this appears to result from careful maintenance of extra- and intravascular water balance and adequate control of electrolytes. Haemorrheological alterations during long term exercise depend on haematological parameters, especially haematocrit and plasma protein levels, which are acutely changed. During exercise, only small deviations of haematocrit from resting values are seen in the short term. This is explained by the usually constant plasma volume which depends on the amount of fluid intake during exercise. In contrast, the exercise-induced elevation of total intravascular protein content significantly increases the levels of plasma proteins, with the exception of fibrinogen. Although this leads to an increase of plasma viscosity, the absence of substantial haematocrit changes accounts for the remarkably small alterations, if any, of blood viscosity which are observed during long term exercise. Endurance training causes haemodilution by expansion of plasma volume, thus resulting in a reduction of blood and plasma viscosity. Red cell deformability is variable with training as well as during exercise. This appears to be related to methodological problems of measurement as well as to the type of endurance exercise performed. Physiological considerations suggest that the importance, for aerobic work capacity, of haemorrheological changes occurring in long term (submaximal) exercise may be limited. By contrast, this may be different during maximal exercise activity, when the entire cardiovascular reserve has been fully recruited.

Haemorheological and haematological parameters were studied in venous blood samples taken from 8 endurance-trained athletes before and after a marathon run. Viscometry was performed in a 20 microns glass capillary and in a Couette viscometer. Apparent blood viscosity was lower in the capillary than in the rotational viscometer, but significant differences between pre- and post-run samples were not observed in either system. This is presumably due to the absence of changes of haematocrit (pre-run [mean +/- SD]: 0.453 +/- 0.016, post-run: 0.456 +/- 0.018). Although protein concentration increased significantly from 70.8 +/- 2.1 g/l (pre-run) to 76.0 +/- 3.9 g/l (post-run), the difference of plasma viscosity was not statistically significant (pre-run: 1.26 +/- 0.03 cP, post-run: 1.30 +/- 0.07 cP). In all samples, plasma viscosity showed a significant positive correlation with total protein, globulin, albumin, but not with fibrinogen concentration. Cone-plate aggregometry and a filtration technique were used to evaluate red cell aggregation and deformability, two determinants of blood rheology which also were not different between pre- and post-run samples. The absence of viscosity changes in relation to the marathon run may be due to the relative stability of blood and plasma volume, which can be deduced from haematological parameters. Alterations of plasma composition (e.g. acidosis or hyperosmolality) seem to cause only minor, if any, changes of microrheological cell properties.

Background Hand amputation can have a truly debilitating impact on the life of the affected person. A multifunctional myoelectric prosthesis controlled using pattern classification can be used to restore some of the lost motor abilities. However, learning to control an advanced prosthesis can be a challenging task, but virtual and augmented reality (AR) provide means to create an engaging and motivating training. Methods In this study, we present a novel training framework that integrates virtual elements within a real scene (AR) while allowing the view from the first-person perspective. The framework was evaluated in 13 able-bodied subjects and a limb-deficient person divided into intervention (IG) and control (CG) groups. The IG received training by performing simulated clothespin task and both groups conducted a pre- and posttest with a real prosthesis. When training with the AR, the subjects received visual feedback on the generated grasping force. The main outcome measure was the number of pins that were successfully transferred within 20 min (task duration), while the number of dropped and broken pins were also registered. The participants were asked to score the difficulty of the real task (posttest), fun-factor and motivation, as well as the utility of the feedback. Results The performance (median/interquartile range) consistently increased during the training sessions (4/3 to 22/4). While the results were similar for the two groups in the pretest, the performance improved in the posttest only in IG. In addition, the subjects in IG transferred significantly more pins (28/10.5 versus 14.5/11), and dropped (1/2.5 versus 3.5/2) and broke (5/3.8 versus 14.5/9) significantly fewer pins in the posttest compared to CG. The participants in IG assigned (mean ± std) significantly lower scores to the difficulty compared to CG (5.2 ± 1.9 versus 7.1 ± 0.9), and they highly rated the fun factor (8.7 ± 1.3) and usefulness of feedback (8.5 ± 1.7). Conclusion The results demonstrated that the proposed AR system allows for the transfer of skills from the simulated to the real task while providing a positive user experience. The present study demonstrates the effectiveness and flexibility of the proposed AR framework. Importantly, the developed system is open source and available for download and further development.

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Arterial blood samples were obtained from six greyhounds during rest, immediately before, and after a 704-m (7/16th mile) race. Measurements were made of various haematological (red cell count, haemoglobin, packed cell volume, white cell count, plasma proteins) and haemorheological variables. Blood and plasma viscosity were determined at high wall shear stresses (67-200 dynes.cm-2, 670-2000 microN.cm-2) in a 20-microns glass capillary device which was designed to take the diameter dependence of blood viscosity (Fahraeus-Lindqvist effect) into account. Compared to values at rest, substantial haemoconcentration occurred before the race, mainly due to splenic discharge of red cells. Additional haemoconcentration was found after the race. The increase of effective blood viscosity caused by elevation of packed cell volume was greater than the increase in O2 binding capacity resulting from the elevated haemoglobin concentration, suggesting that the haemoconcentration observed in the exercising greyhound does not enhance O2 delivery to skeletal muscle. The main physiological effect of red cell discharge from the contracting spleen appeared to be a consequence of the volume rather than the composition of the circulating blood.

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