High-frequency ventilation by bilateral phrenic nerve stimulation in dogs

We succeeded in achieving good gas exchange by oscillatory phrenic nerve stimulation (PNS) in dogs. In 7 out of 14 dogs, adequate gas exchange was attained by PNS at 3, 4 and 5 pulses per sec (pps). VE increased with stimulation frequency up to 4 or 5 pps, but decreased above 6 pps. We also applied sinusoidal oscillation using a piston pump at the trachea in the same dogs to analyze the mechanical properties of the respiratory system. The V/P ratio, oscillatory volume divided by driving pressure, decreased markedly at 6 Hz while the pleural pressure remained constant up to 10 Hz. These facts indicate that the fall in VE is due to mechanical properties of the airway and lung, and not due to failure of the ventilatory pump system. We conclude that frequencies of 3-5 pps in high-frequency ventilation are optimal for maintaining effective gas transport when the diaphragma is used as the oscillatory generator.     

Inhibitory effects of gastric electrical stimulation on ghrelin-induced excitatory effects on gastric motility and food intake in dogs

OBJECTIVE: To investigate the effects of ghrelin on food intake, gastric motility and whether gastric electrical stimulation (GES) is capable of reversing these effects of ghrelin in dogs. MATERIAL AND METHODS: Seven healthy dogs were equipped with a gastric cannula and electrodes for the measurement of antral motility and gastric myoelectrical activity (GMA). Both food intake and gastric motility studies were performed in three sessions (control, ghrelin, 20 microg and ghrelin plus GES) in randomized order, respectively. After a 28-h fast, the animals were provided with unlimited solid food for 1.5 h, 30 min after saline or ghrelin injection. Recordings of antral contractions and GMA in each session were recorded for 30 min at baseline and 45 min after ghrelin/saline injection in the fasting state. GES was performed throughout the experiment initiated 30 min prior to the injection. RESULTS: 1) Ghrelin significantly increased food intake from 475.6+/-75.5 g in the controls to 535.9+/-90.3 g with ghrelin (p=0.04); this excitatory effect was reversed by GES. 2) Ghrelin significantly increased the motility index from 8.6+/-1.6 in the controls to 16.1+/-2.4 with ghrelin (p=0.01) and this effect was also reversed by GES. 3). There were no effects of ghrelin on GMA. CONCLUSIONS: Ghrelin induces antral contractions and increases food intake. GES is capable of blocking these excitatory effects of ghrelin. These findings suggest that GES may inhibit the resistant effect of ghrelin on weight loss.     

Inhibitory effects of gastric electrical stimulation on ghrelin-induced excitatory effects on gastric motility and food intake in dogs

Objective. To investigate the effects of ghrelin on food intake, gastric motility and whether gastric electrical stimulation (GES) is capable of reversing these effects of ghrelin in dogs. Material and methods. Seven healthy dogs were equipped with a gastric cannula and electrodes for the measurement of antral motility and gastric myoelectrical activity (GMA). Both food intake and gastric motility studies were performed in three sessions (control, ghrelin, 20 µg and ghrelin plus GES) in randomized order, respectively. After a 28-h fast, the animals were provided with unlimited solid food for 1.5?h, 30?min after saline or ghrelin injection. Recordings of antral contractions and GMA in each session were recorded for 30?min at baseline and 45?min after ghrelin/saline injection in the fasting state. GES was performed throughout the experiment initiated 30?min prior to the injection. Results. 1) Ghrelin significantly increased food intake from 475.6±75.5?g in the controls to 535.9±90.3?g with ghrelin (p=0.04); this excitatory effect was reversed by GES. 2) Ghrelin significantly increased the motility index from 8.6±1.6 in the controls to 16.1±2.4 with ghrelin (p=0.01) and this effect was also reversed by GES. 3). There were no effects of ghrelin on GMA. Conclusions. Ghrelin induces antral contractions and increases food intake. GES is capable of blocking these excitatory effects of ghrelin. These findings suggest that GES may inhibit the resistant effect of ghrelin on weight loss.     

Elimination of phrenic nerve stimulation occurring during CRT

Background  

Phrenic nerve stimulation (PNS) occurs at follow-up in approximately 20% of patients with bipolar leads. The quadripolar Quartet model 1458Q (St. Jude Medical, Sylmar, CA, USA) left ventricular lead (LV) has four electrodes (one distal tip and three ring) capable of ten different pacing vectors which may allow reprogramming to eliminate PNS.     

