Search PubMed⌕ Search

Biomedical subjects

J C Evans

Publications and source records attributed to J C Evans.

At least 73 records · Page 4Linked to original sources
PubMed1994

The associations of levels of serum potassium and magnesium with ventricular premature complexes (the Framingham Heart Study).

There are conflicting data regarding the impact of serum potassium and magnesium levels on susceptibility to ventricular premature complexes (VPCs) in the clinical setting. The associations of serum potassium and magnesium levels with the prevalence of complex or frequent (> 30/hour, multiform or repetitive) VPCs were examined after adjusting for age, sex, smoking, caffeinated coffee consumption, alcohol consumption, and left ventricular mass in Framingham Offspring Study subjects who were free of clinically apparent heart disease. There were 3,327 eligible subjects (mean age 44 years). Complex or frequent VPCs were present in 183 subjects (5.5%). When age-adjusted prevalences of complex or frequent VPCs were compared among quartiles of serum potassium and magnesium using a trend test, lower potassium (p = 0.002) and lower magnesium (p = 0.010) levels were associated with higher prevalence rates of arrhythmia. In logistic regression analyses that included potassium and magnesium simultaneously, potassium (p = 0.0021) and magnesium (p = 0.0311) levels were inversely associated with the occurrence of complex or frequent VPCs after adjustment for age, sex, smoking, coffee and alcohol consumption, diuretic use, and systolic blood pressure. These associations remained significant after accounting for left ventricular mass. A 1 SD decrement in potassium (0.48 mEq/liter) or magnesium (0.16 mEq/liter) level was associated with a 27% (95% confidence interval 6% to 51%) and a 20% (95% confidence interval 3% to 41%) greater odds of complex or frequent VPCs, respectively. Lower levels of serum potassium and magnesium were concurrently associated with higher prevalence rates of ventricular arrhythmias.

Adult↗
PubMed1994

Left ventricular mass and risk of stroke in an elderly cohort. The Framingham Heart Study.

OBJECTIVE: To evaluate the association of echocardiographically determined left ventricular mass (LVM) with incidence of stroke or transient ischemic attack in an elderly cohort. DESIGN: Cohort study with a follow-up period of 8 years. SETTING: Population-based sample. SUBJECTS: Elderly original cohort subjects of the Framingham Heart Study who were free of cerebrovascular disease and atrial fibrillation at the 16th biennial examination and who had adequate echocardiograms. This group consisted of 447 men (mean age, 67.8 years; range, 60 to 90 years) and 783 women (mean age, 69.2 years; range 59 to 90 years). MAIN OUTCOME MEASURES: Age-adjusted 8-year incidence of stroke was examined as a function of baseline quartiles of LVM-to-height ratio. Proportional hazards regression was used in multivariate analyses to assess risk of stroke as a function of LVM-to-height ratio quartile, adjusting for age, sex, systolic blood pressure, hypertension treatment, diabetes, cigarette smoking, and blood lipid levels. RESULTS: Among the 1230 subjects eligible, 89 cerebrovascular disease events (62 strokes and 27 transient ischemic attacks) occurred during follow-up. In men, 8-year age-adjusted incidence of cerebrovascular events was 18.4% in the highest quartile of LVM-to-height ratio and 5.2% in the lowest quartile. Corresponding values in women were 12.2% and 2.9%. The hazard ratio for cerebrovascular events comparing highest to lowest quartile of LVM-to-height ratio was 2.72 (95% confidence interval [CI], 1.39 to 5.36) after adjusting for age, sex, systolic blood pressure, hypertension treatment, diabetes, cigarette smoking, and the ratio of total cholesterol to high-density lipoprotein cholesterol. After adjusting for age, sex, and cardiovascular disease risk factors, the hazard ratio for cerebrovascular events was 1.45 (95% CI, 1.17 to 1.80) for each quartile increment of LVM-to-height ratio. CONCLUSIONS: Echocardiographically determined LVM-to-height ratio offers prognostic information beyond that provided by traditional cerebrovascular disease risk factors. Echocardiography provides information that facilitates identification of individuals at high risk for stroke and transient ischemic attack.

