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Biomedical subjects

T M Lee

Publications and source records attributed to T M Lee.

At least 91 records · Page 5Linked to original sources
PubMed1997

Rhythm chronotypes in a diurnal rodent, Octodon degus.

Interindividual variations in entrained human circadian rhythms and their relationship to differences in ease of adjustment to phase shifts have been well described. Humans classified as morning type (MT) display phase-advanced temperature minimum, onset of daily activity, and onset of sleep, whereas evening type (ET) individuals demonstrate the opposite pattern with a later phase angle of entrainment for these measures. We examined 15 variables of circadian activity and temperature for diurnal Octodon degus (n = 49; 28 male, 21 female), and noted similar chronotype variations as described for humans. Individuals with extreme MT and ET chronotypes were identified as those who differed from the entire population mean by one or more standard deviations. Compared with MTs (n = 5) and intermediate chronotypes (ITs, n = 34), ETs (n = 10) displayed a significant delay in the phase of temperature minimum, rise in temperature above the daily mean, and decline in activity and temperature below the daily mean, and had longer elevated activity and temperature durations and higher levels of mean daily activity and activity amplitude. MTs also displayed a significant phase advance in the morning temperature rise compared with ITs and ETs. This is the first description of variation in entrained circadian rhythms similar to that described for humans in both an outbred animal population and a diurnal rodent.

Activity Cycles↗
PubMed1997

Percutaneous transvenous mitral balloon valvuloplasty alone in patients with combined aortic and mitral stenosis.

To investigate the feasibility of percutaneous transvenous balloon dilatation of the mitral valve in patients with combined aortic and mitral stenosis, 12 patients were studied by echocardiography and catheterization before and after mitral valvuloplasty. Aortic stenosis was defined from prevalvuloplasty catheterization study as a transaortic pressure gradient of more than 25 mm Hg. All 12 patients underwent transvenous balloon mitral valvuloplasty successfully. Immediately after the procedure, all patients experienced improvement in clinical symptoms and in hemodynamic variables. Mitral valve areas were significantly increased from 0.78 +/- 0.18 to 1.73 +/- 0.21 cm2 (P < 0.0001) by planimetry method. Cardiac output was significantly increased from 3.6 +/- 0.1 to 4.2 +/- 0.5 L/min (P = 0.01). Mean transaortic flow rate increased 33% (from 198 +/- 68 to 254 +/- 41 mL/s, P = 0.002). Mean pressure gradient across the aortic valve after mitral valvuloplasty was not significantly increased, from 34 +/- 7 to 37 +/- 13 mm Hg. Aortic valve areas, derived from the Gorlin formula, were significantly increased from 0.57 +/- 0.12 to 0.73 +/- 0.14 cm2 (P = 0.006) after mitral valvuloplasty. However, continuity equation-derived aortic valve area was independent of increasing flow rate after mitral valvuloplasty from 1.29 +/- 0.35 to 1.30 +/- 0.29 cm2. During follow-up with a mean of twenty four +/- fourteen months, 8 patients were in New York Heart association functional class I, 3 in class II, and 1 in class IV who received pericardiotomy owing to constrictive pericarditis without aortic valve replacement. In conclusion, mitral valvuloplasty alone may be safe and effective in alleviating symptoms in mitral stenosis patients with transaortic pressure gradient > 25 mm Hg. Continuity equation-derived aortic valve areas seem to be flow independent in evaluation of aortic stenosis and are important for decision making.

Adult↗
PubMed1997

Olfactory bulbectomy impedes social but not photic reentrainment of circadian rhythms in female Octodon degus.

Recent studies demonstrated that nonphotic (social) cues markedly accelerate reentrainment to large phase shifts of the light-dark (LD) cycles in female Octodon degus and that such changes are likely effected by chemosensory stimuli. This experiment investigated the effects of olfactory bulbectomies on (1) socially facilitated reentrainment rates of circadian rhythms following a 6-h phase advance of the LD cycle, (2) photic reentrainment rates of circadian rhythms following a 6-h advance of the LD cycle, (3) photic entrainment, and (4) the circadian period (tau) of activity rhythms in constant darkness (DD). olfactory bulbectomies (BX) blocked socially facilitated reentrainment rates but did not alter reentrainment rates of circadian rhythms to photic cues alone. In addition, BX lowered mean daily locomotor activity levels and decreased the amplitude of the activity rhythm in degus housed in entrained (LD 12:12) conditions but did not alter the phase of activity onset or offset, duration (alpha) of activity, or mean daily core body temperature. Bulbectomies also failed to modify tau of free-running activity rhythms. This experiment confirms that the olfactory bulbs and chemosensory cues are necessary for socially facilitated reentrainment. In contrast to their effects in nocturnal rodents, BX do not produce significant circadian photic changes in diurnal degus. This is the first experiment to determine that chemosensory stimuli modulate the circadian system in a diurnal rodent.

