Aerosol therapy and aeroion therapy. Physical and physiological principles, methods of application, indications, and contraindications
Two ways of treating through the air we breathe. Aerosol therapy floats tiny droplets or powder of a drug, saline or mineral water into the airways, and particle size decides where they land. Aeroion therapy fills the air with electrically charged gas molecules. This page covers the physics, the devices, how to inhale, the indications and the contraindications, and how strong the evidence is for each.
- 12 min read
- 5 questions
- Checked 05 Nov 2026
Contents6 sections
At a glance
- An aerosol is a cloud of tiny liquid or solid particles floating in a gas. Inhaled, it puts a drug straight onto the airways: a fast local effect with a small dose and few side effects.
- Size decides where particles land. More than 10 µm: nose and throat. About 5 to 10 µm: large airways. About 1 to 5 µm: small airways and alveoli, the useful range. Much smaller: mostly breathed out.
- Breathing pattern matters too. A slow, deep breath with a breath-hold suits sprays and nebulisers; a dry powder inhaler needs a fast, forceful breath.
- Devices: jet, ultrasonic and mesh nebulisers; pressurised metered-dose inhalers (best with a spacer); dry powder and soft mist inhalers. A spacer works as well as a nebuliser in most acute asthma.
- Aeroion therapy fills the air with charged gas molecules, usually negative ions, as near waterfalls or in mountains. Its old claims are not borne out for the lungs; high-density negative ions may lift mood in seasonal depression.
- Watch for bronchospasm with hypertonic, cold or irritant aerosols; drive nebulisers with air in hypercapnic COPD; keep nebulisers clean; ionisers can emit ozone.
Physical principles
What an aerosol is
Aerosol therapy means breathing in a medicine, saline or mineral water as an aerosol: particles of liquid or solid so small that they float in air. There are two ways to make one, as the book notes: break a liquid into small droplets (dispersion, as in a nebuliser or spray), or let a vapour condense into droplets (condensation, as in steam).
The single most important property is particle size, given as the aerodynamic diameter in micrometres (µm): how the particle behaves in air, whatever its real shape. A device's output is described by its mass median aerodynamic diameter, the size that splits the mass of the cloud in half.
How particles land: three ways to stop
Think of the airways as a branching road with many sharp bends. Particles are like cars, lorries and balloons trying to get through.
| Mechanism | Who | Where | Helped by |
|---|---|---|---|
| Inertial impaction | large, heavy particles | they cannot turn at bends and crash into the throat and large bronchi | fast inhalation, large particles |
| Sedimentation | medium particles, about 1 to 5 µm | they settle by gravity in small airways and alveoli, where the air moves slowly | slow, deep breath and a breath-hold |
| Diffusion | very small particles, below about 0.5 µm | random (Brownian) motion bumps them onto alveolar walls | long residence time |
This gives the deposition map:
| Particle size | Mainly lands in | Clinical target |
|---|---|---|
| More than 10 µm | nose, mouth, throat | upper airway, a local effect; most is swallowed |
| About 5 to 10 µm | trachea and large bronchi | large airways |
| About 1 to 5 µm | small bronchi, bronchioles, alveoli | asthma, COPD, the lungs as a whole |
| Below about 1 µm | many are exhaled again; the very smallest reach alveoli by diffusion |
How the breath changes it
The book's rule: slow, deep breaths carry fine particles deep into the lung, where they settle; fast, shallow breaths stop coarser particles high up by impaction. This holds for nebulisers and pressurised sprays: inhale slowly over 3 to 5 seconds, then hold the breath for about 10 seconds so particles have time to settle.
A dry powder inhaler is the exception. It has no propellant, and the patient's own fast, forceful breath is what breaks the powder into fine particles. A slow breath leaves the dose in the device.
Point at a name or a part to light it.
What decides where an inhaled particle lands is its size. Particles over 10 µm cannot turn at the bends and strike the mouth and throat; 5 to 10 µm land in the trachea and large bronchi; 1 to 5 µm settle in the small airways and alveoli, the target for asthma and COPD. Many particles of 0.1 to 1 µm are breathed out again, and only the smallest reach the alveoli by diffusion. A slow deep breath over 3 to 5 seconds and a hold of about 10 seconds give them time to settle.
Simplified: the airway is a schematic: a handful of branches stands for about twenty generations, and its sizes and angles are not to scale; each size is drawn landing in one place; real deposition curves overlap, and every size lands in more than one place; the particles are drawn far larger than they are, and only in order of size, not to one scale; the airway starts at the mouth, as with an inhaler; breathing through the nose filters out large particles even sooner.
3 sources
- Aleksiev A. Physical Medicine and Rehabilitation for English-speaking MD students. Medical University of Sofia, 2002. Aerosolotherapy.
- Aleksiev AR. Physical Medicine and Rehabilitation, lecture 3 handnotes (aerosol therapy). Medical University of Sofia, 2026.