Aged↗
PubMed1994

Reduced heart rate variability and mortality risk in an elderly cohort. The Framingham Heart Study.

BACKGROUND: The prognostic implications of alterations in heart rate variability have not been studied in a large community-based population. METHODS AND RESULTS: The first 2 hours of ambulatory ECG recordings obtained on original subjects of the Framingham Heart Study attending the 18th biennial examination were reprocessed to assess heart rate variability. Subjects with transient or persistent nonsinus rhythm, premature beats > 10% of total beats, < 1 hour of recording time, processed time < 50% of recorded time, and those taking antiarrhythmic medications were excluded. The associations between heart rate variability measures and all-cause mortality during 4 years of follow-up were assessed. There were 736 eligible subjects with a mean age (+/- SD) of 72 +/- 6 years. The following five frequency domain measures and three time domain measures were obtained: very-low-frequency power (0.01 to 0.04 Hz), low-frequency power (0.04 to 0.15 Hz), high-frequency power (0.15 to 0.40 Hz), total power (0.01 to 0.40 Hz), the ratio of low-frequency to high-frequency power, the standard deviation of total normal RR intervals, the percentage of differences between adjacent normal RR intervals that are > 50 milliseconds, and the square root of the mean of the squared differences between adjacent normal RR intervals. During follow-up, 74 subjects died. In separate proportional hazards regression analyses that adjusted for relevant risk factors, very-low-frequency power (P < .0001), low-frequency power (P < .0001), high-frequency power (P = .0014), total power (P < .0001), and the standard deviation of total normal RR intervals (P = .0019) were significantly associated with all-cause mortality. When all eight heart rate variability measures were assessed in a stepwise analysis that included other risk factors, low-frequency power entered the model first (P < .0001); thereafter, none of the other measures of heart rate variability significantly contributed to the prediction of all-cause mortality. A 1 SD decrement in low-frequency power (natural log transformed) was associated with 1.70 times greater hazard for all-cause mortality (95% confidence interval of 1.37 to 2.09). CONCLUSIONS: The estimation of heart rate variability by ambulatory monitoring offers prognostic information beyond that provided by the evaluation of traditional risk factors.

Aged↗
PubMed1993

Impact of heart rate and PR interval on Doppler indexes of left ventricular diastolic filling in an elderly cohort (the Framingham Heart Study).

The relations of heart rate and PR interval to Doppler-derived diastolic indexes were examined in 260 men (mean age 75 years) and 462 women (mean age 76 years) from the Framingham Heart Study. Subjects receiving any antihypertensive or cardiac medications were excluded from eligibility; those with mitral stenosis or prosthesis, pacemaker, atrial fibrillation, arrhythmia, left bundle branch block, congestive heart failure, previous myocardial infarction, and technically inadequate Doppler study were also excluded. Peak velocity of early (E) and late (A) diastolic left ventricular (LV) filling, ratio of peak velocities E/A, ratio of time velocity integrals E/A, and atrial filling fraction were studied by multivariable analyses adjusting for age, sex, blood pressure, heart rate and PR interval. Heart rate was a major determinant of all 5 Doppler indexes of diastolic filling; heart rate was inversely associated with peak velocity E, E/A, and time velocity integral E/A, and was directly associated with peak velocity A and atrial filling fraction. PR interval was inversely associated with time velocity integral E/A (p < 0.01) and directly associated with atrial filling fraction. The results were largely unaltered after further adjustment for LV wall thickness, LV end-diastolic diameter and left atrial diameter (in addition to age, sex and blood pressure). Heart rate and PR interval are independent contributors to Doppler-assessed LV diastolic filling in the elderly. The atrial contribution to LV filling depends on its timing in the cardiac cycle and on heart rate. Failure to account for heart rate and PR interval may lead to inappropriate assessment of Doppler diastolic filling.

