bluuebunny/crossref_metadata_2025 huggingface dataset:
Umbilical vascular compliance in sheep
Authors: Power G. G. , Gilbert R. D.
Published: December 2017

To explore the mechanical properties of umbilical vessels and to test for possible interactions between maternal and fetal circulations, we recorded pressure-volume curves from isolated in situ placentas of 17 sheep. We estimated static umbilical compliance by extrapolating to infinitely slow rates of volume change. We found that compliance averaged .231 +/- .014 SE ml/mmHg per kg fetal wt under control conditions, a value that increased 26.5% when maternal arterial pressure was lowered 85 mmHg (clamping the aorta), but did not change when venous pressure was raised 37 mmHg (clamping IVC). After replacing blood with kerosene which does not penetrate small vessels because of interfacial tension, we found arteries accounted for 22% and veins for 41% of total compliance, leaving 37% attributable to small placental vessels and surrounding tissue. We conclude that umbilical vessels are about one-half as compliant as adult vessels on a body-weight basis, but only slightly less compliant than vessels elsewhere in the fetal body. When maternal vessels expand they interact with surrounding placental tissue, displacing fetal blood and altering the apparent compliance of umbilical vessels.
Alterations of postural and Valsalva responses in coronary heart disease
Authors: Tristani F. E. , Kamper D. G. , McDermott D. J. , Peters B. J. , Smith J. J.
Published: December 2017

Patients in congestive heart failure are known to have altered autonomic responses to circulatory stress. In this study, two different age groups of male coronary heart disease (CHD) patients, not in failure, as well as normal male subjects, underwent standard 20-min 70 degrees head-up tilt and Valsalva tests. Responses were monitored by noninvasive methods and cardiac output was estamated with a transthoracic impedance method. During tilt, the CHD patients and control subjects had similar heart rate and diastolic pressure responses. However, the CHD patients had a greater decline in pulse pressure during tilt, mainly due to a decrease in systolic pressure. CHD patients had lesser declines in stroke volume and cardiac index and lesser increases in total vascular resistance than did control subjects. In the Valsalva, the heart rate phase increments (and decrements) from control and rate increments (and decrements) between successive phases were less in the coronary patients. The results indicate that coronary patients, not in failure, have diminished circulatory responses to the tilt and Valsalva maneuver and suggest that these tests may be useful functional indices of cardiovascular capability in coronary disease.
Direct calibration of a totally implantable pulsed Doppler ultrasonic blood flowmeter
Authors: Allen H. V. , Anderson M. F. , Meindl J. D.
Published: December 2017

Page H537: H. V. Allen, M. F. Anderson, and J. D. Meindl. “Direct calibration of a totally implantable pulsed Doppler ultrasonic blood flowmeter.” Page H542: Table 1, footnote--the equation for the correlation coefficient should read

(See PDF)

Similarly, the equation for flow should read

(See PDF)
Effect of activation sequence on MVO2 before and after coronary ligation
Authors: Kralios A. C. , Tsagaris T. J.
Published: December 2017

In pentobarbital-anesthetized, open-chest dogs with fixed heart rate, cardiac output, and systemic arterial pressure, ectopic ventricular activation originating from apical as compared to basilar regions of either ventricle was associated with small (3--5%) but significantly (P less than 0.005) lower myocardial O2 consumption (MVO2) and thus higher left ventricular (LV) efficiency without change in LV end-diastolic pressure (LVEDP), work index (LVWI), and LV dP/dt. Data obtained during epicardial and corresponding endocardial activation did not differ. During normal ventricular activation, MVO2 remained unchanged but LVEDP was significantly (P less than 0.005) lower, thus yielding higher LVWI and efficiency. MVO2 differences among ectopic sites were abolished after coronary artery occlusion, whereas data obtained during endocardial and epicardial on normal and ectopic activation were not affected. Thus, normal activation resulting in lower LVEDP is most efficient; apical ventricular activation is less efficient at the same MVO2P basilar is the least efficient, because both MVO2 and LVEDP are higher. Ventricular activation sequence changes do not constitute a substantial determinant of MVO2.
Estimation of the filtration coefficient of pulmonary exchange vessels
Authors: Drake R. , Gaar K. A. , Taylor A. E.
Published: December 2017

Filtration characteristics of the exchange vessels in isolated dog lung were studied by calculating the volume conductance (LP,C) with use of different components of the weight-gain curve following changes in capillary pressure. In one series of lungs, capillary pressure was elevated to levels that produced alveolar edema (29.4 +/- 5.3 (mean +/- SD) mmHg), and total alveolar capillary membrane conductances (LP,T) were calculated using different components of the accumulated weight-gain measurements. These conductance values are similar to those found in the literature for studies in which alveolar edema developed and LP,T was calculated using wet-to-dry weight ratios as a measure of filtered volume. In another series of lungs, capillary pressure was altered by only 5.8 +/- 2.5 mmHg, and LP,C was calculated by estimating the initial filtration rate by an extrapolation method LP,C calculated by use of the extrapolation method (0.71 X 10(-11) cm3/dyn-s) was larger than the LP,T reported in the literature, because LP,T is an estimate of the conductance of the alveolar plus the capillary membrane. Also, for the most calculations of LP,T, tissue forces have changed which causes an overestimation of the filtration driving pressure and thus an underestimate of the capillary volume conductance. After estimating both LP,C and LP,T, the maximum volume conductance of the alveolar membrane (LP,a) was calculated to be 0.13 X 10(-11) cm3/dyn-s.
Potentiation of the cerebrovascular response to intra-arterial 5-hydroxytryptamine
Authors: Eidelman B. H. , Mendelow A. D. , McCalden T. A. , Bloom D. S.
Published: December 2017

