When we perform a collection of data obtained from gas analysis in hypoxia, do we need to conduct some special adaptations in the gas analysers? What is the best gas analyser to do this kind of evaluation? And finally, must we do some treatment in the data obtained, because the analyzers are setting to read in a FiO2 in normabaric enviroment?
Hi Ricardo,
I would say no as a first answer, assuming that your gas analyzer is in your lab at atmospheric pressure. However, irrespective of what you are planing to do, I always calibrate the gas analyzer at the beginning with several known gas mixtures, i.e 5% CO2 in air, N2, 5% CO2 in N2, and air. Even better if you have a wostoff pump.
Regarding the units, most gas analyzer have the option to change the units. Alternatively, after calibration you will be able to do it at your convenience. We have a ML 205 Gas analyser (ADI Instruments, Australia) and it works okay. But I have not been lucky enough to try another.
You might find this publication helpful regarding what we have done:
http://www.sciencedirect.com/science/article/pii/S0031938411000606
Good luck!
Hi Ricardo, let me understand better. There are three cases.
1. You get blood from the subject in normobaric hypoxia and measure gasses at the same BP? No correction needed.
2. Your subject is at low BP, you get blood there and measure gasses at the same BP. No corrections needed if you calibrate the gas analyzer with the appropriate gas mixture at the wanted BP.
3. Your subject is at low BP, you get blood there and measure gasses at the normal BP. In this case you need complex corrections, but first clarify if this is the case.
Best wishes
Michele
Hi. First let me thank you for the Answer.
Let me try to explain better.
The gas analysis is obtained from the collection of gas inhaled and exhaled from the mouth and not to the gas in the blood.
So the questions where:
When we perform a collection of data obtained from gas analysis in hypoxia, do we need to conduct some special adaptations in the gas analysers? What is the best gas analyser to do this kind of evaluation? And finally, must we do some treatment in the data obtained, because the analyzers are setting to read in a FiO2 in normabaric enviroment.
Now I understand better. Sorry, but I am not specialist in this particular kind of measurements and can't suggest you the best gas analyzer for this, but I do not think you need to perform particular corrections in this case.
I agree with Michele, you only need to consider the conversion between STPD or BTPS units:
http://bme.usc.edu/bme403/Section_1/convert1.html
Thank you for the help.
I agree with that but the intend is to delivery the hypoxia by a normobaric system, at sea level.
So the machine is reading 20,9 of o2 but we are delivering a different percentage of O2. That is the principal concern by now.
In a hypoxic tent the system delivery indicates you (and commonly allows for regulation) of real O2 fractional content i.e. 15% O2. A simple alternative is 1) to use a Douglas bag connected to a gas mixing system (air + N2); 2) to delivery, through a face-mask, a known gas mixture from a commercial dealer.
Regarding the expired gas analysis, under normobaric conditions, you can use any usual equipment (Cosmed, Medgraphics or similar) without any kind of corrections.
Hello Ricardo! In my studies in a normobaric hypoxic chamber I used Quark B2B (Cosmed Metabolic Card). It is able to measure the real FIO2 and of course the FEO2. It is important to pay attention on the calibration phase prior the start of the testing session. You need to re-set the calibration range around the value of hypoxia that you want to test. For instance, in normoxia your calibration range is from 17% O2 to 20,9% O2, but if you want to assess a FIO2 of 15% you need to calibrate your machine with a range around this new value (using a gas-bottle with 13 % of O2 content)! Not all the Cosmed products are able to measure the FIO2, for example the portable metabolimeter K4 works with a fixed value of FIO2 (20,9). Another aspect that can bias your results is the ventilation of your subjects. In hypoxia you have a greater ventilation, this is not a problem for intensity below the lactate threshold, but for higher intensity, where you find really great ventilation, your machine could not have the sufficient time to analyze properly every breath thus leading to a subvaluation of your real values!
We have used the Metamax 3x gas analysis system extensively in our research studies. As the above answers suggest you need to calibrate with different gases than you would normally use. We use our normobaric hypoxic chamber at FIO2:0.12 a great deal and subsequently we calibrate with gas mixture of 7%O2, 5%CO2 and 15%O2, 3%CO2. We have compared the validity and reproducibility of these measures to the gold standard douglas bag method with the Haldane transformation. Due to ventilatroy increases the CoV tends to be a little larger than you would expect in a normobaric normoxia.
Hope this helps