ISSN:0009-7322    

出版商:OVID    

年代:1987

数据来源: OVID

ISSN:0009-7322    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

Central and peripheral cardiovascular adaptations to 12 weeks of intense swim training were characterized in 12 previously sedentary middle-aged men and women. Peak oxygen uptake V02) during upright bicycle exercise improved from 29.2 ± 5.6 to 34.7 ± 6.7 ml/kg/min (mean ± SD, p < .01) because of similar increases in peak cardiac output (CO) and calculated arteriovenous oxygen difference (both p = .02). Peak supine V02 was 10% higher after training (p < .005) solely because of enhanced CO (p = .005). Peak heart rate decreased in both postures; therefore stroke volume at peak exercise was greater by 10% and 18% in the upright and supine postures, respectively (p = .05 and p = .005). There was an identical 18% rise (p = .01) in peak supine left ventricular enddiastolic volume index by radionuclide ventriculography but no change in left ventricular ejection fraction or end-systolic volume index (ESVI). Peak systolic blood pressure (SBP) was unchanged in the upright posture but was 8% higher (p = .002) during recumbency despite a similar total peripheral resistance and SBP/ESVI ratio. Maximal calf conductance (Gma,), assessed separately by venous occlusion plethysmography after local ischemic exercise to fatigue, was augmented 20% (p < .02) by training, resulting in an 18% greater hyperemic blood flow (p = .05). Peak VO2, CO, and G,,, were unchanged in five nonexercising control subjects. We conclude that in middle-aged humans, intense swim training for 12 weeks produces adaptations that include a greater capacity for vasodilatation in skeletal muscle and an enhanced cardiac pump capacity.

ISSN:0009-7322    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

We studied the effects of different classes of inotropic drugs on human working myocardium in vitro that was isolated from the hearts of patients with end-stage heart failure, and compared the responses to these drugs with those noted in muscles from nonfailing control hearts. Although peak isometric force generated in response to increased extracellular calcium reached control levels in the muscles from patients with heart failure, the time course of contraction and rate of relaxation were greatly prolonged. The inotropic effectiveness of the, B-adrenergic agonist isoproterenol and the phosphodiesterase inhibitors milrinone, caffeine, and isobutylmethylxanthine was markedly reduced in muscles from the patients with heart failure. In contrast, the effectiveness of inotropic stimulation with acetylstrophanthidin and the adenylate cyclase activator forskolin was preserved. After a minimally effective dose of forskolin was given to elevate intracellular cyclic AMP levels, the inotropic responses of muscles from the failing hearts to phosphodiesterase inhibitors were markedly potentiated. These data indicate that an abnormality in cyclic AMP production may be a fundamental defect present in patients with end-stage heart failure that can markedly diminish the effectiveness of agents that depend on generation of this nucleotide for production of a positive inotropic effect.

ISSN:0009-7322    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

Participants in the Hypertension Detection and Follow-up Program (HDFP) were classified on the basis of baseline standing minus sitting systolic blood pressure into four groups (c -20 [group 1], – 19 to 0 [group 2], 1 to 20 [group 3], and >20 mm Hg [group 4]) to study 5 year mortality. Group 1, 3.3% of the total, contained those participants who had postural hypotension. The 5 year total and age-adjusted mortality rates for these groups were significantly different (p < .04), with group 1 having the highest rates. To account for the possible confounding effects of certain baseline risk factors age, sex, race, prior antihypertensive treatment, randomization group, diabetes, end-organ damage, sitting diastolic and systolic blood pressures, pulse, hematocrit, smoking status, and relative weight (percent of ideal weight) in assessing group differences in mortality rates, a multiple logistic model was used. Relative weight proved to be a confounding factor for the association of drop in postural systolic blood pressure with mortality. However, there is an interaction between history of diabetes and postural change in systolic blood pressure. Thus, postural hypotension may indicate a poor prognosis in diabetic hypertensive patients.

