Extrapulmonary causes of hypoventilation

Which neuromuscular diseases lead to extrapulmonary alveolar hypoventilation?

Extrapulmonary hypoventilation is caused by diseases affecting neuromuscular synapses, nerve trunks, and the respiratory muscles themselves.

• Poliomyelitis, myasthenia gravis, and polyneuritis — cause impaired impulse transmission in the neuromuscular synapses of the intercostal muscles and diaphragm.
• Botulism — leads to the blockade of acetylcholine release, causing respiratory muscle paresis and acute respiratory failure.
• Myalgia and myodystrophy — are associated with direct damage to the intercostal muscles and impaired function.

How does the Tiffeneau index change in restrictive hypoventilation?

In restrictive hypoventilation, the Tiffeneau index remains within normal limits, i.e., equal to or greater than 70%.

This is because when lung expansion is restricted, both key spirometric parameters decrease proportionally: forced expiratory volume in the first second (FEV₁) and forced vital capacity (FVC). As a result, their percentage ratio (FEV₁/FVC), which represents the Tiffeneau index, does not decrease.

How does apneustic breathing differ from periodic breathing?

Apneustic breathing is characterized by a cycle described as a prolonged low-depth inspiration → short expiration → another prolonged inspiration. Its mechanism: prolonged inspiration is associated with a decrease in the pulse amplitude of all types of respiratory neurons except the post-inspiratory pool; the activity of post-inspiratory neurons is prolonged, and the synchronization of inspiratory neurons in the respiratory rhythm generator is disrupted.

Periodic breathing forms referenced in literature include Biot, Cheyne-Stokes, and Kussmaul breathing:

• Cheyne-Stokes respiration: period of apnea lasting from several seconds to 1 minute → shallow breathing → gradual increase in depth to a noisy maximum around the 5th–7th breath → gradual decrease in depth → new period of apnea.
• Biot respiration: alternation of uniform, rhythmic, and deep respiratory movements with periods of apnea.
• Kussmaul respiration: uniform cycles of slow, deep, and noisy inspiration followed by a forced expiration.

Which spinal cord lesions cause respiratory disorders?

Respiratory disorders, according to sources, are caused by the following spinal cord and pathway lesions:

• Lesions of the pathways from the respiratory center to the diaphragm in spinal cord ischemia or trauma, multiple sclerosis, or poliomyelitis. The indicated pathogenesis is the loss of respiratory automatism; breathing becomes irregular and ceases upon falling asleep.
• Lesions of the corticospinal pathways in tumors, trauma, spinal cord ischemia, or syringomyelia. The indicated pathogenesis is the loss of voluntary respiratory control; the patient cannot voluntarily alter the rhythm or depth of breathing.
• Lesions of the descending spinal pathways and motor neurons in spinal cord trauma or ischemia, or poliomyelitis. Clinically, a decrease in the amplitude of respiratory movements and periodic apnea are described.
• Cervical lesion in tick-borne viral encephalitis: paralysis of the diaphragmatic musculature is associated with motor neurons of the anterior horns of C4; combined damage to the neck muscles and diaphragm causes a peripheral-type respiratory disorder.
• Spinal cord injury at the cervical and upper levels: for such patients, monitoring and prevention of hypoventilation are recommended.