Infusion of 5-hydroxytryptamine (5HT) into the internal carotid artery of normal baboons was not accompanied by alteration of gray matter cerebral blood flow. In animals pretreated with depot estrogen and progesterone (dosage equivalent to oral contraceptive preparations), infusion of 5HT produced a marked decrease in gray matter blood flow. A similar decrease in flow was obtained when the 5HT was infused with a concentrate of beta-lipoprotein. Steroid substances appear to enhance the cerebrovascular constrictor responses to 5HT. A further series of six experiments has shown that the monoamine oxidase inhibitor tranylcypromine similarly produced constrictor responses to 5HT. It is possible that the steroids, the beta-lipoprotein, and the tranylcypromine produced constrictor responses to 5HT by the same mechanism (inhibition of cerebrovascular monoamine oxidase).
Decreased reactive hyperemia after coronary perfusion with nonoxygenated solution
Authors: Sugishita Y. , Kakihana M. , Murao S.
Published: December 2017

To gain more knowledge about the factors involved in reactive hyperemia in the coronary vessels, we performed comparative studies on the reactive hyperemia occurring after coronary occlusion and after coronary perfusion with nonoxygenated Tyrode solution. The peak coronary reactive hyperemic flow following 3 min of coronary perfusion with nonoxygenated Tyrode solution increased to only 142 +/- 16% of the control in contrast to 455 +/- 75% following 3 min of coronary occlusion alone. Myocardial oxygen uptake during reactive hyperemia was also much smaller after perfusion with Tyrode solution. First, the evidence suggests that the decreased reactive hyperemia after coronary perfusion with the nonoxygenated Tyrode solution is due to "washout" of the vasodilatory metabolites from the myocardium. Second, it suggests that there is a smaller "energy debt" during perfusion with Tyrode solution, so that deterioration of myocardial function due to oxygen deficiency is less severe than in coronary occlusion alone.
Effect of hypoxia on myocardial high-energy phosphates in the neonatal mammalian heart
Authors: Jarmakani J. M. , Nagatomo T. , Nakazawa M. , Langer G. A.
Published: December 2017

The effect of hypoxia on myocardial high-energy phosphate content in the newborn, 2-wk-old, and adult rabbit was determined and compared with mechanical function. Studies were done on the ventricular septum arterially perfused with Krebs-Henseleit bicarbonate buffer solution equilibrated with 95% O2 and 5% CO2 (control) or 95% N2 and 5% CO2 (hypoxia) at 60 beats/min and 27 degrees C. In the adult, ATP concentration decreased to 68%, 56%, and 39% of control after 2, 30, and 60 min of hypoxia, respectively. After 30 min of hypoxia, ATP concentration was not different from control in the newborn but decreased to 82% of control in the 2-wk-old. After 2 min of hypoxia, creatine phosphate concentration decreased to 55% and 10% of control in the newborn and adult rabbit, respectively. Lactate production increased significantly during hypoxia and was greater in the newborn than in the adult. The data indicate that the newborn rabbit is capable of maintaining glycolysis and normal levels of myocardial ATP during hypoxia, which ensures normal myocardial mechanical function for longer periods than in the adult.
Effect of low fibrinogen concentrations on the rheology of human blood in vitro
Authors: Blattler W. , Straub P. W. , Jeanneret C. , Horak G. S.
Published: December 2017

The influence of low concentrations of fibrinogen on the rheology of normal human blood was investigated with an instrument that permitted simultaneous determination of viscosity and the state of red blood cell aggregation and deformation. Fibrinogen, in concentrations of 9-82 mg/100 ml, decreased blood viscosity at all shear rates below the value obtained with red blood cells suspended in serum. At concentrations above 116 mg/100 ml viscosity was increased. Aggregate formation increased progressively as the fibrinogen concentration increased, necessitating higher dispersing shear rates. The deformation and alignment of the red cells, occurring at a shear rate of 230 s-1, was facilitated by low concentrations. The effect of fibrinogen on low-shear viscosity is explained by the formation of different kinds of aggregates. At low concentrations, the aggregates consist of only few cells forming spherelike particles displaying hemodynamic properties better than those of the single discoid cells. At normal or high concentrations big rodlike aggregates occur and increase resistance to flow.
Lack of fibrin formation in exercise-induced activation of coagulation
Authors: Vogt A. , Hofmann V. , Straub P. W.
Published: December 2017

Strenuous physical exercise leads to a significant shortening of blood clotting in various test systems. Such short times are also characteristic of those observed in sedentary patients with thrombosis or disseminated intravascular coagulation, and of those observed in experimental animals after thrombin infusion. The patients exhibit an increase in circulating fibrinopeptide A, which is attributed to thrombin action on circulating fibrinogen, and to an increase of fibrinogen degradation products, which is thought to indicate reactive fibrinolysis. To check whether physical exercise leads to fibrinemia, 10 healthy male volunteers were subjected to strenuous exercise on a bicycle ergometer. Blood samples were taken immediately before and on completion of the exercise period. Despite a significant shortening of the activated partial thromboplastin time, the thrombin time, and the Reptilase time, no increase of fibrinopeptide A could be demonstrated and the ethanol gelation test remained consistently negative. Simultaneously, the euglobulin lysis time was significantly shortened, whereas the fibrin(ogen) degradation products did not increase. The results indicate that the shortening of the coagulation times associated with physical exercise must be explained by mechanisms other than thrombin-mediated conversion of fibrinogen to fibrin.
Role of vagal afferents in vasodepressor effects of PGE2 in spontaneously hypertensive rats
Authors: Chen D. S. , Donald D. E. , Romero J. C.
Published: December 2017

