Rate of erythropoietin formation in humans in response to acute hypobaric hypoxia

Total haemoglobin mass and spleen contraction: a study on competitive apnea divers, non-diving athletes and untrained control subjects

In diving mammals splenic contraction increases circulating red cell volume, whereas in humans increased haemoglobin concentrations have been reported. It is unknown, however, whether repetitive apnea diving also comprises an adaptive increase in total red cell volume as reported in endurance athletes. The first aim of the study therefore was to investigate the effect of repeated apnea dives on splenic size and putative red cell release in trained apnea divers (n = 10) and control subjects (SCUBA divers performing apneas without long-term apnea training, n = 7). Long-term effects of repetitive apnea diving may elevate the oxygen transport capacity by an adaptive increase in total haemoglobin mass as reported in endurance athletes. The second goal, therefore, was to compare the trained apnea divers' and the control divers' total haemoglobin mass (tHb-mass) with that of endurance-trained (n = 9) and untrained (n = 10) non-divers. Before and immediately after a series of five dives to a depth of 4 m in a heated pool, spleen volume was assessed with ultrasound tomography. tHb-mass and plasma volume were measured using the CO-rebreathing method. In the trained apnea divers, repeated apnea dives resulted in a 25% reduction of spleen size (P < 0.001), whereas no significant effect was observed in the control subjects. While tHb-mass did not differ between trained apnea divers, untrained SCUBA divers performing apneas and untrained non-divers, it was 30% lower than in endurance-trained non-divers. We conclude that prolonged apnea training causes marked apnea-induced splenic contraction. In contrast to athletes in endurance sports, the trained apnea divers did not present with increased total haemoglobin mass and, hence, no increase in blood oxygen stores.

Live High + Train Low: Thinking in Terms of an Optimal Hypoxic Dose

“Live high-train low” (LH+TL) altitude training allows athletes to “live high” for the purpose of facilitating altitude acclimatization, as characterized by a significant and sustained increase in endogenous erythropoietin and subsequent increase in erythrocyte volume, while simultaneously enabling them to “train low” for the purpose of replicating sea-level training intensity and oxygen flux, thereby inducing beneficial metabolic and neuromuscular adaptations. In addition to natural/terrestrial LH+TL, several simulated LH+TL devices have been developed including nitrogen apartments, hypoxic tents, and hypoxicator devices. One of the key issues regarding the practical application of LH+TL is what the optimal hypoxic dose is that is needed to facilitate altitude acclimatization and produce the expected beneficial physiological responses and sea-level performance effects. The purpose of this review is to examine this issue from a research-based and applied perspective by addressing the following questions: What is the optimal altitude at which to live, how many days are required at altitude, and how many hours per day are required? It appears that for athletes to derive the hematological benefits of LH+TL while using natural/terrestrial altitude, they need to live at an elevation of 2000 to 2500 m for >4 wk for >22 h/d. For athletes using LH+TL in a simulated altitude environment, fewer hours (12-16 h) of hypoxic exposure might be necessary, but a higher elevation (2500 to 3000 m) is required to achieve similar physiological responses.

Intermittent hypoxia exposure in a hypobaric chamber and erythropoietin abuse interpretation

The aim of this study was to assess the effect of intermittent hypoxia exposure on direct and indirect methods used to evaluate recombinant human erythropoietin (rhEPO) misuse. Sixteen male triathletes were randomly assigned to either the intermittent hypoxia exposure group (experimental group) or the control normoxic group (control group). The members of the experimental group were exposed to simulated altitude (from 4000 to 5500 m) in a hypobaric chamber for 3 h per day, 5 days a week, for 4 weeks. Blood and urine samples were collected before and after the first and the final exposures, and again 2 weeks after the final exposure. While serum EPO significantly increased after the first [from a mean 8.3 IU x l(-1) (s = 3.2) to 16.6 IU x l(-1) (s = 4.7)] and final exposures [from 4.6 IU x l(-1) (s = 1.4) to 24.8 IU x l(-1) (s = 9.3)], haemoglobin, percentage of reticulocytes, and soluble transferrin receptor were not elevated. Second-generation ON/OFF models (indirect rhEPO misuse detection) were insensitive to intermittent hypoxia exposure. The distribution of the urinary EPO isoelectric profiles (direct rhEPO misuse detection) was altered after intermittent hypoxia exposure with a slight shift towards more basic isoforms. However, those shifts never resulted in misinterpretation of results. The intermittent hypoxia exposure protocol studied did not produce any false-positive result for indirect or direct detection of rhEPO misuse in spite of the changes in EPO serum concentrations and urinary EPO isoelectric profiles, respectively.

Performance of runners and swimmers after four weeks of intermittent hypobaric hypoxic exposure plus sea level training

This double-blind, randomized, placebo-controlled trial examined the effects of 4 wk of resting exposure to intermittent hypobaric hypoxia (IHE, 3 h/day, 5 days/wk at 4,000-5,500 m) or normoxia combined with training at sea level on performance and maximal oxygen transport in athletes. Twenty-three trained swimmers and runners completed duplicate baseline time trials (100/400-m swims, or 3-km run) and measures for maximal oxygen uptake (VO(2max)), ventilation (VE(max)), and heart rate (HR(max)) and the oxygen uptake at the ventilatory threshold (VO(2) at VT) during incremental treadmill or swimming flume tests. Subjects were matched for sex, sport, performance, and training status and divided randomly between hypobaric hypoxia (Hypo, n = 11) and normobaric normoxia (Norm, n = 12) groups. All tests were repeated within the first (Post1) and third weeks (Post2) after the intervention. Time-trial performance did not improve in either group. We could not detect a significant difference between groups for a change in VO(2max), VE(max), HR(max), or VO(2) at VT after the intervention (group x test interaction P = 0.31, 0.24, 0.26, and 0.12, respectively). When runners and swimmers were considered separately, Hypo swimmers appeared to increase VO(2max) (+6.2%, interaction P = 0.07) at Post2 following a precompetition taper and increased VO(2) at VT (+8.9 and +12.1%, interaction P = 0.007 and 0.006, at Post1 and Post2). We conclude that this "dose" of IHE was not sufficient to improve performance or oxygen transport in this heterogeneous group of athletes. Whether there are potential benefits of this regimen for specific sports or training/tapering strategies may require further study.

Effects of intermittent hypoxic training on cycling performance in well-trained athletes

This study aimed to investigate the effects of a short-term period of intermittent hypoxic training (IHT) on cycling performance in athletes. Nineteen participants were randomly assigned to two groups: normoxic (NT, n = 9) and intermittent hypoxic training group (IHT, n = 10). A 3-week training program (5 x 1 h-1 h 30 min per week) was completed. Training sessions were performed in normoxia (approximately 30 m) or hypoxia (simulated altitude of 3,000 m) for NT and IHT group, respectively. Each subject performed before (W0) and after (W4) the training program, three cycling tests including an incremental test to exhaustion in normoxia and hypoxia for determination of maximal aerobic power (VO2max) and peak power output (PPO) as well as a 10-min cycle time trial in normoxia (TT) to measure the average power output (P(aver)). No significant difference in VO2max was observed between the two training groups before or after the training period. When measured in normoxia, the PPO significantly increased (P < 0.05) by 7.2 and 6.6% in NT and IHT groups, respectively. However, only the IHT group significantly improved (11.3%; P < 0.05) PPO when measured in hypoxia. The NT group improved (P < 0.05) P(aver) in TT by 8.1%, whereas IHT group did not show any significant difference. Intermittent training performed in hypoxia was less efficient for improving endurance performance at sea level than similar training performed in normoxia. However, IHT has the potential to assist athletes in preparation for competition at altitude.

Unchanged anaerobic and aerobic performance after short-term intermittent hypoxia

INTRODUCTION

Repeated short-term exposures to a severe degree of hypoxia, alternated with similar intervals of normoxia, are recommended for performance enhancement in sports. However, scientific evidence for the efficiency of this method is controversial with regard to anaerobic performance. Therefore, we conducted a randomized, double-blind, placebo-controlled study to investigate the effects of this new method on both anaerobic and aerobic performance.