- Laube BL, Janssens HM, de Jongh FHC et al. What the pulmonary specialist should know about the new inhalation therapies. European Respiratory Journal, 2011.
Physiological principles
Why inhale a drug rather than swallow it? The lung is built to exchange gas: a huge surface (tens of square metres), a barrier less than a micrometre thick and the whole cardiac output flowing past.
- Local action, small dose. The drug goes straight where it is needed. An inhaled salbutamol dose of 100 to 200 µg acts within minutes; by mouth, milligrams would be needed, with tremor and fast heartbeat.
- Less of it everywhere else. Only about 10 to 30 per cent of a dose reaches the lungs; most lands in the mouth and is swallowed. That is why the mouth is rinsed after an inhaled corticosteroid, to prevent thrush and hoarseness.
- Clearance. Particles on the airway wall are carried up by the cilia and the mucus layer (mucociliary clearance) within about a day; in the alveoli they are absorbed into blood or eaten by macrophages.
- Fast systemic uptake for some drugs. The same surface that makes inhalation work can deliver some drugs into the blood quickly and unpredictably.
That last point explains the book's rule: anticoagulants are not given by inhalation, and drugs that need exact plasma levels are poor candidates. Absorption through the lung varies too much from breath to breath to control the level. (Nebulised heparin is tried only in special settings, such as smoke inhalation injury in burns units.)
Methods of application
Devices
| Device | How it makes the aerosol | Strengths | Limits |
|---|---|---|---|
| Jet nebuliser (compressor) | compressed gas at about 6 to 8 L/min sucks liquid up and shatters it against a baffle (the Venturi effect) | works with any breathing, any age, with a mask; large doses | noisy, slow (10 to 15 minutes), part of the dose stays in the cup |
| Ultrasonic nebuliser | a piezoelectric crystal vibrating at about 1 to 3 MHz throws droplets off the liquid's surface | quiet, large output | warms the liquid; can damage proteins and suspensions (not for budesonide suspension) |
| Vibrating mesh nebuliser | a plate with thousands of laser-drilled holes pushes liquid through as a fine mist | fast, quiet, small, little waste | costly, the mesh needs careful cleaning |
| Pressurised metered-dose inhaler (pMDI) | a propellant fires a measured spray | small, quick | needs coordination; fast spray hits the throat |
| pMDI with spacer or valved holding chamber | the chamber slows the spray and holds it for several breaths | no coordination needed, less throat deposition, more to the lungs | bulky |
| Dry powder inhaler (DPI) | the patient's breath breaks up the powder | no propellant, breath-actuated | needs a strong inspiratory flow: not for young children or a severe attack |
| Soft mist inhaler (SMI) | a spring pushes liquid through fine nozzles as a slow cloud | slow mist, easy to inhale | needs priming, some dexterity |
A spacer with a pressurised inhaler works as well as a nebuliser for a bronchodilator in most acute asthma in adults and children, and children spend less time in the emergency department. Nebulisers are kept for those too ill or too young to use one, for drugs only made as solutions, and for large doses.
- 1
Shake and prime
Shake a pMDI and fit it to the spacer; prime a new inhaler. - 2
Breathe out
Breathe out gently, away from the device. - 3
Fire and inhale slowly
One puff into the spacer, then a slow deep breath (or several calm breaths for a child with a mask). - 4
Hold
Hold the breath for about 10 seconds, so particles settle. - 5
Wait and repeat
About 30 seconds between puffs; rinse the mouth after a steroid.
Other methods in physiotherapy
- Old-school inhalations in a physiotherapy department are graded by temperature and content: steam and warm-moist inhalations of saline or alkaline mineral water to loosen mucus, oil and powder inhalations, given individually or in a group inhalation room. A session takes about 5 to 15 minutes, daily, for a course of about 10 to 15.
- Halotherapy and speleotherapy: sitting in a salt room with a dry sodium chloride aerosol, or in a natural salt mine or cave. Exposure is not standardised, and a review in COPD found too little good evidence to recommend it.
- Natural aerosols of the sea coast (sea salt), mountains and forests are used in climatotherapy, where the book counts them in the aero-chemical complex of climate.
- Electroaerosols: aerosol particles given an electric charge, usually negative, which the old school claimed improves deposition and ciliary action; this has not been shown in controlled trials.
What is inhaled
| Group | Examples | Purpose |
|---|---|---|
| Saline | 0.9 per cent; hypertonic 3 to 7 per cent | moistens; hypertonic draws water into sticky mucus and helps clearance |
| Bronchodilators | salbutamol, ipratropium | relax airway muscle |
| Corticosteroids | budesonide | calm airway inflammation |
| Mucoactive drugs | acetylcysteine, dornase alfa | thin mucus |
| Antibiotics | tobramycin, colistin | chronic Pseudomonas infection in cystic fibrosis and bronchiectasis |
| Others | adrenaline (croup), mineral waters (old-school practice) | swelling of the larynx; mucus |
The dose is that of the drug's prescription; the device and the technique decide how much of it arrives.