Aged↗
PubMed1993

The impact of female hormone usage on the lipid profile. The Framingham Offspring Study.

BACKGROUND: Exogenous female hormone use appears to affect cardiovascular disease risk in both premenopausal and postmenopausal women. The purpose of this study was to evaluate the impact of exogenous female hormone usage on the lipid profile among premenopausal and postmenopausal women. METHODS: One thousand nine hundred thirty female participants of the Framingham Offspring study comprised the study population. Of the 992 premenopausal subjects, 57 were current oral contraceptive users; among the 938 postmenopausal subjects, 80 were current hormone users. The influence of hormone use on lipid and lipoprotein levels was determined using multivariable linear regression models that adjusted for age, body mass index, smoking, alcohol intake, beta-blocker, and diuretic therapy. Adjusted least-squares means were calculated for each lipid and lipoprotein according to female hormone usage and menopausal status. RESULTS: In the premenopausal analysis, pooled oral contraceptive use was significantly related to increased levels of total cholesterol, triglycerides, high-density lipoprotein cholesterol and apolipoprotein A-I. Increased estrogen content was inversely associated with low-density lipoprotein cholesterol, and apolipoprotein B levels, while increased progestin content was inversely related to high-density lipoprotein cholesterol and apolipoprotein A-I levels. Among postmenopausal women, use of premarin only was significantly associated with increased high-density lipoprotein cholesterol and apolipoprotein A-I levels. Combination use of premarin and provera was significantly associated with increased apolipoprotein A-I levels; less powerful but still significant associations with increased high-density lipoprotein cholesterol and decreased low-density lipoprotein cholesterol were also observed. CONCLUSION: In this cross-sectional analysis, oral contraceptive use is associated with both favorable and unfavorable lipid alterations with respect to atherogenic risk. Among postmenopausal women, hormone replacement therapy (both premarin only and combined premarin and provera) appears to be associated with favorable effects on the lipid profile.

Adolescent↗
PubMed1993

Echocardiographic assessment of left ventricular structure and diastolic filling in elderly subjects with borderline isolated systolic hypertension (the Framingham Heart Study).

Abnormalities in left ventricular (LV) structure and function have been shown in patients with diastolic hypertension and recently in subjects with isolated systolic hypertension. The purpose of this study was to determine whether abnormalities of cardiac structure or function are present in elderly subjects with borderline isolated systolic hypertension (defined as systolic blood pressure [BP] between 140 and 159 mm Hg, and diastolic BP < 90 mm Hg). Ninety-one subjects (mean age 77 years) from the original Framingham Heart Study with untreated borderline isolated systolic hypertension, who were free of cardiovascular disease, were compared with 139 normotensive (BP < 140/90 mm Hg) subjects (mean age 76 years). Measurements included M-mode values for LV structure, and 6 Doppler indexes of LV diastolic filling. Subjects with borderline isolated systolic hypertension and the control group differed in mean systolic (147 vs 125 mm Hg) and diastolic (76 vs 70 mm Hg) BP. Borderline systolic hypertension was the most frequent form of untreated hypertension in this elderly group. The sum of LV wall thicknesses (septum+posterior wall) was significantly higher in borderline hypertensive subjects than in normotensive ones (20.5 vs 19.7 mm; p = 0.002). No difference was detected in LV internal dimension or systolic function. After adjustment for age and other clinical variables, comparisons between the groups revealed significant differences in indexes of Doppler diastolic filling. Peak velocity of early filling, and the ratio of early to late peak velocities were lower in the hypertensive group (40 vs 44 cm/s [p = 0.03] and 0.69 vs 0.76 [p = 0.01], respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1993

Coronary artery disease prediction.

