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At least 145 records · Page 8Linked to original sources

PubMed1998

Restricted and regulated overexpression reveals calcineurin as a key component in the transition from short-term to long-term memory.

To investigate the roles phosphatases play in hippocampal-dependent memory, we studied transgenic mice overexpressing a truncated form of calcineurin. These mice have normal short-term memory but defective long-term memory evident on both a spatial task and on a visual recognition task, providing genetic evidence for the role of the rodent hippocampus in spatial and nonspatial memory. The defect in long-term memory could be fully rescued by increasing the number of training trials, suggesting that the mice have the capacity for long-term memory. We next analyzed mice overexpressing calcineurin in a regulated manner and found the memory defect is reversible and not due to a developmental abnormality. Our behavioral results suggest that calcineurin has a role in the transition from short- to long-term memory, which correlates with a novel intermediate phase of LTP.

Animals↗

PubMed1998

Short-term and long-term pancreatic exocrine and endocrine functions after pancreatectomy.

Exocrine and endocrine functions of the pancreas were assessed in 44 Japanese patients who underwent pancreatic head resection. Functions were analyzed comparing levels before surgery, at a short-term follow-up (<2 months), and at a long-term follow-up (12-31 months). The N-benzoyl-L-tyrosyl-p-aminobenzoic acid (BT-PABA) excretion test, fasting blood sugar (FBS) level, and oral glucose tolerance test (OGTT) were used to determine pancreatic function. The patients were divided into three groups according to the size of the main pancreatic duct: group 1, 15 patients with a normal sized duct (< or =3 mm); group 2, 20 with a moderately dilated duct (>3 mm, <10 mm); and group 3, 9 with a markedly dilated duct (> or =10 mm). The mean BT-PABA value (6-hr urinary PABA recovery rate) in group 1 showed no change during the postoperative period. In contrast, the BT-PABA values in groups 2 and 3 had dropped by the short-term follow-up and returned to the preoperative level by the long-term examination. FBS and 120-min OGTT levels were not different between the three groups preoperatively. Although these values showed no change in all the three groups at the short-term measurements, the FBS in group 3 and 120-min levels in all the three groups had increased at the long-term. These findings suggest that exocrine pancreatic function shows a short-term deterioration in patients with a dilated pancreatic duct but recovers to the preoperative level over the long term after pancreatic head resection. Endocrine insufficiency, however, may occur at a long-term point after surgery irrespective of the preoperative pancreatic ductal dilatation.

4-Aminobenzoic Acid↗

PubMed1996

Site specificity of short-term and long-term habituation in the tail-elicited siphon withdrawal reflex of Aplysia.

The study of habituation in animals with relatively simple nervous systems has contributed significantly to the understanding of mechanisms underlying learning and memory. Using the tail-elicited siphon withdrawal reflex of Aplysia, which is mediated in part by bilaterally symmetrical clusters of tail sensory neurons, we found that both short-term and long-term habituation can be restricted laterally, such that habituation produced by stimulation of one side of the tail does not generalize to the other side. Further experiments in this preparation revealed that long-term, laterally restricted habituation is sensitive to the temporal pattern with which stimuli are presented. We also determined that both short-term and long-term habituation can take place in a reduced behavioral preparation, and that short-term habituation can be restricted within relatively small stimulation sites located on the same side of the tail. These results provide insights into the cellular organization of habituation, and they provide a useful preparation for a cellular analysis of this basic form of learning.

Animals↗

PubMed1979

Serum prolactin levels in short-term and long-term use of inert plastic and copper intrauterine devices.

Serum prolactin values were assessed in 59 normally menstruating parous women; groups were divided with respect to short-term (6 weeks) and long-term (4-60 months) use of either the inert plastic IUD (Saf-T-Coil or Lippes Loop) or copper IUD (Cu-7). Preinsertion values served as controls in the short-term study while a separate control group using barrier contraception was used in the long-term study. Prospective analysis of short-term IUD use and retrospective analysis of long-term IUD use revealed no significant differences in mean hPRL compared to control values. Both short- and long-term mean values were within the normal range for serum hPRL. In addition, duration of use had no significant effect on hPRL values.

Adolescent↗

PubMed1995

Short-term and long-term verbal memory: a positron emission tomography study.

