Transient Changes In Blood Pressure Research Articles

Transient blood pressure changes affect the functional magnetic resonance imaging detection of cerebral activation

Functional magnetic resonance imaging (fMRI) provides an indirect measure of cerebral activation that could be altered by factors directly affecting cerebral blood flow independent of changes in neuronal activation. Presently, we investigate how changes in blood pressure (BP) affect the activation detected with fMRI. fMRI scans were acquired in 33 rats under control conditions and following transient BP increases (norepinephrine, IV) or decreases (arfonad, IV) with and without electrical stimulation of the forepaw. Voxels correlating to either the stimulation or the change in BP time courses were identified. During transient hypertension, irrespective of forepaw stimulation, BP increases (i.e., >10 mm Hg) produced a transient increase in the blood oxygen level-dependent (BOLD) intensity resulting in a significant numbers of voxels correlating to the BP time courses ( P < 0.05), and the number of these voxels increased as BP increased, becoming substantial at BP > 30 mm Hg. The activation patterns with BP increases and stimulation overlapped spatially resulting in an enhanced cerebral activation to simultaneous forepaw stimulation ( P < 0.05). BP decreases (>10 mm Hg) produced corresponding decreases in BOLD intensity, causing significant numbers of voxels correlating to the BP decreases ( P < 0.005), and these numbers increased as BP decreased ( P < 0.001). The BP decreases and stimulation time courses and responses were distinct, and hypotension did not affect the detection of the activation response to forepaw stimulation. The results indicate that substantial hypertension accompanying a stimulation paradigm produces a BOLD response that enhances the cerebral activation detected, whereas hypotension does not affect the detection of neuronal activation but does produce responses that could be interpreted as a ‘deactivation’.

Spontaneous arousals during quiet sleep in piglets: a visual and wavelet-based analysis.

The objectives of the study were to characterize spontaneous arousals during NREM sleep in piglets and to compare two methods of identifying these events: a "visual" technique using spectral analysis and an automated technique using wavelets. Our goal was to understand the benefits and limits of these methods when applied to sleep in human infants. Arousals were identified by evaluating rapid changes in EEG low frequency activity, blood pressure (BP), and heart rate (HR). A cortical arousal was defined as a rapid decrease in EEG low frequency activity. An autonomic arousal was defined by a transient increase in heart rate or a transient change in mean arterial BP (MAP). Laboratory study in sleeping and awake piglets. Five 1-2 week old piglets. Chronically instrumented with a femoral arterial line, EEG, EOG, EMG electrodes, and a micro-dialysis probe with its tip located in the rostral ventral medulla. Artificial CSF (aCSF) was dialyzed into the RVM throughout the experiments Measurements: For the visual analysis, the average delta power (0.5-4 Hz) for each 5-second epoch was determined using spectral analysis. MAP and HR were analyzed in 1-second bins. Video images were analyzed for body movements and eye openings. Transient changes in blood pressure, HR, and delta power were then visually identified. For the wavelet analysis, a quantitative, automated technique with a defined "wakefulness threshold" was used to identify rapid decreases in EEG low frequency activity and the rate of change of MAP. Using the visual method, 117 episodes associated with stereotypical hemodynamic, EEG, and behavioral changes (startle) were identified. Seventy five events occurred in isolation or were first in a series of "multiple" events, 41 "multiple" events were defined as events occurring <20 seconds following a previous event. Eighteen events were associated with the termination of apnea. In isolated events or those occurring first in a series, the onset of changes in HR and BP clearly preceded the decrease in EEG amplitude and delta power. Using wavelet analysis, 73 EEG arousals and 115 MAP transients were identified independently; 62% of the EEG events were associated with a transient change in MAP and HR, and in these cases the onset of the hemodynamic events preceded EEG arousals. EEG arousals and MAP transients, however, also occurred alone and not associated with a stereotypical pattern of a startle, changes in MAP and HR and the EEG. Many of these spontaneous arousals represent integrated EEG, hemodynamic, and behavioral processes similar to arousal phenomena described in adult rats and human infants, but the pattern of spontaneous arousals appears to be more heterogeneous than has been described for arousals induced by exogenous stimuli. Both the visual and wavelet analysis identified these events, but the wavelet technique has the potential advantage of better time resolution and automation of the analysis.

An intensive weight loss programme in established type 2 diabetes and controls: effects on weight and atherosclerosis risk factors at 1 year.