Animals↗
PubMed1997

The induction of Fos-like proteins in the suprachiasmatic nuclei and intergeniculate leaflet by light pulses in degus (Octodon degus) and rats.

In nocturnal rodents, exposure to light results in an increase in Fos expression in two regions that receive direct retinal input: the suprachiasmatic nuclei (SCN) of the hypothalamus and the intergeniculate leaflet (IGL) of the thalamus. The induction of Fos within the SCN of nocturnal rodents is phase dependent, with light presented during the subjective night increasing Fos expression and light presented during the subjective day having little effect. By contrast, Fos expression increases in the IGL when light is presented during the subjective day or night. It is unclear whether Fos is part of the pathway mediating light-induced phase shifts in diurnal rodents. In the present study, the ability of light to induce immunostaining for Fos in the SCN and IGL was compared in diurnal rodents, Octodon degus (degus), and nocturnal rats. Degus and rats were either maintained in constant darkness or exposed to a 1-h light pulse at circadian time (CT) 4 or 16. Degus exhibit robust phase shifts at each of those circadian hours, whereas rats demonstrate phase shifts only at CT 16. In degus, exposure to a 1-h light pulse at CT 16 resulted in an increase in the number of Fos-immunopositive (Fos+) cells in the ventrolateral SCN. By contrast, a 1-h light pulse at CT 4 resulted in a decrease in the number of Fos+ cells in the dorsomedial portion of the SCN. In rats, a light pulse presented at CT 16 resulted in an increase in Fos+ cells throughout the SCN, and a pulse at CT 4 had no effect on Fos staining. Both degus and rats showed increases in Fos expression in the IGL after light exposure at CTs 4 and 16. The authors conclude that light pulses presented at times that produce phase shifts in activity rhythms also alter Fos expression in the SCN and IGL of degus. Although these effects of light exposure on Fos expression are not identical in diurnal and nocturnal rodents, it is likely that Fos and other immediate early genes are part of the pathway mediating the effects of light in both diurnal and nocturnal rodents.

Animals↗
PubMed1996

Changes of left ventricular function after percutaneous balloon mitral valvuloplasty in mitral stenosis with impaired left ventricular performance.

The pathophysiological role of mechanical and myocardial factors for impairment of left ventricular performance in mitral stenosis is still not clear. To investigate this controversy, 27 patients of mitral stenosis with left ventricular ejection fraction < 50% were studied. Patients were divided into two groups: Group 1: 20 patients, left ventricular ejection fraction improved to > 50% after valvuloplasty, and Group 2: 7 patients, left ventricular ejection fraction still < 50% after valvuloplasty. The clinical and hemodynamic characteristics were comparable for the two groups before valvuloplasty. Follow-up catheterization done one week later showed similar changes in mitral valve area, cardiac index, pulmonary pressure, left ventricular end-diastolic volume index and systemic vascular resistance between the two groups. However, left ventricular end-systolic volume was significantly decreased after valvuloplasty in Group 1 but not in Group 2, resulting in significantly higher ejection fraction in Group 1 than in Group 2. Postoperatively, regional wall motion scores were lower in Group 1 than in Group 2 (2.0 +/- 0.6 vs. 2.7 +/- 0.5 at the anterolateral wall, P = 0.002; 1.9 +/- 0.6 vs. 2.9 +/- 0.4 at the posterobasal wall, P = 0.0003). Most of our mitral stenosis patients with impaired left ventricular ejection fraction showed improvement after mitral valvuloplasty had released the mechanical obstruction. However, in some patients, impaired ejection fraction persisted after valvuloplasty, suggesting the mechanism of myocardial failure. Thus, both myocardial and mechanical factors play important roles in the pathogenesis of left ventricular ejection performance impairment.

Adult↗
PubMed1996

Excessive papillary muscle traction and dilated mitral annulus in mitral valve prolapse without mitral regurgitation.

This study demonstrated excessive papillary muscle displacement during peak systole but normal mitral annulus function during the cardiac cycle in patients with mitral valve prolapse and no mitral regurgitation. The excessive papillary muscle displacement may play an important role in the pathogenesis of the superior displacement of mitral leaflets in patients with mitral valve prolapse.

Adolescent↗
PubMed1996

Usefulness of transdermal scopolamine for vasovagal syncope.

