Influence of an acute increase in systemic vascular resistance on transpulmonary thermodilution-derived parameters in critically ill patients

OBJECTIVE

The transpulmonary thermodilution technique enables measurement of cardiac index (CI), intrathoracic blood volume (ITBV), global end-diastolic volume (GEDV), and extravascular lung water (EVLW). In this study, we analyzed the robustness of this technique during an acute increase in systemic vascular resistance (SVR).

DESIGN

Prospective, clinical study.

SETTING

Surgical intensive care unit in a university hospital.

PATIENTS AND METHODS

Twenty-four mechanically ventilated septic shock patients, who for clinical indications underwent extended hemodynamic monitoring by transpulmonary thermodilution and continuously received norepinephrine.

INTERVENTIONS AND MAIN RESULTS

After baseline measurements, mean arterial pressure was increased briefly by increasing norepinephrine dosage and hemodynamic measurements were repeated before a control measurement was obtained. At each time point, 15 cc of 0.9% saline (< 8 degrees C) was administered by central venous injection in triplicate. Fluid status and respirator adjustments were kept constant. ANOVA with an all-pairwise comparison method was used for statistical analysis. Heart rate, central venous pressure, and EVLW remained constant throughout, while SVR significantly changed from 551 +/- 106 to 746 +/- 91 dyn*s*cm(-5) and again to 566 +/- 138 dyn*s*cm(-5) (p < 0.05). However, CI and central blood volumes showed a reversible significant increase, i.e., ITBV went from 816 +/- 203 to 867 +/- 195 ml/m(2) and then to 821 +/- 205 ml/m(2) and GEDV from 703 +/- 178 to 747 +/- 175 ml/m(2) and finally to 704 +/- 170 ml/m(2), respectively. In eight patients, 2-D echocardiography was applied and revealed a reversible increase in left-ventricular end-diastolic area.

CONCLUSION

An acute increase in SVR by increasing norepinephrine dosage results in a reversible increase in central blood volumes (ITBV, GEDV) as measured by transpulmonary thermodilution and supported by echocardiography.

Pharmacodynamic model of interleukin-21 effects on red blood cells in cynomolgus monkeys

Interleukin-21 (IL-21) is a novel cytokine that is currently under clinical investigations as a potential anti-cancer agent. Like many other anti-cancer agents, including other interleukins, IL-21 is seen to produce a broad range of biological effects that may be related to both efficacy and safety of treatment. The present analysis investigates the observed pharmacodynamics effects on red blood cells following various treatment schedules of human IL-21 administrated to cynomolgus monkeys. These effects are described by a novel non-linear mixed-effects model that enabled separation of drug effects and sampling effects, the latter believed to be due partly to blood loss and partly to stress induced haemolysis in connection with blood sampling. Two different studies with a total of 9 different treatment groups of cynomolgus monkeys were used for model development. In conclusion, the model describes the IL-21 induced drop in red blood cells to be (1) caused by removal rather than suppression of production, consistent with increased reticulocyte concentration, and (2) considerably delayed compared to dosing, i.e. not related to the drop in red blood cells observed immediately post dose. It is believed that the structural model presented here can be used for other types of drug induced loss of red blood cells, whereas the mechanism for sampling related blood loss is relevant for investigations of anaemia in all pharmacological studies with smaller animals.

Noninvasive evaluation of flow reserve in the left anterior descending coronary artery in patients with cardiac syndrome X

Data on coronary flow reserve (CFR) in patients with syndrome X are still controversial. Further, noninvasive evaluation of epicardial and microvascular flow reserves in these patients has never been performed. In 17 patients with syndrome X and in 17 age- and gender-matched control subjects, CFR in the mid left anterior descending coronary artery (LAD) was evaluated by transthoracic color and pulse-wave Doppler using a 7-mHz probe (Sequoia, Siemens). Peak diastolic LAD flow was calculated at rest and at peak adenosine (140 microg/kg/min intravenously in 90 seconds). Myocardial contrast echocardiography (MCE) was performed at rest and during adenosine use by real-time cadence pulse sequencing and intravenous SonoVue (Bracco; 5 ml at 1 ml/min) and microvascular blood volume (A), velocity (beta), and flow (Axbeta) by replenishing curves (y = A[1 - e(betat)]). CFR was measured by Doppler echocardiography as an adenosine/rest velocity ratio and by MCE as a microvascular volume, velocity, and flow adenosine/rest ratio. Compared with controls, patients with syndrome X demonstrated lower LAD CFR and velocity and flow microvascular flow reserves (p <0.01, <0.005, and <0.005, respectively). In patients with syndrome X, those with angina and ST-segment depression during adenosine testing had even lower LAD CFR and velocity and flow microvascular flow reserves compared with those with no symptoms (p <0.0001, <0.0001, and <0.005, respectively). LAD CFR demonstrated a significant linear correlation with velocity microvascular flow reserve (r = 0.92, p <0.0001) and flow microvascular flow reserve (r = 0.77, p <0.0001). In conclusion, CFR in the LAD, successfully evaluated by transthoracic Doppler echocardiography and MCE, is significantly decreased in patients with syndrome X and even more in those with angina pectoris and ST-segment depression during adenosine testing. Thus, noninvasive evaluation of CFR by echocardiography is feasible and provides information on the severity of microvascular impairment.

