Corticospinal pathway and exercise hyperpnea: lessons from a patient with Arnold Chiari malformation

Respiratory arrest after posterior fossa decompression in patients with Chiari malformations: An overview

Background

Chiari malformation type 1 (CM1) is a structural abnormality in the skull and cerebellum, causing cerebellar tonsils to shift downward. Decompression of the posterior fossa is a common surgical method to relieve symptoms and prevent neurological deterioration. After posterior fossa decompression (PFD), individuals with CM1 were more likely to have respiratory arrest. Here, we present, for the first time, a comprehensive overview of the potential risk factors and causes of respiratory arrest following PFD.

Methods

A review of the literature highlighting the risk factors for postoperative respiratory arrest in CM1 patients was conducted in the databases of PubMed, Medline, and Google Scholar.

Results

Patients with syringomyelia and CM1 are at increased risk for respiratory arrest due to a number of factors, including impaired respiratory mechanics, central respiratory center dysfunction from edema or ischemia, intraoperative brain stem ischemia, and delayed gastric emptying from autonomic dysfunction. Occipitalization of the first cervical vertebra, basilar impression, and fusion of C2-C3 are all risk factors for respiratory arrest.

Conclusion

Implications for CM1 patient care and prospects for further investigation of postoperative respiratory arrest's causes and risk factors were discussed.

Unusual Ventilatory Response to Exercise in Patient with Arnold-Chiari Type 1 Malformation after Posterior Fossa Decompression

We present a case of a 17-year-old Hispanic male with Arnold-Chiari Type 1 [AC-Type 1] with syringomyelia, status post decompression, who complains of exercise intolerance, headaches, and fatigue with exertion. The patient was found to have diurnal hypercapnia and nocturnal alveolar hypoventilation. Cardiopulmonary testing revealed blunting of the ventilatory response to the rise in carbon dioxide (CO₂) resulting in failure of the parallel correlation between increased CO₂ levels and ventilation; the expected vertical relationship between PETCO₂ and minute ventilation during exercise was replaced with an almost horizontal relationship. No new pathology of the brainstem was discovered by MRI or neurological evaluation to explain this phenomenon. The patient was placed on continuous noninvasive open ventilation (NIOV) during the day and CPAP at night for a period of 6 months. His pCO₂ level decreased to normal limits and his symptoms improved; specifically, he experienced less headaches and fatigue during exercise. In this report, we describe the abnormal response to exercise that patients with AC-Type 1 could potentially experience, even after decompression, characterized by the impairment of ventilator response to hypercapnia during exertion, reflecting a complete loss of chemical influence on breathing with no evidence of abnormality in the corticospinal pathway.

Ventilatory response to exercise does not evidence electroencephalographical respiratory-related activation of the cortical premotor circuitry in healthy humans

AIM

The neural structures responsible for the coupling between ventilatory control and pulmonary gas exchange during exercise have not been fully identified. Suprapontine mechanisms have been hypothesized but not formally evidenced. Because the involvement of a premotor circuitry in the compensation of inspiratory mechanical loads has recently been described, we looked for its implication in exercise-induced hyperpnea.

METHODS

Electroencephalographical recordings were performed to identify inspiratory premotor potentials (iPPM) in eight physically fit normal men during cycling at 40 and 70% of their maximal oxygen consumption ((V)·O(2max) ). Relaxed pedalling (0 W) and voluntary sniff manoeuvres were used as negative and positive controls respectively.

RESULTS

Voluntary sniffs were consistently associated with iPPMs. This was also the case with voluntarily augmented breathing at rest (in three subjects tested). During the exercise protocol, no respiratory-related activity was observed whilst performing bouts of relaxed pedalling. Exercise-induced hyperpnea was also not associated with iPPMs, except in one subject.

CONCLUSION

We conclude that if there are cortical mechanisms involved in the ventilatory adaptation to exercise in physically fit humans, they are distinct from the premotor mechanisms activated by inspiratory load compensation.

Responses of the diaphragm to transcranial magnetic stimulation during wake and sleep in humans

The human ventilation depends on bulbospinal and corticospinal commands. This study assessed their interactions in five healthy volunteers (two men, age 25-35) through the description of diaphragm and abductor pollicis brevis (APB) motor potentials (DiMEPs, abpMEPs) evoked by transcranial magnetic stimulation (TMS) during relaxed expiration and tidal inspiration and during wake and sleep. NREM decreased corticospinal excitability and REM further did so, for both the diaphragm and the APB. During wake, inspiration shortened supine DiMEPs latencies (expiration 18.56+/-1.90ms; inspiration 17.37+/-1.48ms, P<0.001). This persisted during sleep in an augmented manner (expiration: 21.05+/-1.39ms; inspiration 18.69+/-1.17ms, P=0.002). Inspiration had no effect on apbMEPs during wake and sleep.

IN CONCLUSION

(1) the tidal bulbospinal input to phrenic motoneurones is sufficient to modulate the throughput of the corticospinal pathway to these neurones; (2) this modulation is best seen after the sleep related removal of corticospinal and/or afferent inputs.

Adult Chiari malformation and sleep apnoea

Chiari malformation (CM) is primarily characterised by herniation of the cerebellar tonsils through the foramen magnum. Clinically, two main types of CM represent the vast majority of cases: type I (in adults) and type II (in infants). CM may result in neuronal impairment of the brainstem, upper spinal cord and cranial nerves. Part of the afferent and efferet systems and the central respiratory controlling system are located in the cranium-cervical transition and may be damaged in these pathologies, leading to respiratory disorders, such as respiratory failure and death. The ventilatory responses to exogenous and endogenous stimuli, such as responses to hypoxia and hypercapnia, are usually diminished, and apnea may be manifested and detected during sleep, allowing for the diagnosis. This study is a review of the relationship between sleep apnoea and adult CM.