摘要:

Simultaneous extracellular and intracellular recordings of normal action potentials, action potentials initiated at a time when the membrane was partially depolarized (by premature beats or elevated extracellular potassium), and action potentials at reduced temperature were made for Purkinje strands from the left ventricle of the dog with a 50μ tungsten extracellur electrode and a special guarded intracellular microelectrode. The peak-to-peak amplitude of the extracellular wave form was proportional to the maximum rate of rise of the intracellular action potential, and the duration of the extracellular wave form was proportional of the duration of the upstroke of the intracellular potential. Wave forms of extracellular potentials were computed from the recorded intracellular potentials with an equation which included the effects of membrane currents away from the point of observation. The computed wave forms accurately reproduced the recorded extracellular wave forms in all cases, and the wave forms were not directly porportional to the second spatial derivative or the second temporal derivative of the intracellular potential. Extracellular potentials are shown to be directly related to the spatial distribution of the intracellular potential and as such are a sensitive index of propagation and a source of information of the kind previously thought to be obtainable only with an intracllular electrode.

ISSN:0009-7330    

出版商:OVID    

年代:1972

数据来源: OVID

摘要:

Definition of the contractile state of the myocardium from force, length, and velocity relationships and measurements of ventricular pressure is a continuum mechanics approach that requires a detailed knowledge of the system under consideration or, in the absence of detailed knowledge, the use of suitable conceptual models. In this paper we proposed a simpler, though still rigorous, approach that required only a general, rather than a detailed, a priori knowledge of the system. Using the theory of thermodynamics, we gained some insight into the physical meaning of the time derivatives of the left ventricular pressure pulse. From integrations and normalizations we obtained power-density functions (energy-averaged power density and power-averaged rate of generation of power density). These functions relating the free energy in the myocardium to the pressure in the blood did not require geometric considerations, and they furnished, to a first approximation, a quantification of the contractile state in a population of 26 normal dogs under anesthesia. Moreover, the functions clearly separated the normal state from abnormal ones created by drug intervention, not only in the same dog, but also in different dogs. The functions appeared to be insensitive to volume loading. In two patients studied before and after surgery, these functions also showed significant changes.

ISSN:0009-7330    

出版商:OVID    

年代:1972

数据来源: OVID

摘要:

This investigation tested the hypothesis that uptake of potassium during respiratory acidosis is secondary to the increased catecholamine activity which accompanies hypercapnia. The plasma K+concentration of simultaneously drawn arterial and coronary sinus blood samples from dogs was determined under three conditions: (1) hypercapnia (25% CO2-75% O2), (2) normocapnia (25% N2-75% O2) + propranolol (a beta-receptor blocker), and (3) hypercapnia + propranolol. The change during hypercapnia from uptake of K+to loss of K+after administration of propranolol (0.05 mg/kg, iv) was statistically significant. However, the administration of propranolol during normocapnia had no effect on myocardial K+movement. Changes in heart rate and myocardial contractility did not explain the change in myocardial K+movement during hypercapnia following the administration of propranolol. These data suggest that uptake of K+is secondary to the increased catecholamine activity which accompanies hypercapnia.

ISSN:0009-7330    

出版商:OVID    

年代:1972

数据来源: OVID

摘要:

Elastic and muscular arteries are known to differ in function and in the magnitude of their response to vasoconstrictor influences. With the isolated thoracic aorta and ear artery of the rabbit as representative arteries, the morphological, physiological, and pharmacological correlates of these differences have been sought among their presynaptic adrenergic mechanisms. The adrenergic nerve plexus in the ear artery is wider and the nodes are denser than they are in the aorta. There is some evidence consistent with the hypothesis that the thicker the plexus, the greater the reuptake of released transmitter, the smaller the transmitter overflow, and the lower the efficiency of uptake of exogenous norepinephrine. Measurements of fractional release of tritiated norepinephrine suggest that qualitative differences in the adrenergic transmitter storage and release mechanisms may exist between the two vessels. Thus the considerable functional difference between the two vessels is in part, at any rate, a consequence of adrenergic mechanisms which differ both quantitatively and qualitatively from each other.

