ISSN:0009-7330    

出版商:OVID    

年代:1976

数据来源: OVID

摘要:

We studied the effect of increasing the rate of stimulation on the maximum rate of rise of the action potential upstroke (Vmax) in guinea pig papillary muscles at various resting membrane potentials and after the addition of quinidine and lidocaine to the perfusate. Increasing rate caused a decrease in Vma, due to interaction of three factors: (1) a metabolic factor, presumably resetting of the Na-K pump, which caused a decrease in Vmaiat all levels of resting potential between -90 and -60 mV, (2) a transient decrease in resting potential which influenced Vma, when the resting potential was less negative than approximately -80 mV, and (3) the recovery characteristics of Vma, which contributed to the decrease in this variable when rate was faster than 5/sec. As a result of these factors the steady state curve relating membrane potential to Vmaiwas itself rate-dependent. Lidocaine and quinidine exaggerated the rate-dependent decrease in Vmox; however, their effects differed. The effect of quinidine was consistent with its known depressant effect on the Na-K pump. The lidocaine effect was consistent with a slowing of recovery of Vma,. Our results help to explain the effects of an increase in rate on Vma, and conduction velocity in normal, partially depolarized, and drug-treated fibers.

ISSN:0009-7330    

出版商:OVID    

年代:1976

数据来源: OVID

摘要:

Plasma renin activity, arterial and venous angiotensin II (A II), plasma aldosterone, and sodium excretion were measured in a group of 101 patients with mild essential hypertension. For the total hour; arterial A II was 5.2 ± 1.0 pg/ml; venous A II was 4.2 ± 0.6 pg/ml; and plasma aldosterone was 5.0 ± 0.45 ng/100 ml. All values were lower than corresponding values for normal subjects on a high salt intake despite the fact that salt intake in the normal subjects exceeded that for the hypertensive group more than 3-fold. Moreover, when the range of diastolic blood pressure up to 114 mm Hg was divided into three successive class intervals of increasing severity, there was a negative correlation between diastolic blood pressure and both PR A and plasma aldosterone. Arterial A II showed an anomalous increase in the class interval 105–114 mm Hg, despite the fact that this group exhibited the lowest level of PR A. At diastolic blood pressures above 114 mm Hg, the PR A appears to rise again. The anomalous increase in arterial A II in the presence of marked suppression of PR A is consistent with the presence of a renin activator or accelerator factor in hypertensive plasma as postulated by others. It also identifies a possible mechanism whereby even small increases in PR A could exert an adverse effect on the hypertensive state.

ISSN:0009-7330    

出版商:OVID    

年代:1976

数据来源: OVID

摘要:

Plasma renin activity, arterial and venous angiotensin II (A II) concentrations, and plasma aldosterone concentration were measured in 16 normal subjects (mean age = 34 years) after 8 hours of recumbency, following 2 hours of ambulation, and again 30 minutes after administration of furosemide intravenously. Measurement s were obtained during periods of sodium restriction and again during sodium surfeit. Both arterial and venous A II exhibited a 3-fold increase from low values of 8.8 ± 2.5 and 8.6 ± 2.5 pg/ml of plasma, respectively, during recumbency on high sodium intake to values of 23.9 ±4.1 and 26.5 ± 6.2 pg/ml, respectively, following intravenous furosemide during sodium restriction. Corresponding values for aldosterone exhibited a 5-fold rise from 5.6 ng/100 ml to 32.0 ng/100 ml, whereas plasma renin activity (PRA) measured by an in vitro assay exhibited a 20-fold rise from 0.6 ± 0.2 ng of angiotensin I (AI) generated per ml per hour to 13.1 ng/ml per hour. Despite the disparity in the magnitude of these increases, significant correlations were identified between all four of the measured parameters, indicating a major role of the renin-angiotensin system in regulating aldosterone output in response to volume and posture-related stimuli. Values of arterial and venous immunoreactive A 11 were closely correlated (r = +0.72,P<0.005), but significant differences were demonstrated between low and high salt periods, suggesting that changes in metabolism of A II in the peripheral circulation may occur during sodium restriction.

