ISSN:0009-7330    

出版商:OVID    

年代:1978

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1978

数据来源: OVID

摘要:

SUMMARY Two theoretical waveforms appear in the study of the ventricular repolarization process: the primary T wave (T,) derived from many local variations in repolarzation properties alone, assuming a uniform starting time, and the secondary T wave (T2) dictated by activation sequence alone, assuming uniform identical action potential durations throughout (‘zero gradient’). Subtraction of the appropriate T, from the observed T wave (T2) following any given sequence of ventricular activation should yield T,. An experimental waveform, the intrinsic T wave (Tt) following total simultaneous depolarization, has been proposed to be identical with T,. This study uses a 1675-element computational model of the left ventricular myocardium to generate eight orthogonal electrocardiographic waveforms representative of left ventricular activation and repolarization. Normal propagation and ectopy were simulated realistically; sequence was based on the electrophysiological properties of the individual elements. The model was assigned experimentally derived recovery times to generate Toand uniform fixed recovery times to generate the true or reference T2. A systematic search was made for the unknown parameter for calculating the secondary T wave, and we found that scanning the normal QRS with an area-sampling shutter 56 msec wide reproduced T2(r = 0.9984). However, correlation between theoretical Ttand experimental T, reached a maximum of 0.9456. The failure of absolute congruence between T, and T, derives from the multiplicity of elements and the resulting frequency distribution of actual local recovery times instead of a single ideal instant to provide the basis for aligning related waves in time.

ISSN:0009-7330    

出版商:OVID    

年代:1978

数据来源: OVID

摘要:

SUMMARY The isolated and perfused dog heart was placed in a cubic container filled with Tyrode+-s solution. Ventricular ectopic beats were produced by electrical stimulation of the left ventricular wall, and initial QRS vectors of these beats were determined with orthogonal leads from the surface of the container. At the same instants, the activated area on the epicardial surface was measured by means of a large number of contiguous bipolar leads from the epicardial surface. The QRS vector and the activated epicardial area were found to be nearly porportional. By use of these results and a calibration system with artificial dipoles, the double layer moment of the ventricular activation wave was calculated as 0.13 mA - cm per unit area. This value corresponds to 60% of the maximal possible strength of the tissue electromotive force. Lowering the conductivity of the surrounding solution increased the QRS voltage but not as much as the potential caused by a constant-current dipole within the solution. The relationship between the QRS voltage and the conductivity of the medium was analyzed by a simplified model of the syste and was found to correspond approximately to that of a constant-current source within a spherical heart with a resistivity 2 to 3 times that of Tyrode+-s solution.

ISSN:0009-7330    

出版商:OVID    

年代:1978

数据来源: OVID

摘要:

SUMMARY A change in vascular reactivity was characterized in the pig during the development of deoxycorticosterone acetate (DOCA) hypertension. Pigs, 8-12 weeks of age, were subjected to unilateral nephrectomy and instrumented with an electromagnetic flowprobe on the ascending aorta and with Tygon catheters in the aorta and thoracic vena cava. Approximately 2 weeks after surgery, Silastic strips impregnated with DOCA (100 mg/kg) were implanted subcutaneously. Within the first 3 days after implantation, mean arterial pressure (MAP) began to rise and reached levels approximately 40% greater than control during the 4th week. Graded intravenous infusions of norepinephrine or angiotensin II were given to unanesthetized pigs before, and at intervals during, the development of hypertension. Changes in total peripheral resistance were calculated from recordings of MAP and cardiac output. Comparison of pre-DOCA response curves with those obtained at intervals following DOCA implantation demonstrated a significant increase in vascular smooth muscle sensitivity (decrease in threshold infusion rates) to both drugs post-DOCA. There also was a shift to the left in the dose-response curves. These changes in systemic vascular reactivity occurred at the time the arterial pressure began to rise. The temporal relationship suggests that the increase in vascular reactivity may initiate the increase in mean arterial pressure.

