Biomedical subjects

W H Warren

Publications and source records attributed to W H Warren.

At least 37 records · Page 2Linked to original sources

PubMed1997

Visual control of braking in goal-directed action and sport.

Reaching a moving object, avoiding an obstacle, or controlling a rotation are common requirements of experts in sport and goal-directed action. Since the original analysis of optic flow, a large number of studies have addressed the problem of perception and control of braking. In this paper, the perception-action strategies described for deceleration control are reviewed; driving, docking, landing, somersaulting, running and reaching are analysed. The role played by 'tau dot', the first temporal derivative of tau, is shown to be critical. However, the so-called constant tau-dot strategy proposed to explain how we regulate our deceleration in such circumstances is critically examined and rejected. New directions in the problem of braking control are proposed that emphasize: (1) the advantage of tau-dot over other kinematic variables; (2) the task specificity of tau-dot; (3) the need to consider tau-dot as a control variable; and (4) the role played by the controller dynamics in the perception-action loop. Several directions for future research are suggested.

Animals↗

PubMed1997

Differential diagnosis of small cell neuroendocrine carcinoma of the lung.

The clinical significance of a tumor classification rests in its usefulness to predict the natural history and response to therapeutic intervention of given tumor types. In this context, the importance of distinguishing between SCNC and neoplasms with which it has been confused is evident. In 1990, we re-evaluated a series of 50 patients who underwent a complete resection for tumors in which the diagnosis of small cell carcinoma was thought to have been established. Adjuvant therapy was given to nearly all patients, either pre- or postoperatively. We re-evaluated the histology of these tumors in light of the differential diagnosis described previously and correlated the diagnosis with the survival curves. We found that WDNC of any subtype has a much better prognosis than SCNC. Even locally advanced WDNC has a better prognosis than stage I completely resected SCNC (Fig. 9). Others have reported similar observations based on their own retrospective studies. Preliminary observations on completely resected chest wall PNETs suggest that these tumors also have a more favorable prognosis than SCNC. Given the difficulty in distinguishing SCNC from other tumors described previously, and the fact that most SCNC are treated without resection, the clinician should be familiar with certain features that are unusual for SCNC, and, therefore, suggest reconsideration of the diagnosis. In our patient population, SCNC is rarely seen in a lifetime nonsmoker and is distinctly unusual in an ex-smoker of 15 years of longer. T with chest wall invasion is a very unusual clinical stage for true SCNC. Small cell neuroendocrine carcinoma can invade the chest wall, but this is almost always in the presence of extensive mediastinal or distant metastases. Clinicians should also be wary of accepting the diagnosis of SCNC when serial radiographs suggest that the lesion is not growing or growing very slowly. Untreated SCNC usually demonstrates some growth over a 3-month period of observation. Finally, SCNC tends to be a chemosensitive neoplasm, at least initially. The occasional tumors that do not respond tend to enlarge and disseminate rapidly. If a tumor neither decreases nor increases in diameter over a 3-month period of presumably appropriate chemo- or radiotherapy, the diagnosis of SCNC should be questioned. Over the last 15 years, several reports have suggested a role for resection in the management of SCNC, especially for tumors diagnosed at an early stage. Other reports may have unwittingly exaggerated the long-term survival of SCNC treated by currently available chemo- and radiotherapy protocols. A careful re-evaluation of the diagnostic material in such cases may lead to more consistent results and the development of more rational therapeutic protocols.

Carcinoma, Small Cell↗

PubMed1996

Motion parallax is used to control postural sway during walking.

Three experiments tested the hypothesis that postural sway during locomotion is visually regulated by motion parallax as well as optical expansion. Oscillating displays of three-dimensional scenes were presented to participants walking on a treadmill, while postural sway was recorded. Displays simulated: (a) a cloud, in which parallax and expansion are congruent, (b) a hallway, (c) the side walls of the hallway, (d) a ground surface, (e) a wall, (f) the wall with a central hole, (g) a hall farther from the observer, and (h) a wall farther from the observer. In contrast to previous results with a hallway, responses with the cloud were isotropic and directionally specific. The other displays demonstrated that motion parallax was more effective than simple horizontal flow in eliciting lateral sway. These results are consistent with the hypothesis that adaptive control of sway during walking is based on congruent expansion and parallax in natural environments.

