Blood Volume in Health and Disease

The interpretation of measured red cell mass and plasma volume in patients with elevated PCV values

Various formulae using both height and weight have been proposed to interpret measured red cell mass (RCM) and plasma volume (PV). This paper compares four different methods for evaluating these measurements in 50 males with PCV values above 0.51 and three different methods for evaluating results in 50 females with PCV values above 0.49. Overall there was close agreement in the RCM result expressions by all methods for both males and females except at extremes of height and/or weight. The incidence of absolute polycythaemia in both sexes was influenced by the width of the normal range. When this was taken into account overall the incidence of polycythaemia was similar, but in a small number of individuals there were discrepancies of interpretation. These individual patient differences establish that decisions regarding further investigations of a patient must not rest on a strict interpretation of a measured RCM. The various methods of measured PV interpretation gave dissimilar results--in particular by one of the male PV interpretation methods. The differences in the methods almost certainly reflect methodological discrepancies in the original techniques used to establish the normal values. The differences in result expression for PV would however lead to a different incidence of relative, low plasma volume, polycythaemia by the various techniques.

Prediction of red cell and blood volumes distribution by various nomograms: do current nomograms overestimate?

BACKGROUND

Currently used formulas for estimation of a person's red cell volume (RCV) by weight and height are decades old and were based on the use of 51Cr isotopes and on a sample population, which may not be reflective of today's population. In this study, the accuracy and precision of the use of 99mTc RCV measurements in volunteers more typical of today's population were evaluated.

STUDY DESIGN AND METHODS

The subjects were volunteers who met the requirements for a standard blood donation.

RESULTS

The mean +/- standard deviation (SD) 99mTc RCV for 127 males (mean weight, 83.2 kg; height, 180 cm) was 2062 +/- 339 mL, and for 101 females (mean weight, 69.5 kg; height, 166 cm) it was 1320 +/- 201 mL. These results were highly correlated with RCV results with the standard extrapolation 51Cr method with stored red blood cells (RBCs) and highly consistent (within +/-10%) by repeated measurements with the same 22 donors over a 3.5-year period. The RCV results correlated with estimates from the current formulas, but were on average 11 to 14 percent lower.

CONCLUSION

The studies demonstrated that 99mTc is a reproducible and precise method for determination of a person's RCV and that current formulas may significantly overestimate the RCV of today's population. This is likely the result of a shift in population characteristics over the past four decades as reflected by an increased mean body mass index (from 25 to 28 kg/m2), which has not resulted in a proportionally increased RCV.

Diagnosis and classification of erythrocytoses and thrombocytoses

An erythrocytosis describes an increased peripheral blood packed cell volume (PCV) and is deemed to be absolute or apparent depending on whether or not the measured red cell mass (RCM) is above the reference range. This reference range must be related to the individual's height and weight to avoid erroneous interpretations using ml/kg total body weight expressions in obesity. Absolute erythrocytoses are divided into primary, where the erythropoietic compartment is intrinsically abnormal, secondary, where the erythropoietic compartment is normal but is responding to external pathological events leading to an increased erythropoietin drive, and idiopathic, where neither a primary nor a secondary erythrocytosis can be established. Both primary and secondary erythrocytoses have congenital and acquired forms. The only form of primary acquired erythrocytosis that has been defined is the clonal myeloproliferative disorder, polycythaemia vera (PV). Modified diagnostic markers for PV are proposed. Thrombocytoses can be classified into primary, where megakaryopoiesis is intrinsically abnormal, secondary, where megakaryopoiesis is normal but increased platelet production is a reaction to some other unrelated pathology, and finally idiopathic. This latter new group would be used for patients not satisfying the criteria for primary or secondary thrombocytoses, if these were more precise and rigidly used than currently is the case. While theoretically congenital and acquired forms of primary and secondary thrombocytoses might exist, only one cause of secondary congenital thrombocytosis has been established, and primary congenital thrombocytosis has not yet been precisely defined. Primary (essential) thrombocythaemia (PT) is one of the forms of primary acquired thrombocytoses. The diagnostic criteria of PT traditionally involve the exclusion of secondary thrombocytoses and other myeloproliferative disorders but marrow histology could hold a key positive diagnostic role if objective histological features of PT were agreed.