In anesthetized, spontaneously hypertensive rats (Okamoto-Aoki), injections of 0.75, 1.5, and 3.0 microgram/kg PGE2 into the jugular vein caused transient decreases (mean +/- SE) in arterial pressure of 21 +/- 2, 37 +/- 3, and 78 +/- 6 mmHg, respectively, before cervical vagotomy and of 1 +/- 1, 15 +/- 4, and 15 +/- 6 mmHg after cervical vagotomy. The vasodepressor effect of jugular vein injections of 3.0 microgram/kg PGE2, but not of lower doses, was depressed by vagotomy in normotensive Wistar-Kyoto and Sprague-Dawley rats. Vagotomy did not reduce the hypotensive response to intra-aortic injections of PGE2 in these hypertensive and normotensive rats. The depressor effect of PGE2 thus appears to have a significant reflex component mediated through cardiopulmonary receptors subserved by vagal afferents, with hypertensive rats exhibiting a lower threshold than normotensive rats. A vagally mediated reflex component to the depressor effect of PGE2 could not be demonstrated in normotensive rabbits or in rabbits and rats with chronic renovascular hypertension. Thus, a naturally occurring vasoactive substance can stimulate cardiopulmonary receptors subserved by vagal afferents in the rat, and spontaneously hypertensive rats appear to be especially sensitive to this effect.
An improved isolated heart preparation for external assessment of myocardial metabolism
Authors: Bergmann S. R. , Clark R. E. , Sobel B. E.
Published: December 2017

To facilitate characterization of myocardial metabolism with the use of positron-emitting tracers, we developed an isolated heart preparation designed to simulate physiological levels of flow and substrate extraction. Isovolumically beating hearts were perfused retrograde at 60 mmHg with modified non-recirculating Krebs-Henseleit (KH) solution with or without washed sheep red blood cells at a hematocrit of 25 or 40 (KH-RBC25, KH-RBC40). Left ventricular (LV) systolic pressure averaged 63 mmHg with KH alone, 78 with KH-RBC25, and 98 with KH-RBC40. LV dP/dt, pressure-time index, and oxygen consumption increased in an analogous fashion. Fatty acid extraction increased from 1.5% with KH to 11.8% in hearts perfused with KH-RBC40, although net uptake was not increased markedly because of the associated differences in flow (4.6 ml.g-1.min-1 with KH and 1.5 with KH-RBC40). Hearts perfused with erythrocyte-rich media exhibited functional and metabolic stability and less edema. The preparation avoids intrinsic limitations encountered with buffer-perfused hearts and should prove useful for characterization of cardiac metabolism with radiolabeled tracers relevant to positron emission transaxial tomography.
Contributions of nerves and metabolites to exercise vasodilation: a unifying hypothesis
Authors: Honig C. R.
Published: December 2017

Neuronal cell bodies exist in arterioles of skeletal muscle and appear to initiate vasodilation during phasic contraction. The following findings indicate that intrinsic nerves rather than metabolites maintain vasodilation during sustained phasic contraction with free flow. 1) Under certain conditions maximal vasodilation can occur without detectable release of metabolites. 2) When metabolites are released during exercise, their concentrations in blood or tissue do not always determine the extent of vasodilation. 3) Vasodilation during sustained contraction can be partly blocked by local anesthetics. The extent of block is inversely proportional to the concentration of metabolites. Dose, time course of block, and other tests of specificity indicate that local anesthetics act on the intrinsic nerves rather than smooth or striated muscle. When contraction stops, neurogenic vasodilation decays rapidly (half time less than 1 min). Sustained vasodilation during recovery is therefore fully accounted for by metabolites. A hypothesis is suggested that integrates the roles of extrinsic nerves, intrinsic nerves, and metabolites in support of muscle contraction.
Rat pulmonary circulation after chronic hypoxia: hemodynamic and structural features
Authors: Rabinovitch M. , Gamble W. , Nadas A. S. , Miettinen O. S. , Reid L.
Published: December 2017

In 55 Sprague-Dawley rats (mean wt, 277 +/- 6.2 g) exposed to hypobaric hypoxia (air at 380 mmHg), and 23 weight-matched controls kept in room air, pulmonary and systemic artery pressures were measured daily for 2 wk via indwelling catheters. After each day of exposure, 1 or 2 hypoxic rats, to a total of 20, and 5 control rats were killed during the experiment. In these rats, the pulmonary arterial tree was injected post mortem with barium-gelatin and inflated with formaldehyde solution, and three structural features were quantified microscopically: 1) abnormal extension of muscle into peripheral arteries where it is not normally present (EMPA); 2) increased wall thickness of the normally muscular arteries, expressed as a percentage of external diameter (%WT); and 3) reduction in artery number expressed as an increase in the ratio of alveoli to arteries (A/a). Mean pulmonary artery pressure (Ppa) rose significantly after day 3 of hypoxic exposure (P less than 0.05) and had doubled by day 14; the mean systemic artery pressure (Psa) of hypoxic rats and Ppa and Psa of control rats were unchanged. The level of Ppa correlated with the degree of structural changes; for EMPA, r = 0.84; for %WT, r = 0.64; and for A/a, r = 0.73 (P less than 0.001 in all.
Aversive conditioning of elevations in total peripheral resistance in dogs
Authors: Anderson D. E. , Yingling J. E.
Published: December 2017

