Search PubMed⌕ Search

Biomedical subjects

R F Davis

Publications and source records attributed to R F Davis.

At least 55 records · Page 3Linked to original sources
PubMed1987

Effects of aortic occlusion on regional spinal cord blood flow and somatosensory evoked potentials in sheep.

Somatosensory evoked potentials (SEPs) were recorded continuously during aortic occlusion in sheep, with simultaneous measurement of spinal cord blood flow (SCBF) by radiolabeled microspheres. Aortic occlusion was associated with disappearance of the SEPs in seven of nine sheep in 7.8 +/- 4.1 (SD) minutes. SCBF at the time of initial cross clamping and 30 minutes after the onset of ischemia revealed a severe reduction in white and gray matter flow in the thoracolumbar cord. Release of the aortic clamp was associated with reactive hyperemia in these ischemic regions. In two animals, the SEP persisted during aortic cross clamping. The total SCBF in the thoracic and lumbar regions of these two animals exceeded 20 ml/100 g/min after 30 minutes of ischemia and was significantly greater than the flow recorded in sheep whose evoked response disappeared. The relation between spinal cord ischemia and evoked potential alterations is discussed in detail.

Afferent Pathways↗
PubMed1987

The effect of sympathectomy on blood flow in bone. Regional distribution and effect over time.

Considerable interest has developed in the role of the autonomic nervous system and its effect on blood flow in bone. Theories pertaining to the long-term physiological effect of sympathectomy on blood flow in bone have been controversial. This study employed the radioactive tracer-microsphere technique to investigate the influence of sympathectomy on regional blood flow in bone over time in dogs. Blood flow was measured in fifteen adult dogs, weighing eighteen to twenty kilograms, at one hour, one day, and one, two, three, four, and six weeks after a transperitoneal sympathectomy from the first to the sixth lumbar level. Absolute control flow values were consistent with those that have been reported previously and had lower standard errors. Blood flow in bone in the femoral regions increased by 24.0 to 41.0 per cent. Greater elevations, of 37.0 to 59.0 per cent, were noted in the tibial sections. The largest increases (58.0 to 67.0 per cent) were seen in the metatarsals and proximal phalanges. All elevated values for blood flow returned to control values by six weeks. The data support the hypothesis that surgical sympathectomy exerts a significant yet transient effect on blood flow in bone. Furthermore, the greater increase distally is the first physiological evidence to support previous anatomical work that concluded that the major site of sympathetic tone lies distally in the lower extremity of the dog.

Animals↗
PubMed1986

A new technique for measuring aortic root pressure during infusion of cardioplegic solution.

Aortic root pressure is an important factor in determining the distribution of cardioplegic solutions. Previously, in order to measure this parameter, it was necessary to insert a separate catheter into the aortic root during cardioplegic infusion. An alternative method for measuring aortic root pressure is described that is both simple and accurate and obviates the need for a second aortic root catheter.

Aorta↗
PubMed1986

Transcutaneous carbon dioxide monitoring during neonatal transport.

We studied the value of transcutaneous carbon dioxide (PtcCO2) monitoring during neonatal transport. Thirty-two neonates with respiratory distress were alternately enrolled in an experimental group (results of PtcO2 and PtcCO2 available for clinical management) and a control group (results of only PtcO2 available). Although differences were not significant, infants in the experimental group had more changes in the intermittent mandatory ventilation (IMV) settings during transport, and more such infants arrived at the receiving hospital with acceptable pH and PCO2 values. On arrival at the receiving hospital, two patients in the control group had acidosis and hypercarbia and were placed on IMV immediately on arrival. No such patients were encountered in the experimental group. For patients needing IMV during transport, the percentage of study time spent with PtcCO2 measurements in the normal range (35 to 45 torr) was greater for the experimental group (p less than .02). Continuous PtcCO2 monitoring during transport offers the opportunity to further decrease the risks of transporting a critically ill neonate.

Blood Gas Analysis↗
PubMed1986

Thoracic epidural anesthesia reduces myocardial infarct size after coronary artery occlusion in dogs.