Short-term and long-term retention of experimentally presented words were compared in a sample of 33 healthy normal volunteers by the [15O]H2O method with positron emission tomography (PET). The design included three conditions. For the long-term condition, subjects thoroughly studied 18 words 1 week before the PET study. For the short-term condition, subjects were shown another set of 18 words 60 sec before imaging, with instructions to remember them. For the baseline condition, subtracted from the two memory conditions, subjects read a third set of words that they had not previously seen in the experiment. Similar regions were activated in both short-term and long-term conditions: large right frontal areas, biparietal areas, and the left cerebellum. In addition, the short-term condition also activated a relatively large region in the left prefrontal region. These complex distributed circuits appear to represent the neural substrates for aspects of memory such as encoding, retrieval, and storage. They indicate that circuitry involved in episodic memory has much larger cortical and cerebellar components than has been emphasized in earlier lesion studies.

Adult↗

PubMed1999

Short-term and long-term safety of budesonide inhalation suspension in infants and young children with persistent asthma.

This article reviews the short-term and long-term safety profile of budesonide inhalation suspension (BIS) for nebulization in infants and young children with persistent asthma. Short-term safety (12 weeks) was assessed by pooling the results from the 3 randomized, double-blind, placebo-controlled, multicenter studies (studies A, B, and C) on the efficacy and safety of once- and twice-daily BIS. Long-term safety of BIS and conventional asthma therapy (CAT) was assessed in 52-week extension studies of the 12-week double-blind trials. CAT consisted of any available therapy for asthma; in 2 studies, CAT could have included treatment with inhaled glucocorticosteroids. Safety was assessed by monitoring adverse events (AEs), physical examinations, and basal and ACTH-stimulated plasma cortisol levels (in a subset of subjects). In the 52-week open-label extensions, the effects of BIS on growth velocity and skeletal age also were determined. In the 12-week studies, a total of 1017 subjects was evaluated for safety; totals of 231, 185, 229, 327, and 45 subjects were randomized to receive placebo or BIS at total daily doses of 0.25 mg, 0.5 mg, 1.0 mg, and 2.0 mg, respectively. Subject demographics and baseline asthma characteristics were similar across treatment groups, except that age, weight, height, and duration of asthma appeared higher in the 2. 0-mg daily dose group. For BIS groups, mean age was 58.9 months; mean weight was 20.3 kg; mean height was 108.9 cm, and mean duration of asthma was 3.2 years. There were no differences in the incidence, severity, or types of AEs reported among the BIS and placebo groups. There were no significant differences between placebo and BIS treatment groups in basal or ACTH-stimulated cortisol levels, physical examinations, clinical laboratory values, or fungal cultures. A total of 670 subjects completed the 52-week extension studies; 223 subjects received CAT and 447 received BIS. Median total daily doses of BIS ranged from 0.50 mg to 1.0 mg in the 3 studies, and the mean duration of treatment exposure was 304 +/- 119 days and 342 +/- 83 days in CAT and BIS groups, respectively. During the 52-week treatment period, the incidences of reported AEs were comparable between treatment groups and were mild-to-moderate in intensity; no new AEs occurred during the 52-week studies compared with 12-week studies. No significant differences were observed between BIS and CAT in basal or ACTH-stimulated cortisol levels, physical examinations, clinical laboratory values, or fungal cultures. There was a small but statistically significant reduction in growth velocity (a difference of 0.8 cm) in the BIS-treated group compared with the CAT group in study A. In studies B and C, growth velocity was not different between BIS and CAT groups. In pooled analyses, no statistically significant differences in growth velocity, standard median heights, or skeletal age were observed between BIS and CAT groups. Short-term and long-term treatment with BIS, over a wide range of doses, was well tolerated for the treatment of persistent asthma in infants and young children.

Administration, Inhalation↗

PubMed1999

Spinal substance P receptor expression and internalization in acute, short-term, and long-term inflammatory pain states.

Inflammatory pain involves the sensitization of both primary afferent and spinal cord neurons. To explore the neurochemical changes that contribute to inflammatory pain, we have examined the expression and ligand-induced internalization of the substance P receptor (SPR) in the spinal cord in acute, short-term, and long-term inflammatory pain states. These inflammatory models included unilateral injection of formalin (8-60 min), carrageenan (3 hr), and complete Freund's adjuvant (CFA; 3 d) into the rat hindpaw as well as adjuvant-induced polyarthritis (21 d). In acute inflammatory pain there is ongoing release of substance P (SP) as measured by SPR internalization in lamina I neurons at both 8 and 60 min after formalin injection. Although there is no tonic release of SP in short-term inflammatory pain, at 3 hr after carrageenan injection, SP is released in response to both noxious and non-noxious somatosensory stimulation with SPR internalization being observed in neurons located in both laminae I and III-IV. In long-term inflammatory pain models (CFA and polyarthritis) the same pattern of SP release and SPR activation occurs as is observed in short-term inflammation with the addition that there is a significant upregulation of the SPR in lamina I neurons. These results suggest that SPR internalization might serve as a marker of the contribution of ongoing primary afferent input in acute and persistent pain states. These stereotypical neurochemical changes suggest that there are unique neurochemical signatures for acute, short-term, and long-term inflammatory pain.

