Comparison of simultaneous continuous intracranial pressure (ICP) signals from a Codman and a Camino ICP sensor

Simultaneous continuous intracranial pressure (ICP) signals from two different sensors were compared. Continuous ICP monitoring from two ICP sensors (i.e. Codman ICP MicroSensor; Johnson & Johnson, Raynham, MA and Camino OLM ICP; Camino Laboratories, San Diego, CA) placed within the brain parenchyma was performed in three patients within the intensive care unit (ICU) as part of routine management of severe subarachnoid hemorrhage. For each 6s time window mean ICP was computed, showing large differences in mean ICP values between the signals. Differences above 5 mmHg were observed in 13% of the 128,425 time windows derived from 214 h ICP recordings in these three patients. In one patient, mean ICP differed more than 10 mmHg in 23% of the time windows. Comparisons of 675,503 individual single pressure wave pairs of these 128,425 time windows revealed marginal differences in single wave amplitude (dP, i.e. pulse pressure) and latency (dT, i.e. rise time) values, suggesting that differences in mean ICP were caused by differences in baseline pressure. For the individual time windows were computed the mean wave amplitude and mean wave latency values according to a new algorithm. There were as well marginal differences between signals of mean wave amplitude and latency values. Thus, changes in baseline pressure affect mean ICP but not single pressure wave characteristics such as amplitude (dP) and (dT) latency values.     

基于大样本重症监护数据库MIMIC-Ⅲ的无创和有创血压测量一致性研究

目的血压是人体基本生命体征,是临床病情判断的重要依据之一,本文基于最新版的多参数重症监护数据库MIMIC-Ⅲ(Medical Information Mart for Intensive Care),研究比较无创和有创血压测量的一致性。方法提取了11 671例患者同时测量的226 093对无创和有创血压测量数据,采用探索性数据分析技术,从年龄和血压分层的角度对比了有创和无创测量结果的一致性,从ICU死亡率判别的角度,分析了两种方法在危重患者病情判断方面的差异性。结果收缩压在[80~120]mmHg(1 mmHg=0.133 k Pa)范围内,有创和无创测量结果的一致性较好;低于80 mmHg,无创高于有创,偏差随血压下降呈增大趋势;高于120 mmHg,无创低于有创,偏差随血压升高也呈增大趋势,Bland-Altman图显示两种测量方法存在难以消除的比例性偏倚。不同年龄分层的收缩压对照分析也呈现相同的现象。从ICU死亡率看,收缩压在低血压片段(80 mmHg)的有创和无创结果存在显著性差异,无创血压所对应的死亡率明显高于有创血压,而基于平均压的判断,无创与有创结果基本一致,在各个血压段的死亡率不存在显著性差异。结论本研究基于大样本临床数据进一步验证了示波法无创血压测量技术的局限性:在各个年龄段,正常血压范围,无创和有创测量方法差异不大,但当血压异常时(无论是高血压还是低血压),二者差异较大,且呈增大趋势;从判断预后的角度而言,无创和有创平均压的结果较一致,比收缩压更适合用于指导ICU患者的治疗。     

基于USB-4221数据采集卡的连续血压测量

针对现有连续无创血压测量系统测量结果离散程度高的问题,设计基于USB-4221数据采集卡的连续血压测量系统。通过AD8232心电传感器和指夹光电脉搏传感器同步获取心电-脉搏信号,设计心电-脉搏硬件调理电路。应用MIMIC数据库中心电-脉搏-血压信号计算脉搏传导时间,并进行回归分析,构建血压测量模型。同时,利用图形可视化工具GUI进行了用户平台的设计。系统采集了若干名志愿者的相关数据,测得的血压值与欧姆龙电子血压计HEM-8713的测量值进行对比,测量误差在±5 mmHg范围内,达到AAMI标准中对测量平均误差的要求。     

ICP measurement control: laboratory test of 7 types of intracranial pressure transducers

