Variations In Blood Volume Research Articles

Radioisotope blood volume measurement in hemodialysis patients

Accurate assessment of blood volume (BV) may be helpful for prescribing hemodialysis (HD) and for reducing complications related to hypovolemia and volume overload. Monitoring changes in relative BV (RBV) using hematocrit, e.g., Crit-Line Monitor (CLM-III), an indirect method, cannot be used to determine absolute BV. We report the first study of BV measurement for assessing volume status in HD patients using the indicator dilutional method. Ten adult HD patients were enrolled in this prospective observational study. BV measurement was performed before and after HD using BV analysis (BVA)-100 (Daxor Corporation, New York, NY, USA). BVA-100 calculates BV using radiolabeled albumin (Iodine-131) followed by serial measures of the radioisotope. Fluid loss from the extravascular space was calculated by subtracting the change in BV from total weight loss. Intradialytic changes in RBV were measured by CLM-III. Eight out of 10 cases had significant hypervolemia, two cases were normovolemic. The range of BV variation from predicted normal was 156 to 1990 mL. Significant inter-individual differences in extravascular space fluid loss ranged from 54% to 99% of total weight loss. Spearman correlation showed a good correlation in the measurement of RBV by BVA-100 and CLM-III in 8 out of 10 patients (r(2) = 0.64). BV measurement using BVA-100 is useful to determine absolute BV as well as changes in BV and correlates reasonably well with CLM-III measurements. Individual refilling ability can be determined as well. This may prove useful in prescribing and monitoring ultrafiltration rates, establishment of optimal BV in HD patients and reducing morbidity and mortality associated with chronic HD.

Ultra-high field 1H magnetic resonance imaging approaches for acute hypoxia

Background. Currently, radiation treatments are being optimised based on in vivo imaging of radioresistant, hypoxic tumour areas. This study aimed at detecting nicotinamide's reduction of acute hypoxia in a mouse tumour model by two clinically relevant magnetic resonance imaging (MRI) methods at ultra-high magnetic field strength. Material and methods. The C3H mammary carcinoma was grown to 200 mm3 in the right rear foot of CDF1 mice. The mice were anaesthetised with ketamine and xylazine prior to imaging. A treatment group received nicotinamide intraperitoneally (i.p.) at the dose 1000 mg/kg, and a control group received saline. MRI was performed at 16.4 T with a spatial resolution of 0.156 × 0.156 × 0.5 mm3. The imaging protocol included BOLD imaging and two DCE-MRI scans. Initial area under the curve (IAUC) and the parameters from the extended Toft's model were estimated from the DCE-MRI data. Tumour median values of 1) T2* mean, 2) T2* standard deviation, 3) DCE-MRI parameters, and 4) DCE-MRI parameter differences between scans were compared between the treatment groups using Student's t-test (significance level p < 0.05). Results. Parametric maps showed intra- and inter-tumour heterogeneity. Blood volume was significantly larger in the nicotinamide-treated group, and also the blood volume difference between the two DCE-MRI scans was significantly larger in the treatment group. Conclusion. Higher blood volume and blood volume variation was observed by DCE-MRI in the treatment group. Other DCE-MRI parameters showed no significant differences, and the higher blood volume was not detected by BOLD MRI. The higher blood volume variation seen with DCE-MRI may be influenced by the drug effect reducing over time, and furthermore the anaesthesia may play an important role.

Blood loss from laboratory diagnostic tests in children

Excessive diagnostic phlebotomy in children and critically ill patients is a frequent phenomenon in many hospitals. However, little attention is paid to a single blood volume taken routinely everyday from thousands of patients worldwide. The objective of the present study was to assess the volume of a single blood sample draw for laboratory testing in a pediatric population in relation to child age and weight, number of diagnostic tests requested by physicians, laboratory needs, and size of collection tube. A single blood volume draw for diagnostic tests was measured in 3136 consecutive routine samples taken from children (from 1 day to 18 years old) and placed into a Microvette® or regular sampling tubes. The serum excess was calculated by taking into account the serum volume needed for the requested number of tests and the dead volume of analyzer. A huge variation in blood volume draws between individual patients, regardless of the number of tests requested, has been observed. The number of blood samples placed into the microvette decreased with patients' age, with 53.9% in children younger than 1 month old and 9.3% in children older than 12 years old. There was a clear-cut increase in the mean value of the blood volume draw with an increase in children's age. Only 2% of children up to 3 years old had a blood volume draw >1 mL/kg body weight. Each pediatric laboratory should have a clear-cut recommendation on the amount on blood volume necessary for the requested number of tests.

