Concurrent inhibition and excitation of phrenic motoneurons during inspiration: phase-specific control of excitability.
(1/1532)
The movements that define behavior are controlled by motoneuron output, which depends on the excitability of motoneurons and the synaptic inputs they receive. Modulation of motoneuron excitability takes place over many time scales. To determine whether motoneuron excitability is specifically modulated during the active versus the quiescent phase of rhythmic behavior, we compared the input-output properties of phrenic motoneurons (PMNs) during inspiratory and expiratory phases of respiration. In neonatal rat brainstem-spinal cord preparations that generate rhythmic respiratory motor outflow, we blocked excitatory inspiratory synaptic drive to PMNs and then examined their phase-dependent responses to superthreshold current pulses. Pulses during inspiration elicited fewer action potentials compared with identical pulses during expiration. This reduced excitability arose from an inspiratory-phase inhibitory input that hyperpolarized PMNs in the absence of excitatory inspiratory inputs. Local application of bicuculline blocked this inhibition as well as the difference between inspiratory and expiratory firing. Correspondingly, bicuculline locally applied to the midcervical spinal cord enhanced fourth cervical nerve (C4) inspiratory burst amplitude. Strychnine had no effect on C4 output. Nicotinic receptor antagonists neither potentiated C4 output nor blocked its potentiation by bicuculline, further indicating that the inhibition is not from recurrent inhibitory pathways. We conclude that it is bulbospinal in origin. These data demonstrate that rapid changes in motoneuron excitability occur during behavior and suggest that integration of overlapping, opposing synaptic inputs to motoneurons is important in controlling motor outflow. Modulation of phasic inhibition may represent a means for regulating the transfer function of PMNs to suit behavioral demands. (+info)
Contribution of extracranial lymphatics and arachnoid villi to the clearance of a CSF tracer in the rat.
(2/1532)
The objective of this study was to determine the relative roles of arachnoid villi and cervical lymphatics in the clearance of a cerebrospinal fluid (CSF) tracer in rats. 125I-labeled human serum albumin (125I-HSA; 100 micrograms) was injected into one lateral ventricle, and an Evans blue dye-rat protein complex was injected intravenously. Arterial blood was sampled for 3 h. Immediately after this, multiple cervical vessels were ligated in the same animals, and plasma recoveries were monitored for a further 3 h after the intracerebroventricular injection of 100 micrograms 131I-HSA. Tracer recovery in plasma at 3 h averaged (%injected dose) 0.697 +/- 0.042 before lymphatic ligation and dropped significantly to 0.357 +/- 0. 060 after ligation. Estimates of the rate constant associated with the transport of the CSF tracer to plasma were also significantly lower after obstruction of cervical lymphatics (from 0.584 +/- 0. 072/h to 0.217 +/- 0.056/h). No significant changes were observed in sham-operated animals. Assuming that the movement of the CSF tracer to plasma in lymph-ligated animals was a result of arachnoid villi clearance, we conclude that arachnoid villi and extracranial lymphatic pathways contributed equally to the clearance of the CSF tracer from the cranial vault. (+info)
Atypical mycobacterial lymphadenitis in childhood--a clinicopathological study of 17 cases.
(3/1532)
AIMS: To assess the clinical and pathological features of atypical mycobacterial lymphadenitis in childhood to define the salient clinical and histological features. METHODS: 17 cases were included on the basis of positive culture or demonstration of bacilli of appropriate morphology and staining characteristics. RESULTS: The mean age at diagnosis was 4.86 years. All children were systemically well, with clear chest x rays. Unilateral cervical lymphadenopathy was the commonest mode of presentation. Differential Mantoux testing played no part in diagnosis. Clinical diagnosis improved with awareness. Treatment varied with surgeons opting for excision and paediatricians adding six months antituberculous chemotherapy. Acid- and alcohol-fast bacilli were identified in nine cases. Bacterial cultures were conducted in 16 cases and were positive for atypical or nontuberculous mycobacteria in 14, the main organism being M avium-intracellulare complex (11 cases). Histologically, 12 cases had bright eosinophilic serpiginous necrosis with nuclear debris scattered throughout the necrotic foci. Langhans type giant cells featured in the majority of cases but infiltration by plasma cells and neutrophils was not consistent. CONCLUSIONS: Atypical mycobacterial lymphadenitis of childhood represents a rare but significant disease with characteristic clinical and histological features. (+info)
Bilateral neck exploration under hypnosedation: a new standard of care in primary hyperparathyroidism?
