This study aimed to determine whether brief hypoxic stimuli in a hypobaric chamber are able to elicit erythropoietin (EPO) secretion, and to effectively stimulate erythropoiesis in the short term. In two different experiments, a set of haematological, biochemical, haemorheological, aerobic performance, and medical tests were performed in two groups of healthy subjects. In the first experiment, the mean plasma concentration of EPO ([EPO]) increased from 8.7 to 13.5 mU.ml-1 (55.2%; P < 0.01) after 90 min of acute exposure at 540 hPa, and continued to rise until a peak was attained 3 h after the termination of hypoxia. In the second experiment, in which subjects were exposed to a simulated altitude of up to 5500 m (504 hPa) for 90 min, three times a week for 3 weeks, all haematological indicators of red cell mass increased significantly, reaching the highest mean values at the end of the programme or during the subsequent 2 weeks, including packed cell volume (from 42.5 to 45.1%; P < 0.01), red blood cell count (from 4.55 x 10(6) to 4.86 x 10(6).l-1; P < 0.01), reticulocytes (from 0.5 to 1.4%; P < 0.01), and haemoglobin concentration (from 14.3 to 16.2 g.dl-1; P < 0.01), without an increase in blood viscosity. Arterial blood oxygen saturation during hypoxia was improved (from 60% to 78%; P < 0.05). Our most relevant finding is the ability to effectively stimulate erythropoiesis through brief intermittent hypoxic stimuli (90 min), in a short period of time (3 weeks), leading to a lower arterial blood desaturation in hypoxia. The proposed mechanism for these haematological and functional adaptations is the repeated triggering effect of EPO production caused by the intermittent hypoxic stimuli.

It was concluded that short-term hypobaric hypoxia can activate the erythropoietic response and improve the aerobic performance capacity in healthy subjects.

We examined the effects of the 5-phosphodiesterase (5-PDE) inhibitor sildenafil on pulmonary arterial pressure and some oxygen transport and cardiopulmonary parameters in humans during exposure to hypobaric hypoxia at rest and after exercise. In a double-blind study, 100 mg sildenafil or placebo was administered orally to 14 healthy volunteers 45 min before exposure to 5,000 m of simulated altitude. Arterial oxygen saturation (SaO2), heart rate (HR), tidal volume (VT), respiratory rate (RR), left ventricular ejection fraction (EF), and pulmonary arterial pressure (PAP) were measured first at rest in normoxia, at rest and immediately after exercise during hypoxia, and after exercise in normoxia. The increase in systolic PAP produced by hypoxia was significantly decreased by sildenafil at rest from 40.9 +/- 2.6 to 34.9 +/- 3.0 mmHg (-14.8%; p = 0.0046); after exercise, from 49.0 +/- 3.9 to 42.9 +/- 2.6 mmHg (-12.6%; p = 0.003). No significant changes were found in normoxia either at rest or after exercise. Measurements of the effect of sildenafil on exercise capacity during hypoxia did not provide conclusive data: a slight increase in SaO2 was observed with exercise during hypoxia, and sildenafil did not cause significant changes in ventilatory parameters under any condition. Sildenafil diminishes the pulmonary hypertension induced by acute exposure to hypobaric hypoxia at rest and after exercise. Further studies are needed to determine the benefit from this treatment and to further understand the effects of sildenafil on exercise capacity at altitude.

In recent years, the altitude acclimatization responses elicited by short-term intermittent exposure to hypoxia have been subject to renewed attention. The main goal of short-term intermittent hypobaric hypoxia exposure programs was originally to improve the aerobic capacity of athletes or to accelerate the altitude acclimatization response in alpinists, since such programs induce an increase in erythrocyte mass. Several model programs of intermittent exposure to hypoxia have presented efficiency with respect to this goal, without any of the inconveniences or negative consequences associated with permanent stays at moderate or high altitudes. Artificial intermittent exposure to normobaric hypoxia systems have seen a rapid rise in popularity among recreational and professional athletes, not only due to their unbeatable cost/efficiency ratio, but also because they help prevent common inconveniences associated with high-altitude stays such as social isolation, nutritional limitations, and other minor health and comfort-related annoyances. Today, intermittent exposure to hypobaric hypoxia is known to elicit other physiological response types in several organs and body systems. These responses range from alterations in the ventilatory pattern to modulation of the mitochondrial function. The central role played by hypoxia-inducible factor (HIF) in activating a signaling molecular cascade after hypoxia exposure is well known. Among these targets, several growth factors that upregulate the capillary bed by inducing angiogenesis and promoting oxidative metabolism merit special attention. Applying intermittent hypobaric hypoxia to promote the action of some molecules, such as angiogenic factors, could improve repair and recovery in many tissue types. This article uses a comprehensive approach to examine data obtained in recent years. We consider evidence collected from different tissues, including myocardial capillarization, skeletal muscle fiber types and fiber size changes induced by intermittent hypoxia exposure, and discuss the evidence that points to beneficial interventions in applied fields such as sport science. Short-term intermittent hypoxia may not only be useful for healthy people, but could also be considered a promising tool to be applied, with due caution, to some pathophysiological states.

