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Biomedical subjects

H L Brooks

Publications and source records attributed to H L Brooks.

At least 37 records · Page 2Linked to original sources
PubMed1990

Comparison of outcome of paramedic-witnessed cardiac arrest in patients younger and older than 70 years.

To obtain further information concerning differences in the mechanism of out-of-hospital cardiac arrest between elderly and younger patients, 381 consecutive patients who experienced out-of-hospital cardiac arrest, and whose arrest was witnessed by paramedics, were studied. In 91% of cases the arrest occurred at the time the patient's cardiac rhythm was monitored. Patients were divided into 2 age groups: elderly patients were greater than 70 years (187) and younger patients were less than 70 years (194). Elderly patients more commonly had a past history of heart failure (25 vs 10%, p less than 0.003) and were more commonly taking digoxin (40 vs 20%, p less than 0.005) and diuretics (35 vs 25%, p less than 0.004). Before the cardiac arrest, elderly patients were more likely to be complaining of dyspnea (53 vs 40%, p less than 0.009), whereas younger patients were more likely to complain of chest pain (27 vs 13%, p less than 0.001). Forty-two percent of younger patients demonstrated ventricular fibrillation as the initial out-of-hospital rhythm associated with the arrest, compared to only 22% of elderly patients (p less than 0.001). Besides patient age, initial cardiac rhythm varied according to the patient's complaint preceding the arrest. Sixty-eight percent of patients with chest pain demonstrated ventricular fibrillation, whereas only 21% of patients with dyspnea demonstrated ventricular fibrillation. Elderly patients could be as successfully resuscitated as younger patients; however, 24% of younger patients survived, compared to only 10% of elderly patients (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1990

Xerophthalmia and cystic fibrosis.

We treated two infants with failure to thrive who presented with clinical evidence of conjunctival and corneal xerosis. One patient was referred with possible infectious corneal ulcer thought to exist because there were deep peripheral ulcerations of the cornea and associated hypopyon. The other patient was initially thought to have a nasolacrimal duct obstruction because of excessive tearing. Xerophthalmia secondary to vitamin A deficiency was suspected and led to the diagnosis and treatment of cystic fibrosis in each case. Therapy with vitamin A promptly resolved the xerosis, but it also caused a transient rise in intracerebral pressure. Xerophthalmia can still be a problem in developed countries when underlying disorders, such as cystic fibrosis, lead to vitamin A malabsorption.

Cystic Fibrosis↗
PubMed1990

Removal of radiation-induced cataracts in patients treated for retinoblastoma.

Experience with removal of radiation-induced cataract in patients treated for retinoblastoma is limited. We retrospectively reviewed the records of 38 patients with retinoblastoma (42 eyes) who underwent removal of radiation-induced cataract from 1973 to 1989. Nineteen eyes (45%) without macular tumors or severe radiation complications had final visual acuities in the range of 20/20 to 20/50. One eye (2.4%) developed a rhegmatogenous retinal detachment and four eyes (9.5%) were noted to have amblyopia after cataract removal. Three eyes (7%) developed retinoblastoma recurrence, one with extension of retinoblastoma into the subconjunctival space through the previous sclerotomy. Exenteration was performed and the patient was alive after 8 years. Cataract removal can be visually beneficial in selected patients with radiation-induced cataracts.

Adolescent↗
PubMed1990

Calcium channel modulation of alpha 1- and alpha 2-adrenergic pressor responses in conscious and anesthetized dogs.

The influence of halothane and isoflurane on alpha-adrenergic-mediated vasoconstriction before and following calcium channel modulation was investigated in chronically instrumented dogs. After ganglionic, cholinergic, and beta-adrenergic blockade, systemic hemodynamic responses following equieffective pressor doses of phenylephrine (0.6 micrograms/kg iv), a selective alpha 1 agonist, and azepexole [B-HT 933] (20 micrograms/kg iv), a selective alpha 2 agonist, were obtained. The calcium channel stimulator Bay k 8644 (0.5 and 1 micrograms.kg-1.min-1) was infused intravenously for 10 min and phenylephrine and azepexole administered at the end of each infusion. On different days, each dog was subsequently anesthetized with equihypotensive concentrations of halothane (1.7%) or isoflurane (2%) in oxygen and the same pharmacologic interventions were repeated in the presence of halothane or isoflurane. Twenty-one experiments (three groups) using seven chronically instrumented dogs were completed. Halothane and isoflurane produced significant (P less than 0.05) attenuation of the increase in arterial pressure after bolus administration of phenylephrine and azepexole. Bay k 8644 augmented the pressor responses mediated by both phenylephrine and azepexole in all three groups. Thus, halothane and isoflurane nonselectively reduced the pressor response to both alpha 1- and alpha 2-adrenergic receptor stimulation and this was probably not mediated by inhibition of transmembrane calcium flux through dihydropyridine sensitive channels.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1990

Treatment of choroidal melanoma: MR imaging in the assessment of radioactive plaque position.

