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Biomedical subjects

A J Coleman

Publications and source records attributed to A J Coleman.

At least 19 recordsLinked to original sources
PubMed1992

Acoustic emission and sonoluminescence due to cavitation at the beam focus of an electrohydraulic shock wave lithotripter.

The acoustic emission from cavitation in the field of an extracorporeal shock wave lithotripter has been studied using a lead zirconate titanate piezoceramic (PC4) hydrophone in the form of a 100-mm diameter focused bowl of 120-mm focal length. With this hydrophone directed at the beam focus of an electrohydraulic lithotripter radiating into water, it is possible to identify signals well above the noise level, at the 1-MHz resonance of the hydrophone, which originate at the beam focus. Light emission, attributed to sonoluminescence, is also shown to originate at the focal region of the lithotripter, and the signal obtained from a fast photomultiplier tube directed at the focus has similarities in structure and timing to the detected acoustic signals. The multiple shock emission resulting from a single discharge of an electrohydraulic source is shown to result in two separate bursts of cavitational activity separated by a period of 3-4 ms. The signal burst corresponding to the primary shock has a duration of about 600 microseconds with little noticeable structure. The signal burst associated with the secondary shock has a reproducible structure with two distinct peaks separated by about 200 microseconds depending on the shock amplitude. THe timing and structure of each burst is shown to be in reasonable agreement with the theoretical predictions made by Church (1989) based on the Gilmore model of bubble dynamics. In particular, it is shown that it is possible to obtain precise measurements of the time delay between the separate peaks within the signal burst detected following the secondary shock and this may, as predicted, provide a method of determining the size of bubbles remaining after the primary shock.

Acoustics↗
PubMed1991

Theoretical predictions of the acoustic pressure generated by a shock wave lithotripter.

A one-dimensional frequency domain model is used to predict the temporal peak acoustic pressures developed near the beam focus during extracorporeal shock wave lithotripsy (ESWL). The model includes consideration of finite amplitude effects, attenuation, diffraction and dispersion, and results are presented for the case of an electrohydraulic source with the beam geometry of the Dornier HM3 lithotripter. Propagation in castor oil, water and tissue is examined. The model predicts that nonlinear effects enhance the peak positive pressure (p+) at the beam focus in 6 cm of tissue in a Dornier type lithotripter by a factor of about 3 above that which would be expected for linear propagation. The negative peak pressure (p-), conversely, is predicted to be depressed by a factor of about 0.7 below the linear theory prediction. The model also indicates the occurrence of excess absorption due to shock formation. This is shown, for a Dornier HM3 type lithotripter, to cause a reduction in the peak positive pressure gain and a broadening of the focal depth as the output of the source is increased. A threshold aperture pressure is identified for a source with the same beam geometry as the Dornier HM3 below which shock formation does not occur. In this region the pressure gain increases and the focal depth narrows as the source output increases. These effects are characteristic of current commercial piezoelectric and electromagnetic lithotripsy fields.

Humans↗
PubMed1989

A survey of the acoustic output of commercial extracorporeal shock wave lithotripters.

A survey of the pressures and intensities generated by different commercial extracorporeal shock wave (ESWL) lithotripters is reported. The lithotripters included in the survey are the Dornier HM3, Wolf Piezolith 2200 and 2300, Siemens Lithostar, Technomed Sonolith 2000 and 3000, and EDAP LT-01. Measurements were made using a polyvinylidene difluoride (PVdF) membrane hydrophone in water. The zero crossing frequency of one complete cycle of the focused pulse from ESWL equipment is in the range 0.1 to 1 MHz. Spatial-peak temporal-peak positive and negative pressures up to 114 MPa and 10 MPa, respectively, have been measured and the rise times of the positive pressure half cycle at maximum output settings are 30 ns or less. The mean spatial-peak temporal-average intensity of the lithotripters is 5.0 x 10(2) W m-2 when operated at a pulse repetition frequency of 1 Hz. The spatial-peak pulse-average intensity ranges from 6.6 x 10(7) to 1.24 x 10(9) W m-2. The estimated acoustic energy in a single pulse (at the focus) at the maximum output setting of the lithotripters varies from 2.0 x 10(-3) J to about 9.0 x 10(-2) J. The beam area in the focal plane varies by a factor of 100 on different lithotripters and the temporal-peak pressure at the position of the skin at the entry point of the beam by a factor of 30. Measurement problems associated with hydrophone damage and the uncertainties in the hydrophone calibration at high pressures are discussed and an estimate of the total uncertainty in the absolute measurements of the spatial-peak temporal-peak positive pressure is given as +/- 36%.

