E-cigarette vapour composition is influenced by a number of factors. Some of which relate to the device physically (battery charge, wattage/temperature control, puffing profile) and others to the e-liquid itself (proportion of propylene glycol and glycerol, amount of nicotine, pH of solution). Standardizing how we study these devices will be key to understanding their impact.
Deposition is dependent on a multitude of factors such as particle size, physiochemical properties of the compound (hydrophobic vs hydrophilic), delivery route (IV vs IT vs aerosol), species, strain, and disease model.
To illustrate the relationship between inhaled particle size and deposition, find below graph from Patton and Byron Nature Reviews Drug Discovery (2007)1 showing that the respirable range is in the <5um range:
Smaller particulates will have better suspension and follow the natural flow of airway geometry to infiltrate further into the lungs. On the other hand, larger particles are heavier and tend to get deposited in the upper and central airways. Deposition is also dependent on species and strain and may vary with disease state.
Variations in Aerosolization Conditions
The recent publication by Lechasseur et al.2 investigates the main variables in e-cigarette aerosolization that may affect particle size and ultimately distribution in the lungs such as:
- Device Modes
- Power-controlled vs Temperature-controlled
- Composition of vehicle
- Ratio of propylene glycol (PG) to vegetable glycerin (VG)
- Nicotine content
The inExpose has been specifically designed for consistent, precise delivery of a compounds by controlling air flow rates and puffing profiles through automated exposure profiles. Since it offers precise control over experimental conditions, outcome variability is minimized among subjects, study, and research groups. This allowed Dr. Lechasseur to focus on isolating specific the effects of the variables, using the following configuration.
- SCIREQ inExpose Whole Body Exposure System
- Puff topography: using flexiWare software, the puff shape, frequency and size in this experiment is defined as the following:
- Shape: half-sinusoidal
- Volume: 70mL
- Frequency: one puff every 30-seconds
- Puff duration: 4.2 seconds per puff
- Bias Flow : 2 LPM
Temperature control mode vs the wattage mode
Temperature-control mode is often promoted by e-cigarette companies as a way to maximize flavour and prevent overheating and coil degradation. Internal tests at SCIREQ show that temperature control mode allows the temperature to be kept constant by adapting power to coil and using resistance as feedback. The power-controlled modes tend to increase temperature over time to sustain a stable power target.
NOTE: Increasing temperatures change the density of e-cigarette smoke produced and the chemical composition.
In Lechasseur et al2 each mode is tested using a consistent ratio of 50% Propylene Glycol, 50% Vegetable Glycerine. They show that increasing power leads to an increase in particle size generated. In contrast, increasing temperature to its highest setting (250oC) yields the smallest particle size.
Nicotine Content and vehicle ratio
E-cigarette liquid mixtures mainly consist of varying percentages of vegetable glycerin (VG), propylene glycol (PG), and nicotine combined with a flavouring of choice. Unfortunately, manufacturing of e-liquids is highly unregulated. There are no standards set for consistency and as such, market e-liquid’s composition vary greatly from batch to batch.
The next step in the Dr. Lechasseur’s experiment is to assess the ratios of PV/VG under constant temperature conditions, in this case 210oC. When increasing the proportion of vegetable glycerine, the particle sizes also increase. This is done in absence of nicotine; however the addition of nicotine also increased the particle size.
E-cigarette liquids come in a variety a flavouring which make them more palatable and marketable to a larger target audience including adolescents. Many studies have shown that the flavours using in e-cigarette liquids have adverse health effects including pulmonary inflammation and oxidative stress (Gerloff et al. 20173, Rahman et al. 20184).
Lechasseur et al2 focused on three main flavourings in this study; specifically vanillin, menthol and matltol, showing that Vanillin significantly increased the particle size while the other flavours did not.
In conclusion, altering the e-cigarette modes (Power/temperature), e-liquid composition and flavouring can impact particle size and distribution, ultimately affect deposition. It is important to take this into consideration when designing an experiment and when reviewing the published literature.
- Patton, J.S., & Byron, P.R. (2007). Inhaling medicines: delivering drugs to the body through the lungs. Nature Review Drug Discover, 6(1): 67-74
- Lechasseur, A., et al. (2019). Variations in coil temperature/power and e-liquid constituents change size and lung deposition of particles emitted by an electronic cigarette. Physiological Reports, 7(10): e14093. Doi.org/10.14814/phy2.14093
- Gerloff, J., et al. (2017). Inflammatory response and barrier dysfunction by different e-cigarette flavoring chemicals identified by gas chromatography-mass spectrometry in e-liquids and e-vapors on human lung epithelial cells and fibroblasts.Appl. In Vitro Toxicol.3, 28–40. doi: 10.1089/aivt.2016.0030
- Muthumalage, T., et al. (2018). Inflammatiory and Oxidative Responses Induced by Exposure to Commonly Used e-Cigarette Flavouring Chemicals and Flavoured e-Liquids without Nicotine. Frontiers in Physiology, 11: doi.org/10/3389/fphys.2017.01130