Adult↗

PubMed1996

Visual control of posture during walking: functional specificity.

Three experiments examined the functional specificity of visually controlled posture during locomotion by presenting large-screen displays to participants walking on a treadmill. Displays simulated locomotion down a stationary hallway, a hallway that traveled with the observer, or a frontal wall that traveled with the observer. A superimposed oscillation specified postural sway in 6 possible directions. With the wall, sway amplitude was isotropic and directionally specific in all conditions. However, with the hallways, sway was anisotropic (lateral > anterior-posterior [AP]), and diagonal responses were flattened into the lateral plane. When the treadmill was turned 90 degrees to the hallway, both the anisotropy and flattening were reversed (AP > lateral), indicating that they are determined by the visual structure of the scene. The results can be explained by postural control laws based on both optical expansion and motion parallax, yielding biases in planar environments that truncate parallax.

Adult↗

PubMed1996

Resonance Tuning in Rhythmic Arm Movements.

The hypothesis was tested that the preferred frequency of rhythmic movement corresponds to the resonant frequency of the muscle-limb system, as proposed by the hybrid spring-pendulum model (Kugler Turvey, 1987). In contrast to previous studies, the resonant frequency and stiffness of the system were estimated independently, which permitted quantitative predictions of the preferred frequency to be made. Human subjects (N = 5) were asked to oscillate their forearms in the vertical plane at their preferred frequency under conditions of added mass and external spring loading. Subjects also oscillated their arms at frequencies below and above the preferred frequency, which enabled the investigators to estimate the resonant frequency and stiffness of the elbow joint by using the phase transfer method (Viviani, Soechting, Terzuolo, 1976). The preferred frequency corresponded to the resonant frequency of the muscle-limb system under each condition, as predicted. The oscillation amplitude varied inversely with the preferred frequency, which was also predicted. Finally, the internal joint stiffness was modulated so that it matched the impedance of the external springs but was unaffected by added mass. The results are consistent with an autonomous oscillator model that incorporates proprioception about the dynamics of the periphery.

Journal Article↗

PubMed1995

Increased numbers of cytokeratin-positive interstitial reticulum cells (CIRC) in reactive, inflammatory and neoplastic lymphadenopathies: hyperplasia or induced expression?

A total of 291 enlarged lymph nodes showing a range of reactive-inflammatory processes, primary and metastatic neoplasms were studied to determine the distribution and immunoprofile of their cytokeratin-positive interstitial reticulum cells (CIRC) in comparison with normal nodes. In 258/291 nodes (89%), CIRC numbers were distinctly increased in the subcapsular, paracortical and, occasionally, in the medullary zones; often, these increased CIRC formed networks around follicles, sinuses and vessels. CIRC had comparatively small, irregularly shaped bodies and dendritic processes; occasionally, giant forms were noted. CIRC contained cytokeratins (CK) 8 and 18 but not 19, as shown by immunohistochemistry, and by gel electrophoresis with subsequent immunoblotting. They co-expressed vimentin consistently, alpha-smooth-muscle actin frequently, and desmin less frequently. They did not contain desmoplakins, Factor VIII, S-100, LCA, B and T lymphocyte- and macrophage-associated antigens, chromogranin A, synaptophysin or the A-80 glycoprotein. We found no clear correlation between the increased CIRC and given nodal disease processes. However, CIRC were most abundant in nodes free of but draining malignant tumours; bizarre CIRC assemblies were noted in HIV lymphadenopathy. CIRC appear to represent a subset of the so-called "fibroblastic reticulum cells" of lymph nodes. Their function remains undetermined; their increase in diverse lymphadenopathies suggests that they partake in nodal reactions to injury. It remains unclear whether the increase in CIRC relative number is due to proliferation or to CK gene induction processes but their presence and potential capability to undergo hyperplasia with dysplastic forms should alert pathologists to possible diagnostic pitfalls. In addition, we discuss that CIRC may undergo transformation and represent the "cell of origin" of certain CK-positive tumours restricted to lymph nodes.