Operant conditioning experiments were performed with 12 chronically instrumented dogs to which aversive stimulation was presented whenever total peripheral resistance (mean pressure/cardiac output) decreased acutely below a criterion level. Initial experiments in which aversive stimulation occurred whenever total peripheral resistance decreased below mean base-line levels resulted in sustained decreases in total peripheral resistance, accompanied by elevations in heart rate, cardiac output, and arterial pressure. Subsequent experiments showed, however, that if aversive stimulation occurred only following large-magnitude decreases in resistance (30% below base-line levels), a progressive cardiovascular response pattern emerged during daily sessions of 5--16 h. This cardiovascular pattern included progressive elevations in resistance (10--50%), accompanied by progressive decreases or no change in heart rate and cardiac output and moderate increases in arterial (up to 20 mmHg) and pulse pressure. These within-session cardiovascular changes were accompanied by sustained inhibition of overt behavioral acitivity and progressive inhibition in respiratory activity. Implications of these observation for behavioral regulation of circulatory function are discussed.
Vascular reactivity of the isolated tibia of the dog
Authors: Driessens M. , Vanhoutte P. M.
Published: December 2017

Experiments were performed to assess the responsiveness of vessels subserving bone tissue to nerve stimulation and to exogenously administered catecholamines and acetylcholine. Tibias of mongrel dogs were isolated and dissected free; the periosteum was left intact. The main nutrient artery was prepared and cannulated. Ring electrodes were placed around the artery. The preparation was perfused at constant flow with aerated (95% O2 - 5% CO2) Krebs-Ringer solution (37 degrees C) by means of a roller pump. The perfusion pressure was continuously recorded. For each preparation, the flow rate was used at which the response to a standard dose of norepinephrine was the largest. Periarterial electrical stimulation caused frequency-dependent increases in perfusion pressure; because these responses were blocked by phentolamine, they must be due to activation of sympathetic nerves. Injections of norepinephrine caused dose-dependent increases in perfusion pressure that were abolished by phentolamine. Acetylcholine caused dose-dependent, atropine-sensitive decrease of the constrictions caused by norepinephrine infusions. These experiments demonstrate that the isolated perfused tibia of the dog is a satisfactory preparation to investigate the direct effects of sympathetic nerve stimulation and naturally occurring vasoactive amines on bone blood vessels.
Cardiovascular changes during spontaneous micturition in conscious cats
Authors: Baccelli G. , Mancia G. , Del Bo A. , Albertini R. , Zanchetti A.
Published: December 2017

The hemodynamic changes occurring during spontaneous micturition were recorded in conscious cats. Arterial blood pressure was continuously measured by chronically implanted arterial catheter, heart rate (HR) by a cardiotachometer, and cardiac output (CO), superior mesenteric (MF), renal (RF), and external iliac blood flows (IF) by chronically implanted electromagnetic flow probes. Spontaneous micturition was accompanied by little change in mean arterial pressure (-9.7 +/- 0.7%), but by a marked decrease in HR (-49.0 +/- 1.2%) and CO (-28.6 +/- 2.5%), and therefore by a marked decrease in total peripheral conductance (-21.0 +/- 3.5%). Visceral and hindlimb blood flows were markedly reduced during micturition (MF, -34.7 +/- 2.1%; RF, -22.6 +/- 1.5%; and IF, -48.7 +/- 1.5%, respectively) due to a marked reduction in regional conductances in both these areas. The vasomotor changes in the regional circulations were prevented by local sympathectomy. Thus spontaneous micturition is associated with marked changes in cardiac function and systemic circulation. Cardiac output is decreased, but diffuse nervous systemic vasoconstriction compensates for this and provides maintenance of arterial blood pressure level.
Evidence of nonuniform sympathetic neural activity to heart regions in guinea pigs
Authors: Schmid P. G. , Dykstra R. H. , Mayer H. E. , Oda R. P. , Donnell J. J.
Published: December 2017

Central neutral activity may selectively influence cardiac regions. As an index of this, rate constants of norepinephrine turnover, KNE, in regions of guinea pig heart were determined by 1) disappearance of [3H]NE from tissues, and 2) conversion of [3H]tyrosine to [3H]NE. In sinoatrial (SA) node and right atrial appendage, KNE averaged 0.084 +/- 0.014 and 0.066 +/- 0.004 (SE) h-1, respectively (P greater than 0.05). In other specialized regions, KNE was lower than in SA node (P less than 0.05). In other contractile regions, KNE was lower than in right atrial appendage (P less than 0.05). Ganglionic blockade reduced KNE to uniform values in all heart regions. Cold stress increased KNE markedly (P less than 0.05) throughout the heart, but selectively more in SA node, AV node, proximal conduction bundles, and right atrial appendage (P less than 0.05). At room temperature, neural activity is greater to the right atrium including SA node than to other cardiac regions. At 4 degrees C, neural activity increases selectively in the right atrium and the conduction system. This suggests that central neural mechanisms contribute significantly to nonuniform cardiac regulation under conditions of progressive sympathetic activation.
Overdrive suppression of automaticity in cultured chick myocardial cells
Authors: Pelleg A. , Vogel S. , Belardinelli L. , Sperelakis N.
Published: December 2017