Acoustics↗
PubMed1989

An experimental shock wave generator for lithotripsy studies.

An electrohydraulic shock wave generator has been constructed to facilitate investigation of the acoustic field generated during extracorporeal shock wave lithotripsy (ESWL). Pressure waveforms at the generator aperture and the beam focus, measured using a PVDF needle hydrophone, are compared with those from a commercial lithotripter, the Dornier HM3.

Acoustics↗
PubMed1987

Physical characteristics of Dornier extracorporeal shock-wave lithotriptor.

Measurements of the pressure, noise, and radiation dose levels from a Dornier lithotriptor are reported. The distribution of the peak pressure around the treatment focus was investigated, and the highest pressures were found to occur within an elongated volume. Within the treatment room, noise levels of 80-90 dB were produced during each shock wave, rising to 95 dB by the patient's head. Ear protection for the staff and patient is recommended, and careful room design is necessary to minimize the sound disturbance to adjacent quarters. Measurements of the radiation skin dose received by patients from the x-ray localization system were relatively high and ranged from 2-55 cGy (rad), with a mean of 12 cGy. The operator needs to be aware of these high doses and should take precautions to minimize them.

Ear Protective Devices↗
PubMed1987

Acoustic cavitation generated by an extracorporeal shockwave lithotripter.

Evidence is presented of acoustic cavitation generated by a Dornier extracorporeal shockwave lithotripter. Using x-ray film, thin aluminum sheets, and relatively thick metal plates as targets, evidence of liquid jet impacts associated with cavitation bubble collapse was observed. The jet impact was violent enough to puncture thin foils and deform metal plates. Furthermore, numerous jet impacts were generated over a volume of greater than 200 cm3. It is likely that such violent cavitation will also occur in tissue, and observed biological effects (e.g. renal calculus disintegration and tissue trauma) may be related to cavitation damage.

Lithotripsy↗
PubMed1979

Cardiovascular effects of intravenous indoramin hydrochloride in man.

Haemodynamic effects of intravenous indoramin (5-20 mg) were measured in ten healthy volunteers. Slight falls in arterial and central venous blood pressures were noted but no significant changes in heart rate, right atrial pressure, cardiac output or derived values occurred, except for a fall in peripheral vascular resistance in three cases. An increase in skin blood flow to the feet was observed. An attempt was made to determine the mechanisms of these responses and it was concluded that the drug was an alpha adrenoceptor blocking agent which appeared to act preferentially on those receptors controlling blood flow to the skin of extremities.

Adult↗
PubMed1977

The pharmacokinetics of ciclazindol (Wy 23409) in human volunteers.

1. The pharmacokinetics and metabolism of ciclazindol, a potential anti-depressant drug, have been studied after oral administration of the compound to male and female volunteers. 2. The mean +/- S.E. mean maximum plasma concentration of the unchanged drug was 422 +/- 31 ng/ml. This level was seen between 2 and 4 h after dosing. 3. Elimination of the ciclazindol from plasma was apparently monexponential with a half-life of approximately 32 h. A large proportion of the drug-related substances in the plasma was unchanged drug. 4. Excretion of radioactivity took place predominantly via the renal route, less than 15% of the dose being recovered in the faeces. The urinary elimination process was apparently monoexponential with a half-life of 28 h. 5. Daily dosing with ciclazindol for 3 weeks did not appear to induce the enzymes of its own metabolism.