Suramin-Restricted Blood Volume in the Placenta of Normal and Diabetic Rats is Normalized by Vitamin E Treatment

Previously maternal and fetal alterations resembling human pre-eclampsia were induced in pregnant rats by injections of the angiogenesis inhibitor Suramin. These alterations were aggravated by maternal diabetes and partly rectified by vitamin E supplementation. In the present study we evaluated the morphology of placentae and kidneys in this model. Non-diabetic and streptozotocin-induced diabetic pregnant rats of two rat strains (U and H) were treated with Suramin or saline, and given standard or vitamin E-enriched food. On gestational day 20 one placenta and the left kidney of the mother were collected for morphological and stereological analysis. In the placental trophospongium Suramin treatment caused cysts, which were further enhanced by maternal diabetes. Vitamin E treatment had no effect on the vacuolization. In the placental labyrinth of the non-diabetic rats Suramin treatment restricted maternal placental blood volume and increased the interface between maternal and fetal circulation. These changes were reversed by vitamin E treatment. Diabetes increased slightly the interface between the circulations in both rat strains. Suramin treatment decreased the interface, and vitamin E further decreased the interface in the diabetic U rats, whereas neither treatment affected the maternal-fetal interface in the diabetic H rats. The kidneys of Suramin-treated and diabetic rats were heavier compared to controls. Suramin treatment and maternal diabetes damaged renal glomeruli to a similar extent. Vitamin E treatment diminished the Suramin- and diabetes-induced glomerular damage in U rats, but not in H rats. The average cell count per glomerulus was decreased by Suramin in the U rats. Vitamin E treatment did not affect cell number per glomerulus in any group. We conclude that Suramin-injected pregnant rats constitute a valid animal model for placental dysfunction and pre-eclampsia, also from the histological perspective. The present work supports the notion that one important effect of untreated maternal diabetes may be impaired placentation, leading to oxidative stress, morphological damage, and compromised placental function.

Pravastatin Decreases Wall Shear Stress and Blood Velocity in the Internal Carotid Artery Without Affecting Flow Volume

Background and Purpose— Despite speculations, it is unknown whether statins affect wall shear stress (WSS). Therefore, the effect of pravastatin on WSS was investigated.

Methods— In 355 elderly individuals participating in the PROSPER study (follow up after 3 years), the effect of 40 mg pravastatin on WSS was assessed in the internal carotid artery using magnetic resonance imaging.

Results— WSS and blood velocity decreased both in the pravastatin group and in the placebo group but decreased faster in the pravastatin group ( P <0.04, P <0.02). Blood volume flow did not differ between the groups.

Conclusions— In elderly subjects, the WSS and blood velocity of the internal carotid artery declines significantly over time and this decline is more pronounced in subjects treated with 40 mg pravastatin compared with the placebo group.

Tumor Antivascular Effects of Radiotherapy Combined with Combretastatin A4 Phosphate in Human Non–Small-Cell Lung Cancer

PURPOSE

The tumor vascular effects of radiotherapy and subsequent administration of the vascular disrupting agent combretastatin A4 phosphate (CA4P) were studied in patients with advanced non-small-cell lung cancer using volumetric dynamic contrast-enhanced computed tomography (CT).

PATIENTS AND METHODS

Following ethical committee approval and informed consent, 8 patients receiving palliative radiotherapy (27 Gy in six fractions, twice weekly) also received CA4P (50 mg/m(2)) after the second fraction of radiotherapy. Changes in dynamic CT parameters of tumor blood volume (BV) and permeability surface area product (PS) were measured for the whole tumor volume, tumor rim, and center after radiotherapy alone and after radiotherapy in combination with CA4P.

RESULTS

After the second fraction of radiotherapy, 6 of the 8 patients showed increases in tumor PS (23.6%, p = 0.011). Four hours after CA4P, a reduction in tumor BV (22.9%, p < 0.001) was demonstrated in the same 6 patients. Increase in PS after radiotherapy correlated with reduction in BV after CA4P (r = 0.77, p = 0.026). At 72 h after CA4P, there was a sustained reduction in tumor BV of 29.4% (p < 0.001). Both increase in PS after radiotherapy and reduction in BV after CA4P were greater at the rim of the tumor. The BV reduction at the rim was sustained to 72 h (51.4%, p = 0.014).