Indications
| Because the aerosol | It is used in |
|---|---|
| opens and calms the airways | asthma, COPD, acute bronchospasm |
| loosens and clears mucus | cystic fibrosis and bronchiectasis (hypertonic saline improves lung function modestly in cystic fibrosis), chronic bronchitis, before airway clearance physiotherapy |
| treats infection where it is | chronic Pseudomonas colonisation |
| soothes the upper airway | laryngitis, croup (adrenaline, budesonide), rhinitis and sinusitis (nasal sprays and rinses) |
Contraindications and cautions
The logic: an aerosol can irritate the airway it is meant to help, a drug can be absorbed too fast, a device can deliver too much oxygen, and dirty equipment can deliver germs.
| Problem | Example | What is done |
|---|---|---|
| Paradoxical bronchospasm | hypertonic saline, acetylcysteine, cold or hypotonic aerosols, preservatives | bronchodilator first; first dose supervised; stop if wheeze |
| Drug unsuited to inhalation | anticoagulants; drugs needing exact plasma levels | not given by this route (the book's absolute and relative contraindications) |
| Oxygen-driven nebuliser in hypercapnic COPD | high oxygen worsens carbon dioxide retention | drive with air; give controlled oxygen separately (if only oxygen is available, no more than about 6 minutes) |
| Allergy to the drug | another drug | |
| Lung that cannot tolerate pressure or irritation | pneumothorax, large bullae, pulmonary haemorrhage, severe respiratory failure (for pressure-assisted inhalation and old-school procedures) | avoid; treat the cause |
| Old-school general contraindications | decompensated heart failure, fever, active tuberculosis | for non-drug inhalation courses |
| Infection | contaminated nebuliser cups spread Pseudomonas and other bacteria; nebulising spreads respiratory viruses to staff | one patient per device, cleaning and drying after each use; in an airborne infection, a spacer instead of a nebuliser where possible |
Aeroion therapy
Physical principles
An air ion is a gas molecule, or a small cluster of them, that carries an electric charge. In nature, cosmic rays, radioactivity from the ground (radon), ultraviolet light and lightning knock electrons off molecules. The freed electron sticks to oxygen to make a negative ion; the molecule it left becomes a positive ion. Each soon gathers a few water molecules around it (a light or small ion). If it sticks to dust or smoke, it becomes a heavy ion and loses any biological activity.
Splashing water makes many negative ions: when drops break, the fine spray carries away negative charge (the Lenard or waterfall effect). So the air is rich in light negative ions near waterfalls, surf, mountains and after a thunderstorm, and poor in them in closed, smoky, crowded or air-conditioned rooms, where ions cling to particles. In the book's climatology, ions are the aero-electric complex of climate.
Artificial sources:
- Corona-discharge ionisers: a high negative voltage on sharp needle points (the old Chizhevsky "chandelier" is the classic) pulls electrons into the air.
- Hydroionisers: water sprayed or broken into droplets, imitating a waterfall.
The dose in the old school is the number of ions inhaled: concentration near the face, times breathing volume, times time. Sessions are short and daily over a few weeks.
Effects and evidence
The old teaching says negative ions calm, slow breathing, help the cilia and lift mood, while positive ions (said to rise before hot, dry winds such as the Föhn) irritate. The slides repeat this. What controlled studies show is narrower:
| Claim | What the evidence shows |
|---|---|
| Better breathing, fewer asthma symptoms | a review of studies from 1933 to 1993 found no appreciable effect of either negative or positive ions on respiratory function |
| Better mood | a 2013 meta-analysis found lower depression scores with negative ions, mainly at high density and in seasonal depression; low-density ionisers, like many home devices, acted like a placebo; no consistent effect on anxiety, sleep or comfort |
| Cleaner air | ionisers make particles charge and stick to surfaces, which lowers airborne dust a little |
Indications and contraindications
- Used (old-school and adjunct): fatigue, stress and sleep problems, seasonal low mood, rooms with poor air; in the old school also as part of climatotherapy for chronic respiratory disease.
- Avoided: ionisers that emit ozone, a lung irritant that worsens asthma and COPD (choose certified low-ozone devices); individual intolerance (headache, irritation); acute respiratory infection and fever; and, in the old lists, malignancy and decompensated heart disease.
Check yourselfAnswer, then say how sure you were: a lucky guess still counts as a weak point.
1A nebulised drug is meant to reach the small airways. Which particle size should the device deliver?
2An older woman with COPD uses a dry powder inhaler with a slow, gentle breath, as she was taught for her old spray inhaler. What is the problem?
3A man with COPD and known carbon dioxide retention needs a nebulised bronchodilator in hospital. How should the nebuliser be driven?
4Before a first dose of nebulised 7 per cent saline in a child with cystic fibrosis, what is done and why?
5A patient asks whether a negative ion generator at home will improve his asthma. What does the evidence show?