By Nathalie Sami and Janice Wong
Certified scuba divers are familiar with the use of hyperbaric oxygen therapy (HBOT) for decompression sickness treatment. However, in the past 50 years, researchers have revealed HBOT’s broad applications to human physiology and medicine. The outlook for HBOT applications for treating wounds, neurological diseases, and even certain cancers appears promising. What once seemed relevant only for scuba divers has now been discovered to benefit members of the general population.
HBOT involves the administration of pure, 100% oxygen in a compression chamber at pressures above atmospheric levels. The resultant increase of oxygen content in blood yields a broad variety of physiological effects, because increased pressure allows oxygen to saturate more effectively in the body. For scuba divers, this increased oxygen pressure reduces the volume of inert-gas bubbles in blood vessels, reversing air embolism or decompression sickness (Danesh-Sani et al. 2012). Moreover, researchers have described several beneficial influences of HBOT on healing damaged tissues: increased white blood cell activity, reduced swelling, healing time reduction, tissue regeneration, and even synergistic activity with antibiotics (Strużyna et al. 2008). The Undersea Hyperbaric Medicine Society recommends many applications for HBOT that have proven successful (Table 1). Beyond these now standard uses, several novel research areas demonstrate further beneficial HBOT applications. HBOT applications to wounds, cancers, and neurological and vascular diseases will be discussed below.
Low oxygen content caused by swelling or burns reduces PH and prohibits wound healing. On the other hand, higher oxygen tension improves healing of wounds by stimulating tissue-forming cells (Danesh-Sani et al. 2012). Hyperbaric oxygenation of wounds thus initiates wound-healing events such as tissue and cell generation and resistance to infection (Shah 2010). Furthermore, oxygen helps fight against infections by killing bacteria that cannot tolerate oxygen (Youn 2001). For example, in treating injuries as common as burns, HBOT reduces healing time and number of infections (Strużyna et al. 2008).
Cholesterol Crystal Embolism (CCE)
Such benefits also apply to patients of cholesterol crystal embolism (CCE), a disease with a high mortality rate. In a case study of a 56-year-old man who developed CCE and who had already undergone an unsuccessful standard treatment, HBOT caused rapid improvement. As seen in Fig. 1, after two months, complete recovery was obtained, leading the authors to conclude that HBOT may serve as an effective treatment in CCE (Gurgo et al., 2011).
Another known application for HBOT is with bone healing, during which HBOT increases white blood cell activity and tissue formation (Danesh-Sani et al. 2012). Also, HBOT may induce the formation of new blood vessels by stimulating an increase of stem cells within the tissues (Shah 2010). An application of bone-healing effects regards the influence of HBOT on bone tissue after the cessation of smoking. Smoking has proven to delay bone healing and impair blood circulation; however, HBOT mitigates the effects of smoking on bone healing, now proving that bone damage caused by smoking may be reversible (Yen et al. 2008).
Surgical injuries present yet another opportunity for HBOT intervention. Danesh-Sani and colleagues (2012) asserted that use of HBOT before surgical treatment significantly reduces risk of postoperative infection and accelerates healing, and other studies demonstrate benefits of post-operative HBOT application. In the case of urethral reconstructive operations, which commonly cause decreased erectile function, findings suggest that HBOT stimulates the regeneration of injured nerves and promotes tissue formation to allow erectile function recovery (Yuan et al. 2011).
Solid tumors, which are often hypoxic, can increase genetic instability and activate invasive growth to exacerbate certain types of cancer (Moen & Stuhr 2012). By providing oxygenation, HBOT induces excessive oxygenation, which causes rapid degeneration and tumor cell destruction. As a result, HBOT is thought to yield beneficial effects in several types of tumors with minimal invasiveness (Danesh-Sani et al. 2012). As well, HBOT could improve and help overcome chemotherapeutic resistance by increasing cellular sensitivity to radiotherapy (Moen & Stuhr 2012).
Breast and Prostate Cancer
The adjunctive use of HBOT with chemotherapy has shown positive effects on reducing breast cancer. As the most frequently occurring cancer in women, breast cancer provides a worldwide threat, and HBOT has shown a strong effect against different mammary cancer cells. HBOT has also led to less aggressive and restricted growth of large tumor cell colonies (Moen & Stuhr 2012). Successful experiments regarding prostate cancer cells with HBOT have also generated affirming results. Cancer of the prostate is the second leading type of cancer for men, and in vitro experiments have demonstrated the efficacy of HBOT in decreasing the cancer cells’ growth rate and increasing their sensitivity to chemotherapy (Moen & Stuhr 2012).
The success of recent studies regarding the use of HBOT in improving neuromuscular pathologies has merited further investigation to confirm its beneficial uses and mechanisms.
The most evidence-supported neurological application for HBOT lies with autism spectrum disorders (ASD), which is currently diagnosed in 1 in 88 children in the US (CDC 2012). ASD includes neurodevelopmental disorders characterized by restrictive and repetitive behaviors as well as impairments in communication and social interaction. Several experiments involving the effects of HBOT on children with autism have reported clinical improvements, citing decreased inflammation and improved blood circulation to the brain. One study resulted in improvements in overall functioning for 80% of autistic children treated with HBOT, leading to the conclusion that HBOT is a safe treatment for as prevalent a neurological disease as ASD (Rossignol et al. 2009).
