Main Breath Metabolites
Commonly used techniques related to breath analysis
Collect and analyze stored breath samples
Diagnosis of disease using volatile biomarkers
Commercial production of breath analyzers for disease detection
Breath is an important matrix for analyzing volatile organic compounds (VOCs) generated in the body. These compounds travel through the blood in the body, reach the alveolar interface and are eventually exhaled. The analysis of exhaled air to detect VOCs can indicate a person’s sick or healthy condition.
Researchers have documented evidence of the presence of detectable VOCs in the breath linked to breast and lung cancer. The scientific community is very interested in identifying all parameters that influence the presence of VOCs in exhaled air. In this regard, it has focused on standardizing breath sampling and analysis methodology. Breath analysis can lead to rapid and non-invasive detection of various diseases, such as diabetes and cancer.
Exhaled breath typically consists of unchanged nitrogen (~74%), argon (~1%), oxygen (~15%), carbon dioxide (~5%) and water vapor (~6%). In addition, several endogenously formed gaseous volatile metabolites are present in the exhaled breath at trace levels, which are measured in parts per million volume (ppmv), parts per trillion volume (pptv), or parts per billion volume (ppbv).
Over thirty days, researchers discovered common breath metabolites in several healthy individuals, such as acetone, methanol, ammonia, acetaldehyde, propanol, isoprene and ethanol. These metabolites were detected by the Selected Ion Flow Tube Mass Spectrometry (SIFT-MS) method. Variability in concentrations of these metabolites was assessed and the log-normal distribution for these metabolites was studied.
Ammonia is present in the body as a breakdown product of proteins via bacterial breakdown in the gut. While much of ammonia is converted to urea and excreted in the urine, a small portion is expelled from the breath. The concentration of ethanol and methanol can be increased by anaerobic fermentation by intestinal bacteria. The presence of isoprene in human breath is considered a marker of cholesterol synthesis. In addition, scientists revealed that an abnormal level of isoprene in human breath points to end-stage renal failure and oxidative stress.
Two of the analytical tools used to analyze breath to detect and quantify trace gases in real time with high sensitivity are Proton Transfer Reaction Mass Spectrometry (PTR-MS) and SIFT-MS. Both PTR-MS and SIFT-MS are known as soft ionization techniques that can detect biomarkers present in the breath samples ranging from ppbv to pptv. Although SIFT-MS is less sensitive than PTR-MS, it is advantageous because it does not use an electric field and reactions take place under thermal conditions.
Researchers have also used ion mobility spectrometry (IMS) and laser absorption spectroscopy (LAS) in breath analysis. Cavity ringdown spectroscopy (CRDS), based on LAS, has been used to measure nitrous oxide (NO) in exhaled air. This technique can quantify VOCs in breath at parts per billion at volume levels.
Electron Noses (e-Noses) is an electronic sensing device containing an array of gas and semiconductor based sensors. Two mass-sensitive sensor-based devices, namely quartz crystal microbalance (QCM) and surface acoustic wave (SAW), are used in breath analysis.
Direct sampling is preferred for breath analysis because it limits the possibility of loss of compounds through diffusion or sample degradation. However, in the scenario where direct sampling is not possible, a suitable storage system of exhaled air is an important aspect. Scientists pointed to the risk of contaminating the breath samples with background emissions of pollutants, which could alter the chemistry of the stored samples.
At present, inert Tedlar bags with many improvements are manufactured by many companies, such as Dupont and SKC Ltd. These bags are transparent or black and are based on different components, such as Nalophan, Flexfoil and Teflon. Previous studies have shown that Nalophan bags are inexpensive and most popular for collecting breath samples. The stability of the breathing components in Tedlar bags has been determined with gas chromatography-MS (GC-MS) and PTR-MS.
The stored breath has been analyzed for the presence of VOCs through various methods, such as needle trap micro-extraction (NTME) in combination with GC and solid phase micro-extraction (SPME).†
Scientists have assessed SIFT-MS and PTR-MS technologies to determine whether they can detect liver disease and control diabetes. In addition, these techniques were also assessed for the diagnosis of various cancers, such as lung, colorectal, bladder and prostate cancer.
Can a simple breath test diagnose a disease? † Billy Boyle | TEDxCambridgeUniversity
In the context of early detection of lung and breast cancer, methylated hydrocarbons have been proposed as biomarkers. Scientists stated that the presence of acetaldehyde in exhaled air above 22 ppb could be of great clinical importance. Although acetaldehyde is an intermediate in the metabolism of ethanol in the liver, alcohol intake significantly increases levels in the breath. Scientists determined the molecular emission of cancer cell lines CALU-1 and SK-MES and found their presence to be higher than physiological levels.
VOCs produced by gut bacteria are transported to and excreted by the lungs. VOCs released by, for example, Helicobacter pylori in the human stomach can be detected in the mouth exhaled air. Helicobacter pylori infect the stomach and intestines, damage the tissues of the gastric mucosa and cause inflammation. This pathogen causes stomach ulcers in humans.
Scientists have designed a breath analyzer for the detection of pulmonary tuberculosis. In this case, the detected biomarker compounds are methyl p-anisate, methylphenylacetate, O-phenylanisole and methylnicotinate.
Owlstone was formed by a group of scientists from the University of Cambridge who manufactured and marketed “Field Asymmetric Ion Mobility Spectrometry (FAIMS)”. Their “Breath Biopsy” technology can accurately profile VOCs present in breath samples.
Breath Diagnostics, a Kentucky start-up company, developed a breath diagnostic device for lung cancer. It stated that their device could distinguish benign tumors from malignant tumors 77% of the time.
New England Breath Technologies is a Massachusetts-based start-up company founded in 2015. This company developed a breath analyzer for the detection of blood sugar levels. Their product is called Glucair, which detects the concentration of acetone in a person’s breath
- Lourenço, C. and Turner, C. (2014) “Breath analysis in disease diagnosis: methodological considerations and applications”, metabolites, 4(2), pp. 465-498. bye: 10.3390/metabo4020465†
- Kaloumenou, M. et al. (2022) “Breath analysis: a promising tool for disease diagnosis – the role of sensors”, Sensors22(3), p. 1238. bye: 10.3390/s22031238†
- (2022) Cen.acs.org. Available at: https://cen.acs.org/articles/82/i13/BREATH-ANALYSIS-MEDICAL-DIAGNOSIS.html (Accessed: June 23, 2022).
- Transformation of disease detection: the power of breath analysis (2021). Available at: https://www.medicaldevice-network.com/sponsored/transforming-disease-detection-breath-analysis/ (Accessed: June 23, 2022).
- Mule, N., Patil, D., and Kaur, M. (2021) “A comprehensive investigation of exhaled breath (EB) examination techniques for the diagnosis of diseases in the human body”, Informatics in Medicine Unlocked26, p. 100715. bye: 10.1016/j.imu.2021.100715†
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