Oxygen transport in anaemia

Cancer-related anemia: pathogenesis, prevalence and treatment

Cancer-related anemia is a cytokine-mediated disorder resulting from complex interactions between tumor cells and the immune system. Overexpression of certain inflammatory cytokines results in shortened survival of red blood cells, suppression of erythroid progenitor cells, impaired iron utilization, and inadequate erythropoietin production. Numerous other factors may also contribute to the development of anemia in cancer patients. The European Cancer Anaemia Survey (ECAS) has provided the most current, comprehensive, prospectively collected data on the incidence and prevalence of anemia among cancer patients, as well as important perspectives on anemia treatment and relationship of hemoglobin and performance status. ECAS enrolled over 15,000 treated and untreated patients with various malignancies from cancer centers in 24 European countries and followed them for up to 6 months. The initial analysis of the ECAS data revealed that 39% of the total cancer patient population was anemic (hemoglobin <12.0 g/dl) at enrollment, although the rate varied according to tumor type, disease status, and cancer treatment status. Of the patients who were not anemic at enrollment and started cancer treatment during the survey, those undergoing chemotherapy--either alone or in combination with radiotherapy--had the highest incidence of anemia (63 and 42%, respectively). Low hemoglobin levels correlated with poor performance status and only 40% of patients who were anemic at some time during the survey received treatment for their anemia. These findings are noteworthy, since a growing body of clinical evidence indicates that the treatment of anemia can significantly improve patients' quality of life and may also improve the clinical outcome.

Significance of an abnormally low or high hemoglobin concentration during pregnancy: special consideration of iron nutrition

An association between moderate anemia and poor perinatal outcomes has been found through epidemiologic studies, although available evidence cannot establish this relation as causal. Anemia may not be a direct cause of poor pregnancy outcomes, except in the case of maternal mortality resulting directly from severe anemia due to hypoxia and heart failure. Preventing or treating anemia, whether moderate or severe, is desirable. Because iron deficiency is a common cause of maternal anemia, iron supplementation is a common practice to reduce the incidence of maternal anemia. Nevertheless, the effectiveness of large-scale supplementation programs needs to be improved operationally and, where multiple micronutrient deficiencies are common, supplementation beyond iron and folate can be considered. High hemoglobin concentrations are often mistaken as adequate iron status; however, high hemoglobin is independent of iron status and is often associated with poor health outcomes. Very high hemoglobin concentrations cause high blood viscosity, which results in both compromised oxygen delivery to tissues and cerebrovascular complications. Epidemiologic studies have also found an association between high maternal hemoglobin concentrations and an increased risk of poor pregnancy outcomes. Evidence does not suggest that this association is causal; it could be better attributed to hypertensive disorders of pregnancy and to preeclampsia. The pathophysiologic mechanism of these conditions during pregnancy can produce higher hemoglobin concentrations because of reduced normal plasma expansion and cause fetal stress because of reduced placental-fetal perfusion. Accordingly, higher than normal hemoglobin concentrations should be regarded as an indicator of possible pregnancy complications, not necessarily as a sign of adequate iron nutrition, because iron supplementation does not increase hemoglobin higher than the optimal concentration needed for oxygen delivery.

Cardiorespiratory response to exercise in patients with thalassemia major

The cardiorespiratory response to exercise was examined in 13 patients, 12 to 22 yr of age, who were in stable condition while receiving regular transfusions for thalassemia major. Before transfusion (Hgb, 10.8 g/dl), the patients had reduced peak oxygen consumption for body weight (by 25%, p less than 0.002) in comparison with 20 age- and sex-matched control subjects (Hgb, 13.8 g/dl). The ventilatory equivalent for carbon dioxide was significantly reduced at all work rates, and end-tidal PCO2 was abnormally high (46.3 versus 40.7 mm Hg, p less than 0.001), but ventilatory reserve, as estimated from pulmonary function tests, was normal. Both heart rate and cardiac output (as estimated by the indirect Fick method) were abnormally high during exercise; at an oxygen consumption of 19 ml/min/kg, heart rate was 13% higher (p less than 0.01) and, at 16 ml/min/kg, cardiac output was 28% higher (p less than 0.001) in the patients than in the control subjects. Nine patients were retested 3 to 8 days after transfusion (Hgb, 13.0 g/dl, p50, 26.4 mm Hg). Neither ventilatory nor circulatory abnormalities improved significantly. In patients 12 to 22 yr of age in stable condition with thalassemia major, we conclude: cardiac output, estimated by the CO2 rebreathing method, is high and arteriovenous O2 extraction is low during exercise; the high cardiac output during exercise is associated with hypoventilation; the high cardiac output is independent of short-term changes in hemoglobin concentration associated with transfusion.

