Pressure In Cats Research Articles

Effect of Pneumatic Suction Ring Placement on Intraocular Pressure in Cats

Purpose: To determine the effect of placing a pneumatic suction ring on intraocular pressure (IOP) in the cat and to design an improved method to generate a stable elevation of IOP. Methods: A pneumatic suction ring was applied to the eye in cats while the IOP was monitored. Three groups of animals (10 per group) were used. A vacuum pressure of 450 mbar was applied in one step to eyes of group 1 (anesthetized) and to group 2 (euthanized) cats. In group 3 (anesthetized) cats, an initial vacuum pressure of 250 mbar was applied, followed by a vacuum of slowly increasing pressure at a rate of 5 mbar/min for a total of 40 min to 450 mbar. Results: After the one-step application of a vacuum (450 mbar) to the eyes of anesthetized cats (group 1), IOP peaked within the first minute from a basal value of 25 ± 2 mm Hg (mean ± SD) to 90 ± 7 mm Hg. It then rapidly decreased to 69 ± 2 mm Hg 5 min later and continued to decrease to 39 ± 4 mm Hg 40 min later. This sharp peak and decline of IOP were also observed in eyes of euthanized cats (group 2). The basal IOP of these eyes was 8 ± 1 mm Hg. It rose to 18 ± 2 mm Hg immediately after the application of vacuum pressure (450 mbar) and returned to the basal level 5 min later. In contrast, the eyes of group 3 receiving an initial vacuum of 250 mbar followed by a 5 mbar/min vacuum increment exhibited a rapid increase in IOP and a very stable plateau (mean IOP = 62–68 mm Hg), lasting the whole study period (40 min). Conclusion: IOP after a one-step application of a vacuum via a pneumatic suction ring is self-adjusting and declines rapidly over time. This decline in IOP can be overcome by a supplementary increment in vacuum pressure.

Effects of 0.005% latanoprost solution on intraocular pressure in healthy dogs and cats.

To evaluate effects of daily topical ocular administration of latanoprost solution on intraocular pressure (IOP) in healthy cats and dogs. 9 domestic shorthair cats and 14 dogs. Latanoprost solution (0.005%) was administered topically to 1 eye (treated) and vehicle to the other eye (control) of all animals once daily in the morning for 8 days. Intraocular pressure was measured twice daily for the 5 days preceding treatment, and IOP, pupillary diameter, conjunctival hyperemia, and blepharospasm were measured 0, 1, 6, and 12 hours after the first 4 treatments and 0 and 12 hours after the final 4 treatments. Measurements continued twice a day for 5 days after treatment was discontinued. Aqueous flare was measured once daily during and for 5 days after the treatment period. Intraocular pressure and pupillary diameter were significantly decreased in the treated eye of dogs, compared with the control eye. Mild conjunctival hyperemia was also detected, but severity did not differ significantly between eyes. Blepharospasm and aqueous flare were not detected in either eye. Intraocular pressure in cats was not significantly affected by treatment with latanoprost. However, pupillary diameter was significantly decreased in the treated eye, compared with the control eye. Conjunctival hyperemia, aqueous flare, and blepharospasm were not detected in either eye. Once-daily topical ocular administration of latanoprost solution (0.005%) reduced IOP in healthy dogs without inducing adverse effects but did not affect IOP in healthy cats. Latanoprost may be useful for treating glaucoma in dogs.

Diurnal Variations of Blood Pressure in Cats

Blood pressure (BP) was analyzed invasively using the telemetry system in unanesthetized, unrestrained healthy adult mongrel cats. After surgical implantation of a telemetry transmitter, BP was transiently elevated due to the invasive nature of the surgery, but it was gradually decreased. BP was largely stabilized seven to ten days postsurgery. Once BP was settled, systolic, diastolic and mean BPs(2) were obtained at 5-min intervals in individual cats. Hourly averages of these BP values revealed a diurnal variation with two peaks at 8:00 and 19:00. We also found that BP was significantly higher when cats were active compared to when they were sleeping or at rest (p<0.05). The average 24-hr BP in 20 healthy cats was 118.4+/-11.0 (systolic), 78.0+/-8.7 (diastolic) and 94.8+/-9.5 mmHg (mean) by the telemetry system.

