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Biomedical subjects

J C Buell

Publications and source records attributed to J C Buell.

At least 19 recordsLinked to original sources
PubMed1993

Usefulness of the impedance cardiogram to reflect left ventricular diastolic function.

The impedance diastolic waveforms, early O wave (zO) and late A wave (zA), were evaluated, and their relation to diastolic mitral flow patterns under changes in loading conditions was assessed. Eight normal subjects and 9 patients with Doppler evidence of delayed ventricular relaxation were studied with simultaneous transmitral Doppler flow and computerized, ensemble-averaged, impedance cardiography in the supine position. Thirty-degree, head-down and head-up tilt were performed to alter preload. Peak Doppler early diastolic velocity (E) and E integral were preload-dependent in both normal and abnormal groups (p < 0.003), but were not significantly different between patients and normal subjects. Peak Doppler late diastolic velocity (A) and A integral, although significantly different between groups (p < 0.001), did not vary significantly with tilt. E/A ratio was significantly different between groups in all positions (p < 0.006). Impedance zA was preload-dependent (p < 0.001) in both groups and significantly different between groups (p < 0.05). Impedance zO was also preload-dependent (p < 0.003), but not significantly different between groups. Impedance zO correlated with Doppler peak E (r = 0.64; p = 0.001). Impedance zA did not correlate with Doppler A. Impedance cardiography diastolic waveforms can be altered by position and may reflect changes in vena caval or pulmonary vein volume flow, or both. This technique, in combination with Doppler mitral flow patterns, may be useful in evaluating diastolic function.

Cardiography, Impedance↗
PubMed1992

Validity of cardiac output measurement by computer-averaged impedance cardiography, and comparison with simultaneous thermodilution determinations.

The accuracy and reproducibility of noninvasive cardiac output determinations by computer-averaged impedance cardiography were compared with those of simultaneously performed thermodilution cardiac output. In all, 43 patients (14 men and 29 women = 201 pairs) were studied by simultaneously performed impedance and thermal determinations. Individual impedance values correlated with paired thermodilution determinations (r = 0.75; p less than 0.0001). Each patient's average thermodilution values correlated with the average impedance values (r = 0.86; p less than 0.0001). Mean thermodilution output was 4.6 +/- 1.37 liters/min. Mean impedance output was 4.5 +/- 1.27 liter/min Reproducibility was comparable for impedance (0.0059 +/- 0.639) and thermodilution cardiac output (0.023 +/- 0.556). There was high agreement between methods by plot of the difference against mean of the 2 methods. Impedance cardiac output values agree and correlate highly with quality-controlled thermodilution outputs across a wide range of clinical conditions and hemodynamic values.

Adult↗
PubMed1991

Coronary artery narrowing due to extrinsic compression by myocardial abscess.

A case of aortic valve endocarditis complicated by perivalvular abscess extending into myocardium is presented. Echocardiography and aortography failed to detect the abscess, but coronary angiography revealed its presence by extrinsic compression of left anterior descending and diagonal arteries. Morphological features of this rare cause for coronary narrowing are described.

Abscess↗
PubMed1988

Hemodynamic effects of labetalol in young and older adult hypertensives.

Twenty young (45 years or younger) and 20 older (55 years or older) adult patients with mild hypertension were enrolled in this study to compare the hemodynamic effects of labetalol versus placebo in two age groups. Ten patients in each group were randomly assigned to receive either a single oral dose of labetalol (200 mg) or placebo. Hemodynamic parameters were recorded immediately before and two hours after ingestion. Labetalol was more effective than placebo in significantly lowering systolic blood pressure (-11 versus + 5 mm Hg, -23 versus + 4 mm Hg), diastolic blood pressure (-9 versus + 2 mm Hg, -12 versus + 5 mm Hg), and total systemic resistance (-259 versus + 42 dynes-sec cm-5, -390 versus + 74 dynes-sec cm-5) in young and older hypertensive subjects, respectively. There was no significant changes in heart rate, stroke volume index, or cardiac index in either age group. These data indicate that labetalol lowers blood pressure in young an older hypertensives primarily by reducing peripheral resistance and that the antihypertensive effect may be somewhat greater in older patients.

