Transcapillary escape rate of albumin in humans during exercise-induced hypervolemia

Molecular biomarkers for assessing the heat-adapted phenotype: a narrative scoping review

Heat acclimation/acclimatisation (HA) mitigates heat-related decrements in physical capacity and heat-illness risk and is a widely advocated countermeasure for individuals operating in hot environments. The efficacy of HA is typically quantified by assessing the thermo-physiological responses to a standard heat acclimation state test (i.e. physiological biomarkers), but this can be logistically challenging, time consuming, and expensive. A valid molecular biomarker of HA would enable evaluation of the heat-adapted state through the sampling and assessment of a biological medium. This narrative review examines candidate molecular biomarkers of HA, highlighting the poor sensitivity and specificity of these candidates and identifying the current lack of a single 'standout' biomarker. It concludes by considering the potential of multivariable approaches that provide information about a range of physiological systems, identifying a number of challenges that must be overcome to develop a valid molecular biomarker of the heat-adapted state, and highlighting future research opportunities.

The influence of exercise volume and posture on exercise-induced plasma volume expansion

Acute high-intensity interval exercise is known to expand plasma volume 24 h after exercise. Upright exercise posture plays a role in expanding plasma volume by influencing lymphatic outflow and redistributing albumin while supine exercise does not. We examined if further upright and weight-bearing exercises could further promote plasma volume expansion. We also tested the volume of intervals needed to induce plasma volume expansion. To test the first hypothesis, 10 subjects performed intermittent high-intensity exercise (4 min at 85% V̇_O2max , 5 min at 40% V̇_O2max repeated 8 times) on separate days on the treadmill and cycle ergometer. For the second study, 10 subjects performed four, six, and eight intervals of the same interval protocol on separate days. Changes in plasma volume were calculated from changes in hematocrit and hemoglobin. Transthoracic impedance (Z₀ ) and plasma albumin were assessed while seated before and postexercise. Plasma volume increased 7.3% ± 4.4% and 6.3% ± 3.5% following treadmill and cycle ergometer exercise, respectively. For four, six, and eight intervals, plasma volume increased by 6.6% ± 4.0%, 4.7% ± 2.6%, and 4.2% ± 5.6%, respectively. The increases in plasma volume were similar for both exercise modes and all three exercise volumes. There were no differences in Z₀ or plasma albumin content between trials. In conclusion, rapid plasma volume expansion following eight bouts of high-intensity intervals appears to be independent of upright exercise posture (treadmill versus cycle ergometer). Meanwhile, plasma volume expansion was similar after four, six, and eight intervals of cycle ergometry.

Transcapillary escape rate of 125I-albumin in relation to timing of blood sampling: the need for standardization

Background

Increased vascular permeability is an early sign of vascular damage and can be measured with the transcapillary escape rate of albumin (TER_alb). Although TER_alb has a multi-exponential kinetic model, most published TER_alb data are based on mono-exponential kinetic models with variation in blood sampling schemes. Aim of this posthoc study was to evaluate the influence of variation in blood sampling schemes and the impact of mono- or bi-exponential analyses on the calculation of TER_alb. Study participants were part of a cross-over intervention study protocol, investigating effects of sodium loading on blood pressure, endothelial surface layer and microcirculation. Multiple blood samples were drawn between 3 and 60 min after injection of radioactive iodide labeled human serum albumin (rHSA).

Results

In total 27 male participants with 54 measurements were included. For all participants the maximum serum radioactivity was reached within 20 min, while 85% of the participants had their maximum serum activity within 10 min. The TER_alb calculated with the subsequently chosen T_{20–60 min} reference scheme (6.19 ± 0.49%/h) was significantly lower compared to the TER_alb of the T_{3–60 min}, T_{5–60 min}, and T_{max – 60 min} schemes. There was no significant difference between the T_{20–60 min} reference scheme and the T_{10–60 min} and T_{15–60 min} schemes. Bi-exponential kinetic modeling did not result in significant different observations compared to the mono-exponential kinetic analysis.

Conclusions

As there is variation in the timing of the maximum serum radioactivity of rHSA, blood sampling schemes starting before 10 min after administration of rHSA will result in a significant overestimation of TER_alb. In addition, variation in kinetic modeling did not result in significant changes in TER_alb. Therefore, we emphasize the need to standardize TER_alb and for practical and logistical reasons advocate the use of a mono-exponential model with blood sampling starting 20 min after rHSA administration.

Role of Regular Physical Exercise in Tumor Vasculature: Favorable Modulator of Tumor Milieu

The tumor vessel network has been investigated as a precursor of an inhospitable tumor microenvironment, including its repercussions in tumor perfusion, oxygenation, interstitial fluid pressure, pH, and immune response. Dysfunctional tumor vasculature leads to the extravasation of blood to the interstitial space, hindering proper perfusion and causing interstitial hypertension. Consequently, the inadequate delivery of oxygen and clearance of by-products of metabolism promote the development of intratumoral hypoxia and acidification, hampering the action of immune cells and resulting in more aggressive tumors. Thus, pharmacological strategies targeting tumor vasculature were developed, but the overall outcome was not satisfactory due to its transient nature and the higher risk of hypoxia and metastasis. Therefore, physical exercise emerged as a potential favorable modulator of tumor vasculature, improving intratumoral vascularization and perfusion. Indeed, it seems that regular exercise practice is associated with lasting tumor vascular maturity, reduced vascular resistance, and increased vascular conductance. Higher vascular conductance reduces intratumoral hypoxia and increases the accessibility of circulating immune cells to the tumor milieu, inhibiting tumor development and improving cancer treatment. The present paper describes the implications of abnormal vasculature on the tumor microenvironment and the underlying mechanisms promoted by regular physical exercise for the re-establishment of more physiological tumor vasculature.

Impact of Trail Running Races on Blood Viscosity and Its Determinants: Effects of Distance

Blood rheology is a key determinant of tissue perfusion at rest and during exercise. The present study investigated the effects of race distance on hematological, blood rheological, and red blood cell (RBC) senescence parameters. Eleven runners participated in the Martigny–Combes à Chamonix 40 km race (MCC, elevation gain: 2300 m) and 12 others in the Ultra-Trail du Mont Blanc (UTMB, 171 km, elevation gain: 10,000 m). Blood samples were collected before and after the races. After the UTMB, the percentage of RBC phosphatidylserine (PS) exposure was not affected while RBC CD235a levels decreased and RBC-derived microparticles increased. In contrast, after the MCC, RBC PS exposure increased, while RBC CD235a and RBC-derived microparticles levels were not affected. The free hemoglobin and hemolysis rate did not change during the races. RBC aggregation and blood viscosity at moderate shear rates increased after the MCC. RBC deformability, blood viscosity at a high shear rate, and hematocrit decreased after the UTMB but not after the MCC. Our results indicate that blood rheology behavior is different between a 40 km and a 171 km mountain race. The low blood viscosity after the ultra-marathon might facilitate blood flow to the muscles and optimize aerobic performance.

Heat-induced hypervolemia: Does the mode of acclimation matter and what are the implications for performance at Tokyo 2020?

Tokyo 2020 will likely be the most heat stressful Olympics to date, so preparation to mitigate the effects of humid heat will be essential for performance in several of the 33 sports. One key consideration is heat acclimation (HA); the repeated exposure to heat to elicit physiological and psychophysical adaptations that improve tolerance and exercise performance in the heat. Heat can be imposed in various ways, including exercise in the heat, hot water immersion, or passive exposure to hot air (e.g., sauna). The physical requirements of each sport will determine the impact that the heat has on performance, and the adaptations required from HA to mitigate these effects. This review focuses on one key adaptation, plasma volume expansion (PVE), and how the mode of HA may affect the kinetics of adaptation. PVE constitutes a primary HA-mediated adaptation and contributes to functional adaptations (e.g., lower heart rate and increased heat loss capacity), which may be particularly important in athletes of "sub-elite" cardiorespiratory fitness (e.g., team sports), alongside athletes of prolonged endurance events. This review: i) highlights the ability of exercise in the heat, hot-water immersion, and passive hot air to expand PV, providing the first quantitative assessment of the efficacy of different heating modes; ii) discusses how this may apply to athletes at Tokyo 2020; and iii) provides recommendations regarding the protocol of HA and the prospect for achieving PVE (and the related outcomes).

Effect of ingesting carbohydrate only or carbohydrate plus casein protein hydrolysate during a multiday cycling race on left ventricular function, plasma volume expansion and cardiac biomarkers

PURPOSE

Multiday racing causes mild left ventricular (LV) dysfunction from day 1 that persists on successive days. We evaluated ingesting casein protein hydrolysate-carbohydrate (PRO) compared with carbohydrate-only (CHO) during a 3-day mountain bike race.

METHODS

Eighteen male cyclists were randomly assigned to ingest 6.7% carbohydrate without (CHO) or with 1.3% casein hydrolysate (PRO) during racing (~ 4-5 h/day; 68/71/71 km). Conventional LV echocardiography, plasma albumin content, plasma volume (PV) and blood biomarkers were measured before day 1 and post race on day 3.