Twitch airway pressure elicited by magnetic phrenic nerve stimulation in anesthetized healthy children

Children with diaphragm dysfunction may be unable to maintain adequate ventilation. Accurate diagnosis is important, but can only be achieved using an appropriate test and reference range. The aim of this study, therefore, was to measure diaphragm contractility and examine the influence of age and maturation, using magnetic phrenic nerve stimulation in healthy children. Anterolateral magnetic stimulation (MS) of the phrenic nerves was performed using a 43-mm figure-eight coil in 23 children (14 male; mean age, 7.8 years; range, 1.8-15.7) anesthetized for minor surgery with sevoflurane gas. The airway was maintained with a cuffed laryngeal mask airway (LMA) which was briefly occluded during MS. Diaphragm contractility was assessed by measuring the airway pressure (TwPaw) elicited by MS. TwPaw responses were obtained in all subjects, with mean (SD) TwPaw 18.2 (6.8) cm H2O bilateral, 7.3 (3.2) cm H2O left unilateral, and 8.6 (3.1) cm H2O right unilateral. Subgroup analysis was performed in 17 of the children who were prepubertal. Their mean (SD) TwPaw was 17.3 (6.8) cm H2O bilateral, 7.1 (3.7) cm H2O left unilateral, and 8.3 (3.3) right unilateral. The mean (SD) intrapatient coefficients of variation for bilateral and left and right unilateral TwPaw were 8.4% (5.2), 6.7% (3.5), and 11.7% (10.3), respectively. Bilateral and left and right unilateral TwPaw were significantly related to age (P < 0.05). In healthy prepubertal children, diaphragm contractility is primarily influenced by age.     

Thermomechanical facilitation of swallowing evoked by electrical nerve stimulation in cats

Application of a cold metal probe to the anterior faucial pillar has been reported to improve swallowing in some patients with dysphagia. Although a variety of stimuli contribute to the initiation of swallowing, the effects of a controlled, cold-thermal stimulus combined with mechanical stimulation have not been examined. It is known that simultaneous stimulation of the glossopharyngeal nerve (IX) and the superior laryngeal nerve may summate to facilitate swallowing in the cat. The goal of this study was to determine whether thermomechanical stimulation of the mucosa innervated by IX would interact with threshold electrical stimulation of the internal laryngeal nerve (ILN) to augment the swallowing response in cats. Four experimental conditions were tested over 24 trials in 4 pentobarbital-anesthetized cats. These included electrical stimulation of ILN, mechanical stimulation of the anterior faucial pillar with a thermode at ambient (room) temperature, concurrent ambient-mechanical and electrical stimulation, and concurrent cold-mechanical and electrical stimulation. Tissue was cooled to 8.9°C during cold-mechanical-electrical stimulation and 25.3°C during ambient-mechanical-electrical and ambient-mechanical alone stimulation. Ambient-mechanical stimulation alone did not produce swallowing. However, both forms of thermomechanical-electrical stimulation elicited a significantly greater number of swallows than did electrical stimulation alone. Therefore, mechanical stimulation with a thermode was capable of modifying the swallowing response in neurologically intact cats. Differences between stimulation with a probe at ambient and at cold temperatures were not significant.     

Diaphragmatic pressures in piglets: Transvenous versus direct phrenic nerve stimulation

We examined transdiaphragmatic pressure (Pdi) generation during both direct (DPNS) and transvenous (TVPNS) modes of phrenic nerve stimulation in anesthetized piglets of varying postnatal age. Pdi measurements during TVPNS were not statistically different from those obtained during DPNS (p > 0.10). Furthermore, a good correlation (r = 0.98, p < 0.001) was obtained when the mean Pdi measurements obtained by both methods were compared. We conclude that TVPNS can be used in lieu of DPNS to generate Pdi. Furthermore, our data suggest that this technique can be used to study the effects of various experimental manipulations on diaphragmatic force output within a developmental context.     

Excitation of afferent cardiac sympathetic nerve fibers induced by vagal stimulation.