We studied short-term effectiveness of transdermal scopolamine in a group of patients with unexplained syncope provoked during head-up tilt testing. This double-blind randomized trial of transdermal scopolamine demonstrated no significant effect of preventing vasovagal syncope.

Administration, Cutaneous↗
PubMed1996

Excessive myocardial contraction in vasovagal syncope demonstrated by echocardiography during head-up tilt test.

The purpose of this study was to gain insight into the mechanism of vasovagal syncope and to test the efficacy of theophylline to prevent syncope. Twenty-six patients with vasovagal syncope underwent two-dimensional echocardiography and theophylline test during head-up tilt test. A standard parasternal short-axis view of echocardiography at the level of the papillary muscle was recorded to measure fraction shorting of the left ventricle, and left ventricular end-diastolic and end-systolic dimensions. Heart rate, blood pressure, and symptoms were recorded. There were three groups; Group 1: no syncope with and without isoproterenol (n = 5); Group 2: syncope only after the infusion of isoproterenol (n = 16); Group 3: syncope without isoproterenol (n = 5). Groups 2 and 3 proceeded to theophylline injection (250 mg). The study showed that the 80 degrees tilt induced an increase in heart rate of 6.6 +/- 4.0, 12.4 +/- 6.6, and 25.4 +/- 4.5 beats/min in Groups 1, 2, and 3, respectively (p < 0.05 in Groups 1 and 2, p < 0.05 in Groups 1 and 3). The addition of isoproterenol during posture change from supine to an 80 degrees tilt made the significant change of fractional shortening from 0.4 +/- 5% to 6 +/- 13% in Group 2 (p = 0.05), compared with no significant change in Group 1. There were no significant differences in left ventricular end-diastolic dimension and end-systolic dimension in each group between baseline and isoproterenol infusion during posture change. Vasovagal syncope was associated with vigorous myocardial contraction, rather than with contraction against an empty left ventricle. The acute loading of theophylline was not effective in preventing vasovagal syncope.

Adrenergic beta-Agonists↗
PubMed1996

Left atrial spontaneous echo contrast in asymptomatic patients with a mechanical valve prosthesis.

BACKGROUND: Valve thromboembolism may be a fatal complication of mechanical valve prosthesis if detected late. Spontaneous echo contrast (SEC) is a well-documented prothrombotic phenomenon; here we report it in asymptomatic patients with a mechanical valve prosthesis. METHODS: Ninety-two asymptomatic patients with a mechanical valve prosthesis for underlying rheumatic heart disease underwent transesophageal echocardiography. Appendage area, peak filling and emptying velocities of the left atrial appendage, and the presence or absence of SEC and thrombi were determined. The results of 56 patients without SEC or thrombi (group I) were compared with those of 24 patients with SEC and no thrombi (group II) and 12 patients with thrombi (group III). RESULTS: Spontaneous echo contrast was present in 39% of the asymptomatic patients with a mechanical valve prosthesis. Although 12 patients had cardiac thrombi, including valve thrombi in 4, no patients presented symptoms. Anticoagulant therapy had no significant association with SEC and atrial thrombi. There was a significantly greater prevalence of atrial fibrillation and mitral prosthesis in groups II and III than in group I. Two patterns of left atrial appendage flow were identified: one was organized biphasic flow with peak filling velocities of 41.2 +/- 17.2 cm/s and emptying velocities of 40.5 +/- 17.5 cm/s. The other showed irregular, very low peak filling velocities (104 +/- 11.5 cm/s) and emptying velocities (12.3 +/- 13.1 cm/s). The former flow pattern was associated with sinus rhythm and the latter form was associated with atrial fibrillation. CONCLUSIONS: There was a relatively high prevalence of SEC and thrombi in patients with a mechanical valve prosthesis. Patients with a valve prosthesis may not have clinical symptoms. Anticoagulation intensity was not associated with the occurrence of SEC and thrombi. Patients with the mitral valve prosthesis and atrial fibrillation were identified as a high-risk of subgroup for the development of SEC and thrombi.

Adult↗
PubMed1996

Case report: reversible systolic heart failure and deep jaundice in hyperthyroidism.

Systolic heart failure because of hyperthyroidism in patients without preexisting heart disease is not common. Thyrotoxic systolic heart failure is rarely diagnosed during life. Reports about thyrotoxicosis-related systolic heart failure have been diagnosed postmortem. However, antemortem diagnosis of this fatal disease has important clinical implications because if detected early, thyrotoxicosis-related systolic heart failure is reversible. Here is a report a patient with Graves' disease, systolic heart failure, and deep jaundice, which resolved after the treatment of antithyroid drugs.

