摘要:

Acute hypotension was produced in heparinized and nonheparinized dogs by hemorrhage and by injections of histamine, and adhesiveness and aggregation of blood elements determined periodically by the screen filtration pressure method. This method measures the pressure required to force blood at a constant rate through a standardized screen with multiple square holes each 20 × 20 micra. In some cases the arterial blood was perfused through a glass wool filter in an extracorporeal system both before and during periods of hypotension. The results of these studies justify the following conclusions:1. Increased adhesiveness and aggregation of platelets and other blood elements which occur during hypotension produced by hemorrhage or intravenous injections of histamine were indicated by an increase in the screen filtration pressure of blood. These changes were not prevented from developing, or significantly altered by heparinization of the animal.2. The amount of blood which could be obtained during arterial hemorrhage was significantly increased by heparinization of the animal.3. The adhesive and aggregated platelets and leucocytes, which formed during hypotension, were removed from the blood when it was perfused through a column of glass wool. This treatment was attended by a decrease in the screen filtration pressure of the blood to or below normal.4. The increase in screen filtration pressure which occurred during hypotension was much less marked if the animals' blood had first been circulated through pyrex glass wool.5. Filtration of blood through pyrex glass wool was also attended by a progressive decrease in the mean arterial blood pressure of the animal.

ISSN:0009-7330    

出版商:OVID    

年代:1964

数据来源: OVID

摘要:

A thermistor was used to record the temperature at regular intervals across the aortic diameter of dogs during the continuous infusion of cold indicator solution at various upstream locations. The results showed that the indicator mixed across the greater part of the diameter of the aorta in the ascending portion and proximal half of the arch but maintained a more streamlined pattern in the distal portion of the arch and descending thoracic aorta. These observations were confirmed by cineangiography. When two thermistors were located in different positions in the aortic root, and when cold saline was injected suddenly in their vicinity, the temperatures recorded by the two thermistors equalized immediately following the onset of systole. Sound waves also were detected during the systolic interval in the ascending but not in the descending aorta.These findings are consistent with the presence of disturbed, but not necessarily turbulent flow in the ascending aorta; and with predominantly streamlined, but not necessarily completely laminar flow in the descending portion. The factors producing disturbed flow in the aortic root and the transition of flow to a more streamlined pattern in the descending portion are discussed in hydrodynamic terms.It is postulated that during systole the blood ejected into the aorta separates from a slower moving boundary layer near the walls and at the edges of the valve cusps. This separation produces disturbed flow and mixing in the entering jet. While the thin layer adjacent to the walls as well as stagnant areas behind the valves do not fully mix with the central stream, they represent a relatively small proportion of the total aortic blood flow. Additional mixing is produced by the prominent backflow in early diastole and by the branchings of the coronary and brachiocephalic arteries.

ISSN:0009-7330    

出版商:OVID    

年代:1964

数据来源: OVID

摘要:

1. Atrial fibrillation was induced in dogs by single electrical shocks. Close bipolar direct electrograms were taken from various parts of the atrium; as many as 22 electrograms and a standard lead II electrocardiogram were recorded simultaneously. Initial phase and recovery phase of fibrillation were analyzed.2. In the initial phase of atrial fibrillation, local firing consisting of rapid tachysystole of 996 to 3000 per minute was observed near the stimulating point in most experiments. Except for the leads showing local firing, the interval between beats at each recording point tended to be constant, and a time gap between two successive beats was observed. A propagation pattern could be plotted which seemed to start from the origin of local firing; some beats were conducted only locally, and others (every second, third or fourth discharge) were conducted widely. The cause of atrial fibrillation was considered to be local firing of one small area of the atrium, i.e., the unifocal theory of the origin of atrial fibrillation was supported.3. During recovery from atrial fibrillation, features similar to those seen in the initial phase often appeared, although local firing disappeared. In some experiments, the atrium was separated electrically into a few groups of cells beating independently, and in others a “circus pathway” appeared to exist in the last beat. It seems that electrical separation of the atrium into many parts and circus movements, or multiple re-entry, may develop during the course of fibrillation, and that these phenomena perpetuate atrial fibrillation.4. During the last beat of atrial fibrillation, the time required for all cells to depolarize was occasionally less than the duration of the normal sinus beat. A similar phenomenon was sometimes observed in the premature beats following atrial fibrillation.

ISSN:0009-7330    

出版商:OVID    

年代:1964

数据来源: OVID

摘要:

Isolated, innervated and acutely or chronically denervated resting skeletal muscle of the dog exhibited high intrinsic vascular tone. Sustained alteration of perfusion pressure or venous pressure evoked autoregulatory responses; vascular resistance increased at elevated driving pressures and decreased at reduced driving pressures. Comparable changes of resistance were observed after sustained alteration of blood flow during pump perfusion. Autoregulation was consistently observed during muscle contractions with constant pressure or constant flow perfusion. In resting and contracting skeletal muscle a low venous blood oxygen saturation (VO2) was characteristic of preparations exhibiting a high degree of autoregulation. In innervated resting muscle autoregulation was concealed by reflex or local stimuli and its disappearance was associated with a decreased vascular resistance and an increased VO2. In resting chronically denervated muscle or in contracting muscle, whether innervated or denervated, such stimuli failed to affect the autoregulatory response. A schema has been proposed to define the “states” of skeletal muscle blood flow and some of the factors responsible for the presence or absence of autoregulation.

