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PubMed1988

Effects of bivalent cations on post-rest adaptation in guinea-pig heart muscle.

In isolated papillary muscles of guinea-pig hearts, the inotropic effects of bivalent cations, Ca2+, Ba2+, Sr2+, and Ni2+, were investigated during post-rest adaptation in order to study their individual action on excitation-contraction coupling. Upon exposure to each cation studied, the force of contraction was transiently enhanced, whereas the steady state force was influenced differently: it increased with Ca2+, Ba2+ and Sr2+ and was depressed by Ni2+. The transmembrane action potentials (measured at 90% repolarization) were slightly prolonged by Sr2+ and even more by Ba2+, and were shortened by Ca2+ and Ni2+. After 10 min rest, the post-rest contractions consisted of a late peak (PII) that was enhanced in high Ca2+-solution an by Sr2+. Ni2+ and Ba2+ depressed PII and during adaptation to pre-rest controls an early peak of contraction (PI) prevailed. There was no simple relation between post-rest adaptation of force and the duration of action potential in the presence of the bivalent cations tested. During post-rest adaptation the two components of contraction can be separated. The results are interpreted in terms of a model of excitation-contraction coupling which derives Ca ions for contractile activation from two sources: transmembrane calcium influx and calcium release from cellular stores. From the different effects on post-rest adaptation it is concluded that the individual cations influence excitation-contraction coupling more specifically and not merely by "screening-off" the negative surface charges.

Action Potentials↗
PubMed1987

Adaptation of the resting states of accommodation.

Without an adequate stimulus to focus, the eyes accommodate for a "resting state" that averages about 1.6 diopter (D) (62 cm). The resting state can be made more "myopic" by adaptation to a near accommodative or vergence stimulus. In the present experiment, 21 subjects were tested for adaptation to both types of stimuli. Resting state was measured before and after adaptation in the dark (dark focus) and in the presence of an illuminated empty field. The authors found that preadaptation resting states were more myopic in the light field than in the dark test conditions; accommodative and vergence stimuli produce myopic shifts in dark and light field resting states; and a subset of the subjects show much larger aftereffects in the light field conditions. These subjects also show the largest difference between preadaptation dark- and light-field measures. Differences between dark- and light-field measures of resting state in these and other experiments may require a re-examination of the hypothesis that there is a single resting state for each subject.

Accommodation, Ocular↗
PubMedDate not supplied

The dynamics of changes in blood electrolyte and lactic acid concentrations, haematocrit, arterial blood pressure and heart rate in canoeists during 4 hours of rest after maximal effort.

In 12 canoeists determinations were carried out of the haematocrit value, and plasma concentrations of sodium, potassium and lactic acid during 4 hours of rest following maximal effort. The age of the sportsmen was from 18 to 21 years. The haematocrit was significantly increased immediately after the effort but in the first hour of restitution it fell below the resting value and increased then reaching the initial value only in the 4th hour. Serum lactic acid concentration increased in the first minutes of rest and then it decreased gradually reaching the resting value in the 4th hour. The concentration of sodium was not significantly changed throughout the whole period of restitution, when the haematocrit changes were taken into account. The concentration of potassium was very high immediately after the effort, but it fell below the resting value in the 15th minute, rose to the resting value in the 1st hour and in the 2nd hour it continued to rise much above the resting value, and only in the 4th it decreased again to the initial value. The author supposes that the second rise of the serum potassium level beginning in the 1st hour of restitution after maximal effort could be due to insufficient supply of ATP for maintaining the needs of the ionic pump or to secondary loss of water from the cells with a consequent rise in the intracellular hydrogen ion concentration.

Adolescent↗
PubMed1994

[Blood pressure variability during rest and left ventricular hypertrophy in the hypertensive patients. A spectrum analytic approach].

