p.p1 VOCs in the sample and reduces the

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Learning goal 1: what is tuberculosis (general)

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A disease caused by the bacteria Mycobacterium Tuberculosis. 
TB mainly affects the lungs but can affect other organs too.

Coughing or sneezing saturates the air with TB molecules. This is the usual way that TB is transmitted. 

Most infections do not have symptoms —> known as latent TB 

People who have latent TB do not show symptoms and therefore don’t spread the disease. 
About 10% of latent TB cases can progress and become active. If left untreated, death results in about 50% of the cases. 
Active infection occurs in those with HIV/AIDS and smokers. 

Classic symptoms:

Chronic cough, with blood containing sputum. 
Night sweats
Weight loss

Diagnosis is based on chest x-rays as well as a microscopic examination and culture of bodily fluids. 
Diagnosis of latent TB relies on tuberculin skin test or blood tests. 

Learning goal 2: what can be found in the exhaled breath analysis? (VOCs, origin (endo/exo))


Environment (exogenous)

Most VOCs originate this way 

Host (endogenous)

Have the potential to provide a snapshot of the physiological state of an individual

Microbiome (microorganisms that inhabit the mouth, lung and gut) 

Microbial VOCs aid in pathogen identification 

Learning goal 3: how are samples collected?

Breathomics pipeline is broken down into: breath sample collection —> sample analysis —> data analysis
A choice must be made as to the portion of breath that can be collected. 

This is divided into: late expiratory, end tidal, mixed expiratory 
Mixed expiratory breath encompasses total exhaled breath and includes dead air space (air not involved in gaseous exchange, e.g. mouth and noise air)
The other types of breath portions aim to eliminate contamination from this dead air space

Late expiratory breath

This discards the initial portion of breath (estimated dead space) and the subsequent capture of air at the end of the breath cycle.
Minimising dead space allows for a greater contribution of endogenous VOCs in the sample and reduces the level of exogenous VOCs

This can be done by excluding the first few seconds of exhalation from and individual before the breath sample is collected or having the subjects breath into a collection reservoir for the breath to flow downstream whilst the air that is close to the donor is collected. 

End tidal/ Alveolar breath

The type of air collected contains high concentrations of endogenous VOCs and minimal contaminants 
CO2 visual control is used to collect end-tidal breath and monitors CO2 concentrations during exhalation. 
During phase 1 of exhalation CO2 levels are low, but rise during the transition (phase 2) and approaches a plateau which signals the start of alveolar phase 3
CO2 levels are monitored with a capnometer that enables visualisation of the various phases for guidance on where to begin with breath capture. 
A well known endogenous VOC that originates from the airways is nitric oxide and indicates asthma. 
Samples are collected during phase 3. 

Mixed expiratory 

This is the simplest type of breath that is obtained as it acquires all phases of exhaled air. 
It is simple, however, contains a large proportion of environmental, mouth and nose contaminants. 
For the method to be effective, subject numbers must be very large in order to reduce the chance of a false positive result (identifying and exogenous VOC as a candidate marker)

Breath collection containers 

Polymer bags encompass the majority of breath collection containers and are most commonly used
Bio-VOC sampler, breath collection apparatus and glass vials are also used for breath collection. 
The ideal container should be: cost and user-friendly, durable, inert and shouldn’t allow environmental nor breath VOCs to enter or leave. 
It should also be compatible with multiple VOC trapping devices. 

Pre-concentration methods

Pre-concentration is needed to detect VOCs that are present in breath at ppm or lower concentrations. 
It is used when dilutions of VOCs occur (as with mixed expiratory breath samples) 
Thermal Desorption tubes

TD tubes account for almost half of the pre-concentration methods
Sorbents (something which collects molecules) are packed into tubes and posses great variability in the range of volatiles that they can trap as well as the stability of the sorbent-compound interaction. 
Sample volume should be considered in order to prevent breakthrough and loss of analytes.