Acute Disease↗

PubMed2001

Impact of short-term versus long-term topical steroids on corneal neovascularization after non-high-risk keratoplasty.

PURPOSE: To analyze incidence and extent of corneal neovascularization (CN) after non-high-risk keratoplasty and to find out whether duration of postoperative topical steroid therapy (6 vs 12 months) affects CN, corneal endothelial cell count, pachymetry, aqueous flare values, and best-corrected visual acuity at 1 year after keratoplasty. METHODS: Patients of the prospective Erlangen non-high-risk keratoplasty study with available high-quality corneal photographs taken preoperatively and 1 year later were analyzed (n=136). Corneal photographs were evaluated by two independent observers in a standardized semiquantitative fashion. Slides were projected with 100x magnification and corneal vessels classified into five grades with regard to the limbus, sutures and host-graft junction in each of 12 corneal sectors. Incidence and extent of CN after keratoplasty and relation to short-term (0-6 months) versus long-term (0-12 months) postoperative topical steroid therapy were analyzed. The effect of duration of topical steroid therapy on corneal endothelial cell count, pachymetry, aqueous flare values, and best corrected visual acuity was also analyzed. Of the 136 patients, 69 (51%) were randomly assigned to short-term and 67 to long-term topical prednisolone acetate 1%. RESULTS: Fifty-eight percent of patients (n=79) developed a CN within 1 year after keratoplasty in at least one corneal sector (mean 3.1 +/- 2.2, range 1-10). At 1 year after keratoplasty, only in 12% of these patients did at least one vessel reach the host-graft junction or grow into the donor cornea, whereas in 51% vessels were seen beyond the outer suture ends of the double running suture without reaching the host-graft junction. In 37%, capillaries were located between limbus and outer suture ends. New vessels usually pointed directly or indirectly to the outer suture ends and usually were located around the 12 o'clock and 6 o'clock positions. There was no significant difference regarding incidence and extent of CN 1 year after keratoplasty between the long-term and the short-term group. Duration of topical steroid therapy had no significant effect on corneal endothelial cell count and thickness, aqueous flare values and best-corrected visual acuity at 6 and 12 months postoperatively (only at 12 months, corneas in the long-term treatment group were slightly thicker; P=0.03). Interobserver correlation of vessel assessment was 0.77 (Kendall's tau B). CONCLUSIONS: CN is a common phenomenon after non-high-risk keratoplasty. New vessels rarely reach the host-graft junction, most commonly develop from the 6 o'clock and 12 o'clock positions and are usually located between epithelium and Bowman's layer (i.e., at the level of the superficial suture). The direction of vessel growth from the limbus towards the outer suture ends suggests release of angiogenic factors in this area. Prolongation of topical steroid therapy after non-high-risk keratoplasty beyond 6 months in this study did not significantly influence incidence and extent of CN, corneal endothelial cell count, aqueous flare values and best-corrected visual acuity observed 1 year after keratoplasty.

Administration, Topical↗

PubMed1994

Glycohemoglobin measured by automated affinity HPLC correlates with both short-term and long-term antecedent glycemia.

We evaluated glycohemoglobin (GHb) and glycated plasma protein (GPP) by automated affinity HPLC for their ability to monitor both short-term and long-term antecedent glycemia in 70 diabetic subjects. We placed 30 subjects on an intervention protocol in which insulin and (or) dietary changes were made twice weekly to acutely decrease glycemia. We monitored 40 subjects at 6-week intervals; changes in the clinical regimen were made at that time only. Despite weekly changes in mean blood glucose in the subjects who received more intensive intervention. GHb concentrations correlated significantly with the weekly (r = 0.66, P < 0.001), 2-week (r = 0.70, P < 0.001), 3-week (r = 0.72, P < 0.001), and 6-week (r = 0.83, P < 0.001) mean glucose concentrations. GPP correlated significantly with measured glycated albumin determined by boronate affinity columns (r = 0.83, P < .001) and correlated best with the 1-week (r = 0.66, P < 0.001), 2-week (r = 0.64, P < .001) and 3-week (r = 0.60, P < 0.001) mean antecedent glucose concentration. Thus, GHb, traditionally considered a marker for only long-term diabetic control, correlated significantly with both short-term and long-term antecedent glycemia.

