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Biomedical subjects

C L Cowan

Publications and source records attributed to C L Cowan.

17 recordsLinked to original sources
PubMed1992

Light hazards in the operating room.

The use of high-intensity illumination devices is routine for many ophthalmic diagnostic and therapeutic procedures. However, the exposure of patients to high-level photic energy may be damaging even in the absence of visible abnormalities. Devices such as the operating microscope, indirect ophthalmoscope, and endoilluminator are capable of irradiances sufficient to cause retinal damage and should be used with a degree of restraint that reflects a recognition of their potential for phototoxicity.

Eye Injuries↗
PubMed1992

Different mechanisms of relaxation of pig coronary artery to bradykinin and cromakalim are distinguished by potassium channel blockers.

Bradykinin relaxes porcine coronary artery in an endothelium-dependent manner that is not dependent on release of nitric oxide or cyclic GMP accumulation. The mechanism of this relaxation was investigated in rings of porcine coronary artery by comparing bradykinin-induced relaxation with that induced by cromakalim, an agent know to cause hyperpolarization mediated by potassium channels. Relaxation to bradykinin was determined in rings treated with methylene blue, indomethacin and captopril to inhibit cyclic GMP accumulation, prostaglandin formation and bradykinin degradation, respectively. Relaxation to cromakalim was inhibited by the potassium channel blockers glybenclamide (10(-6) M), tetraethylammonium (10(-2) M), quinine (3 x 10(-5) M) and procaine (5 x 10(-3) M), whereas barium (10(-4) M) and 4-amino-pyridine (10(-3) M) were without effect. None of these potassium channel blockers had any effect on the relaxation to bradykinin. These results suggest that relaxation of pig coronary artery to cromakalim is mediated by a mechanism sensitive to potassium channel blockers. Also, the mechanism of nitric oxide-independent relaxation to bradykinin is distinct from that of cromakalim.

4-Aminopyridine↗
PubMed1991

Two mechanisms mediate relaxation by bradykinin of pig coronary artery: NO-dependent and -independent responses.

The role of nitric oxide and guanosine 3',5'-cyclic monophosphate (cGMP) accumulation in the endothelium-dependent relaxation of the porcine coronary artery to bradykinin was investigated by comparing relaxation and cGMP accumulation in the presence or absence of NG-monomethyl-L-arginine (L-NMMA) and methylene blue. Rings were treated with indomethacin to eliminate the effects of prostaglandins. Relaxation to bradykinin of rings contracted with the thromboxane A2 mimetic U-46619 was not affected by L-NMMA and was only minimally inhibited by methylene blue. Rings contracted with elevated potassium (25 mM) also relaxed completely to bradykinin. However, L-NMMA or methylene blue effectively inhibited relaxation to bradykinin in rings contracted with potassium. cGMP accumulation was stimulated by bradykinin and inhibited by L-NMMA or methylene blue in rings contracted with either U-46619 or potassium. These results suggest that in the absence of nitric oxide-induced cGMP accumulation, a nonprostanoid mechanism exists that is capable of completely relaxing U-46619-contracted coronary artery. This mechanism is either inhibited in or unable to relax potassium-contracted rings. These results also demonstrate that nitric oxide mediates the bradykinin-induced cGMP accumulation that is largely responsible for the relaxation during contraction with potassium.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1990

Cholinergic regulation of resting coronary blood flow in domestic swine.

Cholinergic vasoconstriction in vivo and the influence of resting cholinergic activity on basal coronary tone were investigated by measuring coronary blood flow, cardiac function, and blood gases during either acetylcholine injection, muscarinic receptor blockade, or vagal ligation, in open-chest chloralose-urethan-anesthetized swine. Intracoronary injections of acetylcholine (0.5-3.0 micrograms) caused significant (P less than 0.05) dose-dependent reductions in coronary blood flow (19.0-75.5%) and conductance (14.3-78.2%). Atropine (200 micrograms) completely blocked these responses. Cholinergic mediation of basal coronary tone was initially evaluated by determining the effects of muscarinic blockade with intracoronary injection of atropine (200 micrograms). Intracoronary injection of atropine had no significant effects on coronary blood flow or conductance. Finally, to ensure that parasympathetically released acetylcholine was not overcoming the muscarinic blockade, vagal ligation was performed during pacing. Neither coronary blood flow nor conductance was significantly altered by vagal ligation. The present studies demonstrate that acetylcholine induces a muscarinic vasoconstriction of coronary arteries in the domestic swine. However, these studies do not support a role for parasympathetic mediation of basal coronary vascular tone.

Acetylcholine↗
PubMed1989

National survey of the prevalence and risk factors of glaucoma in St. Lucia, West Indies. Part I. Prevalence findings.