The effect of vagal stimulation on activity of afferent sympathetic nerve fibers from the dog's left ventricle has been examined. During partial constriction of the coronary artery, a brief electrical stimulation of the cervical vagus nerves resulted in a decrease in blood flow of the constricted artery, systolic bulge of the left ventricle, elevation of the ST segment of electrocardiogram and excitation of the afferent nerve fibers, which continued for up to 15 min. These changes were not produced without coronary artery constriction. Intravenous injection of phentolamine eliminated the decrease in blood flow, and suppressed systolic bulge, elevation of the ST segment and excitation of afferent fibers. Propranolol could not eliminate the decrease in blood flow while suppressed the other changes. Atropine eliminated all of these changes. The results indicate participation of adrenergic alpha-receptors in sustained decrease of coronary blood flow and excitation of afferent cardiac sympathetic nerve fibers which can be produced by a brief vagal excitation.     

Effect of phrenic nerve stimulation on neural transmission and diaphragmatic force generation in the dog

The effect of supramaximal bilateral phrenic nerve stimulation on neural transmission and diaphragmatic force generation was studied in anesthetized dogs. Different combinations of duty cycle and stimulation frequency were examined during intermittent stimulation (pacing) for 15 min. The effect of different stimulation frequencies was also examined during continuous stimulation for 60 sec. Force declined more with increasing stimulation frequency and duty cycle with intermittent stimulation, and with increasing stimulation frequency with continuous stimulation. Neural transmission decreased with increasing stimulation frequencies. The changes were always greater with continuous than with intermittent stimulation. We found no unique relationship between changes in neural transmission and changes in force generation, suggesting that if neural transmission failure is causally responsible for fatigue, it does so by a very complex mechanism.     

Effect of lung volume on the oesophageal diaphragm EMG assessed by magnetic phrenic nerve stimulation.

Previous studies have shown conflicting results on the effect of lung volume on the diaphragm compound muscle action potential (CMAP). Consequently, the ability to quantify the oesophageal diaphragm electromyography (EMG) has been questioned. If lung volume changes have little effect on the diaphragm CMAP the accurate measurement of voluntary EMG, as an index of respiratory drive, may be possible. Furthermore, the measurement of CMAP could provide useful clinical information when evaluating patients with neuromuscular disease. To reassess the effect of lung volume on the oesophageal diaphragm CMAP, six normal subjects were studied using an oesophageal catheter incorporating seven electrodes (number one being proximal and seven distal) that were 1 cm in length and 1 cm apart. Electrode number three was positioned at the centre of the electrically active region of the diaphragm (EARdi) at functional residual capacity (FRC). The diaphragm CMAP elicited by bilateral magnetic stimulation of the phrenic nerves was simultaneously recorded from four electrode pairs. Pair one was created from electrodes one and three, pair two from electrodes two and four, pair three from electrodes three and five, and pair four from electrodes five and seven. Phrenic nerve stimulation was at residual volume (RV), FRC, FRC+1.0 L, FRC+2.0 L, and total lung capacity (TLC). The CMAP recorded from pair one was least influenced by changes in lung volume and the amplitude was 2.41+/-0.39 (mean+/-SD), 2.60+/-0.27, 2.64+/-0.29, and 2.71+/-0.45 mV at RV, FRC, FRC+1.0 L and FRC+2.0 L, respectively. At TLC the CMAP was more variable. The CMAP amplitude recorded from pair two increased with increasing lung volume and at FRC+2.0 L was 3.7 times larger than that at FRC. Pair four usually recorded substantially smaller CMAPs at all lung volumes. This study shows that the diaphragm compound muscle action potential recorded from an oesophageal electrode just above the diaphragm is relatively stable over the lung volume range residual volume to functional residual capacity+2.0 L.     

心脏再同步治疗中膈神经刺激的单中心回顾分析

Objective To analyze the phrenic nerve stimulation and the appropriate treatment during and after CRT/CRT-D implantation. Methods Seventy-nine patients (45 men and 34 women, aged 35 ～ 86 years) received CRT/CRT-D implantation. The patients were followed up for average 24 months. The phrenic nerve stimulations was analyzed and the corresponding treatments were taken. Results Seventy-eight patients received successful implantation(98. 7% ). The incidence rates of the phrenic nerve stimulation is 12. 8% during and after the implantation. Posterior veins and posterior lateral veins are predilection sites. The risk increased in the patients with short stature and enlarged heart. Phrenic nerve stumilation can be eliminated by adjusting the electrode position, output voltage pulse, width and changing the polarity. Nobody needs another operation because of the phrenic nerve stimulation. Conclusions Phrenic nerve stimulation is a common complication of CRT/CRT-D implantation operation. Doctors should take great attention to prevent this complication during the implanting procedure and follow-up.     

