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Biomedical subjects

J D Baker

Publications and source records attributed to J D Baker.

At least 73 records · Page 4Linked to original sources
PubMed1990

The medial rectus muscle insertion site in infantile esotropia.

The distance from the corneoscleral limbus to the insertion site of the medial rectus muscle was measured at several stages of medial rectus recession surgery in 20 patients (40 eyes) with infantile esotropia. Disinsertion of the medial rectus muscle resulted in a mean reduction in the distance from the muscle insertion site to the corneoscleral limbus of 0.903 mm (P less than .001), whereas the use of fixation forceps on the insertion to abduct the eye resulted in an additional mean reduction of 0.306 mm (P less than .01). The strabismus surgeon often uses the muscle insertion site as a reference point in determining the desired location for recessing a muscle. Our results suggest that this method of measurement is unreliable in infantile esotropia because the position of the medial rectus muscle insertion site varies considerably during surgery.

Child, Preschool↗
PubMed1990

Fetal Doppler shift waveforms in intrauterine growth retardation: laplace transform analysis technique.

An approach to the analysis of fetal blood flow velocity/time waveforms is described using a Doppler shift flowmeter. The waveform shape is described in terms of its Laplace transform. Variations in the value of the dominant coefficient in the Laplace transform in the descending thoracic aorta appear to distinguish growth retarded from normally grown fetuses early in pregnancy. Growth retardation was defined by an index of size specifically aimed at detecting the disproportionately grown fetus. Simpler methods of waveform shape description fail to detect the growth retarded fetus early in the second trimester.

Aorta, Abdominal↗
PubMed1990

Hemodynamic assessment of aortoiliac segment.

Routine noninvasive tests often fail to identify advanced aortoiliac stenosis, especially in cases with multilevel disease. At present, direct measurements of femoral artery pressure provide the best assessment of the hemodynamic effect of a proximal lesion, especially when flow is increased in order to simulate exercise. In the future, duplex scanning may replace invasive pressure studies.

Aorta, Abdominal↗
PubMed1990

A modification of the supraclavicular approach to the central circulation.

Traditional anterior or posterior triangle approaches to the central circulation may be at times unsuccessful in the patient whose anatomy makes cannulation difficult. We used a supraclavicular approach to cannulation of the central circulation in 100 patients for intraoperative monitoring or insertion of renal dialysis catheters. We have had only two failures, both in patients for dialysis catheter placement, and no complications. Review of the literature reveals a similar history of success with variations of this approach. The supraclavicular approach is an easy cannulation technique for the inexperienced physician and a useful alternative to traditional approaches for the experienced physician.

Catheterization, Central Venous↗
PubMed1989

Neurotensin-induced polydipsia: a structure-activity study.

Neurotensin (NT) and equimolar concentrations of NT fragments were microinjected into the lateral cerebral ventricle of water-deprived rats. NT (10 micrograms) increased water intake 146% in the first 15 min following injection. While NT1-11 and NT10-13 had no effect on water intake, NT8-13 increased water intake 101%. The polydipsia produced by NT8-13 was statistically equivalent to that produced by NT. The results are discussed in relation to a proposed model of the NT receptor.

Animals↗
PubMed1989

Effects of D2 dopamine receptor blockade with raclopride on intracranial self-stimulation and food-reinforced operant behaviour.

To examine the involvement of D2 dopamine receptors in the neural mechanism of reinforcement, raclopride tartrate, a D2 specific dopamine antagonist with a relatively fast central action, was injected into 32 rats. The D2 antagonist reduced bar-pressing responses reinforced with electrical stimulation of the ventral tegmental area (ED50 = 0.079 mumol/kg) and those reinforced with food (ED50 = 0.58 mumol/kg) in 18-30 min after IP injection. The reduction in response rates could not be attributed to an interference with motor functions. An increase in the frequency of brain-stimulation pulses and a change in the schedule of food reinforcement, which respectively increased the baseline rate of responding, did not alter the effectiveness of raclopride. SCH 23,390, a D1-specific dopamine antagonist, was sensitive to similar manipulation of reinforcement. These results seem to suggest that D1 and D2 antagonists may be acting at different locations in the neural mechanism underlying the reinforcement of operant behaviour.

