Cricoid cartilage and esophagus: CT scan study of the dynamic variability of their relative positions.

INTRODUCTION: Cricoid pressure occludes the esophagus (E) by compressing it between the cricoid cartilage (CC) and the body of the sixth cervical vertebra (C6). This technique is used to prevent passive regurgitation during the induction of anesthesia in patients at high risk for regurgitation. Failures of this technique had been described and a possible displacement of the E relative to the CC had been reported, but there is no study about displacement during antero-posterior movements of the head. AIM: The aim of our study was to evaluate the displacement of the CC relative to the cervical E, during flexion and extension movements of the head. MATERIALS AND METHODS: We retrospectively studied X-ray computed tomography (CT) images of 21 patients with suspected cervical trauma. Patients were in the supine position. In the first series of images, the head was positioned at maximal flexion by means of a support placed under the external occipital protuberance. In the second series of images, the head was maintained in extension by means of a support placed under the shoulders. Each position was obtained as far as possible within the limits of pain and restricted movement. In flexion and extension, we used the lowest slice from the cricoid cartilage. The variables measured were: diameters of CC (CD) and E (OD), left and right lateral displacements of E. RESULTS: A total of 13 CT were analyzed. CD and OD as well as OD/OC ratios did not vary significantly in flexion and extension. We noticed 61.5 and 92.3% (respectively in flexion and in extension) of left or right displacement: 23% of patients presented right displacement in both flexion and extension; 38.5% of patients did not present any right displacement in flexion or in extension; 61.5% of patients presented left displacement in both flexion and extension. More generally, almost 92% of patients presented displacement either in flexion or extension, or both. DISCUSSION: In our study, it can be seen that the E is clearly displaced with regard to the CC, that this displacement is favored by extension. Only 2/13 patients have an "over than 3 mm" displacement in extension whereas 5/13 in flexion. So, even if there are more displacements in extension, they are inferior to 3 mm and may not be considered as significant considering the occlusion of E. According to our results, the extension position of the head produces more displacement of the E but should preserve the containment of the cricoid pressure if we consider the thickness of the E wall.

The clinical and hemodynamic results after axillary-to-popliteal vein valve transplantation.

PURPOSE: To evaluate the results of axillary vein to popliteal vein valve transplantation (VVTX), we reviewed the clinical, phlebographic, and noninvasive hemodynamic results in 15 patients. METHODS: All patients had postthrombotic destruction of deep venous valves as determined by ascending phlebography, whereas descending phlebography demonstrated grade III or IV reflux in all patients. A segment of valve-bearing axillary vein was transplanted to the popliteal vein in the affected limb. Postoperative evaluation was by clinical, noninvasive, and phlebographic means. RESULTS: Over a mean follow-up period of 5.3 years (1.25 to 11 years), 13 of 14 patients (93%) had symptomatic improvement with relief of swelling, whereas all 14 patients who were admitted with pain had relief after operation. Thirteen of 15 patients (87%) returned to work or household duties. Physical findings of edema, skin pigmentation, and lipodermatosclerosis improved in most patients. Only three patients (21%) had development of recurrent ulcers, with an average postoperative ulcer-free interval of 4 years by life-table analysis. The cumulative ulcer-free survival rate for the group averaged 62% at late follow-up. All three patients with ulcer recurrence had a functioning valve by descending phlebography, but recurrent perforating veins were found in two patients, and deep venous thrombosis above a patent VVTX was observed in the third. Late assessment of reflux by venous filling index and valve closure times for the entire sample demonstrated mean values of 4.9 seconds in the latter and 6.8 ml/sec in the former. Residual volume fraction, which correlates with invasive ambulatory venous pressures, was reduced to a mean of 31%. No deterioration in late sequential noninvasive values could be detected. CONCLUSION: VVTX is a durable procedure for preventing recurrent venous ulcers.

An assessment of the positive predictive value and cost-effectiveness of dipyridamole myocardial scintigraphy in patients undergoing vascular surgery.