Androgen therapy in hemodialysis patients: I. Effects on red cell oxygen transport

Measures related to red cell oxygen transport were evaluated in 17 hemodialysis patients receiving androgen therapy, 15 untreated hemodialysis patients and 15 normal subjects. Hemoglobin levels were higher in androgen-treated patients than in the untreated population and were directly related to the reticulocyte index. Hill coefficients were normal, and in vivo P5O values were increased to the same degree in both dialysis groups. However, DPG and serum phosphate explained 70% and 12%, respectively, of the variance in P5O in untreated patients but only 2% and 5% in androgen-treated subjects. In contrast, sample pH explained 34% of the variance in P5O in the androgen-treated group and less than 1% in the untreated dialysis population. Despite the relative importance of pH as a determinant of P5O in patients on androgen therapy, the Bohr coefficient in this group was only about half of that in untreated dialysis subjects. Androgen-treated patients also had lower red cell ATP levels. Finally, the expected correlation of MCHC with pH was noted in untreated dialysis subjects but not in patients receiving androgens. We conclude that androgen therapy in hemodialysis patients in addition to increasing red cell production, directly alters red cell metabolism. Moreover, although the androgen regimens used did not change the net oxygen transport characteristics of hemoglobin, they decreased the responsiveness of hemoglobin-oxygen affinity to changes in pH, DPG and phosphate. Thus, red cell adaptation to changes in oxygen supply and/or demand may be limited in androgen treated patients, and the improvement in clinical performance expected from androgen-stimulated erythropoiesis may not be realized.

[Experiments on the medicamental treatment of the noise-induced cochlear damage. Part I. The effect of dipyridamol and allopurinol on the RMP of the cochlea (guinea pig) after noise (author's transl)]

Dipyridamol has in addition to a coronardilatating effect an ati-thrombotic one too. Moreover it facilitates the release of O2 from haemoglobin by increase of the concentration of 2,3-diphosphoglycerate in the erythrocytes. Allopurinol causes a potential resynthesis of ATP in the cells by inhibition of the metabolism of uric acid. Both substances therefore seemed to be suitable for a medicamental therapy of the noise-induced cochlear damage. The expected favourable effect of Dipyridamol and Allopurinol on the organ of Corti after sound exposure (RMP-measurement before and after exposure to pure tone 120 dB SPL) however had not been confirmed by experiment on animals (guinea pig).

Compensatory mechanisms for the severe anaemia caused by haemoglobin Hammersmith

A severely anaemic, but asymptomatic patient, who is a heterozygous carrier of haemoglobin Hammersmith (beta42 (CD1) phenylalanine - Serine), has been studied to elucidate the mechanisms resulting in physiological compensation for the anaemia. Four factors have been investigated: the oxygen affinity of her blood, the cardiac output at rest and during exercise, the blood gas indices, and pulmonary function. It was found that due to the presence of Heinz bodies within the erythrocytes, the level of functional, haemoglobin was considerably less (50 g/l) than that measured by standard methods (87 g/l). In addition a moderate degree of arterial hypoxaemia (arterial oxygen tension = 10.7 kPa (80.4 mmHg) was present which could not be explained on the basis of abnormal pulmonary function. Both of these factors would result in tissue hypoxia, but the finding of consistently normal oxygen tensions ('mixed' venous oxygen tension = 5.4 kPa (40.3 mmHg) in blood obtained from the right atrium, suggested that hypoxia was not present. This was explained by a decreased whole blood oxygen affinity (P50 = 4.6 kPa (34.5 mmHg) at pH 7.4) and an increase in the cardiac index (5.3 L.min.-1m-2). The latter was the result of an increased stroke volume (125 - 135 ml), the heart rate being normal (63/min.). During moderate exercise, further increases at cardiac output were brought about by a change in heart rate alone. It has been calculated that the decrease in whole blood oxygen per se could not account for adequate tissue oxygenation. This is confirmed by the finding of an increased cardiac output in this patient. It is suggested that in any severe haemolytic anaemia, even if the whole blood oxygen affinity is low, cardiac output is probably increased to achieve complete physiological compensation.