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Biomedical subjects

J F Schmidt

Publications and source records attributed to J F Schmidt.

At least 55 records · Page 3Linked to original sources
PubMed1990

Arterial CO2 tension and cerebral vascular reactivity during the induction of acute hypertension and hypotension in the awake human.

The CO2 reactivity was calculated at mean arterial blood pressure (MABP) values ranging from 40 to 140 mm Hg in 15 normotensive volunteers and in 7 patients with chronic arterial hypertension. The cerebral vascular reactivity (CVR) was estimated from indirect measurements of cerebral blood flow (CBF) by the arteriovenous oxygen saturation method. In all subjects but one of the hypertensive patients, there was a significant linear correlation of CVR with PaCO2 over the total range of MABP. The median CO2 reactivity in the volunteers and in the hypertensive patients was 2.7 and 2.8% CBF/0.1 kPa, respectively (NS). At MABP values corresponding to the plateau of CBF autoregulation (baseline MABP +/- 20%), the median CO2 reactivity was 3.0% CBF/0.1 kPa in both groups. During a cross-sectional correlation analysis of the pooled data from all volunteers, the CO2 reactivity increased with increasing MABP in the range of 50-110 mm Hg. Outside this range there was no correlation of CVR with PaCO2. In conclusion, our results confirmed that during acute hypo- and hypertension, the influence of PaCO2 on the CVR is reduced. The full CO2 reactivity of the cerebral vessel exists only at the plateau of CBF autoregulation.

Journal Article↗
PubMed1989

Cerebral circulation under normal and pathologic conditions.

Autoregulation of the cerebral circulation is the regulating mechanism that keeps cerebral blood flow (CBF) constant within wide limits of arterial pressure. The lower limit is defined as the value of mean arterial pressure below which CBF decreases below the plateau, and the upper limit as the value of mean arterial pressure above which CBF increases above the plateau (60 and 150 mm Hg, respectively). Two possible mechanisms for autoregulation are discussed, myogenic response and metabolic regulation. Stimulation of the sympathetic nervous system and antagonism of the renin-angiotensin system modulate CBF autoregulation by shifting the entire curve toward higher or lower values of arterial pressure, respectively. The autoregulatory curve is shifted toward higher arterial pressures in chronic hypertension. Therefore, the tolerance to acute decreases in arterial pressure is impaired. Concomitantly, the tolerance of the brain to acute increases in arterial pressure is improved. This shift in the limits of autoregulation is due to structural and functional (hemodynamic) changes in the cerebral resistance vessels. These adaptive changes are partly reversible after chronic treatment with antihypertensive agents. The pathophysiology of autoregulation should be taken into consideration before drugs are used to decrease arterial pressure acutely.

Animals↗
PubMed1989

The clinical effect of felodipine and nifedipine in Raynaud's phenomenon.

Sixteen patients participated in a double-blind cross-over trial comparing the effect of two dosages of the new calcium entry blocker, felodipine, with nifedipine in the treatment of Raynaud's phenomenon. The effect was evaluated using a symptom recording system. As no difference was found between the 3 treatments, the lower dose of felodipine (10 mg) may be preferable as only one dose per day is necessary.

Adolescent↗
PubMed1989

Angiotensin converting enzyme inhibition and cerebral blood flow autoregulation in normotensive and hypertensive man.

The acute effect on the lower limit of cerebral blood flow (CBF) autoregulation of an angiotensin converting enzyme (ACE) inhibitor, captopril, was studied in normotensive volunteers and in hypertensive patients. Baseline CBF was measured using xenon-133 inhalation tomography, and changes in CBF were measured using the arterio-venous oxygen difference method. Cerebral blood flow autoregulation was studied in two separate normotensive groups, one group of 12 volunteers serving as a control, and one group of 12 volunteers studied after the administration of captopril 50 mg. In a group of seven hypertensive patients CBF autoregulation was studied before and 1 h after the administration of captopril 25 mg. In the normotensive volunteers the median lower limit of CBF autoregulation was 83 and 74 mmHg in the untreated and the captopril-treated group, respectively, with no significant difference between the two groups. In five of the hypertensive patients the lower limit of CBF autoregulation was lowered by captopril, in median by 22 mmHg. However, in two patients it was increased, by 3 and 13 mmHg, respectively. It is proposed that the shift in the lower limit of CBF autoregulation seen in some of our cases, and which has previously been documented in experimental studies, may be dependent on the activity of the sympathetic nervous system.

Adult↗
PubMed1988

Extraction of [99mTc]-d,l-HM-PAO across the blood-brain barrier.