Overdrive suppression in automatic cells and postdrive hyperpolarization in quiescent cells were examined in cultured embryonic chick heart cells. Cells were enzymatically separated from 3-day-old whole hearts and from 16-day-old atria and ventricles. The dispersed cells were allowed to reaggregate into small spheres (aneural) and maintained in culture for 1--4 wk. Quiescent reaggregates (all ventricular reaggregates and some of the atrial) demonstrated postdrive transient hyperpolarization of up to 5 mV. The spontaneously beating reaggregates (some of the atrial and all of the 3-day-old hearts) demonstrated overdrive suppression of automaticity. The faster the predrive spontaneous firing rate, the shorter was the overdrive suppression period. Prolongation of the drive period increased the duration of the overdrive suppression. The time courses of recovery from both overdrive suppression and postdrive hyperpolarization were similar. Atropine (10(-5) M) did not affect the phenomena. Ouabain (10(-6) M) reduced the postdrive hyperpolarization and shortened the duration of overdrive suppression. It was concluded that overdrive suppression and postdrive hyperpolarization a) occur in cultured chick ventricular and atrail cells; b) occur in early embryonic stages of development; c) occur independently of cholinergic receptors; d) are dependent on stimulation of an elecrogenic Na-K pump.
Effects of pulsations on carotid sinus control of regional arterial hemodynamics
Authors: Cox R. H. , Bagshaw R. J.
Published: December 2017

Studies were conducted in halothane-anesthetized dogs to evaluate the interaction of mean and pulsatile components of carotid sinus perfusion pressure on the control of regional pressure-flow relations. Pressure and flow were measured simultaneously in the ascending aorta, celiac, mesenteric, renal, and iliac arteries. The carotid sinuses were bilaterally isolated and perfused under controlled conditions. Mean (CSP) and pulsatile components (CSPP) of carotid sinus pressure were varied systemically. Values of mean aortic pressure (AP) at the operating point (AP = CSP) decreased with increasing CSPP (127 +/- 5 at CSPP = 0 to 103 +/- 5 at CSPP = 60). Reflex gains at the operating point also decreased with increasing CSPP (-1.35 +/- 0.16 for CSPP = 0 to -0.92 +/- 0.18 for CSPP = 60). Changes in cardiac output and peripheral resistance nonuniformly contributed to these responses, with the former predominating at low CSPP and the later at high CSPP. Operating-point values of regional resistance generally decreased with increasing CSPP but to different degrees in the various beds. With increasing CSPP amplitude, regional resistance sensitivity at the operating point (i.e., slope) increased in the celiac and decreased in the mesenteric, renal, and iliac vascular beds. Separate changes in mean and pulsatile components of carotid sinus pressure about the normal operating point produce quantitatively similar changes in systemic hemodynamic variables.
Sympathetic regulation of the cerebral circulation by the carotid chemoreceptor reflex
Authors: Vatner S. F. , Priano L. L. , Rutherford J. D. , Manders W. T.
Published: December 2017

The effects of carotid chemoreceptor reflex stimulation (intracarotid injection of nicotine 0.2 microgram/kg) were examined in conscious dogs on the cerebral circulation, using the radioactive microsphere technique to measure cerebral blood flow. In intact dogs (n = 18) with ventilation controlled, carotid chemoreceptor reflex stimulation increased (P less than 0.01) mean arterial pressure by 36 +/- 5% (SE) and calculated cerebral vascular resistance by 58 +/- 13%, whereas cerebral blood flow fell by 7 +/- 6% (NS). After bilateral cervical sympathectomy (n = 9), carotid chemoreceptor reflex stimulation induced significantly different (P less than 0.01) effects on cerebral blood flow, which rose by 42 +/- 8%, and cerebral vascular resistance, which did not change. To determine whether the difference in effect was due to the sympathectomy or merely to the repetition of the stimulus, another group of dogs (sham; n = 6) that had intact sympathetic nerves were studied a second time. In "sham" dogs, the repeat response to carotid chemoreceptor stimulation also induced significantly different effects from those in dogs with sympathectomy. After general anesthesia with sodium pentobarbital, or after section of the ipsilateral carotid sinus nerve, carotid chemoreceptor stimulation with nicotine, 0.2 microgram/kg, failed to induce a detectable hemodynamic effect. Thus, in the conscious dog, stimulation of the carotid chemoreceptor reflex elicits significant sympathetically mediated vasoconstriction in cerebral vessels.
Circuit for measurement of instantaneous frequency
Authors: McGillivray R. , Wald R.
Published: December 2017

This paper describes a circuit that measures the instantaneous frequency of a pulse train applied to the input. Analog outputs are provided that are linearly proportional to the interval between successive pulses and to the reciprocal of that same interval. The design is based upon well-established operational amplifier circuits and can be built with readily available components. The range over which the circuit operated can be changed by the selection of a single resistor, and the initial calibration requires the adjustment of only three components.
Induced fetal hyperthyroidism: cardiac output and oxygen consumption
Authors: Lorijn R. H. , Nelson J. C. , Longo L. D.
Published: December 2017

In 13 chronically catheterized fetal lambs, we inserted a subcutaneous osmotic minipump that released triiodothyronine (T3) at a rate of 5.9 microgram x h-1. Five days postoperatively, fetal plasma T3 concentration had increased 10-fold from a control value of 18.4 ng x dl-1; reverse T3 and thyroxine had decreased 83 and 61% from control values of 524 ng x dl-1, and 9.5 microgram x dl-1, respectively. Fetal heart rate increased 29% to 210 from 163 beats x min-1, and blood pressure remained constant. Cardiac output measured with radioactive-labeled microspheres increased 22% to 678 +/- 33 from a control value obtained from another group of animals of 554 +/- 16 ml x min-1 x kg-1. Umbilical blood flow also increased 22%, while coronary flow increased 35%, and pulmonary flow increased 90%. In contrast, flow to the thyroid gland decreased 52%. Fetal oxygen consumption increased 28% to 10.5 +/- 0.5 from 8.2 +/- 1.1 ml x min-1 x kg-1. Placental carbon monoxide diffusing capacity and venous and arterial blood gas values remained unchanged. We conclude that 1) sustained fetal T3 infusion is one of the few factors that can increase fetal cardiac output, and may play a role in increasing cardiac output in the newborn infant, 2) T3 infusion results in an increased rate of metabolism with increased oxygen consumption, and 3) placental reserve for oxygen diffusion exceeds normal oxygen requirements.
Phosphorylation of myosin in perfused rabbit and rat hearts
Authors: High C. W. , Stull J. T.
Published: December 2017