METHODS

During 15 consecutive days, 20 endurance-trained men (V O2max (mean +/- SD) 60.2 +/- 6.8 mL x kg(-1) x min(-1)) were exposed each day to breathing (through mouthpieces) either a gas mixture (11% O2 on days 1-7 and 10% O2 on days 8-15; hypoxia group, N = 10) or compressed air (control group, N = 10), six times for 6 min, followed by 4 min of breathing room air for a total of six consecutive cycles. Before and after the treatment, an incremental cycle ergometer test to exhaustion and the Wingate anaerobic test were performed to assess aerobic and anaerobic performance.

RESULTS

Hypoxic treatment did not improve peak power or mean power during the Wingate anaerobic test, nor did it affect maximal oxygen uptake (V O2max), maximal power output (Pmax), lactate threshold or levels of heart rate (HR), minute ventilation (V E), oxygen uptake (V O2), or blood lactate concentration at the submaximal workloads during the ergometer test. Maximal lactate concentration (Lamax) after the tests and HRmax and maximal respiratory exchange ratio (RERmax) during the ergometer test were not significantly different between groups at any time.

CONCLUSION

The results of this study demonstrated that 1 h of intermittent hypoxic exposure for 15 consecutive days has no effect on aerobic or anaerobic performance.

Erythropoietin regulations in humans under different environmental and experimental conditions

In the adult human, the kidney is the main organ for the production and release of erythropoietin (EPO). EPO is stimulating erythropoiesis by increasing the proliferation, differentiation and maturation of the erythroid precursors. In the last decades, enormous efforts were made in the purification, molecular encoding and description of the EPO gene. This led to an incredible increase in the understanding of the EPO-feedback-regulation loop at a molecular level, especially the oxygen-dependent EPO gene expression, a key function in the regulation loop. However, studies in humans at a systemic level are still very scanty. Therefore, it is the purpose of the present review to report on the main recent investigations on EPO production and release in humans under different environmental and experimental conditions, including: (i) studies on EPO circadian, monthly and even annual variations, (ii) studies in connection with short-, medium- and long-term exercise at sea-level which will be followed (iii) by studies performed at moderate and high altitude.

EPO tecting the endothelium

Erythropoietin is a 30.4 kDa protein that is produced and secreted from the kidney in response to anemia and hypobaric hypoxia. Binding of EPO to its receptor (EPO-R) on bone marrow-derived erythroid progenitor cells results in the stimulation of red blood cell production. Evidence is accumulating however, that the biological effects of recombinant EPO therapy extend beyond the stimulation of erythropoiesis. The discovery that the EPO-R is expressed on vascular endothelial cells suggests that the vasculature may be a biological target of EPO. Indeed, several studies have now demonstrated that the protective effect of EPO administration involves the activation of the protein kinase B/Akt pathway which can protect cells from apoptosis. Future work is likely to provide further insight into the mechanisms by which EPO protects vascular endothelial cells from injury and give us a better understanding of the pharmacological doses that are required to achieve this protection.

Prolonged expiration down to residual volume leads to severe arterial hypoxemia in athletes during submaximal exercise

The goal of this study was to assess the effects of a prolonged expiration (PE) carried out down to the residual volume (RV) during a submaximal exercise and consider whether it would be worth including this respiratory technique in a training programme to evaluate its effects on performance. Ten male triathletes performed a 5-min exercise at 70% of maximal oxygen consumption in normal breathing (NB(70)) and in PE (PE(70)) down to RV. Cardiorespiratory parameters were measured continuously and an arterialized blood sampling at the earlobe was performed in the last 15s of exercise. Oxygen consumption, cardiac frequency, end-tidal and arterial carbon dioxide pressure, alveolar-arterial difference for O(2) (PA(O2) - Pa(O2)) and P(50) were significantly higher, and arterial oxygen saturation (87.4+/-3.4% versus 95.0+/-0.9%, p<0.001), alveolar (PA(O2)) or arterial oxygen pressure, pH and ventilatory equivalent were significantly lower in PE(70) than NB(70). There was no difference in blood lactate between exercise modalities. These results demonstrate that during submaximal exercise, a prolonged expiration down to RV can lead to a severe hypoxemia caused by a PA(O2) decrement (r=0.56; p<0.05), a widened PA(O2) - Pa(O2) (r=-0.85; p<0.001) and a right shift of the oxygen dissociation curve (r=-0.73; p<0.001).

Red blood cell senescence and neocytolysis in humans after high altitude acclimatization

A selective lysis of relatively young erythrocytes (neocytolysis), together with a decrease of erythropoietin (EPO) production, has been described in polycythemic, high altitude acclimatized climbers, after descent to sea level, and in astronauts, soon after exposure to weightlessness (Alfrey CP, Rice L, Udden MM, Driscoll TB. Neocytolysis may represent the physiological down-regulation of red-cell mass. Lancet 349 (1997) 1389-90). To study neocytolysis, we analysed blood samples drawn from 4 mountain climbers at sea level before and after 53 days of high altitude acclimatization (> or = 4500 m). After a 6-day descent to sea level, erythropoietin (EPO) plasma levels were lower than before high altitude acclimatization (mean values: 2.5+/-3.3 versus 10+/-4.5 mIU/ml, p < 0.05). Red blood cell (RBC) populations were separated into low, middle and high density subsets, which, by physical and phenotypical criteria, were characterized as young, middle-aged and old. RBC membrane molecules CD55 and CD59 along with phosphatydylserine and CD47 were measured. The former are partially lost during RBC aging. The latter are involved in the triggering or inhibition of RBC phagocytosis by macrophages. Immunofluorescence and flow cytometry were done on each density subset. Young and middle-aged RBCs largely disappeared after descent from high altitude (from 4.50% (+/-3.10) and 66% (+/-6.90) to 0.19% (+/-0.07) and 1.90% (+/-0.50), respectively). Simultaneously, there was a dramatic increase of high density RBCs (from 29.50% (+/-7) to 97.90% (+/-2.00)). Furthermore, the remaining young and middle-aged RBCs had acquired a senescent-like phenotype, which may account for their increased susceptibility to phagocytosis.

Effect of intermittent normobaric hypoxic exposure at rest on haematological, physiological, and performance parameters in multi-sport athletes

The aim of this study was to determine whether 3 weeks of intermittent normobaric hypoxic exposure at rest was able to elicit changes that would benefit multi-sport athletes. Twenty-two multi-sport athletes of mixed ability were exposed to either a normobaric hypoxic gas (intermittent hypoxic training group) or a placebo gas containing normal room air (placebo group). The participants breathed the gas mixtures in 5-min intervals interspersed with 5-min recovery periods of normal room air for a total of 90 min per day, 5 days per week, over a 3-week period. The oxygen in the hypoxic gas decreased from 13% in week 1 to 10% by week 3. The training and placebo groups underwent a total of four performance tests, including a familiarization and baseline trial before the intervention, followed by trials at 2 and 17 days after the intervention. Time to complete the 3-km run decreased by 1.7%[95% confidence interval (CI) = -0.6 - 3.9%] 2 days after, and by 2.3% (CI = 0.25 - 4.4%) 17 days after, the last hypoxic episode in the training relative to the placebo group. Substantial changes in the training relative to the placebo group also included increased reticulocyte count 2 days (23.5%; CI =-1.9 to 44.9%) and 12 days (14.6%; CI = -7.1 to 36.4%) post-exposure. The effect of intermittent hypoxic training on 3-km performance found in this study is likely to be beneficial, which suggests non-elite multi-sport athletes should expect such training to enhance performance.