Animals↗
PubMed1989

Microinjection of neurotensin into the CNS induces hyperdipsia in the rat.

Neurotensin (NT) is a neuropeptide and putative neurotransmitter that has been shown to exert a variety of effects on digestive and ingestive processes. In order to address the possibility that NT might play a role in the regulation of water intake as well, the peptide was infused into the lateral cerebral ventricle, amygdala, ventral tegmental area, lateral hypothalamus, and preoptic area of the anterior hypothalamus of rats deprived of water for 16 hours. Neurotensin produced a significant and dose-dependent increase in water intake when injected into the ventricular system but had no effect when it was applied to the other brain sites. It was concluded that this peptide may play a physiological role in the control of water ingestion and that central sites of action remain to be determined.

Amygdala↗
PubMed1989

A new approach to the noninvasive measurement of cardiac output using an annular array Doppler technique--II. Practical implementation and results.

An experimental Doppler flowmeter system has been developed which can noninvasively measure blood flow volume rate in a vessel. It is based on the attenuation compensated technique and does not require knowledge of the vessel size or beam-vessel angle. In vitro results have shown that the measurement of volume flow rate is independent of vessel angle to within +/- 4%, and independent of vessel diameter to within +/- 5%. Flow rate linearity is better than +/- 3%. A good comparison has been obtained, in vivo, of aortic diameters measured by an imaging system and with this flowmeter; the r value was 0.98. The noninvasive measurement of cardiac output using this flowmeter has been compared with conventional dilution techniques in 54 patients, with a resulting correlation coefficient of r = 0.96.

Aorta↗
PubMed1989

LaPlace transform analysis of femoral artery Doppler signals: the state of the art.

A followup study was conducted to validate our previous experience with the LaPlace Transform Analysis (LTA) method for processing Doppler ultrasound signals from the common femoral artery to detect significant stenosis of the aorto-iliac segment. The first phase used the same instantaneous mean velocity signal processor as used in the prior study. A comparison of the Doppler examinations with angiograms in 98 legs yielded a sensitivity = 92% and sensitivity = 94% in the identification of 50% or greater stenosis of the aorta-iliac segment, results almost identical to the last study. Because of theoretical disadvantages of using the instantaneous mean velocity signal we carried out a second phase using a peak velocity detector. In 148 limbs sensitivity = 87% and specificity = 98%. The presence or absence of superficial femoral artery occlusion did not affect the accuracy of the waveform analysis in the detection of proximal disease. The LTA parameter related to distal resistance, G, was not found to have clinical value in the assessment of the femoral-popliteal segment.

Arterial Occlusive Diseases↗
PubMed1989

Colloid oncotic pressure as a guide for the anesthesiologist in directing fluid therapy.

One useful but underused parameter of fluid replacement is colloid oncotic pressure. Colloid oncotic pressure (COP) is one of the Starling forces that maintain a balance between intravascular and extravascular fluid. Systemic and pulmonary circulations exhibit differences that limit the usefulness of COP manipulation in the treatment of pulmonary edema, especially that associated with hypoxic damage or pulmonary contusion. Systemic transcapillary fluid transport, however, is governed significantly by COP, and serial measurements of COP can serve as useful guides for colloid replacement. In this paper we present instances in which COP determinations were found to be clinically helpful, and discuss colloid replacement during surgery.

Anesthesia↗
PubMed1989

Acute renal dysfunction in high-risk patients after angiography: comparison of ionic and nonionic contrast media.

A group of 145 high-risk patients who underwent angiography after administration of the nonionic contrast agent iohexol were monitored for the development of acute renal dysfunction. The results in this group were compared with those in 202 high-risk historical control subjects who had undergone angiography after administration of ionic contrast material. All patients in both groups received similar pre- and postangiographic treatment. A greater number of patients in the ionic group had preexisting renal disease, were of advanced age, and had received large volumes of contrast material. Acute renal dysfunction occurred in 20 of the 202 (10%) patients in the ionic group, compared with eight of the 145 (5.5%) patients in the nonionic group; this difference is not statistically significant. Five patients in the ionic group, but none of the patients in the nonionic group, ultimately required dialysis; this difference is not statistically significant. The findings suggest that a randomized trial in high-risk patients should be undertaken before a clinical advantage of the nonionic contrast agent iohexol with regard to renal function can be assumed.

