Central neurogenic hyperventilation

Central neurogenic hyperventilation (CNH) is an abnormal pattern of breathing characterized by deep and rapid breaths at a rate of at least 25 breaths per minute. Increasing irregularity of this respiratory rate generally is a sign that the patient will enter into coma. CNH is unrelated to other forms of hyperventilation, like Kussmaul's respirations. CNH is the human body's response to reduced carbon dioxide levels in the blood. This reduction in carbon dioxide is caused by contraction of cranial arteries from damage caused by lesions in the brain stem. However, the mechanism by which CNH arises as a result from these lesions is still very poorly understood. Current research has yet to provide an effective means of treatment for the rare number of patients who are diagnosed with this condition. Central neurogenic hyperventilation (CNH) is an abnormal pattern of breathing characterized by deep and rapid breaths at a rate of at least 25 breaths per minute. Increasing irregularity of this respiratory rate generally is a sign that the patient will enter into coma. CNH is unrelated to other forms of hyperventilation, like Kussmaul's respirations. CNH is the human body's response to reduced carbon dioxide levels in the blood. This reduction in carbon dioxide is caused by contraction of cranial arteries from damage caused by lesions in the brain stem. However, the mechanism by which CNH arises as a result from these lesions is still very poorly understood. Current research has yet to provide an effective means of treatment for the rare number of patients who are diagnosed with this condition. Symptoms of CNH have been observed to vary according to the progression of CNH. The initial symptoms of CNH include a low arterial partial pressure of carbon dioxide, a high or normal arterial partial pressure of oxygen, high arterial pH, and tachypnea. The partial pressure of carbon dioxide has been noted by Yushi et al. to drop as low as 6.7 mmHg, while oxygen saturation remains at 99-100%. Respiratory alkalosis is induced in people affected with CNH, which stimulates the hyperpnea to attempt to compensate the rise of the blood’s pH. Some of the reported cases of CNH claim alkaline cerebral spinal fluid (CSF). However, not all of the cases experience this effect and other cases of CNH have a local increase in the pH surrounding the tumor that causes the condition. The hyperventilation of CNH patients persists during sleep. Those affected have been observed to not be able to voluntarily control their breathing in order to slow it down and the hyperventilation is predominantly controlled by the diaphragm. CNH has been found to affect people of all ages, ranging from children at the age of seven to adults at the age of eighty-seven. It has affected people while they have been both conscious and unconscious. After Plum and Swanson's initial discovery of CNH it was thought that CNH was rare in conscious patients. More cases of CNH have been observed in conscious patients since then. Additional symptoms of conscious CNH include loss of appetite, difficulty concentrating, poor memory, difficulties in eating or talking, cachexia, vomiting, disorientation, and a generalized confused state that varies from patient to patient. It is generally seen, however, that the mood changes, anxiety, and difficulty concentrating progress as the tumor increases in severity and, in effect, CNH persists. All of these symptoms are not present in each reported case of CNH, and symptoms seem to vary on a case to case basis. Other symptoms that have been associated with CNH are transient epileptic episodes with a temporary loss of consciousness. This condition is thought to result from severe hypocapnia that induces blood vessels in the brain to constrict, leading to brain ischemia. Other symptoms caused by CNH are electrolyte dysequilibrium and mood changes that primarily include anxiety due to the hyperventilation. Once CNH is diagnosed, the condition generally progresses until the patient becomes unconscious or lapses into a coma. Most patients are seen to enter this state two to three months after the onset of CNH. Lange et al. cited a patient that experienced pulmonary edema, bronchitis, and pneumonia prior to death, though all reported cases of CNH describe various progressions of the condition until it worsens to the point of death. CNH is most commonly associated with the central nervous system, and the majority of CNH cases have been associated with infiltrative tumors in the pons. Some cases involve the medulla and other regions of the brain. Primarily, researchers believe that the tumors infiltrate the pontine respiratory centers and central chemoreceptors. CNH has not been found to be associated with any other of the body’s systems. Cardiac, pulmonary, and metabolic disorders have been ruled out as causes of the hyperventilation. Tests such as electrocardiograms, echocardiograms, torso computed tomographic scans, and chest radiographs have revealed that the pulmonary and cardiac systems of CNH are normal. Liver and kidney functions are also normal. Lymph node and thyroid enlargement also have not been detected. Association with the cardiovascular system is seen when the brain tumors reach the medullary cardiovascular centers, at which point the patient usually succumbs to death. Determining the exact cause of CNH has proven to be difficult, specifically because only 21 additional cases have been reported since Plum and Swanson’s initial report of the condition in 1959. These subsequent reports deal only with conscious patients presenting with CNH, though the varied pathophysiologies present in each individual patient makes it nearly impossible to implicate either a particular structural lesion or the destruction of a specific locus as the sole cause of CNH. Compilations of the reports, however, have led to generalized conclusions about the primary role of structural lesions in the initiation of both juvenile and adult cases of CNH. The majority of adult patients experiencing CNH have clinical histories of infiltrative, expanding tumors of the cortex, primarily involving the brainstem. Over three-quarters of the cases reported since the discovery of CNH by Plum and Swanson had tumors clearly involving the pons, with specific consideration given to pathology of the pontine tegmentum. CNH was also reported in patients with tumors affecting the medulla oblongata. Though a diagnosis of CNH is rarely considered without evidence of brainstem infiltration, there have been other reported cases of CNH not directly involving the pons or medulla. CNH was also reported in cases involving a frontal lobe tumor, an invasive laryngeal carcinoma compressing the midbrain, an extension of tumors of the head and neck into the base of the brain, and thalamic hemorrhage. The manifestation of CNH in patients with these non-brainstem related disorders leads to greater debate about the pathophysiology of CNH and the role of other parts of the brain in the regulation of respiration. At this time, there have been no reported cases of CNH associated with stroke. In each case, the nature of the tumor varied, though the two main categories of tumor were classified as either cerebral lymphomas or solid tumors, such as pontine gliomas, anaplastic medulloblastoma, or astrocytomas.