The effect of thoracic epidural anesthesia (TEA) with lidocaine on regional myocardial blood flow (RMBF), hemodynamic performance, and myocardial infarct size after coronary artery occlusion was assessed in 21 dogs. In seven dogs, the left anterior descending coronary artery (LAD) was temporarily occluded twice: once before TEA (control) and once during TEA. Systemic hemodynamic parameters, RMBF (using radionuclide-labeled microspheres), and epicardial electrocardiographic maps (15 sites) were obtained before and 15 min after each temporary LAD occlusion. Compared with the ischemic period before TEA, the following were decreased during ischemia with TEA: heart rate, ST segment elevation, cardiac index, the peak first time derivative of left ventricular (LV) pressure, LV tension-time index, the rate-pressure product, and LV stroke-work index. Ischemic zone endocardial RMBF was increased from a control value of 26 +/- 6% to 36 +/- 6% of normal during TEA (P less than 0.05). An additional 14 dogs randomly received either TEA (1% lidocaine, 10 ml/hr) or epidural saline plus 1% lidocaine (10 ml/hr, intramuscularly), beginning 1 hr after LAD occlusion. After 6 hr, the heart was removed and the left ventricle was sectioned parallel to the atrioventricular groove. The infarcts (tetrazolium-stained) were 46% smaller with TEA than with saline, 15.4 +/- 1.8% vs 28.7 +/- 2.3% of the left ventricle (P less than 0.05). Thus TEA reduced hemodynamic correlates of myocardial O2 consumption, improved regional (ischemic zone) endocardial perfusion, and reduced the extent of myocardial infarction.

Anesthesia, Epidural↗
PubMed1985

Clinical comparison of automated auscultatory and oscillometric and catheter-transducer measurements of arterial pressure.

Arterial pressure measurements recorded from a radial artery catheter-transducer (RAC) system were compared with similar data obtained from an automated sphygmomanometer that uses both oscillometric (OSC) and auscultatory measurement techniques. Data were obtained from 50 patients during and immediately after surgery. The fundamental frequency of the RAC system was 23.7 +/- 6.7 Hz (mean +/- SD; range, 13 to 40 Hz), and the damping coefficient was 0.26 +/- 0.06 (mean +/- SD; range, 0.15 to 0.34). Linear regression analysis of RAC against OSC values (n = 385) revealed the following correlations: (1) systolic pressure: OSC = 0.92(RAC) + 3.5, r = 0.91; (2) diastolic pressure: OSC = 0.92(RAC) + 1.3, r = 0.76; and (3) mean pressure: OSC = 0.96(RAC) + 0.68, r = 0.84. There were significant differences between each pair of pressure values; mean percent differences (RAC pressure minus OSC pressure) were 4.5 +/- 0.3%, 5.5 +/- 0.7%, and - 2.7 +/- 0.5% for systolic, diastolic, and mean values, respectively. Manual and automated auscultatory measurements closely agreed, and both correlated well with OSC values for systolic and diastolic pressure. However, both manual and automated auscultatory, as well as OSC measurements, underestimated RAC systolic and overestimated RAC diastolic pressure.

Adolescent↗
PubMed1985

Regional myocardial lidocaine concentration determines the antidysrhythmic effect in dogs after coronary artery occlusion.

Ischemic ventricular dysrhythmias were produced in 40 of 47 anesthetized mongrel dogs by high ligation of the left anterior descending coronary artery. Dysrhythmias were treated with a single iv bolus of 20, 40, 80, or 120 mg of lidocaine (L) in order to determine the dose at which approximately 50% of animals had an antidysrhythmic response. Cardiac output and regional myocardial blood flow (RMBF) were measured by using radionuclide labeled microspheres. Lidocaine concentration [( L]) was measured from samples of arterial and venous blood and normal and ischemic myocardium. All dogs treated with 40, 80, or 120 mg of L had an antidysrhythmic effect. However, with 20 mg of L the dysrhythmia persisted in 12 and resolved in 14. With 20 mg of L, ischemic myocardial [L] was greater in dogs with an antidysrhythmic effect than in those with persistent dysrhythmias (1.14 +/- 0.12 vs. 0.76 +/- 0.04 micrograms X g-1), but no difference was seen for arterial, venous, and normal myocardial [L]. Ischemic RMBF was higher in the dogs that had an antidysrhythmic effect than in those that did not, 9.8 +/- 1.5 versus 6.9 +/- 1.3% of normal. With 20 mg of L, [L] in ischemic myocardium correlated well with ischemic RMBF. The antidysrhythmic response to L had a threshold at a tissue concentration of greater than or equal to 1.0 microgram X g-1 (chi-square = 8.55, P less than 0.005). For this model, the [L] in ischemic myocardium during acute ischemia correlates with the antidysrhythmic response to L, while the concentration in normal myocardium or blood does not.