OBJECTIVE: To study the relationship between spectral analysis measurement of blood pressure (BP) and heart rate (HR) at rest, in untreated essential hypertension, and their relationship with the development of left ventricular hypertrophy (LVH). DESIGN AND METHODS: 41 untreated hypertensives (25M/16W, age 50 +/- 12, range 23-73) were measured at rest (WHO criteria DBP > 90 mmHg) by digital continuous photoplethysmography (Finapres 2300 (F), 6 mn of measurement in the dorsal decubitus position and standing up). Measurement of LVH (Devereux criteria, left ventricular mass index LVMI, g/m2) to analyse two groups (LVMI+: LVMI > 107 if women and 120 if men; n = 19; LVMI = 137 +/- 25), and (LVMI-; n = 22; LVMI = 92 +/- 17). The overall variability is standard deviation (SD), spectral analysis variability (SA) is FFT of 256 points over 3 periods low (LF: 0.004-0.07Hz), medium (MF: 0.07-0.13Hz), high (HF: 0.13-0.5Hz). Comparisons by Wilcoxon test and Anova (age, sex) (* p < 0.05, ** p < 0.01). RESULTS: By WHO criteria, the SBP was significantly lower in the LVMI-group (153 +/- 10 vs 165 +/- 18**), the DBP was not significantly different (94 +/- 6 vs 96 +/- 10). By continuous measure (F) at rest there was no significant difference for SBP or DBP. On standing up the SBP was significantly lower in the LVMI-group (148 +/- 20 vs 162 +/- 22**). The SD of the DBP at rest was more elevated in the LVMI-group (3.34 vs 3.06*), but not significantly different standing up. There was no significant difference in SBP at rest (6.7 vs 6.32) or standing (9.13 vs 11.5). The Spectral analysis of the MF was significantly elevated in the LVMI-group at rest for SBP (3.56 vs 3.01*), DBP (1.99 vs 1.19*), and HR (1.79 vs 1.77*). This was not significantly different in the LF and HF for SBP, DBP, HR. CONCLUSION: These results are different from those obtained by invasive ambulatory measures. The spontaneous variability in BP and HR at rest is increased when there is no cardiac effect (LVMI-). SA gives additional information in showing that the increase in variability is due to an increase in the Mayer waves, suggesting the existence of an elevation in adrenergic tone in hypertensive patients not having LVH.

Adult↗
PubMed1994

Effects of mild supine exercise during 20 days bed rest on maximal oxygen uptake rate in young humans.

Fourteen sedentary young volunteers performed a maximal exercise test on a bicycle ergometer before, after and eight or nine weeks after 20 days bed rest. They were divided into four groups. They all went through 20 days bed rest; 5 females and 6 males as controls while 3 males performed mild pedaling supine exercise for 30 minutes twice a day. Three other males from the control group started a retraining programme after bed rest performing mild pedaling exercise in the sitting position for an hour a day, 3-4 days a week for eight weeks. VO2max was reduced after bed rest in all groups. In the control group the 6 males decreased VO2max from 2.82 +/- 0.09 1.min-1 before bed rest to 2.42 +/- 0.14 1.min-1 after. The female controls decreased from 2.55 +/- 0.24 1.min-1 to 2.22 +/- 0.23 1.min-1. The exercise regime performed by the three males during bed rest did not prevent a fall in VO2max in that group from 2.76 +/- 0.06 to 2.57 +/- 0.09 1.min-1. The three males who performed bicycle exercise in the recovery period did not attain higher recovery values at 8-9 weeks than the other males. However the 5 female controls did not recover their > 13% loss in VO2max after 8-9 weeks of recovery. Calculation of peak oxygen pulse from VO2max divided by heart rate indicated that these changes in VO2max were caused exclusively by a reduction in stroke volume of the heart, a finding supported by resting echocardiography of left ventricular end-diastolic diameter and stroke volume.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Plasma immunoreactive neuropeptide Y in congestive heart failure at rest and during exercise.

The purpose of the study described here was to study plasma immunoreactive Neuropeptide Y (NPY) at rest and during exercise in patients with congestive heart failure (CHF) and in healthy subjects. Thirty-five patients, mean age 64 years, with CHF in optimal treatment and with a mean ejection fraction of 32%, were studied at rest and during exercise. Twelve age and sex matched healthy subjects were compared for resting values. Another nine healthy subjects were studied at rest and during exercise at a constant low load of 75W and at a high load defined as 80% of their individual maximal capacity. In patients with congestive heart failure mean plasma immunoreactive NPY at rest was 10.3 pmol l-1 and was not significantly different from the control group. No differences between patients with slight and severe CHF were found and there was no correlation between plasma immunoreactive NPY and left ventricular ejection fraction. Mean maximal exercise time was on average 6.3 min. Only three patients exercised more than 10 min. At maximal exercise mean plasma immunoreactive NPY was 10.6 pmol l-1 the same as at rest. Plasma noradrenaline was increased in CHF patients compared to healthy subjects, and rose further during exercise. In healthy subjects plasma immunoreactive NPY rose significantly on both workloads, but more on the high load (p < 0.05), when the rise was first significant after 10 min. Plasma immunoreactive NPY at rest and during exercise was not increased in CHF patients in optimal medical treatment. Consequently plasma immunoreactive NPY is not a useful marker of the severity of CHF in these patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMedDate not supplied

A comparative study of human chorionic gonadotropin, placebo, and bed rest for women with early threatened abortion.