Adult↗
PubMed1988

A practical, cost-effective, noninvasive system for cardiac output and hemodynamic analysis.

Impedance cardiography is a relatively inexpensive, noninvasive technique for measuring cardiac output on the basis of resistive changes in the thorax to electrical current flow. In conjunction with blood pressure monitoring and physiologic maneuvers, the technique may be used to monitor thoracic and total body fluid volume and express a variety of contractility indexes as well as relative and absolute measurements of stroke volume. We have tested hemodynamics in our laboratory by using a cost-effective, powerful microcomputer-based portable noninvasive technique, which makes possible the ensemble averaging of impedance cardiographic waveforms. In conjunction with physiologic maneuvers, the technique has been implemented at our institution and has provided helpful information in our experience in evaluating volume overload, hypertension, hypotension, shock, and heart failure. It is hoped that this noninvasive, relatively cost-effective approach will be more widely appreciated in the future, given the economic realities of medicine today.

Cardiac Output↗
PubMed1987

Lack of superiority of the vectorcardiogram over the electrocardiogram in detecting inferior wall myocardial infarction regardless of time since infarction.

Using more recent VCG and ECG criteria, the relative accuracy of these two tests in detecting inferior wall MI over time was evaluated in 38 of 236 patients undergoing elective left ventriculographic and coronary angiographic studies who had clinical plus angiographic evidence of inferior wall myocardial infarction. The overall sensitivity and specificity of the ECG criteria of the New York Heart Association and Warner did not differ from that of the VCG criteria of Starr and Takatsu. There was a trend toward decreased sensitivity in both VCG criteria and the ECG criterion of Warner in detecting inferior wall myocardial infarction greater than or equal to 18 months, although the difference did not reach statistical significance. Changing the age of infarction to greater than or equal to 3, greater than or equal to 6, greater than or equal to 12, or greater than or equal to 24 months did not yield a different result. It is concluded that VCG is not superior to ECG in the diagnosis of inferior wall MI regardless of time since occurrence of infarction.

Adult↗
PubMed1987

Cardiovascular changes during mental stress: correlations with presence of coronary risk factors and cardiovascular disease in physicians and dentists.

Stress may play a role in the etiology of cardiovascular disease. Research showing that mental stress administered in laboratory settings causes great change in cardiovascular and hemodynamic functioning supports this hypothesis. In a small sample of physicians and dentists, those who showed greater cardiovascular reactivity (hot reactors) to stress were more likely to be hyperlipidemic or to have had a myocardial infarction or coronary bypass surgery. In addition, some of the nonreactive group were hypertensives taking medication, which may have blunted their response to stress. Persons with higher cholesterol, higher triglyceride levels, and lower HDL levels all showed greater increases in blood pressure (BP) in response to stress. Also, the reactive group reported less emotional support and experienced greater numbers of family-related stressful events in the previous year. The degree of aerobic fitness influenced resting hemodynamics and percentage of body fat but not reactivity to stress. Likewise, smoking did not affect reactivity, but former smokers did have a significantly elevated total systemic resistance at rest. While it is impossible to say whether reactivity causes disease, is the result of the presence of risk factors and disease, or is caused by some other factor which also contributes to disease, these results suggest that the presence of cardiovascular reactivity to mental stress is a sign of potential illness and indicates the need for further medical and risk factor study of the patient.

Adult↗
PubMed1985

Role of emotions and stress in the genesis of sudden death.

