The mass and oxygen capacity of the blood in man

Duplicate measures of hemoglobin mass within an hour: feasibility, reliability, and comparison of three devices in supine position

Duplicate measure of hemoglobin mass by carbon monoxide (CO)-rebreathing is a logistical challenge as recommendations prompt several hours between measures to minimize CO-accumulation. This study investigated the feasibility and reliability of performing duplicate CO-rebreathing procedures immediately following one another. Additionally, it was evaluated whether the obtained hemoglobin mass from three different CO-rebreathing devices is comparable. Fifty-five healthy participants (22 males, 23 females) performed 222 duplicate CO-rebreathing procedures in total. Additionally, in a randomized cross-over design 10 participants completed three experimental trials, each including three CO-rebreathing procedures, with the first and second separated by 24 h and the second and third separated by 5-10 min. Each trial was separated by >48 h and conducted using either a glass-spirometer, a semi-automated electromechanical device, or a standard three-way plastic valve designed for pulmonary measurements. Hemoglobin mass was 3 ± 22 g lower (p < 0.05) at the second measure when performed immediately after the first with a typical error of 1.1%. Carboxyhemoglobin levels reached 10.9 ± 1.3%. In the randomized trial, hemoglobin mass was similar between the glass-spirometer and three-way valve, but ∼6% (∼50 g) higher for the semi-automated device. Notably, differences in hemoglobin mass were up to ∼13% (∼100 g) when device-specific recommendations for correction of CO loss to myoglobin and exhalation was followed. In conclusion, it is feasible and reliable to perform two immediate CO-rebreathing procedures. Hemoglobin mass is comparable between the glass-spirometer and the three-way plastic valve, but higher for the semi-automated device. The differences are amplified if the device-specific recommendations of CO-loss corrections are followed.

Determinants and reference values for blood volume and total hemoglobin mass in women and men

Blood volume (BV) is an important clinical parameter and is usually reported per kg of body mass (BM). When fat mass is elevated, this underestimates BV/BM. One aim was to study if differences in BV/BM related to sex, age, and fitness would decrease if normalized to lean body mass (LBM). The analysis included 263 women and 319 men (age: 10-93 years, body mass index: 14-41 kg/m2 ) and 107 athletes who underwent assessment of BV and hemoglobin mass (Hbmass ), body composition, and cardiorespiratory fitness. BV/BM was 25% lower (70.3 ± 11.3 and 80.3 ± 10.8 mL/kgBM ) in women than men, respectively, whereas BV/LBM was 6% higher in women (110.9 ± 12.5 and 105.3 ± 11.2 mL/kgLBM ). Hbmass /BM was 34% lower (8.9 ± 1.4 and 11.5 ± 11.2 g/kgBM ) in women than in men, respectively, but only 6% lower (14.0 ± 1.5 and 14.9 ± 1.5 g/kgLBM )/LBM. Age did not affect BV. Athlete's BV/BM was 17.2% higher than non-athletes, but decreased to only 2.5% when normalized to LBM. Of the variables analyzed, LBM was the strongest predictor for BV (R2  = .72, p < .001) and Hbmass (R2  = .81, p < .001). These data may only be valid for BV/Hbmass when assessed by CO re-breathing. Hbmass /LBM could be considered a valuable clinical matrix in medical care aiming to normalize blood homeostasis.

Intravascular volumes and the influence on anemia assessed by a carbon monoxide rebreathing method in patients undergoing maintenance hemodialysis

INTRODUCTION

Fluid overload is a major challenge in hemodialysis patients and might cause hypervolemia. We speculated that hemodialysis patients reaching dry weight could have undetected hypervolemia and low hemoglobin (Hb) concentration (g/dL) due to hemodilution.

METHODS

The study included hemodialysis patients (n = 22) and matched healthy controls (n = 22). Blood volume, plasma volume, red blood cell volume, and total Hb mass were determined using a carbon monoxide (CO)-rebreathing method in hemodialysis patients reaching dry weight and controls. Blood volume measurements were also obtained by a dual-isotope labeling technique in a subgroup for validation purposes.