OBJECTIVE: To compare the effect of hCG therapy with placebo or bed rest in women with threatened abortion. DESIGN: Random assignment, double-blind. SETTING: Community hospitals. PATIENTS AND INTERVENTIONS: Sixty-one women with viable pregnancies under 8 weeks' gestation on admission to hospital were randomly allocated to receive injections of hCG or placebo, or were advised to rest in bed. MAIN OUTCOME MEASURES: Abortion vs. continuation of pregnancy at 16 weeks' gestation. RESULTS: Thirty-one aborted: 6/20 on hCG, 10/21 on placebo, 15/20 on bed rest. hCG vs. bed rest, P < .01; placebo vs. bed rest, hCG vs. placebo--not significant. Plasma progesterone: continuing pregnancy > abortion, P < .01; continued with hCG vs. aborted on placebo, P < .001; continued with hCG vs. aborted with bed rest, P < .001. No significant differences in pregnancy/birth complications or infants' birth weight. Female/male ratio was 2:1. CONCLUSIONS: hCG is significantly better than bed rest.

Abortion, Threatened↗
PubMed1995

Magnetic resonance imaging quantitation of changes in muscle volume during 7 days of strict bed rest.

BACKGROUND: Prolonged bed rest results in a loss of leg lean body mass. Previous studies using bed rest as a model for microgravity have shown decreases in leg mass after 12 and 14 d, 5 and 17 wk. HYPOTHESIS: As magnetic resonance imaging (MRI) can provide a precise and non-invasive means of determining muscle volume, we sought to determine if changes in leg muscle volume could be detected in bed rest periods as short as 7 d. METHODS: Five young, healthy, male volunteers were subjected to 7 d of absolute bed rest. Each subject underwent MRI quantitation of segmental muscle volumes of the calves and thighs before and after bed rest. Eleven (calf) and nine (thigh) contiguous 1-cm thick transaxial images were generated over prescribed regions using a Technicare MRI imager with a 0.6T superconducting magnet and body coil. Image processing was performed using a generalized 8-bit medical image analysis package developed at University of Texas Medical Branch. Images were analyzed for muscle and non-muscle volumes (including fat, blood vessel, and bone marrow volumes). RESULTS: The MRI quantitation demonstrated bed rest-induced significant decreases in segmental thigh muscle (approximately 3.0%, p < 0.05) volume. CONCLUSIONS: We conclude that computerized image analysis of MRI images provides a sensitive tool capable of detecting leg volume changes of as little as 3.0% over a 7-d period of strict bed rest.

Adult↗
PubMedDate not supplied

[Simultaneous assessment of perfusion and myocardial viability with 2 isotope studies (thallium at rest and sestamibi in exercise). Initial experience in Mexico and Latin America].

UNLABELLED: Rest-stress sestamibi single photon emission computed tomography (SPECT) has sensitivity and specificity similar to those of thallium 201 SPECT for detection of coronary artery disease. However, sestamibi is not ideal agent to study myocardial viability. There is not published experience in Latin American using dual isotope SPECT protocol to evaluate myocardial perfusion and viability. We studied 44 consecutive patients with coronary artery disease, 37 of them with previous myocardial infarction. Coronary angiography was performed in all patients. We used a 3 mCi rest T 201 SPECT followed by stress and 25 mCi sestamibi injection. Sestamibi SPECT was performed 30 minutes after exercise or 1 hour after pharmacologic stress with dipyridamole. To validate perfusion findings patients returning next day for rest sestamibi injection and SPECT. Scintigraphic data were read by two blinded expert using 20 SPECT segment analysis and each segment was scored using 5 points scoring system (0 = normal, 4 = absent uptake). The segmental score agreement between rest thallium 201 and rest sestamibi and the comparison of defect reversibility percentage and non reversibility between both protocols was 90.7%. CONCLUSION: Separate acquisition dual isotope myocardial perfusion SPECT is accurate for coronary artery disease evaluation. It showed a good agreement with rest-stress sestamibi SPECT for assessment of rest perfusion defects and reversibility and it was a better method to evaluate myocardial viability.

