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Query: UMLS:C0595921 (intraocular pressure)
 11,750 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Previous reports suggest that isometric exercise (2-min handgrip at 50% maximal voluntary contraction [MVC]) substantially lowers intraocular pressure (IOP). The authors questioned whether the mechanism for lowered IOP in exercise is secondary to hyperventilation. Accordingly, in this study 11 subjects, with elevated IOP (greater than or equal to 18 mm Hg) and otherwise healthy, did 2 min of handgrip exercise at 50% MVC with and without carbon dioxide supplementation to maintain isocapnic conditions. Compared with a control experiment that involved neither exercise nor CO2 addition, exercise induced a fall in IOP from 18.3 to 15.6 mm Hg (P less than 0.001). This statistically significant decline in IOP persisted for 15 min after the exercise session. At the point of minimum IOP (1 min after the end of exercise), the minute ventilation was elevated from 6.5-8.1 l/min (P less than 0.05), and the end-tidal partial pressure of CO2 (PCO2) was reduced from 37.0 to 33.7 mm Hg (P less than 0.05) with respect to control values. By contrast, adding CO2 sufficient to maintain isocapnic conditions (experimental end-tidal PCO2 = 38.9 versus 38.5 mm Hg in the control study; P = not significant) abolished the exercise-induced ocular hypotension (experimental IOP = 17.8 versus 18.1 mm Hg in the control study; P = not significant). It was concluded that prevention of hypocapnia during isometric handgrip exercise blocks the subsequent fall in IOP, suggesting both that isometric exercise per se has no direct influence on IOP and that therapy for ocular hypertension could involve manipulation of blood gases.
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PMID:Isocapnia blocks exercise-induced reductions in ocular tension. 160 33

Malignant hyperthermia (MH) may occur, when a genetically predisposed individual or pig (MHS) is exposed to triggering agents. The increase in free, ionized sarcoplasmic calcium inducing the vicious circle of MH is believed to result from calcium-induced release with volatile anaesthetics, and from depolarization-induced calcium release with succinylcholine (SCH). The administration of SCH to susceptible humans or pigs frequently produces an increase in masticatory muscle tone. This hitherto ill-defined phenomenon is referred to as "masseter spasm" (MS). We have attempted to elucidate the pathophysiology of MS in a porcine model. METHODS. After the protocol had been approved by the state authorities, 6 MHS pigs were investigated. The pigs were mixed breeds (German Landrace and Dutch Pietrain) and were 9 +/- 1 weeks old with an average body weight of 25.5 kg. Premedication consisted of intramuscular injection of azaperone, 7.5 mg.kg-1. Anaesthesia was induced with piritramide, 1.2 mg.kg-1, administered via a cannulated ear vein. Subsequent to laryngoscopic endotracheal intubation, neuromuscular blockade was achieved with 4 mg pancuronium. Ventilation was set at 12 breaths per minute and adjusted to maintain an end-tidal CO2 concentration of 4.7% by adapting the tidal volume (PhysioFlex). Anaesthesia was maintained with piritramide, 2.25 mg.kg-1.h-1, pancuronium, 0.4 mg.kg-1.h-1, and N2O (60% in O2). Instrumentation included an arterial line, a central venous line, and a fiberoptic pulmonary artery catheter (Oximetrix). Masticatory muscle tone (MMT) was assessed with an intermolar balloon, connected to a pressure transducer and calibrated to zero prior to SCH administration. As a reference variable for effects produced by SCH, intraocular pressure (IOP) was measured manometrically in the anterior chamber. After stabilization of haemodynamic variables, the neuromuscular blockade was allowed to wear off. After recovery of the evoked masseter electromyogram, a paralyzing dose of pancuronium was administered (0.5 mg.kg-1). When paralysis was complete, SCH was administered (1.5 mg.kg-1), followed a few minutes later by dantrolene infusion (5 mg.kg-1 over 10 min). RESULTS. The administration of SCH was followed by clinically unequivocal MH episodes in all pigs, indicated by an increase in oxygen uptake (VO2; PhysioFlex; Fig. 1) and end-tidal CO2 concentration and a decrease in oxygen saturation of mixed venous blood (svO2; Fig. 2). Despite complete neuromuscular blockade (monitored with EMG), SCH produced an increase in MMT in all pigs which was reversed by dantrolene (Fig. 3). The time course of MMT paralleled that of IOP, suggesting a similar underlying mechanism. DISCUSSION. Succinylcholine is a trigger of MH in susceptible individuals; onset of the syndrome may be associated with "masseter spasm". SCH increases extraocular muscle tone, probably by means of stimulating multiply innervated fibers; the resulting IOP increase is not prevented by competitive neuromuscular blockade. The existence of multiple innervated fibers has also been shown in muscle spindles in the deep layers of the masseter, with their stimulation resulting in elevation of the jaw. We speculate that the increases in MMT and IOP observed in this study reflect the same process, i.e. a motor response, initiated by SCH-induced stimulation of the intramyocellular contractile system of multiply innervated muscle fibers, that is independent of neuromuscular transmission. Triggering of MH with SCH despite complete neuromuscular blockage suggests a mechanism other than depolarization-induced calcium increase. And, for the semantics, according to neurological terminology MS should be referred to as contracture not as spasm.
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PMID:[The effect of muscle relaxants on masseter tone. An experimental study in an MH-susceptible swine model]. 161 14