Evaluation of the Effect of Pleural Effusion on Central Venous Pressure in Cats

This study was undertaken to determine if pleural effusion (PEF) increases central venous pressure (CVP) in cats, to define any relationship between volume of PEF and CVP, and to ascertain the significance of CVP alterations in cats having PEF and suspected right heart failure (RHF). CVP was measured from a jugular vein before (CVPpre) and after (CVPpost) bilateral thoracentesis in 9 cats with naturally occurring PEF and under experimental conditions in 3 spontaneously breathing anesthetized cats receiving graded intrathoracic infusion of saline. Volumes of introduced and recovered fluid were recorded. A significant decrease occurred in CVP after thoracentesis in cats with naturally occurring PEF (mean difference, 4.5 cm H2O; range, 0–7.0 cm H2O, P &gt; .005). The magnitude of change in CVP was constant (r = 0.36, P &gt; .05) over the range of volumes recovered (range, 95–450 mL or 16.4–90 mL/kg). Five cats had CVPpre suggestive of RHF (range, 8.16–20.4 cm H2O). After thoracentesis, RHF was ruled out in 1 cat (CVPpost, 4.08 cm H2O) and the CVP declined but remained abnormally high (9.52 cm H2O) in 1 cat with a mediastinal mass. In 2 cats with confirmed RHF (CVPpre, 20.4 and 16.3 cm H2O), CVP decreased after thoracentesis but remained abnormally high (CVPpost, 14.96 and 10.88 cm H2O). In 1 cat with noncardiogenic PEF and inadequate removal of fluid, CVPpost (8.16 cm H2O) did not decrease. Experimentally, a positive linear relationship was observed between CVP and volume of PEF. The threshold volume required to increase CVP (17 mL/kg) approximated that suggested by clinical observation (22 mL/kg). PEF increases CVP and can cause abnormally high CVP in the absence of RHF.

Evaluation of the effect of pleural effusion on central venous pressure in cats.

This study was undertaken to determine if pleural effusion (PEF) increases central venous pressure (CVP) in cats, to define any relationship between volume of PEF and CVP and to ascertain the significance of CVP alterations in cats having PEF and suspected right heart failure (RHF). CVP was measured from a jugular vein before (CVPpre) and after (CVPpost) bilateral thoracentesis in 9 cats with naturally occurring PEF and under experimental conditions in 3 spontaneously breathing anesthetized cats receiving graded intrathoracic infusion of saline. Volumes of introduced and recovered fluid were recorded. A significant decrease occurred in CVP after thoracentesis in cats with naturally occurring PEF (mean difference, 4.5 cm H2O; range, 0-7.0 cm H2O, P < .005). The magnitude of change in CVP was constant (r = 0.36, P > .05) over the range of volumes recovered (range, 95-450 mL or 16.4-90 mL/kg). Five cats had CVPpre suggestive of RHF (range, 8.16-20.4 cm H2O). After thoracentesis, RHF was ruled out in 1 cat (CVPpost, 4.08 cm H2O) and the CVP declined but remained abnormally high (9.52 cm H2O) in 1 cat with a mediastinal mass. In 2 cats with confirmed RHF (CVPpre, 20.4 and 16.3 cm H2O), CVP decreased after thoracentesis but remained abnormally high (CVPpost, 14.96 and 10.88 cm H2O). In 1 cat with noncardiogenic PEF and inadequate removal of fluid, CVPpost (8.16 cm H2O) did not decrease. Experimentally, a positive linear relationship was observed between CVP and volume of PEF. The threshold volume required to increase CVP (17 mL/kg) approximated that suggested by clinical observation (22 mL/kg). PEF increases CVP and can cause abnormally high CVP in the absence of RHF.

Paradoxical sympathetic nerve response to baroreceptor reflex activation

Spectral analysis revealed an enhancement of cardiac-related postganglionic sympathetic nerve discharge (SND) in response to elevated blood pressure in cats. Most of the enhancement occurred at blood-pressure levels above which coherence of SND to the arterial pulse at the frequency of the heart beat became maximal. This raises the possibility that the enhancement is due to mechanisms other than improved phase locking of SND to pulse-synchronous baroreceptor afferent nerve activity.