Animals↗
PubMed1985

Avoidance of malignant hyperthermia in a porcine model for experimental open heart surgery.

The porcine heart is an excellent physiological and anatomical experimental model because of its close similarity to the human heart. However, the pig is difficult to use in chronic experiments because of its propensity to develop malignant hyperthermia (MH). We have employed a technique which greatly reduces the incidence of MH in the chronic pig model, making its use feasible for a variety of experimental protocols.

Anesthesia↗
PubMed1984

Prolonged bleeding time in preterm infants receiving indomethacin for patent ductus arteriosus.

Sequential bleeding times were performed on 25 preterm infants receiving intravenous indomethacin for closure of the patent ductus arteriosus. Prolongation of bleeding time was observed after the initial dose of indomethacin, with an increase from a pretreatment mean of 3.6 minutes to 8.7 minutes. The bleeding time was not further prolonged at the end of the three-dose course of indomethacin, but was still elevated 48 hours after the completion of therapy. Clinical bleeding developed in six of the patients, but was generally limited to occult hematuria. Serial echoencephalography during indomethacin therapy showed progression from mild periventricular-intraventricular hemorrhage to moderate or severe grades in five of 21 infants at risk for this complication. However, no clear temporal relationship between indomethacin administration and intraventricular hemorrhage extension was observed, and no difference in the degree of bleeding time prolongation was noted between infants with and without hemorrhage extension. Other factors, including surfactant deficiency, amount of volume expansion used, and lowest PO2 in the first day of life, did distinguish those with hemorrhage extension. The results suggest that indomethacin-induced platelet dysfunction is not associated with major hemorrhagic complications in the majority of preterm infants with patent ductus arteriosus.

Bleeding Time↗
PubMed1984

Combined high-frequency oscillatory ventilation and intermittent mandatory ventilation in critically ill neonates.

Combined high-frequency oscillatory ventilation (HFOV) and intermittent mandatory ventilation (IMV) was used in 12 neonates with inadequate gas exchange with conventional IMV. Diagnoses included diaphragmatic hernia with hypoplastic lungs, pneumonia, persistent fetal circulation, and severe respiratory distress syndrome. In most patients there was severe air leak. Within 10 hours of beginning HFOV-IMV the mean arterial PCO2 fell from 60 +/- 5 (means +/- SEM) to 38 +/- 2 mm Hg (P less than 0.01) and the mean IMV rate was reduced from 96 +/- 8 to 17 +/- 4 breaths per minute (P less than 0.001). The mean arterial-alveolar oxygen tension ratio rose from 0.05 +/- 0.01 to 0.09 +/- 0.01 (P less than 0.005). Mean airway pressure in the trachea was reduced from 16 +/- 2 to 10 +/- 3 cm H2O (P less than 0.05). Four patients died, three of whom had diaphragmatic hernias with hypoplastic lungs. Five of the eight survivors had mild bronchopulmonary dysplasia requiring supplemental oxygen. These studies demonstrate that in some neonates with respiratory failure who fail to respond to conventional IMV, combined HFOV-IMV can be successful.

Bronchopulmonary Dysplasia↗
PubMed1983

The effect of halothane anesthesia on myocardial necrosis, hemodynamic performance, and regional myocardial blood flow in dogs following coronary artery occlusion.