Adult↗

PubMed2005

Propofol inhibits long-term potentiation but not long-term depression in rat hippocampal slices.

BACKGROUND: Although propofol is known to produce amnesia when used for anesthesia, mechanisms underlying its effects on memory are poorly understood. The current study was designed to examine the effects of propofol on forms of synaptic plasticity thought to contribute to memory processing. METHODS: Extracellular excitatory postsynaptic potentials were recorded from the CA1 region of rat hippocampal slices. Long-term potentiation (LTP) was induced using theta-burst stimulation (10 bursts of 4 pulses at 100 Hz, applied at 5 Hz) of the Schaffer-collateral pathway, while low-frequency stimulation (1 Hz x 900 pulses) was delivered to induce long-term depression. The authors also used higher-frequency stimulation (10 bursts of 4 pulses at 200 Hz, applied at 5 Hz) in the presence of MK-801 to examine the effects of propofol on an N-methyl-D-aspartate receptor-independent form of LTP. RESULTS: At 30 microM, propofol inhibited LTP induction produced by theta-burst stimulation but had less effect on LTP maintenance. Similarly, when LTP was induced by 200-Hz stimulation in the presence of MK-801, propofol also blocked LTP induction. Propofol did not block LTP induction in the presence of picrotoxin, a specific antagonist of gamma-aminobutyric acid type A receptors, suggesting that modulation of gamma-aminobutyric acid type A receptors participates in propofol-mediated LTP inhibition. Propofol did not inhibit long-term depression. CONCLUSIONS: Propofol inhibits LTP induction through modulation of gamma-aminobutyric acid type A receptors but not via inhibition of N-methyl-D-aspartate receptors. However, other factors also possibly contribute to propofol-mediated LTP inhibition.

Anesthetics, Intravenous↗

PubMed2005

Synaptic tagging and cross-tagging: the role of protein kinase Mzeta in maintaining long-term potentiation but not long-term depression.

Protein kinase Mzeta (PKMzeta) is a persistently active protein kinase C isoform that is synthesized during long-term potentiation (LTP) and is critical for maintaining LTP. According to "synaptic tagging," newly synthesized, functionally important plasticity-related proteins (PRPs) may prolong potentiation not only at strongly tetanized pathways, but also at independent, weakly tetanized pathways if synaptic tags are set. We therefore investigated whether PKMzeta is involved in tagging and contributes to a sustained potentiation by providing strong and weak tetanization to two independent pathways and then disrupting the function of the kinase by a selective myristoylated zeta-pseudosubstrate inhibitory peptide. We found that persistent PKMzeta activity maintains potentiated responses, not only of the strongly tetanized pathway, but also of the weakly tetanized pathway. In contrast, an independent, nontetanized pathway was unaffected by the inhibitor, indicating that the function of PKMzeta was specific to the tagged synapses. To further delineate the specificity of the function of PKMzeta in synaptic tagging, we examined synaptic "cross-tagging," in which late LTP in one input can transform early into late long-term depression (LTD) in a separate input or, alternatively, late LTD in one input can transform early into late LTP in a second input, provided that the tags of the weak inputs are set. Although the PKMzeta inhibitor reversed late LTP, it did not prevent the persistent depression at the weakly stimulated, cross-tagged LTD input. Conversely, although the agent did not reverse late LTD, it blocked the persistent potentiation of weakly tetanized, cross-tagged synapses. Thus, PKMzeta is the first LTP-specific PRP and is critical for the transformation of early into late LTP during both synaptic tagging and cross-tagging.

Animals↗

PubMed2006

Global gene expression in Escherichia coli K-12 during short-term and long-term adaptation to glucose-limited continuous culture conditions.