Cytoskeletal Proteins↗

PubMed1995

Subxiphoid pericardial drainage for pericardial tamponade.

As a result of recent reports and enthusiasm for video-assisted thorascopic pericardiectomy, we reviewed our experience with subxiphoid pericardial drainage. From August 15, 1988, to June 7, 1993, 155 patients underwent subxiphoid pericardial drainage for pericardial effusion associated with pericardial tamponade. The group comprised 85 female (55%) and 70 male patients whose ages ranged from 5 weeks to 88 years. The procedure was carried out with general anesthesia in 113 patients (72%) and with local anesthesia and sedation in 42 patients. Underlying cancer was present in 82 patients; 73 patients had benign disease. Follow-up is complete in all patients. The overall 30-day mortality was 20%; in patients with cancer it was 32.9% (27/82) versus 5.4% (4/73) for patients with benign disease. No postoperative death was attributed to the surgical procedure. Recurrent pericardial tamponade necessitating further surgical intervention occurred in four patients (2.5%), two with cancer (2.4%) and two with benign disease (2.7%). Median survival after subxiphoid pericardial drainage in patients with benign disease was more than 800 days versus 83 days in patients with cancer (p < 0.01). Median survival after pericardial drainage in patients with cancer who had malignant pericardial effusion was 56 days compared with 105 days for patients with cancer who did not have tumor in the pericardium (p < 0.05). We believe that subxiphoid drainage is the procedure of choice for patients with pericardial tamponade. It is accomplished quickly, is associated with minimal morbidity, and prevents recurrent tamponade in 97.4% (151/155) of patients.

Adolescent↗

PubMed1995

Why change gaits? Dynamics of the walk-run transition.

Why do humans switch from walking to running at a particular speed? It is proposed that gait transitions behave like nonequilibrium phase transitions between attractors. Experiment 1 examined walking and running on a treadmill while speed was varied. The transition occurred at the equal-energy separatrix between gaits, with predicted shifts in stride length and frequency, a qualitative reorganization in the relative phasing of segments within a leg, a sudden jump in relative phase, enhanced fluctuations in relative phase, and hysteresis. Experiment 2 dissociated speed, frequency, and stride length to show that the transition occurred at a constant speed near the energy separatrix. Results are consistent with a dynamic theory of locomotion in which preferred gaits are characterized by stable phase relationships and minimum energy expenditure, and gait transitions by a loss of stability and the reduction of energetic costs.

Acceleration↗

PubMed1995

Visual control of braking: a test of the tau hypothesis.

Deceleration during braking could be controlled by (a) using the time derivative of the relative rate of optical expansion, relative to a -0.5 margin value of tau-dot (D.N. Lee, 1976) or (b) computing the required deceleration from spatial variables (i.e., perceived distance, velocity, or object size). Participants viewed closed-loop displays of approach to an object and regulated their deceleration with a brake. The object appeared on a checkerboard ground surface (providing velocity, distance, and size information) or with no background (providing only optical expansion). Mean tau-dot during braking was -0.51, and estimates of the critical value of tau-dot based on brake adjustments were -0.44 and -0.52, close to the expected value. There were no overall effects of the ground surface or object size. The results are consistent with a tau-dot strategy, where the direction and magnitude of brake adjustments are regulated using tau-dot.

Acceleration↗

PubMed1995

Perceiving heading in the presence of moving objects.