FINDINGS

In the hemodialysis group, the median specific blood volume was 89.3 mL/kg (interquartile range [IQR]: 76.7-95.4 mL/kg) and was higher than in the control group (79.9 mL/kg [IQR: 70.4-88.0 mL/kg]; p < 0.037). The median specific plasma volume was 54.7 mL/kg (IQR: 47.1-61.0 mL/kg) and 44.0 mL/kg (IQR: 38.7-49.5 mL/kg) in the hemodialysis and control groups, respectively (p < 0.001). Hb concentration was lower in hemodialysis patients (p < 0.001), whereas no difference in total Hb mass was observed between groups (p = 0.11). A correlation was found between blood volume measured by the CO-rebreathing test and the dual-isotope labeling technique in the control group (r = 0.83, p = 0.015), but not the hemodialysis group (r = 0.25, p = 0.60).

DISCUSSION

The hemodialysis group had increased specific blood volume at dry weight due to high plasma volume, suggesting a hypervolemic state. However, correlation was not established against the dual-isotope labeling technique underlining that the precision of the CO-rebreathing test should be further validated. The total Hb mass was similar between hemodialysis patients and controls, unlike Hb concentration, which emphasizes that Hb concentration is an inaccurate marker of anemia among hemodialysis patients.

Eight weeks of heavy strength training increases hemoglobin mass and V̇o2peak in well-trained to elite female and male rowers

O2-transport and endurance exercise performance are greatly influenced by hemoglobin mass (Hbmass), which largely depends on lean body mass (LBM). This study investigated the effects of 8 wk with three weekly sessions of conventional (3-SET: 3 × 10 reps) or high-volume strength training (10-SET: 5-10 × 10 reps) on LBM, Hbmass, muscle strength, and exercise performance in female and male rowers. Hematological parameters were obtained through CO rebreathing and body composition by dual-energy X-ray absorptiometry (DEXA) scans before and after the training period. Concomitantly, V̇o2peak was determined during 2-km ergometer rowing and muscle strength by isometric midthigh pull. There were no differences in training responses between groups for any of the parameters. Pooled data revealed overall increments for Hbmass (10-SET: 882 ± 199 g to 897 ± 213 g; 3-SET: 936 ± 245 g to 962 ± 247 g, P = 0.02) and V̇o2peak (10-SET: 4.3 ± 1.0 to 4.4 ± 0.9 L·min-1; 3-SET: 4.5 ± 0.9 to 4.6 ± 0.9 L·min-1, P = 0.03), whereas LBM remained unchanged (10-SET: 58.7 ± 10.5 to 58.7 ± 10.1 kg; 3-SET: 64.1 ± 10.8 to 64.5 ± 10.6 kg, P = 0.42). Maximal isometric midthigh pull strength increased (10-SET: 224 ± 47 kg to 237 ± 55 kg; 3-SET: 256 ± 77 kg to 281 ± 83 kg, P = 0.001). Strong associations were observed between LBM and Hbmass and V̇o2peak (r2 = 0.88-0.90), entailing sex differences in Hbmass and V̇o2peak. Normalizing V̇o2peak to LBM reduced the sex difference to ∼10%, aligning with the sex difference in Hbmass·LBM-1. Strength training successfully increased Hbmass and V̇o2peak in elite female and male rowers, without an additional effect from increased training volume. Moreover, sex differences in V̇o2peak were mainly explained by differences in LBM, but likely also by differences in Hbmass·LBM-1.NEW & NOTEWORTHY This study in female and male rowers demonstrates that hemoglobin mass (Hbmass), V̇o2peak, and muscle strength increases with 8 wk of heavy strength training and that this response is not different between conventional (3 × 10 repetitions) and high-volume strength training (10 × 10 repetitions). Moreover, female rowers exhibited less hemoglobin per kilogram of lean body mass compared with their male counterparts, which likely contributes to sex differences in V̇o2peak and rowing performance.