Microarray technology was used to study the cellular events that take place at the transcription level during short-term (physiological) and long-term (genetic) adaptation of the faecal indicator bacterium Escherichia coli K-12 to slow growth under limited nutrient supply. Short-term and long-term adaptation were assessed by comparing the mRNA levels isolated after 40 or 500 h of glucose-limited continuous culture at a dilution rate of 0.3 h(-1) with those from batch culture with glucose excess. A large number of genes encoding periplasmic binding proteins were upregulated, indicating that the cells are prepared for high-affinity uptake of all types of carbon sources during glucose-limited growth in continuous culture. All the genes belonging to the maltose (mal/lamB) and galactose (mgl/gal) operons were upregulated. A similar transcription pattern was observed for long-term cultures except that the expression factors were lower than in the short-term adaptation. The patterns of upregulation were confirmed by real-time RT-PCR. A switch from a fully operational citric acid cycle to the PEP-glyoxylate cycle was clearly observed in cells grown in glucose-limited continuous culture when compared to batch-grown cells and this was confirmed by transcriptome analysis. This transcriptome analysis confirms and extends the observations from previous proteome and catabolome studies in the authors' laboratory.

Adaptation, Physiological↗

PubMed2003

Postsynaptic density-95 mimics and occludes hippocampal long-term potentiation and enhances long-term depression.

Previous studies have shown that overexpression of the protein PSD-95 (postsynaptic density-95) selectively enhances AMPA receptor-mediated synaptic responses in hippocampal pyramidal cells. To determine whether this effect is related to synaptic plasticity at these synapses, we examined whether PSD-95 expression mimics long-term potentiation (LTP), and also whether it influences LTP and long-term depression (LTD) in hippocampal slice cultures. Using simultaneous recording from transfected or infected cells and control pyramidal cells, we found that PSD-95, similar to LTP, increases the amplitude and frequency of miniature EPSCs. It also converts silent synapses to functional synapses, as does LTP. In addition, LTP is completely occluded in cells expressing PSD-95, whereas LTD is greatly enhanced. These results suggest that common mechanisms are involved in controlling synaptic AMPA receptors by PSD-95 and synaptic plasticity.

Animals↗

PubMed2005

Heterotopic vs. orthotopic liver transplantation for chronic liver disease: a case-control comparison of short-term and long-term outcomes.

Between 1986 and 1990 we performed heterotopic liver transplantation (HLT) in 17 patients with chronic liver disease. In spite of theoretical advantages and favorable short-term results, we abandoned HLT because of doubts about the long-term outcome and the improved results of standard orthotopic liver transplantation (OLT). There are, however, no studies comparing the long-term survival after HLT and OLT for chronic liver disease. We performed a case-control study of HLT vs. OLT, with long-term patient and graft survival as the main outcome measures. Known confounders and differences in baseline characteristics between HLT and OLT patients were corrected for. At 1 year, 5 of the 17 HLT patients had died, compared with 9 of the 34 OLT patients (relative risk [RR], 1.15; 95% confidence interval [CI], 0.33-4.02; P = 0.83). After correction for confounders, the long-term risk of graft failure (RR, 18.0; 95% CI, 1.5-223.5; P = 0.02) and of death (RR, 5.2; 95% CI, 0.8-34.8; P = 0.09) was higher after HLT than after OLT. The main causes of graft loss and death at more than 1 year after HLT were de novo malignancies and a variety of biliary complications. In conclusion, our data, from 1 of the largest single-center series of HLTs available, showed no significant difference between HLT and OLT in 1-year survival. However, the long-term outcome of HLT was inferior. HLT cannot be recommended as an alternative to OLT for any of the indications we studied, even though only 1 of the late deaths was definitely related to the heterotopic technique.

Adult↗

PubMedDate not supplied

[What mechanisms underlie involvement of different NMDA receptor subunits in the induction of hippocampal long-term potentiation and long-term depression?].

There is a point of view that N-methyl-D-aspartate (NMDA) receptor subunit-specific signaling outcomes determine the direction of modifications of efficacy of synaptic transmission. Activation of NMDA receptors that contain the 2A subunit promotes LTP, while LTD requires activation of NMDA receptors containing 2B subunit. However, this hypothesis is inconsistent with some experimental data. For explanation of these data, we put forward an alternative hypothesis. According to this hypothesis, the activation of diverse subtypes of NMDA receptors can lead to ether LTP or LTD depending on the relation between posttetanic Ca2+ rise and increase in postsynaptic Ca2+ concentration produced by previous stimulation. Activation of NMDA receptors with 2B subunit can promote LTD of excitatory input to the pyramidal cell due to presence of these receptors on inhibitory interneurons, induction of the LTP in interneuron, and potentiation of inhibitory transmission between the interneuron and the target pyramidal cell.

Animals↗

PubMed1998

Evidence for involvement of the cGMP-protein kinase G signaling system in the induction of long-term depression, but not long-term potentiation, in the dentate gyrus in vitro.