Systemic Hypertension and Its Management

The pathophysiology of hypertension in dogs and cats, the methods available to monitor blood pressure, and the signs and treatment of hypertension are reviewed. Clinical signs of hypertension are usually referable to target organ damage, most notably in ophthalmic, renal, and cardiovascular tissues, which have a rich arteriolar supply. Blood pressure should be measured in any animal with renal disease, hyperthyroidism, hyperadrenocorticism, retinal detachment or hemorrhage, hyphema, or echocardiographically determined cardiac hypertrophy. All cats with acquired cardiac murmur should also be evaluated for hypertension. Antihypertensive medication should be administered if the indirect blood pressure in cats is consistently over 170/100 mmHg, or if the indirect blood pressure in dogs is greater than 180/100 mmHg.

Evaluation of an oscillometric blood pressure monitor on anesthetized cats and the effect of cuff placement and fur on accuracy.

(1) To determine the usefulness of one specific oscillometric monitor for making indirect measurements of arterial pressure in cats. (2) To determine the difference between two specific cuff placement sites. (3) To determine if clipping the hair beneath the cuff has an affect on the accuracy of oscillometric blood pressure determination. Prospective study comparing the accuracy of the Datascope Passport (Datascope Corp, Paramus, NJ) with concurrent invasive measurements. Six anesthetized domestic felines weighing 4.5 to 5 kg. The direct arterial pressure was measured using a cannula placed in the right common carotid artery. Oscillometric cuffs of appropriate size were placed on both thoracic limbs distal to the elbow and both pelvic limbs distal to the stifle. The hair in the areas of cuff placement on the right limbs was clipped circumferentially. Measurements of systolic, diastolic, and mean arterial pressure (MAP) were taken for each site during normotension, hypotension, and hypertension. Comparisons between indirect and direct measurements were made using a parametric analysis of method comparison. No significant differences were noted when the clipped limbs were compared with the corresponding limbs which were left unclipped (P > .378) or when the thoracic limb measurements were compared with those of the pelvic limb (P > .088). There were significant differences (P < or = .002) between the two pressure measurement methods for the systolic, diastolic, and mean arterial pressures over all three pressure ranges. The Datascope Passport did not accurately estimate the invasively measured arterial pressure. Use of noninvasive blood pressure monitoring equipment is increasing in use in veterinary medicine, and the accuracy of one specific monitor is reported.

Effects of certain vasoactive agents on the long-term pattern of blood pressure, heart rate, and motor activity in cats

Abstract Objective To determine whether a diurnal pattern exists in cardiovascular variables and motor activity, and whether pharmacologic agents that decrease (angiotensin converting enzyme inhibitor) or increase (Nω-nitro-L-arginine methyl ester [L-NAME]) blood pressure alter the pattern. Animals 6 clinically normal cats. Procedure Radiotelemetric implants were used to measure systemic arterial pressure, heart rate, and motor activity in conscious cats maintained in cages. Measurements were obtained during absence of treatment (control), treatment with dietary salt restriction plus an inhibitor of angiotensin converting enzyme (2.5 mg of lisinopril, PO, daily) and treatment with an inhibitor of nitric oxide production (0.1% L-NAME in the drinking water). Results A diurnal pattern in arterial pressure and motor activity was observed, with highest values obtained during presence of laboratory personnel. Mean values for arterial pressure obtained during light hours varied from those obtained during darkness (P &lt; 0.05), but by &lt; 3 mm of Hg. Dietary sodium restriction did not have an appreciable effect on arterial pressure, but the combined administration of a low sodium diet plus lisinopril decreased (P &lt; 0.05) measured indices of arterial pressure. Administration of L-NAME increased arterial pressure (P &lt; 0.05) and altered its diurnal pattern. Conclusions Although a diurnal pattern of arterial pressure was observed, variations were mostly associated with presence of human beings. Administration of L-NAME, but not lisinopril, altered this diurnal pattern. Clinical Relevance Factors that modify arterial pressure may alter the diurnal pattern of cardiovascular variables. In measuring arterial pressure in cats, the effects of human contact may artifactually increase such variables. (Am J Vet Res 1997;58:647–652)

Responses of neurons of the preoptic region to an increase in systemic blood pressure in cats

