Phrenic Nerve Stimulation: Technology and Clinical Applications

Phrenic nerve stimulation is a technique used to reanimate the diaphragm of patients with central nervous system etiologies of respiratory insufficiency. Current clinical indications include congenital central hypoventilation syndrome, spinal cord injury above C4, brain stem injury, and idiopathic severe sleep apnea. Presurgical evaluation ensures proper patient selection by validating the intact circuit from the phrenic nerve through alveolar oxygenation. The procedure involves placing leads around the phrenic nerves bilaterally and attaching these leads to radio receivers in a subcutaneous pocket. The rate and amplitude of the current is adjusted via an external radio transmitter. After implantation, each patient progresses through a conditioning phase that strengthens the diaphragm and progressively provides independence from the mechanical ventilator. Studies indicate that patients and families experience an improved quality of life and are satisfied with the results. Phrenic nerve stimulation provides a safe and effective means for reanimating the diaphragm for certain patients with respiratory insufficiency, providing independence from mechanical ventilation.

Pseudo-piano playing motions and nocturnal hypoventilation in anti-NMDA receptor encephalitis: response to prompt tumor removal and immunotherapy

Tumor resection is recommended in anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis, however it is often difficult during an early stage of the disease. We report here the efficacy of early tumor removal in a patient with anti-NMDAR encephalitis. This 21-year-old woman was admitted to another hospital with rapidly progressive psychiatric symptoms, a decreased level of consciousness, and seizures. Abdominal CT showed a pelvic mass. On day 1 of admission to our center, she developed hypoventilation requiring mechanical support. She had orofacial dyskinesias with well-coordinated, pseudo-piano playing involuntary finger movements. Based on these clinical features, she was immediately scheduled for tumor resection on day 3. While awaiting surgery, she began to receive high-dose intravenous methylprednisolone. After tumor removal, she received plasma exchange, followed by intravenous immunoglobulin and additional high-dose methylprednisolone. Two weeks after tumor removal, she started following simple commands and progressive improvement, although she remained on mechanical ventilation for 10 weeks due to nocturnal central hypoventilation. Anti-NMDAR antibodies in serum/CSF were detected. Pathological examination showed immature teratoma with foci of infiltrates of B- and T-cells. Early tumor resection with immunotherapy facilitates recovery from this disease, but central hypoventilation may require long mechanical support. Non-jerky elaborate finger movements suggest antibody-mediated disinhibition of the cortico-striatal systems.

Severe Respiratory Compromise Secondary to Cervical Disk Herniation in Two Dogs

Two dogs presented with acute tetraparesis, hypoventilation, and bradycardia with a second-degree atrioventricular heart block. Neurological examination localized both lesions to the cervical spine. Diagnostic imaging revealed a ventral extradural compression at the second to third cervical (C2–C3) region in one dog and at the third to fourth cervical (C3–C4) region in the other. Following surgical correction of the extruded disk, the hypoventilation and bradycardia resolved. Cervical disk extrusions are a common cause of acute tetraparesis in the dog. This report shows that respiratory and cardiac complications may occur concurrently. The authors recommend screening dogs with cervical myelopathies for respiratory and cardiac dysfunctions and treating appropriately. Prompt surgical intervention and supportive care can improve the prognosis.

[Simultaneous, bilateral and permanent ventilation with a diaphragm pacing in childhood: the implantation technique and indications]

The acute effects of external stimulation were well demonstrated by the turn of the century, but the chronic application had to wait until the advent of the modern pacemaker technology. Since 1983 we have implanted bilateral diaphragm pacing in ten infants and adolescents with quadriplegia and central hypoventilation syndrome. The preferred site of implantation was the thoracic phrenic nerve. The electrophysiological status of the phrenic nerve function has before been determined in all patients. We have got bilateral and continuous ventilation, in all patients, but, in quadriplegics is necessary a conditioning period. Long term stimulation of the phrenic nerves to pace the diaphragm is an effective method of ventilatory support in selected cases.

Hemodynamic dysfunction in obesity hypoventilation syndrome and the effects of treatment with surgically induced weight loss

Obesity hypoventilation syndrome (OHS), defined as a PaO2 less than or equal to 55 mmHg and/or PaCo2 greater than or equal to 47 mmHg, was found in approximately 8% of morbidly obese patients undergoing gastric surgery for morbid obesity and was frequently associated with clinically significant pulmonary hypertension and cardiac dysfunction. Forty-six morbidly obese patients, 26 with and 20 without OHS, underwent preoperative pulmonary artery catheterization. Although the two groups had similar values for percent ideal body weight, blood pressure, and cardiac index, the OHS patients had significantly higher mean pulmonary artery pressures (PAP), p less than 0.0001, and pulmonary artery occlusion pressures (PAOP), p less than 0.01. Eighteen OHS patients were restudied 3-9 months after gastric surgery. PaO2 increased from 50 +/- 10 to 69 +/- 14 mmHg, p less than 0.0001, and PaCO2 decreased from 52 +/- 7 to 42 +/- 4 mmHg, p less than 0.0001), after the loss of 42 +/- 19% excess weight. These changes were associated with significant decreases in PAP (from 36 +/- 14 to 23 +/- 7 mmHg, p less than 0.0001) and PAOP (from 17 +/- 7 to 12 +/- 6 mmHg, p less than 0.01). Significant correlations were noted between PAP and PAOP (r = +0.8, p less than 0.0001) and PAP and PaO2 (r = -0.6, p less than 0.0001). Both left ventricular dysfunction, defined as a PAOP greater than or equal to 18 mmHg, as well as pulmonary artery vasoconstriction, defined as PAEDP greater than 5 mmHg above PAOP, contributed to pulmonary hypertension in OHS patients. In conclusion, weight loss after gastric surgery for morbid obesity significantly improved arterial blood gases and hemodynamic function in OHS patients.