Hypoxia: Causes, symptoms, and treatment

What is Hypoxia? 

Hypoxia refers to insufficiency in the level of oxygen supplied to body tissues. In other words, it is a condition that occurs when one body part or organ runs short of the ideal amount of oxygen supplied to tissue cells. According to Neuhaus and Hinkelbein (2014), hypoxia is a situation that occurs when a person’s blood fails to transport adequate blood to body tissues to satiate one’s metabolic needs. When an individual’s blood lacks enough oxygen, organs such as the brain, heart, liver and kidneys experience problems caused by hypoxia. It is a condition that is characterized by symptoms such as skin color changes, rapid breathing, slow heart rate, cough, confusion, sweating and wheezing. Petrassi, Hodkinson, Walters and Gaydos (2012) note that hypoxia is a medical condition that may result from a severe asthma attack, lung diseases, cyanide poisoning, heart problem and anemia leading to the narrowing of airways thereby making it hard for a person to breath in air into one’s lungs. 

Types of Hypoxia 

Five types of hypoxia are recognized in medicine. They include hypoxic hypoxia, anemic hypoxia, histiotoxic hypoxia, metabolic hypoxia and stagnant hypoxia. As Neuhaus and Hinkelbein (2014), explain, hypoxic hypoxia is the most common type that is experienced in the field of aviation. The form of hypoxia is commonly termed as altitude hypoxia and occurs at the lung level. In an unpressurized airplanes, aircraft operators encounter hypoxic hypoxia due to lack of oxygen flowing into their tissues. As the attitude increases molecules of oxygen become fragmented eventually resulting to reduced pressure. During ascension, oxygen percentage remains the same but the air pressure decreases in high altitudes. Lowering of the oxygen partial pressure with increasing altitude impairs the normal functioning of lungs which inhabits oxygen transportation via blood to the tissue cells. Anemic hypoxia occurs in the setting of anemia where due to low hemoglobin levels, the blood experiences reduced ability to carry inhaled oxygen leading to a diminished oxygen supply to body tissues ( Petrassi et al., 2012) . Anemic hypoxia defect is associated with the blood’s inability to supply oxygen due to fewer oxygen binding sites. In this type of hypoxia, the lungs are usually in a perfect working condition. Carbon monoxide is a common cause of anemic hypoxia. The gas binds to hemoglobin with a high affinity ultimately hindering the oxygen binding process. As Petrassi et al., (2012) explain, histiotoxic hypoxia also referred as histoxic hypoxia results when tissues are unable to utilize oxygen supplied to them by the lungs and blood. The condition happens at the tissue and cell level. The cell or the tissue requiring oxygen for normal functioning is impaired implying that it cannot use the supplied oxygen for metabolism. Pilots experience histoxic hypoxia when there is adequate oxygen to inhale but their tissues are unable to accept the circulated supply by the blood. Histoxic hypoxia is caused by three primary factors; cyanide, alcohol and narcotics indulgence. Tissue poisoning makes cells dysfunctional and unable to use oxygen appropriately. Despite the psychologically normal supply of oxygen by the blood and lungs to the cells, the tissues defective status makes them unable to process oxygen ( Johnston, Iremonger Hunt & Beattie, 2012) . 

Metabolic hypoxia results when the body tissues demand more oxygen than the one supplied by blood. During metabolic hypoxia, there is usually normal absorption, transportation and use of oxygen by the tissues but due to a condition that raises metabolism, the oxygen supplied becomes inadequate. The type of hypoxia may result from sepsis which is an overwhelming infection that attacks body tissue cells. Stagnant hypoxia is caused by inadequate blood blow which implies reduced oxygen supply to body tissues. They type occurs at circulatory level when flow of blood is compromised. In the case of pilots, even though there is an adequate oxygen inhalation, body tissue cells fail to get sufficient oxygen to support metabolism ( Legg, Gilbey, Hill, Raman, Dubray, Iremonger & Mündel, 2016) . Stagnant hypoxia can occur due to heart failure to pump effectively, enlarged veins or during a neurological shock which leads to arterial constriction. Exposure to cold temperatures also causes stagnant hypoxia where flow of blood to the lower extremities is reduced. During a rapid flight decompression or when flying an aircraft in cold weather, stagnant hypoxia may occur. 