Verification of the position of an episcleral iodine-125 gold plaque in relation to underlying choroidal melanoma is essential during early radiation therapy to ensure accurate plaque placement and thus optimum dose delivery. The authors used magnetic resonance (MR) imaging to examine 15 patients with choroidal melanoma after plaque placement to assess tumor coverage. The relationship of the plaque to the tumor was well defined in all cases, including two tumors anterior to the ora serrata. MR imaging measurements of the plaques were within 1 mm of the actual plaque sizes, while tumor measurements were within 2 mm of the preoperative ultrasound estimations of tumor dimensions. Tumors as small as 3 mm thick were readily visualized with MR imaging. Associated subretinal effusion was demonstrated in seven cases.

Aged↗
PubMed1990

Enhanced alpha-adrenergic vasoconstriction by n-3 fatty acids in conscious dogs.

The effect of dietary fish oil supplementation on cardiac function and the pressor response to selective agonists of postjunctional alpha 1- and alpha 2-adrenoceptors was investigated in chronically instrumented dogs (n = 12). Following ganglionic, cholinergic, and beta-adrenergic blockade, dose responses to phenylephrine (0.3-1.2 micrograms/kg iv), a selective alpha 1-adrenoceptor agonist, and azepexole (B-HT 933, 5-20 micrograms/kg iv), a selective alpha 2-adrenoreceptor agonist, were obtained in conscious dogs. Fish oil capsules containing eicosapentaenoic acid (1.12 g) and docosahexaenoic acid (480 mg) were administered orally twice daily for 1 wk, and dose-response curves were repeated. Dose-response curves were again obtained 1 wk after fish oil was discontinued. Fish oil supplementation resulted in significantly (P less than 0.05) increased arterial pressure at rest, and after autonomic nervous system blockade there was an increase in peripheral vascular resistance. Cardiac output was reduced in fish oil-treated dogs during autonomic nervous system blockade. The pressor response to selective alpha 1- and alpha 2-adrenoceptor stimulation was increased secondary to elevated peripheral vascular resistance. Hemodynamics and exaggerated vascular reactivity returned to control 1 wk after dietary fish oil was discontinued. The results of this study demonstrate that dietary fish oil supplementation produces an increase in arterial pressure via peripheral vasoconstriction and that the vascular response to alpha-adrenergic stimulation is exaggerated.

Adrenergic alpha-Agonists↗
PubMed1989

Improvement in functional recovery of stunned canine myocardium by long-term pretreatment with oral propranolol.

We investigated the effect of long-term oral pretreatment with the beta-adrenergic antagonist, propranolol (Inderal LA, 160 mg daily for 8 days) on the functional recovery of myocardium after 15-minute coronary artery occlusion followed by 3 hours of reperfusion in barbital-anesthetized dogs. Propranolol-pretreated dogs (N = 9) displayed a significantly lower left ventricular peak-positive rise in ventricular pressure (dP/dt), heart rate, and rate-pressure product throughout the experiment compared with the control group (N = 15). Subendocardial percent segment shortening as measured by sonomicrometry recovered to 65.4 +/- 7.2% of the preocclusion level after pretreatment with propranolol, whereas the control group recovered to only 11.1% +/- 10.2% after 3 hours of reperfusion. To ascertain the beneficial role of a lower heart rate on the recovery of regional contractile function, a third group of dogs (N = 6) was pretreated with propranolol, but heart rate was maintained at control levels by atrial pacing. The beneficial effects of pretreatment with propranolol were abolished in this group. There were no differences between groups in myocardial perfusion in the normal region as measured by the radioactive microsphere technique. However, in postischemic, reperfused myocardium, there was a significantly higher blood flow to subepicardium, mid-myocardium, and subendocardium after reperfusion in the propranolol-pretreated, unpaced group. Thus long-term oral pretreatment with propranolol enhances the contractile recovery of postischemic, reperfused myocardium. This protective effect of beta-adrenergic blockade is primarily related to the reduction in heart rate and enhanced perfusion in the postischemic region.

Administration, Oral↗
PubMed1989

Should the elderly be resuscitated following out-of-hospital cardiac arrest?