CONCLUSION

Radiotherapy enhances the tumor antivascular activity of CA4P in human non-small-cell lung cancer, resulting in sustained tumor vascular shutdown.

Adrenomedullin and adrenomedullin binding protein-1 prevent metabolic acidosis after uncontrolled hemorrhage in rats

OBJECTIVE

Management of trauma victims with uncontrolled hemorrhage remains a major problem in combat casualty care at the far-forward battlefield setting. The neuroendocrine response to hemorrhage is to maintain perfusion to the heart and brain, often at the expense of other organ systems. Decreased organ perfusion after hemorrhagic shock is associated with metabolic acidosis, in which the up-regulated endothelin-1 plays an important role. We have recently shown that vascular responsiveness to adrenomedullin (AM), a newly discovered vasodilator peptide, is depressed after hemorrhage and resuscitation. Down-regulation of AM binding protein (AMBP-1) appears to be responsible for this hyporesponsiveness. We therefore hypothesized that administration of AM/AMBP-1 would prevent metabolic acidosis after uncontrolled hemorrhage via down-regulation of endothelin-1.

DESIGN

Prospective, controlled, and randomized animal study.

SETTING

A research institute laboratory.

SUBJECTS

Male Sprague-Dawley rats (275-325 g).

INTERVENTIONS

A rat model of uncontrolled hemorrhage with an extremely low volume of fluid resuscitation was used to mimic the combat situation.

MEASUREMENTS AND MAIN RESULTS

Both lumbar veins of male adult rats were isolated and severed at the junction to the vena cava. The abdomen was kept open but covered with a saline wet gauze for 45 mins and then closed in layers. The animals received 1 mL of normal saline (vehicle) with or without AM (12 microg/kg of body weight) and AMBP-1 (40 microg/kg of body weight) over 45 mins. Various variables were measured at 4 hrs after resuscitation. The bleed-out volumes in the vehicle group and the AM/ AMBP-1 treatment group were 6.78 +/- 0.19 and 6.81 +/- 0.25 mL/rat, respectively. The results indicate that AM/AMBP-1 administration prevented metabolic acidosis, mitigated organ injury, down-regulated preproendothelin-1 gene expression, and decreased plasma levels of endothelin-1 after hemorrhage.

CONCLUSIONS

AM/AMBP-1 may provide a novel approach for the treatment of uncontrolled hemorrhage. The beneficial effect of AM/AMBP-1 is associated with down-regulation of endothelin-1.

Association of increased myocardial contractility and elevated end-diastolic wall tension with short-term myocardial ischemia: a pressure-volume analysis

OBJECTIVE

Critical myocardial oxygen imbalance as indicated by elevated interstitial lactate levels may occur in cases of rapidly elevated end-diastolic myocardial wall tension during elevated myocardial contractility in the intact myocardium. Simultaneous administration of beta-adrenergic receptor agonist and antagonist reliably allows for investigating the myocardial response.

DESIGN

Experimental using an in vivo animal model.

SETTING

Research institution.

PARTICIPANTS

Animal model.

INTERVENTIONS

Not applicable.

MEASUREMENTS AND RESULTS

Fifteen minipigs were investigated in an open-chest model. After a midline sternotomy, a thin dialysis tube was implanted into the LV midmyocardium. Extracellular lactate in perfusate was analyzed every 5 minutes. End-systolic time-varying elastance and end-diastolic wall tension were measured. After a stable period, dobutamine (10 microg/kg/min) was administered to 8 animals. After 20 minutes, esmolol (0.5-mg/kg bolus, repetitively) was added until heart rate decreased to <100 beats/min. For 20 minutes, esmolol was infused at a rate of 3 mg/kg/h, and then dobutamine alone was continued for 10 minutes. With dobutamine, the lactate level did not change, but wall tension decreased and contractility increased. Simultaneous esmolol initially (in the first 10 minutes) increased lactate, whereas LV end-diastolic wall tension and contractility both increased; but after 10 minutes, lactate and contractility decreased significantly. Lactate again increased within 10 minutes after stopping esmolol. A group of 7 animals received esmolol for 20 minutes and showed no changes in lactate; myocardial wall tension increased and contractility decreased.

CONCLUSION

Results suggest that oxygen demand/supply is balanced until both end-diastolic wall tension and myocardial contractility are elevated to critical levels.

Effect of nitric-oxide synthesis on tumour blood volume and vascular activity: a phase I study

BACKGROUND

Nitric oxide has been implicated in tumour angiogenesis and in the maintaining of vasodilator tone of tumour blood vessels. The tumour vascular effects of inhibition of nitric-oxide synthesis have not been investigated in patients with cancer.