Working perfused rabbit and rat hearts were used to determine whether changes in myosin P-light chain phosphate content could affect cardiac contractility. Control perfused rabbit and rat hearts contained 0.48 +/- 0.02 and 0.61 +/- 0.02 mol phosphate/mol P-light chain, respectively. Perfusion of 1) rabbit hearts with 0.1 microM isoproterenol for 30 s, 2) rabbit or rat hearts with a fivefold increase in perfusate [Ca2+] for 30 s, or 3) rabbit hearts with a threefold increase in [Ca2+] for 5 and 15 min caused significant increases in LV dP/dtmax, but had no effect on P-light chain phosphate content. Perfusion of rabbit hearts with Ca2+-free buffer or buffer containing 22 mM K+ caused complete cessation of contractile activity within 30 s and reduced P-light chain phosphate content to 50 and 70%, respectively, of control values after 30 min. Reperfusion of hearts exposed to 22 mM K+ with control buffer restored LV dP/dtmax to control values within 10 min, whereas P-light chain phosphate content remained at 70% of control value. Thus, changes in cardiac contractile state were not accompanied by changes in the extent of phosphorylation of P-light chain.
Vascular and hematologic effects of hemorrhage in the chicken
Authors: Ploucha J. M. , Scott J. B. , Ringer R. K.
Published: December 2017

Chickens have been reported to have a rate of posthemorrhagic fluid mobilization twice that of mammals and lack a phase of shock irreversible to transfusion. In the present study we measured several hemodynamic and hematologic parameters in chickens subjected to sustained hemorrhagic hypotension. Total peripheral resistance was unaffected or fell slightly and skeletal muscle vascular resistance judged from changes in gastrocnemius resistance was not affected by hemorrhage. Blood compositional changes included a progressive hyperkalemia, hyperglycemia, and hemodilution as evidenced by linear falls in hematocrit, hemoglobin, and plasma total protein concentration. Plasma sodium and osmolality were unchanged, as were arterial pH and oxygen tension; however, there was a fall in carbon dioxide tension. These studies demonstrate that fluid mobilization in the chicken after hemorrhage does not require an increase in precapillary resistance and suggest that, because the chicken does not exhibit intense precapillary constriction, it is spared some of the deleterious effects of inadequate tissue perfusion. Thus, the findings tend to incriminate the peripheral action of the sympathetic nervous system as a major contributor to the development of irreversibility in other species.
Concurrent increases in resistance and transport after coronary obstruction in dogs
Authors: Harris T. R. , Overholser K. A. , Stiles R. G.
Published: December 2017

We have extended earlier studies on coronary vascular permeability-surface area (PS) for [14C]sucrose to include observations of the transcoronary flow resistance before and after partial occlusion of the left anterior descending coronary artery. Multiple-tracer (MT) studies were conducted on 13 anesthetized dogs by inserting an isotope mixture (125I-albumin, 51Cr-red blood cells, [14C]sucrose, 3HOH) into a cannula connecting the carotid and the left anterior descending coronary artery. Analysis of blood sampled from the coronary sinus allowed calculation of PS, extravascular 3HOH volume (VT), and extravascular [14C]sucrose volume (VS). Flow reduction significantly reduced VT and VS and increased PS/VT relative to base line. Coronary resistance distal to the obstruction (R) decreased significantly immediately after flow reduction but then, over the low-flow period, increased significantly above this initial low-flow value. The mean R during reduced flow normalized to R immediately after flow reduction (Ri) correlated significantly with PS/VT during ischemia. Because R/Ri is not correlated with VT alone, we speculate that capillary permeability alterations may play a role in the deterioration of myocardial perfusion during ischemia.
Mitochondrial inner membrane enzyme defects in porcine myocardial ischemia
Authors: Rouslin W. , Millard R. W.
Published: December 2017

Left anterior descending coronary artery occlusion in anesthetized pigs produced a stable transmural ischemia characterized by a rapid and then sustained loss of blood flow and mechanical function. After 2 h of occlusion, mitochondria from the ischemic area exhibited a 36 +/- 6% drop in state 3 respiratory activity (QO2) supported by the NAD-linked substrates, glutamate plus malate, but only a 5 +/- 3% decrease in QO2 with succinate plus rotenone. The activity of electron transfer complex I (NADH-CoQ reductase) decreased commensurately by 33 +/- 4% with the decrease in QO2 with NAD-linked substrates. Consistent with the nearly unchanged QO2 with succinate plus rotenone, the activities of electron transfer complexes III and IV decreased only slightly by 9 +/- 5% and 9 +/- 4%, respectively. Mitochondrial ATPase (complex V) activity decreased by 48 +/- 2% with little change in its oligomycin sensitivity. A 48% drop in ATPase activity was shown, by means of oligomycin titrations, to correspond to a 32% decrease in NAD-linked substrate supported QO2. The decreases observed in NADH-CoQ reductase and ATPase activities each account nearly quantitatively for the impaired mitochondrial phosphorylating respiration observed during sustained myocardial ischemia. These results suggest that mitochondrial inner enzyme complexes I and V are important sites of cellular injury in myocardial ischemia.
Cardiovascular reflexes elicited by passive gastric distension in anesthetized cats
Authors: Longhurst J. C. , Spilker H. L. , Ordway G. A.
Published: December 2017