The initial extraction (E) across the blood-brain barrier (BBB) of [99mTc]-d,l-HM-PAO after intracarotid injection was measured in 14 Wistar rats and 6 patients using the double indicator, single injection method with Na-24 as the cotracer. In both series, cerebral blood flow (CBF) was measured using the initial slope of the xenon-133 washout curve after intracarotid bolus injection. In rats, bolus size (20 or 120 microliters), bolus type (saline or 10% albumin), or CBF were changed. First-pass extraction was dependent on CBF (p less than 0.001): With a small bolus of saline and at resting CBF (0.75 ml/g/min), E was 0.81, decreasing to 0.56 at a high CBF (1.5 ml/g/min). The calculated permeability surface area product (PS) increased linearly from 1.2 to 1.5 ml/g/min when CBF increased from 0.8 to 1.5 ml/g/min (p less than 0.01). E was found to increase when the bolus volume of saline was increased from 20 to 120 microliters, while using a 120 microliters bolus containing 10% albumin resulted in a decrease in E. This suggests that HM-PAO binding to albumin is not totally and rapidly reversible during a single passage through brain capillaries and that binding to blood elements may reduce the apparent extraction across brain capillaries. In patients using a bolus of 1 ml saline, E decreased linearly with increasing CBF (r = -0.81, p less than 0.001). For a CBF of 0.59 ml/g/min and an average apparent E of 0.72, an apparent PS product of 0.76 ml/g/min was calculated.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Quantitative measurements of cerebral blood flow using SPECT and [99mTc]-d,l-HM-PAO compared to xenon-133.

The uptake and retention in a 2 cm thick brain section was recorded serially by SPECT after i.v. injection of [99mTc]-d,l-HM-PAO (HM-PAO). In 16 patients, the fraction of the administered dose retained by the brain was 5.2 +/- 1%, showing a peak after 40-50s, then decreasing by 10% within the first 10 min and then by only 0.4% per hour. The image contrast was measured in each patient as the regional hemispheric asymmetry difference in percent of the highest value of the two regions. It decreased from 31% at 30-40 s to 25% at 10 min. At 24 h, a value of 19% was reached. Using the images obtained at 10 min after injection, a region to region comparison of the original and corrected HM-PAO images to the xenon-133 regional cerebral blood flow (rCBF) images was performed. Forty-four patients with stroke, epilepsy, dementia, basal ganglia disease, and tumors and control subjects were included in this comparison. The algorithm proposed by Lassen et al. was used to correct the original images for back diffusion of tracer (brain to blood); a good correlation very close to the line of identity between the corrected HM-PAO and xenon-133 data was obtained when using a conversion/clearance ratio of 1.5 and when the noninvolved hemisphere was used as a reference region (r = 0.86, p less than 0.0001). Serial arterial and cerebral venous blood sampling was performed over 10 min following i.v. injection of HM-PAO in six patients. An overall brain retention fraction of 0.37 +/- 0.03 (mean +/- SEM) was calculated from the data. An average CBF of 0.62 +/- 0.12 ml/g/min was determined on the basis of the Fick principle; this compared to a value of 0.59 +/- 0.09 ml/g/min (mean +/- SEM) measured by the xenon-133 inhalation method. The two sets of CBF values correlated linearly with a correlation coefficient of 0.97 (p less than 0.01). Inserting the average CBF value for the hemisphere as measured by the Fick principle into the algorithm described by Lassen et al. yields absolute rCBF values (ml/g/min) directly from the corrected HM-PAO images.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗
PubMed1988

Pudendal block in vaginal deliveries. Mepivacaine with and without epinephrine.

Pudendal block with 20 ml 1% mepivacaine with and without epinephrine was performed in 151 patients during the second stage of labor. No differences in efficacy of the block or in Apgar scores between the two groups were found. The maternal mepivacaine concentration was higher in the plain group than in the epinephrine group (p less than 0.01), but toxic levels were never reached. In the infants, no difference in mepivacaine concentration was found between the groups (p greater than 0.05, type II error 9%) and toxic levels were not reached. The time elapsed from the pudendal block until delivery was prolonged when epinephrine was added (p less than 0.02). We found no effect on blood pressure in either of the groups, with or without oxytocin and/or methergin. Twenty ml 1% mepivacaine (plain) is a safe choice for pudendal block without the possible disadvantages of adding epinephrine.

Anesthesia, Obstetrical↗
PubMed1988

Role of angiotensin in autoregulation of cerebral blood flow.

The presence of the renin-angiotensin system (RAS) in extrarenal tissues, namely the vascular wall and brain tissue, is well established. The availability of effective blocking agents, converting-enzyme inhibitors, has made it possible to further elucidate important functions of the extrarenal RAS. We have found that the angiotensin converting-enzyme inhibitor captopril shifts the limits of cerebral blood flow autoregulation to lower blood pressure levels in normotensive and in spontaneously hypertensive rats. This effect may explain our finding of a remarkable preservation of cerebral blood flow, despite significant blood pressure reduction, in patients with chronic heart failure. We suggest that the effect of angiotensin converting-enzyme inhibition on autoregulation of cerebral blood flow is mediated by a dilatation of larger cerebral arteries, which results from inhibition of the vascular tone normally maintained by locally produced angiotensin II.

Angiotensin II↗
PubMed1987

Iatrogenic nasal tip bossae. Etiology, prevention, and treatment.

Bossae formation is a common late complication seen following modification of the nasal tip during rhinoplasty. Prevention is our primary goal, and the incidence of this iatrogenic problem will decrease as the surgeon's understanding of the dynamics of healing in the altered nasal tip increases. We herein review the pertinent nasal anatomy, predisposing patient characteristics, and causative surgical maneuvers, concluding with our recommendations for prevention and treatment.

