Evaluation Of Regional Blood Flow Research Articles

Hemodynamic phenotyping of transgenic rats with ubiquitous expression of an angiotensin-(1-7)-producing fusion protein.

Activation of the angiotensin (Ang)-converting enzyme (ACE) 2/Ang-(1-7)/MAS receptor pathway of the renin-angiotensin system (RAS) induces protective mechanisms in different diseases. Herein, we describe the cardiovascular phenotype of a new transgenic rat line (TG7371) that expresses an Ang-(1-7)-producing fusion protein. The transgene-specific mRNA and the corresponding protein were shown to be present in all evaluated tissues of TG7371 with the highest expression in aorta and brain. Plasma Ang-(1-7) levels, measured by radioimmunoassay (RIA) were similar to control Sprague-Dawley (SD) rats, however high Ang-(1-7) levels were found in the hypothalamus. TG7371 showed lower baseline mean arterial pressure (MAP), assessed in conscious or anesthetized rats by telemetry or short-term recordings, associated with increased plasma atrial natriuretic peptide (ANP) and higher urinary sodium concentration. Moreover, evaluation of regional blood flow and hemodynamic parameters with fluorescent microspheres showed a significant increase in blood flow in different tissues (kidneys, mesentery, muscle, spleen, brown fat, heart and skin), with a resulting decrease in total peripheral resistance (TPR). TG7371 rats, on the other hand, also presented increased cardiac and global sympathetic tone, increased plasma vasopressin (AVP) levels and decreased free water clearance. Altogether, our data show that expression of an Ang-(1-7)-producing fusion protein induced a hypotensive phenotype due to widespread vasodilation and consequent fall in peripheral resistance. This phenotype was associated with an increase in ANP together with an increase in AVP and sympathetic drive, which did not fully compensate the lower blood pressure (BP). Here we present the hemodynamic impact of long-term increase in tissue expression of an Ang-(1-7)-fusion protein and provide a new tool to investigate this peptide in different pathophysiological conditions.

Cardiovascular control during whole body exercise.

It has been considered whether during whole body exercise the increase in cardiac output is large enough to support skeletal muscle blood flow. This review addresses four lines of evidence for a flow limitation to skeletal muscles during whole body exercise. First, even though during exercise the blood flow achieved by the arms is lower than that achieved by the legs (∼160 vs. ∼385 ml·min(-1)·100 g(-1)), the muscle mass that can be perfused with such flow is limited by the capacity to increase cardiac output (42 l/min, highest recorded value). Secondly, activation of the exercise pressor reflex during fatiguing work with one muscle group limits flow to other muscle groups. Another line of evidence comes from evaluation of regional blood flow during exercise where there is a discrepancy between flow to a muscle group when it is working exclusively and when it works together with other muscles. Finally, regulation of peripheral resistance by sympathetic vasoconstriction in active muscles by the arterial baroreflex is critical for blood pressure regulation during exercise. Together, these findings indicate that during whole body exercise muscle blood flow is subordinate to the control of blood pressure.

Disgust stimuli reduce heart rate but do not contribute to vasovagal symptoms

Background and objectivesThe vasovagal response demonstrates a unique form of stress response, common in medical settings yet provoked by a variety of blood-injury-injection stimuli. This study aimed to better understand the psychophysiological mechanisms of the vasovagal response.. Methods16 undergraduates with and 42 without a self-reported history of fainting watched five 3–5 min videos with different emotional content. One documentary clip (Neutral condition) described a campus environmental project while another (Blood/Injury) depicted portions of an open heart surgery. Three additional clips were also used, including Medical, Threat, and Contamination stimuli. Vasovagal symptoms and physiological variables were assessed during each video. ResultsAs predicted, while the disgust-related stimuli (Blood/Injury, Medical, Contamination) were associated with generally lower heart rate, the Blood/Injury video produced the highest symptoms and the only significant difference between previous fainters and non-fainters. The physiological measures also revealed that participants with a fainting history experienced higher stroke volume and lower systolic blood pressure throughout, as well as several main effects of video. LimitationsAn additional decrease in systolic blood pressure and respiration produced by watching the Blood/Injury video may have been sufficient to trigger symptoms in some, though results also suggest that systemic variables do not entirely explain susceptibility to symptoms. More careful evaluation of regional blood flow may be required. ConclusionsParticipants who had previously experienced strong vasovagal responses displayed what appeared to be an anticipatory response to the Blood/Injury video. Finally, disgust stimuli may reduce heart rate but do not appear to contribute to vasovagal symptoms.

