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Biomedical subjects

R P Russell

Publications and source records attributed to R P Russell.

At least 19 recordsLinked to original sources
PubMed2000

Susceptibility-induced loss of signal: comparing PET and fMRI on a semantic task.

Functional magnetic resonance imaging (fMRI) has become a popular tool for investigations into the neural correlates of cognitive activity. One limitation of fMRI, however, is that it has difficulty imaging regions near tissue interfaces due to distortions from macroscopic susceptibility effects which become more severe at higher magnetic field strengths. This difficulty can be particularly problematic for language tasks that engage regions of the temporal lobes near the air-filled sinuses. This paper investigates susceptibility-induced signal loss in the temporal lobes and proposes that by defining a priori regions of interest and using the small-volume statistical correction of K. J. Worsley, S. Marrett, P. Neelin, A. C. Vandal, K. J. Friston, and A. C. Evans (1996, Hum. Brain Mapp. 4: 58-83), activations in these areas can sometimes be detected by increasing the statistical power of the analysis. We conducted two experiments, one with PET and the other with fMRI, using almost identical semantic categorization paradigms and comparable methods of analysis. There were areas of overlap as well as differences between the PET and fMRI results. One anticipated difference was a lack of activation in two regions in the temporal lobe on initial analyses in the fMRI data set. With a specific region of interest, however, activation in one of the regions was detected. These experiments demonstrate three points: first, even for almost identical cognitive tasks such as those in this study, PET and fMRI may not produce identical results; second, differences between the two methods due to macroscopic susceptibility artifacts in fMRI can be overcome with appropriate statistical corrections, but only partially; and third, new data acquisition paradigms are necessary to fully deal with susceptibility-induced signal loss if the sensitivity of the fMRI experiment to temporal lobe activations is to be enhanced.

Adult↗
PubMed1990

Prospective study of the impact of hypertension upon kidney function in diabetes mellitus.

Longitudinal data were obtained on 131 diabetic subjects enrolled in a study designed to evaluate the impact of persistent elevation of the blood pressure (BP) upon progression of renal damage in diabetes mellitus. For both insulin-dependent and non-insulin-dependent diabetes, serum creatinine exhibited a more rapid rise in those individuals whose BP remained elevated above 140 mm Hg despite therapy. Since no significant difference in age, duration of diabetes, diabetic control, or renal function at entry in the study could be identified as possible explanations for these differences, the findings support the conclusion that persistent elevation of the BP adds significantly to the risk of renal damage in both insulin-dependent and non-insulin-dependent diabetes, with more rapid decline occurring in non-insulin-dependent diabetes. Hypertensive subjects exhibited higher levels of plasma angiotensin II during the follow-up period.

Age Factors↗
PubMed1988

Side effects of calcium channel blockers.

Calcium channel blocking drugs are a chemically heterogenous group, so it might be expected that their effects on vascular smooth muscle, cardiac contractility, and conduction tissue may differ. However, the majority of adverse reactions are predictable from their pharmacological actions and may be conveniently grouped in the following categories: 1) vasodilatation, 2) negative inotropic effects, 3) conduction disturbances, 4) gastrointestinal effects, 5) metabolic effects, and 6) drug interactions. Vasodilatory symptoms, namely, dizziness, headaches, flushing sensation, and palpitation, are more likely with nifedipine. Peripheral edema is also common with nifedipine, but the mechanism is uncertain. For a given degree of vasodilation, the greatest negative inotropic effect is seen with verapamil first, diltiazem second, and nifedipine last. Calcium channel blocking drugs are contraindicated in hypertensive patients with second and third degree heart block, sick sinus syndrome, and severe heart failure. Verapamil and diltiazem have a significant effect on cardiac conduction, whereas nifedipine, in therapeutic doses, does not. Local gastrointestinal symptoms, such as nausea and constipation, are common with verapamil. None of the calcium channel blocking drugs have been reported to adversely affect lipid or protein metabolism. However, nifedipine, verapamil, and diltiazem in high doses may inhibit liberation of insulin. The significance of this finding needs to be explored further in hypertensive diabetics. Serum digoxin levels have been shown to increase after administration of verapamil and nifedipine, but there is no evidence that this change has any clinical relevance.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium Channel Blockers↗
PubMed1987

Influence of renin levels on the treatment of essential hypertension with thiazide diuretics.