PURPOSE: The approach to cardiac risk stratification of patients undergoing vascular surgery continues to be controversial. The success of algorithms that use clinical risk factors to determine cardiac risk have been inconsistent. Dipyridamole myocardial scintigraphy (DMS) has been accepted as a sensitive, noninvasive approach to risk stratification with excellent negative predictive value. Low positive predictive value (PPV) of abnormal DMS scans is a shortcoming that contributes to extensive preoperative cardiac evaluation and intervention with associated morbidity, mortality, and cost in most patients who undergo uncomplicated vascular procedures, regardless of DMS results. METHODS: Over 6 years, 237 patients underwent DMS before surgical management of infrarenal aortic aneurysm, aortoiliac, or infrainguinal occlusive disease. The value of multiple clinical factors and DMS were assessed retrospectively for the prediction of perioperative myocardial infarction (MI), heart-related death, or preoperative selection for myocardial revascularization. Only congestive heart failure and two or more reversible defects on DMS were statistically significant on logistic regression analysis. RESULTS: The PPV of DMS was 19% for all patients with reversible defects, 12% for patients with one reversible defect, and 36.7% for patients with two or more reversible defects. The rates of cardiac death and MI were 1.3% and 5.9%, respectively. Perioperative echocardiography revealed unchanged postinfarction ejection fraction in most patients who experienced MI. Cost-effectiveness of DMS screening was evaluated. CONCLUSIONS: The costs per MI and cardiac death averted suggest a decline in cost-effectiveness of screening with DMS over time, assuming improving cardioprotective strategies of patient care. Clinical risk factors were minimally useful in the prediction of perioperative MI, heart-related death, or need for myocardial revascularization. The PPV of DMS is low, and the majority of MIs may be clinically insignificant. The cost-effectiveness of cardiac screening with DMS may not be justifiable given current trends of health care reform.

The activity of neurons in the rostral medulla of the rat during withdrawal from noxious heat.

Neurons of the rostral ventromedial medulla (RVM) have been implicated in the modulation of nociceptive transmission. In order to further analyze their role in pain behavior, we studied their activity while eliciting the tail flick reflex with noxious heat. Recording sites were regions in the RVM from which microstimulation (less than or equal to 10 microA, 400 mu sec, 50 Hz continuous pulse trains) inhibited the tail flick reflex. Extracellular unit activity and tail temperature were recorded, stored, and plotted with reference to either the time of tail flick or the time when the stimulating temperature reached 45 degrees C. Neuronal discharges were found to be either increased (on-cells), decreased (off-cells), or unchanged around the time of the tail flick. The decreases in discharge were more closely correlated with the tail flick behavior than with the temperature of the stimulus. These off-cells were located at sites of lowest threshold for tail flick inhibition and tended to be ventral to on-cells. We propose that off-cells must pause if the tail flick is to occur, and that this pausing allows the transmission of nociceptive input through spinal reflex loops.

The vestibulothalamic pathway: contribution of the ascending tract of Deiters.

Axoplasmic transport techniques were used to determine the contribution of the ascending tract of Deiters (ATD) to the vestibulothalamic projection in cats. Large injections of HRP into the thalamus centered on the border region between the ventrobasal complex and the caudal ventrolateral nucleus resulted in bilateral retrograde labeling of cells in the vestibular nuclear complex and the nucleus prepositus hypoglossi (PH). Similar thalamic injections were also made in animals with extensive bilateral lesions of the medial longitudinal fasciculus (MLF) and the brachium conjunctivum (BC). HRP-positive neurons in these cases were localized principally to the ventral lateral vestibular nucleus and adjacent superior vestibular nucleus ipsilateral to the thalamic injection, evidence that vestibulothalamic neurons in these nuclei may project to the thalamus over the unlesioned ATD. Injections of [35S]methionine into the rostral vestibular nuclear complex in animals with MLF and BC lesions confirmed these findings, demonstrating orthograde transport of radiolabel in the ATD with termination in thalamus. These experiments document a contribution of the ATD to the ipsilateral vestibulothalamic projection; other sources of the vestibulothalamic pathway (PH, Y group) likely travel through projection systems destroyed in the lesions made in the present study.

Excitatory projection from the interpeduncular nucleus to central superior raphe neurons.

The projection from the interpeduncular nucleus (IP) to the central superior raphe nucleus (CS) was studied using electrophysiologic methods. IP stimulation generates monosynaptic EPSPs in a large number of CS neurons studied with latency of 1-2 ms. Intracellular peroxidase injections into CS neurons responding to IP shock confirmed the location and somatic origin of intracellular potentials. These findings document the existence of a direct excitatory projection from IP onto CS neurons.