Female↗
PubMed1996

Effects of increasing flow rate on aortic stenotic indices: evidence from percutaneous transvenous balloon dilatation of the mitral valve in patients with combined aortic and mitral stenosis.

OBJECTIVES: To investigate the effects of transvalvar flow rate on aortic valve resistance and valve area after percutaneous transvenous balloon dilatation of the mitral valve in a homogeneous group of patients with rheumatic heart disease. DESIGN: Retrospective analysis of 12 patients with combined aortic and mitral stenosis who had undergone balloon dilatation of the mitral valve over a period of 9 years. SETTING: Tertiary referral centre. PATIENTS: Twelve (8 women, 4 men; mean (SD) age 37 (9) of 227 consecutive patients with critical mitral stenosis undergoing transvenous balloon dilation of the mitral valve in the centre also had aortic stenosis, defined as a transaortic pressure gradient of more than 25 mm Hg measured at a catheterisation study before valvuloplasty. INTERVENTIONS: Echocardiographic variables (mitral valve area measured by the pressure half-time method and planimetry, and the aortic valve area derived from the continuity equation) and haemodynamic measurements (cardiac output, left ventricular mean systolic pressure, aortic mean pressure, transaortic valve pressure gradient, mitral valve and aortic valve areas derived from the Gorlin formula, and aortic valve resistance) were assessed before and after transvenous balloon dilatation of the mitral valve. Follow up catheterisation to measure haemodynamic variables was performed one week after mitral valvuloplasty. RESULTS: Mean transaortic flow rate increased 33% after mitral valvuloplasty (from 198 (68) to 254 (41) ml/s, P = 0.002). Aortic valve areas derived from the Gorlin formula were significantly increased from 0.57 (0.12) to 0.73 (0.14) cm2 (P = 0.006) after mitral valvuloplasty. However, aortic valve area and valve resistance derived from the continuity equation were independent of the increase in flow rate after mitral valvuloplasty (from 1.29 (0.35) to 1.30 (0.29) cm2 and from 317 (65) to 259 (75) dyn.s.cm-5, both P = NS). CONCLUSION: The Gorlin-derived aortic valve area tends to be flow-dependent, and continuity equation-derived aortic valve area and catheterisation-derived valve resistance seem to be less flow-dependent. In patients with combined mitral and aortic stenosis, these flow-independent indices are important for decision-making.

Adult↗
PubMed1995

Changes in phases and crystallinity of plasma-sprayed hydroxyapatite coatings under heat treatment: a quantitative study.

With three kinds of plasma-sprayed hydroxyapatite coatings (HACs) prepared, the objectives of this study were (1) to establish the calibration methods for quantitatively measuring the concentration of impurity phases and the degree of crystallinity of the HACs, and (2) to explore the effects of postheat treatments at various temperatures in vacuo on the changes of phases and crystallinity of the HACs. By the internal standard method used, the concentrations of impurity phases, such as alpha-TCP, beta-TCP, and TP, of the assprayed HACs were significantly higher than those measured by the direct intensity-ratio method, and the CaO phase was lower than the direct intensity-ratio method. When the HACs were heat treated in the temperature interval 630-850 degrees C, the concentrations of impurity phases obviously decreased, and the coating crystallinity apparently increased. After annealing at 850 degrees C, an HAC consisting of at least 95% crystallinity with few impurity phases was obtained. As the annealing temperatures in the interval 850-1000 degrees C were applied, however, the HA phase seriously decomposed, resulting in the appearance of a large number (higher than 20 wt%) of impurity phases in the HACs. This work suggests that the optimum heat treatment conditions in vacuo for maximizing crystallinity and minimizing impurity phases of the HACs do not occur at the same temperature.

Alloys↗
PubMed1995

Interaction of maternal photoperiod history and food type on growth and reproductive development of laboratory meadow voles (Microtus pennsylvanicus).

The interaction of maternal photoperiod history and four diets were tested by measuring body growth, reproductive development, and pelage development in 9-week-old juvenile meadow voles. Meadow vole dams were housed in long daylengths (LD; 14 h light/day), short daylengths for 2 weeks (SD; 10 h light/day), or short daylengths for 26 weeks (PR; photorefractory) prior to mating. Immediately following parturition, one of four diets was available to dams and pups; (a) a control diet containing no 6-methoxy-2-benzoxazolinone (6-MBOA); (b) the control diet plus sprouted wheat (which contains 6-MBOA); (c) the control diet plus alfalfa harvested in spring (no 6-MBOA); and (d) the control diet plus alfalfa harvested in autumn (no 6-MBOA). By 9 weeks of age, juvenile meadow voles born to photorefractory dams and fed either spring or fall alfalfa or sprouted wheat were significantly larger and more had achieved puberty than juveniles fed only the control diet. Juveniles born to LD dams demonstrated a smaller increase in developmental rate than photorefractory juveniles when fed alfalfa and spring wheat, and juveniles of SD dams showed the smallest effect of alfalfa and sprouted wheat on development. Supplements of spring wheat and both forms of alfalfa had similar positive effects on growth and reproduction. The authors suggest that juvenile meadow voles rely on the interaction of maternal photoperiod history and the availability of nutrient-rich food such as sprouted wheat and alfalfa to time the onset of growth and puberty.

