Derek G. Waller

A qualitative and quantitative study of the incidence, features and aetiology of near death experiences in cardiac arrest survivors

AIMnTo carry out a prospective study of cardiac arrest survivors to understand the qualitative features as well as incidence, and possible aetiology of near death experiences (NDEs) in this group of patients.nnnMETHODnAll survivors of cardiac arrests during a 1 year period were interviewed within a week of their arrest, regarding memories of their unconscious period. Reported memories were assessed by the Greyson NDE Scale. The postulated role of physiological, psychological and transcendental factors were studied. Physiological parameters such as oxygen status were extracted from the medical notes. Patients religious convictions were documented in the interviews and hidden targets were used to test the transcendental theories on potential out of body claims. Those with memories were compared to those without memories.nnnRESULTSn11.1% of 63 survivors reported memories. The majority had NDE features. There appeared to be no differences on all physiological measured parameters apart from partial pressure of oxygen during the arrest which was higher in the NDE group.nnnCONCLUSIONSnMemories are rare after resuscitation from cardiac arrest. The majority of those that are reported have features of NDE and are pleasant. The occurrence of NDE during cardiac arrest raises questions about the possible relationship between the mind and the brain. Further large-scale studies are needed to understand the aetiology and true significance of NDE.

Comparison of radionuclide estimation of glomerular filtration rate using technetium 99m diethylenetriaminepentaacetic acid and chromium 51 ethylenediaminetetraacetic acid

Simultaneous measurements of the clearance rates of technetium 99m diethylenetriaminepentaacetic acid (99mTc-DTPA) and chronium 51 ethylenediaminetetraacetic acid (51Cr-EDTA) were performed in 30 patients with a range of renal function (glomerular filtration rates between 9 and 120 ml/min). Using multiple blood samples, the two clearance values correlated well (r=0.991, standard error 3.9 ml/min), but DTPA clearance was systematically higher by 7.6%. For each radiopharmaceutical, an equation was derived to correct clearance values obtained using only plasma samples taken at 2 and 4 h for the systematic error inherent in this technique compared with analysis of the complete plasma concentration-time curve. The root mean square error remaining after application of these equations was 1.9 ml/min for both the EDTA and DTPA data. The corresponding errors obtained using the equation derived by Brochner-Mortensen for EDTA plasma clearance were 2.2 ml/min and 1.9 ml/min, respectively, these values were not significantly different from those obtained using the equations derived in this study.

The influence of levodopa on gastric emptying in healthy elderly volunteers.

SummaryParacetamol absorption and 99Tc-DTPA measurements have been used to determine the influence of levodopa on gastric emptying in 8 healthy elderly volunteers.In the absence of levodopa 7 subjects showed a rapid gastric emptying pattern by gamma-camera and a single major peak in the plasma concentration-time curve of paracetamol. One subject showed two rapid phases of gastric emptying separated by a period of negligible emptying and had 2 separate peaks in the paracetamol plasma concentration-time curve.In the presence of levodopa, the gamma-camera data for 6 subjects showed a pattern of gastric emptying consisting of 2 rapid phases separated by a plateau. In each case secondary peaks in the plasma concentration-time curve of paracetamol occurred about 30 min after the end of the plateau. The time to 90% emptying on the gamma scan was increased significantly from 40 min to 65 min in the presence of levodopa.Comparison of the present data with those reported previously indicates that levodopa affects gastric emptying in the both elderly and young volunteers to a similar extent.

Lithium and the kidney: an update

It is a little over a decade since Hestbech et al. (1977) reported histological changes in renal biopsy specimens taken from patients who had been treated with lithium. The more recent studies are considered in this review and recommendations for clinical practice are offered

Effect of food and activity on the reproducibility of isotopic GFR estimation.

The reproducibility of the plasma clearance of 99Tcm DTPA was studied in 26 patients under standardized conditions with the subject fasting and at rest. The coefficient of variation of duplicate measurements in patients with glomerular filtration rates (GRFs) ranging from 11-103 ml min-1 was 8%. Mean GFR following a breakfast containing 670 kcal and 31 g protein was increased significantly from 40.7 +/- 28.1 ml min-1 to 43.6 +/- 30.8 ml min-1. When fasted but permitted free exercise there was no consistent trend in GFR but the coefficient of variation of duplicate estimates increased significantly to 12.1%. It is recommended that routine GFR measurement should be carried out fasting or following a light diet with restricted activity.

The influence of two types of meal on the pharmacokinetics of a modified-release formulation of nifedipine (Adalat Retard)

AbstractObjective: The effect of two different types of meal on the absorption of a modified-release formulation of nifedipine (Adalat Retard) was studied.nn Results: A light breakfast produced a delay in gastric emptying (indicated by the rate of paracetamol absorption) compared with the fasting state, but did not alter the tmax or Cmax for nifedipine significantly. After a cooked breakfast, there was less delay in gastric emptying and again no delay in tmax for nifedipine. However, the Cmax for nifedipine was significantly higher than in the fasting state. Neither meal influenced the bioavailability of nifedipine.nn Conclusion: The results suggest that the nature of the meal has an important influence on the absorption profile of this formulation of nifedipine, probably by an effect on its dissolution. This study illustrates the importance of considering the effects of different types of meal before concluding that food does not affect the pattern of drug absorption.