Adult↗
PubMed1977

Studies on the absorption and disposition of meptazinol following rectal administration.

1 Rectal administration of the new analgesic drug, meptazinol, resulted in rapid absorption of the compound both in the monkey and in man. Peak plasma levels were observed within 0.5 h of dosing. 2 Absorption of the drug following rectal administration was extensive as shown by the recovery of 65-90% of the dose in the urine. 3 Despite substantial inter-individual variation in the observed maximum plasma concentrations of the drug, it was still evident that concentrations after rectal dosage were considerably higher than when the same dosage was given orally. 4 Elimination of the drug from plasma took place rapidly in an apparently mono-exponential manner in both species. The half-life of elimination in monkeys was 1.25 h and in man 2.0 h.

Adult↗
PubMed1977

The selective action of beta-adrenoceptor blocking drugs and the nature of beta1 and beta2 adrenoceptors.

1 Purified membranes retaining a catecholamine responsive adenylate cyclase have prepared from rabbit heart, lung and (pseudo-pregnant) uterus. 2 These preparations have the characteristics of plasma membranes and both heart and lung respond to beta-adrenoceptor agonists in the order: (+/-)-isoprenaline greater than (-)-noradrenaline greater than (-)-adrenaline greater than (+)-isoprenaline greater than salbutamol. The sensitivity of the adenylate cyclase to beta-adrenoceptor stimulation is improved by pre-treatment of the animals with reserpine and syrosingopine. 3 Dose-ratios for several concentrations of propranolol (non-selective beta-adrenoceptor blocker), practolol and atenolol (cardio-selective beta-adrenoceptor blockers) have been measured on all three membrane preparations. Schild plots of log (dose ratio -1) vs. log dose were virtually coincident for heart and lung with a dissociation constant (Kb) for propranolol very close to the pharmacological value. The ratio of Kb values was 0.65 for practolol and 1.23 for atenolol compared with pharmacological cardio-selectivity ratios (measured on isolated atria and tracheal chain) of 67.6 and 110 respectively. The uterus/heart Kb ratio was 51.5 for atenolol. Inhibition of the uterus by practolol gave a Schild plot with slope significantly less than 1, indicating a different mechanism of action from the heart. 4 Kb values obtained by measuring adenylate cyclase stimulation in chopped tissue (including preparations of bronchial tree and alveolar tissue as well as whole lung) resembled the membrane values rather than those found in whole organs. 5 The results show that the pharmacological selectivity of practolol and atenolol is maintained at the receptor-adenylate cyclase level, at least as far as heart and uterus are concerned, though the smaller selectivity ratios in the biochemical system suggest that receptor differences is not the only factor and that phase distribution of the drug may also be important. Membranes prepared from whole lung show that phase distribution of the drug may also be important. Membranes prepared from whole lung show an overall beta1 response which may simply reflect the predominance of beta1 cell types containing beta1-adrenoceptors over bronchial smooth muscle.

Adenylyl Cyclases↗
PubMed1976

Anaesthetic induction for Caesarean section with propanidid.