Emotional arousal induces dramatic endocrine responses through either the sympathetic-adrenal medullary system or pituitary-adrenal cortical system. Many of the known actions of cortisol and catecholamines are atherogenic, cardiotoxic and arrhythmogenic. Emotional stress can produce sudden cardiac death in experimental animals, as can the administration of exogenous catecholamines. Previous studies have found that emotional stress is a common precursor to sudden cardiac death. Thus, acute neuroendocrine arousal, superimposed on a substrate of compromised myocardium and electrical instability, may constitute an important, final inciting event in sudden cardiac death.

Adrenal Medulla↗
PubMed1985

Physiologic changes during a marathon, with special reference to magnesium.

In a single case study of a moderately trained, healthy man, physiologic changes during a marathon are reported. Blood was drawn prior to the race, at 1 hour and 2 hours into the race, at the end of the race, and after 1 hour of recovery. By 1 hour into the race, norepinephrine, epinephrine, and dopamine had increased nearly nine-fold, two-fold and five-fold, respectively. After 1 hour of recovery, epinephrine had returned to the pre-race value but norepinephrine and dopamine were still elevated. Cortisol increased gradually and was more than doubled by the end of the race. It was still elevated after 1 hour of recovery. White blood cells gradually increased, reaching their maximum value at the end of the race; a four-to-five-fold increase. Thromboxane B2, which had an inverse relationship to serum magnesium, was below the pre-race value for the first 2 hours but increased nine-fold by the end of the race. Serum magnesium increased from 1.44 meq/l to 1.68 meq/l at 2 hours into the marathon, dropped to 1.07 meq/l by the end of the race, and returned to its pre-race value by 1 hour of recovery. The decrease in serum magnesium at the end of the race may be associated with increased plasma free fatty acid levels.

Adult↗
PubMed1984

Sex-related differences in first-stage impedance cardiographic variables.

Impedance cardiography (ZCG), a noninvasive technique used to determine stroke volume and ventricular performance, is currently being utilized more extensively in psychophysiological research and may also prove a useful tool in the control of hypertension. To date, most studies employing ZCG have tested male subjects or patients. However, women and men differ on two important parameters used to calculate stroke volume: thoracic impedance (Zo), and the first derivative of change in impedance over time (dZ/dtmin). Examination of the clinical records of 19 females and 19 males, all nonmedicated, indicated that women had higher Zo levels (F(1,36) = 46.2, p less than .0001) and higher dZ/dtmin levels (F(1,36) = 51.8, p less than .0001), although calculated stroke volume indexes did not differ. A second sample of 10 women and 8 men, all healthy and nonmedicated, confirmed these findings. The differences in Zo are not due entirely to sex differences in height, weight, percent body fat, and subscapula skin-fold thickness, although these factors differ across sexes. It is important for researchers and clinicians utilizing ZCG with female subjects to be aware of these differences.

Adult↗
PubMed1984

Sex differences in transthoracic impedance: evaluation of effects on calculated stroke volume index.

A recent publication noted that women and men differ in transthoracic impedance (Zo), with women having higher levels, and this might cause underestimation of stroke volume index (SVI) in women when impedance cardiograph (IC) techniques are employed, as Zo is a squared factor in the denominator of the calculation equation. This paper confirmed the observed sex differences in Zo, with women (n = 19) having significantly (p less than 0.0001) higher Zo than men (n = 19) in both seated and supine positions. However, women also had higher dZ/dt (first derivative of impedance signal over time) levels when seated (women: 2.48 +/- 0.58; men: 1.38 +/- 0.35; p less than 0.0001) and when supine (women: 2.62 +/- 0.56; men: 1.58 +/- 0.34; p less than 0.0001). dZ/dt is a factor in the numerator, and, therefore, calculated SVI did not differ across sexes in either position. It was speculated that the Zo difference is due to differences in fat levels. Controlling for percent body fat and subscapula skin-fold differences did not entirely eliminate the sex differences in Zo. However, a group of well-trained females tested later (n = 10) showed lower Zo levels (24.8 vs. 28.2) when compared to the original group of 19 women who were not well-trained. Differences may be due to fat/muscle ratio of the thorax.

Adipose Tissue↗