Introduction
The human body needs oxygen for survival. The respiratory system helps to breathe in oxygen and breathe out carbon dioxide to prevent the build-up of acids in the body. Injury to the spinal cord disrupts the signals to the muscles responsible for inhaling and exhaling air. The level of respiratory impairment depends on the level of spinal injury. Severe respiratory dysfunction requires mechanical ventilation.
How Does the Respiratory System Function?
Respiration requires the activity of three muscles; the diaphragm (at the bottom of the chest), the intercostal muscles (between the ribs), the accessory muscles, and the muscles of the abdomen (over the belly). Inhalation of air involves contraction of the diaphragm and the external intercostal muscles, which allows expansion of the chest cavity to breathe in oxygen. Exhalation is a passive movement by the forceful contraction of the abdominal muscles to breathe out carbon dioxide.
What Is the Role of the Spinal Cord in Respiration?
The brain coordinates the activity of respiration. The brain sends signals through the spinal cord to the phrenic nerves at the 3rd, 4th, and 5th cervical spinal levels for contraction of the diaphragm. The diaphragm is the dome-shaped primary muscle for inspiration (inhalation). It moves down during the contraction. The lungs, rib cage, and abdomen expand during inspiration. Air travels through the windpipe to reach the air sacs in the lungs. This transfers oxygen to the blood. The diaphragm relaxes and moves up during expiration. The lungs, rib cage, and abdomen relax to breathe out carbon dioxide. During a cough, the brain sends signals to the nerves from the thoracic portion of the spinal cord for the contraction of the abdominal muscles and the intercostal muscles.
What Is the Impact of Spinal Cord Injury on the Respiratory System?
Signals sent from the brain cannot pass beyond the damaged spinal cord, and the brain cannot control the muscles of respiration. The extent of respiratory control loss depends on the level of the spinal cord injury.
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A complete high cervical injury injures the spinal cord at or above the cervical 3rd, 4th, and 5th spinal nerves. This results in complete paralysis of both the muscles of inhalation and exhalation. This needs a tracheostomy (an opening created through the neck to reach the trachea -the main airway, for breathing) or a ventilator (a machine that helps to breathe by pushing air into the lungs).
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In a complete lower cervical injury that does not involve the cervical 3rd, 4th, and 5th nerves, the diaphragm function is not disturbed, and a ventilator is not required.
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In incomplete cervical injuries, the extent of diaphragm weakness and loss of control over other muscles depends on the extent of the injury.
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In thoracic level injury, some or complete control over abdominal and intercostal muscles is lost depending on the location and extent of the damage.
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In lumbar or sacral level injury, abdominal and intercostal muscles are not affected.
After the muscle control loss, the muscles functioning work hard to breathe oxygen into the blood and send out carbon dioxide. This results in respiratory problems.
What Are the Common Respiratory Problems?
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Bronchitis - Inflammation of the tubes that carry air to the air sacs in the lungs.
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Pneumonia -Infection of the air sacs in one or both lungs.
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Atelectasis - The collapse of all or a portion of the lung due to mucus build-up.
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Obstructive Sleep Apnea - Obstructive sleep apnea occurs due to loss of muscle tone in the tongue, soft palate, or other soft tissues of the throat during sleep. This collapses the airway and obstructs the flow of air while breathing. This causes a drop in blood oxygen and a rise in carbon dioxide. The brain responds with arousal to start breathing. This disrupts sleep throughout the night.
What Are the Interventions in Respiratory Dysfunction?
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Mechanical Ventilation - High-level spinal cord injury patients need mechanical ventilation. The tracheostomy tube is an invasive ventilation method. Non-invasive ventilators offer comfort, speech, swallowing, and reduced secretions.
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Respiratory Muscle Training - The respiratory muscle function is lost, and cough production and speech are impaired in ventilated individuals. It is possible to train the ventilated muscles for strength and endurance. The muscles are trained by breathing against resistance to cause fatigue. This improves the strength and endurance of the muscle.
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Abdominal Binder - Abdominal binders are commonly used in tetraplegia. This uses inductance pneumography during spontaneous breathing. Abdominal binding influences rib-cage motion over the entire range of inspiratory capacity and increases total lung capacity and rib-cage dimensions in tetraplegic individuals.
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Ventilator-Assisted Speech - Speech is affected in high cervical injuries. Low loudness and short phrases are observed if diaphragm function is not disturbed in cervical injury. Abdominal binders may improve speech in these conditions. If cervical injury impairs diaphragm function, the ventilator is needed, and speech is altered. The nature of the speech depends on the type of ventilator. Speech delivered with tracheostomy tubes differs because ventilator-delivered air enters below the larynx. If the tube is inflated, the person cannot speak. Deflating the tube allows the person to speak. Speech with a phrenic nerve pacer is also abnormal. It is improved by using abdominal binders.
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Respiratory Muscle Pacing - In ventilated tetraplegic patients, conventional bilateral phrenic nerve pacing provides freedom from mechanical ventilation. It eliminates the noise associated with mechanical ventilators. The electrical stimulation of phrenic nerves does this in the neck or by magnetic stimulation.
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Assisted Cough - An impaired cough leads to mucus build-up. Several methods are available to induce coughing and clear the secretions. These procedures are performed with chest physical therapy.
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Spinal Cord Stimulation - Spinal cord stimulation at T9 (thoracic vertebrae 9) and L1 (lumbar vertebrae 1) levels.
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Spontaneous Cough - Spontaneous cough is enhanced if the person is seated and lurches forward.
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Quad Cough - The person is placed in an upright posture and straddled by placing hands under the right and left costal margins. The vigorous pressure applied to the abdomen enhances cough and clears secretions.
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Suction Catheter - This device enhances cough by utilizing negative pressure applied at the opening of the tracheostomy tube.
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Mechanical In-Exsufflation - This device is attached to the tracheostomy tube to remove the secretions.
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Bronchoscopy - Bronchoscopy visualizes and enhances secretion clearance.
Conclusion
Spinal cord injury leads to respiratory dysfunction. Conservative management improves ventilation through respiratory exercises and positive air pressure support. The development of new techniques improves the quality of life in ventilated individuals. Early interventions are essential to increase the strength and endurance of the respiratory muscles.