Functional brain imaging and its application to uncover mechanisms driving food intake in humans

The control of food intake involves complex and powerful neural mechanisms whose functioning has critical repercussions for alimentary behaviours and the regulation of energy balance. Recent research also from cognitive neurosciences indicates that homeostatic (repletion-driven) and hedonic (reward-driven) systems in the brain concur in achieving an integrated regulation of human alimentary activity. Modern societal changes, related to unrestricted availability of energy-dense palatable foods at low costs and widespread presence of compelling alimentary cues, are considered to contribute to a food consumption driven mainly by hedonic properties rather than energy requirements, and result among the causes of worldwide obesity epidemics. Functional neuroimaging permits the exploration of the human brain systems involved under the different conditions of alimentary relevance, through the quantitative evaluation of regional blood flow, metabolic activation of defined cerebral networks or molecular bioavailability of brain receptors specifically traced. Such a framework of different imaging techniques appears uniquely suited to investigate the functional integration of the neural processes which underpin the interplay between homeostatic drive for feeding and the conscious experience of pleasure and reward concurring to the control of food intake. Therefore, these techniques provide an invaluable tool in gaining a detailed comprehension of physiology underlying alimentary behaviours and their derangements, and in detecting new strategies against obesity which interact also on brain mechanisms involved in the control of food intake and energy balance. In the present short review, basic principles of the most used functional neuroimaging techniques will be examined and the commonest acquisition protocols and processing methods will be briefly presented, along with a short overview of the brain systems involved in food intake regulation and a concise report of the main findings obtained with these techniques.

急性期脳梗塞ＣＴ／ＭＲＩ（Ｐｅｒｆｕｓｉｏｎ）の標準化

CT and MR perfusion imaging are useful tools in evaluation of regional blood flow in acute ischemic stroke. However, quantitative results show fluctuations, because scan protocol and analysis method are not standardized. In addition, inadequate settings of scan parameters can induce unnecessary radiation exposure in CT perfusion. Therefore, standardization of scan protocol, analysis methods, and evaluation methods are needed.It is important to standardize scan parameters, in order to assure safety of the patients. Standardization of scan parameters and analysis methods is also important to minimize variations of quantitative values. In order to evaluate the degree of ischemia correctly, defining a universal index for the ischemic lesion, such as DWI-PWI mismatch, is required.In summary, the goal of the standardization is to assure the safety of patients, to ensure the reliability of results, and to establish universal evaluation methods. In Japan, standardization of perfusion imaging, as well as other stroke imaging, is being carried out by ASIST-Japan (Acute Stroke Imaging Standardization).

Vascular reactivity in sepsis: regional differences

In the course of severe sepsis, blood flow distribution is altered, so that regional blood flow may not match demand and focal ischemia ensues. Apart from circulating factors, altered reactivity of the vasculature could partly account for blood flow maldistribution. Indeed, changes in both the endothelium-dependent, acetylcholine-induced vascular relaxation, induction of inducible NO synthase and impaired vascular smooth muscle constrictor responses, differ among isolated small arteries from various vascular beds, incubated with endotoxin. However, it is difficult to define the effect of these changes, elaborated in this review, on blood flow maldistribution. Nevertheless, studies for the treatment of human septic shock with the help of drugs intervening in vascular reactivity should incorporate evaluation of regional blood flow, in order to avoid focal ischemia.

