The international workshop held in November 1999 at the Spinal Cord Injured Centre of the BG- trauma hospital in Hamburg was organised to exchange experience and to provide a view on recent developments concerning respiratory muscle stimulation for treatment of respiratory insufficiency. Despite the highly specialised locality Central Hypoventilation Syndrome was an important part of the meeting, too. Part of the comments and questions at the meeting has changed some texts and is not documented separately. However, after presentation of patient series and cases a lively discussion took place between those preferring phrenic nerve stimulation and those preferring mechanical ventilation for long-term use in C2-tetraplegic patients. In accordance with the literature, no agreement was achieved. Obviously, in children and adolescents there is the danger of creating scoliosis if the stimulation current is not adjusted meticulously to create the minimum sufficient tidal volume only and when the stimulator is used 24 hours a day. The problem has not been seen in adults and not in centres where routinely is switched between daytime stimulation and nocturnal ventilation.
A phrenic nerve stimulator is the ventilatory device of choice for patients with full-time Central Hypoventilation Syndrome. Those with central sleep apnoea are freed from the mechanical ventilator, as are patients with C2-tetraplegia. The possible freedom has to be balanced against the risks of carrying implants life-long; the risk can be expressed numerically. However, no numbers are available on the risks of long-term mechanical ventilation. Additionally, freedom from mechanical ventilation (quality of life) has not yet been transformed into numbers. Full agreement was achieved for the need of controlled studies of the problem.
Patients who use phrenic nerve stimulators are a subgroup of a minority of patients with central apnoea complicated by additional diseases or severe disability. Primary care and life-long follow-up of the whole minority should be concentrated in few centres to allow for accumulation of experience, which is needed to achieve goods results as urgently as cooperation between specialists of different professions.
Electrical stimulation of skeletal muscle at fusion frequency results soon in muscle fatigue. In recent stimulators, fatigue is avoided by stimulation at low frequencies; muscle force decreases simultaneously. Additionally, a conditioning period is needed before disturbing vibration ceases. During the last 15 years new stimulation patterns have been found, which allow for fatigue free stimulation with less loss of muscle force. Use of these patterns might enlarge the group of patients who could benefit from PNS.
Stimulation of other respiratory muscles also might enlarge the group. Stimulation of the expiratory muscles may help tetraplegic patients in the sitting position, might increase coughing ability and can, for short time, provide sufficient ventilation on its own. Results were presented with a device stimulating via surface electrodes. The device should help to find the patients who might benefit from such stimulation. A non invasive method to explore the function of different compartments of the lung might also help to decide, which kind of respiratory muscle stimulation is needed for an individual patient.
