Why the Diaphragm Fails During Choking
The diaphragm doesn't "fail" during choking—it continues to contract vigorously, but the mechanical obstruction in the airway prevents air from entering the lungs despite these forceful respiratory efforts. This creates a paradoxical situation where the respiratory muscles work harder but achieve no gas exchange.
The Mechanical Basis of Airway Obstruction
When a foreign body lodges in the airway, the normal respiratory cycle is disrupted at the level of the pharynx, larynx, or trachea—not at the diaphragm itself 1. The choking process begins with voluntary breath-holding, followed by involuntary laryngospasm when liquid or solid material contacts the oropharynx or larynx 1. During this laryngospasm phase, the victim's respiratory movements may become very active, but there is no exchange of air because of the obstruction at the level of the larynx 1.
The diaphragm continues to contract and descend during inspiration, creating increasingly negative intrathoracic pressure 1. However, because the airway is blocked, this negative pressure cannot draw air into the lungs. Instead, it creates a closed system where the diaphragmatic effort is wasted against a fixed obstruction 1.
Physiological Consequences of Continued Diaphragmatic Effort
The forceful inspiratory efforts against an obstructed airway generate extreme negative intrathoracic pressures that can lead to post-obstructive pulmonary edema 1. These negative pleural pressures increase the hydrostatic pressure gradient across pulmonary capillary walls, causing fluid leak into the interstitial space 1. The victim's respiratory movements become increasingly vigorous as hypoxemia and hypercarbia worsen, but the mechanical obstruction prevents any meaningful air exchange 1.
As arterial oxygen tension drops, the initial laryngospasm eventually abates, and the victim may actively aspirate the obstructing material deeper into the airways 1. Throughout this process, the diaphragm continues functioning—the problem is purely mechanical obstruction preventing airflow despite intact neuromuscular function 1.
Why Back Blows and Chest Thrusts Work
The rationale for back blows and chest thrusts is to create an "artificial cough" by using pressure within the chest cavity 1. Sudden elevation of the diaphragm compresses the lungs, which explosively forces air out through the trachea, ejecting the obstructing object 2. This works precisely because the diaphragm and respiratory muscles are still functional—the intervention simply reverses the direction of pressure to expel rather than inhale 1, 2.
Chest thrusts in infants and abdominal thrusts (Heimlich maneuver) in older children work by rapidly increasing intrathoracic pressure through external compression, which pushes the diaphragm upward and forces residual air out of the lungs with enough force to dislodge the obstruction 1, 3, 2.
Critical Clinical Pitfall
Never perform blind finger sweeps of the pharynx, as these can impact a foreign body deeper into the larynx 1, 4, 5. This common error can convert a partial obstruction into a complete one. The appropriate intervention is to use mechanical maneuvers that harness the diaphragm's continued function to generate expulsive airflow 1, 2.
The Progressive Hypoxic Cascade
As the obstruction persists, oxygen depletion and carbon dioxide retention lead to hypercarbic, hypoxemic, and acidotic states 1. The diaphragm continues contracting throughout this deterioration until circulatory arrest eventually ensues from tissue hypoxia 1. The heart and brain are the two organs at greatest risk for permanent detrimental changes from relatively brief periods of hypoxia 1, making rapid relief of the obstruction critical even though the diaphragm itself remains functional.
In summary, the diaphragm works perfectly well during choking—the problem is that its efforts are futile against a mechanical blockage that prevents air from reaching the lungs despite vigorous respiratory muscle activity 1, 2.