RESULTS

Fourteen cyclists (n = 7 per group) completed the race. PV increased in CHO (mean increase (95% CI), 10.2% (0.1 to 20.2)%, p = 0.045) but not in PRO (0.4% (- 6.1 to 6.9)%). Early diastolic transmitral blood flow (E) was unchanged but deceleration time from peak E increased post race (CHO: 46.7 (11.8 to 81.6) ms, p = 0.019; PRO: 24.2 (- 0.5 to 48.9) ms, p = 0.054), suggesting impaired LV relaxation. Tissue Doppler mitral annular velocity was unchanged in CHO, but in PRO septal early-to-late diastolic ratio decreased (p = 0.016) and was compensated by increased lateral early (p = 0.034) and late (p = 0.012) velocities. Systolic function was preserved in both groups; with increased systolic lateral wall velocity in PRO (p = 0.002). Effect size increase in serum creatine kinase (CK) activity, CK-MB and C-reactive protein concentrations was less in PRO than CHO (Cohen's d mean ± SD, PRO: 2.91 ± 2.07; CHO: 7.56 ± 4.81, p = 0.046).

CONCLUSION

Ingesting casein hydrolysate with carbohydrate during a 3-day race prevented secondary hypervolemia and failed to curb impaired LV relaxation despite reducing tissue damage and inflammatory biomarkers. Without PV expansion, systolic function was preserved by lateral wall compensating for septal wall dysfunction.

Heat and Dehydration Additively Enhance Cardiovascular Outcomes following Orthostatically-Stressful Calisthenics Exercise

Exercise and exogenous heat each stimulate multiple adaptations, but their roles are not well delineated, and that of the related stressor, dehydration, is largely unknown. While severe and prolonged hypohydration potentially “silences” the long-term heat acclimated phenotype, mild and transient dehydration may enhance cardiovascular and fluid-regulatory adaptations. We tested the hypothesis that exogenous heat stress and dehydration additively potentiate acute (24 h) cardiovascular and hematological outcomes following exercise. In a randomized crossover study, 10 physically-active volunteers (mean ± SD: 173 ± 11 cm; 72.1 ± 11.5 kg; 24 ± 3 year; 6 females) completed three trials of 90-min orthostatically-stressful calisthenics, in: (i) temperate conditions (22°C, 50% rh, no airflow; CON); (ii) heat (40°C, 60% rh) whilst euhydrated (HEAT), and (iii) heat with dehydration (no fluid ~16 h before and during exercise; HEAT+DEHY). Using linear mixed effects model analyses, core temperature (T_CORE) rose 0.7°C more in HEAT than CON (95% CL: [0.5, 0.9]; p < 0.001), and another 0.4°C in HEAT+DEHY ([0.2, 0.5]; p < 0.001, vs. HEAT). Skin temperature also rose 1.2°C more in HEAT than CON ([0.6, 1.8]; p < 0.001), and similarly to HEAT+DEHY (p = 0.922 vs. HEAT). Peak heart rate was 40 b·min⁻¹ higher in HEAT than in CON ([28, 51]; p < 0.001), and another 15 b·min⁻¹ higher in HEAT+DEHY ([3, 27]; p = 0.011, vs. HEAT). Mean arterial pressure at 24-h recovery was not consistently below baseline after CON or HEAT (p ≥ 0.452), but was reduced 4 ± 1 mm Hg after HEAT+DEHY ([0, 8]; p = 0.020 vs. baseline). Plasma volume at 24 h after exercise increased in all trials; the 7% increase in HEAT was not reliably more than in CON (5%; p = 0.335), but was an additional 4% larger after HEAT+DEHY ([1, 8]; p = 0.005 vs. HEAT). Pooled-trial correlational analysis showed the rise in T_CORE predicted the hypotension (r = −0.4) and plasma volume expansion (r = 0.6) at 24 h, with more hypotension reflecting more plasma expansion (r = −0.5). In conclusion, transient dehydration with heat potentiates short-term (24-h) hematological (hypervolemic) and cardiovascular (hypotensive) outcomes following calisthenics.

Changes in acid-base and ion balance during exercise in normoxia and normobaric hypoxia

Purpose

Both exercise and hypoxia cause complex changes in acid–base homeostasis. The aim of the present study was to investigate whether during intense physical exercise in normoxia and hypoxia, the modified physicochemical approach offers a better understanding of the changes in acid–base homeostasis than the traditional Henderson–Hasselbalch approach.

Methods

In this prospective, randomized, crossover trial, 19 healthy males completed an exercise test until voluntary fatigue on a bicycle ergometer on two different study days, once during normoxia and once during normobaric hypoxia (12% oxygen, equivalent to an altitude of 4500 m). Arterial blood gases were sampled during and after the exercise test and analysed according to the modified physicochemical and Henderson–Hasselbalch approach, respectively.

Results

Peak power output decreased from 287 ± 9 Watts in normoxia to 213 ± 6 Watts in hypoxia (−26%, P < 0.001). Exercise decreased arterial pH to 7.21 ± 0.01 and 7.27 ± 0.02 (P < 0.001) during normoxia and hypoxia, respectively, and increased plasma lactate to 16.8 ± 0.8 and 17.5 ± 0.9 mmol/l (P < 0.001). While the Henderson–Hasselbalch approach identified lactate as main factor responsible for the non-respiratory acidosis, the modified physicochemical approach additionally identified strong ions (i.e. plasma electrolytes, organic acid ions) and non-volatile weak acids (i.e. albumin, phosphate ion species) as important contributors.

Conclusions

The Henderson–Hasselbalch approach might serve as basis for screening acid–base disturbances, but the modified physicochemical approach offers more detailed insights into the complex changes in acid–base status during exercise in normoxia and hypoxia, respectively.

Electronic supplementary material

The online version of this article (doi:10.1007/s00421-017-3712-z) contains supplementary material, which is available to authorized users.

Heat stress and dehydration in adapting for performance: Good, bad, both, or neither?

Physiological systems respond acutely to stress to minimize homeostatic disturbance, and typically adapt to chronic stress to enhance tolerance to that or a related stressor. It is legitimate to ask whether dehydration is a valuable stressor in stimulating adaptation per se. While hypoxia has had long-standing interest by athletes and researchers as an ergogenic aid, heat and nutritional stressors have had little interest until the past decade. Heat and dehydration are highly interlinked in their causation and the physiological strain they induce, so their individual roles in adaptation are difficult to delineate. The effectiveness of heat acclimation as an ergogenic aid remains unclear for team sport and endurance athletes despite several recent studies on this topic. Very few studies have examined the potential ergogenic (or ergolytic) adaptations to ecologically-valid dehydration as a stressor in its own right, despite longstanding evidence of relevant fluid-regulatory adaptations from short-term hypohydration. Transient and self-limiting dehydration (e.g., as constrained by thirst), as with most forms of stress, might have a time and a place in physiological or behavioral adaptations independently or by exacerbating other stressors (esp. heat); it cannot be dismissed without the appropriate evidence. The present review did not identify such evidence. Future research should identify how the magnitude and timing of dehydration might augment or interfere with the adaptive processes in behaviorally constrained versus unconstrained humans.

Low-Volume Intense Exercise Elicits Post-exercise Hypotension and Subsequent Hypervolemia, Irrespective of Which Limbs Are Exercised

Introduction: Exercise reduces arterial and central venous blood pressures during recovery, which contributes to its valuable anti-hypertensive effects and to facilitating hypervolemia. Repeated sprint exercise potently improves metabolic function, but its cardiovascular effects (esp. hematological) are less well-characterized, as are effects of exercising upper versus lower limbs. The purposes of this study were to identify the acute (<24 h) profiles of arterial blood pressure and blood volume for (i) sprint intervals versus endurance exercise, and (ii) sprint intervals using arms versus legs.

Methods: Twelve untrained males completed three cycling exercise trials; 50-min endurance (legs), and 5^*30-s intervals using legs or arms, in randomized and counterbalanced sequence, at a standardized time of day with at least 8 days between trials. Arterial pressure, hemoglobin concentration and hematocrit were measured before, during and across 22 h after exercise, the first 3 h of which were seated rest.

Results: The post-exercise hypotensive response was larger after leg intervals than endurance (AUC: 7540 ± 3853 vs. 3897 ± 2757 mm Hg·min, p = 0.049, 95% CI: 20 to 6764), whereas exercising different limbs elicited similar hypotension (arms: 6420 ± 3947 mm Hg·min, p = 0.48, CI: −1261 to 3896). In contrast, arterial pressure at 22 h was reduced after endurance but not after leg intervals (−8 ± 8 vs. 0 ± 7 mm Hg, p = 0.04, CI: 7 ± 7) or reliably after arm intervals (−4 ± 8 mm Hg, p = 0.18 vs. leg intervals). Regardless, plasma volume expansion at 22 h was similar between leg intervals and endurance (both +5 ± 5%; CI: −5 to 5%) and between leg and arm intervals (arms: +5 ± 7%, CI: −8 to 5%).

Conclusions: These results emphasize the relative importance of central and/or systemic factors in post-exercise hypotension, and indicate that markedly diverse exercise profiles can induce substantive hypotension and subsequent hypervolemia. At least for endurance exercise, this hypervolemia may not depend on the volume of post-exercise hypotension. Finally, endurance exercise led to reduced blood pressure the following day, but sprint interval exercise did not.