ISSN:0009-7330    

出版商:OVID    

年代:1972

数据来源: OVID

摘要:

The size and the performance of the left ventricle were examined in six conscious dogs early (within 1 week) and late (average 7 weeks) after the production of a large infrarenal arteriovenous fistula. Radiopaque beads were implanted near the endocardium of the left ventricle, and in each study the end-diastolic pressure was adjusted to 22 mm Hg by transfusion or bleeding. The shortening of the minor equator of the left ventricle and its mean velocity of shortening were compared in each dog before and after chronic left ventricular dilatation (ventricular end-diastolic volumes of 71 ml early and 101 ml late,P< 0.05). In five dogs the stroke volume increased by an average of 42% (P< 0.05) between early and late studies, but the percent change in circumference and the mean velocity of shortening remained unchanged (24.2 ± 2% (SE) and 23.6 ± 2%, 1.43 ± 0.12 circumferences/sec and 1.44 ± 0.09 circumferences/sec, respectively) at comparable heart rates. In one animal with congestive heart failure, the percent change in circumference and the mean velocity of shortening fell progressively to 19% and 0.74 circumferences/sec. It is concluded that in the absence of myocardial failure the enhanced performances of the chronically dilated left ventricle is mediated by normal performance of each unit of circumference of the enlarged chamber. The nature of this adaptation supports the application of several measures of contractility used for the assessment of chronic variations of inotropic state. Previously, diastolic sarcomere lengths were shown to be maximal and essentially the same after acute over-transfusion as they were during chronic volume overloading, and the present studies provide physiological support for the view that the chronic adaptation to volume overload need not involve the Frank-Starling mechanism at the sarcomere level. The observed adaptation provides a reserve mechanism, in addition to the usual factors regulating cardiac performance, by which chronic alterations in ventricular geometry allow the delivery of more external work.

ISSN:0009-7330    

出版商:OVID    

年代:1972

数据来源: OVID

摘要:

The major intermediate steps in the renin-angiotensin-vasoconstrictor feedback loop have been experimentally determined. The quantitative relationships between renal perfusion pressure, renin secretion, arterial renin activity, and systemic arterial blood pressure were determined in dogs in which the cardiovascular control loops of the central nervous system were eliminated by spinal cord destruction and decapitation. Step-decreases in renal perfusion pressure to a single kidney were introduced and maintained constant to open the feedback loop of arterial pressure. Renin activity was measured by radioimmunoassay of angiotensin I. Each decrease of 15 mm Hg in renal perfusion pressure between pressures of 100 and 50 mm Hg elevated the net secretion of renin nearly 20 ng min−1g−1kidney an d the arterial renin activity nearly 7.0 ng ml−1hour−1. Renin secretion and arterial renin activity decreased at perfusion pressures below 50 mm Hg. A bioassay procedure for estimating the rate of angiotensin II formation at various increments of arterial renin activity showed that an increase in renin activity of 10 ng ml−1hour−1resulted in an increase in the net production of angiotensin II of 5.0 ng kg−1min−1. The results of these experiments are useful in predicting alterations in the system that follow a decrease in renal artery pressure, and they clarify interactions of the renin-angiotensin system with other homeostatic pressure-regulating systems.

ISSN:0009-7330    

出版商:OVID    

年代:1972

数据来源: OVID

摘要:

Chronic hypertension caused by unilateral constriction of the renal artery in the presence of the opposite untouched kidney can be produced in the dog by progressive plication of the renal artery over a period of several hours. Twenty-three female dogs were studied. Mean arterial blood pressure was measured in the unanesthetized recumbent dog by direct puncture of the femoral artery. Reproducible control blood pressure readings were obtained only after daily training of the animals for at least 2 months. Mean arterial blood pressure for the whole group of animals was 98.25 ± 7.45 (SD) mm Hg prior to constriction. Three months after constriction, the mean arterial blood pressure of the group of dogs with a 50−63% reduction in renal blood flow was 132.4 ± 5.51 (SD) mm Hg (P< 0.001); for the group with a 78−86% reduction in renal blood flow it was 144.68 ± 10.68 (SD) mm Hg (P< 0.001). Six dogs from these two groups underwent ipsilateral nephrectomies 4−16 months after constriction, and their elevated arterial blood pressures returned to preconstriction normal values. It was concluded that this type of experimental hypertension in the dog is renal dependent in both the acute and the chronic stages.

