Lung and trachea squeezes; A freediving guide

Freediving lung and trachea “squeezes” refer to pressure  induced injuries of the lungs or airways during deep breath-hold diving. Occurring in both recreational freedivers exploring shallow reefs as well as competitive athletes seeking new personal bests at extreme depths. In medical terms, they are forms of pulmonary barotrauma that occur during descent, essentially damaging  lung or tracheal tissues from being compressed beyond their limits​

These injuries are a known risk in freediving once divers approach extreme depths or use improper techniques. Below is an overview of the causes and physiology behind squeezes, the risk factors and warning signs, how to prevent them, and guidance on recovery and relevant research findings.

What is a lung squeeze?

A lung squeezes, medically termed “pulmonary barotrauma,” occurs when negative pressure develops in the thoracic cavity at depth. As you descend, ambient water pressure increases, compressing the air in your lungs. Once you pass a certain depth, often correlated with an individual’s residual volume (RV), increasing pressure can pull fluids into the alveoli or cause microtears in lung tissue. This situation leads to inflammation, bleeding, and in severe cases, life-threatening pulmonary edema.

Key points about lung squeeze:

• It typically involves alveolar or capillary damage.
• Symptoms can include chest pain, coughing up blood (hemoptysis), and difficulty breathing.
• It most commonly occurs below 30-45 meters, though it can happen at shallower depths if other contributing factors are present.

What is a trachea squeeze?

A trachea squeeze involves the windpipe (trachea) rather than the deeper lung tissue. It often results from forceful equalization maneuvers, such as tension in the throat, sudden pressure changes in the upper airways, or from tension in the diaphragm and intercostal muscles. In many cases, the main symptom is bright red blood rather than the pink, frothy sputum which is typical of lung squeezes. While trachea squeezes usually present less risk of hypoxia (because gas exchange in the alveoli is unaffected), they can cause alarm for individuals.

Physiological Mechanisms

Descending on a single breath, the lungs and air spaces face increasing ambient pressure. According to Boyle’s Law, as depth increases, lung volume decreases. As the diver reaches the residual volume of their lungs (usually 20-25% of Total lung capacity, reached at 30-40 metres), the lungs do not easily compress anymore.

​Lung squeeze (pulmonary barotrauma) occurs if the lungs are forced below their safe minimal volume, causing stress or rupture of delicate tissues. Key physiological factors include:

Thoracic Compression & Blood Shift

To prevent the lungs from collapsing upon reaching Residual volume, the body employs the blood shift mechanism (one of the triggers of the mammalian dive reflex). The capillaries around the alveoli dilate, leading to blood pooling,  whilst compensating for the loss of volume. This pool of blood allows divers to descend past their residual volume without the lungs being crushed. This may come at a cost as it can lead to rupture of the lung tissues; which in turn can cause alveolar bleeding.

Negative Pressure Effects

 If a freediver has involuntary contractions (especially if not controlled correctly), performs improper reverse packing maneuvers or has any tension building up, negative intrathoracic pressure can develop. This pulls on the lungs and airway walls, contributing edema or tears in blood vessels.

Trachea and Upper Airway Stress

As mentioned above, a trachea squeeze is localized to the windpipe / throat area, resulting in strain in the upper airways. For example, poor head position at depth (such as over-extending the neck to look forward/down) can create unequal pressures or pinching in the trachea​. They typically occur with rapid depth change or improper body alignment that the airway cannot accommodate and improper equalsiation.

In summary, lung and trachea squeezes are caused by pressure-induced trauma when the chest’s limits are exceeded. If the lungs compress beyond their flexibility, alveolar membranes and capillaries can tear (lung squeeze), and if the upper airway is mispositioned or under stress, its delicate lining can bleed (trachea squeeze)​.

Lung and trachea squeeze Causes

Deep diving can cause squeezes if limits are exceeded and certain factors make them more likely.