The physiologic perspective in fluid management in vascular anesthesiology

Vascular surgery patients frequently suffer from atherosclerosis and peripheral arterial occlusive disease generating endothelial dysfunction. Furthermore, ischemia and reperfusion during surgery damage endothelial cells and, especially, the endothelial glycocalix. The damage of the glycocalix promotes an increase in permeability. Not only crystalloids, which freely diffuse between the intravascular and the interstitial compartment, but also colloidal fluids cross from the intravascular space in the interstitial space with the consequence of edema formation. Possible tissue edema may result in an impairment of tissue oxygenation, leading to wound healing disturbances and initiation of inflammatory responses up to tissue apoptosis. Particularly in vascular anesthesia, this possibly means that colloids only should be administered in acute volume resuscitation immediately after unclamping a big vessel for immediate volume restoration. Which colloidal fluid should be administered is still under intense discussion. From a theoretical physiologic point of view, iso-osmolar albumin is the best choice regarding volume effect, antioxidative properties, and protection against destruction of the glycocalix. Nonetheless, albumin experimentally has not lived up to its promise in the clinical setting. Thus, further well-conducted large randomized clinical trials are necessary to ascertain the optimal fluid therapy in vascular surgery patients.

Infusion rate and plasma volume expansion of dextran and albumin in the septic guinea pig

BACKGROUND

Intravenous fluid treatment of hypovolaemia in states of increased capillary permeability, e.g. sepsis, is often accompanied by adverse oedema formation. A challenge is therefore to achieve and maintain normovolaemia using as little plasma volume substitution as possible to minimise interstitial oedema. In the present study, we evaluated the importance of infusion rate for the plasma volume expanding effects of 6% dextran 70 and 5% human albumin in a guinea pig sepsis model.

METHODS

In this prospective, randomised study, 50 anaesthetised adult male Dunkin-Hartley guinea pigs were used. After laparotomy, sepsis was induced by caecal ligation and incision. Three hours later, an infusion (12 ml/kg) of one of the studied fluids was given either over 15 min (bolus group) or over 3 h (continuous group). A sham group underwent the same surgical procedure but did not receive any fluid.

RESULTS

At the end of the experiment 3 h after the start of infusion, plasma volumes in the continuous group and the bolus group, respectively, were: 47.2 ± 5.3 ml/kg and 36.5 ± 3.9 ml/kg (P < 0.001) for 6% dextran 70, and 47.3 ± 7.5 ml/kg and 39.7 ± 2.8 ml/kg (P < 0.01) for 5% albumin. Plasma volume for the sham group at the same time point was 29.9 ± 3.3 ml/kg.

CONCLUSIONS

The study performed on a guinea pig sepsis model showed that the plasma volume expanding effects of fixed volumes of 6% dextran 70 and 5% albumin were greater when given at a slow than at a fast infusion rate.

Importance of the infusion rate for the plasma expanding effect of 5% albumin, 6% HES 130/0.4, 4% gelatin, and 0.9% NaCl in the septic rat

OBJECTIVES

To compare the plasma volume (PV) expanding effect of a fast infusion rate with that of a slow infusion rate of a fixed volume of 5% albumin, of the synthetic colloids, 6% hydroxyethyl starch 130/0.4 and 4% gelatin, and of 0.9% NaCl in a rat sepsis model and to compare the plasma-expanding effect among these fluids.

DESIGN

Prospective, randomized animal study.

SETTING

University hospital laboratory.

SUBJECTS

One hundred and twelve adult male rats.

INTERVENTIONS

Sepsis was induced by cecal ligation and incision followed by closure of the abdomen. After 3 hrs, an infusion of the PV expander under study was started at a volume of 12mL/kg for the colloids and of 48mL/kg for 0.9% NaCl, either for 15 mins or for 3 hrs. A control group underwent the same experimental procedure but no fluid was given.

MEASUREMENTS AND MAIN RESULTS

Three hours after start of the infusion (end of experiment), the plasma-expanding effect was better with a slow than a fast infusion rate for the colloids, especially albumin, but the NaCl groups did not differ significantly from the control group. The PV for the control group was 28.7±3mL/kg. In the slow and the fast infusion groups, it was 38.9±4.3 and 32.6±4.2mL/kg for albumin (p < 0.001), 32.9±4.3 and 29.5±4.4mL/kg for hydroxyethyl starch 130/0.4 (p < 0.05), 31.8±3.9 and 28.2±4.1mL/kg for gelatin (p < 0.05), and 31.8±5.3 and 30.7±6.6mL/kg for NaCl (n.s), respectively.

CONCLUSIONS

The study showed that the PV expansion by a colloid was greater when given at a slow than at a fast infusion rate, an effect more pronounced for albumin. This difference was not seen for NaCl. The PV-expanding effect was poor for NaCl and better for albumin than for the other colloids.

Chronic effect of training on neutrophil functions in humans

We performed this study to evaluate the chronic effect of training on neutrophil functions in humans. Twenty-six university students (14 males and 12 females) with a mean age of 19.1±0.8 years were divided into the athlete group and the control group based on answers given to a written questionnaire. The capacity of circulating neutrophils to ingest bacteria (phagocytosis) and to produce superoxide (nitroblue tetrazolium reduction) was measured under resting conditions in the absence of training activities. In addition, we measured hematological and serum biochemical parameters.The present analyses revealed that the frequency of subjective symptoms concerning susceptibility to infections (sum of males and females) was higher in the athlete group than in the control group (p<0.05). In the investigation of males, hemoglobin and serum protein levels of the athlete group were lower than that of the control group (p<0.01, p<0.05, respectively). Although total and differential leukocyte counts, and phagocytic activity of neutrophils were not significantly different between the groups, superoxide productivity of neutrophils in the male athlete group was higher than that in the control group (p<0.05).Since significant differences were observed in hemoglobin and serum protein levels in the male athletes, the training is considered to have been intense. An increase was noted in the neutrophil superoxide production along with these changes, but no significant difference was observed in the phagocytic activity. Therefore, there is the possibility of superoxide overproduction, which may lead to tissue damage.

Hemolysis induced by an extreme mountain ultra-marathon is not associated with a decrease in total red blood cell volume

Prolonged running is known to induce hemolysis. It has been suggested that hemolysis may lead to a significant loss of red blood cells; however, its actual impact on the erythrocyte pool is unknown. Here, we test the hypothesis that prolonged running with high hemolytic potential decreases total red blood cell volume (RCV). Hemolysis (n = 22) and RCV (n = 19) were quantified in ultra-marathon runners before and after a 166-km long mountain ultra-endurance marathon (RUN) with 9500 m of altitude gain/loss. Assessment of total hemoglobin mass (Hbmass) and RCV was performed using a carbon monoxide rebreathing technique. RUN induced a marked acute-phase response and promoted hemolysis, as shown by a decrease in serum haptoglobin (P < 0.05). Elevated serum erythropoietin concentration and reticulocyte count after RUN were indicative of erythropoietic stimulation. Following RUN, runners experienced hemodilution, mediated by a large plasma volume expansion and associated with a large increase in plasma aldosterone. However, neither Hbmass nor RCV were found to be altered after RUN. Our findings indicate that mechanical/physiological stress associated with RUN promotes hemolysis but this has no impact on total erythrocyte volume. We therefore suggest that exercise 'anemia' is entirely due to plasma volume expansion and not to a concomitant decrease in RCV.

Effects of exercise training on red blood cell production: implications for anemia

Exercise training can increase total Hb and red cell mass, which enhances oxygen-carrying capacity. The possible underlying mechanisms are proposed to come mainly from bone marrow, including stimulated erythropoiesis with hyperplasia of the hematopoietic bone marrow, improvement of the hematopoietic microenvironment induced by exercise training, and hormone- and cytokine-accelerated erythropoiesis. Anemia is one of the most common medical conditions in chronic disease. The effects of exercise training on counteracting anemia have been explored and evaluated. The results of the research available to date are controversial, and it seems that significant methodological limitations exist. However, exercise training might be a promising, additional, safe and economical method to help improve anemia. There is a need for further investigation into the effects of and guidelines for exercise interventions (especially strength training) in this population of patients, particularly among cancer patients who are undergoing or have undergone chemotherapy or radiation treatments. As the available data are limited, additional research to uncover the underlying mechanisms associated with the effects of exercise training on anemia is clearly warranted.

Protein and carbohydrate supplementation during 5-day aerobic training enhanced plasma volume expansion and thermoregulatory adaptation in young men

We examined whether protein and carbohydrate (CHO) supplementation during 5-day training enhanced plasma volume (PV) expansion and thermoregulatory and cardiovascular adaptations in young men. Eighteen men [age 23 ± 4 (SD) yr] were divided into two groups according to supplements: placebo (CNT: 0.93 kcal/kg, 0.00 g protein/kg, n = 9) and protein and CHO (Pro-CHO: 3.6 kcal/kg, 0.36 protein/kg, n = 9). Subjects in both groups performed a cycling exercise at 70% peak oxygen consumption rate (VO2peak), 30 min/day, for 5 consecutive days at 30°C ambient temperature and 50% relative humidity and took either a placebo or Pro-CHO within 10 min after exercise for each day. Before and after training, PV at rest, heart rate (HR), and esophageal temperature (T(es)) during 30-min exercise at 65% of pretraining VO2peak in the same condition as training were determined. Also, the sensitivity of the chest sweat rate (ΔSR/ΔT(es)) and forearm vascular conductance (ΔFVC/ΔT(es)) in response to increased T(es) were determined. After training, PV and cardiac stroke volume (SV) at rest increased in both groups (P < 0.001) but the increases were twofold higher in Pro-CHO than CNT (P = 0.007 and P = 0.078, respectively). The increases in HR from 5 to 30 min and T(es) from 0 to 30 min of exercise were attenuated after training in both groups with greater attenuation in Pro-CHO than CNT (P = 0.002 and P = 0.072, respectively). ΔSR/ΔT(es) increased in CNT (P = 0.052) and Pro-CHO (P < 0.001) and the increases were higher in Pro-CHO than CNT (P = 0.018). ΔFVC/ΔT(es) increased in Pro-CHO (P < 0.001), whereas not in CNT (P = 0.16). Thus protein-CHO supplementation during 5-day training enhanced PV expansion and thermoregulatory adaptation and, thereby, the reduction in heat and cardiovascular strain in young men.

