In 1964, a “monoplace” hyperbaric chamber, the Vickers Hyperbaric Oxygen Bed, was introduced, in which a single patient could be totally immersed in a pure-oxygen environment. In a monoplace chamber, oxygen is inhaled from the atmosphere within the chamber. The monoplace chamber accommodates one person; the patient goes in and the door is closed. The chamber is usually made of acrylic on the top so the patient can see out all around. The oxygen is turned on to pressurize the chamber and one hears a whooshing sound that soon resolves itself into white noise.38
The temperature heats up during compression as a result of more oxygen being compressed. This is not markedly hot, and soon the chamber cools back down to room temperature. In the first few minutes of treatment, the ears will feel full, as they do on an airplane in changing altitudes, and this is when the patient needs to yawn, swallow, or pinch the nose and blow out until the ears “pop.” Sometimes soft earplugs are used to help with the pressure change. In monoplace chambers patients can watch television through the acrylic shell, or they might sleep.
Patients hear the white noise of the O2 blowing in the chamber and many fall asleep in this soothing environment. The patient is connected via speakers and microphones to the person monitoring the “dive” or HBOT session. Once the prescribed amount of time at pressure is over, the chamber is decompressed. The chamber cools somewhat and the patient’s ears normalize once again. “Air breaks” can be delivered by a mask that gives regular air.
Patients report different effects depending on the condition being treated. Some report feeling refreshed or relaxed, some slightly tired, and some patients don’t feel anything at all.
Most monoplace chamber designs are similar in construction: tube-like, with enough space for one or two individuals. Some are made entirely of metal with acrylic portholes designed for observation. Other, more popular, chambers are made largely of acrylic. The acrylic cylinder is held in place by steel tie rods connecting the two end caps. One of the end caps is a removable door that is big enough to easily insert a patient. This door must also meet basic safety requirements to maintain its constitution under atmospheric pressure and allow easy extraction of the patient in an emergency situation.
Inside the chamber, the patient does not wear a mask or oxygen hood, but instead breathes the 100% pure oxygen that is used to pressurize the chamber. Each chamber allows for a precise treatment protocol for patients with specific ailments, which is not possible with a multiple-occupancy multiplace chamber.39
Even though the acrylic chambers allow for better observation of the patient and a less claustrophobic feeling, some patients prefer monoplace chambers made from metal, as they tend to be larger and are more durable. Typically, this is for patients who prefer a roomier environment for their healing. Metal chambers are also preferred in more heavy-duty environments where they will experience rough handling and extreme environmental factors, such as on naval ships and in rugged outdoor locations. The durability of their construction goes so far as to protect the more delicate parts, such as the controls and windows, from the elements. Metal chambers are made from everything from steel to stainless steel or aluminum and have view ports made from fitted acrylic windows in carefully designed openings in the hull. Exact specifications vary between manufacturers.
While the science and the effectiveness of healing is the same no matter what size the chamber is, it should be noted that larger chambers do require more oxygen in order to reach the desired hyperbaric pressure.
The varying sizes and designs of the acrylic chambers and the acrylic windows in metal chambers have all been regulated by the ASME/PVHO-1 based on their experience in the diving industry and their extensive testing on materials and designs. In fact, most of the monoplace chambers manufactured in the U.S. have been made in ordinance with the ASME/PVHO-1. Some monoplace chambers are still being used with unapproved designs even after the ASME had voiced their concerns. Most of these chambers were designed and produced before the PVHO codes were established.