Chromatography paper as a low-cost medium for accurate spectrophotometric assessment of blood hemoglobin concentration

Anemia affects a quarter of the world's population, and a lack of appropriate diagnostic tools often prevents treatment in low-resource settings. Though the HemoCue 201+ is an appropriate device for diagnosing anemia in low-resource settings, the high cost of disposables ($0.99 per test in Malawi) limits its availability. We investigated using spectrophotometric measurement of blood spotted on chromatography paper as a low-cost (<$0.01 per test) alternative to HemoCue cuvettes. For this evaluation, donor blood was diluted with plasma to simulate anemia, a micropipette spotted blood on paper, and a bench-top spectrophotometer validated the approach before the development of a low-cost reader. We optimized impregnating paper with chemicals to lyse red blood cells, paper type, drying time, wavelengths measured, and sensitivity to variations in volume of blood, and we validated our approach using patient samples. Lysing the blood cells with sodium deoxycholate dried in Whatman Chr4 chromatography paper gave repeatable results, and the absorbance difference between 528 nm and 656 nm was stable over time in measurements taken up to 10 min after sample preparation. The method was insensitive to the amount of blood spotted on the paper over the range of 5 μL to 25 μL. We created a low-cost, handheld reader to measure the transmission of paper cuvettes at these optimal wavelengths. Training and validating our method with patient samples on both the spectrometer and the handheld reader showed that both devices are accurate to within 2 g dL(-1) of the HemoCue device for 98% and 95% of samples, respectively.

A case of nafamostat masilate hypersensitivity with an acute and atypical change in blood volume variations during hemodialysis

A case of nafamostat masilate hypersensitivity with an acute and atypical change in blood volume variations during hemodialysis

Heart lung interactions during mechanical ventilation

To survey the recent medical literature examining studies of the hemodynamic effects of mechanical ventilation. Ventilation-induced dynamic changes in arterial pulse pressure and stroke volume variation (PPV and SVV, respectively) identify volume responsiveness. The cause of PPV and SVV are due to intrathoracic pressure-induced variations in right atrial pressure changing intrathoracic blood volume over the ventilatory cycle. This explains why PPV and SVV are inaccurate with smaller tidal volumes used in acute lung injury, but remain useful in one-lung ventilation and prone positioning. Noninvasive measures of PPV and SVV using finger plethysmography and aortic root ultrasound or estimates of intrathoracic blood volume by thoracic impedance also predict volume responsiveness. Finally, the PPV-to-SVV ratio varies with vasomotor tone and can be used to identify vasopressor need in hypotensive patients. The clinical implications of these findings are starting to be realized in recommended management principles. PPV and SVV predict volume responsiveness, but like all monitoring approaches, need to be understood within the framework of their physiologic determinations.

Intraoperative lactate levels and postoperative complications of pediatric cardiac surgery

Correlate arterial lactate levels during the intraoperative period of children undergoing cardiac surgery and the occurrence of complications in the postoperative period. Arterial lactate levels can indicate hypoperfusion states, serving as prognostic markers of morbidity and mortality in this population. Anesthesia for cardiac pediatric surgery is frequently performed on patients with serious abnormal physiological conditions. During the intraoperative period, there are significant variations of blood volume, body temperature, plasma composition, and tissue blood flow, as well as the activation of inflammation, with important pathophysiological consequences. Chart data relating to the procedures and perioperative conditions of the patients were collected on a standardized form. Comparisons of arterial lactate values at the end of the intraoperative period of the patients that presented, or not, with postoperative complications and frequencies related to perioperative conditions were established by odds ratio and nonparametric univariate analysis. After surgeries without cardiopulmonary bypass (CPB), higher levels of arterial lactate upon ICU admission were observed in patients who had renal complications (2.96 vs 1.31 mm) and those who died (2.93 vs 1.40 mm). For surgeries with CPB, the same association was observed for cardiovascular (2.90 mm × 2.06 mm), renal (3.34 vs 2.33 mm), respiratory (2.98 vs 2.12 mm) and hematological complications (2.99 vs 1.95 mm), and death (3.38 vs 2.40 mm). Elevated intraoperative arterial lactate levels are associated with a higher morbidity and mortality in low- and medium-risk procedures, with or without CPB, in pediatric cardiac surgery.