A definition of normovolaemia and consequences for cardiovascular control during orthostatic and environmental stress

The Frank–Starling mechanism describes the relationship between stroke volume and preload to the heart, or the volume of blood that is available to the heart—the central blood volume. Understanding the role of the central blood volume for cardiovascular control has been complicated by the fact that a given central blood volume may be associated with markedly different central vascular pressures. The central blood volume varies with posture and, consequently, stroke volume and cardiac output (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \dot{Q} $$\end{document}) are affected, but with the increased central blood volume during head-down tilt, stroke volume and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \dot{Q} $$\end{document} do not increase further indicating that in the supine resting position the heart operates on the plateau of the Frank–Starling curve which, therefore, may be taken as a functional definition of normovolaemia. Since the capacity of the vascular system surpasses the blood volume, orthostatic and environmental stress including bed rest/microgravity, exercise and training, thermal loading, illness, and trauma/haemorrhage is likely to restrict venous return and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \dot{Q} $$\end{document}. Consequently the cardiovascular responses are determined primarily by their effect on the central blood volume. Thus during environmental stress, flow redistribution becomes dependent on sympathetic activation affecting not only skin and splanchnic blood flow, but also flow to skeletal muscles and the brain. This review addresses the hypothesis that deviations from normovolaemia significantly influence these cardiovascular responses.

Adaptations to high-intensity intermittent exercise in rodents

In humans, exercise-induced plasma volume (PV) expansion is typically associated with an increase in plasma albumin content, due in part to an increase in hepatic albumin synthesis. We tested the ability of a 12-day high-intensity intermittent exercise protocol to induce an increase in PV in rodents. Since albumin synthesis is transcriptionally regulated, we tested the hypothesis that exercise training would induce an increase in hepatic albumin gene expression. Fifty adult male Sprague-Dawley rats weighing between 245 and 350 g were randomly assigned to one of five groups: cage control (CC), sham exercise (sham), continuous moderate-intensity exercise training (MI), high-intensity intermittent exercise training (HI), or a single day of HI training (1-HI). Twenty-four hours after the last training session, rats were anesthetized. PV was determined, and the liver was removed, flash frozen, and stored for later analysis. Citrate synthase (CS) activity of the red quadriceps muscle, a marker of aerobic adaptation, increased with training (MI and HI) and in response to 1-HI (P < 0.05). We did not see a significant exercise-induced PV expansion as PV averaged 23.6 +/- 2.7 ml/kg body wt in the CC group and 26.6 +/- 1.3 ml/kg body wt in the HI group (P > 0.05). However, hepatic albumin mRNA expression, as determined by real-time PCR, increased 2.9 +/- 0.4- and 4.1 +/- 0.4-fold after MI and HI, respectively, compared with CC. A single bout of HI (1-HI) did not alter hepatic albumin mRNA expression. These data demonstrate an increase in both CS activity and hepatic albumin gene expression with 12 days of aerobic exercise training in the rodent with a rapid (within 24 h) adaptation in the skeletal muscle to high-intensity intermittent exercise.

Protein and carbohydrate supplementation after exercise increases plasma volume and albumin content in older and young men

This study examined whether increased plasma volume (PV) and albumin content (Alb(cont)) in plasma for 23 h after exercise were attenuated in older subjects compared with in young adult subjects, and if this attenuation abated by supplementation with protein and carbohydrate (CHO) immediately after exercise. Eight moderately active older (approximately 68 yr) and 8 young (approximately 21 yr) men performed two trials: control (CNT) and Pro-CHO in which subjects consumed placebo (0.5 kcal, 0 g protein, 0.5 mg Na(+) in 3.2 ml total fluid volume/kg body wt) or protein and CHO mixture (3.2 kcal, 0.18 g protein, 0.5 mg Na(+) in 3.2 ml total fluid volume/kg body wt) supplementations, respectively, immediately after high-intensity interval exercise for 72 min [8 sets of 4 min at 70-80% peak oxygen consumption rate (Vo(2peak)) intermitted by 5 min at 20% Vo(2peak)]. PV, Alb(cont), and plasma globulin content (Glb(cont)) were measured before exercise, at the end of exercise, every hour from the 1st to the 5th hour after exercise, and at the 23rd hour after exercise. From 12 h before the start to the end of experiment, food intake was controlled to the age-matched recommended dietary allowances. We found that during the first 4 h after exercise in CNT, Alb(cont) recovered less in the older than the young group by approximately 0.04 g/kg (P < 0.05), while it generally recovered more with Pro-CHO than CNT by approximately 0.09 and approximately 0.04 g/kg in the young and older group, respectively, accompanied by a greater increase in PV by approximately 1 and approximately 2 ml/kg, respectively, during the 23 h after exercise (P < 0.05). Glb(cont) remained constant throughout the experiment in both trials for both age groups. Thus the attenuated responses of Alb(cont) and PV after exercise in older subjects were restored by protein and CHO supplementation immediately after exercise, similarly to young subjects.

Impact of sex and chronic resistance training on human patellar tendon dry mass, collagen content, and collagen cross-linking

Collagen content and cross-linking are believed to be major determinants of tendon structural integrity and function. Sex and chronic resistance training have been shown to alter tendon function and may also alter the key structural features of tendon. Patellar tendon biopsies were taken from untrained men [n = 8, 1 repetition maximum (RM) = 53 +/- 3 kg], untrained women (n = 8, 1 RM = 29 +/- 2 kg), and resistance-trained (10 +/- 1 yr of training) men (n = 8, 1 RM = 71 +/- 6 kg). Biopsies were analyzed for dry mass, collagen content, and collagen cross-linking (hydroxylysylpyridinoline). We hypothesized that these elements of tendon structure would be lower in women than men, whereas chronic resistance training would increase these parameters in men. Tendon dry mass was significantly lower in women than men (343 +/- 5 vs. 376 +/- 8 microg dry mass/mg tendon wet wt, P < 0.01) and was not influenced by chronic resistance training (P > 0.05). The lower tendon dry mass in women tended to reduce (P = 0.08) collagen content per tendon wet weight. Collagen content of the tendon dry mass was not influenced by sex or resistance training (P > 0.05). Similarly, cross-linking of collagen was unaltered (P > 0.05) by sex or training. Although sex alters the water content of patellar tendon tissue, any changes in tendon function with sex or chronic resistance training in men do not appear to be explained by alterations in collagen content or cross-linking of collagen within the dry mass component of the tendon.

Adaptation of coronary microvascular exchange in arterioles and venules to exercise training and a role for sex in determining permeability responses

Studies of physical performance and energy metabolism during and following exercise have shown significant sex-specific musculoskeletal adaptations; less is known of vascular adaptations, particularly with respect to exchange capacity. In response to adenosine (ADO), a metabolite produced during exercise, permeability (P(s)) of coronary arterioles from female pigs changed acutely; the magnitude and direction of the change (Delta P(s)) were determined by training status. In the present study P(s) to albumin was assessed in arterioles (n = 138) and venules (n = 24) isolated from hearts of male (N = 27) and female (N = 59) pigs in the exercise training group (EX). We evaluated the hypothesis that coronary microvessel exchange adapts to endurance exercise training not by altering basal P(s), per se, but by elevating P(s) on exposure to ADO. In contrast, training resulted in a reduction of basal P(s) in all arterioles, and in venules from males, with no change in venules from EX females. Exposure to ADO resulted in the predicted increase in P(s) except for venules from EX males where P(s) was reduced. Delta P(s) responses of arterioles to mediators of adenylyl cyclase (isoproterenol)- and guanylyl cyclase (atrial natriuretic peptide)-signaling pathways were attenuated in EX pigs relative to pigs in the sedentary group. The adaptation of EX arterioles involves an upregulation of a nitric oxide-dependent pathway since nitric oxide synthase inhibition blocks Delta P(s) by ADO. Thus adaptation of microvascular exchange capacity to endurance exercise training not only occurs but also involves multiple mechanisms that differ in arterioles and venules with their relative contribution to net flux being a function of sex.

Patient hydration: a major source of laboratory uncertainty

Movement of body water from compartment to compartment during any time period is attributable to forces active within and upon each space. The result of these forces leads to transfer of water between intravascular and extravascular compartments, as well as shifts between extracellular and intracellular spaces. The importance of these shifts and of the associated mechanism was described by Ernest Starling in 1896 in very much the same manner as it is viewed today. The end result of fluid transfer and its physiological and laboratory consequences has not been fully appreciated. Despite awareness that fluid shifts can affect laboratory analytical results, little recent investigation has addressed the problem in the routine clinical laboratory. Thus, the potential for significant misinterpretation remains. For example, it is known that individual laboratory test values can vary widely, depending on many factors including the subject's posture during and immediately before phlebotomy, leading to significant changes in the interpretation of blood analyte values. Furthermore, a variety of ubiquitous environmental effects have additional impact on fluid distribution and thus on test values. In other words, patient hydration status is a major pre-analytical variable that needs to be addressed by the clinical laboratory. The need to adjust data for patient hydration status is especially important in the case of colloid analytes for which the dynamic range includes a narrow "gray zone" where hydration changes of a few percentage points can change the clinical implications. The crucial importance of this adjustment is underscored by the fact that neither the testing laboratory nor the clinician are aware of this unseen circumstance and are thus compelled to work with data that do not necessarily reflect the clinical situation.