A large number of sulfonamides have now been tested by the topical route for the lowering of intraocular pressure in the normal albino rabbit. Certain compounds with favorable balance between lipid and water solubility, and high activity against carbonic anhydrase, do lower pressure as much as 3 mmHg. MK-927, a thienothiopyrane-2-sulfonamide carrying an alkylamino group of pK 5.8, has desirable physicochemical properties: good water solubility below pH 5.8, a CHCl3/buffer ratio of 0.6 at pH 5.4, and a KI value against carbonic anhydrase of 2-7 nM, depending on assay conditions. Inhibition of CO2 hydration is non-competitive. By comparison with other candidate topically active sulfonamides, it is the most effective in terms of pressure lowering times duration of action. There are no apparent systemic effects or ocular toxicity. The concentration of drug reaching the ciliary process and aqueous humor is of the same order as that following parenteral sulfonamides, so that inhibition of the enzyme exceeds 99%. MK-927 is therefore a candidate for the clinical treatment of glaucoma.
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PMID:Chemical and pharmacological properties of MK-927, a sulfonamide carbonic anhydrase inhibitor that lowers intraocular pressure by the topical route. 230 93

Control of intraocular pressure is a major concern in ophthalmic anesthesia, especially in the presence of glaucoma or penetrating eye injury. The use of succinylcholine under these conditions is controversial. This study was undertaken to assess the effects of the neuromuscular blocking agents succinylcholine, pancuronium, metocurine, vecuronium, and atracurium on the intraocular pressure of dogs. The study was performed on five "conditioned" mature male foxhounds. The dogs were intubated immediately after induction with thiopental 10 mg/kg and ventilated with an O2/N2O mixture (FIO2 = 0.33). The ventilation was controlled to maintain an endtidal CO2 concentration of 5 vol.%. and anesthesia maintained with a fentanyl infusion of 10 micrograms/kg per hour. Direct and continuous measurements were taken of blood pressure (MAP), central venous pressure (CVP), and intra-ocular pressure (IOP), the latter via a 22-gauge needle inserted into the anterior chamber of the eye. A force-displacement transducer was attached to the hindpaw to monitor muscle twitch following supramaximal stimulation of the anterior tibial nerve. These four measurements were displayed on a multi-channel polygraph (Figs. 1 and 2). Control values were obtained and then succinylcholine 1 mg/kg, pancuronium 0.1 mg/kg, metocurine 0.3 mg/kg, vecuronium 0.1 mg/kg, or atracurium 0.4 mg/kg were given in a randomized fashion and on different days. Measurements of heart rate (HR), MAP, CVP, and IOP were noted at 2, 5, 10, 20, and 30 min after giving the neuromuscular blocking agent. The results, as displayed on the polygraphy, indicate that the least effect on IOP and cardiovascular state followed neuromuscular blockade with vecuronium and atracurium.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:[Comparative study of the effect of muscle relaxants on the intraocular pressure]. 288 18

