Contact mechanics of normal tarsometatarsal joints.

BACKGROUND: The current treatment of tarsometatarsal joint injuries is associated with suboptimal long-term results. The objective of the present study was to measure the contact mechanics of the tarsometatarsal joints in normal adult cadaveric feet in order to develop a foundation for more effective treatment. METHODS: Six fresh cadaveric lower legs and feet were subjected to four different axial compressive loads (0.5, 1.0, 1.5, and 2.0 times body weight) at each of five different positions. For each position, load, and tarsometatarsal joint, the contact pressures and areas were measured with use of pressure-sensitive film. Contact forces were calculated from the ratio of pressure to area. Contact pressure, area, and force were analyzed as a function of load, the specific tarsometatarsal joint, and foot position. RESULTS: The forces across these joints ranged from 2 to 541 N, but pressures ranged only from 0.5 to 5.7 MPa. In general, changes in load and foot position, in both the sagittal and the frontal plane, were associated with changes (p<0.05) in tarsometatarsal joint contact areas and forces. In contrast, the contact pressures across these joints varied minimally with changes in load and foot position. CONCLUSIONS: These data suggest that the tarsometatarsal joints are designed to regulate pressure in each joint by means of two mechanisms: (1) at small loads, an intrajoint mechanism regulates tarsometatarsal joint pressure by increasing contact area within the joint in response to increasing force, and (2) at larger loads, an interjoint mechanism engages to regulate tarsometatarsal joint pressure by redirecting force to other tarsometatarsal joints. CLINICAL RELEVANCE: The data provide both absolute (normal contact forces, areas, and pressures) and relative (intrajoint and interjoint regulating mechanisms) performance (functional) criteria for the development of new treatments for diseased or traumatized tarsometatarsal joints.

Treatment of sialorrhea with glycopyrrolate: A double-blind, dose-ranging study.

OBJECTIVE: To determine the safety and efficacy of glycopyrrolate in the treatment of developmentally disabled children with sialorrhea. DESIGN: Placebo-controlled, double-blind, crossover dose-ranging study. SETTING: Outpatient facilities in 2 pediatric hospitals. PATIENTS: Thirty-nine children with both developmental disabilities and excessive and bothersome sialorrhea. MAIN OUTCOME MEASURES: Parent and investigator evaluation of change in sialorrhea and adverse effects. RESULTS: Glycopyrrolate in doses of 0.10 mg/kg per dose is effective at controlling sialorrhea. Even at low doses, 20% of children may exhibit adverse effects severe enough to require discontinuation. CONCLUSIONS: Glycopyrrolate is effective in the control of excessive sialorrhea in children with developmental disabilities. Approximately 20% of children given glycopyrrolate may experience substantial adverse effects, enough to require discontinuation of medication. Arch Pediatr Adolesc Med. 2000;154:1214-1218.

Retinal anatomy of Chorocaris chacei, a deep-sea hydrothermal vent shrimp from the Mid-Atlantic Ridge.

Exploration of deep-sea hydrothermal vents over the past quarter century has revealed that they support unique and diverse biota. Despite the harsh nature of the environment, vents along the Mid-Atlantic Ridge are dominated by large masses of highly motile Bresiliid shrimp. Until 1989, when it was discovered that the vent shrimp Rimicaris exoculata possesses a hypertrophied dorsal eye, many believed that animals populating hydrothermal vents were blind. Chorocaris chacei (originally designated Rimicaris chacei) is a Bresiliid shrimp found at hydrothermal vent fields along the Mid-Atlantic Ridge. Like R. exoculata, C. chacei has a hypertrophied retina that appears to be specialized to detect the very small amount of light emitted from the orifices of black smoker hydrothermal vent chimneys. C. chacei lacks the sophisticated compound eyes common to other decapod crustaceans. Instead, it has a smooth cornea, with no dioptric apparatus, apposed by a tightly packed, massive array of photosensitive membrane. Photoreceptors in the C. chacei retina are segmented into a hypertrophied region that contains the photosensitive membrane and an atrophied cell body that is roughly ten times smaller in volume than the photosensitive segment. The microvillar photosensitive membrane is consistent in structure and ultrastructure with the rhabdoms of decapod and other invertebrate retinas. However, the volume density of photosensitive membrane (> or =60%) exceeds that typically observed in invertebrate retinas. The reflecting pigment cells commonly found in decapod retinas are represented in the form of a matrix of white diffusing cells that exhibit Tyndall scattering and form an axial sheath around the photoreceptors. All photoreceptor screening pigment granules and screening pigment cells are restricted to the region below the photoreceptor nuclei and are thereby removed from the path of incident light. No ultrastructural evidence of rhythmic cycling of photosensitive membrane was observed. The morphological adaptations observed in the C. chacei retina suggest that it is a high-sensitivity photodetector that is of functional significance to the animal.