Time course and magnitude of changes in total body water, extracellular fluid volume, intracellular fluid volume and plasma volume during submaximal exercise and recovery in horses

The purpose of the present study was to determine the time course and magnitude of changes in extracellular and intracellular fluid volumes in relation to changes in total body water during prolonged submaximal exercise and recovery in horses. Seven horses were physically conditioned over a 2-month period and trained to trot on a treadmill. Total body water (TBW), extracellular fluid volume (ECFV) and plasma volume (PV) were measured at rest using indicator dilution techniques (D2O, thiocyanate and Evans Blue, respectively). Changes in TBW were assessed from measures of body mass, and changes in PV and ECFV were calculated from changes in plasma protein concentration. Horses exercised by trotting on a treadmill for 75–120 min incurred a 4.2% decrease in TBW. During exercise, the entire decrease in TBW (mean±standard error: 12.8±2.0 l at end of exercise) could be attributed to the decrease in ECFV (12.0±2.4 l at end of exercise), such that there was no change in intracellular fluid volume (ICFV; 0.9±2.4 l at end of exercise). PV decreased from 22.0±0.5 l at rest to 19.8±0.3 l at end of exercise and remained depressed (18–19 l) during the first 2 h of recovery. Recovery of fluid volumes after exercise was slow, and characterized by a further transient loss of ECFV (first 30 min of recovery) and a sustained increase in ICFV (between 0.5 and 3.5 h of recovery). Recovery of fluid volumes was complete by 13 h post exercise. It is concluded that prolonged submaximal exercise in horses favours net loss of fluid from the extracellular fluid compartment.

Time course and magnitude of fluid and electrolyte shifts during recovery from high-intensity exercise in Standardbred racehorses

The present study characterized the fluid and electrolyte shifts that occur in Standardbred racehorses during recovery from high-intensity exercise. Jugular venous blood was sampled from 13 Standardbreds in racing condition, at rest and for 2 h following a high-intensity training workout. Total body water (TBW), extracellular fluid volume (ECFV) and plasma volume (PV) were measured at rest using indicator dilution techniques (D2O, thiocyanate and Evans Blue, respectively). Changes in TBW were assessed from measures of body mass, and changes in PV and ECFV were calculated from changes in plasma protein concentration. Exercise resulted in a 26.9% decrease in PV. At 10 min of recovery TBW and ECFV were decreased by 2.2% and 16.5% respectively, while intracellular fluid volume was increased by 7.1%. There was a continued loss of fluid due to sweating throughout the recovery period such that TBW was decreased by 3.9% at 90 min of recovery. This decrease in TBW was nearly equally partitioned between the extracellular and intracellular fluid compartments. Plasma Na+ and Cl− contents were decreased at 1 min of recovery, but not different from rest by 40 min of recovery. Plasma K+ content at 1 min post exercise was not different from the pre-exercise value; however, by 5 min of recovery K+ content was significantly decreased and it remained decreased throughout the recovery period. It is concluded that there are very rapid and large fluid and electrolyte shifts between body compartments during and after high-intensity exercise, and that full recovery of these shifts requires 90–120 min.

Exogenous oestradiol and progesterone administration does not cause oedema in healthy young women

OBJECTIVE

Oedema is an increase in the extravascular component of extracellular fluid volume (ECFV). Fluid movement across the ECF is controlled by hydrostatic and oncotic pressures, which are influenced by oestradiol and progesterone. Thus we hypothesized that oestradiol decreases, while combined oestradiol + progesterone increases, protein and fluid movement out of the vasculature.

SUBJECTS

Subjects were eight healthy women (22 +/- 2 years).

DESIGN

Oestrogens and progesterone were suppressed with a gonadotropin-releasing hormone antagonist for 16 days; oestradiol (2 x 0.1 mg/day patches) was added for days 5-16 (E(2)) and progesterone (200 mg/day) was added for days 13-16 (E(2)-P(4)).

MEASUREMENTS

We estimated intravascular (plasma) volume (PV), transcapillary albumin escape rate (TER(alb)), and Starling forces (hydrostatic pressures of plasma and interstitium, plasma colloid pressure, capillary filtration coefficient) in the forearm on days 2 (GnRH antagonist), 9 (E(2)) and 16 (E(2)-P(4)).

RESULTS

In E(2), P([E2]) increased from 85 +/- 26 to 984 +/- 136 pmol/ml (P < 0.05), with no change in P([P4]). In E(2)-P(4), P([E2]) increased to 775 +/- 195 pmol/ml and P([P4]) increased from 6.4 +/- 3.2 to 43.8 +/- 16.2 nmol/l, P < 0.05). TER(alb) was lower during E(2) (5.1 +/- 0.9) and E(2)-P(4) (5.0 +/- 1.1) compared to GnRH antagonist (5.8 +/- 0.9%/h, P < 0.05). Plasma volume was unchanged by E(2), and showed a trend (P = 0.07) for an increase during E(2)-P(4) (48.2 +/- 2.9, 49.0 +/- 3.0 and 53.9 +/- 3.5 ml/kg for GnRH antagonist, E(2), E(2)-P(4), respectively). Starling forces were unaffected by hormone treatments. Plasma renin activity and serum aldosterone concentration increased during E(2)-P(4).

CONCLUSIONS

Neither E(2) nor E(2)-P(4) altered TER(alb) sufficiently to impact Starling forces indicating neither E(2) nor P(4) administration at these levels would likely cause oedema.

Sodium Loading Aids Fluid Balance and Reduces Physiological Strain of Trained Men Exercising in the Heat

PURPOSE

This study was conducted to determine whether preexercise ingestion of a highly concentrated sodium beverage would increase plasma volume (PV) and reduce the physiological strain of moderately trained males running in the heat.

METHODS

Eight endurance-trained (.VO2max: 58 mL.kg(-1).min(-1) (SD 5); 36 yr (SD 11)) runners completed this double-blind, crossover experiment. Runners ingested a high-sodium (High Na+: 164 mmol Na+.L(-1)) or low-sodium (Low Na+: 10 mmol Na+.L(-1)) beverage (10 mL.kg(-1)) before running to exhaustion at 70% .VO2max in warm conditions (32 degrees C, 50% RH, V(a) approximately equal to 1.5 m.s(-1)). Beverages (approximately 757 mL) were ingested in seven portions across 60 min beginning 105 min before exercise. Trials were separated by 1-3 wk. Heart rate and core and skin temperatures were measured throughout exercise. Urine and venous blood were sampled before and after drinking and exercise.

RESULTS

High Na+ increased PV before exercise (4.5% (SD 3.7)), calculated from Hct and [Hb]), whereas Low Na+ did not (0.0% (SD 0.5); P = 0.04), and involved greater time to exercise termination in the six who stopped because of an ethical end point (core temperature 39.5 degrees C: 57.9 min (SD 6) vs 46.4 min (SD 4); P = 0.04) and those who were exhausted (96.1 min (SD 22) vs 75.3 min (SD 21); P = 0.03; High Na+ vs Low Na+, respectively). At equivalent times before exercise termination, High Na+ also resulted in lower core temperature (38.9 vs 39.3 degrees C; P = 0.00) and perceived exertion (P = 0.01) and a tendency for lower heart rate (164 vs 174 bpm; P = 0.08).

CONCLUSIONS

Preexercise ingestion of a high-sodium beverage increased plasma volume before exercise and involved less thermoregulatory and perceived strain during exercise and increased exercise capacity in warm conditions.

EFFECT OF HUMAN SPLENIC CONTRACTION ON VARIATION IN CIRCULATING BLOOD CELL COUNTS

1. The human spleen sequesters 200-250 mL densely packed red blood cells. Up to 50% of this viscous blood is actively expelled into the systemic circulation during strenuous exercise or simulated apnoea (breath-hold) diving. The contribution of splenic contraction to changes in the circulating volume of red blood cells (RBCV), as well as the venous concentration of white blood cells (WBC) and platelets (PLT), was investigated following repeated breath-hold apnoeas. 2. Eighteen trained apnoea divers and 18 intact and six splenectomized subjects without diving experience repeated five maximal apnoeas with face immersion in cold water, with 2 min intervals between successive attempts. Venous blood samples were taken before and between consecutive apnoeas, as well as at 0, 10 and 20 min after the last breath hold. Arterial pressure, heart rate and transcutaneous partial pressure of oxygen and carbon dioxide were monitored continuously. 3. Plasma protein concentration decreased by 5.8, 2.2 and 9% in apnoea divers, untrained and splenectomized subjects, respectively, indicating an expansion of plasma volume. The RBCV and venous concentration of WBC, corrected for changes in plasma volume, increased in both trained apnoea divers (4.9+/-1.0 and 14.9+/-3.1%, respectively) and intact subjects (1.7+/-0.8 and 7.2+/-1.8%, respectively), whereas in splenectomized subjects there was no change in RBCV and a delayed increase in WBC concentration. Furthermore, an initial lymphocytosis detected during repeated breath holds in divers and intact subjects was completely absent in splenectomized subjects. None of the groups showed significant changes in PLT concentrations. The well-recognized diving response to apnoea (bradycardia and increased blood pressure) was seen during all breath-hold attempts in all subjects. 4. Repeated breath-holds (apnoeas) contribute to increased RBCV and venous blood concentrations of WBC through splenic contraction.

