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Toxic and Asphyxiating Hazards in Confined Spaces
Published in Neil McManus, Safety and Health in Confined Spaces, 2018
Stimulation of chemoreceptors in the respiratory centers depends on pH and partial pressure of carbon dioxide in the interstitial fluid of the brain (Leusen 1972, Mitchell et al. 1963, Pappenheimer et al. 1965). These quantities depend on the composition of blood perfusing the medulla and cerebrospinal fluid (CSF). When the composition of CSF is kept constant, large ventilation increases can occur through increased partial pressure of CO2. Carbon dioxide readily penetrates the blood–brain barrier. Thus, the composition of CO2 in the CSF readily follows that in arterial blood. The chemoreceptor cells appear to be equally accessible to changes in CSF and the blood. Thus, response of the central chemoreceptors reflects pH and partial pressure of CO2 in both CSF and blood.
Oxygen Delivery and Acute Hypoxia: Physiological and Clinical Considerations
Published in Anthony N. Nicholson, The Neurosciences and the Practice of Aviation Medicine, 2017
The respiratory chemoreceptors responsible for the reflex responses to changes in arterial PCO2, PO2 and pH are the central chemoreceptors located in the brainstem and the peripheral chemoreceptors in the carotid and aortic bodies. In anaesthetized animal experiments, the central chemoreceptors were originally found to be located near the surface of the ventrolateral medulla (Mitchell et al., 1963; Loeschcke, 1982). More recently, using approaches such as recording the phrenic nerve response to focal acidosis produced by microinjection, central respiratory chemosensitivity has been found in other regions of the brainstem and cerebellum (Richerson et al., 2005; Nattie, 2000). It is not yet clear whether all these regions contribute equally to central chemoreception or whether one group is dominant (Guyenet, 2008).
Determining how different levels of indoor carbon dioxide affect human monotonous task performance and their effects on human activation states using a lab experiment: a tracking task
Published in Ergonomics, 2020
Yali Xia, Shin-ichi Shikii, Yoshihiro Shimomura
When the CO2 levels matched those typically occurring indoors, the task performance and alpha wave band activity were not significantly affected. Interestingly, despite the increase in the CO2 concentration of air, SPO2 did not necessarily change. Inhaling high concentrations of CO2 can increase the PaCO2, stimulating central chemoreceptors, thereby increasing breathing. Then elevations in ventilation could increase the arterial O2 pressure and thus SPO2. However, our results suggested that inhaling a CO2 concentration up to 4000 ppm may be insufficient to affect ventilation, as the participants exhibited stable SPO2 levels over changes in the CO2 concentration. Therefore, we suggest that elevations in CO2 up to 4000 ppm have no measurable influence on ventilation and PaCO2; therefore, they did not affect the monotonous task performance. Moreover, an increase of CO2 in the inspired air is known to cause vascular changes in the brain (Sicard et al. 2005), including increased cerebral blood flow (Ainslie and Duffin 2009), higher CO2 and O2 concentrations in the blood (Xu et al. 2011), as well as decreased ventilatory response to CO2, which is due to reduced CO2 accumulation around the chemoreceptors caused by vasodilation and higher cerebral blood flow amongst the divers (Kerem, Melamed, and Moran 1980). However, the potential effect of CO2 inhalation on neural activity is not clear. Further studies are needed to examine whether cerebral blood flow modulates monotonous tracking tasks.