ISSN:0009-7330    

出版商:OVID    

年代:1976

数据来源: OVID

摘要:

Previous workers have suggested that a rise in plasma renin activity (PR A) may mediate some of the hemodynamic changes associated with exercise.To test this hypothesis in nine dogs chronically instrumented for measurement of aortic pressure (catheter) or cardiac output (ascending aorta electromagnetic flow probe) PRA was measured by radioimmunoassay in blood samples drawn before and during running on a level treadmill at 4-8 miles per hour. Exercise caused increases in heart rate from 96 ± 5 (se) to 186 ± 7 beats/ min, cardiac output from 2.8 ± 0.3 to 6.2 ± 0.6 liters/ min, and mean aortic pressure from US ± 5 to 132 ± S mm Hg (P< 0.01). Mean PRA was 6.6 ± 0.7 (se) ng of angiotensin I/ml per 3 hours before and 7.6 ± 1.2 ng Ang 1 during exercise, values that are not different statistically. Propranolol reduced PRA at rest from 8.6 ± 1.1 to 5.9 ± 1.1 ng Ang 1 (P< 0.05), but there was no significant difference between resting and exercise levels, although the increments in heart rate, cardiac output, and mean aortic pressure were reduced. Standing on hindlimbs for 5 minutes did not cause a change in mean aortic pressure or PRA. However, administration of pentolinium reduced mean aortic pressure, and PRA rose from 6.0 ± 1.1 to 9.8 ± 1.5 ng Ang I. Exercise, with or without /3-adrener-gic blockade, does not cause increased PRA in conscious dogs in which the renin-angiotensin system is normally responsive.

ISSN:0009-7330    

出版商:OVID    

年代:1976

数据来源: OVID

摘要:

The contribution of neural vasomotor reflexes to the control of cerebral blood flow (CBF) was investigated in 30 cats lightly anesthetized with pentobarbital. CBF was measured both by kinetic analysis and by the initial slope technique of the washout curve of a bolus of113Xe. Autoregulation (10 cats) and responsiveness to alteration in arterial Pcos(Paco2) (10 cats) and arterial Po2(Pao2) (five cats) were assessed both before and after bilateral intracranial division of the 9th and 10th nerves. In an additional group (five cats), related changes in CBF to alteration of Paco2were recorded before and after unilateral section of the 7th and 8th nerves. Autoregulation was preserved after division of the 9th and 10th nerves and there was no significant change in the Paco2response curves. Section of the 7th and 8th cranial nerves did not produce conclusive results in the small number of cats studied. A conclusion that the facial nerves are not dominant in responses to hypercapnia seems justified, but a modulating role for these nerves is possible. These studies do not exclude a physiological role for these nerves in the autoregulation of CBF, but do indicate that the cerebral vascular bed apparently is capable of functioning normally after their division.

ISSN:0009-7330    

出版商:OVID    

年代:1976

数据来源: OVID

摘要:

Repeatedly bred male and female rats of many strains develop hyperglycemia, hyperlipidemia, hypertension, and arteriosclerosis spontaneously. The intensity of their arterial disease and related metabolic derangements appears to be related to their reproductive activity. Repeatedly bred spontaneously hypertensive rats (SHR) were found to have severe hypertension, hyperglycemia, hyperlipidemia, elevated creatine phosphokinase (CPK), serum glu-tamic oxaloacetic and glutamic pyruvic transaminase (SGOT, SGPT), and lactic dehydrogenase (LDH), as well as high circulating corticosterone levels. Despite these atherogenic metabolic derangements and their severe hypertension, the breeder SHR did not develop the severe, generalized arteriosclerosis found in other strains of breeder rats. Instead, the arterial lesions, consisting of intimal hyalinization and fibrosis, medial hypertrophy, and occlusion of the lumen, were found only in male breeder SHR and were confined to the intratubular arteries of the testes. It is suggested that the severe hypertension, genetic influences, or differences in hypothalamic-pituitary-adrenal-gonadal function in breeder SHR may not have been conducive to the development of arteriosclerosis in this particular strain of rats.

