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Biomedical subjects

H Lanmüller

Publications and source records attributed to H Lanmüller.

26 records · Page 2Linked to original sources
PubMed1996

Vienna phrenic pacemaker--experience with diaphragm pacing in children.

Eight children, five boys and three girls, aging from 2 to 13 years (M = 9 +/- 3) were treated with the "Vienna phrenic pacemaker". Indication for implantation was central alveolar hypoventilation syndrome (CAH) in one case and total ventilatory insufficiency due to high cervical cord or brain stem lesion (SCI) in seven cases. Four electrodes were applied to each phrenic nerve via sternotomy. Both hemidiaphragms were paced synchronously with increasing duty cycles to condition the diaphragms for continuous electrophrenic respiration (EPR). EPR could be performed successfully in all children but one. Four children could achieve chronical EPR, one is in conditioning period. Two patients could not be discharged from hospital due to parental neglect and died after two and three years of intermittent stimulation. Six children could be discharged from hospital, two of them died after one and four years of chronic pacing. In one case tracheotomy could be closed definitively. Ventilatory insufficiency due to CAH and SCI can be treated even in children with diaphragm pacing, provided the indication for implantation, containing medical and social aspects, was made correctly. Diaphragm pacing probably will not lengthen life of severely injured children but it can increase the quality of their life and therefore should be preferred to positive pressure mechanical ventilation.

Adolescent↗
PubMed1996

[Circulatory support by an electrically stimulated muscle flap. Experimental experiences].

Functional electrical stimulation of the latissimus dorsi muscle flap for circulatory assistance extends the traditional concept of using this flap for reconstructive procedures into the field of cardiac surgery. It requires a transformed muscle which is able to contract for long periods of time without fatigue. Two main groups of experiments have been carried out in sheep. In six sheep the latissimus dorsi muscle (MLD) was transformed into a fatigue-resistant muscle by the means of multichannel stimulation of the supplying motor nerve. After that, stimulation of MLD at a frequency of 70 contractions per minute could be performed continuously without significant muscle fatigue. The loss of maximal force caused by the conditioning procedure was about one third of the initial force. In a second series of acute experiments the MLD was used for cardiomyoplasty. The muscle was divided into two parts which were wrapped around the heart in two different forms. The resting tension of the muscle was preserved. EKG-synchronous stimulation resulted in an increase in left ventricular pressure between 12 and 53%. The increase in arterial pressure was between 10,6 and 58%.

Animals↗
PubMed1995

Monitoring of FES-induced muscle activity by continuous EMG-recording.

Functional Electrical Stimulation (FES) requires information on the stimulated muscle for adjustment of the stimulation current, avoidance of muscle fatigue during the conditioning period and long term follow-up. Several applications of chronical FES are in clinical practice, but a system for direct registration of muscle activity under FES still does not exist. In six sheep the right Latissimus Dorsi Muscle (LDM) and Thoracodorsal Nerve were exposed. Stimulation electrodes were applied to each nerve and 3 EMG-applied sensing electrodes were placed into each LDM. The LDM tendon was connected to a force transducer. Burst stimulation was applied and the amplitude was increased from 0 to 4 mA in steps from burst to burst. EMG (M-wave) was amplified and recorded continuously via modified instrumentation amplifier, oscilloscope and tape recorder. Isometric muscle tension was recorded using force transducer, A/D interface and PC. Continuous EMG-recording was performed in all cases. Simultaneous recording of muscle tension and EMG revealed a close correlation (IrI=0.95, p < 0.0001) between the muscle strength and amplitude of the M-wave. Continuous recording of the EMG seems to be a reliable method for direct monitoring of the stimulated muscle. Three intramuscular electrodes can provide enough information to monitor FES induced muscle activity.

Animals↗
PubMed1991

First experimental application of multichannel stimulation devices for cardiomyoplasty.

The effect of long-term application of epineural electrodes to nerves was investigated in rat experiments. Neural damage reached a maximum of 6% shortly after implantation and decreased to 3% after 1 year. Impedance and threshold of epineural electrode were investigated in sheep experiments for up to 12 months. The mean impedance was in the range of 1 kohm, while the threshold less than 1 mA. The reduction in fatigue produced by multichannel stimulation was demonstrated by sequential isometric contractions of rectus muscles in sheep. The decrease in force was only 10% after 60 minutes of multichannel stimulation as compared to a reduction of 50% for single channel stimulation. Studies of cardiomyoplasty with single channel stimulation confirmed results reported by other investigators. In acute experiments with sheep, we demonstrated fiber-selective stimulation which led to isolated contraction of the left or right distal part or the right proximal part of the latissimus dorsi muscle. Potential advantages in the application of implantable multichannel stimulation devices as compared to single channel stimulation for cardiomyoplasty include: (1) fatigue-free stimulation at submaximal force level; (2) selection of hemodynamically effective electrode combinations; (3) potential for consecutive activation of muscle fiber groups, thereby allowing better simulation of the physiological contraction of the heart muscle; (4) redundancy of electrodes in case of technical failure or dislocation; and (5) stimulation of more than one muscle, if necessary.

Animals↗
PubMedDate not supplied

Multichannel stimulation of phrenic nerves by epineural electrodes. Clinical experience and future developments.

Between 1983 and 1992, 23 patients with complete ventilatory insufficiency of differing etiologies were treated with an eight channel implant (Medimplant Inc., Vienna) for fatigue free stimulation of both phrenic nerves. Data for 15 patients with high spinal cord lesions (ages: 9-51 years) are summarized: 1) level of lesion: C0, 3 patients; C1/C2, 4; C2/C3, 8; 2) time between incident and implantation: 3-14 months; 3) diaphragm training: 1-22 months; 4) chronic pacing: 5-83 months; 5) tracheostomy closed: 7 patients; 6) living permanently at home: 13 patients; 7) respiratory rate per minute: 12-17; 8) duration of inspiration: 1.0-1.3 sec; 9) tidal volume: 7-20 ml/kg body weight; 10) volume per minute: 121-198 ml/kg body weight; 11) pH: 7.39-7.42; 12) pCO2: 22.9-38.6 mmHg; 13) pO2: 81.2-104.5 mmHg; and 14) died by December 1992, 4 patients. All currently available implants for phrenic pacing need an external power supply and radio control. The authors have developed and tested the first fully implantable device. Features of this implant include an electronic circuit based on the microcontroller MC68HC705C8; surface mounted technology (SMD); eight channels; constant current source adjustable to 5 mA in 256 steps, impulse duration: 100-1000 musec, stimulation frequency: 1-33 Hz; and minimum lifetime: 3 years. The implant is programmed via bidirectional radio transmission using an IBM compatible computer. The dimensions, including battery, eight electrode connectors, and antenna, are 67 x 48 x 13 mm. The implant weights 58 g. This new device may improve patients' safety and quality of life in the near future.

Adolescent↗