PURPOSE: Elderly and younger patients who were successfully resuscitated and hospitalized following out-of-hospital cardiac arrest were studied to determine if there was a significant difference in hospital course and long-term survival between the two groups. PATIENTS AND METHODS: The study consisted of 214 consecutive patients, divided into two age groups: elderly (more than 70 years, n = 112) and younger (less than 70 years, n = 102). Hospital charts and paramedic run data were retrospectively reviewed for each patient and findings were compared between the two age groups. RESULTS: Prior to cardiac arrest, 47 of 112 (42 percent) elderly patients had a history of heart failure, compared with 19 of 102 (18 percent) younger patients, and were more commonly taking digitalis (51 percent versus 29 percent) and diuretics (47 percent versus 26 percent). Younger patients, however, more often had an acute myocardial infarction at the time of the cardiac arrest (33 percent versus 16 percent). At the time of cardiac arrest, 83 percent of younger patients demonstrated ventricular fibrillation, compared with 71 percent of the elderly. In contrast, electromechanical dissociation was five times more common in the elderly patients. Although hospital deaths were more common in the elderly (71 percent versus 53 percent), the length of hospitalization and stay in intensive care units were not significantly different between the age groups. The number of neurologic deaths was similar in both age groups, as were residual neurologic impairments. Only five elderly patients and six younger patients required placement in extended-care facilities. Calculated long-term survival curves demonstrated similar survival in both age groups, with approximately 65 percent of hospital survivors alive at 24 months after hospital discharge. CONCLUSION: Resuscitation of elderly patients in whom out-of-hospital cardiac arrest occurs is reasonable and appropriate, according to the findings of this study. Even though elderly patients are more likely than younger patients to die during hospitalization, the hospital stay of the elderly is not longer, the elderly do not have more residual neurologic impairments, and survival after hospital discharge is similar to that in younger patients.

Adult↗
PubMed1989

Clinicopathologic study of organic dye. Laser in the human fundus.

One day before enucleation for choroidal melanoma, four patients consented to experimental laser photocoagulation for the purpose of comparing the histopathologic appearance of acute chorioretinal lesions produced by various dye laser wavelengths with krypton red and argon green laser controls. Three patients had simulated "light" and "heavy" treatment of an extrafoveal choroidal neovascular membrane (CNVM) with wavelengths 577 nm (yellow), 595 nm (orange), and 600 nm (orange). One patient had simulated panretinal photocoagulation (PRP) with four different dye laser wavelengths. Extrafoveal "light" treatment with the three dye wavelengths and both controls spared the inner retina and produced similar effects in the outer retina, pigment epithelium, and choriocapillaris. Choroidal penetration was deepest with the longer wavelengths (590-647 nm) in both "light" and "heavy" treatment groups. "Heavy" treatment gave varying degrees of full-thickness retinal uptake for all dye and both control wavelengths. Both ends of the orange spectrum (590-600 nm) produced the most severe inner retinal uptake. Panretinal photocoagulation produced similar full-thickness retinal uptake for all four dye wavelengths tested. These results indicate that caution should be used when treating "heavily" with 590 and 600 nm in the extrafoveal area.

Choroid↗
PubMed1989

Alterations of alpha 1 and alpha 2 adrenoceptor-mediated pressor responses by halothane and isoflurane anesthesia.

The mechanism by which halothane and isoflurane interfere with catecholamine-mediated vasoconstriction was investigated, utilizing selective agonists of postjunctional alpha1 and alpha2 adrenoceptors in chronically instrumented dogs. After ganglionic, cholinergic, and beta adrenergic blockade, dose responses to phenylephrine (0.3-1.2 micrograms/kg, iv), a selective alpha1 adrenoceptor agonist, and azepexole [B-HT 933] (5-20 micrograms/kg, iv), a selective alpha2 adrenoceptor agonist, were obtained in conscious dogs. Each dog was subsequently anesthetized with either halothane (1.7%) or isoflurane (2%) in oxygen in equihypotensive concentrations. After a 1 h equilibration period, the dose response curves were repeated. Twenty experiments in ten chronically instrumented dogs were completed. Halothane and isoflurane produced significant (P less than 0.05) attenuation of both the increase in systolic and diastolic arterial pressure after bolus administration of all doses of phenylephrine and azepexole. No specific selectivity of either volatile anesthetic for alpha1 or alpha2 mediated pressor responses was found. Therefore, in chronically instrumented dogs, alpha1- and alpha2-mediated pressor responses were similarly influenced by halothane and isoflurane. The present results suggest that both halothane and isoflurane act as functional antagonists to alpha adrenergic mediated vasoconstriction.

Adrenergic alpha-Agonists↗
PubMed1989

Effects of nisoldipine on coronary collateral perfusion and hemodynamics in chronically instrumented dogs.