METHODS

Seven women and 11 men (12 with non-small-cell lung cancer, five prostate cancer, and one cervical cancer) were recruited onto a phase I dose-escalation study and received a single dose of the nitric oxide synthase inhibitor, N-nitro-L-arginine (L-NNA). Dose escalation was done by a modified Fibonacci scale with three patients at each dose level, starting with 0.1 mg/kg. Changes in dynamic contrast-enhanced CT measures of tumour relative blood volume and transfer constant (K) were measured at 1 h and 24 h after L-NNA administration.

FINDINGS

In the 18 patients, toxic effects were self-limiting cardiovascular changes: three patients had Common Toxicity Criteria version 2.0 grade 1 hypertension; two had grade 1 sinus bradycardia; and one had grade 1 palpitation. L-NNA area under the curve (AUC) increased linearly with dose from 163 micromol min(-1) L(-1) at 0.1 mg/kg L-NNA to 2150 micromol min(-1) L(-1) at 0.9 mg/kg L-NNA. In eight patients that underwent dynamic CT scanning, tumour blood volume decreased 1 h after L-NNA treatment (mean 42.9% [range 12.0-62.1]; paired t test p=0.0070), which was sustained for up to 24 h (mean 33.9% [range 6.5-64.9]; p=0.035). This decrease in blood volume was associated with an increase in the number of non-perfused pixels from 7.3% (SD 5.5) at baseline to 25.1% (15.3; p=0.0089) at 1 h, and 18.2% (12.9; p=0.050) at 24 h. There was a significant correlation between L-NNA plasma AUC and the reduction in tumour blood volume at 24 h after L-NNA (r=0.83; p=0.010).

INTERPRETATION

We have shown in vivo in patients with cancer that nitric oxide has a role in maintaining tumour blood supply, and we provide early clinical evidence that inhibition of nitric-oxide synthesis has tumour antivascular activity.

Hemodynamic responses and c-Fos changes associated with hypotensive hemorrhage: standardizing a protocol for severe hemorrhage in conscious rats

The central mechanisms underlying the transition from compensation to decompensation during severe hemorrhage (HEM) are poorly understood. Furthermore, a lack of consistency in HEM protocols exists in the current literature. This study assessed the cardiovascular response and Fos-like immunoreactivity (FLI) in specific brain regions following severe HEM at three rates (2, 1, or 0.5 ml.kg(-1).min(-1)) in conscious rats. Heart rate (HR) and arterial pressure were recorded during the withdrawal of 30% of total blood volume (TBV). Data from animals hemorrhaged at the fast (F-HEM, n = 6), intermediate (I-HEM, n = 7), or slow (S-HEM, n = 7) rates were compared with saline (SAL, n = 5) and hypotensive (hydrazaline-induced, HYDRAZ, n = 5) controls. All HEM rates produced similar degrees of hypotension at the time of 30% TBV withdrawal. All HEM rates also produced bradycardia, but the change in HR was only significant in the F-HEM and I-HEM groups. Associated with I-HEM and F-HEM, but not HYDRAZ treatment were significant increases in FLI in the caudal ventrolateral periaqueductal gray (PAG), the central lateral nucleus of the rostral parabrachial nucleus, and locus coeruleus compared with SAL treatment. I-HEM also induced significant increases in FLI in the dorsomedial PAG, A7 region, and the cuneiform nucleus compared with SAL. S-HEM did not induce any significant change in FLI. Our results suggest that HEM at a rate of 1 ml.kg(-1).min(-1) may be most useful for investigating the potential role of the rostral brainstem regions in mediating hemorrhagic decompensation in conscious rats.

[Effect of volatile inhalational anesthetics on cerebral blood volume and oxygen status in children]

The investigation evaluated the effect of various volatile anesthetics on cerebral blood volume and oxygen status in sick children at the stage of anesthesia induction. Ninety-two children were distributed into 3 groups: Groups 1 (n = 36) and 2 (n = 24) underwent stepwise induction with halothane and enflurane, respectively. Group 3 (n = 32) had vital capacity rapid inhalation induction with sevoflurane. Cerebral oximetry (NIRS method) was used to measure the content of hydroxyhemoglobin, deoxyhemoglobin, the total level of hemoglobin and to assess regional cerebral tissue saturation (rSO2). Halothane was ascertained to increase cerebral blood volume by 20.5% whereas enflurane and sevoflurane increased it only by 8.8 and 9.0%, respectively. In all cases, the value of rSO2 remained comparatively high, by exceeding the baseline level by 3-5%.

fMRI of delayed albumin treatment during stroke recovery in rats: implication for fast neuronal habituation in recovering brains