The effect of halothane anesthesia on myocardial necrosis resulting from coronary artery ligation was examined in 28 anesthetized mongrel dogs. In 18 dogs, the left anterior descending coronary artery (LAD) was ligated immediately proximal to the first apical diagonal branch, and 1 h later the dogs were assigned randomly either to receive halothane, 0.5-1.0% inspired in room air for 12 h (n = 10) or to awaken without further intervention (control, n = 8). Infarct size was measured by staining the myocardium with triphenyl tetrazolium chloride 24 h after LAD ligation. Infarct size in halothane-treated dogs was 17.8 +/- 2.0% of the left ventricle, compared with 27.3 +/- 3.3% in control dogs (P less than 0.05). Myocardial salvage was present transmurally but was greatest in epicardial regions. In 10 additional dogs, hemodynamic variables (heart rate, arterial pressure, left ventricular end-diastolic pressure, peak left ventricular dP/dt, tension-time index, and rate-pressure product) were measured or calculated, and radionuclide-labeled microspheres were injected for measurement of cardiac output and regional myocardial blood flow (RMBF). Thirty minutes after LAD ligation and after initial hemodynamic measurements and microsphere injection, these dogs were assigned randomly to receive either halothane, 1.0%, inspired in room air (n = 5) or no intervention (control, n = 5). After 15 min of halothane inhalation (45 min after LAD ligation in control dogs), measurements were repeated. Halothane inhalation reduced heart rate, arterial pressure, and indexes of left ventricular contractile and pump performance. During halothane treatment, RMBF declined in normal myocardium but not in ischemic regions, while neither normal nor ischemic zone RMBF changed in control dogs. Systemic vascular resistance was unchanged in either group. Thus, halothane was associated with a 35% smaller myocardial infarct, transmural myocardial salvage, reduced heart rate, reduced left ventricular contractile and pump performance, reduced RMBF to nonischemic regions, and unchanged RMBF in the ischemic myocardium.

Anesthesia, Inhalation↗
PubMed1983

The effect of smoking on the stressed template bleeding time.

Tobacco cigarette smoking is known to affect platelet function. The purpose of this study was to determine whether cigarette smoking acutely shortens the bleeding time of healthy men. The mean initial stressed template bleeding time of 12 nonsmokers (9.0 minutes) was not significantly different from that of nine habitual smokers (9.2 minutes) who were asked to abstain from smoking for 12 hours before determination of the bleeding time. The mean bleeding time was the same immediately before and after the 21 men smoked two filtered tobacco cigarettes in 20 minutes. Separate analyses showed that the mean bleeding time of neither the nonsmokers nor the habitual smokers changed significantly after experimental smoking. We conclude that smoking two cigarettes has no effect on the stressed template bleeding time of healthy men.

Adult↗
PubMed1982

In healthy habitual smokers acetylsalicylic acid abolishes the effects of tobacco smoke on the platelet aggregate ratio.

After abstinence for at least 8 hours, 20 healthy habitual smokers smoked two unfiltered cigarettes during each of two 20-minute periods separated by 48 hours. They had taken one 0.32-g tablet of acetylsalicylic acid (ASA) the night before the second period. The mean platelet aggregate ratios in venous blood taken immediately before and after each period of smoking were 0.79 and 0.70 respectively when ASA had not been taken beforehand and 0.89 and 0.91 when it had. The mean after smoking was significantly higher when ASA had been taken beforehand. In conjunction with the previous finding that in nonsmokers ASA prevented a lowering of the platelet aggregate ratio by experimental smoking without affecting the ratio before smoking, the data from the present study suggest that ASA abolishes both acute and longer-lasting effects of tobacco smoke on the platelet aggregate ratio in healthy habitual smokers.

Adolescent↗
PubMed1982

Extension of myocardial necrosis into normal epicardium followng hypotension during experimental coronary occlusion.

In an effort to determine the manner in which hypotension following experimental coronary occlusion affects myocardial infarct size, the left anterior descending coronary artery was occluded in 22 barbiturate anaesthetised dogs, the chest was closed, and the dogs allowed to recover. Thirty minutes following coronary occlusion, seven dogs were haemorrhaged to a mean arterial pressure of 8.2 +/- 0.3 kPa (62 +/- 2 mmHg) and maintained at this pressure; no intervention was undertaken in control dogs. Twenty-four hours after coronary occlusion infarct size in control and hypotensive animals was determined. The hypotensive group developed larger percentages of necrosis of the left ventricles distal to the site of occlusion than did the control dogs (37.8 +/- 2.3 vs 30.4 +/- 1.4 (P less than 0.01)). Although the percentage of infarcted endocardium did not change significantly, the infarction of epicardium was 45% larger in the hypotensive group (34.4 +/- 3.3% vs 23.7 +/- 1.9%, P less than 0.01). Regional myocardial blood flow (RMBF) was determined by means of radioactive microspheres in 5 dogs following coronary occlusion before and after hypotension. RMBF following haemorrhage fell by an equal proportion, 61.9 +/- 3.3% in normal tissue and 61.2 +/- 2.4% in ischaemic zones. In conclusion, hypotension caused infarct extension into the epicardium, ie, into tissue that does not become necrotic under control conditions.

Animals↗