HBOT may reduce the symptoms of vascular diseases by improving circulation and oxygenation.
For instance, vascular dementia, caused by decrease blood flow to the brain, is characterized by loss of memory, confusion, problems with speech and understanding, and an increased dependence on others. While no effective treatment has been established, models have demonstrated HBOT’s ability to improve blood supply and promote nerve tissue formation in the brain and enhance learning and memory. One study found that patients receiving HBOT exhibited better cognitive function than patients of the control group after 12 weeks of treatment (Xiao et al. 2012).
Carbon Monoxide Poisoning
HBOT is also used to treat carbon monoxide poisoning. Usually, hemoglobin proteins in red blood cells transport oxygen. However, carbon monoxide binds more readily to hemoglobin than oxygen. As a result, the body is unable to distribute oxygen throughout the body when exposed to carbon monoxide resulting in hypoxia (Mills and Saulsberry, 2011). HBOT is effectively used to reverse this harmful effect.
Arterial gas embolisms and stroke
One of the common uses of HBOT is to treat arterial gas embolisms. An arterial gas embolism is when that gas in the circulatory system goes through arteries or pulmonary veins and blocks blood flow (Muth and Shank, 2000). In non-diving accidents the cause of arterial gas embolisms are caused by medical mistakes such as accidentally injecting air in patients. These escaped bubbles are very dangerous because they block blood flow to certain areas, resulting in hypoxic tissue. In the brain, reduced blood and oxygen flow can cause a stroke and brain damage. Acute stroke results from impairment of blood flow to the brain, which causes neuron cell death. HBOT may increase available oxygen and reduce brain swelling to prevent further neuron damage (Bennett et al. 2010). Stroke is a leading cause of death in the US, so these discoveries may yield huge implications. Hyperbaric medicine is effective in treating these problems because raising the pressure of the chamber causes the size of gas bubbles to decrease (Bell and Gill, 2004). In addition to the reduction in bubble size, oxygen can more easily dissolve to benefit the previously hypoxic environment (Muth and Shank, 2000).
Another study proved that HBOT creates a substantial increase in insulin sensitivity. The improvement occurs rapidly (e.g., within three treatments) and is sustained at least until the thirtieth treatment. HBOT may induce insulin sensitivity by oxygenating fat tissue and reducing inflammation (Wilkinson et al. 2012). This discovery could have important implications, because insulin insensitivity is associated with diabetes, high blood pressure, heart disease, obesity, and certain types of cancer, which cause the majority of deaths in America (Colberg 2008).
While HBOT provides many beneficial treatments, there are some associated risks, such as oxygen toxicity. Metabolizing oxygen releases highly reactive byproducts that build up over time and saturate in tissue with increasing pressure. Resulting oxygen toxicity can lead to respiratory issues and seizures, because the toxicity often affects the lungs and central nervous system (Almeling et al. 2000). Another risk commonly associated with HBOT is barotraumatic lesions, the result of unequal pressure between the outside and inside of an air containing space. For humans, the middle ear most commonly experiences barotrauma, but other areas include lungs, nasal cavities and sinuses, inner ears, and teeth (Almeling et al, 2000). Equalizing during treatment is important, because people who are unable to equalize their ears during HBOT can experience middle ear barotrauma (Undersea and Hyperbaric Medical Society, 2011). Middle ear barotrauma, the most common side effect of HBOT, occurs when the pressure outside the ear is greater than the pressure of the middle ear.
While there are some risks associated with hyperbaric treatment, careful administration and thorough monitoring can limit the risk of side effects of HBOT. Although HBOT has not yet been adopted as the primary treatment for many of the mentioned conditions, it provides a minimally-invasive opportunity for treatment. The discovery of HBOT’s physiological benefits has demonstrated implications for treating the most prevalent ailments in the US. Thus, the newly-proposed, broadly-reaching benefits of HBOT applications beyond diving injury treatment merit deeper investigations. Indeed, with so many potential treatment functions, HBOT has earned its reputation as “a therapy in search of diseases” (Danesh-Sani et al. 2012).
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About the authors:
Nathalie Sami is a rising sophomore majoring in Environmental Science and Health in the USC Dana and Dornsife College of Letters, Arts, and Sciences. Her interests include playing, coaching and watching basketball, learning about sustainable lifestyles, and volunteering at health sites.
Janice Wong is an incoming sophomore majoring in environmental science and health at the USC Dana and David Dornsife College of Letters, Arts and Sciences.
Editor’s note: Scientific Research Diving at USC Dornsife is offered as part of an experiential summer program offered to undergraduate students of the USC Dana and David Dornsife College of Letters, Arts and Sciences through the Environmental Studies Program. This course takes place on location at the USC Wrigley Marine Science Center on Catalina Island and throughout Micronesia. Students investigate important environmental issues such as ecologically sustainable development, fisheries management, protected-area planning and assessment, and human health issues. During the course of the program, the student team will dive and collect data to support conservation and management strategies to protect the fragile coral reefs of Guam and Palau in Micronesia.
Instructors for the course include Jim Haw, Director of the Environmental Studies Program in USC Dornsife, Assistant Professor of Environmental Studies David Ginsburg, Lecturer Kristen Weiss, SCUBA instructor and volunteer in the USC Scientific Diving Program Tom Carr and USC Dive Safety Officer Gerry Smith of the USC Wrigley Institute for Environmental Studies