ISSN:0009-7330    

出版商:OVID    

年代:1978

数据来源: OVID

摘要:

SUMMARY Krjplon-81m has been continuously eluted in 5% dextrose from a cyclotron-made rubidium-81 generator. The unique physical properties of this inert freely diffusible gas (half-life 13 seconds) have allowed the development of a technique for the constant infusion of this tracer into the aortic sinuses of 25 dogs. Theoretical considerations suggest that an equilibrium of ‘*Kr activity in the myocardium is principally dependent on blood flow. Experiments have tested the delivery of this indicator and have recorded quantitative high spatial resolution images of the heart with a gamma camera and digital computer. The systematic error was determined by comparing changes in regional blood flow (in ml/g per min, using an electromagnetic flow probe) and changes in calculated flow (ml/g per min) using the regional activity of81mKr (P = < 0.001;r= 0.97;y= 908 × + 0.105;n= 60). The random error and uncertainties concerning mixing and streaming of the indicator were tested by repeating measurements with alterations in heart rate, blood pressure, coronary flow, and total myocardial *“Kr activity using different interventions (reproducibility,P= 0.001,r= 0.982;y= 0.982x + -0.257,n= 100 observations). Any quantification of changes in the myocardial activity of81mKr must consider the stability of the arterial concentration of this indicator and washout of “Kr at high values of myocardial blood flow. This ultra-short-lived radionuclide will, however, provide an assessment of changes in the distribution of regional myocardial perfusion.

ISSN:0009-7330    

出版商:OVID    

年代:1978

数据来源: OVID

摘要:

SUMMARY The blood pressure (BP) response to a competitive inhibitor of angiotensin II (saralasin), was evaluated serially along with renal hemodynamics and sodium clearance in dogs with constriction of the thoracic inferior vena cava which were undergoing chronic sodium and water balance studies. Plasma renin activity (PRA), plasma and urinary aldosterone, and plasma volume were measured periodically. In 14 normal dogs under anesthesia, saralasin infusion, 6μg/kg per min, produced a transient agonistic pressor response. In 14 dogs after caval constriction, sodium balance became markedly positive, PRA and plasma and urine aldosterone increased, and sodium clearance decreased. Now saralasin infusion caused a decrease in BP. In five dogs, avid sodium retention persisted. In nine, after a variable period of time, sodium balance became less positive, PRA and plasma and urine aldosterone decreased, and sodium clearance increased. Saralasin infusion at this time again produced a transient agonistic pressor response. Renal hemodynamics remained stable throughout. Plasma volume increased following caval constriction. These data suggest that initially, following caval constriction, the renin-angiotensin-aldosterone system is responsible for BP maintenance. Following a period of salt and water retention and extracellular volume expansion, sodium excretion increases, the renin-angiotensin-aldosterone system is suppressed, and BP becomes sodium-volume dependent. These dynamic physiological adjustments which lead to great variability in caval dogs may help to reconcile some of the conflicting findings reported for this model of salt and water retention, as well as for its clinical counterparts.

ISSN:0009-7330    

出版商:OVID    

年代:1978

数据来源: OVID

摘要:

SUMMARY Although the heart contains lysosomes, it has been uncertain whether these organelles and their proteolytic enzymes can play an important role in cardiac protein degradation. Recent studies have demonstrated that fetal mouse hearts in organ culture sustain selective derangements in lysosomal structure and function during exposure to chloroquine or nonmetabolizable sugars. Accordingly, we tested the effects of these agents on cardiac proteolysis under controlled conditions in vitro using two techniques (measurement of loss of radioactivity from trichloroacetic add-precipitable protein after prelabeling with tritiated phenylalanine and measurement of loss of cold phenylalanine after blockade of protein synthesis with cycloheximide). Chloroquine (0.1 DM) reduced the average rate of protein breakdown in hearts of matched littermates from 45%/24 hours to 32%/24 hours (P< 0.01) and decreased the release of cold phenylalanine by 31 ± 5%(0.108 vs. 0.075 nmol/mg per hour,P< 0.01). Exposure to 100 DIM sucrose for 24-48 hours reduced the rate of breakdown from 44%/24 hours to 33%/24 hours (P< 0.01) and decreased the release of cold phenylalanine by 35 ± 9% (0.092 vs. 0.060 nmol/mg per hour,P< 0.01). The results suggest that interference with lysosomal function in cultured fetal mouse hearts causes a significant reduction in the cardiac capacity to degrade proteins.