Leukocyte's Hif-1 expression and training-induced erythropoietic response in swimmers

PURPOSE

Altitude training is popular among athletes to augment oxygen delivery capabilities to tissues and to improve physical performance. Hypoxia inducible factor-1 (HIF-1) controls the expression of several genes' encoding involved in physiological responses towards reduced oxygen availability, in particular by increasing serum erythropoietin (EPO). It may be involved in the individual variability for erythropoietic markers and/or sea-level performance of athletes using altitude during their training. Therefore, we investigated whether, before training, evolutions of hif-1alpha and ahif (HIF-1alpha natural antisense) transcript amounts and HIF-1alpha protein quantities in leukocytes measured during an acute hypoxia normobaric test (3 h at 3000 m at rest) could allow to predict poor and good responders for hematological markers after a "living high-training low" protocol.

METHODS

Eighteen elite swimmers were divided into two groups that followed a 13-d training program: "living low-training low" (1200 m) (LL) or "living high (2500-3000 m)-training low (1200 m)" (LH).

RESULTS

During the initial hypoxia test, a strong interindividual variability in the amounts of HIF-1alpha mRNA, aHIF transcript, and HIF-1alpha protein was observed in athlete leukocytes (after vs before): -82%/+396%, -100%/+229%, and -100%/+633%, respectively. After the test, serum erythropoietin concentration was increased (11.2 +/- 0.8 vs 9.8 +/- 0.8 IU.L(-1); +18%, P = 0.01). After the training protocol, total red cell volume (+7.6%, P = 0.04) and circulating hemoglobin amount (48.8 +/- 2.8 vs 45.5 +/- 3.0 mmol; i.e., +7.9%, P = 0.02) were significantly augmented in LH.

CONCLUSION

We conclude that hif-1alpha gene expression quantification in leukocytes after a 3-h hypoxia test performed before training does not predict poor and good responder athletes to "living high-training low" model.

Biochemistry, physiology, and complications of blood doping: facts and speculation

Competition is a natural part of human nature. Techniques and substances employed to enhance athletic performance and to achieve unfair success in sport have a long history, and there has been little knowledge or acceptance of potential harmful effects. Among doping practices, blood doping has become an integral part of endurance sport disciplines over the past decade. The definition of blood doping includes methods or substances administered for non-medical reasons to healthy athletes for improving aerobic performance. It includes all means aimed at producing an increased or more efficient mechanism of oxygen transport and delivery to peripheral tissues and muscles. The aim of this review is to discuss the biochemistry, physiology, and complications of blood doping and to provide an update on current antidoping policies.

Increased serum erythropoietin but not red cell production after 4 wk of intermittent hypobaric hypoxia (4,000-5,500 m)

This study tested the hypothesis that athletes exposed to 4 wk of intermittent hypobaric hypoxia exposure (3 h/day, 5 days/wk at 4,000-5,500 m) or double-blind placebo increase their red blood cell volume (RCV) and hemoglobin mass (Hbmass) secondary to an increase in erythropoietin (EPO). Twenty-three collegiate level athletes were measured before (Pre) and after (Post) the intervention for RCV via Evans blue (EB) dye and in duplicate for Hbmass using CO rebreathing. Hematological indexes including EPO, soluble transferrin receptor, and reticulocyte parameters were measured on 8-10 occasions spanning the intervention. The subjects were randomly divided among hypobaric hypoxia (Hypo, n = 11) and normoxic (Norm, n = 12) groups. Apart from doubling EPO concentration 3 h after hypoxia there was no increase in any of the measures for either Hypo or Norm groups. The mean change in RCV from Pre to Post for the Hypo group was 2.3% (95% confidence limits = -4.8 to 9.5%) and for the Norm group was -0.2% (-5.7 to 5.3%). The corresponding changes in Hbmass were 1.0% (-1.3 to 3.3%) for Hypo and -0.3% (-2.6 to 3.1%) for Norm. There was good agreement between blood volume (BV) from EB and CO: EB BV = 1.03 x CO BV + 142, r2 = 0.85, P < 0.0001. Overall, evidence from four independent techniques (RCV, Hbmass, reticulocyte parameters, and soluble transferrin receptor) suggests that intermittent hypobaric hypoxia exposure did not accelerate erythropoiesis despite the increase in serum EPO.

ACE gene polymorphism and erythropoietin in endurance athletes at moderate altitude

PURPOSE

To determine the role of the ACE (I/D) gene polymorphism on erythropoietic response in endurance athletes after natural exposure to moderate altitude.

METHODS

Erythropoietic activity was measured in 63 male endurance athletes following natural exposure to moderate altitude (2200 m) during 48 h. Erythropoietin (EPO) levels and hemoglobin (Hb) concentrations were measured at baseline and 12, 24, and 48 h after reaching the set altitude. Reticulocyte counts were determined at baseline and 48 h thereafter. Subjects were grouped into two groups (responders and nonresponders) based on significant increase in EPO levels (median: > 16.5 ng x m(-1)) after 24 h at altitude. ACE gene polymorphism was ascertained by polymerase chain reaction (DD, 31 (49%); ID, 24 (38%); II, 8 (13%)).

RESULTS

Overall, EPO levels significantly increased at 12 (70%; P = 0.0001) and 24 h (72%; P = 0.0001) above baseline concentration following exposure to 2200 m. Thereafter, EPO concentration decreased at 48 h, but a significant increase in Hb levels (4.6 +/- 4%; P = 0.0001) and reticulocyte count (50.5 +/- 79%; P = 0.0001) was observed at the end of the experiment, suggesting negative feedback. There were no significant differences in EPO and Hb concentration profiles between subjects with DD genotype and those with other genotypes (ID/II). Moreover, responders (N = 42; DD, 50%; ID/II, 50%) and nonresponders (N = 21; DD, 48%; ID/II, 52%) showed a similar erythropoietic profile during the experiment and the ACE gene polymorphism did not influence the time course of the erythropoietic response.

CONCLUSIONS

The ACE gene polymorphism does not influence erythropoietic activity in endurance athletes after short-term exposure to moderate altitude.

L-arginine supplementation enhances exhaled NO, breath condensate VEGF, and headache at 4,342 m

We examined the effect of dietary supplementation with L-arginine on breath condensate VEGF, exhaled nitric oxide (NO), plasma erythropoietin, symptoms of acute mountain sickness, and respiratory related sensations at 4,342 m through the course of 24 h in seven healthy male subjects. Serum L-arginine levels increased in treated subjects at time 0, 8, and 24 h compared with placebo, indicating the effectiveness of our treatment. L-arginine had no significant effect on overall Lake Louise scores compared with placebo. However, there was a significant increase in headache within the L-arginine treatment group at 12 h compared with time 0, a change not seen in the placebo condition between these two time points. There was a trend (p = 0.087) toward greater exhaled NO and significant increases in breath condensate VEGF with L-arginine treatment, but no L-arginine effect on serum EPO. These results suggest that L-arginine supplementation increases HIF-1 stabilization in the lung, possibly through a NO-dependent pathway. In total, our observations indicate that L-arginine supplementation is not beneficial in the prophylactic treatment of AMS.

Diurnal normobaric moderate hypoxia raises serum erythropoietin concentration but does not stimulate accelerated erythrocyte production

This study was performed to examine the effect of diurnal normobaric hypoxia on hematological parameters. Eleven healthy male volunteers were randomly selected to be in either the hypoxic group (n=6) or the control group (n=5). The hypoxic group was exposed to 8 h of normobaric hypoxia in hypoxic tent systems that elicited a target peripheral O(2) saturation of 81+/-2% on three consecutive days. The control group spent three consecutive 8-h days in modified tent systems that delivered normoxic air into the tent. Venous blood samples were collected before the exposure (days -5, 0), after each day of the exposure (days 1, 2, 3), and for 3 weeks after the exposure (days 7, 10, 13, 17, 24). Serum erythropoietin concentration significantly increased from 9.1+/-3.3 U.L(-1) to 30.7+/-8.6 U.L(-1) in the hypoxic group. Although there were significant increases in hematocrit (4%), hemoglobin concentration (5%), red blood cell count (4%) on day 7 in the hypoxic group, these observations were likely due to dehydration or biological variation over time. There was no significant change in early erythropoietic markers (reticulocyte counts or serum ferritin concentration), which provided inconclusive evidence of accelerated erythroid differentiation and proliferation. The results suggest that the degree of hypoxia was sufficient to stimulate increased erythropoietin production and release. However, the duration of hypoxic exposure was insufficient to propagate the erythropoietic cascade.