Responses of neurons of the lateral and medial parts of the preoptic regionRPO (LPO andMPO, respectively) and the supraoptic nucleus (SO) of the hypothalamus to an increase in systemic blood pressure were studied in acute experiments on ketamine-anesthetized cats. The blood pressure increase resulted from the injection of a 0.002% phenylephrine hydrochloride solution in the femoral vien. Responses of theRPO neurons to suprathreshold pressor stimulation were monophasic activation (48% of units), monophasic inhibition (10%), or two-phase activational-inhibitory complex (14%). The rest of the neurons did not respond to the systemic pressure increase. Pressor stimulations evoked the responses only of the first and third type inMPO neurons, and only of the first and second type inLPO neurons, whileSO neurons generated responses only of the first type. Hysteresis of a varying degree was manifested in the changes of neuronal spike activity accompanying shifts of the systemic pressure. In some neurons there was no strict correlation between the pressor effect and the onset of neuronal response. Osmosensitivity of a part of neurons was tested. The responses of most of theRPO andSO neurons to pressor influences and infusions of hypertonic saline were of similar direction, whereas responses to infusions of hypotonic saline were opposite.

Central muscarinic M-1 receptors in the regulation of the arterial blood pressure in cats

Central muscarinic M-1 receptors in the regulation of the arterial blood pressure in cats

Effects of LY267108, an erythromycin analogue derivative, on lower esophageal sphincter function in the cat

Background/Aims: Erythromycin (EM-A) and some of its analogues stimulate gastrointestinal smooth muscle contractions. Because gastroesophageal reflux disease (GERD) in humans is in part caused by a reduction in lower esophageal sphincter (LES) pressure, the aim of this study was to investigate the effect of LY267108 (an EM-A analogue with no significant antimicrobial activity) on LES function. Methods: In ketamine-anesthetized cats, LES pressure was recorded using a Dent sleeve. Results: In cats, LY267108 increased LES pressure, as did motilin and EM-A. Neither LY267108, EM-A, nor motilin altered LES relaxation in response to a swallow. LY267108 increased LES pressure in cats in which the basal LES pressure was lowered experimentally by perfusing the distal esophagus with HCl (0.1 N for 3 days) or following isoproterenol (3.0 μg/ kg intravenously). In summary, LY267108 increases LES pressure in normal cats, did not affect the relaxation of the LES in response to a swallow, and increases LES pressure in animals with an experimentally induced decrease in LES pressure. Conclusions: The results suggest that LY267108 may be useful in treating GERD because of its ability to increase LES pressure and thus present a barrier for gastroesophageal reflux.

Intravenous NBQX inhibits spontaneously occurring sympathetic nerve activity and reduced blood pressure in cats

2,3-Dihydroxy-6-nitro-7-sulfamoyl-benzo( F)quinoxaline (NBQX) has been demonstrated to be a specific and competitive non-N- methyl- D-aspartate (non-NMDA) glutamate receptor antagonist. Our previous data obtained with the NMDA receptor antagonist MK-801 indicate that blockade of the NMDA receptor affects blood pressure. The purpose of this study was to determine whether the same is true with blockade of the non-NMDA receptor. For this purpose we administered three doses of NBQX (1, 3 and 10 mg/kg i.v.) to anesthetized, artificially ventilated and paralyzed cats while monitoring spontaneously occurring cardiac sympathetic nerve activity, arterial blood pressure and heart rate. The 1 mg/kg dose of NBQX i.v. reduced both sympathetic nerve activity (−29 ± 7%, P < 0.05, n = 4) and blood pressure (−27 ± 5 mm Hg, P < 0.05). Injection of 3 mg/kg NBQX produced a greater decrease in sympathetic nerve activity (−78 ± 11%, P < 0.01, n = 8) and mean arterial pressure (−47 ± 5 mm Hg) and also reduced heart rate (−11 ± 2 beats/min, P < 0.01). The depressant effects of NBQX on sympathetic nerve activity, blood pressure and heart rate were similar regardless of whether activity was recorded from pre- or postganglionic cardiac nerves, or from animals subjected to baroreceptor denervation. Intravenous injection of a total dose of 10 mg/kg NBQX completely inhibited sympathetic nerve activity (−100 ± 0%, P < 0.05, n = 3) and this effect was associated with reductions in mean arterial pressure (−49 ± 10 mm Hg, P < 0.05) and heart rate (−30 ± 6 beats/min, P < 0.05). The data indicate that NBQX i.v. decreases sympathetic nerve activity, blood pressure and heart rate in a dose-dependent manner and that the primary site of these effects is likely in the central nervous system.