The effect of a new dihydropyridine slow-channel calcium blocking agent, nisoldipine, on hemodynamics and myocardial blood flow in normal and collateral-dependent areas distal to a chronic coronary artery occlusion were studied in chronically instrumented, conscious dogs. Nisoldipine produced significant and dose-related decreases in arterial blood pressure, an elevation of heart rate and large increases in coronary blood flow velocity. In dogs with an Ameroid constrictor previously implanted to enhance coronary collateral development, this agent produced large increases in perfusion distal to a chronic coronary artery occlusion. In addition, despite a reduction in arterial pressure, nisoldipine preserved renal cortical, intestinal and skeletal muscle blood flow while increasing tissue flow within liver and cerebral cortex. Thus, nisoldipine increases oxygen supply to collateral-dependent myocardium in the presence of reduced driving pressure for collateral perfusion.

Animals↗
PubMed1988

Steroid-induced enhancement of functional recovery of postischemic, reperfused myocardium in conscious dogs.

The effects of methylprednisolone sodium succinate (20 mg/kg, intravenously administered) on the time course of functional recovery of myocardium following a 15-minute coronary artery occlusion period and subsequent 5 hour reperfusion period were studied in chronically instrumented, conscious dogs. In comparison to a control group, animals receiving methylprednisolone 90 minutes prior to coronary occlusion demonstrated less depression of regional segment shortening following 15 minutes of reperfusion (52 +/- 13% vs control levels of 23 +/- 7% of preocclusion values) and improved recovery at 5 hours postreperfusion (106 +/- 6% vs control levels of 54 +/- 4% of preocclusion values). In animals receiving methylprednisolone immediately prior to reperfusion, there was also similar recovery of segment shortening at 5 hours (97 +/- 3%). In contrast, dogs receiving methylprednisolone 15 minutes after the onset of reperfusion or sodium succinate (5.5 mg/kg, intravenously administered) 90 minutes prior to occlusion demonstrated no improvement in recovery of function. Experiments in dogs not subjected to coronary occlusion documented that methylprednisolone sodium succinate lacked inotropic and vasodilator properties. The results suggest that methylprednisolone administered prior to or during coronary artery occlusion but not after reperfusion enhances the functional recovery of hypokinetic, postischemic, reperfused myocardium. These effects are unrelated to any direct hemodynamic action of steroids or to the sodium succinate salt.

Animals↗
PubMed1988

Cyclical carotid artery flow reduction in conscious dogs: effect of a new thromboxane receptor antagonist.

Under sterile conditions, dogs were instrumented for continuous measurement of hemodynamics, and an Ameroid constrictor was positioned around the left carotid artery to produce slowly progressive narrowing of the vessel. In the awake, unsedated state, carotid cyclical blood flow reduction abruptly appeared on day 5.1 +/- 0.6 (mean +/- S.E.M.) at a frequency of 6.7 +/- 0.6 cycles per 30 minutes and usually remained present for only 1 day. The vessel was totally occluded on day 7.9 +/- 0.8. No focal neurologic deficit was observed. Following administration of the new thromboxane receptor antagonist, BM 13.505 (4-[2-(4-chlorobenzene-sulfonamide)-ethy]-benzene acetic acid), 50 and 100 micrograms/kg intravenously, the cyclical reduction in carotid blood flow was abolished for 30 +/- 5 and 45 +/- 15 minutes, respectively. No changes in systemic hemodynamics were observed over the course of the experiment. It is concluded that slowly progressive constriction of the carotid artery may provide an in vivo model for the study of perfusion deficits present in transient ischemic attacks. In addition, the results support the hypothesis that platelet aggregation plays a major role in cyclical carotid flow reduction, and the phenomenon can be eliminated by treatment with a new thromboxane receptor antagonist, BM 13.505.

Animals↗
PubMed1988

Induction of cyclic flow reduction in the coronary, carotid, and femoral arteries of conscious, chronically instrumented dogs. A model for investigating the role of platelets in severely constricted arteries.