The factors age, gender, cigarette-smoking, blood cholesterol, high-density lipoprotein (HDL) cholesterol, blood pressure, left ventricular hypertrophy, and diabetes mellitus have been used in the Framingham Heart Study for the prediction of coronary artery disease (CAD) in a middle-aged cohort of 2590 women and 2983 men aged 30 to 74 years at baseline. During 12 years of follow-up, there were 385 cases of CAD among men (12-year incidence of 5% at ages 30 to 39, rising to 26% at ages 70 to 74), and 241 cases among women (12-year incidence of 1% at ages 30 to 39, rising to 20% at ages 70 to 74). This review includes examples of the calculation of risk factor estimates from logistic regression equation output, discusses the role of attributable risk, provides information concerning the applicability of risk factor estimates to other populations, and contrasts the factors responsible for the occurrence of CAD with those that are important in other vascular diseases such as stroke.

Adult↗
PubMed1993

Prognosis after the onset of coronary heart disease. An investigation of differences in outcome between the sexes according to initial coronary disease presentation.

BACKGROUND: Differences exist between men and women in prognosis after the onset of coronary heart disease (CHD). METHODS AND RESULTS: All Framingham Heart Study subjects with the onset of clinically apparent coronary disease from 1951 through 1986 were studied to compare prognosis in men and women according to CHD presentation. Coronary disease presentations included angina, coronary insufficiency (unstable angina), recognized myocardial infarction, unrecognized myocardial infarction, and coronary death. Less than 1% of subjects were lost to follow-up for overall mortality. Cox modeling was used to examine the sex differences in outcome for each coronary presentation. New nonfatal coronary disease developed in 750 men (mean age, 63 years) and 583 women (mean age, 67 years). After onset of angina, men were at greater risk than women for myocardial infarction (hazards ratio [HR], 2.20; 95% confidence interval [CI], 1.45 to 3.34) and coronary death (HR, 2.11; 95% CI, 1.32 to 3.36) after adjustment for age and coronary disease risk factors. After a recognized myocardial infarction, there was a trend toward greater risk for overall mortality in women than men after adjustment for age and risk factors (HR, 0.75; 95% CI, 0.53 to 1.08). In contrast, after an unrecognized myocardial infarction, men were at increased risk for death compared with women (HR, 2.01; 95% CI, 1.28 to 3.15). CONCLUSIONS: Women fare at least as poorly as men after recognized myocardial infarction, whereas women have a more favorable outlook than men after the onset of angina or unrecognized myocardial infarction. The favorable outcome in women after angina and unrecognized myocardial infarction is due, in part, to greater misclassification of these coronary events in women than in men.

Adult↗
PubMed1992

Intra- and interobserver reproducibility of Doppler-assessed indexes of left ventricular diastolic function in a population-based study (the Framingham Heart Study).

The reproducibility of a variety of Doppler indexes of diastolic function in an epidemiologic setting and in atrial fibrillation have not been reported. This study examined the reproducibility of left ventricular inflow in subjects in sinus rhythm (n = 80) and atrial fibrillation (n = 12), randomly selected from the original cohort of the Framingham Heart Study. The following Doppler indexes were assessed for all subjects: peak and integral of early (E) diastolic inflow velocity, acceleration slope and time, deceleration slope and time, and pressure half-time. For subjects in sinus rhythm, the following parameters also were measured: the peak and integral of late (A) diastolic inflow velocity, ratios of peak velocities and integrals E/A, and atrial filling fraction. Intraobserver and interobserver variability were evaluated by statistical methods including Student's t test of the systematic differences (bias), percent bias, correlation coefficients, measurement precision, and percent precision. In subjects in sinus rhythm, although the interobserver bias was statistically significant for most of the parameters, it was < 10% for all but 1 parameter (acceleration time). For the peak and integral measures, the intra- and interobserver correlations were > or = 0.89, with intra- and interobserver percent precision measures within 2.2 to 13.0% of the corresponding mean values. The acceleration, deceleration and pressure half-time measures had somewhat lower correlations (interobserver correlations ranging from 0.59 to 0.96), with percent precision measures further from the corresponding means (interobserver percent precision ranging from 10.1 to 19.5%).(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1992

Prognostic implications of subclinical left ventricular dilatation and systolic dysfunction in men free of overt cardiovascular disease (the Framingham Heart Study).