ISSN:0009-7322    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

The independent contributions of ST segment depression and/or T wave abnormality (ST-T abnormalities) on the baseline resting electrocardiogram to risk of 11.5 year coronary heart disease (CHD) mortality were explored among 9203 white men and 7818 white women who were 40 to 64 years old and without definite CHD at entry in the Chicago Heart Association Detection Project in Industry. At baseline, prevalence rates of ST-T abnormalities were age related for both sexes, and at every age the rate was higher in women than men (age-adjusted prevalence rates 12.3% and 8.1%, respectively). Univariate analysis showed that ST-T abnormalities were associated with significantly increased risk of death from CHD for both men and women. However, men with ST-T abnormalities had much greater age-adjusted and multiple risk factor-adjusted absolute excess risk and relative risk than women with such electrocardiographic abnormalities. When baseline age, diastolic pressure, serum cholesterol, cigarettes/day, history of diabetes, and baseline use of antihypertensive medication were included in the multivariate analysis, ST-T abnormalities remained significantly related to death from CHD in men but not women. The interaction term between sex and ST-T abnormalities was at a borderline level of statistical significance by Cox regression analysis. In conclusion, ST-T abnormalities indicate an increased risk of subsequent death from CHD independent of major coronary risk factors for middle-aged U.S. men, but this is not clearly so for women.

ISSN:0009-7322    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

We postulated that the abnormal shape, size, and function of the right heart and adjoining ventricular septum in adults with Ebstein's anomaly of the tricuspid valve might in turn alter the shape and function of the left ventricle. Seven adult patients with uncomplicated Ebstein's anomaly were studied. Left ventricular geometry was determined by two-dimensional echocardiography. Left ventricular function was assessed by treadmill exercise and radionuclide angiography at rest and with exercise. Paradoxic ventricular septal motion was consistently present. Left ventricular eccentricity (ratio of two minor axes in the short-axis view) was uniformly abnormal, averaging 1.35 0.23 (normal = 1.02 ± 0.05). The ratio of right to left ventricular cavity size averaged 1.70 ± 0.44 (normal 0.65 ± 0.30), and tricuspid valve displacement into the right ventricular cavity averaged 52% (normal 8%). Functional right atrial size averaged 27.6 ± 5.2 cm2 (normal right atrial area = 13.1 ± 2.2 cm2). Resting left ventricular ejection fractions were below 50% in all but two patients. In response to Bruce protocol exercise stress, there were consistently appropriate increments in heart rate, blood pressure, and peak double product and, with one exception, radionuclide left ventricular ejection fraction. There were significant correlations between tricuspid valve displacement and functional right atrial size versus resting left ventricular ejection fraction and left ventricular eccentricity. These data support the hypothesis that derangements in right heart morphology and function in Ebstein's anomaly contribute to significant alterations in left ventricular geometry, but the geometric alterations are associated with tangible but less significant changes in left ventricular systolic function.

ISSN:0009-7322    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

The physiology of oxygen delivery was studied in 118 stable patients from 3 months to 20 years old with congenital heart disease. During cardiac catheterization, oxygen consumption (V02), arterial and venous blood gases and oxygen saturations (range 41% to 98%), hemoglobin concentration, diphosphoglycerate (2,3-DPG), and P50 levels were measured, and then cardiac output, systemic oxygen transport (SOT), arterial and venous oxygen contents, and the V02/SOT ratio (fractional 02 extraction) were calculated. P50 averaged 31 mm Hg, compared with 27 mm Hg in 10 control children (p < .01). The composite 02-hemoglobin dissociation curve in vivo was broad: Po2 varied from 37 to 65 mm Hg at 80% saturation. P50, 2,3-DPG, hemoglobin concentrations, and 02 saturation varied widely and inconsistently with Po2 and arterial and venous 02 content, but resulted in clustering of the arterial oxygen content near 165 23 (SD) ml/liter over a wide range of Po2 and hemoglobin concentrations. SOT varied in direct relation with flow (r = .82, p < .001), but not with oxygen content, Po2, or P50. V02 varied widely at normal or high levels of SOT, but decreased linearly at SOT levels below 400 ml/min/m2. Oxygen extraction varied inversely with venous 02 content, rising to about 50% and plateauing below venous contents of 100 ml/liter. 02 extraction did not correlate with Po2, arterial 02 content, or P50. These data suggest that: (1) 02 saturation cannot be predicted or calculated accurately from measured Po2, but must be measured directly, (2) 2,3-DPG, hemoglobin concentration, and P50 fluctuate to stabilize arterial oxygen content, (3) SOT is determined primarily by cardiac output in subjects who are adapted chronically, (4) 02 extraction rises, due to a fall in venous 02 content, to maintain V02 as transport falls, (5) below a critical level of SOT, 02 extraction ceases to rise and V02 falls with further reduction in transport.