The use of a continuity equation of fluid mechanics to reduce the abnormality of the cardiovascular system: A control mechanics of the human heart

The paper is aimed at presenting the differential equations for the cardiovascular system with the help of continuity equation of fluid mechanics to reduce the abnormality of the rate of blood flow and variation of blood volume in different parts of the system. The equations are used to explain the Frank-Starling mechanism, which plays an important role in the maintenance of the stability of the distribution of blood in the system. This is a reasonable approach based on mathematical considerations as well as being further motivated by the observations that many physiologists cite optimization as a potential influence in the evolution of biological systems. We present a model as an application in the provision of a basis for developing information on steady state relations and also to study the nature of the controller and key controlling influences. The model further provides an approach for the study of complex physiological control mechanisms of the cardiovascular system and possible pathways of interaction between the cardiovascular and respiratory control systems. The study also provides an easy way for students of both physics and mathematical sciences, with no previous knowledge of human physiology, to understand the basic systems in cardiovascular concept. Key words: Continuity equations, fluid mechanics, cardio-vascular system.

Glicemia perioperatória e complicações pós-operatórias em cirurgia cardíaca pediátrica

Anesthesia for pediatric cardiac surgery is systematically performed in severely ill patients under abnormal physiological conditions. In the intraoperative period, there are significant variations in blood volume, body temperature, plasma composition, and tissue blood flow, in addition to activation of inflammation, with important consequences. Serial measurements of blood glucose levels can indicate states of exacerbation of the neuroendocrine-metabolic response to trauma, serving as prognostic markers of morbidity in that population. To correlate perioperative blood glucose levels of children undergoing cardiac surgery with the occurrence of postoperative complications, and to compare intraoperative blood glucose levels according to perioperative conditions. Information regarding the surgical/anesthetic procedure and perioperative conditions of patients was collected from the medical records. The mean perioperative blood glucose levels in the groups of patients with and without postoperative complications and the frequencies of perioperative conditions were compared by use of odds ratio and non-parametric univariate analyses. Higher intraoperative blood glucose levels were observed in individuals who had postoperative complications. Prematurity, age group, type of anesthesia, and character of the procedure did not influence the mean intraoperative blood glucose level. The use of extracorporeal circulation (ECC) was associated with higher blood glucose levels during surgery. In procedures with ECC, higher blood glucose levels were observed in individuals who had infectious and cardiovascular complications. In surgeries without ECC, that association was observed with infectious and hematological complications. Higher intraoperative blood glucose levels are associated with higher morbidity in the postoperative period of pediatric cardiac surgery.

Effect of tidal volume, intrathoracic pressure, and cardiac contractility on variations in pulse pressure, stroke volume, and intrathoracic blood volume