Effects of intracisternally injected serotonin on cerebral blood flow in cats during winter and summer, and after dark exposure.

This investigation reports on two experiments: (a) The examination of the effects of intracisternally injected serotonin on cerebral blood flow and systemic pressure in cats during winter (1/10-3/7) and summer (7/6-9/3) at a latitude of 39' 40", and (b) the effects of similarly injected serotonin on the same parameters in 11 cats after exposure to 3 days of continuous darkness during the summer months. Serotonin (5 mg) injected intracisternally produced significant decreases in cerebral blood flow and systemic pressure that lasted from 60 to 180 min after injection. Blood flow decreases, expressed as percentage change from baseline, seen during winter (n = 24) periods were significantly greater [analysis of variance (ANOVA), p < 0.02] from decreases seen during summer (n = 25) periods. Following serotonin injection, systemic pressure decreases between the winter and summer cats were not significantly different. Eleven summer cats were subjected to 3 days of continuous darkness before being injected with serotonin. Blood flow decreases in the dark-exposed cats were significantly (p < 0.05) greater than those seen in normal light-exposed cats, whereas systemic pressure changes were not different. These studies suggest that the seasonal photoperiod may affect the sensitivity of cerebral vessels to intracisternally injected serotonin in cats.

Effects of selective obstruction of intracranial venous sinuses on systemic arterial pressure, cerebral perfusion pressure, intracranial pressure and intrasinal pressure in cats

In order to evaluate the safe ligation time and sites of dural venous sinuses during neurosurgical operation, systemic arterial pressure(SAP), cerebral perfusion perssure(CPP), intracranial pressure (ICP) and intrasinal pressure(ISP) were measured in cats through neuromonitor before and after obstruction of anterior 1/3, middle 1/3, posterior 1/3 of the superior sagittal sinus and the results were as follows. There were no significant increases of pressures after obstruction of anterior 1/3 of the superior sagittal sinus. In the obstructed middle 1/3 of the superior sagittal sinus group, significant increases were seen un the m-SAP within 2, 4 and 6 minutes, the m-ICP within 2-7 minutes, the m-ISP within 1-4 minutes after obstruction. In the obstructed posterior 1/3 of the superior sagittal sinus group, there were significant increases of m-SAP within 2, 4 and 6 minutes, the m-ICP within 2-7 minutes, the m-ISP within 1-3 minutes. In the obstructed Torcular Herophili group, there were significant increases of the m-SAP within 1-2 and 4-7 minutes, the m-ICP within 3-6 minutes and the m-ISP within 1-7 minutes and less significant dercreases of the m-CPP within 5-7 minutes after obstruction. In the obstructed right transverse sinus group, significant increases of the m-ICP and the m-ISP were seen within 1-7 minutes after obstruction, there were no remarkable changes in the obstructed left transverse sinus group.

Evaluation of the Doppler ultrasonic method of measuring systolic arterial blood pressure in cats

Summary The accuracy of the Doppler technique for indirect systolic blood pressure measurement was assessed in 16 anesthetized cats. Eight cats were anesthetized with isoflurane and 8 were anesthetized with halothane. Anesthetic depth and mode of ventilation were varied to obtain a wide range of arterial blood pressure. A Doppler transducer was placed on the palmer surface of the left forelimb over the common digital branch of the radial artery to detect blood flow, and a blood pressure monitoring cuff with a width 37% the limb circumference was placed half way between the elbow and the carpus. To enable direct arterial pressure measurements, the left femoral artery was catheterized and the blood pressure waveforms recorded simultaneously. Systolic blood pressure measured by use of the Doppler ultrasonic technique was significantly lower than that obtained from the femoral artery catheter. Using linear regression, we determined a clinically useful calibration adjustment for Doppler indirect blood pressure measurement in cats: femoral systolic pressure = Doppler systolic pressure + 14 mm of Hg.