Exercise Test↗
PubMed1998

Divergent effects of verapamil and amlodipine at rest and during exercise.

OBJECTIVE: To evaluate, in healthy volunteers, the effects of acute administration of two calcium antagonists with different pharmacological profiles, verapamil and amlodipine, on haemodynamics at rest and during exercise. SUBJECTS AND METHODS: Six healthy volunteers (aged 20-29 years) were randomly assigned to receive single oral doses of amlodipine (5 mg), slow-release verapamil (240 mg) or a placebo during a double-blind cross-over study. Systolic (SAP), diastolic and mean arterial pressures (measured using a cuff sphygmomanometer), heart rate (HR), cardiac index (CI, bioimpedance), rate-pressure product (SAP x HR), and noradrenaline and adrenaline plasma levels were measured at rest before drug administration, and at rest and during graded bicycle exercise (steps of 50, 100 and 150 W during 3, 3 and 4 min, respectively) started 3 h after drug administration. RESULTS: At rest arterial pressure, HR, rate-pressure product and catecholamine plasma levels did not change after verapamil or amlodipine administration, whereas CI significantly decreased after verapamil (from 3.9 +/- 0.4 to 3.3 +/- 0.4 l/min per m2) but not after amlodipine (3.9 +/- 0.3 and 4.1 +/- 0.5 l/m per m2) administration. During exercise the increases in SAP and HR were slightly but not significantly higher after amlodipine than after verapamil administration, rate-pressure product and CI were higher after amlodipine (22 +/- 1 x 10(3) mmHg x beats/min and 13 +/- 2 l/min per m2, respectively) than after verapamil (20 +/- 1 x 10(3) mmHg x beats/min and 10 +/- 2 l/min per m2, respectively) administration. Plasma levels of noradrenaline and adrenaline were similar at rest after each treatment and were slightly more increased after amlodipine administration during exercise. CONCLUSIONS: In contrast to amlodipine, verapamil induced a slight myocardial depressive effect at rest and did not potentiate the myocardial effects of the sympathetic stimulation induced by exercise. The myocardial action of verapamil is such as to induce some decrease in myocardial oxygen demand, both at rest and during exercise.

Adult↗
PubMed1998

Plasma catecholamines, neuropeptide Y and leucine-enkephalin in uremic patients before and after dialysis during rest and handgrip.

UNLABELLED: We have studied the effects of handgrip on plasma levels of catecholamines, neuropeptide Y (NPY), and leu-enkephalin before and after hemodialysis of uremic patients. A cuprophan dialyzer was used. We found, that dopamine level was higher in uremia group before hemodialysis both during rest (0.38 +/- 0.39 pmol/ml) and handgrip (1.13 +/- 1.00 pmol/ml) compared to control (0.17 +/- 0.19, and 0.66 +/- 0.83 pmol/ml respectively). Hemodialysis leads to further increase of its level (0.49 +/- 0.35 pmol/ml) at rest. Epinephrine level was almost the same in uremic patients before (0.43 +/- 0.51 pmol/ml) and after dialysis (0.46 +/- 0.60) as in control subjects (0.41 +/- 0.37 pmol/ml) during the rest. Its level measured after the handgrip was the highest in uremic group after dialysis (2.10 +/- 2.00 pmol/ml), significantly lower before dialysis (1.26 +/- 0.85 pmol/ml), and the lowest in control group (0.78 +/- 0.43 pmol/ml). Norepinephrine level were very similar in uremic group before dialysis (1.54 +/- 1.05 pmol/ml), after dialysis (1.79 +/- 1.29 pmol/ml) and in control group (1.46 +/- 1.06 pmol/ml) during the rest. During the handgrip test its level was higher in uremic group after hemodialysis than before it (adequate values 8.78 +/- 4.61 and 6.70 +/- 4.74 pmol/ml). The difference between uremia group before dialysis and control group did not reach significance. The level of NPY has the tendency to increase in uremic patients. Dialysis leads to following increase of its level, but the changes did not reach the significance both in rest and handgrip. Leu-enkephalin level was higher in uremic group (9.21 +/- 7.62 pmol/ml) compared to control (5.22 +/- 1.53 pmol/ml). We observed non-significant fall of this level after dialysis (6.79 +/- 4.76 pmol/ml). We found the same tendency during the handgrip, and the changes were significant. IN CONCLUSION: uremia per se leads to increase the level of dopamine and leu-enkephaline during the rest and handgrip, but the level of epinephrine only during the handgrip; dialysis leads to further increase of dopamine during the rest, but epinephrine, norepinephrine and leu-enkephaline only during the handgrip.

