HiQ gases from Afrox are ‘made for purpose’, and each has to comply with a specific set of specifications. This is particularly pertinent in the health sector, where the purity and accuracy of the gas mixtures used have a direct bearing on the health and treatment of patients.
Afrox’s Special Products Manager for HiQ gases, Hans Strydom, spoke to gasworld about the South African company’s high-purity gas mixtures for respiratory medicine in the health sector; lung function and capacity testing; and the use of Heliox, a breathing gas designed to help people suffering from airway restriction diseases.
“We supply the testing gas to measure how effectively a patients lungs are working, for example. When we breathe in, oxygen (O2) in the air goes through bronchial tubes and into its smallest branches, called bronchioles, which have tiny air sacs called alveoli at their ends,” explains Strydom.
Blood passes through capillaries in the alveoli and takes up the oxygen that diffuses through the capillary wall from freshly breathed air. At the same time, carbon dioxide (CO2) is passed from the bloodstream and into the alveoli ready for exhaling. “This process keeps us alive, and smoking, age and lung diseases all cause health problems by blocking the pick up of O2 to by blood.”
Lung diffusion testing is used to assess how well this process works. By breathing in a HiQ test gas, the efficiency of the alveoli and capillaries in exchanging O2 for CO2 can be measured.
HiQ lung diffusion gas mixtures use small percentages of carbon monoxide (CO) in a helium (He)- O2 gas mixture to perform this test. CO emulates the O2 molecule, forming carboxyhemoglobin – instead of oxyhemoglobin – which is very stable and remains in the bloodstream.
By knowing the exact percentage of CO in the diffusion gas mixture and accurately measuring how much is breathed out, the effectiveness of the diffusion and absorption capacity of the lungs can be determined. Higher percentages of absorbed CO indicate healthier lungs, while compromised alveoli and capillary walls will result in lower absorption and higher percentages of CO in the exhaled gas.
“This also depends on lung capacity, which is generally measured at the same time,” adds Strydom. Hence the use of He in the HiQ mix, which measures the total alveolar volume and gives an indication of the number of contributing alveoli sacs transferring O2 and CO2 when breathing.
When breathing in He, it will diffuse through the alveoli membrane more quickly and easily than any other gas. By measuring the change in helium concentration after breathing out normally, the functional residual capacity (FRC) of the lungs can also be established, which is the volume of gas left in the deflated lungs.
Strydom quotes Christo van der Westhuizen, clinical technologist for pulmonology at the Lung Function Laboratory at Charlotte Maxeke Johannesburg Hospital (CMJA), who says that the gas analysers for lung function equipment are very sensitive and precise. If the gas mixture is not within specifications, the equipment will not function and/or the calibration values will be out of the accuracy range.
“Special gas mixtures are equipment specific and need to be ordered from a reputable gas supplier who can verify the accuracy of the gas mixtures. Afrox Special Gas is a reputable manufacturer for the supply of accurate gas mixtures as specified by the equipment manufacturers,” says Van der Westhuizen.
As well as using the Carbon Monoxide 4 mixture for the Unit’s Jeager Lung analysing system, CMJA also has a Sentry Suite System that uses the 0.3% Acetylene 5 mixture, which combines small percentages of acetylene, methane and CO to determine the absorption capacity of the alveoli. Both of these machines also use Afrox’s 9.5% He 3 mixture, a very pure gas with reduced nitrogen (N2), 9.5% He and 20% O2.
The Lung Testing Laboratory at CMJA also uses nSpire and ZAN Systems for lung function and diffusion testing, for which CO 4 and 5% CO2 3 mixtures are specified.
In addition to capacity testing, Afrox also offers He-rich Heliox gas mixtures to help people with respiratory problems. “Heliox can be used when the bronchial channels become restricted for some reason, due to asthma or emphysema, for example, to get O2 through to the weaker and smaller alveoli.”
“Normal medical Heliox is mixture of 21% O2, the same as in air, with 79% He, although other combinations are available such as 70/30 and 60/40. “The He in Heliox generates less airway resistance than the N2 in air, so reduces the ‘work of breathing’,” Strydom explains.
“Through our HiQ gases and healthcare programmes and in partnership with health professionals, we at Afrox strive to provide the highest possible standards in healthcare.”
“We also support research by clinicians and academic institutions to enable them to deliver of the right gas to the right organ in the right dose, optimising patient care and outcomes,” concluded Strydom.