ISSN:0009-7330    

出版商:OVID    

年代:1964

数据来源: OVID

摘要:

Data obtained in 94 tests in nine anesthetized, thoracotomized dogs were re-examined to determine relationships among oxygen uptake per minute (qO2), cardiac frequency (F), mean aortic pressure (P), stroke volume (V), and heart weight (G).Statistical analysis supports the concept that during each systoleqO2/Gis empirically related most closely to the peak mechanical tension (T) developed by a spherical heart, in accord with the relationshipqO2/G-b/F=aT, in whichaandbare derived constants for each heart. Peak tension is half the product of the mean pressure and the radius (estimated from the stroke volume).Myocardial oxygen uptake is viewed as developing through a mechanical positive feedback mechanism which triggers the shortening of contractile elements. The number of such elements triggered in each beat determines the peak tension, the oxygen requirement of that beat, the resulting energy release, and the work. The oxygen costs of tension increase with the size of the heart since tension must be applied throughout the entire surface of each shell of contractile elements. Mechanical efficiency varies with the square of the stroke radius; it is not directly affected by mean aortic pressure or cardiac frequency. Factors affecting the all-or-none phenomenon, mobilization of tension, myocardial efficiency, the law of the heart, myocardial oxygen uptake, and the coronary flow are discussed in light of these findings.

ISSN:0009-7330    

出版商:OVID    

年代:1964

数据来源: OVID

摘要:

Hypertension was induced in rats by constricting the aorta between the origins of the renal arteries. The left kidney, which became ischemic and atrophic (“endocrine kidney”), caused a malignant type of hypertension associated with weight loss, cardiac hypertrophy, hypertension, cardiac necrosis, nephrosclerosis of the right kidney, and arteritis. Amounts of pressor substances were increased in the left kidney and decreased in the right as compared with those in kidneys of normal rats.Aqueous extracts of ischemic kidneys, of kidneys contralateral to ischemic kidneys and of normal kidneys were prepared and the supernatant solutions were injected subcutaneously into test rats which had been uninephrectomized a few hours previously. Extracts of ischemic kidneys caused hypertension, cardiac hypertrophy, weight loss, and renal and vascular lesions mimicking the signs which result from renal ischemia. The extracts from the other kidneys were inactive. Administration of renin in doses roughly equivalent in pressor activity to the extracts of ischemic kidneys caused a rise in pressure, diuresis, and proteinuria but no lesions when given subcutaneously.It is proposed as a working hypothesis that renal hypertensive disease results not only from increased secretion of renin and formation of angiotensin but from simultaneous release from kidneys with reduced perfusion pressure of a substance which augments the enzymatic formation of angiotensin. This substance is presumably absent from normal kidneys and from semipurified renin preparations.

ISSN:0009-7330    

出版商:OVID    

年代:1964

数据来源: OVID

摘要:

When a platinized platinum electrode is polarized at the potential of the standard calomel electrode, the current generated is proportional to the concentration of dissolved hydrogen gas. The effects of physiological variations in oxygen tension, pH, temperature, and ascorbic acid concentration were found to be negligible. Although absolute calibration in vivo is not possible, the rate of tissue hydrogen saturation or desaturation can be measured by needle-shaped electrodes inserted into the tissue. Arterial and venous concentration can be measured with catheter electrodes. Solubility of hydrogen gas in kidney slices was found to be the same as in blood. With the assumption that tissue is in instantaneous diffusion equilibrium with local venous blood with respect to hydrogen, the local blood flow per volume of tissue can be calculated according to the Fick principle from the rate of tissue desaturation when arterial concentration is lowered to zero.The method was tested on dogs in myocardium, kidney, and skeletal muscle. Hydrogen was administered by respiration or by intra-arterial infusion of hydrogen-saturated saline, giving an arterial concentration of 3% to 5% saturation. Tissue desaturation curves were recorded simultaneously from two to three tissue electrodes. Good agreement with flow measured simultaneously with other methods was obtained in myocardium and renal cortex, while the data on skeletal muscle do not permit any definite conclusion. The main virtue of this method lies in the fact that repeated measurements of local blood flow can be obtained without access to arterial or local venous blood. Reliable measurements of regional blood flow were also obtained from continuously recorded venous desaturation curves, which also provide information on the distribution of blood flow.

ISSN:0009-7330    

出版商:OVID    

年代:1964

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1964

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1964

数据来源: OVID