We evaluated the impact of increasing tidal volume (V (t)), decreased chest wall compliance, and left ventricular (LV) contractility during intermittent positive-pressure ventilation (IPPV) on the relation between pulse pressure (PP) and LV stroke volume (SV(LV)) variation (PPV and SVV, respectively), and intrathoracic blood volume (ITBV) changes. Sixteen pentobarbital-anesthetized thoracotomized mongrel dogs were studied both before and after propranolol-induced acute ventricular failure (AVF) (n=4), with and without chest and abdominal pneumatic binders to decrease chest wall compliance (n=6), and during V (t) of 5, 10, 15, and 25ml/kg (n=6). SV(LV) and right ventricular stroke volume (SV(RV)) were derived from electromagnetic flow probes around aortic and pulmonary artery roots. Arterial pressure was measured in the aorta using a fluid-filled catheter. Arterial PPV and SVV were calculated over three breaths as (max-min)/[(max+min)/2]. ITBV changes during ventilation were inferred from the beat-to-beat volume differences between SV(RV) and SV(LV). Arterial PP and SV(LV) were tightly correlated during IPPV under all conditions (r (2)=0.85). Both PPV and SVV increased progressively as V (t) increased and with thoraco-abdominal binding, and tended to decrease during AVF. SV(RV) phasically decreased during inspiration, whereas SV(LV) phasically decreased 2-3 beats later, such that ITBV decreased during inspiration and returned to apneic values during expiration. ITBV decrements increased with increasing V (t) or with thoraco-abdominal binding, and decreased during AVF owing to variations in SV(RV), such that both PPV and SVV tightly correlated with inspiration-associated changes in SV(RV) and ITBV. Arterial PP and SV(LV) are tightly correlated during IPPV and their relation is not altered by selective changes in LV contractility, intrathoracic pressure, or V (t). However, contractility, intrathoracic pressure, and V (t) directly alter the magnitude of PPV and SVV primarily by altering the inspiration-associated decreases in SV(RV) and ITBV.

Postmaximal contraction blood volume responses are blunted in obese and type 2 diabetic subjects in a muscle-specific manner

The purpose of this study was to determine whether there are differences in postisometric contraction blood volume and oxygenation responses among groups of type 2 diabetes mellitus (T2DM), obese, and lean individuals detectable using MRI. Eight T2DM patients were individually matched by age, sex, and race to non-T2DM individuals with similar body mass index (obese) and lean subjects. Functional MRI was performed using a dual-gradient-recalled echo, echo-planar imaging sequence with a repetition time of 1 s and at two echo times (TE = 6 and 46 ms). Data were acquired before, during, and after 10-s isometric dorsiflexion contractions performed at 50 and 100% of maximal voluntary contraction (MVC) force. MRI signal intensity (SI) changes from the tibialis anterior and extensor digitorum longus muscles were plotted as functions of time for each TE. From each time course, the difference between the minimum and the maximum postcontraction SI (ΔSI) were determined for TE = 6 ms (ΔSI(6)) and TE = 46 ms (ΔSI(46)), reflecting variations in blood volume and oxyhemoglobin saturation, respectively. Following 50% MVC contractions, the mean postcontraction ΔSI(6) values were similar in the three groups. Following MVC only, and in the EDL muscle only, T2DM and obese participants had ∼56% lower ΔSI(6) than the lean individuals. Also following MVC only, the ΔSI(46) response in the EDL was lower in T2DM subjects than in lean individuals. These data suggest that skeletal muscle small vessel impairment occurs in T2DM and body mass index-matched subjects, in muscle-specific and contraction intensity-dependent manners.

Effectiveness of Closed-Loop Stimulation (CLS) Function in Circulating Blood Volume Variation during Dialysis in Bradycardiac Dialysis Patients

Background: Recently we measured beat-to-beat heart rate (HR), systolic blood pressure (SBP), cardiac output (CO) and total peripheral resistance (TPR) using a cardiac function measurement device (Task Force Monitor (NIHON KOHDEN)) and reported the effectiveness of CLS function in recovering blood pressure drop during dialysis with little body motion. We reported that when SBP dropped 20 mmHg, PR increased 30 ppm responsively within about 18 seconds (29 beats). Purpose: We measured changes in HR, SBP, CO and TPR when changing the water removal rate during dialysis and evaluated the effectiveness of CLS function. Methods: We measured these variables on a beat-to-beat basis with the device for a 70-year-old female with complete atrioventricular block. The programmed pacing mode was DDD-CLS. Results: Pacemaker events during dialysis were As-Vp 3% and Ap-Vp 97%. When water removal rate was increased from 500 ml/h to 600 ml/h during dialysis, PR increased 20 ppm. Discussion: These beat-to-beat measurement results suggest that PR increased with the physiological load increase caused by circulating blood volume reduction during dialysis with little motion. Conclusion: CLS function may work effectively to control circulating blood volume variation during dialysis.

