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Oxygen Delivery and Acute Hypoxia: Physiological and Clinical Considerations
Published in Anthony N. Nicholson, The Neurosciences and the Practice of Aviation Medicine, 2017
Humans without carotid bodies show no significant increase in ventilation when breathing hypoxic gas mixtures (Lugliani et al., 1971; Swanson et al., 1978), which suggests that, in humans, the hypoxic ventilatory response is mediated almost entirely by the carotid bodies. A response can be demonstrated if these subjects are exposed to hypoxia when their arterial PCO2 is also experimentally raised by about 10 mm Hg, but even then the response is very small (Swanson et al., 1978). These patients would be particular vulnerable at high altitude, especially above about 10,000 feet (c. 3,000 metres), as their lack of ventilatory response (see Figure 6.9 and below) would result in more severe hypoxia than in normal subjects.
Altitude
Published in David G. Newman, Flying Fast Jets, 2014
In general, hypoxia is associated with a slow and progressive decline in performance (mental and physical). This is sometimes accompanied with a sense of euphoria. The reduced oxygen saturation of the blood is detected quite early by the chemoreceptors, and a well-documented hypoxic ventilatory response (HVR) is triggered, leading to hyperventilation (which is an attempt to compensate for the low oxygen content by increasing both the rate and depth of respiration).
Repeated remote ischaemic preconditioning can prevent acute mountain sickness after rapid ascent to a high altitude
Published in European Journal of Sport Science, 2022
Zhen Wang, Bo Lv, Lin Zhang, Ran Gao, Wenbo Zhao, Lin Wang, Zhaojun Min, Zhen Mi, Yang Song, Jing Zhang, Yabin Yu, Xunming Ji, Junjie Li, Liyong Wu
The precise pathogenic mechanisms underlying AMS remain to be elucidated. Hypoxia likely plays a central role in its pathogenesis (Taylor, 2011). Hypoxia at a high altitude can lead to hypoxemia, and the condition is aggravated by a reduced level of carbon dioxide through respiratory alkalosis and inhibition of the hypoxic ventilatory response (HVR) (Taylor, 2011). Hypoxemia induces the upregulation of hypoxia-inducible factor 1 and vascular endothelial growth factor and the formation of free radicals, which, together with hypoxemia, affect cerebrovascular permeability (Wilson, Newman, & Imray, 2009). A series of compensatory mechanisms, including adenosine production, potassium ion accumulation and nitric oxide release, may facilitate vasodilatation and alleviate cerebral hypoxia, although researchers have proposed that the exaggerated activity of these compensatory mechanisms may contribute to altitude maladaptation (Wilson et al., 2009).
Altitude training in endurance running: perceptions of elite athletes and support staff
Published in Journal of Sports Sciences, 2019
Gareth Turner, Barry W Fudge, Jamie S M Pringle, Neil S Maxwell, Alan J Richardson
In the development of an altitude training strategy both benefits and drawbacks must be considered. A high proportion of responses citing difficulties, risks or challenges were themed around “Training” and “Return to sea level”. Within the training theme “avoiding overtraining” and “difficulty controlling pacing” were frequently reported. There was also a high incidence of personal issues, such as, “some altitude training camps are too basic” or “there are more health risks”. A suppression of the immune system has been reported when training at altitude, which can be prevented with adequate personal hygiene and nutrition (Flaherty et al., 2016). Interestingly, the drawbacks from support staff did not mention return to sea level for competition (most frequently mentioned by athletes) but were centred on a variety of issues that appeared to be specific to the athletes they were coaching. The concern ranged from the trivial (“travel boredom”) to fundamental (“weight loss during camps”), along with complications that were beyond their control (“limited by finance and time away”). Support staffs were also concerned about disruption of training (“disrupted training when travelling overseas”) and sleep loss (“disrupted sleep when using tents, hypoxia”). Many of these issues have been previously reported (Bailey & Davies, 1997), and with sufficient pre-screening of individual athletes’ responses to training at altitude, some of these concerns can be alleviated. Indeed, pre-screening may provide support staff with a tool to reduce the incidence of overtraining, illness, reduced training intensity and poor performance at sea level. For example, the hypoxic ventilatory response, degree of oxygen (de)saturation and erythropoetic changes in response to acute hypoxia have been previously studied (Chapman, Stray-Gundersen, & Levine, 2010; Friedmann et al., 2005), but all require further investigation due to often inconclusive findings.