摘要:

Circulatory adjustments during hypoxia act to redistribute blood flow and maintain arterial pressure. Redistribution of blood flow is accomplished by a local effect of hypoxia, which produces dilatation incoronary and cerebral vessels, and the chemoreceptor reflex, which produces vasoconstriction in skeletal muscleand the splanchnic bed and dilatation in coronary vessels. Arterial pressure is maintained primarily by thechemoreceptor reflex. If the chemoreceptor reflex fails to maintain arterial pressure, hypoxia and hypotensiontogether activate the central pressor response. Compensatory mechanisms usually are sufficient to maintainhomeostasis during hypoxia. However, when a hypotensive stress is superimposed during hypoxia, compensatorymechanisms may fail to maintain arterial pressure. Thus, systemic hypoxia interferes with autonomic cardiovascular adjustments.

ISSN:0009-7322    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

Fifty consecutive patients undergoing aortic valve replacement for isolated aortic regurgitationwere studied prospectively by echocardiography, electrocardiography and cardiac catheterization. Goodquality echocardiograms were obtained in 49 of the 50 patients. Left ventricular (LV) dilatation was present inall 49 patients. LV systolic function, as assessed by echocardiographic percent fractional shortening, was normalin many patients but was moderately to severely reduced (> 25%) in 14 patients (29%). Echocardiographicstudies 6 months postoperatively revealed significant reductions in LV end–diastolic dimension (73.8mm vs 58.7 mm; p < 0.01), and serial echocardiographic studies early and late after operation revealed thatthe decrease in LV size had occurred by the time of the early study (8‐22 days postoperatively), with little additionalchange thereafter. Operative deaths occurred in three of the 49 patients (6%). Eight of the 49 patients(16%) died of congestive heart failure (CHF) after hospital discharge at times ranging from 5–43 months afteroperation. Preoperative echocardiographic measurements of the LV end–systolic dimension and percent fractionalshortening were strongly associated (p < 0.01) with these late CHF deaths. Preoperative LV endsystolicdimension > 55 mm and fractional shortening < 25% identified the high–risk group: nine of 13patients (69%) in this group died either at operation or subsequently from CHF. In contrast, of 32 patients withLV end–systolic dimension < 55 mm, only one died at operation and one died late from CHF. Thus, the populationat high risk of late death from CHF was identified before operation by echocardiograp.

ISSN:0009-7322    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

A recent echocardiographic study of symptomatic patients who had aortic valve replacement for isolated aortic regurgitation indicated that patients in whom preoperative left ventricular end–systolic dimension (LVD[SYS]) exceeded 55 mm or fractional shortening (%FS) was less than 25% were at high risk of developing congestive heart failure and dying after an otherwise successful operation. Because indices of left ventricular systolic function might identify asymptomatic patients with aortic regurgitation who might benefit from earlier operation, 37 such patients were evaluated with serial echocardiograms (mean follow–up 34 months). Fourteen patients (38%) subsequently developed symptoms and were recommended for operation (SUBSQ OP). Twenty–three patients (62%) remain asymptomatic during follow–up (NON OP). LVD(SYS) and %FS were the most sensitive measurements for distinguishing on initial examination the patients who subsequently required operation from those who have not (LVD[SYS] 53.0 mm SUBSQ OP vs 44.3 mm NON OP, p = 0.001; %FS 28.8% SUBSQ OP vs 33.9% NON OP,p = 0.002). During serial studies, the maximum rate of change in end–systolic dimension exceeded 7 mm per year in only one patient. Four of five patients (80%) with end–systolic dimension greater than 55 mm developed symptoms and came to operation during a mean follow–up of 39 months. Of the 20 patients whose initial end–systolic dimension was 50 mm or less, only four patients (20%) developed symptoms and required operation, and none died during follow–up. Thus, an asymptomatic patient with aortic regurgitation whose end–systolic dimension is less than 50 mm appears to be at low risk and can be safely followed with echocardiograms at yearly intervals. Asymptomatic patients with end–systolic dimension of 50–54 mm are being followed with serial echocardiograms every 4–6 months. Operation is now being recommended to patients with end–systolic dimensions of 55 mm or greater, even in the absence of symptom.

