Breath gas analysis

Breath gas analysis is a method for gaining information on the clinical state of an individual by monitoring

It is known that since the times of

Overview

Identification and quantification of potential disease biomarkers can be seen as the driving force for the analysis of exhaled breath. Moreover, future applications for medical diagnosis and therapy control with dynamic assessments of normal physiological function or pharmacodynamics are intended.

The simplest model relating breath gas concentration to blood concentrations was developed by Farhi[16]

${\displaystyle C_{A}={\frac {C_{\bar {v}}}{\lambda _{\text{b:air}}+{\dot {V}}_{A}/{\dot {Q}}_{c}}},}$

where ${\displaystyle C_{A}}$ denotes the alveolar concentration which is assumed to be equal to the measured concentration. It expresses the fact that the concentration of an inert gas in the alveolar air depends on the mixed venous concentration ${\displaystyle C_{\bar {v}}}$, the substance-specific blood:air partition coefficient ${\displaystyle \lambda _{\text{b:air}}}$, and the

${\displaystyle {\dot {V}}_{A}/{\dot {Q}}_{c}}$

${\displaystyle \lambda _{\text{b:air}}=340}$

${\displaystyle \lambda _{\text{b:air}}=0.75}$

E.g., multiplying the proposed population mean of approximately ${\displaystyle 1\mu g/L}$ acetone in end-tidal breath by the partition coefficient ${\displaystyle \lambda _{\text{b:air}}=340}$ at body temperature grossly underestimates observed (arterial) blood levels spreading around ${\displaystyle 1mg/L}$. Furthermore, breath profiles of acetone (and other highly soluble volatile compounds such as 2-pentanone or methyl acetate) associated with moderate workload ergometer challenges of normal healthy volunteers drastically depart from the trend suggested by the equation above; hence some more refined models are necessary. Such models have been developed.^[18][19]

Applications

Breath gas analysis is used in a number of breath tests.

• Asthma detection by exhaled nitric oxide^[20]
• Blood alcohol testing^[21]
• Carbon monoxide poisoning
• Diabetes mellitus^[22]
• Diabetes detection
• Diagnosis of bad breath
• Fructose malabsorption with hydrogen breath test
• Helicobacter pylori with urea breath test
• Lung cancer detection^[23]
• Measurement of endogenous metabolic processes^[24]
• Monitoring uptake of disinfection by-products following swimming^[25]
• Organ rejection
• Smoking cessation

Breath collectors

Breath can be collected using a variety of home-made and commercially available devices. Some examples of breath collection tools used across the research industry for VOC analysis are:

• Coated stainless steel canister
• End tidal air collector
• Tedlar bag

These devices can be used as a vehicle for direct introduction of a gas sample into an appropriate analytical instrument, or serve as a reservoir of breath gas into which an absorption device such as an SPME fiber is placed to collect specific compounds.

Online analysis

Breath can also be analyzed online, which allows for insight into a person's metabolism without the need for sample preparation or sample collection.^[26] Technologies that enable real-time analysis of breath include:

• Proton Transfer Reaction Mass Spectromerty (PTR-MS)
• Secondary Electrospray Ionization Mass Spectrometry (SESI-MS)^[27]
• Selected ion flow tube mass spectrometry (
  SIFT-MS)^[26]

Breath analysis is very vulnerable to confounding factors. Analyzing breath in real-time has the advantage that potential confounding factors associated with sample handling and manipulation are eliminated. Recent efforts have focused on standardizing online breath analysis procedures based on SESI-MS, and to systematically study and reduce other confounding sources of variability.^[28]

Analytical instruments

Breath analysis can be done with various forms of mass spectrometry, but there are also simpler methods for specific purposes, such as the Halimeter and the breathalyzer.

• Gas chromatography-mass spectrometry
  GC-MS
• Gas chromatography-UV spectrometry GC-UV
• Proton transfer reaction mass spectrometry
  PTR-MS and PTR-TOF
• Selected ion flow tube mass spectrometry
  SIFT-MS
• Ion mobility spectrometry IMS
• Fourier transform infrared spectroscopy
  FTIR
• Laser spectrometry Spectroscopy
• Individual
  Chemical sensors or chemical sensor arrays, operate as Electronic noses
• Secondary electrospray ionization SESI-MS

References