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Biomedical subjects

R H Merrill

Publications and source records attributed to R H Merrill.

17 recordsLinked to original sources
PubMed1994

Gender-related differences in the baroreceptor reflex control of heart rate in normotensive humans.

The present study investigates the baroreceptor reflex control of heart rate (HR) of normotensive male and female human volunteers under two conditions: bolus- and infusion-evoked elevations of blood pressure by intravenous administration of phenylephrine. Average age and blood pressure were similar in both sexes, but females had a significantly lower heart period (HP; higher HR). A major difference existed between the two sexes when the blood pressure was elevated by the bolus method. Females had a significantly (50%) smaller baroreflex sensitivity (regression coefficient), which inferred a gender-related difference in baroreceptor reflex control of HR. However, because a positive correlation existed between basal HP and baroreflex sensitivity, it was important to investigate whether this difference was related to the significantly lower basal HP in females. This possibility was ruled out because a similar difference still existed when the data were collected from another group of females who had basal HP values similar to those of males. This gender-related difference in baroreceptor reflex control of HR seems to depend on the pattern by which the pressor stimulus is evoked. The baroreceptor HP response to a slowly developing pressor response that was maintained at a steady-state level was very similar in both sexes. Because the HP response to abrupt (bolus-evoked) pressor stimuli mainly reflects the activity of the vagal component, our findings suggest that the cardiac vagal component seems to play a substantially smaller role in the baroreflex-mediated bradycardia in females.

Adult↗
PubMed1991

The technique of slow continuous ultrafiltration. Steps to maintain fluid balance without hemodynamic instability.

Slow continuous ultrafiltration (SCUF) is ideally suited for fluid overloaded patients with renal insufficiency, and for patients who need intravenous fluids in amounts that exceed renal excretory capacity. Like other methods of continuous ultrafiltration, including CAVH and CAVHD, SCUF can be performed in the intensive care unit with a minimum of equipment. During SCUF, arterial blood (usually from the femoral artery) is passed through a hollow-fiber hemofilter; an ultrafiltrate of serum collects at a rate that is determined by the patient's blood pressure. Replacement of intravenous fluids is generally not required with SCUF. The amount of ultrafiltrate that is removed can be titrated to achieve the desired fluid balance.

Acute Kidney Injury↗
PubMed1991

Techniques of continuous arteriovenous hemofiltration and hemodialysis. Renal replacement in the ICU for hypervolemic, uremic patients.

Continuous arteriovenous hemofiltration (CAVH) and continuous arteriovenous hemodialysis (CAVHD) are extracorporeal ultrafiltration techniques that permit ongoing removal of plasma water and uremic toxins. Both techniques are performed in the ICU with a minimum amount of equipment and achieve overall fluid balance more readily than intermittent hemodialysis. CAVH is used to manage hypervolemia, electrolyte imbalance, and/or mild uremia. CAVHD is used in hypercatabolic patients with acute renal failure who are hypervolemic and uremic; a dialysate fluid is used for more efficient solute removal. The most serious complications of CAVH and CAVHD relate to bleeding associated with cannulation or anticoagulation. Excess fluid and electrolyte losses may also occur.

Acute Kidney Injury↗
PubMed1988

Coombs'-negative spherocytic hemolytic anemia and severe necrotizing renal vasculitis.

Vasculitis may be complicated by either hypoproliferative or hemolytic anemias. We have described a patient with a Coombs'-negative spherocytic hemolytic anemia and severe necrotizing renal vasculitis, two disorders not having been previously linked. The disorders were temporally related and both responded to immunosuppressive therapy. The precise cause of the hemolytic anemia remains unknown.

Aged↗
PubMed1987

Effect of acute ethanol administration on the baroreceptor reflex control of heart rate in normotensive human volunteers.