In most models of heading from optic flow a rigid environment is assumed, yet humans often navigate in the presence of independently moving objects. Simple spatial pooling of the flow field would yield systematic heading errors. Alternatively, moving objects could be segmented on the basis of relative motion, dynamic occlusion, or inconsistency with the global flow, and heading determined from the background flow. Displays simulated observer translation toward a frontal random-dot plane, with a 10 deg square moving independently in depth. The path of motion of the object was varied to create a secondary focus of expansion (FOE') 6 deg to the right or left of the actual heading point (FOE), which could bias the perceived heading. There was no effect when the FOE was visible, but when the object moved in front of it, perceived heading was biased toward the FOE' by approximately 1.9 degrees with a transparent object, and approximately 3.4 degrees with an opaque object. The results indicate that scene segmentation does not occur prior to heading estimation, which is consistent with spatial pooling weighted near the FOE. A simple template model based on large-field, center-weighted expansion units accounts for the data. This may actually represent an adaptive solution for navigation with respect to obstacles on the path ahead.

Analysis of Variance↗

PubMed1995

Surgical techniques in the dissection and reconstruction of the pulmonary artery.

This article discusses technical approaches to the pulmonary artery, as well as techniques used in the pulmonary arterioplasty. Although pulmonary artery reconstruction can be performed now with minimal perioperative morbidity and mortality, the long-term survival rate is still disappointingly low, chiefly because of the development of distant metastases.

Anastomosis, Surgical↗

PubMed1994

Postthoracotomy pain management using continuous epidural analgesia in 1,324 patients.

Continuous epidural analgesia consisting of an opioid with or without a local anesthetic agent is a commonly employed technique for pain relief after thoracotomy. In this study, we prospectively evaluated the use of continuous epidural analgesia in 1,324 patients undergoing elective thoracotomy between 1987 and 1993. Epidural pain management was continued for 1 to 3 postoperative days. Patients experienced excellent pain relief, with mean visual analog pain scores of 2.4, 1.7, and 1.4 on postoperative days 1, 2, and 3, respectively. Side effects occurred most frequently in the first 24 hours postoperatively; the incidence of pruritus was 14.1%; nausea, 11.2%; hypotension, 4.3%; sedation, 3.3%; and numbness, 1.1%. Respiratory depression (< 8 breaths per minute) occurred in 1 patient who received 16 mg of supplemental morphine sulfate over a 2-hour period. The incidence of inadequate analgesia (a visual analog pain score of 7 or more persisting for 1 to 2 hours after an epidurally administered bolus) was 3.8%. The results from this study support the use of standard protocols for dosing guidelines, the treatment of inadequate analgesia, and the management of side effects. Daily evaluation by a team member of the postoperative analgesia services section of the Department of Anesthesiology enhances patient care and minimizes adverse effects.

Adult↗

PubMed1994

Clinical experience with Montgomery salivary bypass stents in the esophagus.

Thirty-seven patients with locally advanced malignancy (18, esophageal obstruction; 19, esophageal fistula formation) underwent attempted placement of a Montgomery salivary stent in the esophagus. This was unsuccessful in 3; in 2, because of inability to dilate, and, in 1, because of perforation. After dilation of the esophagus, there was no detectable underlying stricture in 11 patients; none of these patients experienced stent migration. Overall, there was 100% success in obliterating the fistulous tract, an 8.1% incidence of retrograde migration, no incidence of prograde migration, and no incidence of stent obstruction after discharge. Of the 34 patients with successfully placed stents, 27 were discharged from hospital, and were able to eat and drink without the need for intravenous supplementation or gastrostomy tube feedings. The survival in patients presenting with obstruction ranged from 1 to 13 months (mean, 8.0 months); the survival in patients presenting with a fistula ranged from 2 to 7 months (mean, 5.3 months).

Esophageal Fistula↗

PubMed1994

Malignant pleural mesothelioma. Extrapleural pneumonectomy and pleurectomy.

Diffuse malignant pleural mesothelioma is an uncommon, uniformly fatal malignancy. Controversy continues to surround the optimal surgical procedure, both extrapleural pneumonectomy or pleurectomy, which should be utilized in conjunction with post-operative chemotherapy and/or radiotherapy. This retrospective study reviews a single institution's experience with extrapleural pneumonectomy and pleurectomy in the multimodality treatment of diffuse malignant pleural mesothelioma.