Accumulating experimental and clinical data suggest that albumin may be neuroprotective for stroke. Here, we use functional magnetic resonance imaging (fMRI) to evaluate the therapeutic efficacy of albumin and its effects on the recovery of stimuli-induced cerebral hemodynamics. For this purpose, fMRI activity in the ipsilesional somatosensory (SS) cortex was assessed using a well established rat model of transient 90 min focal ischemia and electrical forelimb stimulation. Rats were treated with either saline or albumin via intracerebroventricular injections at 12 h post-stroke onset. Despite this delayed treatment time, when compared to the saline-treated rats (n=7), there were significant enhancements of the fMRI activation in the albumin-treated rats (n=6) for both blood oxygenation level dependence (BOLD) and functional cerebral blood volume (fCBV) responses. Interestingly, the temporal characteristics of the ipsilesional SS BOLD responses in the albumin-treated rats appeared considerably altered compared to those of contralesional responses while such temporal alterations were not pronounced for the fCBV responses. These characteristic fMRI temporal profiles of the albumin-treated brains may be due to altered neuronal responses rather than altered integrity of neurovascular coupling, which implies an unusually fast habituation of neuronal responses in the lesional SS cortex. The correlation between various MRI-derived structural parameters and the fMRI response magnitude was also characteristic for albumin and control groups. Taken together, these data suggest that restoration of fMRI response magnitudes, temporal profiles, and correlations with structure may reveal the extent and specific traits of albumin treatment associated stroke recovery.

Involvement of anteroventral third ventricular AMPA/kainate receptors in both hyperosmotic and hypovolemic AVP secretion in conscious rats

The area of the brain called the anteroventral third ventricular region (AV3V) includes three different subtypes of glutamate receptor, as well as neural circuits controlling fluid balance and cardiovascular and neuroendocrine functions. Although our previous data indicate the ability of AV3V N-methyl-d-aspartate (NMDA) and metabotropic receptors to provoke vasopressin (AVP)-releasing, pressor and hyperglycemic responses, the roles of non-NMDA receptors selective for alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid and kainate have not been elucidated to date. To address this question, the effects of intracerebral infusion with FWD or NBQX (specific agonist and antagonist for non-NMDA receptors, respectively) on plasma AVP, glucose, osmolality, electrolytes and cardiovascular parameters were examined in conscious rats in the absence or presence of an osmotic or volemic stimulus. When applied topically to AV3V structures such as the median preoptic nucleus, FWD augmented plasma AVP, osmolality, glucose and arterial pressure in a dose-associated fashion. All responses of the variables were abolished by pre-administering NBQX, which exerted no conspicuous effect on any variable except arterial pressure. It was revealed that NBQX administration in AV3V structures such as the median preoptic nucleus and the periventricular nucleus inhibited the rise of plasma AVP in response to intravenous infusion with hypertonic saline or removal of systemic blood through the femoral artery. Elevation of plasma osmolality and sodium evoked by osmotic load, and elevation of plasma osmolality, glucose and angiotensin II and decrease of arterial pressure caused by bleeding, were not significantly affected by NBQX treatment. These results suggest that AV3V non-NMDA receptors, as well as NMDA receptors, may elicit AVP-releasing, pressor and hyperglycemic actions when stimulated in the basal state, and may facilitate AVP secretion under both hyperosmotic and hypovolemic conditions, without contributing to cardiovascular, blood glucose or other responses.

Beyond diuretics: management of volume overload in acute heart failure syndromes

Diuretics are an established foundation of therapy for patients with chronic heart failure (HF) as well as for those hospitalized for treatment of acute HF syndromes. Despite the accepted use of diuretics in acute HF syndromes, treatment patterns with diuretics vary widely, and there are no data from randomized studies on the benefit of diuretics on morbidity or mortality in patients hospitalized with acute HF syndromes. Additional pharmacologic therapies that complement or replace diuretics in this setting, especially in patients with diuretic resistance, include positive inotropes, nitrovasodilators, and natriuretic peptides, but data are likewise lacking on important clinical outcomes. Ultrafiltration has also been used as a nonpharmacologic strategy to treat patients with acute HF syndromes who exhibit resistance to diuretics. Effective monitoring of volume status with newer modalities may allow more selective use of diuretics and diuretic-like modalities, but additional randomized trial data are clearly needed to establish ideal strategies to promote volume removal in acute HF syndromes.

