The physiological effects of hypobaric hypoxia versus normobaric hypoxia: a systematic review of crossover trials

Much hypoxia research has been carried out at high altitude in a hypobaric hypoxia (HH) environment. Many research teams seek to replicate high-altitude conditions at lower altitudes in either hypobaric hypoxic conditions or normobaric hypoxic (NH) laboratories. Implicit in this approach is the assumption that the only relevant condition that differs between these settings is the partial pressure of oxygen (PO2), which is commonly presumed to be the principal physiological stimulus to adaptation at high altitude. This systematic review is the first to present an overview of the current available literature regarding crossover studies relating to the different effects of HH and NH on human physiology. After applying our inclusion and exclusion criteria, 13 studies were deemed eligible for inclusion. Several studies reported a number of variables (e.g. minute ventilation and NO levels) that were different between the two conditions, lending support to the notion that true physiological difference is indeed present. However, the presence of confounding factors such as time spent in hypoxia, temperature, and humidity, and the limited statistical power due to small sample sizes, limit the conclusions that can be drawn from these findings. Standardisation of the study methods and reporting may aid interpretation of future studies and thereby improve the quality of data in this area. This is important to improve the quality of data that is used for improving the understanding of hypoxia tolerance, both at altitude and in the clinical setting

Hypogonadism in Systemic Diseases

Serum testosterone is often lower than normal in patients with acute or chronic systemic diseases. The underlying mechanisms involved in the reduced testosterone secretion depend on the type of systemic disease; thus, many pathogenetic mechanisms might be involved. These mechanisms involve the hypothalamus and the pituitary (secondary hypogonadism), the testis (primary hypogonadism), or both. The resulting low-serum testosterone could be reversible or not depending on the pathogenetic mechanism. Furthermore, the relationships between hypogonadism and the systemic disease are complex since these two clinical conditions may interact with each other in a bidirectional interplay. How to interpret low-serum testosterone in systemic diseases is not easy and univocal. Biochemical hypogonadism should be differentiated into overt clinical hypogonadism and functional hypogonadism, and testosterone treatment should be offered taking into account the primary systemic disease and the possible beneficial or harmful effect on it, as well as the presence of signs and symptoms of hypogonadism. In this chapter the main systemic illnesses associated with hypogonadism will be discussed together with their underlying pathogenetic mechanisms, clinical significance, relevance, and clinical and practical implications