Adult↗
PubMedDate not supplied

[Energy expenditure at rest: indirect calorimetry vs the Fick principle].

UNLABELLED: The objectives of this study ere to assess the reproducibility of the energy expenditure at rest in patients with mechanical ventilation, using the indirect calorimetry method and the Fick principle, and to verify whether both methods of measuring the energy expenditure, are interchangeable. 15 critically ill patients on mechanical ventilation were studied. Each study consisted of the determination, in duplicate, of the energy expenditure at rest, using indirect calorimetry and the Fick principle. Each patient was studied on two occasions, thus yielding a total of 30 studies. The determination of the energy expenditure at rest using indirect calorimetry was carried out using an apparatus based on the closed circuit method (Calorimet), and the Fick principle was carried out using a thermodilution catheter placed in the pulmonary artery. The reproducibility coefficient of the indirect calorimetry method was 132 kcal/day, which is equivalent to 7% of the average energy expenditure at rest. The reproducibility coefficient of the Fick method was 344 kcal/day, which is equivalent to 18% of the average energy expenditure at rest. The difference between both methods, 6 +/- 50 kcal/day, was not significant. The corresponding limits in both methods were between-306 kcal/day and 294 kcal/day, which is equivalent to 15% of the average energy expenditure at rest. CONCLUSIONS: The determination of the energy expenditure at rest using the Fick method, has a worse reproducibility coefficient that obtained by indirect calorimetry, but from a clinical point of view, both methods are interchangeable.

Calorimetry↗
PubMed1999

Decongestant effects on hemodynamics at rest, exercise, and recovery from exercise during--6 degrees of head down tilt.

HYPOTHESIS: Ten males were studied to examine the effects of a decongestant, pseudoephedrine hydrochloride, on rest, exercise, and recovery from exercise during -6 degrees of head down tilt (HDT). METHODS: Subjects were positioned in the HDT for a total of 6 hr: 2 hr 45 min rest, 30 min exercise, and 2 hr 45 min recovery. Sessions were identical except for the ingestion of a drug or placebo. Variables evaluated during rest, exercise, and recovery conditions were: systolic blood pressure (SBP), diastolic blood pressure (DBP), heart rate (HR), stroke volume (SV), cardiac output (Q), pulse pressure (PP), mean arterial pressure (MAP), total peripheral resistance (TPR), and forearm blood flow (FBF). RESULTS: During rest PP at 120 min was less than resting baseline, and MAP increased throughout rest. There was a treatment effect for SBP which increased up to 90 min from resting baseline for the placebo treatment only. Normal changes were found with exercise, with all variables increasing above baseline except for TPR which decreased. DBP showed no change during exercise. During the recovery condition for the drug treatment HR decreased, while SBP increased from 30 min. In addition, DBP and MAP were higher for the placebo at 30 min and higher for the drug at 90 min. CONCLUSION: The results show that ingestion of the sympathomimetic agent pseudoephedrine hydrochloride has no significant effects on the cardiovascular system during simulated microgravity.

Adult↗
PubMed1999

Prognostic value of a treadmill exercise score in symptomatic patients with nonspecific ST-T abnormalities on resting ECG.

