The Circulatory and Metabolic Responses to Hypoxia in Humans – With Special Reference to Adipose Tissue Physiology and Obesity

Abstract

Adipose tissue metabolism and circulation play an important role in human health. It is well-known that adipose tissue mass is increased in response to excess caloric intake leading to obesity and further to local hypoxia and inflammatory signaling. Acute exercise increases blood supply to adipose tissue and mobilization of fat stores for energy. However, acute exercise during systemic hypoxia reduces subcutaneous blood flow in healthy young subjects, but the response in overweight or obese subjects remains to be investigated. Emerging evidence also indicates that exercise training during hypoxic exposure may provide additive benefits with respect to many traditional cardiovascular risk factors as compared to exercise performed in normoxia, but unfavorable effects of hypoxia have also been documented. These topics will be covered in this brief review dealing with hypoxia and adipose tissue physiology.

Cardiovascular adaptation to hypoxia and the role of peripheral resistance

“…The effects of hypoxia in mammals have been studied in humans and a range of animals( Korner and Edwards, 1960 ; Butler, 1967 ; Yasuma and Hayano, 2000 ; Heinonen et al, 2016 ; Kawaguchi et al, 2005 ). Curiously, published measurements to date indicate that almost all studies examining the cardiovascular effects of hypoxia have been carried out either over long time frames, that is, weeks and months, as part of studies of high altitude adaptations, or over very short time frames of approximately 5 to 10 min, typically under anaesthesia.…”

“…Hypoxia also occurs in various tissues if there are high levels of oxygen demand, e.g., in skeletal muscle during exercise. Work undertaken over the last 50 years has shown that acute systemic hypoxia in mice, rats, rabbits, chickens, dogs, sheep and humans causes acute tachycardia and hypertension ( Korner and Edwards, 1960 ; Butler, 1967 ; Yasuma and Hayano, 2000 ; Campen et al, 2004 ; Campen et al, 2005 ; Walsh and Marshall, 2006 ; Heinonen et al, 2016 ; Giussani et al, 1993 ; Fletcher, 2000 ). Prolonged hypobaric hypoxia in humans has also been shown to cause tachycardia and hypertension (these studies have primarily been undertaken in high altitude environments or models thereof)( Schultz et al, 2014 ; Calbet, 2003 ; Naeije, 2010 ; Hainsworth et al, 2007 ; Vogel and Harris, 1967 ).…”

Daily Intermittent Normobaric Hypoxia Over 2 Weeks Reduces BDNF Plasma Levels in Young Adults – A Randomized Controlled Feasibility Study

“…Several field experiments in the mountains and environmental studies in chambers report physiological effects of hypoxia ( Heinonen et al, 2016 ). These experiments show that hypoxia can induce cardiovascular stress, can increase sympathetic neural activation and can alter energy metabolism.…”

Altitude sickness and altitude adaptation

“…The interplay between chronic hypoxia and obesity is most interesting and complex and may be of very high relevance for the treatment of metabolic syndrome spectrum disorders.…”

“…While obesity affects more women than men, the male type of obesity (‘apple‐shaped type’) predisposes to metabolic syndrome. Exercise training combined with hypoxic exposure may provide additive benefits in patients with according cardiovascular risk factors, while more detailed studies are necessary to rule out potential unfavourable effects …”