The efficacy, safety, and effect on cardiovascular risk factors of two intensive weight loss programmes in overweight Type 2 diabetic subjects were studied. The patients were recruited from hospital diabetic clinics and control obese subjects from the community. Obese (BMI >30) patients with Type 2 diabetes mellitus and controls were offered intensive conventional diabetic advice or a very low calorie diet. Weekly 2 h sessions were conducted in two day-room areas of adjacent medical wards of Torbay Hospital. Non-diabetic and diabetic very low calorie diet groups reduced BMI by 6 and 5 kg m(-2), respectively, at 1 year. Waist-hip ratios (-0.06 and -0.05) were also reduced (p = 0.04 and p = 0.01), while HDL/total cholesterol ratios increased (+0.04 and +0.06, p = <0.01). Transient changes in blood pressure and antioxidant vitamin status occurred in the intensive conventional diet group. Fourteen of diabetic very low calorie diet subjects discontinued insulin and oral hypoglycaemic agents for the whole year, and psychological well-being transiently improved. Substantial weight loss and improvement in cardiovascular risk factors could be maintained for 1 year in Type 2 diabetic patients by the use of a very low calorie diet.

In vivo adaptive responses of the aorta to hypertension and aging.

To investigate the dynamic behavior of the aorta of freely moving rats during the maintenance of hypertension, a longitudinal study was performed in renal hypertensive (Goldblatt 1 kidney, 1 clip) rats aged 3, 6, and 9 mo in which hypertension was maintained for 1, 3, and 6 mo, respectively. The pulsatile caliber of the thoracic aorta was measured (electrolytic strain gauge chronically implanted) simultaneously with aortic pressure under basal conditions and during transient changes of blood pressure. Aortic thickness was determined postmortem by morphometry. Establishment of hypertension (179 +/- 5 mmHg) by increasing the stress developed by the aorta caused increases in the resting values of caliber (20%), thickness (21%), and strain (95%); the maintenance of hypertension for a 6-mo period caused a further increase in thickness (58% vs. age-matched normotensive aortas) but not in aortic caliber and strain, the subsequent alterations of which were due only to growth/aging. Although different calibers, thicknesses, and dynamic strains were presented, the stress-strain relationship during transient blood pressure changes was similar for all hypertensive and normotensive groups with the exception of renal hypertensive rats aged 6 mo, which presented a steeper relationship (a large transitory increase in aortic distensibility was observed at that age). Dynamic adaptive responses of the aorta to hypertension compensate for geometric changes in such a way as to maintain a near-constant distensibility. It was concluded that, in contrast to the extrathoracic vessels, the adaptive responses of the aorta to hypertension were directed to maintain its compliance without changing the distensibility and stress-strain relationship, contributing to partially counterbalance the increased pressure and the decreased compliance of the more peripheral components of the arterial tree.

Modulation of cutaneous nociceptor activity by electrical stimulation in the brain stem does not inhibit the nociceptive excitation of dorsal horn neurons

In anesthetized cats, recordings were obtained from single lumbar dorsal horn neurons and from primary afferent fibers of the posterior tibial nerve excited by controlled noxious radiant heating of glabrous hindpaw skin. Electrical stimulation in four brain stem regions (periaqueductal gray and lateral reticular formation in the midbrain, raphe and reticular formation in the medulla) during noxious skin heating markedly reduced the nociceptive excitation of the dorsal horn neurons. In contrast, such brain stem stimulation had small and variable effects upon the noxious heat-evoked activity in the primary afferent fibers; both increases and decreases were observed. The brain stimulation also produced transient changes in blood pressure, suggesting that circulatory effects may underlie the mechanism of nociceptor modulation. It is concluded that brain stem stimulation can modulate cutaneous nociceptor activity, but that this modulatory effect on nociceptor inflow is too small and inconsistent to explain the marked descending inhibition of the nociceptive excitation of dorsal horn neurons.