ISSN:0009-7330    

出版商:OVID    

年代:1972

数据来源: OVID

摘要:

Microelectrode techniques were used to study isolated canine Purkinje fibers perfused alternately with Tyrode's solution and extracorporeally circulated arterial blood from heparinized donor dogs. Action potential amplitude and resting membrane potential were similar in both perfusates and varied with the potassium concentration of the perfusate. Action potential duration also varied with the potassium concentration of the perfusate, being shorter when potassium concentration was higher. Conduction in free-running Purkinje fibers usually was more rapid in blood than in Tyrode's solution; this difference often was not related to changes in potassium concentration, maximal slope of phase 0, and action potential amplitude. Automaticity was comparable in both perfusates. Because conduction time in isolated tissues differs during perfusion with blood and Tyrode's solution, it would seem that experiments on conduction performed during blood perfusion might reflect in vivo events more closely than results obtained using Tyrode's solution.

ISSN:0009-7330    

出版商:OVID    

年代:1972

数据来源: OVID

摘要:

Blood-tissue transport of42K,86Rb, and22Na was studied in perfused gracilis muscles of dogs to ascertain the influence of capillary wall, interstitial space, and muscle cell membranes on overall transport kinetics. Single-injection and continuous-infusion techniques were used, with T-1824 or51Cr-hemoglobin as nondiffusible references. Results were as follows: (1) Extraction (E) of the diffusible solutes was incomplete even in the earliest samples of venous outflow. (2) ERbequaled EKin the first few samples, but later, as both declined, the ratio of ERbto EKbecame less than one; stable ratios between 0.6 and 0.8 were established in different experiments. (3) ENawas initially slightly less than ERbor EKbut declined much more sharply in successive samples. (4) Steadystate ERband EKdecreased with increasing blood flow but maintained a constant ratio. Vasomotion sometimes changed ERband EKbut had little effect on their ratio. Local anesthetics (procaine or cocaine) brought the ratio of ERbto EKcloser to one. Analysis in terms of capillary and interstitial barriers, which do not discriminate between K, Rb, or Na, in series with a muscle cell membrane barrier, which does, leads to the following conclusions. (1) For K, the nondiscriminating barrier (mainly capillary wall) offers about 70% of the total resistance to transport and the discriminating barrier (cell membrane) about 30%. (2) For Rb, each barrier offers half the total resistance. (3) The resting muscle cell membrane is 2.5 times more permeable to K than to Rb. Local anesthetics reduce cell permeability to both ions and decrease this ratio. (4) For Na, resistance at the capillary wall is about 1.3 times that for K or Rb. Resistance at the cell membrane is, of course, very much greater.

ISSN:0009-7330    

出版商:OVID    

年代:1972

数据来源: OVID

摘要:

Norepinephrine metabolism, arterial blood pressure, and electrolytes were studied in rats maintained on either potassium-deficient or control diets. After 3 weeks on the test diets, the arterial blood pressure was significantly lower and the ratio of [Na] to [K] in cardiac tissue was significantly higher in potassium-deficient rats as compared to controls. Ten minutes after intravenous injection of3H-norepinephrine the specific activity of cardiac norepinephrine was similar in the control and potassium-deficient groups despite a significant increase in endogenous norepinephrine concentration in the potassium-deficient hearts. But 24 hours after injection, there was a significant increase in3H-norepinephrine specific activity, concentration, and content in the potassium-deficient group. Cardiac tissue monoamine oxidase activity was similar in both groups. The increased3H-norepinephrine retention and concentration and the decreased arterial blood pressure of the potassium-deficient rate suggest an impairment in norepinephrine release by the sympathetic neurons.

ISSN:0009-7330    

出版商:OVID    

年代:1972

数据来源: OVID