ISSN:0009-7322    

出版商:OVID    

年代:1980

数据来源: OVID

ISSN:0009-7322    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

Surface features of 19 stenotic aortic valves from patients undergoing valve replacement were investigated by scanning electron microscopy. Villi, prominent on five valves, were distributed either singularly or in clusters and differed in shape. Endothelial cells had microvilli and bulbous surface projections. Endothelial disruption with a focal loss of endothelial cells was uniformly observed. Erythrocytes were found scattered over the exposed subendothelial surface or enmeshed within fibrin networks on 11 of the valves. Activated leukocytes were seen on four valves and showed veil-like projections as well as microvilli. Platelets, observed on three valves, displayed pseudopodial formation and hyalomeric spreading, signifying an increased degree of membrane response. Most platelet aggregates were composed entirely of dendritic forms (reversible aggregates), but a few also contained spread forms (irreversible aggregates). Focal deposits of crystalline material, presumably containing calcium, were observed in areas of endocardial disruption.

ISSN:0009-7322    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

A genetic–epidemiologic study was undertaken of a white Colorado population of 207 patients who had a myocardial infarction before age 55 years. Nineteen independent variables were compared between the 207 cases and 621 controls, matched 3:1. The highest risk ratios were associated with a positive family history for ischemic heart disease (IHD). The heritability of IHD was 63% when families with the monogenic forms of hyperlipoproteinemia were included, and 56% when they were excluded. A risk index was developed that incorporates family history into a data base of risk factors, which can be readily assessed by the clinician obtaining a screening history, physical and standard laboratory tests. A scale of 0–10 was devised and the predictive value of the index was tested against another data set. The efficiency of the index was maximal at a screening level of 5. This study suggests that it is logistically feasible to seek patients at high risk for intensive management in a clinical setting (high–risk strategy) using risk indices similar to the one developed for this study, which emphasize the very important familial component to IHD.

ISSN:0009-7322    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

A simulated randomized clinical trial in coronary artery disease was conducted to illustrate the need for clinical judgment and modern statistical methods in assessing therapeutic claims in studies of complex diseases. Clinicians should be aware of problems that occur when a patient sample is subdivided and treatment effects are assessed within multiple prognostic categories. In this example, 1073 consecutive, medically treated coronary artery disease patients from the Duke University data bank were randomized into two groups. The groups were reasonably comparable and, as expected, there was no overall difference in survival. In a subgroup of 397 patients characterized by three–vessel disease and an abnormal left ventricular contraction, however, survival of group 1 patients was significantly different from that of group 2 patients. Multivariable adjustment procedures revealed that the difference resulted from the combined effect of small imbalances in the distribution of several prognostic factors. Another subgroup was identified in which a significant survival difference was not explained by multivariable methods.These are not unlikely examples in trials of a complex disease. Clinicians must exercise careful judgment in attributing such results to an efficacious therapy, as they may be due to chance or to inadequate baseline comparability of the groups.

ISSN:0009-7322    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

Turbulent flow in arteries produces sound recognized at the skin surface as a bruit. Spectral analysis of such bruits (phonoangiography) is the basis for a simple, noninvasive method of quantifying arterial stenosis. In human studies of carotid stenoses, the spectral break frequency of the bruit (f0) (frequency beyond which bruit amplitude drops sharply) was directly related to the angiographic residual lumen diameter (d), i.e.,d = U/fo, where U is flow velocity. In the clinical situation, flow velocity remains relatively constant because of cerebrovascular autoregulation. In order to test the effects of flow velocity on bruit frequency, we have correlated,under controlled conditions, stenosis anatomy, blood flow, and the sounds originating from an abdominal aortic stenosis produced in adult mongrel dogs by external application of a 5-mm wide Teflon band.Aortic flow was measured in arbitrary units with an electromagnetic flowmeter and varied by stepwise constriction of bilateral femoral arteriovenous fistulas. Bruits were recorded on tape and analyzed by computer.The relationship between flow through the stenosis and break frequency of the bruit was linear (r = 0.89) in 10 dogs. Where d was altered in three other dogs, the relationship between flow and break frequency remained linear for each different d.The data suggest that the relationship between break frequency, flow velocity and residual lumen diameter holds over a wide range of values of each of those variables.