Techniques to Assess the Effect of Sodium-Glucose Cotransporter 2 Inhibitors on Blood Volume in Patients with Diabetic Kidney Disease

BACKGROUND

Sodium-glucose cotransporter 2 (SGLT2) inhibitors exert a kidney protective effect in patients with diabetic kidney disease. Several mechanisms have been proposed, but why precisely SGLT2 inhibition has a kidney protective effect is incompletely understood. Clinical trials using SGLT2 inhibitors have found them to induce a rapid weight loss likely due to loss of sodium and subsequently fluid. While SGLT2 inhibitors are reported to increase hematocrit, it remains unknown whether the natriuretic and aquaretic effect reduces patient's blood volume and whether this could partly explain its kidney protective effects. A blood volume reduction could induce several beneficial effects with reduction in arterial and venous blood pressure as two central mechanisms. The aim of this paper was to review current techniques for assessing patient blood volume that could enhance our understanding of SGLT2 inhibitors' physiological effects.

SUMMARY

Changes induced by SGLT2 inhibitors on erythrocyte volume and plasma volume can be assessed by tracer dilution techniques that include radioisotopes, indocyanine green (ICG) dye, or carbon monoxide (CO). Techniques with radioisotopes can provide direct estimates of both erythrocyte volume and plasma volume but are cumbersome procedures and the radiation exposure is a limitation for repeated measures in clinical studies. Methods more suitable for repeated assessment of erythrocyte and plasma volume include dilution of injected ICG dye or dilution of inhaled CO. ICG dye requires higher precision with timed blood samples and provides only a direct estimate of plasma volume wherefrom erythrocyte volume is estimated. Inhalation of CO is a time-effective and automated method that provides measure of the total hemoglobin mass wherefrom erythrocyte and plasma volumes are estimated.

KEY MESSAGES

A kidney protective effect has been observed in clinical trials with SGLT2 inhibitors, but the underlying mechanisms are not fully understood. Significant weight loss within weeks has been reported in the SGLT2 inhibitor trials and could be related to a reduction in blood volume secondary to increased natriuresis and aquaresis. Alterations in blood volume compartments can be quantified by tracer dilution techniques and further improve our understanding of kidney protection from SGLT2 inhibitors.

A semi-automated device rapidly determine circulating blood volume in healthy males and carbon monoxide uptake kinetics of arterial and venous blood

We examined whether a semi-automated carbon monoxide (CO) rebreathing method accurately detect changes in blood volume (BV) and total hemoglobin mass (tHb). Furthermore, we investigated whether a supine position with legs raised reduced systemic CO dilution time, potentially allowing a shorter rebreathing period. Nineteen young healthy males participated. BV and tHb was quantified by a 10-min CO-rebreathing period in a supine position with legs raised before and immediately after a 900 ml phlebotomy and before and after a 900 ml autologous blood reinfusion on the same day in 16 subjects. During the first CO-rebreathing, arterial and venous blood samples were drawn every 2 min during the procedure to determine systemic CO equilibrium in all subjects. Phlebotomy decreased (P < 0.001) tHb and BV by 166 ± 24 g and 931 ± 247 ml, respectively, while reinfusion increased (P < 0.001) tHb and BV by 143 ± 21 g and 862 ± 250 ml compared to before reinfusion. After reinfusion BV did not differ from baseline levels while tHb was decreased (P < 0.001) by 36 ± 21 g. Complete CO mixing was achieved within 6 min in venous and arterial blood, respectively, when compared to the 10-min sample. On an individual level, the relative accuracy after donation for tHb and BV was 102-169% and 55-165%, respectively. The applied CO-rebreathing procedure precisely detect acute BV changes with a clinically insignificant margin of error. The 10-min CO-procedure may be reduced to 6 min with no clinical effects on BV and tHb calculation. Notwithstanding, individual differences may be of concern and should be investigated further.

Comparison of the automatised and the optimised carbon monoxide rebreathing methods