ISSN:0009-7330    

出版商:OVID    

年代:1976

数据来源: OVID

摘要:

Adrenal and vascular responsiveness to graded doses of angiotensin II (A II) were recorded for seven normal subjects and 12 patients with essential hypertension while in balance on an intake of 200 mEq sodium/100 mEq potassium. Patients with essential hypertension had been previously studied and known to have normal responses of plasma renin activity to sodium restriction and upright posture. All was administered for 30 minutes at rates of 0.1, 0.3, 1, and 3 ng/kg per minute and plasma aldosterone responses were assessed 20 and 30 minutes later; blood pressure was monitored at intervals of 1 minute during infusion of A 11 at each rate. A significant increment in plasma aldosterone occurred at an infusion rate of 0.3 ng/kg per minute in patients with hypertension. This change was not seen until the infusion rate reached 1.0 ng/kg per minute in the normotensive control subjects. Even at an A II infusion rate of 1 ng/kg per minute, the increment in plasma aldosterone levels in normotensive subjects (4.2 ± 0.6 ng/dl) was significantly less (P< 0.001) than that in patients with essential hypertension (19 ± 3 ng/dl). In both groups, a significant rise in mean arterial blood pressure occurred at an A II dose of 0.3 ng/kg per minute, but the pressor response of the hypertensive group was significantly greater at the highest infusion rate (3 ng/kg per minute) (P< 0.05). Thus, enhanced adrenal and pressor responsiveness to infused A II was observed in the hypertensive subjects, suggesting a change in A II receptor affinity.

ISSN:0009-7330    

出版商:OVID    

年代:1976

数据来源: OVID

摘要:

We investigated the combined effectiveness of intra-aortic ballooon counterpulsation and hyperosmotic mannitol (25%) on regional myocardial blood flow during acute coronary insufficiency. Cardiac output and paced heart rate were held constant in chloralose-anesthetized dogs during right heart bypass. Acute coronary insufficiency was produced by ligation of the proximal left anterior descending coronary artery (LAD). Regional myocardial blood flow was measured using radioactive microspheres. Left ventricular end-diastolic pressure, mean aortic pressure, maximum left ventricular dp/dt, and hematocrit were unchanged by combined mannitol infusion and balloon pumping. Studies of combined treatment with balloon pumping and mannitol immediately after the second of two 13-minute consecutive reversible ligations of the LAD demonstrated that (1) collateral coronary blood flow increased 46% (P< 0.02) in ischemic myocardium compared with mannitol infusion alone during the first LAD ligation, and (2) collateral coronary blood flow increased 27% (P< 0.05) in ischemic myocardium compared with balloon pumping along during the first LAD ligation. Studies in which combined treatment was delayed until 20 minutes after LAD ligation demonstrated that collateral coronary blood flow was elevated by 33% (P< 0.05) in ischemic myocardium compared to control studies in which balloon pumping alone had no effect. The results suggest that the increase in collateral coronary blood flow was in part a result of an increased transmural pressure gradient produced by balloon diastolic augmentation and the ability of mannitol to reduce coronary vascular resistance in ischemic myocardium.

ISSN:0009-7330    

出版商:OVID    

年代:1976

数据来源: OVID

摘要:

To clarify the postulate that turbulence may produce ejection murmurs, point velocity and sound were measured in the ascending aorta of 13 subjects: six with normal aortic valves, six with aortic valvular disease, and one with a Björk-Shiley prosthetic aortic valve. Velocity was measured with a catheter-tip hot film anemometer probe, and sound was measured with a catheter-tip micromanome-ter. Ejection murmurs detected intra-arterially were always found to be associated with turbulent or highly disturbed flow. Conversely, in the absence of intra-arterial sound during ejection, only minor disturbances of flow were detected. A linear relation between the sound energy density and turbulent energy density was shown (r = 0.92) and a linear relation between the acoustic power output (sound intensity) and turbulent power supply (r = 0.87) also was shown. Studies in vitro of sound and point velocity distal to a porcine valve inserted within a cast of the aorta, which permitted precise centering of the transducers along the axis of flow, confirmed these observations. When the power generated by the turbulence exceeded 3 ergs/sec per cm2, the murmurs were audible at the chest wall. The clinical gradation of the intensity of the murmurs increased as the power of turbulence increased. In conclusion, in this study we have demonstrated a clear association between turbulent blood flow and systolic ejection murmurs.

ISSN:0009-7330    

出版商:OVID    

年代:1976

数据来源: OVID