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Biomedical subjects

S H Johnson

Publications and source records attributed to S H Johnson.

At least 73 records · Page 4Linked to original sources

After Cruzan. The U. S. Supreme Court's decision settles the case but raises new questions.

In its Cruzan v. Director, Missouri Department of Health, decision the U.S. Supreme Court addressed only states' authority in the refusal of medical treatment. But the case itself drew national attention to the issue, and physicians and healthcare facilities should expect to see living wills and durable powers of attorney increase as a result. Legal concerns will also arise as a result of misconceptions regarding the law. The Court was careful to qualify and limit its support of the Missouri Supreme Court's decision. As opposed to the latter's nearly outright denial of an individual's right to refuse medical treatment, the U.S. Supreme Court's majority opinion asserted that a competent person has a "constitutionally protected liberty interest in refusing unwanted medical treatment." And although the Court upheld Missouri's requirement that there be "clear and convincing evidence" of an incompetent patient's previously expressed wishes before treatment can be discontinued, it did not make such evidence mandatory for states with different law. Finally, in a separate concurring opinion Justice Sandra Day O'Connor asserted that a patient-designated proxy could be an acceptable "source of evidence" of a patient's intent. If the proxy does in fact have some constitutional status, this status should motivate state courts and legislatures to recognize the practice.

Adult↗

Intraoperative perfusion contrast echocardiography. Initial experience during coronary artery bypass grafting.

Intraoperative evaluation of the effectiveness of myocardial revascularization has been limited by an inability to assess regional myocardial perfusion. Microbubbles of sonicated diatrizoate sodium and diatrizoate meglumine (Renografin) have been an effective echocardiographic contrast agent and have been employed clinically during cardiac catheterization. This recent development in contrast-enhanced two-dimensional echocardiography permits real-time imaging of transmural myocardial blood flow but has not been evaluated in the operating room. This study represents the initial surgical application of this directed technique and was designed to evaluate the safety and efficacy of intraoperative perfusion contrast echocardiography in assessing the results of coronary artery bypass grafting. Twenty men with significant coronary artery disease ranging in age from 49 to 73 years were studied. Direct contrast agent injection into completed saphenous vein bypass grafts caused the myocardium supplied by each graft to be well delineated and provided a tomographic view of contrast distribution. The enhanced region was well correlated with the size and distribution of the native vessel. Rapid contrast washout (less than 20 seconds) indicated satisfactory regional perfusion. Contrast echocardiography prolonged the operation less than 10 minutes and did not result in any perioperative complications.

Aged↗

Anaphylactoid reactions mediated by autoantibodies to cholesterol in miniature pigs.

Antoantibodies to cholesterol were detected and purified from normal (nonimmunized) pig serum. The antibodies were assayed by ELISA with crystalline cholesterol as an Ag and by C-dependent damage to cholesterol-laden liposomes. Intravenous injection of liposomes containing cholesterol into anesthetized animals caused decreased hemolytic complement titers, and induced a reaction consisting of transient neutropenia, thrombocytopenia, respiratory distress, cyanosis, pulmonary and systemic hypertension, and decreased cardiac output. Plasma levels of thromboxane B2 and 6-keto-prostaglandin F1 alpha increased 1300 and 200%, respectively, and leukocyte and platelet counts decreased by 36 and 38%, respectively. Injection of cholesterol-free liposomes did not induce the reaction. These results show that naturally occurring autoantibodies to cholesterol can initiate C activation and can be associated with anaphylactoid reaction to exogenously administered cholesterol in pigs.

Anaphylaxis↗

Arginine8-vasopressin reduces spinal cord blood flow after spinal subarachnoid injection in rats.

Arginine8-vasopressin (AVP) causes hindlimb paralysis, loss of nociceptive responsiveness and increased arterial pressure after spinal subarachnoid injection in rats. In these experiments, the effects of paralytic intrathecal doses of AVP on rat brain and spinal cord blood flow, vascular resistance and cardiac output were measured using radiolabeled microspheres. Ten minutes after injection, AVP (10-100 pmol) elevated mean arterial pressures significantly, increased vascular resistances in thoracic and lumbosacral spinal cord and reduced blood flow to the lumbosacral spinal cord without altering cardiac output, total peripheral resistance and blood flow to brain and other spinal cord regions. Lumbosacral blood flows remained significantly reduced 30 min after injection of 100 pmol of AVP, and recovered to pretreatment base-line levels by 60 min postinjection. Lactic acid concentrations were elevated significantly in spinal cerebrospinal fluid samples removed 5 to 15 min after AVP injection (100 pmol). The selective AVP V1 receptor antagonist [1-(beta-mercapto-beta,beta-cyclopentamethylene propionic acid), 2-(O-methyl)tyrosine] arg8-vasopressin, which previously blocked the effects of AVP on hindlimb motor and nociceptive function, in these experiments also blocked the AVP-induced increases in arterial pressure and reductions in lumbosacral perfusion. Intravenous infusion of the vasodilators papaverine and nifedipine failed to block AVP-induced hindlimb paralysis. Nifedipine, however, did accelerate subsequent recovery of hindlimb motor function, although it did not alter the lumbosacral blood flow reductions measured at 10 and 30 min after AVP injection. These findings indicate that AVP has significant vascular effects in the rat spinal cord that are associated with ischemia and neurological dysfunction.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

Comparison of the keratometer and the lens bench in measuring intraocular lens power.

Intraocular lenses (IOLs) from six manufacturers were measured on a Terry keratometer and on a calibrated lens bench for lens power. Differences between the two methods appeared when the IOLs were a different refractive index than polymethylmethacrylate (PMMA) and a shape other than planoconvex. These differences were consistent for ultraviolet absorbing PMMA and for meniscus lenses.

Lenses, Intraocular↗

Iris transillumination defect and microhyphema syndrome.

We present a previously undescribed delayed complication attributable to sulcus-fixated posterior chamber lenses with elliptical polypropylene haptics containing a 10 degrees anterior angulation. Clinical signs of this complication are crescent-shaped iris transillumination defects overlying the lens haptics in the peripheral iris; in some cases these are associated with single or recurrent visually significant microhyphemas. This series describes 41 eyes that contain these transillumination defects; eight of the eyes have had lens-induced intraocular hemorrhage. We estimate the overall incidence of transillumination defects in our sulcus-fixated posterior chamber lens patient population to be between 5% and 15%. Those patients who have had lens-induced hemorrhage represent slightly greater than 1%, which is higher than our incidence of cystoid macular edema or retinal detachment. It is important for all ophthalmologists to be aware of this syndrome in evaluating patients with posterior chamber lenses who present with a transient obscuration of vision.

Aged↗

Clinical experience with the Nd:YAG laser.

This study presents the results and complications of 389 patients who were treated with the Nd:YAG laser between September 1982 and November 1983 with at least a six-month follow-up. The majority of patients had a secondary discission of the posterior capsule. Other procedures included vitreolysis, iridotomy, pupilloplasty, synechialysis, intraocular suture cutting, cutting of intraocular lens haptics, and removal of anterior pseudophakic pigmented precipitates. We have purposely avoided performing preoperative laser anterior capsulotomies and have been unsuccessful in reopening freshly sealed trabeculectomy sites. The visual acuity improved in 83.1% of patients. No statistically significant difference in visual outcome was detected in relation to the time interval between surgery and Nd:YAG laser treatment. The most common adverse finding was an increase in intraocular pressure, which occurred to some degree in 63% of patients. Rare complications included cystoid macular edema and retinal detachment. No statistical correlation between these complications and preexisting conditions or intraoperative variables could be found.

Aphakia↗