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     

Comparative effects of propofol, pentobarbital, and isoflurane on cerebral blood flow and blood volume

While intravenous and volatile anesthetics have widely differing effects on cerebral blood flow (CBF), clinical studies suggest that the relative differences in their effects on intracranial pressure (ICP) may be smaller. Because acute changes in ICP are determined primarily by changes in cerebral blood volume (CBV), we compared the impact of propofol, pentobarbital, and isoflurane on CBF and CBV in rats. Equipotent doses of the three agents were determined by tail-clamp studies. Animals were then anesthetized with propofol (20 mg/kg load, 38 mg.kg-1.h-1 infusion), pentobarbital (30 mg/kg load, 20 mg.kg-1.h-1 infusion), or isoflurane 1.6-1.8%. Two hours later, CBF and CBV were measured using 3H-nicotine as a CBF tracer, and 14C-dextran and 99mTc-labeled red cells as markers for cerebral plasma and red blood cell volumes (CPV and CRBCV), respectively. Total CBV was the sum of CPV and CRBCV. CBF was 2.0-2.6 times greater with isoflurane than with propofol or pentobarbital (137 vs. 67 and 52 ml.100 g-1.min-1, respectively). By contrast, while CBV was greater in the isoflurane group than in either the propofol or pentobarbital groups, the magnitude of the intergroup differences were much smaller (propofol = 2.49 +/- 0.28 ml/100 g; pentobarbital = 2.27 +/- 0.15 ml/100 g; isoflurane = 2.77 +/- 0.24 ml/100 g, mean +/- SD). These results suggest that the simple measurement of CBF may not adequately describe the cerebrovascular effects of an anesthetic, at least with respect to predicting the magnitude of the agents likely effects on ICP.     

Relationship between cytochrome P-450 induction by rifampicin, hepatic volume and portal blood flow in man

OBJECTIVE: Induction of hepatic cytochrome P-450-dependent oxidative metabolism is related to an almost identical increase (30%) in both the liver weight and portal blood flow in animals. In humans by contrast, an increased liver blood flow (44%) but no significant increase in liver volume has been reported. DESIGN: Therefore, we studied prospectively the relationship between P-450 induction by rifampicin, hepatic volume and portal blood flow in 10 healthy volunteers. METHODS: After a pre-treatment phase (day 1 to 7) the 10 volunteers received 600 mg/day of rifampicin from day 7 to 12. The urinary 6-beta-hydroxycortisol output as a measure of oxidative metabolism (CYP3A4) and portal blood flow (pulsed Doppler ultrasound) were determined on days 1, 7, 11 and 13. Hepatic magnetic resonance volumetry was performed on days 1 and 13. RESULTS: Urinary 6-beta-hydroxycortisol output increased in all volunteers (P = 0.0051) from a median of 2.15 micrograms/day/kg (1.8-3.3 micrograms/day/kg) on day 1 to 9.9 micrograms/day/kg (5.7-14 micrograms/day/kg) on day 13. In 9 of 10 volunteers induction by rifampicin was related to an increase (P = 0.0218) in liver volume from a median of 1570 cm3 (1390-1830 cm3) to a median of 1690 cm3 (1420-1860 cm3). The portal flow as assessed by colour Doppler ultrasound did not change significantly between day 1 (median 22 cm/s (15-35 cm/s)) and day 13 (median 19 cm/s (16-39 cm/s)). CONCLUSION: A fourfold increase of urinary 6-beta-hydroxycortisol output after induction of cytochrome P-450 by rifampicin is associated with a significant but less than 10% increase in human liver volume. No increase of portal perfusion as assessed by Doppler ultrasound could be detected in this study.     

Post-exercise rehydration in man: effects of volume consumed and drink sodium content

The interaction between the volume and composition of fluids ingested was investigated in terms of rehydration effectiveness. Twelve male volunteers, dehydrated by 2.06 +/- 0.02% (mean +/- SE) of body mass by intermittent cycle exercise, consumed a different drink volume on four separate weeks; six subjects received drink L (23 mmol.l-1 Na+) in each trial and six were given drink H (61 mmol.l-1 Na+). Volumes consumed were equivalent to 50%, 100%, 150%, and 200% of body mass loss (trials A, B, C, and D, respectively). Blood and urine samples were obtained before exercise and for 7.5 h after exercise. Less urine was excreted following rehydration in trial A than in all other trials. Cumulative urine output (median ml) was less in trial B (493, range 181-731) than D (1361, range 1014-1984), which was not different from trial C (867, range 263-1191) in group L. In group H, the volume excreted in trial B (260, range 137-376) was less than trials C (602, range 350-994) and D (1001, range 714-1425), and the volume in trial C was less than in trial D. These results suggest that both sodium concentration and fluid volume consumed interact to affect the rehydration process. A drink volume greater than sweat loss during exercise must be ingested to restore fluid balance, but unless the sodium content of the beverage is sufficiently high this will merely result in an increased urinary output.     