Seven healthy young men were submitted twice to a hypoxia tolerance test at a simulated altitude (3000 m). Their first acute exposure was in a hypobaric chamber; and the second, in a hypoxic tent. Cardiorespiratory parameters and heart rate variability measurements were obtained under each hypoxic condition. A significant decrease of 6% to 8% compared to normal oxygen conditions was observed in arterial oxygen saturation (SpO 2 ) in both hypoxic conditions at rest; whereas exercise led to decreases of 10% in SpO 2 despite an increase of 27% in respiratory minute volume. The low frequency (LF) and high frequency (HF) components of heart rate variability significantly changed from normoxia (LF: 37.1, HF: 62.9, LF/HF: 1.27) to hypobaric hypoxia (HH) (LF: 49.1, HF: 50.6, LF/HF: 1.96). However, these changes were not observed under normobaric hypoxia. Thus, heart rate variability behaved differently in the two hypoxic conditions, supporting the hypothesis that normobaric hypoxia and hypobaric hypoxia are not equal stimuli to the cardiovascular and respiratory systems. A correlation was found between sympathetic and vagal modulations in normoxia and SpO 2 at exercise under hypobaric hypoxia (HH). Individuals with higher sympathetic modulation (LF%) in normoxia had higher SpO 2 at exercise under HH (r = 0.808, P < 0.05) and individuals with higher vagal modulation (HF%) in normoxia showed a trend to lower SpO 2 in exercise under HH (r = −0.636, P = 0.125). This opens up the possibility of using this correlation as a tool for predicting the individual capacity to altitude acclimatization. © 2011 Consell Català de l'Esport. Generalitat de Catalunya. Published by Elsevier España, S.L. All rights reserved. * Corresponding author. E-mail address: gviscor@ub.edu (G. Viscor). PALABRAS CLAVEVariabilidad de la frecuencia cardiaca; Prueba de tolerancia a hipoxia; Tienda hipóxica; Cámara hipobárica; Saturación arterial de oxígeno Parámetros cardiorrespiratorios durante ejercicio submáximo en hipoxia aguda hipobárica y normobáricaResumen Siete jóvenes sanos y en buena condición física realizaron dos pruebas de tolerancia a hipoxia a una altitud simulada de 3.000 m. La primera fue en cámara hipobárica, mientras que la segunda se efectuó en una tienda hipóxica. Se registraron varios parámetros cardiorrespiratorios y la variabilidad de la frecuencia cardiaca. En comparación con las condiciones de normoxia, se observó un decremento significativo del 6% al 8% en la saturación de oxígeno arterial (SpO 2 ) en reposo en ambas condiciones de hipoxia. El ejercicio desencadenó descensos de un 10% en SpO 2 pese a un incremento del 27% del volumen minuto ventilatorio. Tanto los componentes de baja (LF) como alta frecuencia (HF) de la variabilidad del ritmo cardiaco cambiaron significativamente en hipoxia hipobárica (LF: 49,1, HF: 50,6, LF/HF: 1,96) respecto a normoxia (LF: 37,1, HF: 62,9, LF/HF: 1,27). Estos cambios no se apreciaron en condiciones de hipoxia normobárica, lo cual apoya la hipótesis de que la hipoxia hipobárica y norm...

After short-term intermittent exposure to hypobaric hypoxia, subjects increased their ventilatory response and SaO2 during exercise at simulated altitude. These changes may be interpreted as acclimatization to altitude. The monitoring of ventilatory response and SaO2 during moderate exercise in hypobaric hypoxia may be used to detect the first stages of acclimatization to altitude.

The difference between genders has generated increasing interest in recent years. It is well known that women and men show differences in their respiratory system: different red blood cell counts, haemoglobin and 2,3-diphosphoglycerate plasma concentrations. Recently, further differences have been found in the ventilatory response to hypoxia and exercise and the evolution of some respiratory illnesses. In this study it was found that during rest at sea level, the haemoglobin oxygen saturation, as measured by pulse oxymetry, is slightly higher in women than in men (98.6 (SD 1.1)% versus 97.9 (SD 0.9)%; p = 0.001). These findings are consistent with other studies, which found gender differences in the transcutaneous or tissue PaO(2). The difference in oxygen saturation is not related to differences in ventilation. The disparity is modest and does not seem to produce great differences in the oxygen content of arterial blood, but combined with the different affinity of haemoglobin for oxygen or different metabolic rate, may play a role in the course of elite competition sports, high altitude ascents or the evaluation of critically ill patients. Further studies are needed to establish the degree, extent and clinical importance of these differences in the saturation of haemoglobin.

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