Role of catecholaminergic neurones of the caudal ventrolateral medulla in cardiovascular responses induced by acute changes in circulating volume in rats

Several findings suggest that catecholaminergic neurones in the caudal ventrolateral medulla (CVLM) contribute to body fluid homeostasis and cardiovascular regulation. The present study sought to determine the effects of lesions of these neurones on the cardiovascular responses induced by changes in circulating volume. All experiments were performed in male Wistar rats (320-360 g). Medullary catecholaminergic neurones were lesioned by microinjection of anti-dopamine beta-hydroxylase-saporin (6.3 ng in 60 nl; SAP rats, n = 14) into the CVLM, whereas sham rats received microinjections of free saporin (1.3 ng in 60 nl, n = 15). Two weeks later, rats were anaesthetized (urethane, 1.2 g kg(-1), i.v.), instrumented for measurement of mean arterial pressure (MAP), renal blood flow (RBF) and renal vascular conductance (RVC), and infused with hypertonic saline (HS; 3 m NaCl, 0.18 ml (100 g body weight)(-1), i.v.) or an isotonic solution (volume expansion, VE; 4% Ficoll, 1% of body weight, i.v.). In sham rats, HS induced sustained increases in RBF and RVC (155 +/- 7 and 145 +/- 6% of baseline, at 20 min after HS). In SAP rats, RBF responses to HS were blunted (125 +/- 6%) and RVC increases were abolished (108 +/- 5%) 20 min after HS. Isotonic solution increased RBF and RVC in sham rats (149 +/- 10 and 145 +/- 12% of baseline, respectively, at 20 min). These responses were reduced in SAP rats (131 +/- 6 and 126 +/- 5%, respectively, at 20 min). Pressor responses to HS were larger in SAP rats than in sham rats (17 +/- 5 versus 9 +/- 2 mmHg, at 20 min), whereas during VE these responses were similar in both groups (6 +/- 3 versus 4 +/- 6 mmHg, at 20 min). Immunohistochemical analysis indicates that microinjections of anti-DbetaH-saporin produced extensive destruction within the A1/C1 cell groups in the CVLM. These results suggest that catecholaminergic neurones mediate the cardiovascular responses to VE or increases in plasma sodium levels.

Effects of a new perfluorocarbon emulsion on human plasma and whole-blood viscosity in the presence of albumin, hydroxyethyl starch, or modified fluid gelatin: an in vitro rheologic approach

BACKGROUND

Artificial oxygen carriers such as perfluorocarbon (PFC) emulsions have reached Phase III clinical trials as alternatives to homologous blood, but their rheologic effects have not been characterized. In this study, the rheologic effects of PFC emulsion in the presence of clinically used volume expanders were investigated.

STUDY DESIGN AND METHODS

The effects of a new PFC emulsion (small droplet size with narrow size distribution) at two PFC concentrations (4 and 8 g/dL) on plasma and whole-blood viscosity in the presence of human albumin solution (HAS), hydroxyethyl starch (HES), or modified fluid gelatin (MFG) were investigated. Three hematocrit (Hct) levels were investigated: 30, 20, and 13 percent. Plasma, PFC emulsions, and whole-blood viscosity, with a Couette viscometer, and RBC elongation, with an ektacytometer, were measured for shear rates of 0.2 to 128 per second.

RESULTS

The two PFC concentrations increased plasma and whole-blood viscosities. Viscosity values similar to physiologic ones (Hct level, 40%) were observed at: 1) Hct level of 13 percent, with 4 or 8 g per dL MFG-PFC; 2) Hct level of 20 percent, with 4 g per dL MFG-PFC; and 3) Hct level of 30 percent, with 4 g per dL HES-PFC and 4 and 8 g per dL HAS-PFC. RBC deformability was unchanged.

CONCLUSION

It is concluded that this new PFC emulsion increases plasma and blood viscosity and that among the three studied volume expanders, the interaction with MFG can result in viscosity values above the physiologic one even at low Hct values. The possible consequences of the increased viscosity at low Hct values are discussed.

Altered regional blood volume in chronic cannabis smokers

The quantitative measurement of cerebral perfusion is crucial for the study of both normal and impaired human brain function. Although cannabis is the most commonly abused illicit substance in the United States, its effects on cerebral blood volume (CBV) have not been fully examined. The objective of the present study was to examine differences in relative regional blood volume in focal regions of interest--including the frontal lobe, the temporal lobe, and the cerebellum--during a period of supervised abstinence from cannabis. Dynamic susceptibility contrast MRI data were collected on 12 current, long-term daily cannabis users between 6 and 36 hr after the subjects' last reported cannabis use. Resting-state CBV images were also acquired in 17 healthy comparison subjects. Data were acquired in the axial plane with a 1.5-Tesla GE Signa scanner following a bolus of gadolinium contrast agent. Cannabis users demonstrated significantly increased blood volumes in the right frontal area (p < .05), in the left temporal area (p < .005), and in the cerebellum (p < .005) relative to comparison subjects. Among the cannabis users, there were no significant correlations between regional blood volumes and either total lifetime episodes of smoking or urinary tetrahydrocannabinol concentrations. These findings have important implications for understanding the effects of chronic heavy cannabis use on brain function. It would be of interest to extend the investigation beyond 6-36 hr of abstinence from cannabis to determine whether increased CBV values persist for several weeks or eventually normalize.

