Circulation research
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Circulation research · Jan 1987
ReviewAn examination of the measurement of flow heterogeneity in striated muscle.
This review leads us to a number of conclusions and suggestions for further study. First, we find wide differences in the meaning of flow heterogeneity, arising as a result of the different methods used. These differences will have to be reconciled to form a comprehensive view of the role of heterogeneity in determining vascular function. ⋯ Sixth, flow heterogeneity may also influence capillary hematocrit and/or red cell spacing by producing cell separation at bifurcations and a resultant reduction in mean capillary tube hematocrit. There is as yet no agreement on why and how these hematocrits influence tissue oxygenation and function. Although several hypotheses are advanced to explain the distribution of blood flow and red cells within microcirculation, each lacks a critical experimental test at present.(ABSTRACT TRUNCATED AT 400 WORDS)
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Circulation research · Dec 1986
Effects of lung inflation on blood flow during cardiopulmonary resuscitation in the canine isolated heart-lung preparation.
Using an isolated, fibrillated canine heart-lung preparation, we studied the effects of simultaneous lung inflation and chest compression on blood flow in a model of cardiopulmonary resuscitation. The heart and lungs were placed in an artificial thorax with the great vessels and trachea exteriorized and attached to an artificial perfusion circuit and respirator, respectively. The blood volume of the system was adjusted to obtain various levels of static equilibrium pressure. ⋯ In contrast, lung inflation caused a decrease in blood flow when changes in pleural pressure were high and when blood volume was low. These results suggest that the driving pressure for blood flow during chest compression may be increased by lung inflation when the pulmonary blood vessels are filled with blood. However, blood may become trapped in the right heart and unavailable for transfer to the periphery during chest compression if lung inflation causes the alveolar blood vessels to collapse.
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Circulation research · Sep 1986
Atrial natriuretic peptide decreases circulatory capacitance in areflexic rats.
The short-term hemodynamic response to atrial natriuretic peptide appears to be partly mediated by decreased venous return, which could result from increased circulatory capacitance or decreased blood volume. To determine if rat atrial natriuretic peptide 99-126 (0.5 microgram/kg/min IV for 30-70 minutes) dilated capacitance vessels or decreased blood volume, mean circulatory filling pressure (measured during brief circulatory arrest by inflating an intraatrial balloon) and blood volume (51Cr-erythrocytes) were measured in anesthetized rats. Mean circulatory filling pressure, central venous pressure, and blood volume decreased by 0.4 mm Hg, 0.5 mm Hg, and 3.4 ml/kg, respectively. ⋯ Similar results were obtained in spinal-cord-transected rats that had initial vascular tone restored to a greater level by norepinephrine infusion. In anephric rats, atrial natriuretic peptide decreased central venous pressure by 0.3 mm Hg and blood volume by 1.6 ml/kg. The results indicate that short-term infusion of atrial natriuretic peptide reduced circulatory capacitance in rats and suggest that this reduction resulted from diminished blood volume due to urinary fluid loss followed by passive vascular recoil and active venoconstriction.(ABSTRACT TRUNCATED AT 250 WORDS)
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Circulation research · Aug 1986
Myocardial oxygen tension determines the degree and pressure range of coronary autoregulation.
Experiments were designed to separate effects of myocardial oxygen tension and oxygen consumption on coronary autoregulation. The approach was to measure coronary hemodynamic and metabolic responses to decreases in perfusion pressure during interventions that altered the balance between myocardial oxygen supply and demand. Studies were conducted in anesthetized heart-blocked dogs with the left coronary artery perfused from a pressure-controlled blood reservoir. ⋯ The observed variations in the autoregulation index were largely explained by differences in the prevailing venous oxygen tension. Furthermore, the upper pressure limit for autoregulation was dependent on venous oxygen tension with a threshold oxygen tension for autoregulation of 32 mm Hg. These results indicate that coronary autoregulation is closely coupled to the prevailing venous oxygen tension but not oxygen consumption and is facilitated at low venous oxygen tension.
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Circulation research · Oct 1985
The renal sympathetic baroreflex in the rabbit. Arterial and cardiac baroreceptor influences, resetting, and effect of anesthesia.
Curves relating renal sympathetic nerve activity and mean arterial pressure were derived in conscious rabbits during ramp changes in mean arterial pressure, elicited by perivascular balloon inflation. The renal sympathetic nerve activity-mean arterial pressure relationship consisted of a high-gain sigmoidal region about resting, where renal sympathetic nerve activity rose or fell in response to moderate falls and rises of mean arterial pressure. With larger pressure rises, renal sympathetic nerve activity first fell to a lower plateau and then reversed at even higher mean arterial pressure. ⋯ In other experiments, we studied the effects of sustained alterations in resting mean arterial pressure induced by infusing nitroprusside and phenylephrine, which produced rapid resetting of the renal baroreflex. The latter could be accounted for, in part, by resetting of the threshold of the arterial baroreceptors and in part by contributions from other afferents, probably the cardiac receptors. During resetting associated with nitroprusside-induced falls in resting blood pressure, high-gain reflex adjustments in renal sympathetic nerve activity to moderate changes in mean arterial pressure were preserved, but during resetting associated with phenylephrine-induced rises in resting mean mean arterial pressure, the resting renal sympathetic nerve activity lay on the lower curve plateau, resulting in reduction in the apparent gain of the reflex renal sympathetic nerve activity response to moderate changes in mean arterial pressure.