The role of respiratory analysis in the diagnosis of diseases

Typically, exhaled breath consists of unmodified nitrogen (~74%), argon (~1%), oxygen (~15%), carbon dioxide (~5%), and water vapor (~6%). Additionally, several endogenously formed gaseous volatile metabolites are present in exhaled breath at trace levels, which are measured in parts per million volume (ppmv), parts per trillion volume (pptv), or parts per billion volume. volume (ppbv).

The researchers detected common respiratory metabolites in several healthy individuals for thirty days, 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. The variability of the concentrations of these metabolites was evaluated and the log-normal distribution of these metabolites was studied.

Ammonia is present in the body as a breakdown product of proteins via bacterial breakdown in the gut. Although a large part of the ammonia is converted into urea and eliminated through urine, a small part is expelled through the breath. The concentration of ethanol and methanol may increase due to anaerobic fermentation by intestinal bacteria. The presence of isoprene in human breath has been considered a marker of cholesterol synthesis. Additionally, scientists have revealed that an abnormal level of isoprene in human breath indicates end-stage renal disease 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 capable of detecting biomarkers present in 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 the reactions occur under thermal conditions.

The researchers also used ion mobility spectrometry (IMS) and laser absorption spectroscopy (LAS) in breath analysis. Cavity Reduction Spectroscopy (CRDS), based on LAS, was used to measure nitrous oxide (NO) in expired air. This technique can quantify VOCs in the breath below parts per billion by volume levels.

Electron Noses (e-Noses) is an electronic sensing device that contains an array of gas and semiconductor-based sensors. Two devices based on mass-sensitive sensors, 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, an appropriate exhaled breath storage system is an important aspect. Scientists indicated the risk of contamination of breath samples with background emission of pollutants, which could alter the chemistry of stored samples.

At present, inert Tedlar bags with many advancements are manufactured by many companies, such as Dupont and SKC Ltd. These bags are transparent or black and are based on various components, such as Nalophan, Flexfoil and Teflon. Previous studies have indicated that Nalophan bags are inexpensive and the most popular for collecting breath samples. The stability of the respiratory components in the Tedlar bags was determined by gas chromatography-MS (GC-MS) and PTR-MS.

Stored breath was analyzed for the presence of VOCs via various methods such as needle trap micro-extraction (NTME) combined with GC and solid-phase micro-extraction (SPME).

Scientists evaluated SIFT-MS and PTR-MS technologies to determine if they can detect liver disease and monitor diabetes. Moreover, these techniques have also been evaluated for the diagnosis of various types of cancers such as lung, colorectal, bladder and prostate cancer.

Could a simple breath test diagnose a disease? | Billy Boyle | TEDxUniversity of CambridgeTo play