Pharmacological FMRI in the development of new analgesic compounds

Chronic pain is a major problem for the individual and for society. Despite a range of drugs being available to treat chronic pain, only inadequate pain relief can be achieved for many patients. There is therefore a need for the development of new analgesic compounds. The assessment of pain depends to date entirely on the subjective report of the patient, in contrast to many other clinical conditions where biomarkers that help determine the severity and stage of the disease enable the physician to monitor the course of the disease and treatment effects longitudinally. In this article, we illustrate that magnetic resonance-based imaging techniques have the potential to provide sensitive and specific biomarkers of the pain experience, as well as clarifying disease mechanisms. Functional magnetic resonance imaging (FMRI) is particularly suited to investigating the effects of pharmacological agents on pain processing within the human central nervous system. Combination of FMRI and drug administration is termed pharmacological FMRI (phFMRI). In addition to outlining several methodological considerations that have to be taken into account when performing phFMRI, we discuss phFMRI studies that have already used this technique to study the effects of analgesic compounds. These studies provide promising data for the use of phFMRI as sensitive tool in assessing a potential drug effect. Such pharmacodynamic readouts obtained early in the process of drug development would not only save the pharmaceutical industry substantial amounts of money, but would also avoid the unnecessary exposure of patients to molecules with limited or no therapeutic value. We are therefore optimistic that phFMRI will be used as a tool with high sensitivity and specificity for evaluating analgesic agents in early drug development and clinical studies.

Dynamic CT perfusion imaging with acetazolamide challenge for evaluation of patients with unilateral cerebrovascular steno-occlusive disease

BACKGROUND AND PURPOSE

Perfusion CT (PCT) has the ability to measure quantitative values and produce maps of cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT). We assessed cerebral hemodynamics by using these parameters and acetazolamide challenge in patients with cerebrovascular steno-occlusive disease.

METHODS

Fifteen patients underwent PCT with acetazolamide challenge. Comparison of mean CBF, CBV, and MTT was determined between hemispheres and before and after acetazolamide challenge. Hemispheric ratio and percent change due to acetazolamide administration were also calculated. Absolute values and percent changes 2 SDs outside the mean from the nonstenotic hemispheres were defined as abnormal.

RESULTS

Significant decreases in CBF (-25.1%, P = .003) and significant increases in MTT (47.1%, P < .001) were found in stenotic hemispheres. After acetazolamide challenge, significant changes in CBF (-39.5%, P < .001) and MTT (92.9%, P < .001) were also seen. The acetazolamide test significantly decreased CBF hemispheric ratio (-20.3%, P < .001) and increased MTT hemispheric ratio (30.8%, P = .002), making both maps more asymmetric. Significance in CBF and MTT percent changes (P < .001 and P = .005, respectively) was found between hemispheres. When CBF percent changes were assumed to represent the true determinant of hemodynamic impairment, normal ranges of baseline MTT value and MTT percent changes demonstrated sensitivities of 66.7% and 100% and specificities of 58.3% and 75%, respectively, for detecting patients with hemodynamic impairment.

CONCLUSION

Parameters obtained from PCT with acetazolamide are promising for the evaluation of cerebral hemodynamics in patients with cerebrovascular steno-occlusive disease.

Effects of Midazolam and Morphine on Cerebral Oxygenation and Hemodynamics in Ventilated Premature Infants

BACKGROUND

Midazolam sedation and morphine analgesia are commonly used in ventilated premature infants.

OBJECTIVES

To evaluate the effects of midazolam versus morphine infusion on cerebral oxygenation and hemodynamics in ventilated premature infants.

METHODS

11 patients (GA 26.6-33.0 weeks, BW 780-2,335 g) were sedated with midazolam (loading dose 0.2 mg/kg, maintenance 0.2 mg/kg/h) and 10 patients (GA 26.4-33.3 weeks, BW 842-1,955 g) were sedated with morphine (loading dose 0.05 mg/kg, maintenance 0.01 mg/kg/h). Changes in oxyhemoglobin (Delta cO2Hb) and deoxyhemoglobin (Delta cHHb) were assessed using near infrared spectrophotometry. Changes in cHbD (= Delta cO(2)Hb - Delta cHHb) reflect changes in cerebral blood oxygenation and changes in concentration of total hemoglobin (Delta ctHb = Delta cO2Hb + Delta cHHb) represent changes in cerebral blood volume (DeltaCBV). Changes in cerebral blood flow velocity (DeltaCBFV) were intermittently measured using Doppler ultrasound. Heart rate (HR), mean arterial blood pressure (MABP), arterial oxygen saturation (saO2) and transcutaneous measured pO2 (tcpO2) and pCO2 (tcpCO2) were continuously registered. Statistical analyses were carried out using linear mixed models to account for the longitudinal character study design.