Recently, a new automated carbon monoxide (CO) rebreathing method (aCO) to estimate haemoglobin mass (Hb_mass) was introduced. The aCO method uses the same CO dilution principle as the widely used optimised CO rebreathing method (oCO). The two methods differ in terms of CO administration, body position, and rebreathing time. Whereas with aCO, CO is administered automatically by the system in a supine position of the subject, with oCO, CO is administered manually by an experienced operator with the subject sitting. Therefore, the aim of this study was to quantify possible differences in Hb_mass estimated with the two methods. Hb_mass was estimated in 18 subjects (9 females, 9 males) with oCO using capillary blood samples (oCOc) and aCO taking simultaneously venous blood samples (aCOv) and capillary blood samples (aCOc). Overall, Hb_mass was different between the three measurement procedures (F = 57.55, p < .001). Hb_mass was lower (p < .001) for oCOc (737 g ± 179 g) than for both aCOv (825 g ± 189 g, -9.3%) and aCOc (835 g ± 189 g, -10.6%). There was no difference in Hb_mass estimated with aCOv and aCOc procedures (p = .12). Three factors can likely explain the 10% difference in Hb_mass: differences in calculations (including a factor for myoglobin flux), body position (distribution of CO in blood circulation) during rebreathing, and time of blood sampling. Moreover, the determination of Hb_mass with aCO is possible with capillary blood sampling instead of venous blood sampling.

Blood volume and hemoglobin mass in long-term heart transplant recipients with and without Anemia

BACKGROUND

In systolic chronic heart failure, a heterogeneous blood volume (BV) regulation can be found with plasma volume expansion in many cases, possibly leading to pseudoanemia. Little is known about the volume status after heart transplantation (HTX). So far, anemia of HTX recipients was solely investigated using hemoglobin-concentration that may be misleading in a clinical context. The objective of the study was whether a difference in plasma volume and red cell volume can be observed in clinically stable heart transplant recipients compared to matched control subjects. Secondary, the aim was to describe anemia in the long-term after HTX based on quantitative data.

METHODS

Blood volume and its constituents red cell volume and plasma volume were quantified using an abbreviated carbon monoxide rebreathing method (aCORM) with focus on its primary measure total hemoglobin mass (Hbmass) and coincidental anemia in 36 (7 women) heart transplant recipients. For comparison, a matched control group of 46 (5 women) healthy subjects was selected.

RESULTS

Neither Hbmass nor blood volumes were significantly different in HTX patients compared to matched healthy control group subjects. The prevalence of anemia 6.3 ± 4.3 years after transplantation was 19%. Hbmass and red cell volume were significantly lower in anemic HTX patients compared to non-anemic patients while plasma volume was not expanded. Various immunosuppressant regimens did not have an effect on Hbmass, plasma volume or red cell volume.

CONCLUSIONS

There was no difference in blood volumes and Hbmass between HTX patients and control subjects. The pathophysiologic blood volume regulation in chronic heart failure does not seem to be longer active in long-term HTX recipients. However, in the long-term after HTX, anemia occurs in a considerable number of patients as true anemia without a clear association with immunosuppression.

TRIAL REGISTRATION

German registry for clinical studies, DRKS00006078. Registered 09 May 2014, https://www.drks.de/drks_web/navigate.do?navigationId=trial . HTML&TRIAL_ID=DRKS00006078.

Reproducibility of the CO rebreathing technique with a lower CO dose and a shorter rebreathing duration at sea level and at 2320 m of altitude

Total hemoglobin mass (Hb_mass) is routinely assessed in studies by the carbon monoxide (CO) rebreathing. Its clinical application is often hindered due to the consequent rise in carboxyhemoglobin (%HbCO) and the concern of CO toxicity. We tested the reproducibility of the CO rebreathing with a CO dose of 0.5 mL/kg body mass (CO_0.5) compared to 1.5 mL/kg (CO_1.5) and when shortening the CO rebreathing protocol. Therefore, CO rebreathing was performed 1×/day in eight healthy individuals on four consecutive days. On each day, either CO_0.5 (CO_0.5-1 and CO_0.5-2) or CO_1.5 (CO_1.5-1 and CO_1.5-2) was administered. Venous blood samples to determine %HbCO and quantify Hb_mass were obtained prior to, and at 6 (T₆), 8 (T₈) and 10 min (T₁₀) of CO rebreathing. This protocol was tested at sea level and at 2320 m to investigate the altitude-related measurement error. At sea level, the mean difference (95% limits of agreement) in Hb_mass between CO_0.5-1 and CO_0.5-2 was 26 g (-26; 79 g) and between CO_1.5-1 and CO_1.5-2, it was 17 g (-18; 52 g)_. The respective typical error (TE) corresponded to 2.4% (CO_0.5) and 1.5% (CO_1.5), while it was 6.5% and 3.0% at 2320 m. With CO_0.5, shortening the CO rebreathing resulted in a TE for Hb_mass of 4.4% (T₈ vs. T₁₀) and 14.1% (T₆ vs T₁₀) and with CO_1.5, TE was 1.6% and 5.8%. In conclusion, the CO dose and rebreathing time for the CO rebreathing procedure can be decreased at the cost of a measurement error ranging from 1.5-14.1%.