Under sterile conditions, dogs were instrumented for continuous measurement of hemodynamics, and an Ameroid constrictor was positioned around either the left carotid, left femoral, or left anterior descending coronary artery to produce slowly progressive narrowing of the vessel. Cyclic flow reduction (CFR) developed in the carotid artery in seven of nine dogs on day 5.1 +/- 0.8 (mean +/- S.E.M.) at a frequency of 6.7 +/- 0.6 cycles per 30 min. This phenomenon was abolished for 30 +/- 5 and 45 +/- 15 min with intravenous administration of 50 and 100 micrograms/kg, respectively of the thromboxane receptor antagonist, BM 13.505, 4-[2-(4-chloro-benzene-sulfonamide)-ethyl]-benzene acetic acid. Total carotid artery occlusion occurred on day 7.9 +/- 0.8. CFR developed in the femoral artery in one of three dogs on day 4 at a frequency of 7 cycles per 30 min and was abolished for 82 min after BM 13.505 (50 micrograms/kg i.v.). The vessel became totally occluded on day 7. Finally, CFR developed in the left anterior descending coronary artery in three of five dogs on day 9.3 +/- 4.9 at a frequency of 6.2 +/- 0.9 cycles per 30 min. CFR was abolished for 37 min after BM 13.505 (50 micrograms/kg i.v.) and for several hours after an oral dose of aspirin (650 mg). Total coronary occlusion was observed on day 17.4 +/- 2.6. The present results demonstrate that CFR can be induced in various arteries in conscious, chronically instrumented dogs by slowly progressive narrowing via Ameroid constrictors. This phenomenon may serve as a model for transient ischemic attack, claudication, and unstable angina. Because the conscious state is maintained, drug interactions with anesthetics are avoided. The usefulness of inhibitors of platelet aggregation in this model documents the potential benefit of such compounds in various vascular disease states.

Animals↗
PubMed1988

Improvement of postischemic, contractile function by the calcium channel blocking agent nitrendipine in conscious dogs.

The effect of the new calcium channel blocking agent, nitrendipine, on recovery of contractile function following a 10-min left anterior descending coronary artery occlusion was studied in conscious dogs instrumented with sonomicrometers in the subendocardium of ischemic and normal regions. Nitrendipine (1.0 and 2.5 micrograms/kg/min i.v.) or drug vehicle was administered 30 min prior to the onset of coronary artery occlusion and continued for 30 min following reperfusion accomplished by inflation and deflation of a vascular balloon cuff. Nitrendipine produced a dose-related reduction in arterial pressure and an increase in heart rate and left circumflex coronary blood flow velocity. At 6 h following reperfusion in control dogs (N = 8), segment shortening was significantly reduced from control levels (71 +/- 10% of control). In comparison, dogs pretreated with nitrendipine (3 micrograms/kg/min i.v.) (n = 8) had significantly greater recovery of segment shortening throughout the reperfusion period (102 +/- 10% of control at 6 h following reperfusion). The data demonstrate that pretreatment with the calcium channel blocking agent enhances the recovery of function in postischemic, reperfused, "stunned" myocardium.

Animals↗
PubMed1988

Comparative effects of inotropic agents on coronary and systemic hemodynamics of conscious dogs: actions of milrinone, dopamine, ouabain and MCI-154.

The hemodynamic actions of a new inotropic agent, MCI-154, were compared to dopamine, ouabain and milrinone in conscious, chronically instrumented dogs. MCI-154 and milrinone produced similar hemodynamic changes: increases in heart rate, diastolic coronary blood flow velocity and peak positive dP/dt. Neither agent had significant effects on arterial pressure while both drugs reduced left ventricular end-diastolic pressure in a dose-related fashion and myocardial segment length, indicating a decrease in diastolic left-ventricular size. MCI-154 was found to be approximately twice as potent as milrinone. In contrast, dopamine and ouabain produced little change in left ventricular end-diastolic pressure or myocardial segment length during diastole, while both drugs produced increases in arterial and left ventricular systolic pressures. An increase in left ventricular afterload was not observed with either MCI-154 or milrinone, highlighting an important advantage of the latter compounds.

Animals↗
PubMed1988

Hemodynamic and electrocardiographic actions of the new intracellular calcium antagonist, KT-362, in the conscious dog.

Effects of the intracellular calcium antagonist, KT-362, on systemic and coronary hemodynamics and the electrocardiogram were evaluated in chronically instrumented, awake dogs during intravenous infusion or bolus administration. Both methods of administration resulted in systemic hypotension, tachycardia and decreases in left ventricular pressure and peak positive left ventricular dP/dt. KT-362 produced a transient increase in mean coronary blood flow velocity only during bolus injection, while subendocardial segment shortening was depressed only by drug infusion. Prolongation of QRS duration and the QT interval (corrected for change in heart rate, QTc) also occurred during drug infusion. The results suggest that the hemodynamic effects of intracellular calcium antagonism by KT-362 are qualitatively similar to those of other calcium channel blocking agents which inhibit extracellular calcium influx. In contrast, the actions of KT-362 on cardiac conduction may be different from those of other slow channel calcium blocking agents.

Animals↗