Hemodynamic responses to passive gastric distension were examined in alpha-chloralose anesthetized cats. Gastric balloons were distended with 37 degrees C fluid at slow (50 ml/min) and rapid (250 ml/min) infusion rates before and after laparotomy. Passive gastric distension at the slow infusion rate significantly (P less than 0.05) increased mean arterial pressure (MAP) by 28%, dP/dt at 40 mmHg developed pressure by 29%, and systemic vascular resistance (SVR) by 35%. Likewise, the rapid distension rate significantly (P less than 0.05) increased MAP (20%), dP/dt (16%), and SVR (23%). Heart rate, aortic flow, and left ventricular end-diastolic pressure remained unchanged at both distension rates. Cardiovascular responses to passive gastric distension were similar before and after laparotomy. Section of the vagus nerve at the diaphragm did not alter the responses, whereas abdominal splanchnic nerve section significantly (P less than 0.05) reduced the changes in mean arterial pressure and dP/dt. These results indicate that passive gastric distension in the cat elicits cardiovascular reflexes sufficient to increase myocardial oxygen demand. Such a reflex response could potentially contribute to postprandial angina in humans.
Oxygen fields in specific spinal loci of the canine spinal cord
Authors: Stokes B. T. , Garwood M. , Walters P.
Published: December 2017

Oxygen tension (PO2) measurements were made in the dog spinal cord with a small recessed-tip oxygen microelectrode. The use of vibration and specific marking techniques has allowed the elimination of tissue compression artifacts and the mapping of regional PO2 in the thoracic spinal cord. A symmetrical distribution of PO2 values can be shown for the lateral white funiculi; the gray matter and dorsal columns have multimodal distributions. Statistical evaluation showed all these areas to have different PO2 profiles; PO2 values (mmHg) were 61.2 +/- 12.4 for the lateral white funiculi, 55.3 +/- 19.0 for the dorsal columns, and 30.0 +/- 13.6 in spinal gray. The relatively normal distribution patterns of these oxygen tensions indicate that traditional statistical methods may be used to compare and evaluate oxygen diffusion fields in the adult spinal cord.
Renal nerves are not necessary for onset or maintenance of DOC-salt hypertension in rats
Authors: Dzielak D. J. , Norman R. A.
Published: December 2017

The effect of renal denervation on the onset and maintenance of mineralocorticoid-salt [deoxycorticosterone (DOC)-salt] hypertension was determined. A unilateral right nephrectomy was performed on all rats. Rats were divided into renal-denervated and sham-operated groups. All rats received 10 mg/wk of DOC pivalate and 0.9% saline to drink ad libitum. Renal denervation was repeated at 3-wk intervals to prevent renal nerve regeneration. Renal denervation had no effect on the onset or maintenance of DOC-salt hypertension. Hypertension developed over the same time course in both the renal-denervated and sham-operated rats regardless of the time frame of unilateral nephrectomy and renal denervation. Tail-cuff pressure measurements reached plateau levels of 187 +/- 5.7 mmHg in sham-operated and 183 +/- 4.6 mmHg in renal-denervated rats after 4 wk of DOC-salt administration. Mean arterial pressure averaged 197 +/- 10.3 mmHg in sham-operated and 200 +/- 7.9 mmHg in renal-denervated rats after 8 wk of treatment. Intact renal nerves are not necessary for the development or maintenance of DOC-salt hypertension in rats.
Phase resetting and annihilation in a mathematical model of sinus node
Authors: Reiner V. S. , Antzelevitch C.
Published: December 2017

A mathematical model of primary sinoatrial pacemaker activity was developed using modifications of Hodgkin-Huxley type equations of voltage- and time-dependent membrane currents. The computer simulation of action potential activity incorporates the results of several existing cardiac models and recent biological data in an attempt to generate a model that more closely approximates the phase-resetting behavior of sinoatrial pacemakers observed biologically in response to subthreshold or electrotonic stimuli. The model was also used to study annihilation, i.e., the cessation of rhythmic activity induced by a critically timed subthreshold stimulus. Perturbation analysis performed by scanning the pacemaker cycle with 50-ms subthreshold current pulses yielded biphasic phase-response relationships that closely resembled the biological data. The pacemaker current, although relatively unimportant in determining the degree of phase 4 depolarization in the simulated sinus nodal pacemaker, was nevertheless prominent in determining phase-resetting behavior. The characteristics of annihilation were studied in normal, “depressed,” and hyperpolarized states. In all cases, successful annihilation depended in large part on the dynamic interaction between the slow inward and delayed rectifier outward currents. The annihilation point was found to be an unstable singularity point in which a critical combination of stimulus intensity and timing could cause the pacemaker to approach but never achieve a state of complete quiescence. The model provides the basis for further investigation of complex arrhythmias that may arise as a consequence of multiple-pacemaker interaction within the heart.
Coronary response to large decreases of hemoglobin-O2 affinity in isolated rat heart
Authors: Stucker O. , Vicaut E. , Villereal M. C. , Ropars C. , Teisseire B. P. , Duvelleroy M. A.
Published: December 2017