Apparent polycythaemia

Patients with apparent polycythaemia are characterised by a raised packed cell volume (PCV; males above 0.51, females above 0.48) but normal red cell mass (RCM; less than 25% greater than predicted). Prediction and interpretation of RCM and PV should be based on height and weight, since the use of body weight alone is misleading. Patients with PCV values up to 0.60 may have apparent polycythaemia but only 18% have a reduced PV (relative polycythaemia). Therefore, the most common cause of the raised PCV is a change in RCM and/or PV within their normal ranges. The clinical associations and possible causes for the RCM/PV changes include male sex, obesity, dehydration, diuretics, smoking, hypertension, alcohol, arterial oxygen desaturation, renal disease and increased catecholamine levels. Retrospective studies of patients with apparent polycythaemia and information from other groups of polycythaemic patients suggest an increased risk of vascular occlusion, although other factors, such as hypertension and smoking, are also involved. Proposed management includes modification of possible underlying causes and examination for risk factors for vascular occlusion. In patients with PCV levels chronically above 0.54 venesection should be used, but patients with PCV values below this level should only be venesected if they are considered to be at risk of vascular occlusion. The suggested target value for PCV for venesected patients is 0.45 or below.

Early adaptations in gas exchange, cardiac function and haematology to prolonged exercise training in man

In order to determine the effect of short-term training on central adaptations, gas exchange and cardiac function were measured during a prolonged submaximal exercise challenge prior to and following 10-12 consecutive days of exercise. In addition, vascular volumes and selected haematological properties were also examined. The subjects, healthy males between the ages of 19 and 30 years of age, cycled for 2 h per day at approximately 59% of pre-training peak oxygen consumption (VO2) i.e., maximal oxygen consumption (VO2max). Following the training, VO2max (l.min-1) increased (P less than 0.05) by 4.3% (3.94, 0.11 vs 4.11, 0.11; mean, SE) whereas maximal exercise ventilation (VE,max) and maximal heart rate (fc,max) were unchanged. During submaximal exercise, VO2 was unaltered by the training whereas carbon dioxide production (VE) and respiratory exchange ratio were all reduced (P less than 0.05). The altered activity pattern failed to elicit adaptations in either submaximal exercise cardiac output or arteriovenous O2 difference. fc was reduced (P less than 0.05). Plasma volume (PV) as measured by 125I human serum albumin increased by 365 ml or 11.8%, while red cell volume (RCV) as measured by 51chromium-labelled red blood cells (RBC) was unaltered. The increase in PV was accompanied by reductions (P less than 0.05) in haematocrit, haemoglobin concentration (g.100 ml-1), and RBCs (10(6) mm-3). Collectively these changes suggest only minimal adaptations in maximal oxygen transport during the early period of prolonged exercise training. However, as evidenced by the changes during submaximal exercise, both the ventilatory and the cardiodynamic response were altered.(ABSTRACT TRUNCATED AT 250 WORDS)

Interpretation of measured red cell mass and plasma volume in males with elevated venous PCV values

A method of interpretation of red cell mass (RCM) and plasma volume (PV) data is described. The results in 188 males with PCV's over 0.50 places the patients in 4 groups: true (absolute) polycythemias, relative (low plasma volume) polycythemias, high normal red cell mass (HNRCM) and 'physiological variant'. Absolute polycythemias were increasingly frequent at higher PCV levels but only reached 100% at a PCV of 0.60. They showed an 18% incidence in the lower PCV range of 0.500-0.519. Relative (low PV) polycythaemia was found in 18% of the patients with PCV values in the range 0.500 to 0.599. Although the HNRCM and 'physiological variant' types found mainly in the lower PCV ranges they occurred at the 0.54 level. While this method of interpretation of RCM and PV data is perhaps arbitrary, it does provide a basis for the proper study of the common group of patients with raised PCV levels in which classification, course and treatment are uncertain. In addition the findings suggest that both RCM and PV should be measured at all levels of PCV over 0.50; that relative (low PV) polycythaemia is a real entity but less common than sometimes believed; that diuretics do not have a notable part in its causation and that the common HNRCM, 'physiological variant' groups are incompletely understood and require further study.