Effects of short-term normobaric hypoxia on haematology, muscle phenotypes and physical performance in highly trained athletes

This study aimed to determine the impact of short-term normobaric hypoxia on physiology and performance in highly trained athletes. Twelve (7 male and 5 female) athletes were randomly assigned into two groups and spent 8 h per night for two consecutive nights a week over 3 weeks under either short-term normobaric hypoxia (simulating 3636 m altitude, inspired O2=13%) or in normobaric normoxia in a single-blind study. Following a 3 week washout period, athletes were then exposed to the other condition. Athletes were tested for maximal oxygen consumption and time to exhaustion on an electromagnetically braked cycle ergometer before and after each treatment in addition to being tested for anaerobic performance (Wingate test) on a modified Monark cycle ergometer. Blood samples were taken throughout the experiment and vastus lateralis muscle biopsies were taken before and after each treatment. Increases in red blood cell count, haematocrit, haemoglobin, platelet number and erythropoietin concentration were observed following short-term normobaric hypoxia. Except for a modest decrease in phosphofructokinase activity following short-term normobaric hypoxia, no changes were observed in muscle enzyme activities, buffer capacity, capillary density or morphology. No performance measures were changed following short-term normobaric hypoxia or normobaric normoxia. Although short-term normobaric hypoxia exposure increased levels of a number of haematological parameters, this was not associated with improved aerobic or anaerobic performance in highly trained athletes.

Eighteen days of "living high, training low" stimulate erythropoiesis and enhance aerobic performance in elite middle-distance runners

The efficiency of "living high, training low" (LHTL) remains controversial, despite its wide utilization. This study aimed to verify whether maximal and/or submaximal aerobic performance were modified by LHTL and whether these effects persist for 15 days after returning to normoxia. Last, we tried to elucidate whether the mechanisms involved were only related to changes in oxygen-carrying capacity. Eleven elite middle-distance runners were tested before (Pre), at the end (Post1), and 15 days after the end (Post2) of an 18-day LHTL session. Hypoxic group (LHTL, n = 5) spent 14 h/day in hypoxia (6 nights at 2,500 m and 12 nights at 3,000 m), whereas the control group (CON, n = 6) slept in normoxia (1,200 m). Both LHTL and CON trained at 1,200 m. Maximal oxygen uptake and maximal aerobic power were improved at Post1 and Post2 for LHTL only (+7.1 and +3.4% for maximal oxygen uptake, +8.4 and +4.7% for maximal aerobic power, respectively). Similarly oxygen uptake and ventilation at ventilatory threshold increased in LHTL only (+18.1 and +12.2% at Post1, +15.9 and +15.4% at Post2, respectively). Heart rate during a 10-min run at 19.5 km/h decreased for LHTL at Post2 (-4.4%). Despite the stimulation of erythropoiesis in LHTL shown by the 27.4% increase in serum transferrin receptor and the 10.1% increase in total hemoglobin mass, red cell volume was not significantly increased at Post1 (+9.2%, not significant). Therefore, both maximal and submaximal aerobic performance in elite runners were increased by LHTL mainly linked to an improvement in oxygen transport in early return to normoxia and probably to other process at Post2.

Effects of intermittent hypoxic training on aerobic and anaerobic performance

The aim of the present study was to determine whether short-term intermittent hypoxic training would enhance sea level aerobic and anaerobic performance over and above that occurring with equivalent sea level training. Over a 4-week period, two groups of eight moderately trained team sports players performed 30 min of cycling exercise three times per week. One group trained in normobaric hypoxia at a simulated altitude of 2750 m (F(I)O2= 0.15), the other group trained in a laboratory under sea level conditions. Each training session consisted of ten 1-min bouts at 80% maximum workload maintained for 2 min (Wmax) during the incremental exercise test at sea level separated by 2-min active recovery at 50% Wmax. Training intensities were increased by 5% after six training sessions and by a further 5% (of original Wmax) after nine sessions. Pre-training assessments of VO(2max), power output at onset of 4 mM blood lactate accumulation (OBLA), Wmax and Wingate anaerobic performance were performed on a cycle ergometer at sea level and repeated 4-7 d following the training intervention. Following training there were significant increases (p < 0.01) in VO(2max) (7.2 vs. 8.0%), Wmax (15.5 vs. 17.8%), OBLA (11.1 vs. 11.9%), mean power (8.0 vs. 6.5%) and peak power (2.9 vs. 9.3%) in both the hypoxic and normoxic groups respectively. There were no significant differences between the increases in any of the above-mentioned performance parameters in either training environment (p > 0.05). In addition, neither haemoglobin concentration nor haematocrit were significantly changed in either group (p > 0.05). It is concluded that acute exposure of moderately trained subjects to normobaric hypoxia during a short-term training programme consisting of moderate- to high-intensity intermittent exercise has no enhanced effect on the degree of improvement in either aerobic or anaerobic performance. These data suggest that if there are any advantages to training in hypoxia for sea level performance, they would not arise from the short-term protocol employed in the present study.

Changes in erythropoietin and haemoglobin concentrations in response to saturation diving

A reduction in haemoglobin concentration is consistently reported after deep saturation dives. This may be due to a downregulation of erythropoietin (EPO) concentration or to a toxic effect of the hyperoxia associated with the dives resulting in an increased destruction rate of erythrocytes. In this study haemoglobin concentration, blood cell counts, serum ferritin, bilirubin, haptoglobin and EPO concentrations were measured before, during and after a 19 day saturation dive to 240 m. The partial pressure of oxygen (PO(2)) was 35-70 kPa during the 7 day compression and bottom phase, and 30-50 kPa during the 12 day decompression phase. There was a reduction in EPO concentration from 8.4+/-1.4 (mean +/- 1SD) to 6.3 +/- 1.9 U.L(-1) on Dive day 2. On Dive days 7 and 17 EPO concentrations were not significantly different from baseline despite the continued exposure to hyperoxia. Immediately after the dive and return to a normoxic environment there was an increase in the EPO concencentration to 14.5 +/- 4.7 U.L(-1). Haemoglobin concentration, erythrocyte and reticulocyte counts were decreased at the end of the dive, and there was an increase in serum ferritin. There were no changes in bilirubin or haptoglobin concentrations indicative of haemolysis. It appears that the change in PO(2), rather than the sustained exposure to a hyperoxic environment, induces the changes in the EPO concentrations and erythropoietic activity.

Austrian Moderate Altitude Study (AMAS 2000): Erythropoietic Activity and Hb–O2 Affinity During a 3-Week Hiking Holiday at Moderate Altitude in Persons with Metabolic Syndrome

Moderate altitude hypoxia (1500 to 2500 m) is known to stimulate erythropoiesis and to improve oxygen transport to tissue by a reduction of Hb-O(2) affinity. Whether this adaptation also occurs in tourists with metabolic syndrome has not yet been investigated sufficiently. Thus, we performed a prospective field study to measure erythropoietic parameters and oxygen transport properties in 24 male volunteers with metabolic syndrome during a 3- week holiday program at 1700 m consisting of four guided, individually adapted hiking tours per week. The following examinations were performed: baseline investigations at 500 m (T1); examinations at moderate altitude on day 1 (T2), day 4 (T3), day 9 (T4), and day 19 (T5); and postaltitude tests (T6) 7 to 10 days after return. On day 1 and day 19, a walk on a standardized hiking test route with oxygen saturation (SpO(2)) measure points was performed. Hemoglobin, packed cell volume, and red cell count showed changes over time, with higher values at T5 as compared to baseline. Reticulocyte count and erythropoietin (EPO) were increased at T2 and increased further until T5. EPO declined toward prealtitude values. P50-value (blood PO(2) at 50% hemoglobin oxygen saturation at actual pH) increased during the altitude sojourn (maximum increase at T5 by +0.40 kPa). At T5 all volunteers had a higher SpO(2) before, during, and at the end of the test route compared to T1. During adaptation to moderate altitude, persons with metabolic syndrome exhibit an increase in EPO and a rightward shift of the oxygen dissociation curve that is similar to healthy subjects.