Pulmonary Blood Volume Variation Decreases after Myocardial Infarction in Pigs: A Quantitative and Noninvasive MR Imaging Measure of Heart Failure

To prospectively evaluate the usefulness of magnetic resonance (MR) imaging for estimating pulmonary blood volume (PBV) and the variation in PBV throughout the cardiac cycle in experimental heart failure. The animal care committee approved this prospective study. Seven pigs were studied before and after myocardial infarction. PBV measurement was validated in a phantom and calculated as the product of cardiac output determined with velocity-encoded MR imaging and the pulmonary transit time for an intravenous bolus of contrast material to pass through the pulmonary circulation. The difference in arterial and venous pulmonary flow during the cardiac cycle was integrated for calculation of the PBV variation (expressed as percentage of stroke volume). Differences were evaluated with the Wilcoxon test. Calculated and direct phantom measurements of PBV differed by a mean of 4% +/- 3 (standard deviation) (R(2) = 0.97, P < .001). Infarction induced a decrease in left ventricular stroke volume (44 mL +/- 6 vs 27 mL +/- 7; P = .02), ejection fraction (55% +/- 5 vs 41% +/- 4; P = .02), and PBV variation (61% +/- 12 vs 43% +/- 15; P = .04) but not PBV (225 mL +/- 23 vs 211 mL +/- 42; P = .50). The mean pulmonary artery pressure increased after infarction (19 mm Hg +/- 6 vs 27 mm Hg +/- 4; P = .04). Following infarction, the PBV variation but not PBV decreased. PBV variation was the noninvasive measure exhibiting the greatest percentage of change following infarction. MR imaging can be used to assess the variation of the PBV during the cardiac cycle as a marker of heart failure.

Rocuronium Profile During Orthotopic Liver Transplantation: Effect of Changing the Order of Vascular Clamp Release at Reperfusion of the Hepatic Graft

Background Clearance of rocuronium in the neohepatic period may be a criterion for graft function during orthotopic liver transplantation (OLT). Our goal was to demonstrate that changes in rocuronium elimination are caused mainly by variations in blood volume at reperfusion. We have explored the influence on rocuronium plasma concentrations of changing the order of vascular unclamping at graft reperfusion. Methods Thirty patients were randomized at graft reperfusion: initial arterial revascularization (IAR; n = 14) wherein the hepatic artery was released first, and initial portal revascularization (IPR; n = 16) wherein the portal vein was released first. Tracheal intubation was facilitated by rocuronium (1 mg/kg) with an infusion initiated at 0.25 mg kg −1 h −1 to maintain a response to the first stimulus of the train of four <25% of controls. Rocuronium plasma concentrations (RPC) were measured throughout the transplantation. Results No differences were observed in rocuronium consumption at different stages. RPCs decreased after reperfusion, with primarily portal unclamping responsible. In 6 patients of the IAR group and 5 patients of the IPR group, RPC at 60 minutes after reperfusion was higher than previous values. Indicators of graft dysfunction among those 11 did not differ from the other patients. Two patients in the IPR group required retransplantation without any relation to changes in RPCs. Conclusion The increase of blood flow produced by portal vein unclamping influenced RPCs; no relation was observed between RPCs and graft outcomes.

Phase II study of sunitinib and irinotecan in patients with recurrent high-grade glioma (HGG).