ISSN:0009-7322    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

To test the hypothesis that an area of slow conduction is present during reentrant ventricular tachycardia in man, and that the earliest activation site during ventricular tachycardia is within or orthodromically just distal to the area of slow conduction in the reentry loop, we studied 12 episodes of ventricular tachycardia (mean rate 185 ± 32 beats/min) that were induced in nine patients with ischemic heart disease. Rapid ventricular pacing was performed at selected sites during ventricular tachycardia while recording electrograms from an early activation site relative to the onset of the QRS complex (site A) and from a site close to the pacing site (site B). Rapid pacing from the right ventricular apex during ventricular tachycardia with a right bundle branch block pattern and from selected left ventricular sites during ventricular tachycardia with a left bundle branch block pattern (mean pacing rate 202 ± 38 beats/min) resulted in constant ventricular fusion beats on the electrocardiogram except for the last captured beat (i.e., the ventricular tachycardia was entrained) in 11 of 12 episodes. During entrainment: (1) sites A and B were activated at the pacing rate, (2) conduction time from the last pacing impulse to the last captured ventricular electrogram at site A (St-A interval) was 359 ± 69 msec and spanned the diastolic interval, while that at site B (St-B interval) was only 28 ± 13 msec, (3) site A had the same ventricular electrogram morphology as that during ventricular tachycardia, while site B had a different electrogram morphology, indicating that site A was activated in the same direction during entrainment as during ventricular tachycardia. Eight episodes of ventricular tachycardia were entrained at two or more different pacing rates. The St-A interval increased during pacing at the faster rate(s) in four of eight episodes, while the St-B interval remained unchanged. Rapid ventricular pacing performed from the same site during sinus rhythm (mean pacing rate 201 ± 37 beats/min) resulted in an St-A interval of 103 ± 37 msec (p < .001 vs the value during entrainment) and an St-B interval of 31 ± 15 msec (p = NS vs the value during entrainment). It is concluded that an area of slow conduction not demonstrable during sinus rhythm exists during ventricular tachycardia, and that the earliest activation site during ventricular tachycardia is at or orthodromically distal to this area of slow conduction.

ISSN:0009-7322    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

T wave concordance in the normal human electrocardiogram (ECG) generally is explained by assuming opposite directions of ventricular depolarization and repolarization; however, direct experimental evidence for this hypothesis is lacking. We used a contact electrode catheter to record monophasic action potentials (MAPs) from 54 left ventricular endocardial sites during cardiac catheterization (seven patients) and a new contact electrode probe to record MAPs from 23 epicardial sites during cardiac surgery (three patients). All patients had normal left ventricular funtion and ECGs with concordant T waves. MAP recordings during constant sinus rhythm or right atrial pacing were analyzed for (1) activation time (AT) = earliest QRS deflection to MAP upstroke, (2) action potential duration (APD) = MAP upstroke to 90% repolarization, and (3) repolarization time (RT) = AT plus APD. AT and APD varied by 32 and 64 msec, respectively, over the left ventricular endocardium and by 55 and 73 msec, respectively, over the left ventricular epicardium. On a regional basis, the diaphragmatic and apicoseptal endocardium had the shortest AT and the longest APD, and the anteroapical and posterolateral endocardium had the longest AT and the shortest APD (p < .05 to < .0001). RT was less heterogeneous than APD, and no significant transventricular gradients of RT were found. In percent of the simultaneously recorded QT interval,- epicardial RT ranged from 70.8 to 87.4 (mean 80.7 ± 3.9) and endocardial RT ranged from 80 to 97.8 (mean 87.1 4.4) (p < .001). Plotting of APD as a function of AT, independent of the recording site, revealed a close inverse relationship, such that progressively later activation was associated with progressively earlier repolarization The linear regression slope of this relationship averaged from all 10 hearts was – 1.32 ± 0.45 (r = – .78 ± .10). These data suggest a transmural gradient of repolarization,with earlier repolarization occurring at the epicardium. The negative correlation between AT and APD, which was found at both the endocardial and epicardial surface and had an average slope of greater than unity, may further contribute to a positive ventricular gradient and T wave concordance.

ISSN:0009-7322    

出版商:OVID    

年代:1987

数据来源: OVID