心脏再同步治疗中膈神经刺激的单中心回顾分析

目的 探讨心脏再同步治疗(CRT)植入术中、术后膈神经刺激发生情况及处理方法.方法 心力衰竭患者79例,其中男性45例,女性34例,年龄35～86岁,接受CRT/CRT-D植入术.术后平均随访24个月,观察膈神经刺激发生情况,同时给予相应的处理措施.结果 78例患者成功植入,成功率为98.7%.植入术中、术后膈神经刺激发生率为12.8%.后静脉、侧后静脉是其好发部位,身材偏矮小及心脏增大的患者CRT植入中出现膈神经刺激危险性增高.调整电极导线位置、输出电压和脉宽以及改变极性等方法,可以有效消除膈神经刺激.结论 膈神经刺激是CRT/CRT-D植入术中、术后的常见并发症;严格做好术中预防、术后随访,及时采取有效的干预手段,以减少或避免膈神经刺激的发生.     

心脏再同步治疗中膈神经刺激的单中心回顾分析

Objective To analyze the phrenic nerve stimulation and the appropriate treatment during and after CRT/CRT-D implantation. Methods Seventy-nine patients (45 men and 34 women, aged 35 ～ 86 years) received CRT/CRT-D implantation. The patients were followed up for average 24 months. The phrenic nerve stimulations was analyzed and the corresponding treatments were taken. Results Seventy-eight patients received successful implantation(98. 7% ). The incidence rates of the phrenic nerve stimulation is 12. 8% during and after the implantation. Posterior veins and posterior lateral veins are predilection sites. The risk increased in the patients with short stature and enlarged heart. Phrenic nerve stumilation can be eliminated by adjusting the electrode position, output voltage pulse, width and changing the polarity. Nobody needs another operation because of the phrenic nerve stimulation. Conclusions Phrenic nerve stimulation is a common complication of CRT/CRT-D implantation operation. Doctors should take great attention to prevent this complication during the implanting procedure and follow-up.     

Conditioning of the diaphragm with phrenic nerve stimulation after prolonged disuse

We studied the effect of electrical stimulation of the phrenic nerve on the force frequency relationship of the disused diaphragm. A high quadriplegic who had been totally ventilator dependent for 6 months following a C2 fracture received bilateral phrenic nerve stimulators. During a 6-wk period of conditioning by electrical stimulation, the force of diaphragm contraction was assessed by measurement of transdiaphragmatic pressures during stimulation of each nerve over a range of frequencies. Tidal volume as well as rib cage and abdominal motion were studied. There was an upward shift of the force frequency relationship of the diaphragm over the 4-month period of phrenic nerve pacing using repetitive stimulus trains of 14 to 28 Hz. This improvement appeared to plateau at about 11 wk. The increase in contractility was accompanied by a progressive diminution in the stimulus frequency at which fusion of the contraction occurred. The disused diaphragm, like other skeletal muscle, may be conditioned with electrical stimulation.     

Influence of lung volume and rib cage configuration on transdiaphragmatic pressure during phrenic nerve stimulation in man

Transdiaphragmatic pressure was recorded during bilateral supramaximal percutaneous phrenic nerve stimulation at 1 Hz (twitch Pdi) to investigate the effect of lung volume and rib cage configuration on diaphragm contractility in man. Stimulations were performed in 5 normal supine subjects at resting end expiration (FRC) and at lung volumes above and below FRC, during relaxation against a closed airway and during isovolume manoeuvres. Twitch Pdi at FRC was 24.4 cm H2O. At lung volumes above FRC, twitch Pdi decreased by 7.04 +/- 3.2 cm H2O per litre of volume change. At lung volumes below FRC, twitch Pdi increased by 12.4 +/- 8.6 cm H2O per litre of volume change. When the diaphragm was lengthened during an isovolume manoeuvre at FRC, twitch Pdi increased. A similar relationship between lung volume and twitch Pdi was obtained during stimulations performed with abdominal binding. These results demonstrate that the pressure developed by the diaphragm during phrenic nerve stimulation is significantly affected both by increases and decreases in lung volume and by the rib cage configuration at which stimulation is performed.