Severe elevation of red blood cell number is often associated with hypertension and thromboembolism resulting in severe cardiovascular complications. However, some individuals such as high altitude dwellers cope well with an increased hematocrit level. We analyzed adaptive mechanisms to excessive erythrocytosis in our transgenic (tg) mice that, due to hypoxia-independent erythropoietin (Epo) overexpression, reached hematocrit values of 0.8 to 0.9 without alteration of blood pressure, heart rate, or cardiac output. Extramedullar erythropoiesis occurred in the tg spleen, leading to splenomegaly. Upon splenectomy, hematocrit values in tg mice decreased from 0.89 to 0.62. Tg mice showed doubled reticulocyte counts and an increased mean corpuscular volume. In tg mice, plasma volume was not elevated whereas blood volume was up to 25% of the body weight compared with 8% in wild-type (wt) siblings. Although plasma viscosity did not differ between tg and wt mice, tg wholeblood viscosity increased to a lower degree (4-fold) than expected from corresponding hemoconcentrated wt blood (8-fold). This moderate increase in viscosity is explicable by the up to 3-fold higher elongation of tg erythrocytes at physiologic shear rates. Apart from the nitric oxide-mediated vasodilation we reported earlier, adaptation to high hematocrit levels in tg mice involves regulated ele- IntroductionHigh hematocrit levels are observed in patients suffering from erythrocytoses such as polycythemia vera and chronic mountain sickness, as well as in lowlanders at high altitude and erythropoietin (Epo)-abusing athletes. Severe elevation of the hematocrit level is often associated with hypertension and thromboembolism, leading to severe clinical complications and frequently to death. 1 However, several reports demonstrate that some individuals can cope with excessive erythrocytosis. One case report describes a Chilean miner working at 5950 m above sea level who reached an hematocrit level of 0.75 without showing impaired health conditions or reduced physical activity. 2 In keeping with this, Peruvian miners living and working at extreme altitude and exposed to cobalt (known to induce Epo expression) have been found to reach hematocrit levels of 0.75 to 0.91. 3 One should keep in mind, however, that adaptive mechanisms of high altitude dwellers might be population dependent as recently shown by differences in nitric oxide (NO) metabolism of the lung in Tibetans and Bolivian Aymara. 4 Excessive erythrocytosis is also found in sports medicine: an endurance athlete with an autosomal dominant erythrocytosis 5 resulting in hematocrit levels up to 0.68 has won several Olympic gold medals in the past. 6 These and other reports 7 indicate that adaptive mechanisms to excessive erythrocytosis exist. Because the blood's flow resistance is regulated mainly by the radius of the vessel and the whole-blood viscosity (reviewed in Pearson and Path 8 ) it is conceivable to expect that adaptation to highly increased hematocrit levels involves vasodilation and reduced vi...

Our data clearly demonstrate that there is a marked activation of blood coagulation and fibrin formation after prolonged cardiac arrest and CPR in humans that is not balanced adequately by concomitant activation of endogenous fibrinolysis. These changes may contribute to reperfusion disorders, such as the cerebral "no-reflow" phenomenon, by inducing fibrin deposition and formation of microthrombi.

Progressive muscle wasting is a central feature of cancer-related cachexia and has been recognized as a determinant of poor prognosis and quality of life. However, until now, no easily assessable clinical marker exists that allows to predict or to track muscle wasting. The present study evaluated the potential of myoglobin (MG) plasma levels to indicate wasting of large locomotor muscles and, moreover, to reflect the loss of MG-rich fiber types, which are most relevant for daily performance. In 17 cancer-cachectic patients (weight loss 22%) and 27 age- and gender-matched healthy controls, we determined plasma levels of MG and creatine kinase (CK), maximal quadriceps muscle cross-sectional area (CSA) by magnetic resonance imaging, muscle morphology and fiber composition in biopsies from the vastus lateralis muscle, body cell mass (BCM) by impedance technique as well as maximal oxygen uptake (VO(2)max). In cachectic patients, plasma MG, muscle CSA, BCM, and VO(2)max were 30-35% below control levels. MG showed a significant positive correlation to total muscle CSA (r = 0.65, p< 0.001) and to the CSA fraction formed by type 1 and 2a fibers (r = 0.80, p < 0.001). However, when adjusted for body height and age by multiple regression, MG yielded a largely improved prediction of total CSA (multiple r = 0.83, p < 0.001) and of fiber type 1 and 2a CSA (multiple r = 0.89, p < 0.001). The correlations between CK and these muscle parameters were weaker, and elevated CK values were observed in 20% of control subjects despite a prior abstinence from exercise for 5 days. In conclusion, plasma MG, when adjusted for anthropometric parameters unaffected by weight, may be considered as a novel marker of muscle mass (CSA) indicating best the mass of MG-rich type 1 and 2a fibers as well as VO(2)max as an important functional readout. CK plasma levels appear to be less reliable because prolonged increases are observed in even subclinical myopathies or after exercise. Notably, cancer-related muscle wasting was not associated with increases in plasma MG or CK in this study.