Progesterone increases plasma volume independent of estradiol

Adequate plasma volume (PV) and extracellular fluid (ECF) volume are essential for blood pressure and fluid regulation. We tested the hypotheses that combined progesterone (P4)-estrogen (E2) administration would increase ECF volume with proportional increases in PV, but that P4would have little independent effect on either PV or ECF volume. We further hypothesized that this P4-E2-induced fluid expansion would be a function of renin-angiotensin-aldosterone system stimulation. We suppressed P4and E2with a gonadotropin-releasing hormone (GnRH) antagonist in eight women (25 ± 2 yr) for 16 days; P4(200 mg/day) was added for days 5–16 (P4) and 17β-estradiol (2 × 0.1 mg/day patches) for days 13–16 (P4-E2). On days 2 (GnRH antagonist), 9 (P4), and 16 (P4-E2), we estimated ECF and PV. To determine the rate of protein and thus water movement across the ECF, we also measured transcapillary escape rate of albumin. In P4, [Formula: see text] increased from 2.5 ± 1.3 to 12.0 ± 2.8 ng/ml ( P < 0.05) with no change in [Formula: see text] (21.5 ± 9.4 to 8.6 ± 2.0 pg/ml). In P4-E2, plasma concentration of P4remained elevated (11.3 ± 2.7 ng/ml) and plasma concentration of E2increased to 254.1 ± 52.7 pg/ml ( P < 0.05). PV increased during P4(46.6 ± 2.5 ml/kg) and P4-E2(48.4 ± 3.9 ml/kg) compared with GnRH antagonist (43.3 ± 3.2 ml/kg; P < 0.05), as did ECF (206 ± 19, 244 ± 25, and 239 ± 27 ml/kg for GnRH antagonist, P4, and P4-E2, respectively; P < 0.05). Transcapillary escape rate of albumin was lowest during P4-E2(5.8 ± 1.3, 3.5 ± 1.7, and 2.2 ± 0.4%/h for GnRH antagonist, P4, and P4-E2, respectively; P < 0.05). Serum aldosterone increased during P4and P4-E2compared with GnRH antagonist (79 ± 17, 127 ± 13, and 171 ± 25 pg/ml for GnRH antagonist, P4, and P4-E2, respectively; P < 0.05), but plasma renin activity and plasma concentration of ANG II were only increased by P4-E2. This study is the first to isolate P4effects on ECF; however, the mechanisms for the ECF and PV expansion have not been clearly defined.

Effects of estrogen and progesterone administration on extracellular fluid

To determine the effect of estrogen and progesterone on plasma volume (PV) and extracellur fluid volume (ECFV), we suppressed endogenous estrogen and progesterone by using the gonadotropin-releasing hormone (GnRH) antagonist ganirelix acetate in seven healthy women (22 ± 1 yr). Subjects were administered GnRH antagonist for 16 days. Beginning on day 5 of GnRH antagonist administration, subjects were administered estrogen (E2) for 11 days, and beginning on day 12 of GnRH antagonist administration, subjects added progesterone (E2-P4) for 4 days. On days 2, 9, and 16 of GnRH antagonist administration, we estimated ECFV (inulin washout), transcapillary escape rate of albumin (TERalb), and PV (Evans blue dye). Plasma E2concentration increased from 17.9 ± 4.5 (GnRH antagonist) to 195.9 ± 60.1 (E2, P < 0.05) to 245.6 ± 62.9 pg/ml (E2-P4, P < 0.05). Compared with GnRH antagonist (1.3 ± 0.5 ng/ml), plasma P4concentration was unchanged during E2(0.9 ± 0.3 ng/ml) and increased to 9.4 ± 3.1 ng/ml during E2-P4( P < 0.05). Both E2(44.1 ± 3.1 ml/kg) and E2-P4(47.7 ± 2.8 ml/kg) increased PV compared with GnRH antagonist (42.8 ± 1.3 ml/kg, P < 0.05). Within-subjects TERalbwas a strong negative predictor of PV (mean r = 0.92 ± 0.03, P < 0.05), and TERalbwas lowest during E2-P4(5.7 ± 0.5, 4.1.0 ± 1.1, and 2.8 ± 0.9%/h, P < 0.05, for GnRH antagonist, E2, and E2-P4, respectively). ECFV was reduced during E2(227 ± 31 ml/kg, P < 0.05) compared with both GnRH antagonist (291 ± 37 ml/kg) and E2-P4(283 ± 19 ml/kg). Thus the percentage of extracellular fluid in the plasma compartment increased to 21.0% ( P < 0.05) during E2compared with GnRH antagonist (16.1%) and E2-P4(17.2%) admistration. Thus E2increased PV via actions on the capillary endothelium to lower TERalband favor intravascular water retention, whereas during E2-P4PV increased via the combined responses of ECFV expansion and lower TERalb.

Reduced blood-to-tissue albumin movement after plasmapheresis

We tested the hypothesis that a decrease in the blood-to-tissue movement of albumin contributes to the recovery of plasma albumin and plasma volume after acute plasma protein depletion (plasmapheresis). Awake and unrestrained male Sprague-Dawley rats (220-320 g) fitted with jugular catheters were plasmapheresed, and plasma volume, plasma albumin, and total plasma protein content were measured at 1, 5, 24, and 48 h postplasmapheresis. Plasma volume recovered to baseline within 1 h (4.6 +/- 0.42 vs. 4.7 +/- 0.46 mL/100 g body weight (bw), remained at baseline from 5 h to 24 h but increased to 5.5 + 0.57 mL/100 g bw at 48 h (P < 0.05). Plasma albumin and total protein content recovered rapidly but remained below baseline levels at 1 h (10.05 +/- 0.98 vs. 12.33 +/- 1.29 and 19.75 +/- 1.75 vs. 24.73 +/- 2.56 mg/100 g bw, respectively). Plasma protein content retumed to baseline by 5 h of recovery. Tissue uptake of I125-labeled albumin decreased in the heart, skin, skeletal muscle, and small Intestines of plasmapheresed rats (P < 0.05). These data support the hypothesis that a reduction in albumin efflux from the vascular space contrlbutes to the recovery of plasma albumin and total protein content during plasma volume recovery and eventual expansion after plasmapheresis.

Human albumin synthesis is increased by an ultra-endurance trial

PURPOSE

The purpose of this study was to determine whether an ultra-endurance event is a strong stimulus to increase albumin synthesis involved in the process of intravascular albumin mass increase associated with transient hypervolemia.

METHODS

The albumin synthetic rate was measured in six young men, 3 d before (C) and on the 1st (R1) and 8th (R8) days of the recovery from an ultra-endurance trial (5 h daily for 4 d). Albumin fractional (FSR) and absolute (ASR) synthetic rate were determined using a primed-constant infusion of [1(-13) C] leucine. Plasma volume (PV) using Evans Blue dye dilution and total body water (TBW) using bioelectrical impedance analysis were measured on C, R1, and R8.

RESULTS

On R1 as compared with C: 1). PV (+23.3 +/- 3.2%; P<or= 0.001) and TBW (+4.2 +/- 0.8%; P<or= 0.01) expanded; 2). FSR and ASR both increased from 5.36 +/- 0.46 to 6.86 +/- 0.62%.24 h (+ 29.0 +/- 7.1%; P<or= 0.01) and from 103 +/- 10 to 153 +/- 19 mg.kg body weight (-1).24 h (-1) (+47.5 +/- 6.8%; P<or= 0.01); and 3). plasma albumin and protein masses increased (P<or= 0.05) from 1.92 +/- 0.08 to 2.22 +/- 0.14 g.kg body weight (-1) (i.e., +15.3 +/- 4.9%) and from 3.15 +/- 0.18 to 3.56 +/- 0.21 g.kg body weight (-1) (+13.3 +/- 3.9%), respectively. By R8, all these parameters had returned to their control levels except for albumin mass (1.73 +/- 0.08 g.kg body weight(-1), which was lower than C ( P<or= 0.05).

CONCLUSION

The increase in the albumin synthetic rate the day after an ultra-endurance trial is a major event associated with a greater circulating protein mass. The impact of exercise on albumin synthesis has disappeared 8 d later, as did PV and total protein mass expansion.

Effects of exercise training on thermoregulatory responses and blood volume in older men

We assessed the effects of aerobic and/or resistance training on thermoregulatory responses in older men and analyzed the results in relation to the changes in peak oxygen consumption rate (VO(2 peak)) and blood volume (BV). Twenty-three older men [age, 64 +/- 1 (SE) yr; VO(2 peak), 32.7 +/- 1.1 ml. kg(-1). min(-1)] were divided into three training regimens for 18 wk: control (C; n = 7), aerobic training (AT; n = 8), and resistance training (RT; n = 8). Subjects in C were allowed to perform walking of ~10,000 steps/day, 6-7 days/wk. Subjects in AT exercised on a cycle ergometer at 50-80% VO(2 peak) for 60 min/day, 3 days/wk, in addition to the walking. Subjects in RT performed a resistance exercise, including knee extension and flexion at 60-80% of one repetition maximum, two to three sets of eight repetitions per day, 3 days/wk, in addition to the walking. After 18 wk of training, VO(2 peak) increased by 5.2 +/- 3.4% in C (P > 0.07), 20.0 +/- 2.5% in AT (P < 0.0001), and 9.7 +/- 5.1% in RT (P < 0.003), but BV remained unchanged in all trials. In addition, the esophageal temperature (T(es)) thresholds for forearm skin vasodilation and sweating, determined during 30-min exercise of 60% VO(2 peak) at 30 degrees C, decreased in AT (P < 0.02) and RT (P < 0.02) but not in C (P > 0.2). In contrast, the slopes of forearm skin vascular conductance/T(es) and sweat rate/T(es) remained unchanged in all trials, but both increased in subjects with increased BV irrespective of trials with significant correlations between the changes in the slopes and BV (P < 0.005 and P < 0.0005, respectively). Thus aerobic and/or resistance training in older men increased VO(2 peak) and lowered T(es) thresholds for forearm skin vasodilation and sweating but did not increase BV. Furthermore, the sensitivity of the increase in skin vasodilation and sweating at a given increase in T(es) was more associated with BV than with VO(2 peak).