Phase II radioimmunotherapy trial with131I-CC49 in colorectal cancer

Radiolabeled CC49, a second generation high affinity monoclonal antibody (MoAb) reactive with tumor-associated glycoprotein 72 (TAG72) has undergone previous Phase I testing in patients with colon cancer. Based on this report, the authors treated 15 refractory metastatic colon cancer patients with 131I-CC49 to determine its overall toxicity and the response to therapy of patients treated with it. Patients received 75 mCi/m2 131I-CC49 (20 mg MoAb) intravenously for a period of 30-60 minutes. Whole body retention was derived from the measured dose-rate of I-131 monitored daily at 1 m using an ion chamber. Two whole-body and static-gamma camera images were taken of patients on days 4 and 7 after the infusion. Nonhematologic toxicity (Grade 1-2) consisted of nausea (two patients), arthralgias (three patients), transient fever and chills (two patients), and transient blood pressure changes (two patients). At 4-5 weeks posttreatment, reversible Grade 3-4 thrombocytopenia was observed in 7 of 15 patients, and reversible Grade 3-4 granulocytopenia was observed in 6 of 15 patients. Twelve of 13 patients tested developed human anti-mouse antibody (range, 161 to > 20,000 ng/ml) at 6-8 weeks postinfusion. Mean +/- SD whole-body half-life (whole-body retention) of 131I-CC49 was 57.3 +/- 13.4 hours. Tumors were seen in all patients. In two of three patients treated a second time, an increased whole body clearance rate correlated with elevated human anti-mouse antibody, reduced uptake in tumor, and enhanced uptake in the thyroid. Estimated tumor doses ranged from 19-667 rads. Red marrow dose estimated from whole body retention ranged from 60 to 117 rads and correlated with decreases in platelet count. No objective tumor responses (i.e., partial or complete) were observed. Despite minimal toxicity and favorable tumor uptake, efficacy has been limited at this dose and schedule.

Accuracy of a continuous blood pressure monitor based on arterial tonometry.

A validation study of the continuous noninvasive tonometric blood pressure monitor called JENTOW was performed in 20 normotensive subjects and 10 hypertensive patients. Tonometric and intra-arterial blood pressures were simultaneously recorded at supine rest and during a Valsalva maneuver and tilting test. The results of the strict evaluation of the instrument's capacity for reproducing intra-arterial blood pressure were as follows: 1) The overall frequency response of the transcutaneous blood pressure-monitoring system based on arterial tonometry was flat, with negligible delay to intra-arterial blood pressure in the range of 0-5 Hz. 2) The largest discrepancy between intra-arterial and tonometric pressure waveforms was found at the early systolic phase; except for this phase, the tonometric waveform was almost equal to the intra-arterial waveform. 3) The beat-to-beat variability of tonometric pressure corresponded to that of intra-arterial pressure almost perfectly in the physiologically significant frequency range of 0-0.5 Hz. 4) During resting conditions, the averages of the systolic and diastolic values measured tonometrically corresponded well to those measured intra-arterially. 5) The changes in the between-method discrepancy of blood pressure values during the Valsalva maneuver were statistically significant but small (< 5 mm Hg). 6) No significant effect of postural tilting was found on the between-method discrepancy. We conclude that this method is clinically acceptable and reliable except for its limited capacity for recording the higher frequency intra-arterial waveform and for responding to the relatively rapid and large transient changes in blood pressure.

Transient changes in blood pressure during spontaneous deep breaths in rats with sinoaortic deafferentation.

Sinoaortic deafferentation (SAD) in rats produces moderate increases in mean arterial pressure (MAP) along with a large augmentation of arterial pressure lability (APL). The mechanisms generating this APL are incompletely understood. To study the possible influence of breathing activity on APL in conscious SAD rats, we simultaneously recorded pulmonary ventilation and arterial blood pressure. The general pattern of pulmonary ventilation was the same in normal, sham-operated, and SAD rats. In all groups single large tidal volumes were regularly interposed in 1- to 2-min periods of shallower breathing. In SAD rats these single large inspirations were consistently accompanied by substantial and abrupt reductions of MAP, whereas this effect was markedly smaller or absent in normal and sham-operated rats. The data reflect the lack of fast moment-to-moment control of arterial pressure normally exerted by the aortic and carotid baroreceptors. In this context, effects of ventilatory changes must be considered along with humoral and neurogenic factors to explain APL after SAD.