CONTEXT: Exercise testing of patients with ST-T abnormalities on the resting electrocardiogram (ECG) is problematic because in the presence of pre-existing ST-T abnormalities, the exercise test is less specific for the diagnosis of coronary artery disease. The prognostic capability of the Duke treadmill score in patients with ST-T abnormalities vs those with normal findings on resting ECG has, to our knowledge, not been evaluated. OBJECTIVE: To compare the prognostic accuracy of the Duke treadmill score in patients with nonspecific ST-T abnormalities vs those with normal results on resting ECG. DESIGN: Inception cohort study with 7 years of follow-up. SETTING: Nuclear cardiology laboratory of a US referral center. PATIENTS: All symptomatic patients who underwent exercise thallium testing between 1989 and 1991,939 of whom had nonspecific ST-T abnormalities and 1466 of whom had normal findings on resting ECG. Exclusion criteria included congenital, valvular, or cardiomyopathic heart disease; prior coronary artery revascularization; resting ECG with secondary ST-T abnormalities; or missing data. MAIN OUTCOME MEASURES: Rates of overall mortality and cardiac death for subjects classified by Duke treadmill score risk group. RESULTS: For the end point cardiac death, 7-year survival in the study population in the low-, intermediate-, and high-risk groups was 97%, 92%, and 76%, respectively (P<.001). Compared with the control group, the study group had lower 7-year survival (94% vs 98%; P<.001), fewer low-risk patients (426 [45%] vs 811 [55%]; P<.001) with worse 7-year survival (97% vs 99%; P= .008), and more high-risk patients (49 [5%] vs 34 [2%];P<.001) with a nonsignificant trend toward worse 7-year survival (76% vs 93%; P= .36). CONCLUSIONS: The Duke treadmill score can effectively risk-stratify patients with ST-T abnormalities on the resting ECG. In classified risk categories, patients with ST-T abnormalities have a worse prognosis than those with normal results on resting ECG.

Aged↗
PubMed1996

Resting microglial cells in vitro: analysis of morphology and adhesion molecule expression in organotypic hippocampal slice cultures.

Neurons in organotypic hippocampal slice cultures (OHSCs) are known to preserve morphological and physiological features of the in vivo situation; however, little is known about the properties of microglial cells under these in vitro conditions. In this study, we addressed the question whether microglial cells in OHSCs are initially activated following explantation but return to a resting state during in vitro cultivation. Thus, we analyzed a) microglial cell morphology, b) microglial cell distribution, and c) expression of integrin adhesion molecules as putative markers of microglial activation. Hippocampal slices fixed immediately following explantation showed only resting microglial cells, mainly located in the paraventricular regions. After 3 days in vitro (div) OHSC surfaces were covered by activated microglia, whereas intermediate layers contained fewer microglial cells, giving the slices a sandwich-like appearance with the intact hippocampal formation being surrounded by glial tissue. After 3 div, microglial cells in intermediate layers of OHSCs showed activated morphology with ovaloid cytoplasm and no or merely few cytoplasmic processes; after 6 div, however, an increasing degree of ramification could be observed. After 9 div, microglia in intermediate layers had almost regained the morphological appearance of resting cells with filigrane cytoplasmic processes extended in all directions. The integrin adhesion molecules LFA-1 (alpha and beta chains) and VLA-4 were expressed on most microglial cells with activated morphology, as verified by co-localization with double immunofluorescence labeling for LFA-1 or VLA-4 and Griffonia simplicifolia isolectin B4 (GFS-B4). In contrast, only low levels of integrin adhesion molecule expression were also found on reactive astrocytes along slice surfaces. However, LFA-1 or VLA-4 were never found on ramified microglial cells, and double immunofluorescence labeling of LFA-1 or VLA-4 with ramified GFS-B4+ microglia never occurred. We conclude that a) originally resting microglial cells activated in an early phase of in vitro culture but regain a resting status after at least 6 div; and b) integrin adhesion molecules LFA1 and VLA-4 are potential markers of microglial activation, as they were found on activated but never on resting microglial cells. This enables further investigations on immunological and electrophysiological features of resting and activated microglial cells under in vitro conditions.

Animals↗
PubMed1985

Rest-exercise radionuclide angiographic assessment of left ventricular function in chronic aortic regurgitation: significance of serial studies in medically versus surgically treated groups.