At 3-hr intervals over a 24-hr span, 36 systemic, serologic and urinary variables were examined in 7 men in their mid 20's in the Spring of 1969, and again in the same 7 men in the Spring of 1979 under a similar chronobiologic protocol, using the same chemical and numerical analytical procedures. The variables examined for rhythms by cosinor were: vital signs--blood pressure (systolic, diastolic, pulse pressure and mean arterial pressure), heart rate, intraocular pressure (left and right), oral temperature; serum components--albumin, albumin/globulin ratio, total bilirubin, calcium, carbon dioxide, chlorides, bilirubin, cholesterol, globulin, glucose, potassium, sodium, sodium/potassium ratio, transaminase, triglycerides, total protein, urea nitrogen; and urine components--calcium, calcium/magnesium ratio, creatinine, magnesium, pH, potassium, sodium, sodium/potassium ratio, urea clearance, urea nitrogen, volume and zinc. Although all subjects appeared clinically healthy in 1969 and in 1979, certain inter-study differences were observed in a number of rhythm parameters of different variables. Statistically significant increases in mesor for the group as a whole were observed for serum Ca, cholesterol, Cl, CO2, K, Na, and while statistically significant mesor decreases for a group as a whole were noted in serum glucose and transaminase. Statistically significant increases in amplitude for the group as a whole were observed in serum chloride and urinary Na/K ratio, while statistically significant decreases were observed in amplitude for blood pressure, heart rate, serum albumin, A/G ratio, globulin, glucose, protein, sodium and transaminase.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Ten-year-replicated circadian profiles for 36 physiological, serological and urinary variables in healthy men. 321 57

Observations of intraocular pressure (IOP) variations in response to CO2, adrenaline, speech and compression of the neck veins were documented by continual monitoring of IOP by radiotelemetry. Carbon dioxide increased IOP in the supine, but not in the erect, conscious subject. Adrenaline 2% caused a rapid short-lived painful increase in IOP, followed by a profound decrease. This was due to an increase in facility of outflow and was associated with paralysis of the sympathetic supply to the iris. Speech caused a small rise in IOP which was reversed by rest in silence. Compression of the neck veins caused a variable increase in IOP. These physiological variations in IOP may contribute to the errors of tonometry.
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PMID:Progress in continual eye pressure monitoring. 641 42

The effects of atracurium on intraocular pressure (IOP) were compared with those of pancuronium in 20 patients less than 45 years-of-age requiring surgery for trauma of one eye. After a standard premedication and the application of topical analgesia to the upper airway, anaesthesia was induced with thiopentone i.v. and the trachea was intubated without the use of neuromuscular blockade. Following 20 min of steady state anaesthesia during which measurements of IOP, arterial pressure, heart rate, FIO2, FE'CO2 and CVP were recorded, one group of patients received atracurium 0.45 mg kg-1 and the other pancuronium 0.1 mg kg-1. The observations were repeated for a further 15 min before surgery commenced. Neither atracurium nor pancuronium produced any change in IOP. Atracurium was associated with greater cardiovascular stability than pancuronium.
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PMID:Effects of atracurium on intraocular pressure. 642 93

