Anomalous "VVI" Pacing of a Dual Chamber Pacemaker When Programmed in DDI(R) Mode

We describe the case of a dual chamber rate responsive pacemaker (Relay, model 294-03, Intermedics, Angleton, TX, USA) implanted in a 68-year-old male for sick sinus syndrome, which was not working properly when programmed in the DDIR mode, thus determining occasionally a sort of "VVI" pacing. However, the pacemaker performed well when programmed in the DDDR mode. We discovered that this was not a malfunction of a single device but rather a general behavior of this family of Intermedics dual chamber pacemakers (also not rate responsive), caused by a software problem.     

Intrapatient Comparison Between Chronic VVIR and DDD Pacing 'In Patients Affected by High Degree AV Block Without Heart Failure

MENOZZI, C., ET AL.: Intrapatient Comparison Between Chronic VVIR and DDD Pacing in Patients Affected by High Degree AV Block Without Heart Failure. In patients affected by high degree AV block without preexisting congestive heart failure there is no definite demonstration that DDD pacing gives real clinical advantages in respect to VVIR pacing. We performed an intrapatient, long-term study between the two pacing modes in 14 high degree AV block patients, using the Medtronic Synergyst 7027 dual chamber pacemaker, who could be programmed alternatively in DDD or VVIR mode. After a 4-week run-in period following the pacemaker implant, patients completed a randomized, double-blind, cross-over study to compare the effect of 6-week period VVIR and DDD pacing on symptoms and cardiovascular parameters. A semiquantitative score scale was used to quantify the symptoms of general well-being, palpitations, dizziness, pulsating sensation in the neck or abdomen, shortness of breath at rest and during effort, chest pain, and NYHA classification. The sum of symptom scores was 10.4 ± 6.7 in VVIR period and 4.6 ± 2.7 in DDD period (p < 0.001); five patients (36%) crossed over early from VVIR to DDD because of intolerable symptoms; overall, eight patients preferred the DDD mode and no one preferred the VVIR. Cardiac output at rest (echo-Doppler method) was 4.7 ± 1.4 versus 5.7 ± 1.6 liter/min (p < 0.01), body weight was 65.9 ± 6.6 versus 64.9 ± 6.1 kg (p < 0.02), atrial natriuretic peptide was 236 ± 112 versus 198 ± 110 pg/mL (p < 0.01), respectively, during VVIR and DDD modes. Effort tolerance was similar with the two modes of pacing (68 ± 15 vs 70 ± 18 watt/min). In conclusion, hemodynamic advantages of atrial synchronization reflect a better quality of life for the patients even if an individual variability exists.     

The effects of sleep deprivation in humans: topographical electroencephalogram changes in non‐rapid eye movement (NREM) sleep versus REM sleep

Studies on homeostatic aspects of sleep regulation have been focussed upon non‐rapid eye movement (NREM) sleep, and direct comparisons with regional changes in rapid eye movement (REM) sleep are sparse. To this end, evaluation of electroencephalogram (EEG) changes in recovery sleep after extended waking is the classical approach for increasing homeostatic need. Here, we studied a large sample of 40 healthy subjects, considering a full‐scalp EEG topography during baseline (BSL) and recovery sleep following 40 h of wakefulness (REC). In NREM sleep, the statistical maps of REC versus BSL differences revealed significant fronto‐central increases of power from 0.5 to 11 Hz and decreases from 13 to 15 Hz. In REM sleep, REC versus BSL differences pointed to significant fronto‐central increases in the 0.5–7 Hz and decreases in the 8–11 Hz bands. Moreover, the 12–15 Hz band showed a fronto‐parietal increase and that at 22–24 Hz exhibited a fronto‐central decrease. Hence, the 1–7 Hz range showed significant increases in both NREM sleep and REM sleep, with similar topography. The parallel change of NREM sleep and REM sleep EEG power is related, as confirmed by a correlational analysis, indicating that the increase in frequency of 2–7 Hz possibly subtends a state‐aspecific homeostatic response. On the contrary, sleep deprivation has opposite effects on alpha and sigma activity in both states. In particular, this analysis points to the presence of state‐specific homeostatic mechanisms for NREM sleep, limited to <2 Hz frequencies. In conclusion, REM sleep and NREM sleep seem to share some homeostatic mechanisms in response to sleep deprivation, as indicated mainly by the similar direction and topography of changes in low‐frequency activity.     

Developing Actionable Dietary Guidance Messages: Dietary Fat as a Case Study

Although consumers say they are concerned about nutrition and are aware that eating a healthful diet is important for good health, this knowledge does not always translate into healthful diet behaviors or motivate behavior change. In an effort to better understand consumer attitudes about nutrition and to explore alternatives for communicating dietary advice in language that is meaningful and motivates behavior change, the International Food Information Council (IFIC) conducted qualitative research with consumers (using focus groups) and registered dietitians (using telephone interviews) in 1998 and 1999. Results of the research are presented using dietary fat as a case study. Findings from the IFIC research were reported to the Dietary Guidelines Advisory Committee to assist the Committee in developing meaningful and action-oriented dietary advice related to dietary fat for inclusion in the 2000 Dietary Guidelines for Americans that would be motivating and easy for consumers to implement. The recommendation to moderate fat intake in the new dietary guideline, "Choose a diet that is low in saturated fat and cholesterol and moderate in total fat" is consistent with communication recommendations in the IFIC research. Further, the moderate fat message is empowering because it suggests an achievable dietary regimen and reduces guilt and worry about foods. It allows flexibility to enjoy desired foods and promotes using common sense when it comes to diet. Several issues emerged from the IFIC research that apply to general nutrition communications with consumers, whether it be through national nutrition recommendations or in one-on-one counseling situations: to be effective, messages to consumers about nutrition, and specifically dietary fat, must address sources of discomfort about dietary choices; they must engender a sense of empowerment; and they should motivate both by providing clear information that propels toward taking action and appeals to the need to make personal choices.     

