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Biomedical subjects

D C Merrill

Publications and source records attributed to D C Merrill.

At least 19 recordsLinked to original sources
PubMed1992

Ontogeny of baroreflex control of renal sympathetic nerve activity and heart rate.

The purpose of this study was to characterize the developmental changes in baroreflex function during fetal and postnatal life in sheep. Resting mean arterial blood pressure increased significantly from 55 +/- 2 mmHg in fetuses to 86 +/- 3 mmHg in newborn lambs and to 105 +/- 4 mmHg in 4- to 6-wk-old lambs. The sensitivity (gain) of the renal sympathetic nerve activity (RSNA) response to baroreceptor stimulation was greater (P < 0.05) in fetuses (-7.7 +/- 1.9%/mmHg) than in newborn (-2.9 +/- 0.1%/mmHg) and 4- to 6-wk-old lambs (-2.2 +/- 0.2%/mmHg). The threshold and saturation pressures for the baroreflex function curve were lower (P < 0.05) in fetuses (44 +/- 2 and 61 +/- 2 mmHg) than in newborn (59 +/- 4 and 106 +/- 5 mmHg) or 4- to 6-wk-old lambs (78 +/- 5 and 132 +/- 6 mmHg). Similar findings were observed when the heart rate response to baroreceptor stimulation was examined. Additional experiments were performed in newborn and 4- to 6-wk-old lambs to determine whether the rise in arterial blood pressure associated with postnatal maturation contributed to baroreflex resetting. Sustained elevation of arterial blood pressure by 15-20 mmHg for over 90 min did not reset the baroreflex function curve in either newborn or 4- to 6-wk-old lambs.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Fetal medicine.

Fetal therapy continues to be an exciting yet controversial field. In utero treatment of a variety of fetal conditions is discussed: parvovirus B19 infection, fetal thyroid dysfunction, fetal ovarian cysts, twin-twin transfusion syndrome, and fetal hemolytic disease. Fetal surgery continues to be controversial. Despite considerable publicity, fetal surgery appears to be rarely, if ever, truly indicated. A new area of fetal therapy, ie, antenatal transplantation of fetal liver stem cells, is discussed.

Cystic Adenomatoid Malformation of Lung, Congenita↗
PubMed1991

Patient satisfaction with Mentor inflatable penile prosthesis.

Patient satisfaction with the Mentor inflatable penile prosthesis was assessed by sending a thirty-six-item questionnaire to 251 patients who had undergone implantation of the device by the senior author (D.C.M.). A total of 152 (61%) of the patients responded. Recovery time, satisfaction, reasons for dissatisfaction, perceptions of erection quality, and psychosexual parameters were evaluated. Eight-eight percent of the patients were engaging in regular sexual activity. Depending on the definition of satisfaction, 81-89 percent of the respondents reported that they were satisfied with the prosthesis. Sixty-eight percent of the survey group were satisfied with the length, width, and firmness of their prosthetic-induced erection. The majority of patients reported improvement in psychosexual functioning after implantation. Reasons for dissatisfaction included inadequate penile length, insufficient firmness, and difficulty with inflation and deflation of the penile cylinders.

Adult↗
PubMed1990

Whole bladder photodynamic therapy: critical review of present-day technology and rationale for development of intravesical laser catheter and monitoring system.

Present-day whole bladder photodynamic therapy (WBPDT) is cumbersome and time consuming because cystoscopic and ultrasonic manipulations are necessary to position the light emitter within the bladder. More important, WBPDT is inherently unsafe and often ineffective since neither uniform photoirradiation nor accurate light dosimetry can be achieved with the techniques employed to photoirradiate the bladder wall. The intravesical laser catheter (IVLC) eliminates the need for cystoscopy and ultrasonography because passage of the treatment fiber into the catheter's central lumen automatically positions its light-diffusing tip within the center of the bladder. Use of the IVLC delivery system also assures accurate photoirradiation of the bladder wall since inflation of the catheter's balloon transforms the asymmetric bladder into a sphere of known diameter. The light sensor incorporated in the balloon wall provides a method to monitor light fluence and measure total light dose. When provided the parameters of bladder volume, laser energy output, and desired light dose, the computerized control system calculates treatment time and automatically adjusts the period of photoirradiation to compensate for variations in laser light production, energy losses during transmission, and for variations in light intensity resulting from the integrating sphere effect of the bladder wall. This delivery system also increases the safety of WBPDT since the monitor automatically discontinues treatment if any unsafe situation, with respect to light fluence, develops during photoirradiation.