Quantitative evaluation of regional blood flow in pulmonary sarcoidosis with bull's eye analysis

Lung perfusion scintigraphy was performed in 23 patients with pulmonary sarcoidosis and in 11 normal volunteers. Bull's eye analysis was used to analyze regional pulmonary blood flow quantitatively. First, whole lung perfusion images were divided into three regions by three concentric circles. Then radial axes were projected from the center to define 36 x 10 degrees sectors. The counts for each sector were calculated and a Bull's eye image was displayed. The counts were compared with the lower limit of normal (mean - 2SD), and as the indices of reduction in perfusion, extent score (ES) and severity score (SS) were calculated. ES and SS showed significant reduction in perfusion 16 patients (70%) with sarcoidosis. In stage II sarcoidosis, both ES and SS were significantly higher than in stage I sarcoidosis (p less than 0.05). In comparison with the findings of transbronchial lung biopsy, both ES and SS had correlations with the degree of alveolitis and ES had a correlation with the degree of angiitis. Both ES and SS have no correlation with 67Ga scintigraphy findings. In comparison with clinical data, ES had a positive correlation with serum angiotensin-converting enzyme activity (p less than 0.05), and SS had a significant positive correlation with bronchoalveolar lavage fluid.CD+/CD8+ ratio (p less than 0.05). The Bull's eye analysis was considered useful for the quantitative evaluation of regional pulmonary blood flow in pulmonary sarcoidosis, and it was suggested that the mechanism of reduction in perfusion might be resulted mainly in its alveolitis and angiitis. Ventilation abnormality, which may happen prior to reduction in perfusion, may be an important factor of reduction in perfusion.

Multiparametric Imaging of Blood Flow and Metabolism after Middle Cerebral Artery Occlusion in Cats

In anesthetized adult cats, acute stroke was produced by transorbital occlusion of the left middle cerebral artery. A battery of imaging techniques was used for simultaneous evaluation of regional blood flow, glucose utilization, protein synthesis, pH, and the regional tissue content of glucose, ATP, and potassium. The electrophysiological impact of stroke was monitored by EEG frequency analysis and recording of somatosensory evoked potentials. Two hours after vascular occlusion, a close correlation existed between the degree of electrophysiological changes and biochemical alterations, in particular with the extent of tissue acidosis, ATP depletion, decrease of tissue potassium content, and suppression of protein synthesis. However, there was only a poor correlation with blood flow and glucose utilization. Both of these exhibited a greatly inhomogeneous pattern with regions of reduced, normal, or increased rates. In areas remote from the infarct, the content of biochemical substrates was normal but blood flow was reduced globally by approximately 50% and glucose utilization by approximately 20%. An anatomically defined regional pattern of cerebral or cerebellar diaschisis was not observed. It is concluded that during the acute phase of stroke, imaging of blood flow and glucose utilization does not provide an accurate estimate of the actual functional or metabolic disturbance. For the clinical evaluation of the development or treatment of stroke, in consequence, alternative noninvasive techniques such as imaging of protein synthesis and/or pH may be more relevant.

Acute effect of propranolol on splanchnic circulation in normal and portal hypertensive rats

Propranolol decreases portal venous pressure in patients with cirrhosis but no method is available in man to study the effect of this beta-blocker on splanchnic organ blood flow. Because in rats, the microsphere method allows evaluation of regional blood flow, the acute effect of propranolol on both splanchnic and systemic circulations was studied in normal rats and in rats with portal hypertension due to portal vein stenosis. Portal venous pressure significantly decreased during propranolol administration in normal (5.6 +/- 1.0-4.7 +/- 1.1 mm Hg; mean +/- SD) as well as in portal hypertensive rats (11.7 +/- 2.3-10.3 +/- 1.8 mm Hg). Propranolol slightly decreased cardiac output and arterial pressure in all rats. Portal tributary blood flow was significantly reduced by propranolol in normal rats (17.4 +/- 3.0-11.3 +/- 2.2 ml/min) and in portal hypertensive rats (23.7 +/- 5.0-16.6 +/- 3.3 ml/min). Accordingly vascular resistance of the different organs in the portal venous territory increased in these rats receiving propranolol. The percentage of the decrease in portal tributary blood flow was significantly more marked than the percentage of reduction in cardiac output in portal hypertensive rats but, in normal rats, these percentages were parallel. Hepatic arterial blood flow did not change or slightly increased and, consequently, hepatic arterial vascular resistance decreased. These findings further clarify the marked effects of propranolol on splanchnic circulation.