Poor Equalisation Technique or timing

Mistiming or using improper technique can increase the causality of trachea squeezes. EQ needs to be on point. Unconscious reverse packs are usually the leading cause of squeezes. Reverse Packing after reaching RV becomes significantly more challenging. If the diver pushes from the belly or causes any unnecessary tension in the chest, this can lead to a trachea squeeze.

Lack of chest flexibility

A stiff thoracic cage or diaphragm that hasn’t been trained for compression will resist the volume reduction, making injury more likely. Insufficient flexibility or warm-up means the chest tissues don’t yield as pressure increases​. Daily specific stretching or FRC / RV diving can greatly help.

Depth Progression Errors

Rapid jumps in depth, exceeding physiological as well as mental adaptations are a leading cause to squeezing. Newer divers sometimes push below 30 meters without gradually building thoracic flexibility, mastering safe equalization as well as basic skills, such as relaxation. Similarly, overtraining or repetitive deep dives with insufficient recovery can accumulate stress – for example, doing many deep dives in one day or diving deep on consecutive days. Notably, divers appear more prone to squeeze on a second day of deep dives if the lungs hadn’t fully recovered from the first day​.

Lack of relaxation / Tension

This is largely looked over. Many divers think they are relaxed without even the basics in play. Relaxation is the foundation of freediving. Improper relaxation will not allow the blood to shift from the extremities and pool into the lungs efficiently. Stress or panic at depth can lead to muscle tension in the chest and throat. A tight chest reduces chest compliance and increases injury risk. Strong involuntary contractions (diaphragmatic breathing reflex “urges”) against a closed airway are especially risky – these abrupt internal “sucking” motions can bruise lung tissue​. Likewise, sudden or awkward movements such as a jerky turn on the line or stretching the neck/arms can momentarily cause strain.

Environmental Factors; Cold Water

Increases muscle tension, restricting lung compliance and comes in the way of relaxation Currents or Abrupt Movements: Reaching for a speargun or adjusting buoyancy in strong currents can disrupt posture, creating uneven thoracic pressure distribution.

Signs and symptoms

These can range from subtle squeezes that manifest right after or even a couple of hours after the dive, to severe ones that will be noticeable right after surfacing. The lung tissue has very few nerve endings so a diver will not feel immediate pain, if at all. Common signs and symptoms include:

• Chest Discomfort or Pain: Tightness, ache or mild pain is a symptom often noticed after the diver surfaces. A feeling of bruising deep inside the chest. This indicates something further down the trachea. Trachea squeezes usually result with feelings in the throat; soreness or something stuck.
• Breathing Difficulty: Following a squeeze, the diver often complains they are short of breath. A deep wheezing sound may occur because of fluid in the airways, resulting in the diver wanting to cough something up.
• Coughing up blood: A famous sign of lung or trachea squeeze is coughing, especially coughing up blood-tinged sputum. It may appear as foamy pink fluid (mixed with air, which is  a sign of alveolar lung edema) or bright red blood (more likely from airway/tracheal injury)​. Even a few flecks of blood after a deep dive indicate a mild squeeze. In severe cases, significant amounts of blood can be brought up with coughing. Any post-dive hemoptysis (spitting/coughing blood) should be treated as a squeeze until proven otherwise.
• General tiredness: Fatigue or feeling weak after squeezing is common. It is quite a noticeable feeling, often being referred to as a feeling of being ‘wiped out’
• Severe Signs: Blue lips, which is a sign of lack of oxygen in the system, is a more serious type of squeeze. Coupled with rapid breathing, inability to speak or gasping for air.