Administration, Intravesical↗
PubMed1989

Clinical evaluation of FasTENS, an inexpensive, disposable transcutaneous electrical nerve stimulator designed specifically for postoperative electroanalgesia.

Previous studies have shown that electroanalgesia is an effective method of reducing postoperative pain in patients who have urologic surgery. All prior studies of postperative transcutaneous electrical nerve stimulation (TENS) have employed TENS stimulators which were designed for the control of chronic pain. Disadvantages to the use of standard TENS stimulators in postoperative patients include the high cost of the devices and their operative complexity which make it difficult for staff and patients to use them. FasTENS is a lightweight, relatively inexpensive disposable TENS stimulator which has been designed specifically for use in postoperative patients. We evaluated the effectiveness of FasTENS in patients who had implantation of an inflatable penile prosthesis, radical retropubic prostatectomy, or radical nephrectomy. Patients treated with FasTENS used 60 percent less pain medication (P less than 0.001) and made 61 percent fewer requests for Demerol injections (P less than 0.001) than did control patients who were not treated with postoperative electroanalgesia. FasTENS was most effective in patients who had radical prostatectomy or penile prosthetic surgery. FasTENS was not cost-effective or practical in patients who had radical nephrectomy.

Acetaminophen↗
PubMed1989

Effect of plasma sodium on aldosterone secretion during angiotensin II stimulation in normal humans.

Studies were carried out in normal male subjects (n = 6, age 20-35 years) to determine the interaction of angiotensin II and plasma sodium on aldosterone secretion. These relations were quantified by elevation of plasma sodium with an infusion of 5% sodium chloride (4 ml/kg/30 min i.v.) with measurements of plasma aldosterone, atrial natriuretic factor (ANF), and arginine vasopressin (AVP) over 3 hours. Two hours before sodium chloride infusion, an intravenous infusion of angiotensin II was begun at 0.5 or 5.0 ng/kg/min and continued throughout the study. Plasma potassium was maintained constant by the addition of potassium to the infusate. NaCl/KCl infusion raised plasma sodium 4 meq/l with no decreases of plasma potassium. Plasma aldosterone averaged 7 +/- 1.8 ng/dl before NaCl infusion in subjects infused with 0.5 ng angiotensin II and was not significantly reduced with sodium chloride infusion. Angiotensin II infused at 5 ng/kg/min resulted in average plasma aldosterone levels of 31 +/- 3.6 ng/dl, which sodium chloride infusion decreased to 16.6 +/- 1.3 ng/dl (p less than 0.05) in 60 minutes. Plasma aldosterone remained depressed for the remaining period of study. Plasma ANF increased from 40 to 60 pg/ml with sodium chloride infusion. We conclude that small physiological elevations of plasma sodium concentrations can signal substantial decreases of plasma aldosterone in normal human subjects in situations where plasma angiotensin II is moderately elevated. The precise mechanisms of these responses remain to be determined.

Adult↗
PubMed1989

Mentor inflatable penile prostheses.

The standard Mentor inflatable is an extremely reliable prosthesis that will provide complete satisfaction in 87 to 99 per cent of the patients in whom it is implanted. The proved long-term reliability and superior functional characteristics of the three-component Mentor prosthesis make it a standard investigators may use to compare the recently introduced mechanical and modified inflatable prostheses. The short-term results of the new Mentor GFS prosthesis also are encouraging. The new prosthesis provides an attractive alternative to the standard inflatable prosthesis in patients with normal-sized genitalia, especially for surgeons who prefer to implant the device through a penoscrotal incision.

Humans↗
PubMed1988

Treatment of metastatic prostate cancer. Factors that influence treatment selection and methods to increase acceptance of orchiectomy.