Acute Kidney Injury↗
PubMed1989

A rational approach to anaesthetic premedication.

Rational use of premedication for anaesthesia must always be modified and updated to keep pace with the evolving fields of anaesthesiology and surgery, as well as to meet changing patient needs and preferences. It is no longer axiomatic that all patients require, and therefore should receive, premedication. Unfortunately, a variety of traditional reasons have been proposed to justify routine premedication in many institutions. Smoothing induction, decreasing reflexes and arrhythmias, decreasing nausea and vomiting, decreasing pain, decreasing secretions, and producing sedation and amnesia have all been claimed historically as beneficial results of premedication. Modern anaesthetic agents and techniques have come a long way towards eliminating the routine need for premedication. In the preoperative period, the goal of an anxiety-free patient who is physiologically uncompromised requires an individualised approach based on experience and an adequate knowledge of current pharmacology. As our knowledge of potential problems associated with anaesthesia has expanded, we have added other classes of drugs such as the H2-histamine receptor blockers and antacids to our premedicant armamentarium. Outpatient and short-stay patients have further challenged our preoperative goal of an anxiety-free patient by requiring individuals to be 'street ready' within a brief period of time after surgery. Even for in-house elective procedures, not every patient is a candidate for routine premedication. A frank preoperative discussion is all that is necessary to effectively allay anxiety in many persons. In these and other special situations, this article will hopefully guide the reader toward a more rational approach to premedicating patients.

Barbiturates↗
PubMed1989

Marfan syndrome in the parturient.

Early recognition of the Marfan Syndrome and knowledge of its potentially lethal complications facilitates successful treatment of these individuals. It is through a joint effort by many specialist physicians such as the obstetrician, cardiologist, and anesthesiologist that these patients can be managed safely through pregnancy, labor, and delivery.

Adult↗
PubMed1989

Intraoperative infusion of lytic drugs for thrombotic complications of revascularization.

Between August 1983 and December 1987, 23 patients received a 30-minute intraoperative, intraarterial infusion of streptokinase (seven patients) or urokinase (16 patients) because of residual thrombus or persistent ischemia or both after thromboembolectomy. Ages ranged from 21 to 77 years (mean, 58 years). In 15 patients intraoperative lytic therapy was part of the initial operation, whereas in eight patients intraoperative lytic therapy was performed during a secondary operation to treat thrombosis of a recently placed graft. Seven patients in the latter group had hypercoagulable conditions (five had heparin-induced thrombosis; one had protein C deficiency; one had polycythemia with thrombocytosis). Improvement after intraoperative lytic therapy was seen on angiography performed after infusion in 13 of 17 (76%) patients in whom angiography was performed both before and after intraoperative lytic therapy. Grafts in 12 of these patients remained patent without additional intervention, and in one graft thrombus formed again. In contrast, among four patients without angiographic evidence of improvement, thrombus formed again in four grafts (p less than 0.004). Intraoperative lytic therapy was considered successful in 74% of instances (17/23), including four of seven patients with hypercoagulable states. Three of six patients whose grafts failed had major amputations, whereas there were no amputations after successful infusions. Twelve patients were heparinized after intraoperative lytic therapy. Ten patients in this group were considered treatment successes, and two were considered treatment failures. Three of 11 patients not heparinized after intraoperative lytic therapy were considered treatment failures. Four hematomas occurred in the former group and none in the latter (p less than 0.03). No hematomas occurred in the heparin-induced thrombosis group in spite of anticoagulation with sodium warfarin (Coumadin). Only one hematoma occurred within 6 hours of intraoperative lytic therapy, and thus it was attributable to the infusion. We conclude that intraoperative lytic therapy is an effective adjunct to manage residual thrombus or persistent ischemia or both after lower extremity revascularization. Postinfusion angiography is of prognostic value. Heparinization after intraoperative lytic therapy seems beneficial but significantly increases the risk of bleeding complications.

Adult↗