Measurement of glomerular filtration rate with 99mTc-DTPA: A comparison of gamma camera methods

A comparison has been made between three gamma camera methods for estimation of glomerular filtration rate (GFR) using 99mTc-DTPA in a group of 27 patients with widely different renal function. Plasma clearance of 99mTc-DTPA by multiple blood sampling was used as the reference. Percentage uptake of chelate in the bladder and kidneys at 20 min after injection gave the lowest standard error of 8.0 ml/min. Techniques using early uptake of isotope in the kidneys at 2 min after injection gave less accurate estimates. Correction for the vascular activity in the renal region of interest improved the results for the 2 min uptake technique. Gamma camera techniques provide rapid estimates of GFR which are less accurate than those obtained by plasma clearance of labelled chelate.

81mKr equilibrium radionuclide ventriculography for the assessment of right heart function

Right heart81mKr equilibrium radionuclide ventriculography was used to derive right ventricular ejection fraction (RVEF) in 12 healthy male volunteers. Anatomical lung subtraction using99mTc-MAA perfusion scintigraphy was compared with conventional background correction and the effect of imaging projection on the techniques of image analysis evaluated. Both intra and inter observer variability were reduced by anatomical lung subtraction when compared to conventional background correction. In the right anterior oblique (RAO) projection, background corrected RVEF was lower than lung subtracted RVEF - 0.544 ±0.05 and 0.612±0.08 (mean ± SD) (P<0.02). Lung subtracted RVEF in the anterior projection was lower than that with background correction (P<0.05) and lower than lung subtracted RVEF in the RAO projection (P < 0.001). We conclude that optimal separation of right heart structures is achieved in the RAO projection and that reproducibility of the analytical technique is improved by anatomical lung subtraction.

Treatment and prevention of ventricular fibrillation: Are there better agents?

Ventricular fibrillation occurs in diverse clinical settings and differing pathogenic mechanisms make it unlikely that a single drug treatment will be universally effective. Drugs may be used as an adjunct to electrical defibrillation in circulatory collapse, to prevent recurrence after successful resuscitation or as a prophylactic treatment in high-risk patients. Various drugs are available for intravenous administration in the acute management of ventricular fibrillation and the choice among them will depend on several factors: proven efficacy, comparative efficacy and their safety including haemodynamic effects. Although several drugs have been shown to suppress ventricular ectopic beats and ventricular tachycardia, ventricular fibrillation and sudden death can occur despite abolition of these less serious ventricular arrhythmias [ 11. Animal studies have suggested the concept of separate ‘antiarrhythmic’ and ‘antilibrillatory’ action of drugs. Drugs with antifibrillatory properties increase the energy threshold for production of ventricular fibrillation while many conventional antiarrhythmic drugs have no effect [2,3]. However, an effect on fibrillation threshold does not necessarily indicate a reduction in energy requirements for successful electrical defibrillation. The major criticism of such models is that the substrate for generation of ventricular fibrillation is usually different in clinical ventricular fibrillation. Lignocaine and bretylium are the current standard drugs for management of acute ventricular fibrillation. This review examines the claims of other antiarrhythmic drugs to supplant or supplement these agents (Table I). Figure 1 shows a representation of the normal cardiac action potential. Initial depolarisation (phase 0) is achieved by rapid influx of sodium ions which is slowed by agents which belong to class 1 of the Vaughan Williams and Singh classification. These compounds are subdivided by their effect on the duration of the action potential: Class la drugs lengthen it, Class lb shorten it, while Class lc have no effect. Class II drugs are the beta blockers which have no direct effect on the action potential but antagonise myocardial stimulation by catecholamines. The Class III agents delay phase 3 repolarisation and prolong the duration of the action potential. Class IV drugs are calcium channel blockers which reduce the influx of calcium into cells, in particular reducing the spontaneous depolarisation of phase 4 in the atrio-

Right ventricular function at rest and during submaximal exercise assessed by 81Krm equilibrium ventriculography in normal subjects

81Krm equilibrium ventriculography was used to study right ventricular function in 37 healthy male volunteers. Anatomical lung subtraction using 99Tcm lung perfusion scintigraphy was compared with conventional background correction in the calculation of resting right ventricular ejection fraction (RVEF). Resting RVEF was significantly greater following anatomical lung subtraction than that using background correction (0.59 +/- 0.06 versus 0.55 +/- 0.05). The exercise response of the normal right ventricle was defined in 23 subjects during exercise. Right ventricular ejection fraction showed a progressive increase during graded submaximal exercise (0.55 +/- 0.05 at rest, 0.60 +/- 0.05 at 50 W and 0.66 +/- 0.05 at 100 W). Right heart 81Krm equilibrium ventriculography is well suited to the evaluation of right ventricular function at rest and during exercise. The absolute value of RVEF will however be dependent upon the method of image analysis.