Pancreatic ductal and interstitial pressures in cats with chronic pancreatitis

We investigated the etiology of interstitial hypertension in chronic pancreatitis by examining the relationship between pancreatic ductal and interstitial pressures in cats. The main pancreatic duct was cannulated in the tail of the gland and perfused at 1, 2, or 5 ml/hr, to simulate pancreatic secretion. Intraductal and interstitial pressures were measured in four groups of animals: (1) normal cats; (2) normal cats after acutely narrowing the main duct to 25% of its original diameter; (3) normal cats after encasing the body and tail in a rigid latex capsule; and (4) cats with chronic pancreatitis created by narrowing the main duct five weeks earlier. Duct perfusion increased intraductal pressure in all of the cats, but significantly more in groups 2, 3, and 4 compared to group 1. Pancreatic interstitial pressure was unchanged by duct perfusion in groups 1 and 2, but increased in groups 3 and 4. We concluded that the compliant tissue of the normal pancreas expanded to effectively dissipate the increase in duct pressure associated with duct perfusion. In chronic pancreatitis, the inelastic parenchyma and capsule limited the distensibility of the gland, which resulted in elevated interstitial pressures during duct perfusion.

PRESSURE TRANSFER BETWEEN THE PERILYMPH AND THE CEREBROSPINAL FLUID COMPARTMENTS IN CATS

This is a review of our studies of the labyrinthine fluid pressure in cats subjected to pressure changes in the middle ear (implosive routes) and the cerebrospinal fluid compartment (explosive routes) as well as to changes in vascular and ambient pressures. The perilymph, cerebrospinal fluid (CSF), middle ear, venous and arterial pressures were measured with the cochlear aqueduct (CA) patent as well as surgically blocked. Experiments on explosive pressure changes revealed that the perilymph pressure was regulated by the CSF in case of CA patency. The CSF influence was dominant enough to obscure any direct effect on the labyrinth from other sources. With the CA obstructed the CSF influence on the labyrinth was apparently mainly via the endolymphatic sac and duct although limited and much delayed. Systemic arterial pressure changes had a pronounced influence on the perilymph pressure, but this effect was revealed only when the CSF influence was reduced by CA obstruction. Experiments on implosive and ambient pressure changes suggested that there was no fundamental difference in the perilymph response to equivalent levels of implosive versus hypobaric pressure. Three factors determined the effect of implosive and hypobaric pressure: the patency of the CA, the rate of the pressure change, and the eustachian tube function.

Paraben Preservatives Do Not Increase Intracranial Pressure in Cats

It has been hypothesized recently that succinylcholine-associated increases in intracranial pressure (ICP) are caused by the paraben preservatives contained in multidose vials. We tested that hypothesis in a standard feline model to determine the effects on ICP of equal-volume injections of preservative-free succinylcholine, succinylcholine with preservatives from multi-dose vials that contain both propylparaben and methylparaben, these preservatives alone at five times the dose contained in the succinylcholine, and normal saline. The preservatives alone increased ICP by 0.08 +/- 0.08 mmHg (+/- standard error; not significant). Normal saline had no effect on ICP. Preservative-free succinylcholine and succinylcholine with preservatives increased ICP by 4.2 +/- 0.10 and 3.8 +/- 0.07 mmHg respectively (P less than 0.01 compared to the preservatives alone and normal saline). The 99% upper confidence limit for the increase in ICP induced by the preservatives alone was 0.42 mmHg. This result suggests that parabens do not cause or substantially augment the ICP increase associated with succinylcholine administration.

Effects of thiopentone, propofol, alphaxalone-alphadolone, ketamine and xylazine-ketamine on lower oesophageal sphincter pressure and barrier pressure in cats

The anaesthetic induction agents thiopentone, propofol and alphaxalone-alphadolone were administered to cats intravenously and ketamine and xylazine-ketamine-atropine were administered intramuscularly in order to determine their effects on gastric pressure, lower oesophageal sphincter pressure, and barrier pressure. Manometric measurements were made with a non-perfused catheter tip pressure transducer. All the anaesthetic induction agents decreased the tone of the lower oesophageal sphincter but the reduction was least with ketamine. Lower oesophageal sphincter tone was significantly higher in cats anaesthetised with either xylazine-ketamine-atropine or propofol than in cats anaesthetised with either thiopentone or alphaxalone-alphadolone. Despite a higher gastric pressure in the cats anaesthetised with ketamine rather than with the other drugs except propofol, the barrier pressure was also significantly higher in cats anaesthetised with ketamine than in cats anaesthetised with any of the other drugs except xylazine-ketamine-atropine. The risk of gastrooesophageal reflux seemed to be higher with alphaxalone-alphadolone than with thiopentone if the lower oesophageal sphincter pressure and gastric pressure are used as indicators of likely reflux.