e12537 Background: The prognosis of patients (pts) with recurrent HGG is poor with a median survival of 3 to 6 months. To date, no second line of treatment is recognized as standard. Enhanced angiogenesis has been recognized as a marker of HGG. Antiangiogenetic agents combined to irinotecan (I) have shown major antitumor activity in recurrent HGG. Sunitinib (S) is a selective inhibitor of multiple tyrosine kinases including VEGFR and PDGFR that crosses the blood-brain barrier. We investigated the safety and activity of the combination of S and I in the treatment of pts with recurrent HGG. We also analyzed tissue expression of markers of angiogenesis and dynamic contrast enhanced magnetic resonance imaging (DCE- MRI) as predictive factors of response. Methods: A total of 30 patients with recurrent HGG were screened between April 2008 and September 2009. Eligibility criteria included ECOG PS ≤ 2, prior RT and TMZ-based CT, measurable disease. Exclusion criteria included prior antiangiogenic therapy and prior intracranial hemorrhage or other bleeding diathesis. Primary endpoint was time-to-progression (TTP) defined as progression or death. Each 6-weeks cycle consisted of S administered at a starting dose 50 mg/day for 4 weeks and I at 180 mg/sqm administered every 2 weeks. After 2 cycles, patients were evaluated clinically and by DCE-MRI. Results: 6 pts were enrolled. Median age was 48 years (range 43-53). Median number of administered cycles was 3 (range 1- 5). All pts required reduction of the starting dose of S and the median dose of S was 25 mg/day. Overall, the treatment was well tolerated with no grade III-IV adverse events. Analysis of response included stable disease (SD) in 1 pt and progressive disease (PD) in 5 pts. Median TTP and OS were 1.5 months and 3 months, respectively. All pts experienced reduction of steroid and diuretics requirements while on treatment. DCE-MRI showed correlation between variations of cerebral blood volume (rCBV) and antiangiogenic activity of S. Conclusions: In this study, the combination of S and I at the tested doses is safe but showed insufficient antitumor activity despite transient antiedema effect. A modified schedule or S dose intensification could provide clinical advantage in selected pts. No significant financial relationships to disclose.

Effect of Posture on Brain Hemodynamics in Preterm Newborns Not Mechanically Ventilated

Background: Changes in head posture influence brain hemodynamics. Optimal positioning has been recommended as 1 of 10 potentially better practices to reduce the incidence of brain injury in preterm newborns. Objectives: The aim of this study was to evaluate by near-infrared spectroscopy (NIRS) the effect of different head and body positions and the influence of gestational age (GA) and nasal continuous positive airway pressure on brain hemodynamics in very preterm newborns. Methods: 24 stable preterm newborns were studied by NIRS in 6 different postures including head rotation and head inclination in both supine and prone positions. Changes in normalized tissue hemoglobin index (nTHI) and tissue oxygenation index (TOI) were measured after posture variations. Results: No statistically significant changes in nTHI and in TOI were found in the 6 postures. nTHI variations, expression of cerebral blood volume variations, were influenced by GA. A reduction in nTHI, with a stable TOI, in the less mature infants (with GA ≤26 weeks), occurred on head rotation; nTHI increased again when the head was derotated. Conclusions: Hemodynamic changes after posture variations depend on GA. Head rotation in newborns with GA ≤26 weeks produced a reduction in nTHI with stable TOI. Possible physiopathological mechanisms are discussed.

Quantitative helical dynamic contrast enhanced computed tomography assessment of the spatial variation in whole tumour blood volume with radiotherapy in lung cancer

We aim to assess the spatial distribution of blood volume (BV) in whole lung tumours in patients undergoing radiotherapy using helical dynamic contrast enhanced computed tomography (DCE-CT), and to determine whether conventional single level, or whole tumour measurements is more representative of the vascular effects of radiotherapy. Following ethical approval and informed consent, 15 patients with histologically proven non-small cell lung cancer underwent paired helical DCE-CT studies at baseline to assess repeatability, and after two fractions of radiotherapy (9 Gy total dose). Tumour BV was calculated for individual contiguous 10 mm axial slices, and for the entire tumour volume on a pixel-per-pixel basis. Baseline tumour BV was heterogeneous varying by 15.33% ± 17.11 between adjacent 10 mm axial slices. Within subject coefficient of variation was 36.72% with conventional single tumour level evaluation, and 13.62% with whole tumour measurements. Following radiotherapy, one patient had an increase in BV greater than baseline variation (derived from the 95% limits of change) using single level evaluation; in contrast, seven patients had an increase in BV when the whole tumour was assessed. As a group, following radiotherapy, mean BV increased by 17.27% (paired t-test, p = 0.20) with single level evaluation and 19.26% ( p = 0.049) with whole tumour assessment. Tumour BV measured using DCE-CT is spatially heterogeneous. Given the slice-by-slice variation in blood volume, our results demonstrate that whole tumour DCE-CT measurements are more repeatable, and may be a better predictor of vascular changes following therapy, compared to conventional single tumour level evaluations.