Intracranial pressure (ICP) monitoring has become an important parameter in the assessment of comatose patients, with raised intracranial pressure. The transducers in use have to fulfill the criteria of measurement accuracy, practicability and cost-effectiveness. However, these requirements are not always met in clinical practice. The need for ongoing quality control through independent laboratories remains. We have developed a laboratory set-up for the evaluation of intracranial pressure probes. Seven different types of currently used transducers have been tested for measurement accuracy. Under in vitro conditions 3 parameters were assessed: measurement accuracy, a 24 h drift and 10 day drifts. Tests for measurement accuracy were performed at increasing pressure levels of up to 80 mmHg. They were repeated 10 times per probe. This test allowed the simultaneous assessment of 5 different ICP probes. Drift was evaluated for 24 h and 10 days, at 6 pressure levels between 0 and 50 mmHg. Seven different types of ICP probes were tested (HanniSet, Camino, Codman, Spiegelberg, Medex, Epidyn and Gaeltec). Measurement accuracy was best with HanniSet probes. The maximum errors with this transducer were 3 mmHg. Camino and Codman showed similar results. Spiegelberg had slightly larger deviations. With Epidyn and Gaeltec the highest error were noted, up to 10 mmHg in the high pressure range. The 24 h drift was lowest with HanniSet (0.2 mmHg) and Camino (0.8 mmHg). The largest drifts were seen with Medex, Spiegelberg and Gaeltec (1.8 mmHg). Ten day drift was lowest with HanniSet (0.1 mmHg/day) and Codman (0.2 mmHg/day). The highest long-term drifts were found with Epidyn and Gaeltec (1.5 mmHg/day). Drift did not exhibit a linear pattern. After an initial rise in drift during the first 24-72 h, it decreased slowly during the next 7 days. Most ICP probes revealed measurement inaccuracy and drift. These results emphasize the necessity for ongoing evaluations of ICP probes. Therefore, tests for quality assurance are essential to establish a consistent standard of proficiency of ICP transducers.     

脉搏波波速法无创血压测量中多模量血压计算模型研究

针对脉搏波波速法无创血压测量中血压计算模型建模困难和模型计算精度较低的问题,结合T_PTT、ln(T_PTT)及(1/T_PTT)²等模量建立多模量血压计算模型。首先,利用99名随机测试者的实验数据确定多模量模型参数,并基于实验数据计算各模型性能评价指标,其中多模量血压计算模型拟合相关系数最大,为0.891,误差方差最小,仅为6.1,实验表明,多模量血压计算模型具有更好的拟合效果和更低的计算误差。然后,利用医用水银血压计和自主设计的多模量血压测量系统两种方法采集另外36名随机测试者的收缩压和舒张压数据,并计算两种方法采集数据间的相关参数,其中收缩压差值的绝对值d<6 mmHg,差值均值E_d=0.55 mmHg,差值的标准差δ_d=2.98 mmHg;舒张压差值的绝对值d<6 mmHg,差值均值E_d=0.57 mmHg,差值的标准差δ_d=3.42 mmHg,完全符合美国医疗仪器促进协会SP10-199中对电子血压计测量差值＜8 mmHg的要求。最后,采用Bland-Altman差值法,对两种方法测量数据一致性进行检验,发现舒张压与收缩压的95 %一致性界限分别为(-5.3,6.4)和(7.2,-6.2),完全在临床血压测量可接受范围之内,较好地证明多模量血压计算模型用于无创血压测量的有效性。研究结果表明,多模量血压计算模型可以应用于脉搏波波速法无创血压测量。     

Hypothermia related changes in electrocortical activity at stepwise increase of intracranial pressure in piglets.

Recent experimental studies have demonstrated that mild hypothermia can be effective in the control of intracranial hypertension. However, investigations to analyze the effects of hypothermia on changes in brain oxygen metabolism and electrocortical activity caused by increased intracranial pressure (ICP) are lacking. We examined the effects of mild hypothermia on electrocorticogram (ECoG) in combination with measurement of regional cerebral blood flow (CBF) and estimation of brain oxygen metabolism during stepwise increase of ICP. For this purpose thirteen female piglets (14 days old, 4-5 kg b.w.) were anaesthetized and mechanically ventilated. An epidural balloon was gradually inflated in order to increase ICP to 25 mmHg, 35 mmHg and 45 mmHg every 30 minutes at adjusted mean arterial blood pressures (MAP). This procedure resulted in gradual cerebral perfusion pressure (CPP) reduction of about 70%, 50%, and 30% of baseline [baseline CPP: normothermia (NT) 80+/-3 mmHg; hypothermia (HT) 84+/-3 mmHg]. Control animals were maintained in a normothermic state (38.6+/-0.2 degrees C). HT animals were surface cooled and maintained at 31.9+/-0.1 degrees C. ECoG, regional CBF, cerebral oxygen delivery (cDO2) and the cerebral metabolic rate of oxygen (CMRO2) were estimated during the normothermic period, after hypothermic stabilization, and after the gradual CPP reductions. The baseline ECoG showed the typical delta-dominated frequency pattern for isoflurane anaesthesia. At the hypothermic level, a frequency shift was seen from delta activity towards the higher frequencies (theta- and alpha activity) and the total spectral power was significantly reduced (56+/-17% from baseline, p < 0.05). the cortical CBF decreased markedly to 67+/-10% (p < 0.05), whereas the medulla oblongata blood flow increased slightly. During controlled increase of ICP by regional mass expansion from epidural balloon inflation, we found at mild and moderate stages of ICP increase (25 and 35 mmHg) only minimal changes in the ECoG in hypothermic animals compared to the hypothermic baseline, whereas the ECoG in normothermic animals showed a marked decrease in frequency, amplitude and total spectral power. We conclude that mild hypothermia produces an arousal-like ECoG activity with marked frequency shift to alpha activity and a change from high to low voltage activity. Furthermore, the hypothermic brain showed a preserved neuronal function at moderate stages of ICP. Obviously, hypothermia improves the functional tolerance of the brain to impaired oxygen supply.     

