At the University of Szeged, photoacoustic spectroscopy research and development began in 1994 in the Photoacoustic Research Group led by Gábor Szabó and Zoltán Bozóki. With practical applications in the focus, the group’s research and development efforts have led to the emergence of an instrumentation pool and knowledge base. For example, in recent years they have developed instruments to measure ammonia emissions from artificial fertilizers for agriculture, and others to determine hydrogen sulphide and water vapour concentrations for the natural gas industry. Medical applications include the study of the gas composition (e.g. methane content) of exhaled breath for diagnostic purposes.
For photoacoustic signal generation, a gas sample is illuminated with laser light of the appropriate wavelength. The gas molecules that absorb the excitation light are excited from the ground state to a higher energy state. These molecules then return to the ground state, as a result of which the released energy heats up the surroundings of the light-absorbing molecules. “If the excitation light is periodically modulated, heat generation in the illuminated sample will also be periodic. Periodic temperature changes lead to periodic pressure changes, i.e. acoustic waves, which can be detected with a microphone. During photoacoustic signal generation, the amplitude of the produced sound is proportional to the amount of light absorbed, i.e. ultimately to the concentration of light-absorbing molecules,” explained Árpád Mohácsi, Head of ELI ALPS’ Vacuum Technology Group and former member of the Photoacoustic Research Group. He said that the instrument brought to the blood donation event is so sensitive that it can detect one or two methane molecules out of a million air molecules. The instrument’s sensitivity could be enhanced even more with higher power lasers, and possibly at other wavelengths.
According to Petra Hartmann, Associate Professor at the Department of Traumatology and Orthopaedics at SZTE SZAKK (University of Szeged’s Szent-Györgyi Albert Clinical Centre), methane in exhaled human breath can only come from the small intestine, which harbours methanogenic archaea or archaic bacteria as part of the microbiome. (Like bacteria, they are single-celled prokaryotic organisms, i.e. organisms whose cells lack a defined nucleus). The produced methane diffuses through the intestinal wall into the bloodstream, from where it is transported to the lungs and finally exhaled.
However, methane concentration in exhaled breath decreases in case of a sudden, severe blood loss. This is because the body immediately triggers a compensatory response – the blood vessels in the small intestine constrict, reducing methane production. However, there is currently no method for measuring or estimating the extent of blood loss on a continuous basis. Related information can only be obtained from indirect data such as augmented heart rate or lower blood pressure, or from haemoglobin and haematocrit values from repeated blood tests. It would therefore be useful to have an instrument to estimate the extent of blood loss and be able to adjust the therapy accordingly. The researchers believe that the device developed at the University of Szeged may be suitable for measuring methane concentration in exhaled breath.
For cooperating patients, the procedure is very simple and not strenuous at all, as they only need to exhale into a sensor through a mouthpiece. During surgeries, the procedure is even simpler, as in intubated patients the exhaled carbon dioxide level is measured anyway; methane concentration can be measured simply by introducing a portion of the exhaled air into the methane meter through a Y-connector. Petra Hartmann and her colleagues have already shown an increase in exhaled methane levels in polytraumatized patients as a result of fluid replacement therapy. Subsequently, exhaled methane levels were analyzed during hip replacement surgeries, but no significant relationship was found between blood loss and exhaled methane. This can be explained by the following: during such interventions, blood loss equals only 200–300 mL, but due to sufficient fluid replacement, the body’s compensatory response is not pronounced. Blood donation, on the other hand, is an excellent opportunity for methane concentration measurements, as nearly 500 mL of blood is removed from the body in a short time (ten minutes).
The blood donation event organized at ELI ALPS Laser Research Institute was attended by 26 donors (ELI ALPS employees). Members of the University’s research team could measure methane concentration in breath exhaled by four of them. In case of one donor, the methane level decreased for seven to eight minutes during the donation process, and then it started to increase in the last two minutes. According to Petra Hartmann, 30 per cent of people are methane producers, which can be explained by variations in the microbiome. She believes that with special solutions the study could be extended to non-methane producers too. “As a traumatologist, I am interested in how we could objectively measure the extent of blood loss. The more information we have about our patients, the more efficiently we can treat them. If we can prove that blood loss is closely related to the amount of methane exhaled, as well as the level of fluid and blood replacement, we will have a method useful for medical purposes. The result would be a major scientific breakthrough,” she said in summary.
Photos: Gábor Balázs
Author: Zoltán Ötvös