Increased Red Cell Volume Is a Relevant Contributing Factor to an Expanded Blood Volume in Compensated Systolic Chronic Heart Failure

BACKGROUND

In patients with chronic heart failure (CHF), volume overload is usually described as an expansion of plasma volume. Additional red cell volume (RCV) expansion is less commonly recognized. So far, little is known about quantitative differences in blood volume status and its different components in patients with stable CHF compared to healthy controls.

METHODS

This study aimed to quantify blood volume and its constituents, RCV and plasma volume, by using an abbreviated carbon monoxide rebreathing method with particular focus on its primary measure total hemoglobin mass in 47 patients (10 women) with systolic CHF and a left ventricular ejection fraction of 29.0 ± 9.4%. These were compared to an age-matched control group of 84 healthy subjects (44 women) using the same method.

RESULTS

In both absolute and body-surface-area-corrected analysis, hemoglobin mass (446 ± 81 vs 353 ± 64 g/m²) as well as RCV (1293 ± 231 vs 1033 ± 176 mL/m²) were significantly increased in CHF. In addition, significant plasma volume expansion was observed in CHF (2069 ± 400 vs 1750 ± 231 mL/m²) and, in conjunction with RCV, constituted a significantly increased blood volume (3361 ± 574 vs 2783 ± 369 mL/m²). In 66% of patients with compensated CHF, RCV was excessive compared to 14% in the control group.

CONCLUSIONS

An increased RCV is a relevant contributing factor to hypervolemia in stable CHF. This is associated with an increased oxygen-carrying capacity, so it may be regarded as a possible compensatory mechanism for a reduced ejection fraction.

CORP: The assessment of total hemoglobin mass by carbon monoxide rebreathing

In this Cores of Reproducibility in Physiology (CORP) article, we present the theory and practical aspects of the carbon monoxide (CO) rebreathing method for the determination of total hemoglobin mass in humans. With CO rebreathing, a small quantity of CO is diluted in O2and rebreathed for a specified time period, during which most of the CO is absorbed and bound to circulating hemoglobin. The dilution principle then allows calculation of the total number of circulating hemoglobin molecules based on the number of absorbed CO molecules and the resulting changes in the fraction of carboxyhemoglobin in blood. Total hemoglobin mass is derived by multiplication with the molar weight of hemoglobin. CO rebreathing has been used for >100 yr and has undergone steady improvement so that today excellent values in terms of accuracy and precision can be achieved if the methodological precautions are carefully followed.

A modern literature review of carbon monoxide poisoning theories, therapies, and potential targets for therapy advancement

The first descriptions of carbon monoxide (CO) and its toxic nature appeared in the literature over 100 years ago in separate publications by Drs. Douglas and Haldane. Both men ascribed the deleterious effects of this newly discovered gas to its strong interaction with hemoglobin. Since then the adverse sequelae of CO poisoning has been almost universally attributed to hypoxic injury secondary to CO occupation of oxygen binding sites on hemoglobin. Despite a mounting body of literature suggesting other mechanisms of injury, this pathophysiology and its associated oxygen centric therapies persists. This review attempts to elucidate the remarkably complex nature of CO as a gasotransmitter. While CO's affinity for hemoglobin remains undisputed, new research suggests that its role in nitric oxide release, reactive oxygen species formation, and its direct action on ion channels is much more significant. In the course of understanding the multifaceted character of this simple molecule it becomes apparent that current oxygen based therapies meant to displace CO from hemoglobin may be insufficient and possibly harmful. Approaching CO as a complex gasotransmitter will help guide understanding of the complex and poorly understood sequelae and illuminate potentials for new treatment modalities.