Influence of postural changes on the variations of blood volume in hemodialysis and reincidence post-dialysis blood volume

The aim of the present work is to study the possible increment of blood volume, in the seated as well as the lying position, and to analyse the influence of changes of posture on the changes of blood volume during the hemodialysis. 17 patients were studied, evaluating the variations of the hematocrit in the extracorporeal circuit on entry into the dialyzer, by means of a photometric system (Crit-Line Instrument, Izasa). Every 15 minutes the values of the hematocrit were taken and heir repercussion in the blood volume in different changes of posture. Initially all of the patients improved their blood volume, both seated and lying down. During the session of hemodialysis and ultrafiltration, with the patient in a seated position, an important drop in the blood volume was noticed; this was the case in the 1st, 2nd and 3rd hours. This drop improved when the patient adopted a lying position and there was a "reincidence of post-dialysis blood volume" at the end. According to these results, the supine posture improves the refill, confirming that the patients position influences the vascular refill.

임피던스법을 이용한 혈압 및 혈류 변화량 검출 시스템 구현

본 연구에서는 혈압 측정 시 생체 임피던스가 변화하는 현상을 이용하여 혈류량 변화를 검출하는 시스템을 구현하였다. 혈압의 측정은 오실로메트릭법을 적용하였으며, MAA 알고리즘을 이용하여 평균 동맥압을 산출한 후 평균 동맥압에 대한 여러 가지 특성비율을 설정하여 수축기 및 이완기 혈압을 추정하였다. 인체 임피던스 측정은 교류 정전류원과 락인-증폭기를 이용하였으며, 측정 부위에 인가되는 커프 압력에 의해 생체 임피던스 변화량을 이용하여 혈류량 변화를 측정하였다. In this study, detection system of the blood flow variation rate was implemented using the variation effect of bio electric impedance at time of the blood pressure measurement by means of impedance method. The blood pressure measurement was performed by the oscillometric method. The mean arterial pressure was calculated using maximum amplitude algorithm. The systolic and diastolic pressure were estimated by establishment of the various characteristic ratio according to mean arterial pressure range. Alternative static current source and lock_in amplifier were introduced to impedance measurement. The variation of blood volume was measured using variation bio impedance according to induced cuff pressure at measuring area.

Repeatability of a dual gradient‐recalled echo MRI method for monitoring post‐isometric contraction blood volume and oxygenation changes

The purpose of this study was to assess the repeatability of a dual gradient-recalled echo (GRE) muscle functional MRI technique. On 2 days, subjects (n = 8) performed 10 s isometric dorsiflexion contractions under conditions of: (1) maximal voluntary contraction (MVC), (2) 50% MVC (50% MVC), or (3) 50% MVC with concurrent proximal arterial cuff occlusion (50% MVC(cuff)). Functional MRI data were acquired using single-slice dual GRE (TR/TE = 1000/6, 46 ms)-echo planar imaging for 20 s before, during, and for 180 s after each contraction. The mean signal intensity (SI) time courses at each TE (SI(6) and SI(46), reflecting variations in blood volume and %HbO(2), respectively) from the tibialis anterior (TA) and extensor digitorum longus (EDL) muscles were characterized with the post-contraction change in SI and the time-to-peak SI (DeltaSI and TTP, respectively). DeltaSI(6) following an MVC was 36% higher than that obtained after a 50% MVC (p = 0.048). For DeltaSI(6), the highest intraclass correlation coefficients (ICCs) were observed for the TA muscle in the 50% MVC and MVC conditions, with values of 0.83 (p = 0.01) and 0.88 (p = 0.005), respectively. Bland-Altman plots revealed repeatability coefficients (RCs) for the 50% MVC and MVC conditions in the TA muscle of 1.9 and 1.4, respectively. The most repeatable measures for DeltaSI(46) were obtained for the 50% MVC and MVC conditions in the EDL muscle (p = 0.01 and p = 0.04, respectively). Bland-Altman plots revealed RC's for 50% MVC and MVC conditions in the EDL muscle of 3.9 and 5.7, respectively. DeltaSI(6) and DeltaSI(46) increased as a function of the contraction intensity. The repeatability of the method depends on the muscle and contraction condition being evaluated, and in general, is higher following an MVC.