Aged↗

PubMed1994

Segmentectomy versus lobectomy in patients with stage I pulmonary carcinoma. Five-year survival and patterns of intrathoracic recurrence.

One hundred seventy-three patients with stage I (T1 N0, T2 N0) non-small-cell lung cancer underwent either a segmental pulmonary resection (n = 68) or lobectomy (n = 105) from 1980 to 1988. Four patients were lost to follow-up, but the remaining 169 patients were followed up for 5 years. Survival and the prevalence of local/regional recurrence were assessed. Although no survival advantage of lobectomy over segmental resection was noted for patients with tumors 3.0 cm in diameter or smaller, a survival advantage was apparent for patients undergoing lobectomy for tumors larger than 3.0 cm. The rate of local/regional recurrence was 22.7% (15/66) after segmental resection versus 4.9% (5/103) after lobectomy. A review of histologic tumor type, original tumor diameter, and segment resected revealed no risk factors that were predictive of recurrence. An additional resection for recurrence was performed in four patients. Lobectomy is the preferred operative procedure for patients with stage I tumors larger than 3.0 cm. Because the rate of local/regional recurrence was high after segmental resections, diligent follow-up of these patients is mandatory.

Adenocarcinoma↗

PubMed1993

Thoracotomy for colon and rectal cancer metastases.

Between 1978 and 1990, 23 patients underwent 35 thoracotomies for metastatic colorectal cancer. The pulmonary disease was diagnosed within an interval of 0 to 105 (average, 33.4) months after colon resection. Fifteen patients underwent a single thoracotomy; 12 patients had solitary lesions, and three patients had multiple nodules. Eight patients underwent multiple thoracotomies. The median survival following thoracotomy was 28 months; three-year survival was 45 percent, and five-year survival was 16 percent. Factors that had no significant bearing on survival included origin and stage of the primary tumor and patient age and sex. An interval before thoracotomy of three years had an impact on survival approaching statistical significance (P = 0.17). Patients who underwent multiple thoracotomies had a significantly prolonged survival (P = 0.04). Patients who underwent a single thoracotomy for a solitary lesion had a significantly prolonged survival compared with patients who had a single thoracotomy for multiple metastases. After thoracotomy, 14 patients eventually developed recurrent disease, which was confined to the lung in only four patients. Of these 14 patients, 11 subsequently died of cancer. We conclude that thoracotomy for metastatic disease should be considered when the primary tumor is controlled, the lungs are the only site of metastatic disease, and there is adequate lung reserve to withstand surgery. Survival following thoracotomy may be influenced by the interval before diagnosis, the number of pulmonary nodules, and the number of thoracotomies performed.

Adult↗

PubMed1993

Neuroendocrine neoplasms of the lung. A 10 year perspective of their classification.

Based on clinical and pathologic data, neuroendocrine neoplasms of the bronchopulmonary tract may be classified into 3 groups: bronchial carcinoid; well differentiated neuroendocrine carcinoma (WDNC); poorly differentiated neuroendocrine carcinoma. The criteria of classification and the problems of multidirectional differentiation are discussed in detail.

Carcinoid Tumor↗

PubMed1993

Infant bouncing: the assembly and tuning of action systems.

We outline a theory of infant skill acquisition characterized by an assembly phase, during which a task-specific, low-dimensional action pattern emerges from spontaneous movement in the context of task constraints, and a tuning phase, during which adjustment of the system parameters yields a more energetically efficient and more stable movement. 8 infants were observed longitudinally when bouncing while supported by a harness attached to a spring. We found an initial assembly phase in which kicking was irregular and variable in period, and a tuning phase with more periodic kicking, followed by the sudden appearance of long bouts of sustained bouncing. This "peak" behavior was characterized by oscillation at the resonant frequency of the mass-spring system, an increase in amplitude, and a decrease in period variability. The data are consistent with a forced mass-spring operating at resonance.

Biomechanical Phenomena↗