The involvement of the cGMP-protein kinase G (PKG) signaling pathway in the induction of long-term depression (LTD) and long-term potentiation (LTP) was investigated in the medial perforant path of the dentate gyrus in vitro. Low-frequency stimulation (LFS)-induced LTD of field EPSPs was inhibited by bath perfusion of the selective soluble guanylyl cyclase inhibitor 1H-[1,2,4] oxadiazolo[4,3, -a]quinoxalin-1-one (ODQ). LFS-induced LTD of EPSPs and whole-cell patch-clamped EPSCs was also blocked by bath perfusion and postsynaptic intracellular injection, respectively, of the selective PKG inhibitor KT5823. Elevation of intracellular cGMP by perfusion of the cGMP phosphodiesterase inhibitor zaprinast resulted in induction of LTD of field EPSPs and EPSCs. Occlusion experiments showed mutual inhibition between LFS-induced LTD and zaprinast-induced LTD. The zaprinast-induced LTD of field EPSPs was inhibited by perfusion of ODQ and KT5823. In addition, zaprinast-induced LTD of EPSCs was inhibited by postsynaptic application of KT5823. Glutamate receptor stimulation, especially that of metabotropic glutamate receptors (mGluRs), was required for zaprinast-induced LTD, because cessation of test stimulation or perfusion with the mGluR antagonist (+)-alpha-methyl-4-carboxyphenylglycine (MCPG) inhibited zaprinast-induced LTD. No inhibitory effect of ODQ or KT5823 on the induction of LTP of EPSPs or EPSCs was found. These data indicate that the cGMP-guanyly cyclase-PKG signaling pathway in the dentate gyrus is essential for induction of LTD, although not of LTP, in the dentate gyrus.

3',5'-Cyclic-GMP Phosphodiesterases↗

PubMed1993

Short-term and long-term reproducibility of dietary history interview data.

This study gives results for comparisons between dietary history interviews repeated at short-term (4-8 months) and long-term (4-7 years) intervals in conjunction with the Finnish Mobile Clinic Health Examination Survey. Interviews surveying the whole range of consumable foods over the preceding year were completed in 1967-1976. Short-term study was accomplished among 93 adults, and long-term study among 1844 adults. Comparisons were made for intakes of 32 food groups and 32 nutrient indices. In the short term, the intraclass correlation coefficients for nutrient indices ranged from 0.16 to 0.80, with 90% of values higher than 0.5. The corresponding figures for repeated measurements at long-term interval were generally poorer, being in the range 0.12-0.60, with 45% of values > 0.5. When studied in population subgroups, long-term agreement in dietary data was not found to be affected by sex, age, body mass index or smoking status, but it may be reduced among heavier drinkers (> or = 20 g alcohol per day). The intraclass correlation coefficients for separate nutrients tended to be higher than those for different food groups. In conclusion, we suggest that the reproducibility of the dietary history method used was acceptable, and that the dietary patterns of examinees were sufficiently stable to be compatible with the needs of epidemiological follow-up studies.

Diet Surveys↗

PubMed1989

Short-term and long-term changes of left ventricular volumes during rate-adaptive and single-rate pacing.

To evaluate the adaptation of the heart to exercise during pacing, 15 patients with permanent endocardial pacemakers were studied; nine patients had atrioventricular universal (DDD) pacemakers (Symbios 7005) and six patients had activity detecting rate-responsive ventricular (VVIR) pacemakers (Activitrax 8403). Left ventricular function in each patient during rate variable pacing was compared to ventricular function during VVI single-rate pacing. End-systolic and end-diastolic volume changes during exercise were measured by radionuclide angiography and the amount of volume change was used to assess left ventricular function. Both short-term (within 4 hours) and long-term measurements (after at least 4 weeks) were made at rest and at 50% of the maximal exercise capacity in DDD or VVIR mode and were compared with VVI single-rate pacing. All patients, when changed from DDD or VVIR mode to VVI single-rate pacing showed a significant increase of the end-diastolic volume during exercise, which increased even more after long-term VVI pacing. During long-term rate variable pacing, there was no increase of the end-diastolic volume during exercise. DDD or VVIR pacing initially showed a substantial increase of the end-systolic volume during exercise combined with a decrease of left ventricular ejection fraction, suggesting a decrease of the left ventricular contractility. After 4 weeks, contractility improved both with DDD and VVIR pacing. We conclude that short-term DDD and VVIR pacing induces a temporary impairment of left ventricular function that improves after 4 weeks, whereas long-term VVI pacing is associated with left ventricular dilatation even at moderate levels of exercise.

Adaptation, Physiological↗