Although blacks appear to be at higher risk for blindness from glaucoma, there is little information available on the epidemiology of this disease in this population. Using a cluster sampling technique with systematic allocation of clusters, the authors conducted a national survey of black individuals 30 years of age and older, in St. Lucia. A total of 1679 individuals underwent a screening examination that included visual acuity, intraocular pressure (IOP) measurement, and cup/disc (C/D) evaluation. Every third person had a screening field on the Humphrey field analyzer. Individuals with either elevated IOP, abnormal C/D ratio, or an abnormal screening visual field were referred for a definitive examination and threshold visual fields. A total of 520 people were referred. Identified by stringent criteria for the diagnosis of glaucoma, which required reliable threshold visual fields abnormal by the mirror image method, 147 individuals had glaucoma for a prevalence of 8.8% in the 30 years of age and older population.

Adult↗
PubMed1989

Pasteurella multocida corneal ulcer following a baseball injury.

Pasteurella multocida is an ubiquitous organism that can be isolated from a variety of animals and birds. It is an infrequent ocular pathogen but can cause infection as a result of injury or animal exposure. This article reports a case of P multocida corneal ulcer following a baseball injury.

Adolescent↗
PubMed1987

Endogenous Bacillus cereus panophthalmitis.

Over the past seven years we have treated three cases of drug abusers in whom endogenous Bacillus cereus endophthalmitis rapidly progressed to panophthalmitis. Ocular features of infection with this organism include severe pain, chemosis, proptosis, corneal infiltration and ring abscess, subretinal exudation, retinal hemorrhages, and perivasculitis. The process becomes fulminant in an explosive manner and may be accompanied by fever and leukocytosis. Ophthalmologists should be cognizant of the apparent susceptibility of drug abusers to Bacillus cereus infections and should consider this organism in any severe, rapidly evolving intraocular infectious process.

Adult↗
PubMed1986

Ocular disturbances in vitiligo.

One hundred fifty-six patients with vitiligo were examined for ocular abnormalities. A 2:3 ratio of white to black patients allowed us to evaluate the role of race in the occurrence of ocular disturbances. A large percentage (40%) of all patients showed some degree of fundal pigment disturbance including pigment clumps, focal hypopigmented spots, and choroidal nevi. Although racial variations were found in the incidence of choroidal nevi (p = 0.001) and iris transillumination (p = 0.0012), these variations were believed to reflect normal differences found in patients without vitiligo.

Adolescent↗
PubMed1986

When should sarcoidosis be treated?

About 80 percent of sarcoidosis cases are benign and do not require treatment, but 20 percent will have chronic unremitting disease for which therapy is essential. It is important that the physician identify this group and begin therapy promptly. If the disease is active, treat. If it is inactive, do not treat. Activity depends upon three major tests: serum angiotensin converting enzyme, gallium 67 scan, and bronchoalveolar lavage. The other consideration is involvement of vital organ systems; ie, active ocular disease, progressive pulmonary involvement as evidenced by increasing symptoms, impaired and deteriorating pulmonary function, or radiographic changes; hypercalcemia or hypercalciuria; central nervous system involvement; disfiguring cutaneous lesions; and myocardial sarcoidosis. Following a therapeutic decision to treat, adrenocorticoids are the drugs of choice. Methylprednisolone, prednisone, and cortisol are listed in order of benefit. Alternate day and/or low-dose steroids are increasing in popularity. Chloroquine phosphate is beneficial for skin lesions, while oxyphenbutazone has been found to be at least as effective as prednisone. Immunosuppressives may be used also. Chlorambucil and azathioprine have shown variable results. Cyclosporine (Cyclosporin A) shows promise and is now undergoing therapeutic trials.

Adult↗
PubMed1979

Extended-wear contact lenses and intraocular lenses for aphakic correction.

We evaluated extended-wear soft contact lens use in 128 aphakic eyes of 113 patients, 44 of whom had been unable to wear conventional contact lenses; 116 eyes (91%) have been successfully fitted and have worn the extended-wear lenses without significant complication. Eleven patients were unable to wear the lens or had to be discontinued for transient lens-related problems. In 103 eyes successfully fitted the lens is removed for cleaning less often than monthly. Ninety six of the 116 eyes fitted have visual acuity as good as, or better than, with aphakic correcting spectacles. The results obtained with the extended-wear soft contact lens are similar to those obtained with intraocular lenses, except for the recent high incidence of inflammation seen after intraocular lens insertion when using ethylene-oxide-sterilized lenses.

Adolescent↗
PubMed1979

Bacillus cereus panophthalmitis after intravenous heroin.

Two healthy young black men developed panophthalmitis after intravenous heroin injections. Bacillus cereus, considered to be a relatively noncommon pathogen for man, was found to be the causative agent as it was recovered from the anterior chamber and viterous cavity of both cases. The ocular findings were unilateral in each case, and neither patient had any sistemic involvement from the bacteremia. The onset of visual symptoms varied from 24 to 36 hours after the last intravenous injection with the eye becoming rapidly blind. Photographs of the early fundus lesions included preretinal hypopyon-like lesions and peculiar changes in the blood vasculature. Intracameral gentamicin and steroids did not alter the cause, and treatment was enucleation.

Adult↗