Diffusive insights: on the disagreement of Christian Bohr and August Krogh at the Centennial of the Seven Little Devils

The year 2010 is the centennial of the publication of the "Seven Little Devils" in the predecessor of Acta Physiologica. In these seven papers, August and Marie Krogh sought to refute Christian Bohr's theory that oxygen diffusion from the lungs to the circulation is not entirely passive but rather facilitated by a specific cellular activity substitute to secretion. The subjects of the present reevaluation of this controversy are Christian Bohr, Professor and Doctor of Medicine (1855-1911), nominated three times for the Nobel Prize; August Krogh, Doctor of Philosophy (1874-1949), Christian Bohr's assistant and later Nobel Prize laureate (1920); and Marie Krogh, née Jørgensen, Doctor of Medicine and wife of August Krogh (1874-1943). The controversy concerned is the transport of oxygen from the lungs into the bloodstream: are passive transport and diffusion capacity together sufficient to secure the oxygen supply in all circumstances or is there an additional specific ("energy consuming" or "active") mechanism responsible for the transport of oxygen from the alveoli into the bloodstream? The present discussion purports to show that the contestants' views were closer than the parties themselves and posterity recognized. Posterity has judged the dispute unilaterally from the Nobel laureate's point of view, but it is evident that August Krogh's Nobel Prize was awarded for the discovery of a cellular activity (Christian Bohr's expression), represented by Krogh's discovery of capillary recruitment. Christian Bohr appears to have been correct in the narrower sense that the diffusion capacity at rest is not great enough to explain the transport during work; a special mechanism intervenes and optimizes the conditions under which diffusion acts. August Krogh, of course, was right in the wider sense that the transport mechanism itself is always entirely passive.

CHANGES IN THE VOLUME OF PLASMA AND ABSOLUTE AMOUNT OF PLASMA PROTEINS IN NEPHRITIS

1. We have not observed gross increases in plasma volume in glomerulonephritis, nephrosis, or nephrosclerosis, even when the concentration of plasma proteins was much below normal. Our results indicate the probability that "hydremic plethora" does not occur. 2. The low protein concentration frequently observed in the plasma in nephritis is not due to increased plasma volume but to a decrease of the total amount of plasma protein in the body. 3. Changes in plasma volume showed no constant relationship to changes in edema.

Stability of hemoglobin mass over 100 days in active men

The purpose of this study was to investigate the suggestion in a recent meta-analysis that variability in hemoglobin mass increases when time between measurements increases from days to months. Hemoglobin mass of six active men was measured with the carbon monoxide method every 1–6 days for 100–114 days (42 ± 3 measurements, mean ± SD). Measurement error for each individual's series was estimated from the standard deviation of consecutive pairwise changes and compared with his total error (standard deviation of all values). Linear trends and periodicities in each series were quantified by regression and spectral analysis. Series with known random error and periodicity were also simulated and analyzed. There were clear differences in the pairwise error of measurement between subjects (range 1.4–2.7%). For five men, there was little difference between the total and pairwise errors; their mean ratio (1.06, 90% confidence limits 0.96–1.17) was less than ratios for simulated sinusoidal series with random error of 2%, amplitude of 2%, and periods of 20–100 days (ratios 1.13–1.21). Spectral analysis clearly revealed such periodicities in the simulated series but not in the series of these subjects. The sixth man, who had donated blood 12 days before commencing measurements, showed errors, trend, and periodicity consistent with gradual restoration of hemoglobin mass. Measurement error of hemoglobin mass does not increase over 100 days. Consequently, hemoglobin mass may be suitable for long-term monitoring of small changes that might occur with training or erythropoietin abuse, taking into consideration the small differences between athletes in errors and trends.

Time and Sample Site Dependency of the Optimized CO-Rebreathing Method

PURPOSE

A new method to estimate hemoglobin mass (Hbmass) requires capillary blood and rebreathing a carbon-monoxide (CO) bolus for 2 min. We hypothesized that incomplete circulatory mixing of CO could confound this method, so we compared capillary with venous blood to determine whether sampling site altered the percentage of carboxyhemoglobin (%HbCO) and the reliability and accuracy of the "2-min Hbmass." The conventional 20-min CO-rebreathing procedure was used as the Hbmass criterion.