Orchiectomy is the preferred method for treating patients with metastatic adenocarcinoma of the prostate (MAP) because it is safer and more reliable than estrogen therapy. Nonetheless, a survey of Northern California urologists showed that 57 percent of their patients with MAP were treated with diethylstilbestrol (DES) rather than orchiectomy. Factors which determined treatment selection include the physician's belief that estrogen therapy was either equally (35%) or more (22%) effective than orchiectomy and the patients' rejection of orchiectomy even if it were recommended to them (20-30%). The survey also showed that previous attempts to increase the acceptability of orchiectomy by performing a subcapsular procedure have failed because urologists do not believe the procedure is effective (45%), or that subcapsular orchiectomy provides a satisfactory cosmetic result (20%). Recent laboratory and clinical investigations have shown that complete and subcapsular orchiectomy were equally effective in reducing serum testosterone. Patient acceptance of subcapsular orchiectomy may be increased by utilizing the term testicular curettage, which does not imply castration, to describe the procedure and by implantation of intracapsular testicular prostheses to restore normal testicular anatomy after the testicles' hormone-producing tissue has been removed.

Adenocarcinoma↗
PubMed1988

Control of adrenocorticotropin secretion and adrenocortical sensitivity in neurohypophysectomized conscious dogs: effects of acute and chronic vasopressin replacement.

We examined the effect of neurohypophysectomy with and without vasopressin replacement on the ACTH response to hypotension and ovine CRF infusion and on the adrenocortical response to ACTH and angiotensin II infusion in conscious dogs. Nitroprusside hypotension (decrease in mean arterial pressure of 25 mm Hg) in the intact state resulted in large increases in plasma arginine vasopressin (pAVP; from 2.6 +/- 0.3 to 296 +/- 63 pg/ml) and ACTH (from 35 +/- 6 to 395 +/- 92 pg/ml). Neurohypophysectomy resulted in greatly attenuated pAVP (8.4 +/- 1.6 pg/ml) and ACTH (80 +/- 10 pg/ml) responses to hypotension which were not normalized by physiological low dose vasopressin replacement (6-18 pg/kg.min continuously, iv, for 2 weeks). However, acute administration of vasopressin (4-6 ng/kg.min) simultaneously with hypotension in the neurohypophysectomized (neurohypox) dog, which produced pAVP levels equivalent to the hypotensive response to intact dogs, almost completely normalized the ACTH response to hypotension (to 248 +/- 74 pg/ml). The ACTH response to 20 ng/kg.min ovine CRF, iv (from 43 +/- 8 to 268 +/- 77 pg/ml), was not attenuated by neurohypophysectomy. The cortisol responses to infusion of 0.5 and 2 ng/kg.min ACTH-(1-24), iv, were essentially normal in neurohypox dogs. However, the ACTH and aldosterone responses to 5 ng/kg.min angiotensin II infusion iv were attenuated in neurohypox dogs off AVP replacement. Histological examination revealed normal adrenal glands and anterior pituitaries in neurohypox dogs. Immunocytochemical staining for vasopressin and neurophysin revealed normal cell bodies in the paraventricular and supraoptic nuclei of the hypothalami from neurohypox dogs. However, median eminence staining for AVP and neurophysin was greatly diminished in neurohypox dogs. In summary, neurohypophysectomy 1) attenuated the ACTH response to hypotension and angiotensin II, but not to CRF, and 2) attenuated the aldosterone response to high dose angiotensin II. Furthermore, the deficit in ACTH secretion was almost completely normalized by increasing plasma AVP levels to those observed in the intact dogs. We conclude that an action of circulating pAVP increases ACTH secretion by a direct effect at the pituitary and by activating afferent input to the hypothalamus.

Adrenal Cortex↗
PubMed1986

Vasopressin responses to corticotropin releasing factor and hyperosmolality in conscious dogs.

We recently reported that ovine corticotropin releasing factor (CRF) infusion in conscious dogs elevated plasma vasopressin. The present study examines the vasopressin, adrenocorticotropic hormone (ACTH), and cortisol responses to CRF infusion (20 ng X kg-1 X min-1), to hypertonic saline infusion (NaCl 0.054 meq X kg-1 X min-1), and to simultaneous coinfusion of CRF and NaCl (CRF + NaCl) without (no-dex) or with (dex-treated) dexamethasone pretreatment in six conscious dogs (6-8 experiments/dog). CRF had no significant effect on plasma sodium or osmolality, blood pressure, or heart rate. NaCl increased plasma sodium from 146 +/- 1 to 151 +/- 1 meq/l and plasma osmolality from 298 +/- 3 to 305 +/- 3 mosmol/kg. Vasopressin increased significantly during CRF (2.1 +/- 0.5 to 4.8 +/- 1.1 pg/ml) and NaCl (1.9 +/- 0.3 to 5.0 +/- 0.8 pg/ml). Coinfusion of CRF and NaCl resulted in a response larger than the sum of the two infusions alone (3.0 +/- 1.6 to 31.4 +/- 18.5 pg/ml). The ACTH response to CRF (45 +/- 8 to 288 +/- 88 pg/ml) was not augmented by coinfusion with NaCl. DEX attenuated the vasopressin and ACTH responses to each infusion. We conclude that CRF-induced increases in vasopressin are augmented by a simultaneous osmotic stimulus. In addition, the plasma vasopressin responses to CRF and/or hypertonic saline infusion are inhibited by glucocorticoid pretreatment.