To determine the prognostic significance of asymptomatic left ventricular (LV) dilatation and LV systolic dysfunction, 1,493 men who were free of symptomatic cardiovascular disease underwent M-mode echocardiography and were then followed for a mean of 4.15 years. At baseline examination, 170 men (11.4%) had an abnormally high end-diastolic LV internal dimension (> or = 56 mm) and 76 (5.1%) had an abnormally low fractional shortening (< or = 30%). During the follow-up period, 68 men experienced 92 cardiovascular disease events. After adjusting for age and traditional cardiovascular disease risk factors in proportional-hazards analyses, fractional shortening was a significant independent predictor of cardiovascular risk (relative risk [RR] = 1.42, 95% confidence interval [CI] 1.12 to 1.81, for decrease of fractional shortening by 4%). Increased risk was also associated with combinations of low fractional shortening and high end-diastolic internal dimension (RR = 3.77, 95% CI 1.59 to 8.93) and with low percent fractional shortening with LV hypertrophy (RR = 5.93, 95% CI 1.97 to 17.85). In conclusion, subclinical LV dilatation and LV systolic dysfunction, although uncommon in men free of overt cardiovascular disease, are associated with increased risk for new cardiovascular disease events.

Adult↗
PubMed1992

Determinants of Doppler indexes of left ventricular diastolic function in normal subjects (the Framingham Heart Study).

Normative Doppler values and determinants of left ventricular (LV) diastolic function in healthy subjects have not been fully elucidated. Subjects from the Framingham Heart Study were examined to describe reference values and determinants of echocardiographic Doppler indexes of diastolic function. One hundred twenty-seven randomly selected, rigorously defined, normal subjects, approximately evenly distributed by sex and age from the third through the eighth decades were studied by Doppler echocardiography. Normative values for 7 frequently used Doppler indexes of LV diastolic function are presented. Doppler indexes of LV diastolic function change dramatically with age; the peak velocity of early filling divided by late filling (peak velocity E/A) ranges from a mean of 2.08 +/- 0.55 for subjects in their third decade to 0.84 +/- 0.29 for those in their eighth decade. A peak velocity E/A ratio less than 1 is abnormal in subjects aged less than 40 years, but occurs in most subjects aged greater than or equal to 70 years. The high correlations between age and Doppler indexes of LV diastolic function are not greatly attenuated after adjustment for other clinical parameters associated with diastolic function; the multivariate partial correlation coefficient between age and peak velocity E/A is -0.80 (p less than 0.0001). Heart rate, PR interval, LV systolic function, sex and systolic blood pressure are minor determinants of Doppler indexes of diastolic function. Body mass index, left atrial diameter, and LV wall thickness, internal dimension and mass have little or no association with Doppler indexes in healthy subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Association of HbA1c with prevalent cardiovascular disease in the original cohort of the Framingham Heart Study.

We studied the cross-sectional relationship between HbA1c and cardiovascular disease (CVD) in the survivors of the original cohort of the Framingham Heart Study (n = 1045). HbA1c was significantly related to prevalent CVD among women but not men. HbA1c was also related to hypertension and to the ratio of total to high-density lipoprotein cholesterol levels. In regression analyses that controlled for these and other potential risk factors, HbA1c remained significantly related to CVD among women. The relative odds of CVD increased 1.39-fold (95% confidence interval 1.06-1.83) for increases in HbA1c of 1% (e.g., for HbA1c from 5 to 6%). The relationship was not weakened when known diabetic subjects or subjects taking beta-blocker or thiazide medications were excluded from analysis. In contrast, there was no significant relationship between "casual" blood glucose and prevalent CVD. Our results reveal a strong, significant, independent association between hyperglycemia, measured by HbA1c, and CVD among older women.