Correlation between regional cerebral blood flow and oxidative metabolism. In vivo studies in man

To test the hypothesis that regional cerebral blood flow (rCBF) is normally regulated by regional metabolic activity, rCBF and the regional cerebral metabolic rate for oxygen (rCMRO2) were compared in selected human subjects. In normal subjects and patients with chronic, stable diseases of brain, rCBF correlated well with rCMRO2. In one individual with mild dementia, rCBF and rCMRO2 were measured before and during exercise of the hand and forearm contralateral to the hemisphere studied. Appropriate parallel changes occurred in both rCBF and rCMRO2 during hand exercise. In patients with acute diseases affecting the hemisphere studied, however, the correlation between rCBF and rCMRO2 was unpredictable.     

30～50岁男性前列腺体积与体重指数、血压、血脂及血糖的相关性分析

目的:了解30～50岁男性前列腺体积与体重指数、血压、血脂及血糖的相关性.方法:从石景山区社会保险中心登记信息中随机抽取1 010名30～50岁男性作为研究对象,行体格检查并计算体重指数(body mass index,BMI),经腹B超测定并计算前列腺体积(prostate volume,PV);空腹抽血检测血糖(blood glucose,BG)、血胆固醇(blood cholesterol,CHOL)、甘油三酯(triglyceride,TG)、低密度脂蛋白(low density lipoprotein,LDL)、高密度脂蛋白(high density lipoprotein,HDL)等,测量血压(blood pressure,BP),应用SPSS13.0统计软件对PV和BMI、BP、BG、CHOL、TG、LDL、HDL的相关性进行统计学分析.结果:符合标准并资料全面者1002人,前列腺体积与年龄、BMI、BG、CHOL、LDL、HDL等因素有明显的相关性,P值分别为0.000、0.013、0.032、0.040、0.032、0.017,相关系数r值分别为0.62、0.57、0.52、0.51、-0.50、-0.48.与TG、收缩压(systolic pressure,SP)、舒张压(diastolic pressure,DP)无明显相关性,P值分别为0.313、0.213、0.782.调整年龄因素后,PV与BMI、LDL仍有较强的相关性,P值分别为0.029、0.001,相关系数r值分别为0.53、-0.49.与BG、CHOL、LDL、HDL、TG、SP、DP无明显相关性(P＞0.05).结论:在30～50岁男性人群中,前列腺体积和BMI及血脂异常明显相关,BMI、血脂异常是前列腺体积增大的危险因素.     

Isotope study of the effects of a nitrate derivative on pulmonary blood volume. Application in the treatment of cardiogenic pulmonary edema

Isotopic study of pulmonary and ventricular blood volumes after the ingestion of 5 mg of isosorbide dinitrate showed that cardio-pulmonary blood volume decreased by 380 ml without any change in total circulating blood volume. The demonstration of this effective "internal venesection" explains the fall in capillary pressure seen after the administration of nitrate derivatives. It justifies their use in the treatment of acute pulmonary oedema or refractory cardiac failure and explains the results observed.     

Role of tidal volume, FRC, and end-inspiratory volume in the development of pulmonary edema following mechanical ventilation