ISSN:0009-7322    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

Controversy persists regarding the role of tubular reabsorption and secretion in the renal handling of digoxin. To determine the effect of reduction in renal perfusion pressure and blood flow on digoxin clearance during acute and chronic digoxin administration, renal clearances of digoxin and inulin were measured in pentobarbital–anesthetized dogs before and after repeated unilateral renal artery constriction. After reduction of renal arterial mean pressure to 67% of the control level, both inulin and digoxin clearances fell sharply, by 62–86% (p < 0.001). The digoxin–to–inulin clearance ratio in the arterially constricted kidney decreased only slightly, from 0.82 to 0.76 (p < 0.02) after unilateral renal artery constriction in the chronically digitalized group as determined by3H counts in serum and urine of dogs given 12 α-[3HJ digoxin. No significant change in the digoxin–to–inulin clearance ratio after renal arterial constriction was found by radioimmunoassay determination of digoxin in chronically dosed dogs. Digoxin–to–inulin clearance ratio also did not change significantly with renal artery constriction in the acutely digitalized group (0.72 vs 0.71). Slightly higher digoxin–to–inulin clearance ratios in chronically (mean 0.82) compared with acutely (mean 0.73; p = 0.038) digitalized dogs may be accounted for by renal parenchymal digoxin binding under non–steady–state conditions of acute digoxin administration. These data support the concept that glomerular filtration is the principal mechanism of renal digoxin excretion. Reduction in renal arterial pressure, with consequent decrease in glomerular filtration and urine flow, produces a marked fall in digoxin clearance but no appreciable change in the digoxin–to–inulin clearance ratio in dogs given digoxin acutely or dosed chronically to attain a steady state. This is consistent with the absence of any important change in net tubular reabsorption of digoxin under these experimental circumstances. These experiments show that renal excretion of digoxin in the dog closely approximates the filtered load over a broad range of renal arterial perfusion pressures and urine flow rates.

ISSN:0009-7322    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

The effects of 15, 30, 60 and 120 mg of isosorbide dinitrate (ISDN) on systolic blood pressure (SBP) and heart rate (HR) were compared after acute oral administration and during sustained therapy four times daily with ISDN in six patients. After any given dose, plasma ISDN levels were higher during sustained therapy than during acute therapy. The average peak reduction in standing SBP occurred at 2 hours after 15, 30, 60 and 120 mg of ISDN; the values were 39, 42, 45 and 46 mm Hg, respectively, after acute therapy and 21, 20, 26 and 24 mm Hg, respectively, during sustained therapy (p < 0.01). Compared with placebo, the reduction in SBP was still apparent 6 hours after any given dose of ISDN during acute but not during sustained therapy (p < 0.01). HR increased significantly only after acute therapy.The rapidity of development of tolerance to ISDN and cross–tolerance to glyceryl trinitrate (GTN) was evaluated in eight other patients. The average peak reduction in SBP after the first dose of 15 mg of ISDN was 36 mm Hg, but after therapy with ISDN every 6 hours, the fifth dose of 15 mg of ISDN produced a peak reduction in SBP of only 7 mm Hg (p < 0.001). The first dose of 0.6 mg GTN before therapy with ISDN produced a peak reduction in SBP of 40 mm Hg, but after therapy with ISDN every 6 hours for 5 days, the same dose of GTN produced a maximum reduction in SBP of only 10 mm Hg (p < 0.001).The results show that partial circulatory tolerance to ISDN and cross–tolerance to GTN developed rapidly during regular therapy with ISDN. The plasma ISDN concentrations were higher during sustained than after acute therapy, suggesting that the tolerance (tachyphylaxis) to nitrates in man is due to the diminution of the end organ response and not to the accelerated metabolism of nitrates.

ISSN:0009-7322    

出版商:OVID    

年代:1980

数据来源: OVID