Adrenocorticotropic Hormone↗
PubMed1986

Vasopressin excess: relative contribution of volume retention versus direct actions on renin secretion and sodium excretion.

Three groups of dogs were studied to determine to what extent the suppression of plasma renin activity (PRA), natriuresis, and hyponatremia, seen with chronic elevations of plasma vasopressin (AVP), were caused by volume expansion or some other more direct actions of AVP. The dogs of group 1 (n = 7) were infused with AVP (0.36 ng/kg/min, i.v.) for 2 weeks, while water intake was maintained at a constant level. The dogs of group 2 (n = 6) were permitted to drink ad libitum during AVP infusion. The dogs of group 3 (n = 7) were infused with AVP while total body weight and volume were maintained at a constant level by use of an electronically servocontrolled water infusion system. Group 1, with fixed water intake, retained a large fluid volume (1.4 L), with an associated 36 mm Hg rise in mean arterial blood pressure (MAP). Associated with this hypertension and increased volume were a suppression of PRA and substantial decreases in plasma sodium concentration with increased excretion of sodium. With ad libitum drinking (group 2), only mild volume expansion occurred, with no significant elevations of MAP or changes in sodium excretion. With a volume expansion of 300-400 ml, there was a significant decrease of PRA and plasma sodium concentration. Group 3, servocontrolled dogs, exhibited no change in MAP, plasma sodium concentration, or PRA throughout the 2-week period of AVP infusion. Sodium excretion was mildly elevated only on the first day of AVP infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1979

Laboratory comparison of urethral profilometry techniques.

A comparison of urethral pressure profiles performed with the air infusion, water infusion, membrane catheter, and transducer tip catheter techniques was made in a canine model. The gas and water infusion methods gave statistically identical results if the gas studies were performed at flow rates of 100 ml./min. and pull rates of 5 cm./min. The transducer tip catheter and the gas and water infusion techniques gave accurate recordings of peak urethral pressure but were incapable of detecting multiple areas of urethral compression. The transducer tip catheter measurements often were difficult to interpret because of rotation and flexion artifact. The membrane catheter was capable of recording multiple areas of urethral compression but gave spuriously high recordings of peak urethral pressure. We conclude that none of the methods tested will give accurate recordings of urethral pressure in all clinical situations.

Animals↗
PubMed1979

The treatment of detrusor incontinence by electrical stimulation.

Cystometrograms were done on 20 patients before and during transrectal stimulation to determine if electrical stimulation increased the detrusor reflex threshold. In 4 patients the detrusor reflex threshold was increased during stimulation and urinary continence was restored. However, each patient became incontinent when transrectal stimulation was discontinued for 1 to 5 days. Thus, cyclic periods of stimulation were necessary to maintain the beneficial effects of electrical stimulation and a permanent pelvic floor stimulator was implanted since chronic transrectal stimulation was inconvenient.

Adult↗
PubMed1978

Effect of baclofen and dantrolene on bladder stimulator-induced detrusor-sphincter dyssynergia in dogs.

The effect of baclofen (Lioresal) and dantrolene (Dantrium) on bladder stimulation-induced detrusor-sphincter dyssynergia was studied in normal and chronic T-10 paraplegic dogs. Dantrolene, which depresses skeletal muscle contractility, had little effect on electrically evoked contractions of the urethral sphincter in dogs. Baclofen, which acts centrally by potentiating presynaptic inhibition, depressed the pudendal to pudendal nerve reflex and decreased urethral resistance during bladder stimulation.

Aminobutyrates↗