Mechanical ventilation with high peak inspiratory pressure and large tidal volume (VT) produces permeability pulmonary edema. Whether it is mean or peak inspiratory pressure (i.e., mean or end-inspiratory volume) that is the major determinant of ventilation-induced lung injury is unsettled. Rats were ventilated with increasing tidal volumes starting from different degrees of FRC that were set by increasing end-expiratory pressure during positive-pressure ventilation. Pulmonary edema was assessed by the measurement of extravascular lung water content. The importance of permeability alterations was evaluated by measurement of dry lung weight and determination of albumin distribution space. Pulmonary edema with permeability alterations occurred regardless of the value of positive end-expiratory pressure (PEEP), provided the increase in VT was large enough. Similarly, edema occurred even during normal VT ventilation provided the increase in PEEP was large enough. Furthermore, moderate increases in VT or PEEP that were innocuous when applied alone, produced edema when combined. The effect of PEEP was not the consequence of raised airway pressure but of the increase in FRC since similar observations were made in animals ventilated with negative inspiratory pressure. However, although permeability alterations were similar, edema was less marked in animals ventilated with PEEP than in those ventilated with zero end-expiratory pressure (ZEEP) with the same end-inspiratory pressure. This "beneficial" effect of PEEP was probably the consequence of hemodynamic alterations. Indeed, infusion of dopamine to correct the drop in systemic arterial pressure that occurred during PEEP ventilation resulted in a significant increase in pulmonary edema. In conclusion, rather than VT or FRC value, the end-inspiratory volume is probably the main determinant of ventilation-induced edema. Hemodynamic status plays an important role in modulating the amount of edema during lung overinflation but does not fundamentally modify the characteristics of this edema which is consistently associated with major permeability alterations. These results may be relevant for ventilatory strategies during acute respiratory failure.     

Effects of immersion in water and changes in intrathoracic blood volume on lung function in man

1. In healthy, normal subjects simultaneous peripheral venous occlusion of all four limbs caused a small but significant increase in vital capacity (VC) and single-breath carbon monoxide transfer factor (DLCO) without significantly changing total lung capacity (TLC), residual volume (RV), pulmonary gas flow or pulmonary compliance. 2. Immersion in water to the neck resulted in a small but significant fall in VC, FEV 1.0/FVC and TLC, and a rise in DLCO, but flow/volume curves and 'closing volume' were unchanged. Peripheral venous occlusion during immersion only significantly increased VC and DLCO; pulmonary compliance and flow/volume curves did not alter significantly. 3. It is concluded that peripheral venous occlusion produces these effects by altering intrathoracic blood volume. Water immersion reduces TLC, mainly from the hydrostatic pressure, and VC is reduced from both the hydrostatic pressure and the increase in intrathoracic blood volume consequent on immersion. The increase in DLCO is due, almost entirely, to the increase in intrathoracic blood volume.     

Cerebral cortex regional blood flow and tissue oxygen tension during the trigeminal depressor response in rabbits

The paradox of pancytopenia despite cellular bone marrows (BM) was investigated in 120 patients with myelodysplastic syndromes (MDS). Detailed cell cycle kinetics were examined following in vivo infusions of iodo--and/or bromodeoxyuridine (IUdR/BrdU), while the incidence of apoptosis was measured by in situ end labeling (ISEL) of fragmented DNA. Results showed that MDS are highly proliferative disorders with an equally high incidence of apoptotic intramedullary cell death accounting for the paradox of cellularity/cytopenia. By double-labeling BM biopsy sections for ISEL/BrdU we found the peculiar situation of "signal antonymy" where S-phase cells were frequently apoptotic, a phenomenon so far only seen in MDS biopsies. The cause-effect relationship of this excessive proliferation/apoptosis is discussed at length.     

Regional cerebral blood volume after severe head injury in patients with regional cerebral ischemia

OBJECTIVE: Recent early cerebral blood flow (CBF) studies in cases of severe head injury have revealed ischemia in a substantial number of patients with a variety of computed tomographically demonstrated diagnoses. The underlying derangements causing this early ischemia are unknown, but cerebral blood volume (CBV) measurements might offer some insight into this pathological abnormality. METHODS: For this purpose, stable xenon-enhanced computed tomography was used for assessment of CBF, and a dynamic computed tomographic imaging technique was used for determining CBV. Based on the occurrence of regional ischemia (CBF < 20 ml/100 g/min), seven patients with varying anatomic lesions revealed by computed tomography were identified for comparison between CBF and CBV in ischemic and nonischemic areas. RESULTS: Both CBF (15+/-4.3 versus 34+/-11 g/min, P < 0.002) and CBV (2.5+/-1.0 versus 4.9+/-1.9 ml/100 g) exhibited significantly lower values in the ischemic zones than in the nonischemic zones (means+/-standard deviations). Among 26 patients with or without ischemia observed during their initial follow-up studies, which were conducted between Days 2 and 8, all patients showed CBF and CBV values within the low-normal range. CONCLUSION: These data evidently support the suggestion that compromise of the microvasculature is the cause of early ischemia, rather than vasospasm of the larger conductance vessels.     