The influence of intermittent altitude exposure to 4100 m on exercise capacity and blood variables

This study was performed to investigate the effects of intermittent hypoxic exposure on blood and exercise parameters. Eight sea level residents were exposed to 2 h daily stimulus to 4100 m altitude in a hypobaric chamber for a total of 14 days. Exercise performance was evaluated at sea level before and after the hypoxic stimulation. Blood samples were obtained before, during, and at time points up to 14 days after the hypoxic exposure. No changes were observed in haemoglobin, haematocrit, reticulocytes, serum transferrin receptors, or EPO levels in the blood. Submaximal cycle (150 W) ergometer exercise corresponded to a oxygen uptake of 1.9+/-0.1 and 1.9+/-0.1 L min(-1) before and after the intermittent altitude exposure, respectively. At maximal exercise the workloads attained were 343+/-17 and 354+/-27 W before and after the exposure, with corresponding oxygen uptakes of 4.0+/-0.2 and 4.2+/-0.2 L min(-1). It is concluded that intermittent hypoxic exposure to 4100 m altitude for 2 h daily and a total of 14 days does not affect exercise capacity.

Erythropoietin response in critically ill mechanically ventilated patients: a prospective observational study

Introduction

Anemia is a common problem in critically ill patients. The etiology of anemia of critical illness is often determined to be multifactorial in the clinical setting, but the pathophysiology remains to be elucidated. Erythropoietin (EPO) is an endogenous glycoprotein hormone that serves as the primary stimulus for erythropoiesis. Recent evidence has demonstrated a blunted EPO response as a factor contributing to anemia of critical illness in specific subsets of patients. Critically ill patients requiring mechanical ventilation who exhibit anemia have not been the subject of previous studies. Our goal was to evaluate the erythropoietic response to anemia in the critically ill mechanically ventilated patient.

Methods

A prospective observational study was undertaken in the medical intensive care unit of a tertiary care, military hospital. Twenty patients admitted to the medical intensive care unit requiring mechanical ventilation for at least 72 hours were enrolled as study patients. EPO levels and complete blood count were measured 72 hours after admission and initiation of mechanical ventilation. Admission clinical and demographic data were recorded, and patients were followed for the duration of mechanical ventilation. Twenty patients diagnosed with iron deficiency anemia in the outpatient setting were enrolled as a control population. Control patients had baseline complete blood count and iron panel recorded by primary care physicians. EPO levels were measured at the time of enrollment in conjunction with complete blood count.

Results

The mean EPO level for the control population was 60.9 mU/ml. The mean EPO level in the mechanically ventilated patient group was 28.7 mU/ml, which was significantly less than in the control group (P = 0.035). The mean hemoglobin value was not significantly different between groups (10.6 g/dl in mechanically ventilated patients versus 10.2 g/dl in control patients; P > 0.05).

Conclusion

Mechanically ventilated patients demonstrate a blunted EPO response to anemia. Further study of therapies directed at treating anemia of critical illness and evaluating its potential impact on mechanical ventilation outcomes and mortality is warranted.

Effects of Hypoxic Interval Training on Cycling Performance

PURPOSE

The aim of this study was to test the hypothesis that intermittent hypoxic interval training improves sea level cycling performance more than equivalent training in hypoxia or normoxia.

METHODS

Thirty-three well-trained cyclists and triathletes (25.9 +/- 2.7 yr, VO(2max) 66.1 +/- 6.1 mL.min(-1).kg(-1)) were divided into three groups: intermittent hypoxic (IHT, N = 11, P(I)O(2) of 100 mm Hg), intermittent hypoxic interval training (IHIT, N = 11) and normoxia (Nor, N = 11, P(I)O(2) of 160 mm Hg) and completed a 7-wk training program, consisting of two high-intensity (100 or 90% relative peak power output) interval training sessions each week. Each interval training session was performed in a laboratory on the subject's own bicycle, in normoxic or hypoxic conditions for the Nor and the IHT group, respectively. The IHIT group performed warm-up and cool-down plus recovery from each interval in hypoxic conditions. In contrast to IHT, interval exercise bouts were performed in normoxic conditions.

RESULTS

Mean power output during a 10-min cycle time trial improved after the first 4 wk of training by 5.2 +/- 3.9, 3.7 +/- 5.9, and 5.0 +/- 3.4% for IHIT, IHT, and Nor, respectively, without significant differences between groups. Moreover, mean power output did not show any significant improvement in the following 3 wk in any group. VO(2max) (L.min(-1)) increased only in IHIT during the training period (8.7 +/- 9.1%; P < 0.05). No changes in cycling efficiency or in hematological variables (P > 0.05) were observed.

CONCLUSION

Four weeks of interval training induced an improvement in endurance performance. However, short-term exposure to hypoxia (approximately 114 min.wk(-1)) did not elicit a greater increase in performance or any hematological modifications.

Hematological Change in Venous Blood of the Lower Leg during Prolonged Sitting in a Low Humidity and Hypobaric Environment

The present study examined the effects of low humidity and hypobaric conditions on hematological change in venous blood of the lower leg during quiet prolonged sitting. Ten healthy male students participated as the subjects after singing a consent form to participate in this study. Their diet and water intake were controlled from 19:00 on the day before the experiments. The subjects sat for 130 min in a climatic chamber. Four experimental conditions in the chamber were designed from a combination of relative humidity (20% or 60%) and air pressure (sea level or equivalent to an altitude of 2,000 m). Ambient temperature was maintained at 24 degrees C in every condition. Venous blood was sampled from the lower leg before and after exposure to the experimental conditions, and was analyzed for blood viscosity and hematological indices. Also, body weight and leg circumference were measured as indices of total water loss and edema, respectively. Regarding the results of ANOVA, significant interactions between humidity and time were observed in blood viscosity, red blood cell count and hematocrit (each p<0.05). However, there were no significant differences in these indices among the conditions. Significant increases were observed in leg circumference (p<0.01), platelet count (p<0.05) and total protein (p<0.05) after the exposure compared with those before the exposure. There were no noticeable effects of hypobaric conditions in every measurement. In conclusion, prolonged sitting seems to be a more hazardous factor for thrombogenesis low humidity and hypobaric conditions during a long-distance flight.

Red cell macrocytosis in hypoxemic patients with chronic obstructive pulmonary disease

Macrocytosis is a common finding in patients with chronic obstructive pulmonary disease (COPD). The cause for the elevation of mean corpuscular volume (MCV) in these patients remains elusive. In an attempt to determine the extent of macrocytosis in COPD patients and search for possible causative factors, we evaluated the hematologic parameters, F-cell percentage, blood gases and serum erythropoietin (Epo) Levels in 32 COPD clinically stable patients and 34 sex- and age-matched non-smoker healthy volunteers. An increased MCV was observed in almost half of the hypoxemic COPD cases (14/32 or 43.75%), while erythrocytosis developed to a lesser degree (37.5%). The erythropoietic response did not correlate with the severity of hypoxia. Moreover, no significant correlation was found between macrocytosis and hypoxemia or erythrocytosis and red cell size. In some cases the two phenomena occurred independently. The F-cell percentage was significantly elevated in the COPD group (P < 0.01) and was associated with MCV values (n = 32, r5 = 0.41, P < 0.05). This finding supports the hypothesis we put forward to explain the macrocytosis often observed in COPD, i.e., that the acute erythropoietic stress occurring repeatedly in these patients as a result of the frequent exacerbations may lead to waves of release of relatively immature, large red cells from the marrow, including an increased number of F-cells, reflecting the recruitment of normally dormant BFU-E (bursts forming units of erythrocyte precursors), which maintain the program for gamma-chain synthesis. The fact that erythrocytosis and macrocytosis, both being triggered by hypoxemia, do not occur consistently in all COPD patients indicates that many other factors may also intervene.