Humans↗
PubMed1987

Gastric contents and pH after oral premedication.

Forty women, aged 26-40 years, were investigated with regard to gastric contents and pH before general anaesthesia. The patients were divided into two groups (20 in each). Group 100 received 0.3 mg kg-1 diazepam orally with 100 ml of water 2 h before surgery. Group 50 received 0.3 mg kg-1 diazepam with 50 ml of water 2 h before surgery. The amount of gastric content was significantly greater in Group 100 than in Group 50 (P less than 0.05). There was no statistical difference in pH values between the groups. The number of patients with both gastric pH less than 2.5 and gastric volume greater than 25 ml was significantly higher in Group 100 compared to Group 50 (P less than 0.05). We cannot recommend the use of oral premedication using these amounts of water, considering the increased risk of aspiration of gastric contents.

Administration, Oral↗
PubMed1986

Auditory evoked potentials during isoflurane anaesthesia.

Brainstem auditory evoked potentials (BAEP) were determined in 12 volunteers. The effect of isoflurane anaesthesia on BAEP was determined in six patients. Body temperature and end-tidal CO2% were controlled. Increasing end-tidal isoflurane concentration from 0.6-2.4% increased BAEP wave I, III and V latencies. The amplitude of wave V decreased with increasing isoflurane concentration. Thus a dose-related change was demonstrated between end-tidal concentration of isoflurane and BAEP latencies.

Adult↗
PubMed1986

Peroperative buprenorphine: do high dosages shorten analgesia postoperatively?

Fifty-two patients undergoing biliary surgery were investigated in a prospective randomized study, in which they received buprenorphine 10, 20, 30, and 40 micrograms X kg-1, respectively, as sole intravenous analgesic as a bolus 15 min before induction of anaesthesia. The anaesthetic was uneventful in all four groups, although when receiving 10 and 20 micrograms X kg-1 almost two-thirds of the patients needed supplemental analgesics during the operation. When receiving buprenorphine in the dosage of 30 and 40 micrograms X kg-1, 50% of the patients requested an analgesic within 5 min of extubation. In contrast, when receiving 10 and 20 micrograms X kg-1 none of the patients requested an analgesic within 1 h of the operation. These findings accord to a certain extent with the presence of a bell-shaped dose-response curve for buprenorphine in humans.

Biliary Tract Surgical Procedures↗
PubMed1986

Comparison of oral controlled release morphine and epidural morphine in the management of postoperative pain.

Oral controlled release morphine (CRM) was compared in a double-blind study with epidural morphine (EM) for postoperative pain relief in 20 patients undergoing knee arthrotomy under epidural anesthesia. Ten patients received 30 mg CRM orally and saline epidurally (CRM group), and ten patients received placebo tablets orally and 4 mg morphine epidurally (EM group), both at the time of skin incision and then every 8 hr for 48 hr during which patients evaluated pain intensity using a visual analog scale. Nine of the ten patients in the EM group had good relief of pain throughout the study period. Seven of the ten patients in the CRM group needed rescue analgesics within 6 hr of the initiation of the study (P less than 0.01). We conclude that CRM is not suitable for the control of early postoperative pain, whereas epidural morphine is excellent.

Administration, Oral↗
PubMed1985

Postoperative pain relief with naloxone. Severe respiratory depression and pain after high dose buprenorphine.

Buprenorphine 30 and 40 micrograms/kg was given as the sole intravenous analgesic in balanced anaesthesia to 12 patients undergoing cholecystectomy. Significant and severe respiratory depression was found 15 minutes after preoperative loading with buprenorphine. In the immediate postoperative period six patients were in pain. They were treated with naloxone 0.08-0.4 mg leading to a long lasting period of pain relief (median 22 hours).

Adult↗
PubMed1985

Sublingual buprenorphine for premedication and postoperative pain relief in orthopaedic surgery.

The effect of sublingual buprenorphine (Temgesic) as a premedicant and for postoperative pain relief compared with morphine/pethidine was studied in 50 patients scheduled for elective surgery of the knee joint. Twenty-five patients received buprenorphine 0.4 mg sublingually 1 h before surgery and the same dose on demand postoperatively. Twenty-five patients were given morphine intramuscularly (7.5 mg or 10 mg to females and males respectively) 1 h preoperatively. This group received pethidine (75 mg) intramuscularly on demand postoperatively. All the patients were anaesthetized with halothane N2O/O2 after induction with thiopentone. No significant differences were found with regard to sedation, dizziness, nausea and vomiting during the study period. Emergence shivering, confusion and restlessness just after termination of the operation were equal in the two groups. In the recovery room, however, there was a higher frequency of shivering (P less than 0.05) in the morphine group. During the first 24 h postoperatively the buprenorphine group was given an average of 3.8 doses compared with 2.3 in the pethidine group (P greater than 0.05). It is concluded, that buprenorphine sublingually is as good as morphine intramuscularly for premedication and therefore should be recommended to patients who wish to avoid injections. For postoperative pain relief the initial dose of buprenorphine should be given intravenously. Only minor and unimportant side effects were seen.

Administration, Oral↗