Histamine, histamine antagonists and regional blood flow

The effects of mepyramine, a selective histamine H1-receptor antagonist, and metiamide, a selective histamine H2-receptor antagonist, have been determined on the cardiovascular response to intravenous infusions of a large dose of histamine, 1 X 10(-7) mol/kg/min. Pretreatment with either mepyramine, 2.5 X 10(-6) mol/kg, or metiamide, 2 X 10(-6) mol/kg/min, had no significant effect on the fall in blood pressure or fall in total peripheral resistance during histamine infusion. Pretreatment with mepyramine, 2.5 X 10(-6) mol/kg, and metiamide, 2 X 10(-6) mol/kg/min, abolished the fall in blood pressure and total peripheral resistance during infusion of histamine. Histamine-induced vasodilatation in the stomach was unaltered by pretreatment with mepyramine but abolished by pretreatment with metiamide. Histamine-induced coronary vasodilation was reduced slightly by pretreatment with mepyramine and substantially by pretreatment with metiamide. Coronary vasodilatation was abolished by treatment with mepyramine and metiamide.     

Improving MR quantification of regional blood volume with intravascular T1 contrast agents: accuracy, precision, and water exchange

The goal of this work was to develop a comprehensive understanding of the relationship between vascular proton exchange rates and the accuracy and precision of tissue blood volume estimates using intravascular T1 contrast agents. Using computer simulations, the effects of vascular proton exchange and experimental pulse sequence parameters on measurement accuracy were quantified. T1 and signal measurements made in a rat model implanted with R3230 mammary adenocarcinoma tumors demonstrated that the theoretical findings are biologically relevant; data demonstrated that over-simplified exchange models may result in measures of tumor, muscle, and liver blood volume fractions that depend on experimental parameters such as the vascular contrast concentration. As a solution to the measurement of blood volume in tissues with exchange that is unknown, methods that minimize exchange rate dependence were examined. Simulations that estimated both the accuracy and precision of such methods indicated that both the inversion recovery and the transverse-spoiled gradient echo methods using a "no-exchange" model provide the best trade-off between accuracy and precision.     

A new method for quantitative regional cerebral blood volume measurements using computed tomography

BACKGROUND AND PURPOSE: Knowledge of cerebral blood volume (CBV) is invaluable in identifying the primary cause of brain swelling in patients with stroke or severe head injury, and it might also help in clinical decision making in patients thought to have hemodynamic transient ischemic attacks (TIAs). This investigation is concerned with the development and clinical application of a new method for quantitative regional CBV measurements. METHODS: The technique is based on consecutive measurements of cerebral blood flow (CBF) by xenon/CT and tissue mean transit time (MTT) by dynamic CT after a rapid iodinated contrast bolus injection. CBV maps are produced by multiplication of the CBF and MTT maps in accordance with the Central Volume Principle: CBV = CBF x MTT. The method is rapid and easily implemented on CT scanners with the xenon/CBF capability. It yields CBV values expressed in milliliters of blood per 100 grams of tissue. RESULTS: The method was validated under controlled physiological conditions causing changes that were determined both with our technique and from pressure-volume index (PVI) measurements. The two independent estimates of CBV changes were in agreement within 15%. CBV measurements using this method were carried out in normal volunteers to establish baseline values and to compare with values using the ratio-of-areas method for calculating both CBF and CBV from the dynamic study alone. Average CBV was 5.3 mL/100 g. The method was also applied in 71 patients with severe head injuries and in 1 patient with hemodynamic TIAs. CONCLUSIONS: The primary conclusions from this study were (1) the proposed method for measuring CBV accurately determines changes in CBV; (2) the MTT x CBF determinations are in agreement with the ratio-of-areas method for CBV measurements in normal volunteers and are consistent with other methods reported in the literature; (3) MTTs are significantly prolonged early after severe head injury, which when combined with the finding of decreased CBF and increased arteriovenous difference of oxygen indicates increased cerebrovascular resistance due to narrowing of the microcirculation consistent with the presence of early ischemia; and (4) CBV in the patient with TIAs was increased in the hemisphere with the occluded internal carotid artery, indicating compensatory vasodilation and probable hemodynamic cause.     

Cerebral edema in acute hepatic failure: clinicopathologic correlation

A child developed acute fulminant viral hepatitis and cerebral edema confirmed on postmortem examination. Clinical evidence of herniation, effacement of cortical sulci on computed tomography, and elevated cerebrospinal fluid pressure preceded complicating terminal events, demonstrated that cerebral edema was associated with acute hepatic failure, rather than complicating factors, and led to the patient's death. The mechanism is unknown.