Pure erythrocytosis: reappraisal of a study of 51 cases

Fifty-one cases of pure, primary erythrocytosis were identified and followed at Hôpital Saint-Louis, Paris, and compared with 350 cases of polycythemia vera (PV) observed during the same period. At the initial evaluation, these cases did not differ from PV cases with respect to age, sex ratio, degree of red cell volume increase, and clinical symptoms. They did differ by the absence of splenomegaly, granulocytosis and thrombocytosis. At a late stage of evolution only a few cases developed classical criteria of PV. From this group of apparently homogeneous cases, two subgroups evolved. Sixty percent of the cases were highly responsive to myelosuppression with 32P. The median duration of the first remission was greater than five years, the mean yearly dose of 32P was very low, and there was a low incidence of complications. The other group (40% of cases) was relatively resistant to myelosuppressive agents. The development of better methods of investigate this disorder might help in discriminating these two groups from both an etiological and pathophysiological viewpoint. The thromboembolic risk of these diseases suggests that myelosuppressive therapy should be utilized in older patients with higher risk of vascular accidents, reserving phlebotomy for younger patients and those who are shown to be resistant to 32P therapy.

The pathogenesis of hyperadrenergic postural hypotension in diabetic patients

Patients with diabetes generally exhibit normal plasma catecholamine responses to standing. Some have blunted norepinephrine responses and postural hypotension-hypoadrenergic postural hypotension due to classic diabetic adrenergic neuropathy. Others, including some with postural hypotension, have exaggerated norepinephrine responses to standing. In order to clarify the pathogenesis of this hyperadrenergic state which occurs in a subset of diabetic patients, we studied aldosterone secretion, vascular and metabolic responsiveness to the administration of norepinephrine, and intravascular volumes in four diabetic patients who were selected for their exaggerated plasma norepinephrine responses to standing. Three of the four patients also exhibited (hyperadrenergic) postural hypotension. None of the hyperadrenergic diabetic patients had evidence of hypoaldosteronism or vascular resistance to norepinephrine, but all four patients had subnormal red blood cell masses and the mean (+/-SE) red blood cell mass (13.1 +/- 1.0 ml/kg) was approximately half of that of age- and sex-matched diabetic controls (26.5 +/- 2.7 ml/kg, p less than 0.01). Thus, intravascular volume contraction, specifically a reduction in the red blood cell mass, may play an important role in the pathogenesis of hyperadrenergic state observed in a subset of diabetic patients and in the pathogenesis of hyperadrenergic postural hypotension in affected diabetic patients.

Effect of long-term physical training on total red cell volume

Six months of military training elicited a significant 4% mean increase in total red cell volume (TRC) measured by the 51Cr-labelled red cell method. This increase was associated with a mean 16% increase in predicted maximal oxygen uptake (VO2max). The increases in TRCV and predicted VO2max were inversely related to their initial levels. A statistically highly significant correlation between TRCV and predicted VO2max was observed (r = 0.59). The trained group had larger initial TRCVs than the sedentary group and the subjects who became well conditioned had a significant increase in TRCV, which contrasted with the unchanged TRCV in the subjects who did not become well conditioned. The greatest increase in TRCV (11%) was found in corporals, who had the hardest training. A statistically significant correlation between the changes in TRCV and estimated plasma volume was observed (r = 0.62), P less than 0.001). Owing the 1.8% increase in body weight the TRCV and predicted VO2max in terms relative to the body weight did not demonstrate the changes as clearly as did the absolute values. The factors affecting the TRCV increase are discussed.

Interpretation of measured red cell mass in the diagnosis of polycythaemia

Expression of predicted and measured red cell mass (RCM) in terms of ml/kg body wt. lacks precision. The use of formulae for prediction of normal mean red cell mass derived from the blood volume prediction (BV) of Nadler et al (1962) has been examined. It is proposed that a more accurate determination of mean normal predicted red cell mass (MNRCM) is obtained by using: 0.47 X 0.91 X BV = MNRCM for males; 0.43 X 0.91 X BV = MNRCM for females. The MNRCMs given by these formulae agree with those given by predictions based on lean body mass and surface area. Examination of the '95% confidence limits' of the 'Nadler' prediction indicates that males with measured RCMs greater than 25% and females with measured RCMs greater than 30% above their MNRCM may be regarded as having polycythaemia.