METHODS

In the first experiment (N=12), both fingertip capillary and antecubital venous blood were sampled 4 and 6 min after commencing 2 min of CO-rebreathing. Within 8 d, these subjects completed two 2-min and one 20-min CO-rebreathing periods. For the latter, capillary and venous blood were collected simultaneously after two 10-min periods of rebreathing. In a second experiment (N=6), both capillary and venous blood were sampled 4, 6, 8, 10, and 12 min after commencing 2 min of CO-rebreathing. A third experiment (N=6) evaluated the reliability of a modified 2-min CO-rebreathing test with capillary blood sampled at minutes 8 and 10.

RESULTS

Typical error (TE) for the first two 2-min tests was 1.1% (90% confidence limits 0.9-1.8%), but the average Hbmass from 2-min capillary blood was 4.8% lower than from venous blood for the 20-min procedure. In the second experiment, peak venous %HbCO occurred at minute 6, and the difference between capillary and venous values was minimal (mean+/-SD; 0.08+/-0.07, 0.01+/-0.09) at minutes 8 and 10. TE for the third experiment was 1.2% (0.8-2.5%).

CONCLUSION

A modified 2-min CO-rebreathing procedure using capillary or venous blood sampled 8 and 10 min after starting CO-rebreathing allows complete circulatory mixing and provides an accurate and reliable estimate of Hbmass.

Errors of measurement for blood volume parameters: a meta-analysis

The volume of red blood cells (V(RBC)) is used routinely in the diagnostic workup of polycythemia, in assessing the efficacy of erythropoietin administration, and to study factors affecting oxygen transport. However, errors of various methods of measurement of V(RBC) and related parameters are not well characterized. We meta-analyzed 346 estimates of error of measurement of V(RBC) for techniques based on Evans blue (V(RBC,Evans)), 51chromium-labeled red blood cells (V(RBC,51Cr)), and carbon monoxide (CO) rebreathing (V(RBC,CO)), as well as hemoglobin mass with the carbon-monoxide method (M(Hb,CO)), in athletes and active and inactive subjects undergoing various experimental and control treatments lasting minutes to months. Subject characteristics and experimental treatments had little effect on error of measurement, but measures with the smallest error showed some increase in error with increasing time between trials. Adjusted to 1 day between trials and expressed as coefficients of variation, mean errors for M(Hb,CO) (2.2%; 90% confidence interval 1.4-3.5%) and V(RBC,51Cr) (2.8%; 2.4-3.2%) were much less than those for V(RBC,Evans) (6.7%; 4.9-9.4%) and V(RBC,CO) (6.7%; 3.4-14%). Most of the error of V(RBC,Evans) was due to error in measurement of volume of plasma via Evans blue dye (6.0%; 4.5-7.8%), which is the basis of V(RBC,Evans). Most of the error in V(RBC,CO) was due to estimates from laboratories with a relatively large error in M(Hb,CO), the basis of V(RBC,CO). V(RBC,51Cr) and M(Hb,CO) are the best measures for research on blood-related changes in oxygen transport. With care, V(RBC,Evans) is suitable for clinical applications of blood-volume measurement.

Respiratory measurements of cardiac output: from elegant idea to useful test

The measurement of cardiac output was first proposed by Fick, who published his equation in 1870. Fick's calculation called for the measurement of the contents of oxygen or CO2 in pulmonary arterial and systemic arterial blood. These values could not be determined directly in human subjects until the acceptance of cardiac catheterization as a clinical procedure in 1940. In the meanwhile, several attempts were made to perfect respiratory methods for the indirect determination of blood-gas contents by respiratory techniques that yielded estimates of the mixed venous and pulmonary capillary gas pressures. The immediate uptake of nonresident gases can be used in a similar way to calculate cardiac output, with the added advantage that they are absent from the mixed venous blood. The fact that these procedures are safe and relatively nonintrusive makes them attractive to physiologists, pharmacologists, and sports scientists as well as to clinicians concerned with the physiopathology of the heart and lung. This paper outlines the development of these techniques, with a discussion of some of the ways in which they stimulated research into the transport of gases in the body through the alveolar membrane.

A review of the varieties of human haemoglobin in health and disease

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