Forty consecutive asymptomatic patients with chronic aortic regurgitation who underwent three serial yearly rest and postexercise radionuclide angiograms were compared with 27 consecutive patients with chronic aortic regurgitation and aortic valve replacement who were studied preoperatively, 3 and 15 months postoperatively. Patients were divided into four subgroups based upon the resting left ventricular ejection fraction and the functional reserve on the initial study. Of the 40 medically treated patients, 19 (47.5%) and 24 (60%) demonstrated a response at least one type lower at 12 months and 24 months, respectively. Initial functional reserve, initial duration of exercise, and the change in exercise duration during the 24 months was not associated with changes in resting or postexercise left ventricular ejection fraction. A seesaw pattern was observed between the resting and the postexercise left ventricular ejection fraction as ventricular function deteriorated. We observed in the surgical groups a reversal of the seesaw interaction between the resting and postexercise ejection fraction seen in the medical patients. In the surgical groups the left ventricular end-diastolic pressure, initial functional reserve, initial duration of exercise, and change in exercise duration postoperatively were not predictors of improvement in left ventricular function at 15 months. Comparing medical and surgical serial data, we suggest yearly radionuclide angiographic determination of rest left ventricular ejection fraction in asymptomatic patients with chronic aortic regurgitation. When the rest ejection fraction is less than 50%, exercise angiography should be performed to determine functional reserve. When functional reserve is also abnormal, surgery should be recommended.

Adolescent↗
PubMed2003

Clinical validation of technetium-99m MIBI-gated single-photon emission computed tomography (SPECT) for avoiding false positive results in patients with left bundle-branch block: comparison with stress-rest nongated SPECT.

BACKGROUND: Septal perfusion defects are common on myocardial perfusion single-photon emission computed tomography (SPECT) slices in patients with left bundle-branch block (LBBB) in the absence of coronary artery disease. HYPOTHESIS: The use of gated myocardial perfusion SPECT imaging in such patients should be clinically validated. The aims of this study were, therefore, to validate clinically the use of gated myocardial SPECT imaging to avoid false positive septal perfusion defects in patients with LBBB and to compare nongated and gated SPECT imaging techniques in the same patients in the same imaging session. METHODS: We performed stress-rest myocardial perfusion SPECT and resting gated SPECT using Technetium-99m MIBI in 25 patients with LBBB and in 6 control subjects. Stress-rest SPECT images and end-diastolic and end-systolic gated SPECT slices were assessed visually and quantitatively (septum/lateral wall count ratio). Coronary angiography was performed in 15 patients with LBBB and in all 6 control subjects. RESULTS: Stress-rest (nongated) SPECT slices and end-diastolic and end-systolic gated SPECT images were normal in all control subjects. Stress-rest (nongated) SPECT imaging revealed septal perfusion defect in 20 (11 reversible, 9 irreversible) patients with LBBB, whereas the figures were 15 and 5 for end-systolic and end-diastolic gated SPECT images, respectively. Coronary angiography results were normal in all control subjects and in 15 patients with LBBB. Quantitative analysis of gated SPECT images revealed no statistically significant difference between patients with LBBB and control subjects in end-diastolic mean septum/lateral wall count values (0.86 +/- 0.19 in LBBB vs. 0.98 +/- 0.15 in normal subjects, p > 0.05), but the difference was statistically significant for end-systolic, stress, and rest values (p < 0.001 for all). CONCLUSION: Gated SPECT imaging, particularly end-diastolic images, revealed fewer false positive results and thus can be used to avoid false positive septal perfusion defects commonly seen in stress-rest (nongated) myocardial perfusion SPECT in patients with LBBB.

Bundle-Branch Block↗
PubMed2005

Effect of prior cognitive state on resting state networks measured with functional connectivity.

To address the extent to which functional connectivity measures an absolute brain state, we observed the effect of prior performance of a language task on resting-state networks in regions associated with language. Six subjects were imaged during rest before and after a block-design language task. Connectivity maps were generated for each of four language regions (identified from analysis of the language activation portion of the study) in each subject for both rest periods. Conjunction analysis demonstrated distinct networks of voxels for each seed region, indicating separate functional subnetworks associated with the different regions. In a comparison of rest before and after the activation task widespread and significant changes were observed in all individuals, suggesting that the measured resting state network reflects a dynamic image of the current brain state. At the group level, an extended network was observed that was largely persistent over time. Even at the group level an increase in connectivity was observed between left and right middle frontal gyri, and between posterior cingulate cortex and medial frontal cortex in the rest after the language task. These results suggest that functional connectivity may be a powerful measure of cognitive state, sensitive to differences between controls and patients together with the particular cognitive processing occurring during the rest state.

Brain Mapping↗