ISSN:0009-7330    

出版商:OVID    

年代:1978

数据来源: OVID

摘要:

SUMMARY Autologous femoral veins grafted between the external iliac arteries in 18 dogs provided a model for studying the hemodynamics and histopathology of vein graft bypasses. The angle of proximal anastomosis was varied by groups (<90°, 90°, >90°) to produce a wide range of flow conditions within the grafts. Four months after implantation, point velocity measurements of blood flow and histological examination of the superior and inferior walls were made at proximal, middle, and distal locations in each graft. Hot-film velocity measurements revealed outwardly skewed velocity profiles in the proximal locations in all grafts, and flow visualization models showed secondary fluid motions and separation zones at those regions. Velocity profiles in the middle and distal regions of the grafts were more symmetrical and showed no flow separation. Histological examination of wall sections along the graft length showed that intimal proliferation occurred focally and ranged from 1 to 100 fita in thickness. No signficant correlation between graft angle and degree of intimal proliferation was found. However, there was a weak inverse correlation between the apparent fluid shear rate and the corresponding degree of intimal proliferation, with the greatest proliferation occurring in the regions experiencing the lowest shearing forces. Regions of low shear rate should be avoided by maintaining adequate flow rates through the grafts and thus minimising losses of patency due to both thrombus formation and intimal proliferation.

ISSN:0009-7330    

出版商:OVID    

年代:1978

数据来源: OVID

摘要:

SUMMARY Considerable controversy exists as to what extent left atrial receptors play a role in the physiological regulation of antidiuretic hormone (ADH) secretion. We studied conscious dogs during a stable water diuresis induced by continuous infusion of hypotonic saline, in whom acute inflation of a chronically implanted pulmonary artery balloon consistently produced antidiuresis. Following balloon inflation in nine dogs, glomerular filtration rate (GFR) (67 ± 8 to 70 ± 6 ml/min,P< 0.2) and osmolar clearance (CsOsm) (3.1 ± 0.2 to 3.3 + 0.2 ml/min,/> > 0.2) did not change. Despite a fall in plasma osmolality (287 ± 6 to 281 ± 5 mOsm/kg H 2O,P< 0.025) and rise in mean systemic arterial pressure (100 ± 3.6 to 110 ± 3.8 mm Hg,P< 0.01), urine osmolality rose markedly (88 ± 8 to 234 ± 45 mOsm/kg H 2O,P< 0.02), and urine flow (10.1 ± 0.8 to 6.3 ± 0.9 ml/min,P< 0.01) and renal free water clearance (C Hl0) (7.1 ± 0.8 to 2.9 ± 0.7 ml/min,P< 0.01) both fell. This acute decrease in water excretion was shown to be the consequence of a rise in plasma levels of ADH (0.72 ± 0.07 to 2.06 ± 0.20 μU/ml) which returned toward control levels following balloon deflation (1.14 ± 0.18 μU7ml). The changes in ADH levels were shown to be associated with reciprocal changes in left atrial pressure (10.7 ± 1.7 to 6.1 ± 1.5 mm Hg after balloon inflation, returning to 12.2 ± 1.8 mm Hg after deflation). We conclude that in conscious dogs the effects of a small fall in left atrial pressure can predominate over the combined effects of a rise in systemic arterial pressure, continued infusion of hypotonic saline, and a fall in plasma osmolality, to produce a rise in plasma levels of ADH and antidiuresis.

ISSN:0009-7330    

出版商:OVID    

年代:1978

数据来源: OVID