In this study, the consequences of large increases of P50 (O2 partial pressure at 50% oxyhemoglobin saturation) on coronary blood flow (CBF) were investigated in isolated Wistar rat heart. Rightward shifts of the O2 dissociation curve (ODC), obtained by lysing and resealing erythrocytes to encapsulate inositol hexaphosphate (IHP), led to a very large increase in P50 without side effects. Each heart was perfused alternatively with control stored human blood [P50 = 18.8 +/- 0.3 (SE) mmHg] and IHP-treated human blood (P50 = 47.1 +/- 1.7 mmHg), according to the technique of Langendorff (mean perfusion pressure 80 mmHg; hematocrit 25%). Arterial PO2 of 180 mmHg was maintained to keep arterial O2 content identical for both types of blood. When hemoglobin affinity was lowered, CBF decreased from 5.32 +/- 0.20 to 3.40 +/- 0.14 ml X min-1 X g-1, coronary sinus PO2 (PcsO2) rose from 39.9 +/- 0.9 to 69.9 +/- 4.2 mmHg, and myocardial O2 consumption (MVO2) rose slightly from 0.125 +/- 0.005 to 0.149 +/- 0.010 ml O2 X min-1 X g-1 (P less than 0.05). A significant negative correlation was found between CBF and P50 (r = -0.90; n = 32) and a significant positive correlation between PcsO2 and P50 (r = +0.84; n = 28). The coronary blood flow response to high P50 values was not abolished when maximal dilation was induced by adenosine, so this response seems independent of metabolic needs. These experiments have demonstrated that if O2 uptake by erythrocytes remains constant, in the presence of a high P50, sufficient O2 supply may be achieved with substantially less blood flow.(ABSTRACT TRUNCATED AT 250 WORDS)
Considerations in use of microspheres for flow measurements in anesthetized rat
Authors: Tuma R. F. , Vasthare U. S. , Irion G. L. , Wiedeman M. P.
Published: December 2017

The results of single injections of different doses of microspheres (60,000, 100,000, and 375,000) demonstrated a significant reduction in measured heart and kidney blood flows as a function of the number of microspheres injected. Measured flow to other organs was unaffected by a single injection of these doses of microspheres. The injection of microspheres at a faster rate (0.8 ml/min microsphere injection; 1.0 ml/min flush) resulted in higher calculated heart flow when compared with the slow rate (0.2 ml/min microsphere injection; 0.25 ml/min flush). A significant decrease (approximately 21%) in measured blood flow to the right side of the brain that was observed in all the groups is due to the occlusion of the right carotid artery by the cannulation procedure. Intra-aortic injection of microspheres resulted in reduced measured brain blood flow when compared with intraventricular injections. Accurate and reliable heart and brain blood flows were not obtained with intra-aortic injection of microspheres. However, intra-aortic injection of microspheres does provide accurate and reliable flow measurements for more distal organs.
Neurogenic antinatriuresis during development of acute cardiac tamponade
Authors: Osborn J. L. , Lawton M. T.
Published: December 2017

Renal function was measured during the development of cardiac tamponade in anesthetized dogs. Tamponade was induced by infusion of isotonic saline (37 degrees C) into the pericardial space. Step increases in pericardial fluid volume in 20-ml increments from 0 to 160 ml increased renal efferent nerve activity by a total of 140 +/- 58% of control (from 205 +/- 70 microV/s). Since renal nerve traffic was elevated by pericardial fluid volume infusion prior to any changes in arterial pressure, renal function was determined before and after increasing pericardial pressure (PCP) by approximately 5 and 10 mmHg. Increasing PCP by 5 mmHg decreased urinary sodium excretion and increased renin secretion rate without changing mean arterial pressure, renal blood flow, or glomerular filtration rate (GFR). Further elevation of PCP to approximately 10 mmHg also decreased urinary sodium excretion as well as arterial pressure and GFR. Renal denervation prevented both of these antinatriuretic responses to elevated PCP. In a third group of dogs, similar antinatriuresis was induced by increasing PCP by approximately 5 and 10 mmHg. Bilateral cervical vagotomy abolished the antinatriuretic response to increased PCP by 5 mmHg but was ineffective when PCP was increased by 10 mmHg, which was accompanied by decreased arterial pressure. These results demonstrate that elevation of pericardial fluid volume, and consequently PCP, reflexly decreases urinary sodium excretion via activation of renal sympathetic outflow. Early reflex antinatriuresis results primarily from activation of cardiopulmonary or splanchnic receptors with vagal afferents, whereas, at larger PCP, reflex antinatriuresis may result from hypotension and unloading of high pressure baroreceptors.(ABSTRACT TRUNCATED AT 250 WORDS)
Fastigial nucleus cardiovascular response and brain stem lesions in the beagle
Authors: Dormer K. J. , Andrezik J. A. , Person R. J. , Braggio J. T. , Foreman R. D.
Published: December 2017

Changes in the excitatory cardiovascular response (heart rate, arterial blood pressure, left ventricular pressure, and LV dP/dt as an index of myocardial contractility) resulting from electrical stimulation of the cerebellar fastigial nucleus (FN) were recorded after placement of DC or radio-frequency lesions or after microinjections of kainic acid into brain stem areas that receive FN projections and have been shown to be involved in central cardiovascular control. FN-induced increases in heart rate, blood pressure, and contractility were reduced or abolished by lesions made in the restiform body or the A5 area, which is homologous to the catecholamine-containing region in cats and rats. Lesions in the paramedian reticular nucleus, rostral and caudal to obex, failed to reduce the FN cardiovascular response. Nucleus of the solitary tract lesions augmented the FN pressor response and tachycardia. Kainic acid (1 microliter of 100 mM solution) caused profound depression of heart rate, blood pressure, and contractility and reduced or eliminated the FN-induced cardiovascular response when injected into the A5 area, previously identified by the pressor response following electrical stimulation. We concluded from these observations that a descending fastigiobulbar sympathoexcitatory pathway courses through a previously identified A5 pressor area that is also capable of a depressor response when the cell bodies alone are activated.