Upper airway obstruction presenting as exercise-induced asthma.

A patient presented with a ten-year history of exercise-induced wheezing. After trials of metaproterenol and cromolyn failed to improve her symptoms, she was observed during exercise. She proved to have inspiratory stridor caused by collapse of the posterior aryepiglottic folds over the vocal cords during inspiration only following exercise. Symptoms primarily improved with physical conditioning. Further improvement came after treatment of her chronic rhinitis and post-nasal drip with a steroid nasal spray.

Vasocilators in the canine mesenteric circulation. Evaluation of a potential aid in the diagnosis of gastrointestinal bleeding.

Radiodiagnostic potential of intra-arterially injected vasodialting agents was investigated by their effect on total and segmenal resistances (VR) of mesenteric vasculature, blood flow in superior mesenteric artery and its bleeding branch; heart rate and ventricular and systemic blood pressure. Dipyridamole, isoxsuprine, protricular and systemic blood pressure. Dipyridamole, isoxsuprine, prochlorperazine, lidocaine, meglumine diatrizoate and carbon dioxide were poor dilators. Phentolamine produced hypotension; glucagon and serpasil an extremely long dilation. A large and short vasodilation was produced with tolazoline and nylidrin, but both agents increased VR of the postcapillary segment and caused transient hypotension and arrhythmias, nylidrin's side effects were smaller. Oxygen produced large and long vasodilation and minimal systemic effects. It is concluded that oxygen or possibly nylidrin are suitable agents should an intermittently bleeding mesenteric artery be dilated for diagnostic purposes prior to angiography.

Similarity of arterial and intravenous vasopressin on portal and systemic hemodynamics.

The effects of superior mesenteric arterial and intravenous infusions of vasopressin and low and high dose intravenous infusions of vasopressin on splanchnic and systemic hemodynamics were compared in 20 anesthetized dogs. The following parameters were evaluated: flow in the superior mesenteric artery and portal vein, portal and systemic blood pressure, and cardiac output. In the comparison of selective arterial and intravenous infusions, no statistically significant difference was found between the degree of changes in portal flow, portal and systemic blood pressure, and cardiac output. Only the superior mesenteric artery flow showed a greater decrease with the selective arterial injection. In a comparison of intravenous high dose (corresponding to that used clinically) and low dose (one-fifth) infusions of vasopressin, a relatively high splanchnic and low systemic effectiveness of the low dose was found. It resulted in only a 15 to 20% smaller effect on flow in the superior mesenteric artery and portal vein and portal pressure; however, about 40% lesser systemic effect on arterial blood pressure and cardiac output than the high dose. The results of this experimental work warrant exploration in clinical practice, preferably by a controlled study. If clinical success in controlling hemorrhage confirms these hemodynamic results, an intravenous. low dose infusion of vasopressin would appear to be the method of choice in the vasoconstrictive therapy of gastrointestinal bleeding from varices.

Vasopressin and hepatic artery. Effect of selective celiac infusion of vasopressin on the hepatic artery flow.

Electromagnetic flow measurement study was performed in 20 anesthetized dogs to evaluate the effect of selective celiac infusion of vasopressin on the hepatic arterial vasculature. Teh hepatic arterial flow showed a biphasic response with an initial decrease followed by a substantial increase in spite of a continued infusion. The left gastric, splenic, and superior mesentric arteries showed a monophasic response with persistent decrease of flow during the whole infusion. The biphasic response of the hepatic arterial flow is thought to be due to autoregulatory dilative action of the liver to a decrease of the portal flow. The results and previous clinical experience suggest that the selective infusions of vasopressin into arteries supplying the liver can be used for short-term vasoconstrictive therapy of acute gastrointestinal bleeding in patients without liver damage. Further experience is necessary to evaluate the safety of prolonged hepatic infusions in patients with liver damage.