Plasma compartment filling after exercise or heat exposure

PURPOSE

The present study was assessed to study the restoration of the vascular compartment by rehydration after heat exposure or exercise.

METHODS

Eight subjects completed four trials in a randomized order: 2.7% dehydration of body mass by passive controlled hyperthermia once with rehydration and once without rehydration during recovery, and 2.7% dehydration of body mass by treadmill exercise once with rehydration and once without rehydration during recovery. An isotonic glucose electrolyte beverage was provided twice during the recovery period for a total volume, which was equivalent to the target value of body mass loss during dehydration procedures. Plasma volume (PV) was measured using Evans Blue dilution technique, and PV changes (deltaPV) were determined using hematocrit and hemoglobin measurements.

RESULTS

PV was better maintained during exercise than during heat exposure, and the difference in deltaPV between the two patterns of dehydration was maintained during the first 3 h of recovery. Plasma protein seemed to be accountable for the difference in deltaPV during heat exposure and exercise but not during the 270 min of recovery. Rehydration partly restored body fluid losses, but the plasma compartment was privileged, because 26-30% of the net fluid gain was found in the plasma compartment (about 300 mL). Rehydration restored plasma osmolality and diminished the drive for arginin-vasopressin response.

CONCLUSION

The similar selective retention of water in the plasma compartment might essentially be explained by osmotic factors provided by the beverage. As PV was completely restored by rehydration after exercise and only partly restored after heat exposure, the volume of ingested beverage should be higher after heat exposure to completely restore the plasma compartment.

Capillary leak syndrome after cardiopulmonary bypass in elective, uncomplicated coronary artery bypass grafting operations: does it exist?

OBJECTIVE

Operations coupled with cardiopulmonary bypass may provoke a systemic inflammatory response, and it has been suggested that this responses causes capillary leakage of proteins, edema formation, and even organ failure. However, capillary leak syndrome is mainly a clinical diagnosis and has not been verified as yet by actual demonstration of protein leakage from the circulation. We have therefore measured the disappearance of labeled plasma protein before and after cardiopulmonary bypass.

METHODS

Sixteen patients scheduled for elective coronary artery bypass grafting were enrolled in a prospective controlled study. The cardiopulmonary bypass circuit was primed with crystalloids only. Tumor necrosis factor alpha, interleukin 6, interleukin 8, anaphylatoxin C3a, and terminal complement complex C5b9 levels were determined before, during, and 3 hours after cardiopulmonary bypass. The transvascular escape rate of plasma protein from the intravascular compartment was assessed by measuring the disappearance of intravenously injected Evans blue dye before and during the third hour after cardiopulmonary bypass.

RESULTS

A significant inflammatory response could be demonstrated by means of the 5 measured mediators after bypass. The maximal increase, as compared with the baseline value, was found for interleukin 6 (36-fold). The transvascular escape rate of Evans blue dye was similar before and after bypass (7.6 +/- 0.6%/h vs 7.3 +/- 0.6%/h).

CONCLUSIONS

The above data confirm the systemic inflammatory response induced by cardiopulmonary bypass. Contrary to expectations, the transvascular escape rate of Evans blue dye did not change when comparing values before and after bypass. The data do not support the concept of increased protein leakage in the exchange vessels after bypass. We were unable to demonstrate a capillary leak syndrome.

Modifications of microvascular filtration capacity in human limbs by training and electrical stimulation

This study investigated whether an increase in microvascular surface area as a result of endurance training, which increases human skeletal muscle capillarity, would translate to greater capacity for fluid filtration compared with strength training, which does not affect capillary supply. Values for filtration capacity, Kf, derived from the slope of calf volume change, Jv, measured by venous occlusion plethysmography, against cuff pressure during a protocol of small cumulative pressure steps, were significantly higher in endurance athletes (5.78 +/- 0.88 mL min(-1) 100 mL(-1) mmHg(-1) x 10(-3), P < 0.05) than controls (3.38 +/- 0.32 mL min(-1) 100 mL(-1) mmHg(-1) x 10(-3) whereas strength-trained athletes had values similar to control (4.08 +/- 0.56 mL min(-1) 100 mL(-1) mmHg(-1) x 10(-3), ns), suggesting that surface area is important. However, when sedentary subjects underwent either a 4-week unilateral dynamic plantarflexion training programme (70% peak power, 20 min day(-1), 5 days week(-1) or a calf muscle electrical stimulation programme (8 Hz, 3 x 20 min day(-1), 5 days week(-1), neither of which caused limb blood flow to alter after training nor would be expected to increase capillarity, only the stimulation group showed a significant increase in Kf (6.68 +/- 0.62 mL min(-1) 100 mL(-1) mmHg(-1) x 10(-3) post-training vs. 3.38 +/- 0.38 pre-training, P < 0.05). This may be because stimulation enhances perfusion preferentially to glycolytic fibres, or maintains high levels of vascular endothelial growth factor (VEGF) or changes lymph clearance.

Increased renal tubular sodium reabsorption during exercise-induced hypervolemia in humans

We tested the hypothesis that renal tubular Na(+) reabsorption increased during the first 24 h of exercise-induced plasma volume expansion. Renal function was assessed 1 day after no-exercise control (C) or intermittent cycle ergometer exercise (Ex, 85% of peak O(2) uptake) for 2 h before and 3 h after saline loading (12.5 ml/kg over 30 min) in seven subjects. Ex reduced renal blood flow (p-aminohippurate clearance) compared with C (0.83 +/- 0.12 vs. 1.49 +/- 0.24 l/min, P < 0.05) but did not influence glomerular filtration rates (97 +/- 10 ml/min, inulin clearance). Fractional tubular reabsorption of Na(+) in the proximal tubules was higher in Ex than in C (P < 0.05). Saline loading decreased fractional tubular reabsorption of Na(+) from 99.1 +/- 0.1 to 98.7 +/- 0.1% (P < 0.05) in C but not in Ex (99.3 +/- 0.1 to 99.4 +/- 0.1%). Saline loading reduced plasma renin activity and plasma arginine vasopressin levels in C and Ex, although the magnitude of decrease was greater in C (P < 0.05). These results indicate that, during the acute phase of exercise-induced plasma volume expansion, increased tubular Na(+) reabsorption is directed primarily to the proximal tubules and is associated with a decrease in renal blood flow. In addition, saline infusion caused a smaller reduction in fluid-regulating hormones in Ex. The attenuated volume-regulatory response acts to preserve distal tubular Na(+) reabsorption during saline infusion 24 h after exercise.

Effect of lymphatic outflow pressure on lymphatic albumin transport in humans

The effects of posture on the lymphatic outflow pressure and lymphatic return of albumin were examined in 10 volunteers. Lymph flow was stimulated with a bolus infusion of isotonic saline (0.9%, 12.6 ml/kg body wt) under four separate conditions: upright rest (Up), upright rest with lower body positive pressure (LBPP), supine rest (Sup), and supine rest with lower body negative pressure (LBNP). The increase in plasma albumin content (Delta Alb) during the 2 h after bolus saline infusion was greater in Up than in LBPP: 82.9 +/- 18.5 vs. -28.4 mg/kg body wt. Delta Alb was greater in LBNP than in Sup: 92.6 vs. -22.5 +/- 18.9 mg/kg body wt (P < 0.05). The greater Delta Alb in Up and Sup with LBNP were associated with a lower estimated lymphatic outflow pressure on the basis of the difference in central venous pressure (Delta CVP). During LBPP, CVP was increased compared with Up: 3.8 +/- 1.4 vs. -1.2 +/- 1.2 mmHg. During LBNP, CVP was reduced compared with Sup: -3.0 +/- 2.2 vs. 1.7 +/- 1.0 mmHg. The translocation of protein into the vascular space after bolus saline infusion reflects lymph return of protein and is higher in Up than in Sup. Modulation of CVP with LBPP or LBNP in Up and Sup, respectively, reversed the impact of posture on lymphatic outflow pressure. Thus posture-dependent changes in lymphatic protein transport are modulated by changes in CVP through its mechanical impact on lymphatic outflow pressure.

Enhanced synthesis of albumin and fibrinogen at high altitude

The acute effects of active and passive ascent to high altitude on plasma volume (PV) and rates of synthesis of albumin and fibrinogen have been examined. Measurements were made in two groups of healthy volunteers, initially at low altitude (550 m) and again on the day after ascent to high altitude (4,559 m). One group ascended by helicopter (air group, n = 8), whereas the other group climbed (foot group, n = 9), so that the separate contribution of physical exertion to the response could be delineated. PV was measured by dilution of (125)I-labeled albumin, whereas synthesis rates of albumin and fibrinogen were determined from the incorporation of isotope into protein after injection of [ring-(2)H(5)]phenylalanine. In the air group, there was no change in PV at high altitude, whereas, in the foot group, there was a 10% increase in PV (P < 0.01). Albumin synthesis (mg. kg(-1). day(-1)) increased by 13% in the air group (P = 0.058) and by 32% in the foot group (P < 0.001). Fibrinogen synthesis (mg. kg(-1). day(-1)) increased by 40% in the air group (P = 0.068) and by 100% in the foot group (P < 0.001). Hypoxia and alkalosis at high altitude did not differ between the groups. Plasma interleukin-6 was increased modestly in both groups but C-reactive protein was not changed in either group. It is concluded that increases in PV and plasma protein synthesis at high altitude result mainly from the physical exercise associated with climbing. However, a small stimulation of albumin and fibrinogen synthesis may be attributable to hypobaric hypoxia alone.