Granisetron

Granisetron (BRL 43694) is a highly selective 5-HT3 receptor antagonist which possesses significant antiemetic activity, likely mediated through antagonism of 5-HT3 receptors on abdominal vagal afferents and possibly in or near the chemoreceptor trigger zone. Clinical trials in cancer patients demonstrate that, compared with placebo, granisetron significantly reduces the incidence of nausea and vomiting for 24 hours after administration of high-dose cisplatin. In large comparative trials, 70% of patients who received granisetron prior to cisplatin or other chemotherapy experienced complete inhibition of vomiting with little or no nausea for 24 hours after antineoplastic administration; these results were similar to those obtained with high-dose metoclopramide plus dexamethasone, and superior to a combination of chlorpromazine plus dexamethasone, or prochlorperazine plus dexamethasone, or methylprednisolone monotherapy. The most frequently reported adverse event associated with granisetron administration is headache which occurs in about 10 to 15% of patients while constipation, somnolence, diarrhoea and minor transient changes in blood pressure have been reported less frequently. Extrapyramidal effects, which can occur with high-dose metoclopramide and may be a limiting factor in its use, have not been noted with granisetron administration. Thus, granisetron is an effective, well tolerated and easily administered agent for the prophylaxis of nausea and vomiting induced by cancer chemotherapy which appears to be devoid of extrapyramidal side effects associated with metoclopramide. As a member of a new class of drugs, the selective 5-HT3 receptor antagonists, granisetron provides the medical oncologist with a new, potentially more acceptable antiemetic therapy.

LACK OF SYMPATHETIC AUGMENTATION IN RESPONSE TO INTRAVENOUS LOAD OF GLUCOSE IN RABBITS

1. We investigated a link between sympathetic nervous function and carbohydrate metabolism by measuring renal sympathetic nerve activity in response to intravenous load of glucose in alpha-chloralose-urethane anaesthetized rabbits. 2. Intravenous infusion of a 25% glucose solution (0.5 g/kg) over 3 min caused a transient increase in arterial blood pressure and a decrease in renal sympathetic nerve activity. Thereafter, these parameters were restored and remained around preload levels while plasma glucose and insulin concentrations were still elevated. 3. Equimolar mannitol solution produced similar patterns of change in blood pressure and nerve activity without an elevation of plasma glucose and insulin levels. 4. The transient changes in blood pressure and renal nerve activity could be attributed to acute hypervolaemia indicated by similar changes in plasma osmolality and haematocrits in the two groups of treatment. 5. The present study did not support a close relationship between carbohydrate metabolism and the sympathetic nervous system regulating cardiovascular function.

Research connections

Two studies are reviewed, one regarding the effects of music therapy on psychophysiologic stress in coronary care unit patients and one regarding the effects of age and gender on cardiovascular autonomic reactivity in healthy adults. Music therapy is determined to be safe for coronary care unit patients and effective in modulating the psychophysiologic manifestations of stress. The second study suggests that age--gender interactions may influence autonomic cardiovascular responsiveness. It is suggested that older adults be taught methods to reduce straining, so that rapid transient changes in blood pressure are avoided.

Evidence suggesting that the 5–HT2 antagonist ICI 169, 369 activates vagal afferents and in addition has a central hypotensive action in anaesthetized rats

1. The cardiovascular effects of the 5-HT2 antagonist ICI 169,369 have been investigated in pentobarbitone anaesthetized rats and in pithed rats whose blood pressure was supported by a vasopressin infusion. 2. In anaesthetized rats, cumulative doses (0.1-3.0 mg kg-1) of ICI 169,369 caused dose-related large transient falls in heart rate and blood pressure followed by a slow dose-related decline in both parameters. 3. Pretreatment with atropine methonitrate (1 mg kg-1) alone or in combination with atenolol (1 mg kg-1) or bi-vagotomy blocked the transient changes in blood pressure and heart rate caused by ICI 169,369. The long-term fall in heart rate was also attenuated by either atropine or atenolol; however, the combination of atenolol and atropine was more effective. None of the above pretreatments affected the long-term fall in blood pressure caused by ICI 169,369. 4. The cardiovascular effects of ICI 169,369 were unaffected by pretreatment with MDL 72222 (1 mg kg-1) and failed to show cross-tachyphylaxis with phenylbiguanide. 5. In pithed rats whose blood pressure was maintained with vasopressin, ICI 169,369 failed to cause any of the above transient and long-term effects on blood pressure and heart rate. 6. The study indicates that ICI 169,369 is capable of stimulating cardiopulmonary afferents through a non 5-HT3 receptor mechanism and has a central hypotensive action.

Microfilters in fluid resuscitation

Surprising numbers of particulate contaminants are present in small-volume parenteral products, while large-volume infusion fluids have far fewer. Patients on the intensive care unit will frequently receive at least 107 particles > 2 μm, of which small-volume drugs and medications account for over 90%. The consequences from these remain uncertain, and the evidence is only convincing clinically for infusion phlebitis and experimentally for reducing transient changes in blood pressure and platelet numbers. From such evidence the use of 0.2 μm in-line filtration is not recommended for the large-volume infusions used during emergency resuscitation. In patients receiving multiple small-volume medications or intra-arterial infusions filtration would seem appropriate. Microaggregates in blood or blood products may cause pulmonary dysfunction, but the evidence that microfiltration of blood reduces the incidence of dysfunction remains only partly convincing. On balance, it would seem justifiable to fit in-line screen filters for patients where large-volume blood transfusions may be anticipated.