RESULTS

Within 15 min after the loading dose of midazolam, a decrease in saO2, tcpO2 and cHbD was observed in 5/11 infants. In addition, a fall in MABP and CBFV was observed 15 min after midazolam administration. Immediately after morphine infusion a decrease in saO2, tcpO2 and cHbD was observed in 6/10 infants. Furthermore, morphine infusion resulted in a persistent increase in CBV.

CONCLUSIONS

Administration of midazolam and morphine in ventilated premature infants causes significant changes in cerebral oxygenation and hemodynamics, which might be harmful.

Effects of Rapid versus Slow Infusion of Sodium Bicarbonate on Cerebral Hemodynamics and Oxygenation in Preterm Infants

BACKGROUND

Sodium bicarbonate (NaHCO3) is often used for correction of metabolic acidosis in preterm infants. The effects of NaHCO3 administration on cerebral hemodynamics and oxygenation are not well known. Furthermore, there is no consensus on infusion rate of NaHCO3.

OBJECTIVES

To evaluate the effects of rapid versus slow infusion of NaHCO3 on cerebral hemodynamics and oxygenation in preterm infants.

METHODS

Twenty-nine preterm infants with metabolic acidosis were randomized into two groups (values are mean +/-SD): In group A (GA 30.5 +/- 1.7 weeks, b.w. 1,254 +/- 425 g) NaHCO3 4.2% was injected as a bolus. In group B (GA 30.3 +/- 1.8 weeks, b.w. 1,179 +/- 318 g) NaHCO3 4.2% was administered over a 30-min period. Concentration changes of oxyhemoglobin (cO2Hb) and deoxyhemoglobin (cHHb) were assessed using near infrared spectrophotometry. Changes in HbD (= cO2Hb - cHHb) represent changes in cerebral blood oxygenation and changes in ctHb (= cO2Hb + cHHb) reflect changes in cerebral blood volume. Cerebral blood flow velocity was intermittently measured using Doppler ultrasound. Longitudinal data analysis was performed using linear mixed models (SAS procedure MIXED), to account for the fact that the repeated observations in each individual were correlated.

RESULTS

Administration of NaHCO3 resulted in an increase of cerebral blood volume which was more evident if NaHCO3 was injected rapidly than when infused slowly. HbD and cerebral blood flow velocity did not show significant changes in either group.

CONCLUSION

To minimize fluctuations in cerebral hemodynamics, slow infusion of sodium bicarbonate is preferable to rapid injection.

[Study on the effect of volume expansion by 0.9% and 1.8% sodium solution on cardiac-renal reflex in rabbits]

AIM

To study the effect of volume expansion by 0.9% and 1.8% sodium solution on cardiac-renal reflex activity and the role of cardiac-renal reflex in the regulation of integrated function.

METHODS

18 health pentobarbital-anaesthetized rabbits were divided evenly into 2 groups at random, bilateral sino-aortic denervation, intubated via right jugular vein to monitor CVP, left renal nerve separated and ending sectioned to record ERSNA, bilateral ureter intubated to collect urine, right femoral intubated to get blood sample. 15% of whole body blood volume of 0.9% and 1.8% sodium solution were injected via jugular vein 10 ml per minute respectively. The CVP, ERSNA, bilateral urine volume and coefficient of sodium excretion were measured before treated, during treated, one minute, five minutes and ten minutes after treated.

RESULTS

Volume expansion by 0.9% and 1.8% sodium solution respectively resulted in the increase of CVP by 64.00% +/- 15.56% and 77.00% +/- 23.74%; the decrease of the frequency of ERSNA by 44.00% +/- 13.64% and 63.00% +/- 12.49%, the average burst time of ERSNA by 37.00% +/- 16.49% and 31.00% +/- 10.69%, the increase of average interval of ERSNA bursts by 60.00% +/- 18.38% and 68.00% +/- 27.04%; the increase of urine volume by 158.00% +/- 28.10% and 640.00% +/- 155.39% in left kidney, 192.00% +/- 32.26% and 1343.00% +/- 429.95% in the right; the increase of coefficient of sodium excretion by 132.00% +/- 35.23% and 376.00% +/- 121.72% in the left, 300.00% +/- 76.99% and 856.00% +/- 261.48% in the right.

CONCLUSION

Volume expansion by different solution stimulate the receptors of cardiopulmonary and regulate the water and sodium excretion of the kidney by the cardiac-renal reflex to modulate the stabilization of blood volume.