Importance of post-exercise hypotension in plasma volume restoration

The aim of this study was to test the hypothesis that post-exercise hypotension was the mechanism for the plasma volume and albumin gain during recovery. Seven healthy young men completed two experiments (> or =1 week apart) to exercise continuously at 65% of peak aerobic capacity for 60 min followed by the recovery without (experiment 1) or with phenylephrine infusion (experiment 2) to counteract post-exercise hypotension. Heart rate, arterial pressure (Finapres), plasma volume (PV, Evans blue dye dilution), haematocrit, haemoglobin, plasma total solutes (refractometer), albumin, total proteins (colorimetric method), [Na+] and [K+] were not different prior to the experiments. Exercise decreased PV -13.7% (-521 mL) and -14.2% (-566 mL) at the end of 60 min in experiments 1 and 2, respectively, associated with increases in the concentrations of plasma albumin, total protein and solutes. These changes were similar between the two experiments. Following 30 min recovery in experiment 1 the decreased PV was not significantly different from the baseline. Although the volume restoration was complete at the end of 90 min recovery, the change in the albumin concentration was still above zero, indicating a gain of 11 g albumin (P < 0.05). When phenylephrine was infused during recovery, there was no gain in intravascular albumin associated with a sustained decrease in PV (-7% or -280 mL, P < 0.05) observed at the end of experiment 2. These data suggest that post-exercise hypotension may be the mechanism for a gain of intravascular albumin via the lymph return, which enhances plasma water retention and PV restoration during recovery from exercise induced hypovolaemia, even without rehydration.

Acute plasma volume expansion alters cardiovascular but not thermal function during moderate intensity prolonged exercise

To investigate the hypothesis that the increase in plasma volume (PV) that typically occurs with training results in improved cardiovascular and thermal regulation during prolonged exercise, eight untrained males (Vo2peak = 3.52 ± 0.12 L·min-1) performed 90 min of cycle ergometry at 62% Vo2peak before and after acute PV expansion. Subjects were infused with a PV-expanding solution (dextran (6%) or Pentaspan (10%)) equivalent to 6.7 mL·kg-1 body mass (PVX) or acted as their own control (CON) in a randomized order. PVX resulted in a calculated 15.8% increase in resting PV, which relative to CON, was maintained throughout the exercise (P < 0.05). During PVX, heart rate was lower (P < 0.05) and stroke volume and cardiac output were higher (P < 0.05) during the exercise. Mean arterial pressure and total peripheral resistance, although altered by exercise (P < 0.05), were not different between the two conditions. Core temperature, which was progressively increased by the exercise (P < 0.01), was not affected by PVX. A similar decrease in body weight was observed between the conditions as a result of the exercise (P < 0.01). These results indicate that acute PVX alters cardiovascular performance without affecting the thermoregulatory response to prolonged cycle exercise.Key words: cardiovascular, prolonged exercise, acute plasma volume expansion, thermoregulation, hypervolemia.

Heat acclimation improves regulation of plasma volume and plasma Na(+) content during exercise in horses

This study determined the plasma volume (PV) and ion responses to heat acclimation and exercise in six trained Thoroughbred horses during 21 days of exposure to heat and humidity (33 degrees C, 83% relative humidity) for 4 h/day. During the 2nd h on days 0, 3, 7, 14, and 21, horses performed a standardized treadmill test, running at 50% of peak O(2) uptake until pulmonary artery temperature reached 41.5 degrees C. Heat acclimation resulted in an increase in PV from 21.3 +/- 1.1 liters on day 0 to 24.3 +/- 1.0 liters on day 14, returning to 22.6 +/- 0.9 liters on day 21. The corresponding total plasma protein contents were 1,273 +/- 53, 1,455 +/- 81, and 1,377 +/- 57 g, respectively, and increases in total plasma Na(+) plus Cl(-) content were 5,145 +/- 126, 5,749 +/- 146, and 5,394 +/- 114 mmol, respectively. Thus changes in PV were accompanied by direct changes in plasma protein and osmolyte contents. With exercise on day 0, PV decreased by 7.1 +/- 0.7% at 5 min of exercise and remained decreased (-6.7 +/- 1.3%) at 5 min of recovery. By day 21, PV decreased significantly less than on day 0 (by 5.2 +/- 0.9% at 5 min of exercise), was decreased by only 2.0 +/- 1.6% at 5 min of recovery, and was fully restored at 15 min of recovery. Plasma Na(+) concentration increased 3 meq/l during the first 5 min of exercise and was normalized by 5 min of recovery on day 0 and by end exercise on day 21. It is concluded that improved ability to regulate PV during exercise in response to heat acclimatization is associated with an increased PV and an improved conservation of Na(+).

Intense exercise stimulates albumin synthesis in the upright posture

We tested the hypothesis that an elevation in albumin synthetic rate contributes to increased plasma albumin content during exercise-induced hypervolemia. Albumin synthetic rate was measured in seven healthy subjects at 1-5 and 21-22 h after 72 min of intense (85% peak oxygen consumption rate) intermittent exercise and after 5 h recovery in either upright (Up) or supine (Sup) postures. Deuterated phenylalanine (d(5)-Phe) was administrated by a primed-constant infusion method, and fractional synthetic rate (FSR) and absolute synthetic rate (ASR) of albumin were calculated from the enrichment of d(5)-Phe in plasma albumin, determined by gas chromatography-mass spectrometry. FSR of albumin in Up increased significantly (P < 0.05) from 4.9 +/- 0.9%/day at control to 7.3 +/- 0.9%/day at 22 h of recovery. ASR of albumin increased from 87.9 +/- 17.0 to 141.1 +/- 16.6 mg albumin. kg body wt(-1). day(-1). In contrast, FSR and ASR of albumin were unchanged in Sup (3.9 +/- 0.4 to 4.0 +/- 1.4%/day and 74.2 +/- 8.9 to 85.3 +/- 23.9 mg albumin. kg body wt(-1). day(-1) at control and 22 h of recovery, respectively). Increased albumin synthesis after upright intense exercise contributes to the expansion of greater albumin content and its maintenance. We conclude that stimuli related to posture are critical in modulating the drive for albumin synthesis after intense exercise.

Unbound rather than total concentration and saturation rather than unsaturation determine the potency of fatty acids on insulin secretion

Isolated mouse islets were used to compare the effects of three saturated (myristate, palmitate and stearate) and three unsaturated (oleate, linoleate and linolenate) long-chain fatty acids on insulin secretion. By varying the concentrations of fatty acid (250-1250 micromol/l) and albumin simultaneously or independently, we also investigated whether the insulinotropic effect is determined by the unbound or total concentration of the fatty acids. Only palmitate and stearate slightly increased basal insulin secretion (3 mmol/l glucose). All tested fatty acids potentiated glucose-induced insulin secretion (10-15 mmol/l), and the following rank order of potency was obtained when they were compared at the same total concentrations: palmitate approximately = stearate > myristate > or = oleate > or = linoleate approximately = linolenate. The effect of a given fatty acid varied with the fatty acid to albumin molar ratio, in a way which indicated that the unbound fraction is the important one for the stimulation of beta cells. When the potentiation of insulin secretion was expressed as a function of the unbound concentrations, the following rank order emerged: palmitate > myristate > stearate approximately = oleate > linoleate approximately = linolenate. In conclusion, the acute and direct effects of long-chain fatty acids on insulin secretion are due to their unbound fraction. They are observed only at fatty acid/albumin ratios higher than those normally occurring in plasma. Saturated fatty acids are stronger insulin secretagogues than unsaturated fatty acids. Unbound palmitate is by far the most potent of the six common long-chain fatty acids.

Mechanism for the posture-specific plasma volume increase after a single intense exercise protocol

To test the hypothesis that exercise-induced hypervolemia is a posture-dependent process, we measured plasma volume, plasma albumin content, and renal function in seven healthy subjects for 22 h after single upright (Up) or supine (Sup) intense (85% peak oxygen consumption rate) exercise. This posture was maintained for 5 h after exercise. Plasma volume decreased during exercise but returned to control levels by 5 h of recovery in both postures. By 22 h of recovery, plasma volume increased 2.4 +/- 0.8 ml/kg in Up but decreased 2.1 +/- 0.8 ml/kg in Sup. The plasma volume expansion in Up was accompanied by an increase in plasma albumin content (0.11 +/- 0.04 g/kg; P < 0.05). Plasma albumin content was unchanged in Sup. Urine volume and sodium clearance were lower in Up than Sup (P < 0.05) by 5 h of recovery. These data suggest that increased plasma albumin content contributes to the acute phase of exercise-induced hypervolemia. More importantly, the mechanism by which exercise influences the distribution of albumin between extra- and intravascular stores after exercise is altered by posture and is unknown. We speculate that factors associated with postural changes (e.g., central venous pressure) modify the increase in plasma albumin content and the plasma volume expansion after exercise.