Aged↗
PubMed1992

Do postsuctioning transcutaneous PO2 values change when a neonate's movements are restrained?

The purpose of this research was to examine the effects of containment (restraint of an infant's movements) on premature infants' postsuctioning transcutaneous PO2 values. The hypothesis was that premature infants receiving containment would have significantly different postsuctioning transcutaneous PO2 levels than infants receiving no containment. Premature infants with respiratory disease require suctioning to remove excess secretions from their lungs. Research studies document a variety of infant responses to suctioning; hypoxia, hypoxemia, increased blood pressure, bradycardia, increased intracranial pressure, and increased cerebral blood flow velocity. Most studies have examined only a few isolated variables and the magnitude and duration of hypoxemia in response to suctioning. Our sample comprised 24 infants less than 72 hours of age, who had respiratory distress syndrome and had been born at between 24 and 33 weeks' gestational age. The setting was a neonatal intensive care unit of a large county hospital. The same nurse performed the suctioning and containment procedures in all subjects. Student's t-tests and analysis of variance were carried out to determine the effect of the technique.

Blood Gas Monitoring, Transcutaneous↗
PubMed1992

Reducing the hypoxemia, bradycardia, and apnea associated with suctioning in low birthweight infants.

Hypoxemia and bradycardia are major complications associated with suctioning the neonate. Apnea has been reported following caregiving during peak hours of activity in a neonatal intensive care unit (NICU). This study determined the incidence of hypoxemia, bradycardia, and apnea associated with the standard suction protocol used in one NICU. None of the 17 low birthweight infants suctioned between the peak caregiving activity hours of 8 and 11 AM exhibited bradycardia or apnea. Eleven of the 17 infants experienced no hypoxemia. Six infants displayed hypoxemia that lasted for less than 3 minutes. None of the infants exhibited bradycardia or apnea in association with this suction protocol. Patterns of escalating blood pressure noted in this study are worrisome because of the increased risk of intraventricular hemorrhage.

Analysis of Variance↗
PubMed1991

The role of the liver in the production of free radicals during halothane anaesthesia in the rat. Quantification of N-tert-butyl-alpha-(4- nitrophenyl)nitrone (PBN)-trapped adducts in bile from halothane as compared with carbon tetrachloride.

Halothane or CCl4 was co-administered with the spin trap N-tert-butyl-alpha-(4-nitrophenyl)nitrone (PBN) to rats fitted with bile duct cannuli or to isolated perfused liver preparations. Rats maintained under halothane anaesthesia generated significant amounts of free radicals, and 5-9 nmol was excreted in bile over 1 h. No adducts were detected in urine or plasma. The hepatic origin of these free radicals was confirmed by studies on isolated perfused livers where the addition of halothane to the perfusate resulted in the biliary elimination of the same PBN-trapped radical adducts. Similarly, following CCl4 administration, the same radical species were eliminated in bile in the whole animal and the perfused liver preparation. In the perfused liver, over 3 h the total biliary elimination of radicals derived from halothane or CCl4 (administered at equimolar concentrations) was approximately the same (5-7 nmol); however, the elimination of halothane-derived radicals was more rapid over the first 1 h.

Animals↗
PubMed1991

The use of electron spin resonance to measure microviscosity.

The viscosities of a series of mixtures of glycerol and water were measured by electron spin resonance (ESR), photon correlation spectroscopy and Ostwald viscometry. Close agreement was obtained between the last two methods but viscosity as measured by ESR was always significantly lower. The difference, the magnitude of which depended on the spin probe used, was attributed to interaction between water and glycerol. Similar results were obtained using water-sorbitol and water-sucrose mixtures.

Electron Spin Resonance Spectroscopy↗