Indications et limites de l'utilisation d'érythropoïétine recombinée en réanimation

OBJECTIVE

To analyze the data from the literature on erythropoietin and the future indications of recombinant human erythropoietin in intensive care unit (ICU) patients.

DATA SOURCE

References were obtained from computerized bibliographic research (Pubmed) from 1986 to 2003, except for some physiologic data.

DATA SELECTION

Original articles, reviews, and letters to editor in French and English were selected and analyzed.

DATA SYNTHESIS

An anemia is often observed in patients hospitalized in ICU. This anemia may be due to many reasons. The management of anemia consists on the treatment of the underlying disease associated with the transfusion of red blood cells. Recent studies provided evidence of an association between transfusions and mortality in ICU patients. The anemia of ICU patients is compared to the anemia of chronic diseases, which is characterized by a blunted erythropoietin. A treatment with rHuEPO may be a future therapeutic of the anemia in such patients. A multicentric study shows the efficacy of recombinant erythropoietin therapy on a decrease in the use of red blood cell, and another clinical trial highlights a decrease of the proportion of ICU patients receiving red blood cell. Recombinant erythropoietin could be an alternative to transfusion in certain conditions and certain ICU patients. Further studies are needed to determine the consequences on mortality rate and to clarify the place of this therapy in ICU patients.

Intermittent normobaric hypoxia does not alter performance or erythropoietic markers in highly trained distance runners

This study was designed to test the hypothesis that intermittent normobaric hypoxia at rest is a sufficient stimulus to elicit changes in physiological measures associated with improved performance in highly trained distance runners. Fourteen national-class distance runners completed a 4-wk regimen (5:5-min hypoxia-to-normoxia ratio for 70 min, 5 times/wk) of intermittent normobaric hypoxia (Hyp) or placebo control (Norm) at rest. The experimental group was exposed to a graded decline in fraction of inspired O2: 0.12 (week 1), 0.11 (week 2), and 0.10 (weeks 3 and 4). The placebo control group was exposed to the same temporal regimen but breathed fraction of inspired O2 of 0.209 for the entire 4 wk. Subjects were matched for training history, gender, and baseline measures of maximal O2 uptake and 3,000-m time-trial performance in a randomized, balanced, double-blind design. These parameters, along with submaximal treadmill performance (economy, heart rate, lactate, and ventilation), were measured in duplicate before, as well as 1 and 3 wk after, the intervention. Hematologic indexes, including serum concentrations of erythropoietin and soluble transferrin receptor and reticulocyte parameters (flow cytometry), were measured twice before the intervention, on days 1, 5, 10, and 19 of the intervention, and 10 and 25 days after the intervention. There were no significant differences in maximal O2 uptake, 3,000-m time-trial performance, erythropoietin, soluble transferrin receptor, or reticulocyte parameters between groups at any time. Four weeks of a 5:5-min normobaric hypoxia exposure at rest for 70 min, 5 days/wk, is not a sufficient stimulus to elicit improved performance or change the normal level of erythropoiesis in highly trained runners.

Do alterations of endogenous angiotensin II levels regulate erythropoietin production in humans?

AIMS

Recent evidence suggests a potential role of angiotensin II in the physiological regulation of erythropoietin (Epo) production. While the administration of exogenous angiotensin II (AII) has been used so far to study its effects, the role of endogenous AII has remained unclear.

METHODS

To alter endogenous AII in humans experimentally we used furosemide bolus injection as a short-term (study 1) and dietary salt as a long-term modulator (study 2). In an open crossover design, 12 healthy male volunteers received furosemide (F) 0.5 mg kg(-1) intravenously or placebo (P) in random order (study 1). With the same design, 12 volunteers received high-salt (HS), normal-salt (NS) and low-salt (LS) diet (study 2). Plasma renin activity (PRA) was analysed along with AII. Inulin and paraaminohippurate (PAH) clearances were used to indicate glomerular filtration rate (GFR) and renal plasma flow (RPF), respectively.

RESULTS

While F stimulated AII and PRA and decreased GFR and RPF significantly, no concomitant alteration of Epo was observed [AUCEpo: placebo 5709 +/- 243 (% of baseline x h), furosemide: 5833 +/- 255 (% of baseline x h); 95% confidence interval (CI) -608.4, 856.0; P = 0.73]. F decreased GFR (from 103.6 +/- 4.0 to 90.6 +/- 4.8 ml min(-1) 1(-1) 73 m-2; 95% CI 1.1, 24.9; P < 0.05), but not RPF (study 1). Correspondingly, LS stimulated and HS decreased AII and PRA significantly. HS increased GFR and RPF. Again, Epo concentrations were not affected (AUCEpo: normal sodium 44 +/- 6.7 mIU x day ml(-1), low sodium 39 +/- 2.4 mIU x day ml(-1), high sodium 48.5 +/- 6.1 mIU x day ml(-1); normal salt/low salt 95% CI -11.9, 21.9, P = 0.54; normal salt/high salt 95% CI -14.4, 23.3, P = 0.63; study 2).

CONCLUSIONS

We conclude that, at least in the physiological setting in healthy volunteers, increased concentrations of endogenous AII may not be a major factor of Epo regulation.

Nucleated red blood cell counts: not associated with brain injury or outcome

The objective was to determine whether an elevated nucleated red blood cell count at birth after perinatal depression is associated with brain injury as measured by (1) proton magnetic resonance spectroscopy and (2) abnormal neurodevelopmental outcome at 30 months of age. The nucleated red blood cell counts from the first 24 hours of life were statistically analyzed in 33 term infants enrolled in a prospective study of the value of magnetic resonance imaging for the determination of neurodevelopmental outcome after perinatal depression. Nucleated red blood cell counts were elevated in 13/33 (39%). Abnormal outcome (19/33, 54%) was associated with Score for Neonatal Acute Physiology-Perinatal Extension (P = 0.04), decreased N-acetylaspartate to choline ratio in the basal ganglia (P = 0.009), and increased lactate to choline ratio in the basal ganglia (P = 0.02), but not with cord pH, Apgar score, or nucleated red blood cell value. In a logistic regression model, increasing nucleated red blood cell counts did not increase the odds of an abnormal outcome at 30 months of age (OR 1.02, P = 0.17). In a population of neonates with perinatal depression, the nucleated red blood cell count at birth does not correlate with magnetic resonance spectroscopy or 30-month neurodevelopmental outcome. The nucleated red blood cell count should not be used as a surrogate marker for subsequent brain injury.

Effect of maternal exercise and fetoplacental growth rate on serum erythropoietin concentrations

OBJECTIVE

This study was undertaken to test the null hypotheses that neither weight-bearing exercise nor fetoplacental growth has a short- or long-term effect on the maternal serum erythropoietin level.

STUDY DESIGN

Serial blood samples were obtained before and after exercise from seven women who exercised regularly and seven physically active controls before pregnancy and at 8, 16, 24, 32, and 38 weeks' gestation. Fetoplacental growth was assessed both in midpregnancy (ultrasound) and at birth (morphometry).

RESULTS

Maternal serum erythropoietin levels rose with advancing gestation in both groups. Individual patterns, however, were quite variable and not related to differences in fetoplacental growth. There were no significant between-group differences at any time point, but levels rose after exercise in mid and late pregnancy.

CONCLUSION

The highly variable, pregnancy-associated changes in maternal serum erythropoietin were unrelated to variability in fetoplacental growth or maternal hematocrit. Absolute levels of erythropoietin are not influenced by regular exercise before or during pregnancy, but small acute elevations are seen after exercise in mid and late pregnancy.