(4/1532)
OBJECTIVE: The authors review their experience with initial bilateral neck exploration under local anesthesia and hypnosedation for primary hyperparathyroidism. Efficacy, safety, and cost effectiveness of this new approach are examined. BACKGROUND: Standard bilateral parathyroid exploration under general anesthesia is associated with significant risk, especially in an elderly population. Image-guided unilateral approaches, although theoretically less invasive, expose patients to the potential risk of missing multiple adenomas or asymmetric hyperplasia. Initial bilateral neck exploration under hypnosedation may maximize the strengths of both approaches while minimizing their weaknesses. METHODS: In a consecutive series of 121 initial cervicotomies for primary hyperparathyroidism performed between 1995 and 1997, 31 patients were selected on the basis of their own request to undergo a conventional bilateral neck exploration under local anesthesia and hypnosedation. Neither preoperative testing of hypnotic susceptibility nor expensive localization studies were done. A hypnotic state (immobility, subjective well-being, and increased pain thresholds) was induced within 10 minutes; restoration of a fully conscious state was obtained within several seconds. Patient comfort and quiet surgical conditions were ensured by local anesthesia of the collar incision and minimal intravenous sedation titrated throughout surgery. Both peri- and postoperative records were examined to assess the safety and efficacy of this new approach. RESULTS: No conversion to general anesthesia was needed. No complications were observed. All the patients were cured with a mean follow-up of 18 +/- 12 months. Mean operating time was <1 hour. Four glands were identified in 84% of cases, three glands in 9.7%. Adenomas were found in 26 cases; among these, 6 were ectopic. Hyperplasia, requiring subtotal parathyroidectomy and transcervical thymectomy, was found in five cases (16.1%), all of which had gone undetected by localization studies when requested by the referring physicians. Concomitant thyroid lobectomy was performed in four cases. Patient comfort and recovery and surgical conditions were evaluated on visual analog scales as excellent. Postoperative analgesic consumption was minimal. Mean length of hospital stay was 1.5 +/- 0.5 days. CONCLUSIONS: Initial bilateral neck exploration for primary hyperparathyroidism can be performed safely, efficiently, and cost-effectively under hypnosedation, which may therefore be proposed as a new standard of care. (+info)
Neck soft tissue and fat distribution: comparison between normal men and women by magnetic resonance imaging.
(5/1532)
BACKGROUND: Obesity and increased neck circumference are risk factors for the obstructive sleep apnoea/hypopnoea syndrome (SAHS). SAHS is more common in men than in women, despite the fact that women have higher rates of obesity and greater overall body fat. One factor in this apparently paradoxical sex distribution may be the differing patterns of fat deposition adjacent to the upper airway in men and women. A study was therefore undertaken to compare neck fat deposition in normal men and women. METHODS: Using T1 weighted magnetic resonance imaging, the fat and tissue volumes in the necks of 10 non-obese men and 10 women matched for age (men mean (SE) 36 (3) years, women 37 (3) years, p = 0.7), body mass index (both 25 (0. 6) kg/m2, p>0.9), and Epworth Sleepiness Score (both 5 (1), p = 0.9) were assessed; all denied symptoms of SAHS. RESULTS: Total neck soft tissue volume was greater in men (1295 (62) vs 928 (45) cm3, p<0. 001), but the volume of fat did not differ between the sexes (291 (29) vs 273 (18) cm3, p = 0.6). The only regions impinging on the pharynx which showed a larger absolute volume of fat in men (3.2 (0. 7) vs 1.1 (0.3) cm3, p = 0.01) and also a greater proportion of neck fat in men (1.3 (0.3)% vs 0.4 (0.1)%, p = 0.03) were the anterior segments inside the mandible at the palatal level. CONCLUSIONS: There are differences in neck fat deposition between the sexes which, together with the greater overall soft tissue loading on the airway in men, may be factors in the sex distribution of SAHS. (+info)
Volume flow estimation by colour duplex.
(6/1532)
OBJECTIVE: To assess the accuracy of volume blood flow using a digitised colour duplex scanner. DESIGN: Observer-blinded experimental study. MATERIALS AND METHODS: Method comparison was performed with linear regression analysis of 89 paired observations in 11 anaesthetised pigs. A Siemens Sonoline Elegra ultrasound system was used for transcutaneous volume flow estimation using invasive transit time flowmetry by Cardiomed as a reference. RESULTS: For the individual measurement we found a standard error of the estimate (SEE) of 22 ml/min. For the regression line, however, the SEE was only 0.2 ml/min. CONCLUSIONS: Digitised colour-duplex sonography has a volume flow measurement error that is too high for single measurements in the individual patient for the method to be useful in clinical decision making, but sufficient for examinations of groups and comparison of groups. (+info)
Dural arteriovenous fistula of the cervical spine presenting with subarachnoid hemorrhage.
(7/1532)
We describe a case of dural arteriovenous fistula (DAVF) presenting with subarachnoid hemorrhage (SAH). The diagnosis of DAVF was based on spinal angiography. A review of the literature revealed that five of 13 previously reported DAVFs of the cervical spine were accompanied by SAH. SAH has not been observed in DAVFs involving other segments of the spinal canal. (+info)
Can nuchal cord cause transient increased nuchal translucency thickness?
(8/1532)
When detected in a first trimester scan, an increased thickness of nuchal translucency (NT) may be associated with chromosomal, cardiac or genetic disorders. However, less attention has been devoted to the outcome of those fetuses who have confirmed normal anatomies and karyotyping, but have abnormal first trimester scans. Thus, a challenging new issue is how to counsel such cases of transient increased NT in which the translucency rapidly vanishes with no evidence of other underlying abnormalities. Two cases of transient increased thickness of NT are reported. In both, a nuchal cord was ultrasonographically demonstrated and a thorough work-up revealed chromosomally and anatomically normal fetuses. The pathophysiological theories behind these observations and their significance are discussed. Based on these observations, we suggest that transvaginal sonography combined with Doppler flow studies should be utilized for the presize detection of cord patterns to accomplish the work-up in cases of increased NT. (+info)