The effects of topical application of the carbonic anhydrase inhibitor trifluormethazolamide (TFM) on intraocular pressure (IOP), ascorbate and CO2 concentrations in aqueous humor, and aqueous humor flow were studied in rabbits. These effects were compared with those produced by systemic treatment with methazolamide. The decrease in IOP observed after TFM was accompanied by changes in the composition of the aqueous humor. Posterior aqueous ascorbate concentration showed a marked increase (up to 1.7-fold), whereas the anterior aqueous ascorbate did not change significantly. Similar changes were found in rabbits after systemic treatment with methazolamide. A small but statistically significant decrease in the CO2 content of both posterior and anterior aqueous was observed after topical TFM application. Methazolamide yielded a more profound lowering in the CO2 content of the aqueous humor, a reflection of the significant decrease in plasma CO2 content. For topical TFM or systemic methazolamide doses yielding complete inhibition of carbonic anhydrase in the eye, a 55-59% reduction of aqueous flow was calculated from the ascorbate data using the Kinsey and Palm equation. However, a 31-42% reduction in aqueous flow was obtained from the same data using an equation based only on posterior chamber data. The reasons for using only posterior aqueous ascorbate data for calculating the changes in aqueous humor flow are discussed.
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PMID:The effects of carbonic anhydrase inhibitors on aqueous humor chemistry and dynamics. 643 87

In this retrospective study, we examine the efficiency of cyclocryocoagulation in eyes with secondary and congenital glaucoma. We studied 137 eyes with advanced, inadequately controlled glaucoma, which were operated from 1984 to 1993. Besides the intraocular pressure (IOP), we assessed the effect on the visual acuity and the optic nerve. We also compared the efficiency of two different cryomethods (CO2/N2 cyclocryocoagulation). Fifty eyes were cyclocryocoagulated with CO2 and 87 with N2. After a period of 6 months, 90 eyes were regulated (IOP between 7 and 21 mm Hg). At this time the mean IOP was 16 mmHg, whereas it had been 40 mm Hg before the cyclocryocoagulation. Serious complications like a phthisis bulbi were seen in only 18 eyes. Five eyes became blind despite therapy because of an absolute glaucoma. Concerning the different types of glaucoma, the neovascular glaucoma was the most difficult type to regulate. We obtained better and more lasting results with N2 cyclocryocoagulation (68% regulation) than with CO2 cyclocryocoagulation (62% regulation). Thus, cyclocryocoagulation represents a good method for the treatment of advanced, inadequately controlled glaucoma eyes when other methods have failed.
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PMID:[Cyclocryocoagulation in treatment of special types of glaucoma]. 754 47

Fenoldopam (FE), a dopamine DA1-receptor agonist, has been introduced for treatment of arterial hypertension and heart failure and for preservation of renal function. Vasodilators are generally assumed to affect all vascular beds including the cerebral circulation. We have evaluated effects of FE-induced (4 micrograms.kg-1.min-1) arterial hypotension on intracranial pressure (ICP) and intraocular pressure (IOP) under conditions of normal and increased intracranial elastance. ICP and IOP responses to hypertension were tested by infusion of angiotensin II (15 micrograms.kg-1.min-1), and the response to hypercapnia was tested by elimination and reintegration of soda lime canisters in the breathing circuit. Intracranial elastance was increased by infusing mock cerebrospinal fluid (CSF) into the lateral ventricle (20 +/- 3 ml.h-1). Arterial hypotension induced with FE did not increase ICP. With increased intracranial elastance, the infusion rate of mock CSF had to be reduced while administering FE to avoid a rise in ICP (p < 0.05 compared with preinfusion value); this indicates a shift on the volume-pressure curve to the right. There were no indicators that cerebral autoregulation or CO2 reactivity of the cerebral vasculature were affected by FE in this anesthetized porcine model, as speculated from analysis of the time course of delta ICP. There are, however, indicators of increased intracranial elastance, most likely caused by vasodilation. Caution should hence be exercised when FE is administered to patients with increased intracranial elastance.
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PMID:Effects of fenoldopam on intracranial pressure and hemodynamic variables at normal and elevated intracranial pressure in anesthetized pigs. 791 22


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