Inadequate ventilatory response to exertion was indicated by the fact that, despite resting values in the normal range, 
  
    
      
        
          
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    {\displaystyle {P_{et_{CO_{2}}}}}
   rose markedly with exertion even when the divers breathed air at a depth of only a few feet.A variety of reasons exists for carbon dioxide not being expelled completely when the diver exhales:

The diver is exhaling into a vessel that does not allow all the CO2 to escape to the environment, such as a long snorkel, full-face diving mask, or diving helmet, and the diver then reinhales from that vessel, causing increased dead space.
Brown-Séquard syndrome (also known as Brown-Séquards hemiplegia, Brown-Séquards paralysis, hemiparaplegic syndrome, hemiplegia et hemiparaplegia spinalis, or spinal hemiparaplegia) is caused by damage to one half of the spinal cord, i.e. hemisection of the spinal cord resulting in paralysis and loss of proprioception on the same (or ipsilateral) side as the injury or lesion, and loss of pain and temperature sensation on the opposite (or contralateral) side as the lesion. It is named after physiologist Charles-Édouard Brown-Séquard, who first described the condition in 1850. Causes
Brown-Séquard syndrome may be caused by injury to the spinal cord resulting from a spinal cord tumor, trauma [such as a fall or injury from gunshot or puncture to the cervical or thoracic spine], ischemia (obstruction of a blood vessel), or infectious or inflammatory diseases such as tuberculosis, or multiple sclerosis. In its pure form, it is rarely seen. The most common cause is penetrating trauma such as a gunshot wound or stab wound to the spinal cord. Decompression sickness may also be a cause of Brown-Séquard syndrome.The presentation can be progressive and incomplete. It can advance from a typical Brown-Séquard syndrome to complete paralysis. It is not always permanent and progression or resolution depends on the severity of the original spinal cord injury and the underlying pathology that caused it in the first place.