Propanidid was used for the induction of anaesthesia at Caesarean section in 50 healthy mothers. All parturients were considered to have normal placental function. Anaesthesia was maintained with nitrous oxide, oxygen, muscle relaxant and controlled ventilation. The patients were tilted laterally with a 15 degrees rubber wedge during the procedure in order to obviate the effects of aorta-caval occlusion. At the time of delivery, arterial blood was drawn from the mother and from the vessels of a double clamped section of umbilical cord, for blood-gas analysis. The results obtained are compared with those previously reported in a similar series anaesthetised with thiopentone, gas, oxygen and relaxant. Maternal blood-gas and acid-base levels were similar in the two groups at delivery. The clinical status of the infants in the present series, as judged by the modified Apgar score at 2 minutes after birth, was satisfactory. Umbilical venous and arterial pH values after propanidid were both 0-054 units (P less than 0-001) less than those following thiopentone; and average base deficits were 3-1 (Uv) and 3-9 (Ua) mEq/litre greater after propanidid (P less than 0-001). Mean oxygen levels in the umbilical cord bloods were 8-0 (Uv) and 3-5 (Ua) mmHg lower (P less than 0-001 & P less than 0-025 respectively) in the propanidid group. Derived oxygen contents was also significantly less than in the previous thiopentone series. (Ma-Uv) and (Ma-Ua) gradients were 0-053 and 0-051 pH units higher after propanidid than that following thiopentone (P less than 0-001). Mean (Ma-Uv) and (Ma-Ua) base deficits were 3-5 and 3-9 mEq/litre greater (P less than 0-001). Five patients offered definite evidence of factual recall, of whom three experienced pain. Propanidid, therefore, appeared to be associated with a greater degree of foetal acidaemia than did thiopentone. In addition, painful factual recall during surgery was encountered in 6 percent of cases. It is concluded that propanidid, although theoretically offering advantages over thiopentone to the obstetric anaesthetist, in practice, did not fulfil this promise.

Anesthesia, Intravenous↗
PubMed1975

Ethrane anaesthesia for caesarean section.

Fifty patients scheduled for elective Caesarean section were anaesthetised with nitrous oxide, oxygen, relaxant, and 0,5 - 1,5% Ethrane. The mothers were tilted laterally throughout the operation. Analysis of the maternal blood gas status before induction and at delivery revealed a mild respiratory alkalosis with an associated metabolic acidosis. The mean modified Apgar score (Apgar minus colour) of the infants 1 minute after delivery, was 7/8. All infants achieved the maximum score at 5 minutes. Blood gas studies on umbilical cord blood indicated a relative lack of fetal acidaemia. The results suggest that Ethrane does not cause significant perinatal depression, and that fetoplacental exchange is well maintaned during anaesthesia. The anaesthetic was well tolerated by the mothers and there were no instances of factual recall, no cardiac arrhythmias were observed, no significant hypotension was encountered and blood loss was average.

Acidosis↗
PubMed1975

Propanidid for anaesthetic induction at Caesarean section.

In 50 healthy mothers scheduled for elective Caesarean section, anaesthesia was induced with propanidid (7 mg/kg body weight). Thereafter, ventilation was controlled with nitrous oxide, oxygen and muscle relaxants. A further dose of propanidid (1 mg/kg body weight) was administered 3 minutes after the initial injection of this drug, as a means of preventing maternal awareness during equilibration with the anaesthetic gas mixture. The acid-base status of the mothers before the induction of anaesthesia, and at delivery, revealed a mild degree of respiratory alkalosis with a compensatory metabolic acidosis. Umbilical cord blood gas results indicated the presence of significant fetal acidosis, both respiratory (mean pCO2 Uv 46,3 torr (SD 11,3) and Ua 54,3 torr (SD 12,0)), and metabolic (mean base excess Uv-9 mEq/l (SD 4,2) and Ua-11,8 mEq/l, (SD 5,0)) in origin. The average umbilical cord blood oxygen tensions were Uv 25,9 torr (SD 10), and Ua 15,4 torr (SD 8,5); mean maternal to fetal base-excess gradients were Ma-Uv 4,1 mEq/l (SD 2,8) and Ma-Ua 6,5 mEq/l (SD 3,5). Five mothers (10%) offered convincing evidence of factual recall during surgery, and 3 of these were aware of pain. Nausea and vomiting occurred in 5 patients and in 4 there were clinical signs of postoperative chest infection. The degree of fetal biochemical asphyxia, and the incidence of maternal awareness during surgery, were significantly greater than previously reported when thiopentone was used for the induction of anaesthesia for Caesarean section. The results obtained are discussed, and the conclusion is drawn that propanidid for anaesthesia appears to offer no advantage over thiopentone in obstetric practice.

Acidosis↗