Initial plasma renin activity (PRA) was measured in 213 patients with untreated hypertension before beginning thiazide (chlorothiazide and hydrochlorothiazide) therapy alone to test whether patients with low-renin hypertension exhibited a greater response to diuretic therapy. Diastolic blood pressure response to treatment in the low, mid-range, and high PRA groups did not differ significantly (delta diastolic blood pressure, -13.6 +/- 1.6, -11.6 +/- 1.5, and -10.8 +/- 2.6 mm Hg, respectively). Moreover, eight subjects with the highest PRA values exhibited the same magnitude of decrease in diastolic blood pressure as did the low PRA group (15.0 +/- 4.2 vs 13.6 +/- 1.6, respectively). This study thus provides no evidence for increased sensitivity to diuretic therapy among patients with low-renin essential hypertension.

Adolescent↗
PubMed1985

Cure of cryptococcal infection during continued immunosuppressive therapy.

Cryptococcus neoformans is a significant pathogen in immunosuppressed patients. In renal transplant recipients receiving prednisone, the development of cryptococcosis is associated with a poor prognosis. When such patients develop cryptococcosis they pose a particularly difficult clinical dilemma since withdrawal of prednisone, to facilitate cure of their fungal infection, may predispose to loss of their transplanted kidney. We report our experience with cryptococcal infection in 13 renal transplant patients. In 11 of these patients maintenance immunosuppression was cautiously continued to preserve allograft function. The results of our study suggest that maintenance immunosuppressive therapy may be continued throughout the period of antifungal therapy and does not preclude eradication of the infecting organisms. Our experience indicates that the prognosis for the renal transplant patient who has cryptococcosis can be improved.

Amphotericin B↗
PubMed1984

Renal artery angioplasty. Technical considerations and results.

Renal angioplasty was attempted on 38 renal arteries in 34 patients and was technically successful in 84.2%. Twenty-four patients were followed for 1 to 36 months (mean 15.3 months). The hypertension was cured or improved in 18 (75%), unchanged in 2 and recurrent after an initial period of improvement in four. Six patients were not available for further evaluation as five had additional renovascular surgery and one was lost to followup. Four patients had major complications; loss of the kidney occurred in one patient (2.9%). Respiratory renal mobility, predilatation with tapered teflon catheters and the contralateral femoral approach were found to be important technical aids for successful renal artery angioplasty.

Adolescent↗
PubMed1984

Cure of cryptococcemia and preservation of graft function in a renal transplant recipient.

Disseminated cryptococcosis with cryptococcemia occurred in a renal transplant patient in whom immunosuppression was continued throughout antifungal therapy in an effort to ensure graft viability. Despite the initial presence of positive fungal cultures of blood, urine, and CSF, infection cleared rapidly, and there has been no evidence of recurrence. Throughout this period, renal function remained unaltered. This favorable outcome suggests that the prognosis for the renal transplant recipient with disseminated cryptococcosis may be improved.

Adolescent↗
PubMed1983

Five-year blood pressure control and mortality following health education for hypertensive patients.

Three health education interventions for urban poor hypertensive patients were introduced sequentially in a randomized factorial design: 1) an exit interview to increase understanding of and compliance with the prescribed regimen; 2) a home visit to encourage a family member to provide support for the patient's regimen; and 3) invitations to small group sessions to increase the patient's confidence and ability to manage his/her problem. Previous evaluation of the initial two-year experience demonstrated a positive effect of the educational program on compliance with the medical treatment and blood pressure control. Data accumulated over an additional three years, including mortality analysis, are now presented. The study group consisted of the same cohort of 400 ambulatory hypertensive outpatients in the eight experimental and control groups. The five-year analysis shows a continuing positive effect on appointment keeping, weight control, and blood pressure control. All-cause life table mortality rate was 57.3 per cent less for the experimental group compared to the control group (12.9/100 vs 30.2/100, p less than .05), while the hypertension-related mortality rate was 53.2 per cent less (8.9/100 vs 19.0/100, p less than .01). The results from this longitudinal study provide evidence to encourage health practitioners to utilize such educational programs in the long-term management and control of high blood pressure.

Behavior↗