Blockade of cardiac nerves by intrapericardial local anaesthetics in the conscious rabbit.

Local anaesthetic drugs were instilled into the pericardial sac of conscious rabbits through a chronically implanted catheter. Twenty mg of procaine HCl always caused complete blockade of cardiac vagal and sympathetic efferent nerves, tested by eliciting the baroreceptor-heart rate reflex, and abolished the reflex depression of renal sympathetic nerve activity elicited by impeding left ventricular outflow. It also slowed heart rate by a direct effect on the sinoatrial pacemaker. When the same dose of procaine was given intravenously there were only transient changes in blood pressure, heart rate and the baroreceptor-heart rate reflex. Lignocaine HCl and bupivacaine HCl were relatively less effective in blocking cardiac sympathetic efferent nerves. Intrapericardial procaine can be used in conscious animals to elucidate the part played by the cardiac receptor reflexes in control of the circulation.

Cardiovascular changes during classical conditioning in the squirrel monkey.

ABSTRACTChanges in blood pressure (BP) and heart rate (HR) were classically conditioned in squirrel monkeys using light as the conditional stimulus, and electric shock as the unconditional stimulus. The transient (lasting less than 5 min) and sustained (maintained for a half‐hour or more) changes in BP and HR in response to light‐shock (LS) pairs and light alone (L) were measured while varying rates of presentation and shock intensity. LS presentation produced transient increases in both BP and HR. The magnitude of the change increased with shock intensity and decreased as stimulation rate increased. Transient changes in BP and HR in response to L presentation were induced by conditioning with LS. The conditioned transient response to L alone was greater when the LS conditioning period preceding it had greater shock intensity or slower presentation rate. Sustained changes in BP and HR were also produced by LS, the magnitude of which were directly related to the frequency of aversive stimulus presentation. Transient changes, in contrast, decreased in magnitude with more frequent presentation.

Third ventricular injection of hypertonic NaCl and natriuresis in cats.

Third ventricular injection of hypertonic NaCl and natriuresis in cats.

Immune hemolytic transfusion reactions in monkeys: activation of the kallikrein system.

Abstract : Five monkeys were infused with isologous, isoimmune IgG of high hemolytic titer, and five control monkeys received isologous or autologous nonimmune IgG. The former experienced severe intravascular hemolysis, manifested by a fall in hematocrit and a rise in plasma hemoglobin, and disseminated intravascular coagulation (DIC), manifested by a fall in platelet count, fibrinogen, factor V, VIII, and X concentrations and prolongation of thrombin time. The plasma kallikrein system was activated as evidenced by a rise in spontaneous kallikrein activity and a fall in kallikreinogen and kallikrein inhibitor. One monkey demonstrated particularly striking changes with complete disappearance of kallikrein inhibitor and marked decrease in kallikreinogen. Hageman factor (XII) levels also decreased consistently. These changes were associated with sustained arterial hypotension in three of the five animals. Control monkeys had no intravascular hemolysis or DIC, only transient blood pressure changes, and minor fluctuations in the plasma kallikrein system. It is concluded that hemolysis and DIC induced by immune IgG may be accompanied by arterial hypotension activation of the kallikrein system. (Author)

Intracellularly recorded responses of nerve cells to oxygen deprivation.

Transmembrane potentials of cat motoneuron somata were recorded with concentric microelectrodes (one inside and one outside, 20–40 µ apart) during several minutes of anoxia by artificial respiration with nitrogen or by asphyxia. Both large and small changes in membrane potential—some spontaneously reversible—were seen following .5–5 min of anoxia or asphyxia. Most large and many smaller changes were correlated with transient blood pressure changes. Sometimes membrane potential could be restored by mechanical adjustment of the micropipette. Especially when blood pressure was stabilized with an infusion of hexamethonium chloride, some motoneurons could withstand 4–5 min of anoxia or asphyxia with membrane potential changes of no more than 2–5 mv, close to the limit of significance with this technique. Some small potential changes may be the direct effect of hypoxia on motoneuron membrane or of a change in interneuron background activity, but after eliminating the effects of electrode movement the motoneuron is remarkably insensitive to anoxia.