Effect of short-term and intermittent normobaric hypoxia on endogenous erythropoietin isoforms

The aim of the present study was to evaluate whether the Epo isoforms in blood, induced by short-term and intermittent hypoxia, are different from those at normoxia at sea level and if this could be an impediment to the use of a direct Epo doping test based upon the electric charge of the Epo isoforms. Ten healthy subjects, 9 men and 1 woman, participated in the study. Median age was 22 years (range 20-32). Normobaric hypoxia was administered differently in 3 sub-groups; two groups with 12 h hypoxia and 12 h normoxia up to 10 days: IM 2000 and IM 2700 living in 16.2% and 14.9% O2, corresponding to 2000 and 2700 m above sea level, respectively, and training in normoxia. The third group, C 2700, lived in hypoxia, 14.9% O2 corresponding to 2700 m, continuously for 48 h. The mean serum Epo level increased from 10.9 IUL(-1) (range 8.8-12.5) to 23.5 IUL(-1) (15.6-29.1) after 2 days followed by 19.7 IUL(-1) (16.1-24.1) after 10 days exposure for intermittent hypoxia. The highest values 39.5 IUL(-1) (31.5-50) were obtained for the group exposed for continuous hypoxia for 48 h. The median electrophoretic mobility of the serum Epo isoforms was above the cut-off limit of 670 AMU, previously estimated for discrimination between recombinant and endogenous Epo, in all samples taken before and after exposure to hypoxia. The highest values, mean 730 mAMU (range 703-750) were obtained after 10 days of intermittent hypoxia.

CONCLUSION

If the method had been used as a doping test, no false positive results would have been registered for the 15 serum samples from the 10 individuals exposed for hypoxia. Thus, the results indicate that the basic principle for direct detection of recombinant Epo doping, based upon the change in electric charge on Epo, can be used also on individuals having lived in a hypoxic milieu.

Why is erythropoietin made in the kidney? The kidney functions as a 'critmeter' to regulate the hematocrit

The normal hematocrit is not a random number, but one that maximizes oxygen delivery. While the feedback loop wherein tissue oxygen pressure determines the production of erythropoietin, which further drives the production of red blood cells in the bone marrow, explains how the hematocrit is generated, it does not speak to how the hematocrit is regulated. The regulation of the hematocrit requires the coordination of the plasma volume and the red cell mass. By controlling red cell mass via erythropoietin and plasma volume through excretion of salt and water, the kidney is able to generate the hematocrit. It is hypothesized that the kidney functions as a critmeter by sensing the relative volumes of each component of the blood through the common signal of tissue oxygen tension. The kidney's unique ability to sense ECF volume through tissue oxygen signal allows it to coordinate these two volumes to produce the normal hematocrit. Hence, it may be the kidneys ability to report a measure of ECF volume as a tissue oxygen signal and thus to regulate the hematocrit that establishes it as the logical site of erythropoietin production. The critmeter is proposed to be a functional unit located at the tip of the cortical labyrinth at the juxta-medullary region of the kidney where erythropoietin is made physiologically. Renal vasculature and nephron segment heterogeneity in sodium reabsorption likely provides the anatomical construct to generate the marginal tissue oxygen pressure required to trigger the production of erythropoietin. The balance of oxygen consumption for sodium reabsorption and oxygen delivery is reflected by the tissue oxygen pressure. This balance hence determines RBC mass adjusted to plasma volume. Factors that affect blood supply and sodium reabsorption in a discordant manner may modulate the critmeter, e.g. angiotensin II. The objective of this work is to describe the hypothesis of the kidney's function as a critmeter, including the anatomical and physiological components, and the role of the renin-angiotensin system in modulating erythropoietin. Clinical examples of the dysregulation of the critmeter may be found in the anemia of renal failure and in sports anemia.

Effects of intermittent exposure to high altitude on blood volume and erythropoietic activity

The purpose of this review is to describe changes in blood volume and erythropoietic activity occurring under different types of intermittent exposure to hypoxia. These hypoxic episodes can vary from a few seconds or minutes to hours, days, or even weeks. Short hypoxic episodes like sleep apnea only lead to a small increase in hemoglobin concentration, which is mainly due to a hormonal-mediated decrease in plasma volume. In most of these cases the cumulative time spent under hypoxia does not exceed the critical threshold of about 90 min. Endurance athletes and mountaineers who voluntarily expose themselves to hypoxia for some hours or during the night while spending the day at normoxia ("sleep high-train low" concept) do improve their physical performance. Despite raising erythropoietic activity, indicated by elevated plasma concentrations of EPO and the transferrin receptor, the postulated increase in red cell volume has not satisfactorily been proved. Frequent changes between low and high altitudes, which are usual in some South American and Asian countries, provoke similar adaptations in red cell mass as occur in high altitude residents. However, the plasma volume decreases at altitude and increases again when staying at sea level. Even after more than 20 yr of regular moving between low and high altitude, the total blood volume, hemoglobin concentration and hematocrit, as well as the plasma EPO concentration, noticeably oscillate during every hypoxic-normoxic cycle. We assume these changes to be an optimal rapid adaptation of the oxygen transport system to the prevailing hypoxic or normoxic environment. However, possible risks for the organism cannot be excluded.

Intermittent hypoxic training: fact and fancy

Intermittent hypoxic training (IHT) refers to the discontinuous use of normobaric or hypobaric hypoxia, in an attempt to reproduce some of the key features of altitude acclimatization, with the ultimate goal to improve sea-level athletic performance. In general, IHT can be divided into two different strategies: (1) providing hypoxia at rest with the primary goal being to stimulate altitude acclimatization or (2) providing hypoxia during exercise, with the primary goal being to enhance the training stimulus. Each approach has many different possible application strategies, with the essential variable among them being the "dose" of hypoxia necessary to achieve the desired effect. One approach, called living high-training low, has been shown to improve sea-level endurance performance. This strategy combines altitude acclimatization (2500 m) with low altitude training to ensure high-quality training. The opposite strategy, living low-training high, has also been proposed by some investigators. The primacy of the altitude acclimatization effect in IHT is demonstrated by the following facts: (1) living high-training low clearly improves performance in athletes of all abilities, (2) the mechanism of this improvement is primarily an increase in erythropoietin, leading to increased red cell mass, V(O2max), and running performance, and (3) rather than intensifying the training stimulus, training at altitude or under hypoxia leads to the opposite effect - reduced speeds, reduced power output, reduced oxygen flux - and therefore is not likely to provide any advantage for a well-trained athlete.

Interval hypoxic training

Interval hypoxic training (IHT) is a technique developed in the former Soviet Union, that consists of repeated exposures to 5-7 minutes of steady or progressive hypoxia, interrupted by equal periods of recovery. It has been proposed for training in sports, to acclimatize to high altitude, and to treat a variety of clinical conditions, spanning from coronary heart disease to Cesarean delivery. Some of these results may originate by the different effects of continuous vs. intermittent hypoxia (IH), which can be obtained by manipulating the repetition rate, the duration and the intensity of the hypoxic stimulus. The present article will attempt to examine some of the effects of IH, and, whenever possible, compare them to those of typical IHT. IH can modify oxygen transport and energy utilization, alter respiratory and blood pressure control mechanisms, induce permanent modifications in the cardiovascular system. IHT increases the hypoxic ventilatory response, increase red blood cell count and increase aerobic capacity. Some of these effects might be potentially beneficial in specific physiologic or pathologic conditions. At this stage, this technique appears interesting for its possible applications, but still largely to be explored for its mechanisms, potentials and limitations.