Disposition and Metabolism of [14C]Dibenzo[c,g]carbazole Aerosols in Rats after Inhalation

Disposition and Metabolism of [^l4C]Dibenzo[c,g]carbazole Aerosolsin Rats after Inhalation. Bond, J. A. Ayres, P. H., Medinsky,M. A., Cheng, Y. S., Hirshfield, D., and McClellan, R. O. (1986).Fundam Appl Toxicol. 7, 76-85. Dibenzo[c.£]carbazole (DBC)is a nitrogen-containing polycyclic aromatic hydrocarbon thathas been detected in tobacco tars, industrial oils, and dieselengine exhaust fumes. DBC is carcinogenic in respiratory tracttissue of hamsters and in lungs, kidneys, and livers of mice.The purpose of this research was to determine the respiratorytract deposition, distribution in tissues, metabolism, and excretionof DBC in rats after inhalation. Rats were exposed nose-onlyto 1.1 or 13 Mg [¹⁴C]DBC/liter air for 60 min. Activity medianaerodynamic diameters for the two concentrations of DBC rangedfrom 0.7 to 0.8 pm. Unne. feces, and selected tissues were collectedfor various times after exposure. The fractional depositionfor the 1.1 and 13 ug/liter exposure concentrations was similar,13 and 16%, respectively. The dominant route of excretion of¹⁴C following exposure to either concentration of DBC was thefeces, accounting for approximately 95% of the total 14C eliminated.Half-time for fecal excretion was 20 ± 6 hr (x ±SE). Gastrointestinal absorption of [I4C]DBC was 43%. Radioactivitywas widely distributed to all tissues examined, with the respiratorytract (lung, trachea, larynx, and nasal turbinates), upper gastrointestinaltract (stomach and small intestine), the liver, and the adrenalscontaining the highest concentrations of [I4C]DBC equivalentswithin 1 hr after exposure. At both concentrations of DBC tested,clearance of I4C from tissues was rapid, with approximately60 to 98% of the initial tissue burden being cleared with half-timesranging from 1 to 16 hr. The remaining 2 to 40% in the tissueswas cleared with half-times that ranged from 1.5 to 14 days.Several metabolites were detected in the urine and feces, noneof which appeared to be either glucuronide or sulfate conjugates.Small quantities of [I4C]DBC were detected in the urine, althoughquantities were less than 1% of the initial respiratory tractburden of [I4C]DBC. The results from this research indicatethat DBC was rapidly absorbed from the lungs and translocatedto many tissues. Prior to elimination, primarily in the feces,DBC was extensively metabolized There appeared to be no effectof exposure concentration on the toxicokinetics of inhaled DBC.     

Spontaneous Occurrence of the Induced Cardioinhibitory Vasovagal Reflex

ECG recording of spontaneous, neurally-mediated syncope is rare. We have observed ten patients who sustained 70 syncopal episodes in whom: (1) ECG monitoring recorded syncope caused by ventricular asystole (AV block, three patients; sinus arrest; seven patients); (2) syncope and the spontaneously observed arrhythmias were reproducible by carotid sinus massage, upright tilt test, or eyeball pressure; and (3) no discernable cause of precipitating factors were detected. Two patients had a history of cardiac disease and four patients had only mild nonclinical ECG or echocardiographic abnormalities. Syncopal episodes recorded during Holter monitoring were of sudden onset in four patients and preceded by prodromal symptoms in six patients. The maximum RR pause was 9.4 +/- 3.7 seconds (range 4.5-15). Electrophysiological evaluation was normal in seven patients. Slight sinus node dysfunction or atrioventricular conduction abnormalities were noted in three others. The clinical characteristics of spontaneous and induced episodes strongly suggest that increased vagal tone played a role in causing the spontaneous events. Vagal stimulation tests are useful for the diagnosis of syncope of unknown origin.     

Plasma vitamin D metabolites in a patient with sporadic hypophosphataemic osteomalacia (adult-onset type)

Sporadic hypophosphataemic osteomalacia (adult-onset type) was demonstrated in a 40-year-old man on the basis of severe osteomalacia, hypophosphataemia, hyperphosphaturia and glycinuria. Plasma immunoreactive parathyroid hormone (iPTH) concentration was 9.3 ng prot./ml (normal range: 4-8 ng prot./ml). Plasma 25-hydroxy-vitamin D and 24,25-dihydroxy-vitamin D concentrations were 11 and 2.4 ng/ml respectively. Basal 1 alpha,25-dihydroxy-vitamin D concentrations were slightly elevated (116 and 96 pg/ml) and increased to 240 pg/ml after 3 days on a low-phosphorus diet. The patient was put on oral treatment with 25-hydroxycholecalciferol (100 microgram per day) and phosphorus (1500 mg per day). On the 4th month on treatment, a clinical improvement was apparent. Plasma 25(OH)D was 44 ng/ml, plasma 1,25(OH)2D was 256 pg/ml. However, plasma phosphorus remained low (0.77 mmol/l). On the 9th month of treatment a radiological improvement was evident despite a persistent hypophosphataemia (0.68 mmol/l). These facts suggest in our patient the existence of a vitamin D-independent renal phosphorus leak.