Progression of Symptoms

1. Mild:
   • Dry cough
   • Slight chest tightness
   • Pink, frothy sputum
2. Moderate:
   • Hemoptysis (coughing up blood)
   • Noticeable chest pain or discomfort
   • Shortness of breath (dyspnea)
3. Severe:
   • Persistent coughing of blood
   • Hypoxia (blue lips, confusion)
   • Acute respiratory distress

Immediate Response Protocols

At the first sign of a severe squeeze:

• Abort the dive: Never continue diving after symptoms appear. The added stress of multiple dives can worsen the injury.
• Minimize exertion: Swim calmly to the surface, focus on slow, controlled breaths.
• Seek 100% oxygen: Administering oxygen can alleviate hypoxia and aid healing. This is only needed when the squeeze is severe.
• Positioning: Avoid lying flat (supine) if breathing difficulty is present; upright or slightly reclined positions help airway drainage.
• Medical Evaluation: If you suspect a moderate to severe squeeze, consult a medical professional promptly.

Squeeze Prevention

Preventing lung and trachea squeezes centres on proper training, gradual adaptation, attentive technique and the power of observation. Finding an instructor with a keen attention to detail will help nail down the cause of squeezes.

Gradual Depth Progression:

Progression over time is detrimental for squeeze prevention. This gives time for the mind to adapt. Avoid the temptation to rapidly push new depths without repeating and observing the dive. Once you reach the 50 metre mark, being adding one metre at a time.

Thoracic Flexibility and Stretching

Improving the flexibility of the rib cage, intercostal muscles, and diaphragm will help the compression of the lungs. A flexible chest wall accommodates compression more evenly and delays the onset of negative pressure in the lungs.

Daily Stretches: Incorporate uddiyana bandha, intercostal stretches, and yoga-based routines (e.g., the cat-camel pose).

Example Protocol:

• Uddiyana Bandha: 3 sets of 30-second holds
• Side Rib Stretch: 2–3 sets each side, 20 seconds per hold
• Prone Chest Expansion (on a yoga ball): 2 sets, 30-second hold

These routines can increase diaphragmatic range of motion, decrease residual volume, and enhance the body’s ability to handle pressure changes.

Proper Equalization Technique:

Learning how to properly and effectively reverse pack is crucial to avoiding any type of trachea squeeze. Once you reach the 30 metre mark and it becomes difficult, learn how to refine all the other skills in your dive. Work mostly on relaxation. See what happens. Most likely, you will go beyond what you’ve already reached. Then it’s time for the Mouthfill technique. Be gentle with your equalisations and make sure to equalize early and often during the descent. If you feel certain sensations near the throat or the upper chest area, stop your descent and turn around. Proper training with an instructor who understands is highly advised.

Frenzel Tips:

1. Learn how to frenzel not only in K lock, but also in T lock
2. Keep your jaw, neck, and shoulders relaxed.
3. Focus on using the back of the tongue to move air, not chest pressure.
4. Practice reverse packing on a partial exhale on land
5. Only use the amount of pressure needed.

Relaxation and Body Positioning

Relaxation is key! It lays the foundation for a successful dive, starting from the initial preparation. From breathing techniques to Yoga Nidra, setting the right state of mind is crucial, not just before the dive, but throughout the entire experience. Maintaining a relaxed posture during the dive is critical, whilst tension in the torso can make a squeeze more likely. Further working on relaxation will help. Avoid stretching out your neck or reaching out with your arms at depth as such actions can strain the airways​. Your chin should be tucked in, shoulder neutral, pelvis slightly tucked and a soft belly. Instead, keep your head in line with your body (neutral spine) or tuck your chin slightly. Avoid sudden, jerky movements during your turn or ascent – move slowly and fluidly. A proper freefall posture will reduce stress on the chest.

Build CO₂ Tolerance & Do Warm-Up Dives

A gradual build up of CO2 causes involuntary diaphragm contractions at depth. Another variable that contributes to squeezing. Training CO2 tolerance and learning how to delay the onset of contractions will help. Another important factor is the direction and reaction of the belly during a contraction. If the belly is pushing out, this will most certainly cause a squeeze. The belly should be going in and up towards the chest. Warm up dives, besides helping the mind adapt, setting the right ‘state’, can also assist in delaying contractions for the coming dives. Starting a deep dive with your body already adapted to high CO₂ levels means you are less likely to experience violent contractions at depth.