Determinants of erythropoietin release in response to short-term hypobaric hypoxia

We measured blood erythropoietin (EPO) concentration, arterial O(2) saturation (Sa(O(2))), and urine PO(2) in 48 subjects (32 men and 16 women) at sea level and after 6 and 24 h at simulated altitudes of 1,780, 2,085, 2,454, and 2,800 m. Renal blood flow (Doppler) and Hb were determined at sea level and after 6 h at each altitude (n = 24) to calculate renal O(2) delivery. EPO increased significantly after 6 h at all altitudes and continued to increase after 24 h at 2,454 and 2,800 m, although not at 1,780 or 2,085 m. The increase in EPO varied markedly among individuals, ranging from -41 to 400% after 24 h at 2,800 m. Similar to EPO, urine PO(2) decreased after 6 h at all altitudes and returned to baseline by 24 h at the two lowest altitudes but remained decreased at the two highest altitudes. Urine PO(2) was closely related to EPO via a curvilinear relationship (r(2) = 0.99), although also with prominent individual variability. Renal blood flow remained unchanged at all altitudes. Sa(O(2)) decreased slightly after 6 h at the lowest altitudes but decreased more prominently at the highest altitudes. There were only modest, albeit statistically significant, relationships between EPO and Sa(O(2)) (r = 0.41, P < 0.05) and no significant relationship with renal O(2) delivery. These data suggest that 1) the altitude-induced increase in EPO is "dose" dependent: altitudes > or =2,100-2,500 m appear to be a threshold for stimulating sustained EPO release in most subjects; 2) short-term acclimatization may restore renal tissue oxygenation and restrain the rise in EPO at the lowest altitudes; and 3) there is marked individual variability in the erythropoietic response to altitude that is only partially explained by "upstream" physiological factors such as those reflecting O(2) delivery to EPO-producing tissues.

Erythropoietin concentrations during 10 days of normobaric hypoxia under controlled environmental circumstances

Serum erythropoietin levels (s-[epo]), haemoglobin concentration ([Hb]), haematocrit (hct), and ferritin concentration ([fer]) were measured in seven healthy male volunteers (20-23 years) exposed continuously to hypoxia (PO(2) 14 kPa) for 10 days. Serum erythropoietin concentration increased significantly from 9.5 +/- 3.51 to 33.6 +/- 11.64 U L(-1) (P < 0.05) after 2 days of hypoxia. Thereafter, s-[epo] decreased. However, after 10 days s-[epo] was 18.7 +/- 5.83 U L(-1) which was still increased above the pre-hypoxia level (P < 0.05). Serum haemoglobin concentration and hct increased over the 10 days of hypoxia, [Hb] from 152 +/- 8.9 to 168 +/- 9.2 gL(-1) (P < 0.001), and hct from 43 +/- 2.4 to 49 +/- 2.6% (P < 0.001). Ferritin concentration decreased significantly during the hypoxic exposure from 82 +/- 46.9 to 44 +/- 31.7 mmol L(-1) after 10 days (P < 0.01). In conclusion, the initial increase of s-[epo] under controlled normobaric hypoxia was marked, 353%, and levelled off after 5-10 days at 62-97% above normoxia level. There was also a significant increase in [Hb] and hct and a decrease in [fer] after 10 days of exposure to normobaric hypoxia.

Erythropoietin response to hypoxia in patients with diabetic autonomic neuropathy and non-diabetic chronic renal failure

AIMS

An erythropoietin (EPO)-deficient anaemia is recognized in Type 1 diabetic patients with early nephropathy and symptomatic autonomic neuropathy (DN). The aim of this study was to determine whether the EPO response to hypoxia was deficient in order to clarify the mechanisms involved in this process.

METHODS

Five Type 1 diabetic patients DN (age 39 (28-48) years (mean (range))) with EPO-deficient anaemia (haemoglobin, Hb 10.6 (9.5-12.0) g/dl, EPO 5.0 (3.2-6.5) IU/l) and early diabetic nephropathy (persistent proteinuria 1161.6 (130-2835) mg/day, serum creatinine 97.6 (63-123) micromol/l)) were compared with nine normal subjects (age 31 (24-39) years, Hb 13.4 (11.8-15.7) g/dl, EPO 7.6 (5.6-10.3) IU/l) and four patients with non-diabetic advanced chronic renal failure RF (proteinuria 2157.5 (571-4578) mg/day, serum creatinine 490.2 (406-659) micromol/l, Hb 10.3 (9.0-11.3) g/dl, EPO 4.6 (2.9-8.5) IU/l). The subjects were exposed to 6 h of hypoxia (inspired oxygen 11.6-12.6%) by breathing a gas mixture via a hood. Hourly serum EPO levels were measured.

RESULTS

All groups showed a rise in EPO production after 2 h. The diabetic DN group achieved a similar maximal response to the normal subjects at 6 h (EPO 17.3 +/-5.4 vs. 17.8 +/-7.9 IU/l). The renal failure patients mounted an EPO response to hypoxia but at lower EPO levels.

CONCLUSIONS

Although the DN patients have inappropriately low EPO levels for the severity of their anaemia, they can mount an appropriate EPO response to moderate hypoxia. The mechanism underlying the EPO-deficient anaemia present in some diabetic patients remains unclear.

Current trends in altitude training

Recently, endurance athletes have used several novel approaches and modalities for altitude training including: (i) normobaric hypoxia via nitrogen dilution (hypoxic apartment); (ii) supplemental oxygen; (iii) hypoxic sleeping devices; and (iv) intermittent hypoxic exposure (IHE). A normobaric hypoxic apartment simulates an altitude environment equivalent to approximately 2000 to 3000m (6560 to 9840ft). Athletes who use a hypoxic apartment typically 'live and sleep high' in the hypoxic apartment for 8 to 18 hours a day, but complete their training at sea level, or approximate sea level conditions. Several studies suggest that using a hypoxic apartment in this manner produces beneficial changes in serum erythropoietin (EPO) levels, reticulocyte count and red blood cell (RBC) mass, which in turn may lead to improvements in postaltitude endurance performance. However, other studies failed to demonstrate significant changes in haematological indices as a result of using a hypoxic apartment. These discrepancies may be caused by differences in methodology, the hypoxic stimulus that athletes were exposed to and/or the training status of the athletes. Supplemental oxygen is used to simulate either normoxic (sea level) or hyperoxic conditions during high-intensity workouts at altitude. This method is a modification of the 'high-low' strategy, since athletes live in a natural terrestrial altitude environment but train at 'sea level' with the aid of supplemental oxygen. Limited data regarding the efficacy of hyperoxic training suggests that high-intensity workouts at moderate altitude (1860m/6100ft) and endurance perfor- mance at sea level may be enhanced when supplemental oxygen training is utilised at altitude over a duration of several weeks. Hypoxic sleeping devices include the Colorado Altitude Training (CAT) Hatch (hypobaric chamber) and Hypoxico Tent System (normobaric hypoxic system), both of which are designed to allow athletes to sleep high and train low. These devices simulate altitudes up to approximately 4575 m/15006 ft and 4270 m/14005 ft, respectively. Currently, no studies have been published on the efficacy of these devices on RBC production, maximal oxygen uptake and/or performance in elite athletes. IHE is based on the assumption that brief exposures to hypoxia (1.5 to 2.0 hours) are sufficient to stimulate the release of EPO, and ultimately bring about an increase in RBC concentration. Athletes typically use IHE while at rest, or in conjunction with a training session. Data regarding the effect of IHE on haematological indices and athletic performance are minimal and inconclusive.

Hypoxia-dependent protein expression: erythropoietin

Normal cell homeostasis relies on the ordered flow of nutrients and substrates through metabolic pathways. Any perturbation of this flow eventually leads to dysfunction, impairment of defense mechanisms, loss of viability and death. High altitude and pathological hypoxia represent a serious and frequent cause for the loss of cell viability. Although organisms customarily respond by triggering adaptive or maladaptive mechanisms, all forms of life eventually succumb to hypoxia if it is severe enough, irrespectively of the primary cause. This paper reviews one of the mechanisms by which organisms respond to hypoxia: erythropoiesis. Although such response is not always beneficial, the discovery of the biochemical mechanisms underlying erythropoiesis has triggered an active field of research that is actually applying lessons learned in the mountains to a more clinical environment.