Animals↗
PubMed1995

Sex differences and effects of social cues on daily rhythms following phase advances in Octodon degus.

Two experiments were designed to determine whether social cues could enhance the rate of resynchronization in body temperature and general activity rhythms in male or female Octodon degus following a 6 h phase advance. The first experiment examined average resynchronization rates for animals in each condition. The second experiment examined resynchronization rates for a smaller group of animals, each treated as its own control. Female phase-shifters resynchronized temperature and activity rhythms significantly faster when housed with an entrained (donor) female than those females housed with another phase-shifting female or housed alone. Females housed with entrained males resynchronized their temperature rhythms significantly slower than females housed with entrained females. No differences in resynchronization rate for phase-shifting males existed between test conditions. However, activity rhythms of male controls (housed alone) reentrained significantly faster than those of female controls. These experiments demonstrate a sex difference in (i) reentrainment rate by photic cues alone; (ii) donors' effect on female phase-shifters' resynchronization; and (iii) phase-shifters' resynchronization response to donor cues. In these studies, resynchronization in the presence of another animal could either have been achieved by entrainment of the pacemaker or by masking of the circadian rhythms.

Animals↗
PubMed1995

Estrus- and steroid-induced changes in circadian rhythms in a diurnal rodent, Octodon degus.

Diurnal Octodon degus exhibited marked alterations in activity and temperature in conjunction with the 3 wk estrous cycle when housed in LD12:12 light cycle. On the day of estrus, mean daily activity increases 109%, mean core temperature rises .4 degree C, activity onset is advanced 2 h, and amplitudes of both rhythms decline compared with the 3 days prior to estrus. On the day following estrus, activity onset was delayed 4.9 h, and mean activity and core temperature fell below that of the preestrus period. Ovariectomy significantly reduced mean temperature (.98 degree C) but did not significantly alter mean activity, and eliminated cyclic effects of estrus. Estrogen replacement led to a nonsignificant elevation in mean activity and core temperature with no change in the phase angle of entrainment. Progesterone replacement significantly reduced mean core temperature and mean activity, while only the phase angle difference between temperature minimum and activity onset was significantly altered. Intact degus maintained in constant darkness displayed only transient fluctuations in activity onset and temperature minimum during and after estrus. Estrogen or progesterone treatment of ovariectomized, free-running degus altered mean temperature and activity levels, but did not influence tau. Changes in phase angle of entrainment during estrus are not the result of hormone effects on the circadian clock but likely reflect increased or decreased levels of activity.

Animals↗
PubMed1995

Spontaneous coronary artery dissection in an elderly woman with acute inferior myocardial infarction. A case report.

Spontaneous coronary artery dissection is a rare cause of acute myocardial infarction. It usually occurs in relatively young patients and is frequently found at autopsy. Because of the low incidence, the treatment of choice for spontaneous coronary artery dissection is still not settled. Here the authors report a sixty-six-year-old woman with coronary lesions judged as spontaneous coronary artery dissection. She presented with chest pain. Under diagnosis of acute inferior myocardial infarction, she was treated with recombinant tissue-type plasminogen activator. Coronary arteriography performed two weeks later revealed a dissection involving a long segment of right coronary artery. The left coronary arteries and uninvolved portion of right coronary artery were smooth and patent. She suffered no hypertension and gave no definite history of trauma. This patient was treated medically with aspirin, isosorbide dinitrate, and metoprolol and remained in stable condition after a follow-up period of six months.

Aged↗
PubMed1995

Anomalous origin of left circumflex artery in a scimitar syndrome. A case report.

This report concerns a twenty-seven-year-old woman with scimitar syndrome of abnormal origin of the left circumflex artery from the pulmonary artery. Operation was performed to redirect the abnormal venous return to the left atrium and abnormal origin of the left circumflex artery to the aorta. Unfortunately, pulmonary hypertension with hemoptysis occurred nineteen months after the operation. A second angiogram showed total occlusion of the graft to the left circumflex artery and impaired left ventricle function, rather than thrombosis of the anastomosis to the scimitar vein, as the cause of pulmonary hypertension.

Adult↗