A partial pressure is the pressure of an individual gas within an atmosphere. When the atmosphere is a mixture as is our own, the partial pressure of a gas is equal to the percentage of that particular gas, multiplied by the atmospheric pressure. A simple example of this would be the partial pressure of oxygen at sea level. Since sea level is 1 ata (atmospheres absolute) and oxygen makes up 21% of the atmospheric mixture, the partial pressure of oxygen is 0.21 ata. Partial pressure is often abbreviated and you may see the above calculation written, ppO2 = 0.21 ata, where pp stands for partial pressure and O2 would be oxygen or any other gas that was being calculated.
Okay, onto the second part of the question… Why should you care? Well, if you are as interested in hyperbaric as I am… then this is a crucial component of the science you must understand. That is, if you ever desire to move beyond the rhetoric of those simply repeating information without actually understanding what they are repeating.
When working with 100% oxygen, it is really easy to calculate the partial pressure as the ppO2 will be equal to the atmospheres absolute (ata). So, if you were in a chamber at 1.5 ata w/ 100% oxygen, then the ppO2 = 1.5 ata. However, if the chamber is only filled with ambient room air of 21% O2, then the ppO2 = 0.315 ata. A very substantial difference! Not necessarily better or worse, just different.
My point is that treatment dosage is partly made up of the treatment pressure and oxygen concentration, among other components such as duration. Neglecting to mention the oxygen concentration accurately is an injustice to the patient and the industry. Let me give you an example: Portable hyperbaric chambers are often supplemented with oxygen from an oxygen concentrator at flow rates as high as 10 LPM. On average, these oxygen concentrators produce 90-95% oxygen (dependent on flow rate). On the other hand, the chamber is pressurized and air flow remains constant throughout the session at a rate of 60 to 200 LPM (dependent on chamber and manufacturer). For the sake of simplicity, lets assume that the air compressor is generating 90 LPM and the O2 concentrator is producing 10 LPM, a combined total of 100 LPM. Even if the oxygen concentrator was producing 100% oxygen, the mixture of gas inside the chamber wouldn’t change more than 10% as the oxygen coming from the o2 concentrator only represents that much of the mixture. Therefore, in this example, the patient may only be breathing 30% oxygen at 1.3 ata. Of course, if the oxygen is fed into the chamber through an auxiliary port and then connected to a mask, the high concentration of oxygen is directed to the patients mouth and nose, thus the breathing mixture can be much greater, as high as 85%. Where I become upset and where the industry is misrepresenting itself lies in the act of a facility informing a patient in the above scenario that they are receiving 1.3 ata w/ 95% oxygen. I can’t even tell you how many times people have told me that the facility they were visiting informed them that this was the treatment they were receiving. In many of these cases, when I asked if they were wearing a mask… the reply was No! Then how were they receiving 95% oxygen? Answer… they weren’t. This is not to say that they may not have still reaped great benefit, and this is were the real problem is. Not that they received benefit, rather that the treatment dosage was misrepresented because the administrators didn’t know any better. Next, the patient goes on to share their story with others and perpetuates the misinformation regarding their treatment with 95% oxygen.
Now, imagine another office is setting up the chamber in the exact same manner yet they actually understand the dynamics and inform potential patients that they would receive 1.3 ata w/ 30% oxygen. The potential patient may respond… “No thank you, I will go someplace else. I need 95% oxygen.” The patient ends up going to another facility, one who mis-informs them of the treatment dosage and mechanics of treatment. If this patients treatment is successful, then the vicious circle perpetuates itself.
Part of what I am eluding to is that a high concentration of oxygen is not necessarily necessary in order to receive benefits from hyperbaric treatment for a wide array of conditions. However, if we continue to speak incorrectly in regards to the treatment dosage, then the industry and public awareness of this fact will never come to complete fruition.
With that said, I ask anyone reading this post to forward a link to anyone who could benefit from its content. Whether they be a reseller of equipment or the administrator of a facility, even the doctor themselves. If you come across an individual who misrepresents treatment dosage, politely correct them and share this post as an educational tool. It takes no effort on behalf of an individual to represent the treatment correctly; however, the effort necessary to combat the misrepresentation of the industry is tremendous.
Greg Harris - Hyperbaric Warrior