The effects of acute ethanol administration on blood pressure, heart rate and the baroreceptor reflex control of heart rate were studied in normotensive subjects who served as their own control. Baroreceptor reflex control of heart rate was measured by two methods: the ramp method and the steady state method. None of the doses of ethanol had any effect on blood pressure during the observation period, except for the highest dose where a slight elevation was evident for a short period of time. On the other hand, the heart rate showed a slight but consistent dose-related increase. In general, ethanol attenuated the baroreceptor mediated bradycardia but this effect was dependent on the way in which blood pressure was elevated. A dose-related impairment of baroreceptors was evident when the ramp method was used, i.e. ethanol significantly depressed baroreflex sensitivity, expressed as delta heart period (HP)/delta mean arterial pressure (MAP). In contrast, delta HP/delta MAP was not influenced by ethanol when the steady state method was used. However, the steady state baroreflex curves were reset about a higher median blood pressure (MAP50), suggesting that the baroreceptors will be operative at higher blood pressure levels after ethanol. The pressor responsiveness was also influenced differently by ethanol depending on the method of injecting phenylephrine. An increase in pressor responsiveness was evident, though not dose-related, after ethanol only when blood pressure was elevated by the ramp method, suggesting that the inverse relationship between baroreflex sensitivity and pressor responsiveness is more prominent with the ramp method and/or when impairment rather than resetting of baroreceptors occurs. That the decrease in baroreflex sensitivity and the increase in MAP50 were related to peak ethanol levels in blood and that the blood pressure was not influenced by ethanol strongly suggest these effects were ethanol mediated. The weakened buffering action of the baroreflexes would be expected to favour the development of higher blood pressure.

Adult↗
PubMed1985

Familial thrombotic microangiopathy.

A family in which there were two certain and three possible cases of thrombotic microangiopathy in two generations is presented. All afflicted members studied presented with acute renal failure, and accelerated hypertension. No abnormal platelet-aggregating activity could be identified in the plasma of asymptomatic family members or in the surviving patient in remission. Although an increase in the Factor VIII: von Willebrand's factor level was found in the sole surviving patient, the multimer pattern was normal. Platelet-associated IgG level was also normal in this individual. Thus, individuals predisposed to this familial form of thrombotic microangiopathy do not have a demonstrable marker which can be implicated in the development of the disorder. Long-term study of this kindred is required to determine the factors which are important in the pathogenesis of thrombotic microangiopathy in the affected individuals.

Acute Kidney Injury↗
PubMed1980

Scanning electron microscopic observations on glomeruli: its use in thermally injured patients with renal impairment.

Previous scanning electron microscopic (SEM) studies have suggested that morphological changes occur in the glomeruli of animals with experimental acute renal failure (ARF). No SEM studies have been reported on human glomeruli in ARF. Sixteen thermally injured patients were studied by SEM and the observations were correlated with the light microscopic findings and clinical data. The group studied contained patients with normal renal function as well as patients with varying degrees of renal impairment, including ARF. The findings failed to demonstrate specific morphological alterations associated with ARF in the human.

Acute Kidney Injury↗
PubMed1979

The use of lyophilized vein grafts in vascular access for chronic hemodialysis.

The feasibility of utilizing lyophilized veins for creation of A-V fistulas was examined in two studies. In Study I, the longevity of lyophilized vein fistulas was found to be comparable to that of fresh veins in the experimental animal. Study II showed that lyophilized cadaveric veins performed at least as well as bovine grafts when used for vascular access in chronic hemodialysis patients. The advantages of lyophilized veins for creation of A-V fistulas in dialysis patients are described.

Animals↗
PubMed1976

Acute venous hemodialysis using the unipuncture apparatus.

Hemodialysis is a well recognized treatment modality for the support of patients with acute renal failure. In such patients, rapid access to the circulation for hemodialysis is important. For those patients with self-limited acute renal failure in whom recovery is expected, a rapid means of gaining temporary access to the circulation would be particularly desirable. The Seldinger technic for femoral vein catheterization and the use of the unipuncture dialysis apparatus have been combined to meet this requirement. The efficiency of unipuncture dialysis through a single femoral catheter compares favorably with the efficiency of dialysis by the standard two catheter technic.

Acute Kidney Injury↗
PubMed1976

Positive mono-spot test in histiocytic medullary reticulosis.

A case of rapidly fatal histiocytic medullary reticulosis in which two positive mono-spot tests were found is presented. In addition, there was a low liter antibody to EB virus. The patient died with a bleeding diathesis terminally. Postmortem examinations confirmed the diagnosis of histiocytic medullary reticulosis.

Adult↗