Facilities for hyperbaric oxygen therapy that are suitable for animal experimental research are scarce. In this paper, the authors introduce a hyperbaric oxygen chamber that was developed specifically for animal experimental purposes. The hyperbaric oxygen chamber was designed to meet a number of criteria regarding safety and ease of use. The hyperbaric oxygen chamber conforms to 97/23/EC (Pressure Equipment Directive), Conformity Assessment Module G Product Group 1. It provides easy access, and can be run in manual mode, semi-automatic mode and full-automatic mode. Sensors for pressure level, oxygen level, temperature, humidity and carbon dioxide level allow full control. This state-of-the-art hyperbaric oxygen chamber for animal experimental purposes permits the investigation of the biological mechanisms through which hyperbaric oxygen therapy acts at a fundamental level.
Patients who are treated for head and neck cancer often undergo a combination of tumour resection and radiotherapy. Tumour resection often involves surgical removal of parts of the surrounding normal tissues, such as jaw bone, tongue and floor of the mouth as well. This may result in large tissue defects, which need to be corrected by means of reconstructive surgery. Concurrent radiotherapy may result in decreased regenerative capacity of these normal tissues. As a result, wound healing after reconstructive surgery is compromised, which can have negative consequences for the patient’s quality of life.
Hyperbaric oxygen therapy (HBOT) is considered to be able to partly or completely reduce radiation-induced tissue damage by stimulating cell proliferation, neovascularisation, and oxygenation in the irradiated tissues. Thus, HBOT improves the success rate of reconstructive surgery in previously irradiated tissues. Although HBOT has been clinically applied for several years, the exact biological mechanisms through which HBOT acts are not completely understood. The scientific literature shows that there is need for further pre-clinical research on this topic .
Animal studies that focus on investigating the effects of HBOT on irradiated tissues of the head and neck area are desired but HBOT facilities that are suitable for animal experimental research are scarce. Clinical HBOT facilities are often not suitable for various reasons. In this paper, the authors introduce a hyperbaric oxygen chamber that was developed specifically for animal experimental purposes.
Characteristics of the hyperbaric oxygen chamber
The hyperbaric oxygen chamber (HBO Test Vessel P1460) ( Fig. 1 ) has been developed in collaboration with a company with extensive expertise in the field of hyperbaric technology (Hytech BV, Raamsdonksveer, the Netherlands, www.hyperbaric-technology.com ). The hyperbaric oxygen chamber was designed to meet a number of criteria regarding safety and ease of use.
The HBO chamber conforms to 97/23/EC (Pressure Equipment Directive), Conformity Assessment Module G Product Group 1. It has been certified by TÜV (TÜV Industrie Service GmbH, TÜV SÜD Gruppe, Dampf- und Drucktechnik, München, Germany). The laboratory in the Erasmus Laboratory Animal Science Centre, where the HBO chamber is located, has been modified to meet the requirements for safe installation of hyperbaric oxygen chambers. The HBO chamber is connected to the central oxygen supply system of the laboratory, which provides pressurized pure oxygen so separate oxygen bottles are not needed to supply the HBO chamber with oxygen. This eliminates the risk of running out of oxygen during hyperbaric oxygen treatment because of the limited volume of an oxygen bottle. There is no need to replace depleted oxygen bottles with full ones, which saves time and minimizes the chances of operator errors whilst changing the oxygen bottles.
The cylindrical HBO chamber is 70 cm in diameter and 115 cm long. The HBO chamber has a volume of 420 l and weighs 600 kg. Inside the chamber there is a level, rectangular platform, on which animal cages can be placed, measuring 95 cm in length and 47.5 cm in width. Despite its weight, the roll-out unit and hand grip allow the HBO chamber to open and close smoothly. A safety pin is integrated to prevent the HBO chamber from opening whilst under pressure. The maximum working pressure for this vessel is 5 bar (equivalent to approximately 5 atmosphere absolute, whereas the normal air pressure at sea level is 1 atmosphere absolute). A safety valve is present which gradually reduces the pressure in case it exceeds 5 bar.
By installing the HBO chamber on a storage trolley suitable for its dimensions and weight, the HBO chamber is mobile and can be easily transported if necessary. All the materials used are suitable for exposure to pure oxygen and high pressure. The materials used should be able to withstand corrosion and should not be flammable in contact with pure oxygen. The maximum working pressure of 5 bar is equivalent to the weight of a column of water at approximately 50 m depth, therefore the materials used should be able to withstand such high pressure.
When the connector is plugged into a single-phase 230 V AC electric socket, all electrical devices on the HBO chamber are supplied with electricity. These electronic devices can be controlled from the control box and include a water machine (for circulating cool or hot water into the heating/cooling system), two LED lights (5 W each) inside the chamber, a gas/pressure analyser, a temperature analyser, a ventilator, a heating/cooling system, an alarm buzzer, and a data recorder ( Fig. 2 ).
The HBO chamber was designed to fit the most commonly used small laboratory animals, ranging from mice to rabbits. It is large enough to accommodate multiple animals simultaneously (the total number depending on the size of the animals used). There is easy access to the HBO chamber for placing the animals in the vessel, and the inner surfaces are easy to clean after use. A clear view into the vessel is provided by high-pressure proof acrylic windows, whilst the two LED lights provide sufficient light to be able to monitor the behaviour of the animals during treatment.
Human subjects who undergo hyperbaric oxygen therapy are usually placed in a chamber that is pressurized with normal air, whilst the pure oxygen is administered through oxygen masks. Animal subjects often do not tolerate such oxygen masks, so the HBO chamber is designed as a chamber in which the complete volume of air inside the vessel is replaced by pure oxygen. In this case, no oxygen masks are necessary.
Sensors are able to measure the oxygen concentration, the carbon dioxide concentration, the pressure, the temperature and the humidity inside the HBO chamber. A data recorder with thin-film transistor (TFT) screen is integrated to store the data on internal hard disk, compact flash memory card, or external USB device.
The system can run in three different modes: manual, semi-automatic, and fully automatic. When operating in manual mode, the operator controls the pressure level and oxygen level by adjusting the oxygen valves and purge flow meter by hand. The fully automatic mode relieves the operator from continually having to adjust the valves, by executing a program with pre-set values for pressure build-up time and desired oxygen level. The HBO chamber allows the operator to store up to ten pre-set programs. The semi-automatic mode can be used when the user needs to adjust the pressure and oxygen level manually at first, and let the automatic system take over to maintain the manually achieved oxygen and pressure levels.
The integrated climate control system helps to maintain a constant temperature in order to minimize temperature-related stress in the animals, as the temperature will fluctuate as a result of changes in pressure. A purge flow meter enables the operator to control the refresh rate of pure oxygen. This is important, as living creatures exhale carbon dioxide during their treatment inside the HBO chamber. By adjusting the purge flow meter, it is possible to maintain an oxygen concentration level of 100%.