High Frequency Electrocardiography of Three Orthogonal Leads in Dogs During a Coronary Artery Occlusion

The ability to detect cardiac ischemia in dogs was studied using high frequency electrocardiography and signal averaging technique. Ischemia was induced via a balloon occluding cuff placed around the left anterior descending coronary artery. Three surface orthogonal bipolar leads (X, Y, and Z) were recorded prior to inflation of the occluding cuff. The cuff was then inflated, causing a complete occlusion of the coronary artery. The surface electrocardiogram was recorded before and during ligation and during reperfusion. The recorded waveforms were divided info sequential 10–15 second segments representing diferent stages of the ischemic state and were aligned using cross-correlation scheme, averaged and band pass filtered between 150–250 Hz. Analysis of the filtered high frequency QRS complexes revealed that coronary ligation was accompanied by changes in waveform morphology including the appearance of zones of reduced amplitude. In seven out of ten experiments reduced amplitude zones were absent before the ligation, present during the occlusion and absent following reperfusion. In two experiments, reduced amplitude zones that were present prior to ligation became wider during occlusion. In one experiment no reduced amplitude zone was present during any stage of the experiment. Such zones may represent slow conduction in regions of the heart rendered ischemia during coronary Iigation. Therefore, the morphology of the high frequency QRS complex, as determined by analysis of the signal averaged electrocardiogram, may provide useful information regarding the presence of myocardial ischemia.     

A Plethora of Cardiac Chloride Conductances: Molecular Diversity or a Related Gene Family

Molecular Basis of Cardiac CI^? Channels. Recent electrophysiologic studies have provided evidence suggesting that as many as six different CI^? conductances can be identified in the sarcolemma of cardiac myocytes isolated from various animal species and areas of the heart. These include CI^? conductances activated by stimulation of protein kinase A, protein kinase C, extracellular ATP, intracellular Ca²⁺, membrane stretch, and a basally active CI^? conductance. Many basic biophysical and pharmacologic properties of these channels are presently unknown, and the only molecular information presently available suggests that the cAMP-activated CI^? conductance is due to cardiac expression of an isoform of the cystic fibrosis transmembrane conductance regulator (CFTR) CI^? channel normally found in epithelial cells. We used the polymerase chain reaction (PCR) to amplify four distinct regions corresponding to the cardiac CFTR gene product from several cardiac tissues to determine if the molecular distribution of CFTR matches the distribution of cAMP-dependent CI^? channels in native myocytes. Amplification of regions corresponding to the first nucleotide binding domain (NBD1), transmembrane segments (TS) VII-XII, and the regulatory (R) domain showed a precise correlation to tissues that electrophysiologically exhibit sarcolemmal cAMP-dependent CI^? channels, whereas region TS I-VI exhibited a distribution independent of the presence of cAMP-dependent CI^? channels. Since the TS I-VI region of the CFTR gene product is believed to comprise the pore region of the channel, we propose that one explanation for the anomalous expression of this region of CFTR in cardiac tissues that do not exhibit cAMP-dependent CI^? currents but do exhibit other types of macroscopic CI^? currents may be sequence homology in a molecularly conserved pore region common to different types of cardiac CI^? channels.     

Self-monitoring cognitive performance during sleep deprivation: effects of modafinil,d-amphetamine and placebo

Self-monitoring refers to the ability to assess accurately one's own performance in a specific environment. The present study investigated the effects of the stimulating drugs modafinil (300 mg) and d-amphetamine (20 mg) on the ability to self-monitor cognitive performance during 64 h of sleep deprivation (SD) and sustained mental work. Two cognitive tasks were investigated: a visual (perceptual) judgment task and a complex mental addition task. Subjects in the placebo condition displayed marked circadian and SD effects on cognitive task performance but their self-monitoring was substantively undisturbed by SD. Subjects performing under the influence of d-amphetamine likewise displayed highly proficient self-monitoring throughout the SD period. In contrast, modafinil had a disruptive effect on self-monitoring, inducing a reliable «overconfidence» effect (i.e. an overestimation of actual cognitive performance), which was particularly marked 2–4 h post-dose. Although modafinil has proven to be a safe and effective countermeasure to the effects of extensive SD on cognitive task performance, we encourage a more comprehensive understanding of the relation between its subjective and performance enhancing effects before the drug is recommended as a viable fatigue countermeasure.     

The Effects of Nuclear Magnetic Resonance Imagers on External and Implantable Pulse Generators

This study evaluates the effect of nuclear magnetic resonance (NMR) scanning on pacemaker function. It must be emphasized that each manufacturer's pulse generators and each pacing modality may behave differently and, therefore, require individual evaluation. According to our results, patients with pacemakers should have their pacing activity monitored continuously during scanning with the NMR 1500 gauss imaging system. External pulse generators should be set to the asynchronous mode and placed outside the NMR image volume but within the radiofrequency (RF) shield. Implanted pacemakers should be verified for type and mode of operation. All implantable pulse generators evaluated reverted from the demand to the asynchronous mode within the magnetic field of the scanner. There was no observable damage to the discrete pacemaker components that were tested. In vivo testing of implantable single-chamber pulse generators did not significantly alter the pacemaker's operating parameters. Changes in stimulation rate analogous to the RF field pulse rate were seen. In single-chamber devices the resultant rate was a multiple of the RF frequency, changing to a value less than the normal asynchronous magnetic rate. With more sophisticated dual-chamber devices the results varied. With VDD pacing during RF scanning, the cardiac stimulation rate increased to a value analogous to the RF field modulation period. More extensive in vivo testing using different models of pulse generators of various manufacturers is needed to identify specific device susceptibility to the RF, time variance and steady-state magnet fields. From these data a comprehensive statement about NMR scanning of patients with implanted pacemakers can be made.     

Isolation by distance: reply to Lalouel and Morton

Lalouel's assertion that I misinterpreted Malécot's work on isolation by distance may or may not be correct. If so, my assertions of error in Malécot's derivation are wrong, although they do apply to others who have used models involving a spatial continuum. Lalouel's other claims of error in my derivations of the consequences of a spatially continuous model of population reproduction and migration are incorrect, with the exception of one isolated misprint.     

Transnasal butorphanol for postoperative analgesia following paediatric surgery in a third world country

The authors present their experience with transnasal butorphanol to provide analgesia following orthopaedic and plastic surgical procedures in children. Transnasal butorphanol was administered to eight patients ranging in age from eight to 17 years and in weight from 34 to 64 kg. Following the surgical procedure, the patient and a parent were instructed on how to use the medication. They were instructed to administer one spray into one nostril every three h as needed for pain. The quality of analgesia was assessed twice a day using a visual analogue score of 0 to 10 (0 = no pain, 10 = worst pain imaginable). Intranasal butorphanol provided adequate analgesia in all eight patients with visual analogue scores of zero to two. Adverse effects from the medication included one report of nausea, one complaint of transient dizziness, and two reports of a bitter taste and some mild throat irritation. None of these was severe enough to preclude its subsequent use. Our preliminary experience suggests that transnasal butorphanol may offer an alternative route of delivery when intravenous administration is not feasible. Future studies are needed to compare its efficacy to intravenous and non-parenteral routes of administration. It may prove to be useful in other situations when intravenous access is lacking such as prior to invasive procedures in the outpatient clinic or emergency room.