Body chemistry during a Hypoxia Event 

During a hypoxia occurrence, oxygen sensors which include NAD(P)H and hydroxylase enzymes family provide a physiologic pathway response to inadequate oxygen supply. The body is stimulated to release ROS from the mitochondria to regulate posttranslational and transcriptional response to hypoxic conditions ( Greer, Metcalf, Wang & Ohh, 2012) . Protein centers such bas succinate-coenzyme Q reductase mediates the electron transport in the mitochondria which generates a free radical called ubiquinol from ubiquinone. The unpaired electron O 2 is donated by the free radical leading to generation of superoxide. According to Greer et al., (2012), the ROS generation process during hypoxia is amplified. Inhibitors such as rotenone and myxothiazol inhibit mitochondrial electron transport leading to oxidization of ubiquinone pool and abrogation of complex III which increases during hypoxic conditions. Oxidant stress increases due to oxidation of fluorescent probes. The stress results to reduced glutathione pools and increased radicals. The inhibition of ROS impairs transcriptional responses due to reduced oxygen supply. The macromolecular synthesis is also inhibited to enable energy conservation. The hypophosphorylation of mTOR and its effectors such as rpS6 and 4E-BP1 are also reversibly trigged. 

Reversing Hypoxic Symptoms 

Increasing level of oxygen intake would help reverse hypoxic symptoms. Oxygen therapy is a common intervention used in supplying additional oxygen during hypoxic conditions ( Thropp, Scallon & Buza, 2018) . The method entails using a mechanical equipment to redistribute oxygen. The added oxygen reverses hypoxia thereby bosting oxygen supply into a person’s blood and simplifying the degree of work that a hypoxic person’s lungs or heart does ( Gradwell & Rainford, 2016) . Liquid oxygen can also be used to reverse hypoxia. The method involves feeding through tubes connected to a liquid oxygen container to a person who has experienced hypoxia. In an aircraft, hypoxia can be reversed by donning an oxygen mask to get supplemental oxygen ( National Transport Safety Board (NTSB), n.d) . 

Personal Symptoms of Hypoxia 

Some of the hypoxic symptoms that manifested during my chamber experience include; breathlessness, euphoria, impairment of mental task and fatigue. Additional signs were excessive yawning, loss of consciousness, impairment of muscular coordination, sensory loss and irritability. I also experienced reduced night vision, headache, a feeling of fuzziness when thinking and blue tinge on lips and fingers. 

Accident whose Primary Case was attributed to Hypoxia 

The Cessna T182 aircraft crash in Ludlow, Calif occurred as a result of hypoxia. During a cross county flight, the controllers noticed that the aircraft had started to descend when the plane was about 150 miles away from landing. Upon being questioned, the controllers noted that the pilot responses were unintelligible and garbled. The aircraft passed through an 11,000 feet while continuing on a meandering descent eventually crashing. Post-accident investigations unraveled that the pilot had flown at altitudes exceeding 12,500 feel for 40 minutes without using supplemental oxygen which made him hypoxic ( Li, 2017) . The pilot never used the cockpit oxygen ports leading to the aircraft crash. The airplane lost control due to the pilot’s impairment caused by hypoxia. 

References 

Legg, S. J., Gilbey, A., Hill, S., Raman, A., Dubray, A., Iremonger, G., & Mündel, T. (2016). Effects of mild hypoxia in aviation on mood and complex cognition.  Applied ergonomics ,  53 , 357-363. 

Li, W. C. (2017). The Causal Factors of Aviation Accidents Related to.  Decision Making in Aviation , 363. 

Gradwell, D., & Rainford, D. (Eds.). (2016).  Ernsting's Aviation and Space Medicine 5E . CRC Press. 

Greer, S. N., Metcalf, J. L., Wang, Y., & Ohh, M. (2012). The updated biology of hypoxia ‐ inducible factor.  The EMBO journal ,  31 (11), 2448-2460. 

Johnston, B. J., Iremonger, G. S., Hunt, S., & Beattie, E. (2012). Hypoxia training: symptom replication in experienced military aircrew.  Aviation, space, and environmental medicine ,  83 (10), 962-967. 

Neuhaus, C., & Hinkelbein, J. (2014). Cognitive responses to hypobaric hypoxia: implications for aviation training.  Psychology research and behavior management ,  7 , 297. 

National Transport Safety Board (NTSB) (n.d). Safety Recommendation A-00-117, https://www.ntsb.gov/investigations/AccidentReports/_layouts/ntsb.recsearch/Recommendation.aspx?Rec=A-00-117 

Petrassi, F. A., Hodkinson, P. D., Walters, P. L., & Gaydos, S. J. (2012). Hypoxic hypoxia at moderate altitudes: review of the state of the science.  Aviation, space, and environmental medicine ,  83 (10), 975-984. 

Thropp, J. E., Scallon, J. F., & Buza, P. (2018). PERCLOS as an indicator of slow-onset hypoxia in aviation.  Aerospace medicine and human performance ,  89 (8), 700-707.