Blood pressure changes validate phase related external suction,a controlled method for stimulation of human baroreceptors

Summary Phase related external suction (PRES), a new controlled method for manipulating activity in human baroreceptors, applies precisely timed bursts of suction and pressure within the cardiac cycle through an external neck cuff. Seven healthy adult men participated in 32 pseudo-random trials of baroreceptor stimulation and inhibition. Blood pressure was assessed both intra-arterially and with a noninvasive device. In the present study, PRES baroreceptor stimulation elicited invasively measured blood pressure decreases of about 2.5 mmHg (0.33 kPa) and heart rate decreases of about 5 beats · min^–1, while baroreceptor inhibition increased invasively measured blood pressure by about 1.5 mmHg (0.20 kPa) and heart rate about 2.5 beats · min^–1. It was concluded that PRES is an effective method for baroreceptor manipulation with weaker size effect but better control of nonspecific factors in human subjects than other baroreceptor manipulation techniques. The noninvasive blood pressure measurement device was less sensitive to experimental variation than was the invasive device.     

The frequency domain versus time domain methods for processing of intracranial pressure (ICP) signals

Two methods for analyzing intracranial pressure (ICP) waveforms were compared. The frequency domain (FD) method converts the signal from the time domain to the frequency domain by a fast Fourier transform (FFT), while the time domain (TD) method calculates peak-to-peak value of the pulse waveform directly from the time samples. First, the ICP signal was regenerated from the first harmonic of the FFT and compared against the time domain raw ICP signal. We found that the FD method may underestimate pulse amplitude if there is heart rate variability or a high harmonic distortion. Second, to explore the significance in a larger data set, differences between FD- and TD-derived pulse amplitudes were determined for a total of 50,978 6-s time windows of 79 head injury patients. The mean difference in pulse pressure amplitude was 2.9 mmHg for the 50,978 6-s time windows. Differences between TD- and FD-derived pulse amplitudes were >or= 2.0 mmHg in 58.8% of the 50,978 time windows. In about 33% of time windows FD amplitudes were <2 mmHg when TD amplitudes were >or= 4 mmHg, and vice versa. Hence, the TD method is superior to the FD method for calculation of pulse amplitudes. Nevertheless, in this material both the TD and FD methods revealed significantly elevated pulse amplitudes in head injury patients with bad outcome (i.e. Glasgow Outcome Score 1-3).     

Intracranial flow patterns at increasing intracranial pressure

Summary In the course of a pilot study, changes in intracranial pressure were compared with the transcranial Doppler findings of the middle cerebral artery. The cases of five patients were discussed who developed dissociated brain death in spite of intensive therapeutic measures. The studies showed that changes of the intracranial pressure influenced the flow patterns considerably: at increasing intracranial pressure (decreasing cerebral perfusion pressure) a progressive reduction of the systolic and above all diastolic flow velocities and finally a pendular flow occurred. These changes could be recorded quantitatively by means of the Pourcelot index and the mean flow velocity. Acute changes of the intracranial pressure can be detected at an early stage by noninvasive transcranial Doppler studies and can be followed by adequate intensive therapy.Abbreviations CPP Mean cerebral perfusion pressure - ICP Intracranial pressure - MAP Mean systemic arterial pressure - MCA Middle cerebral artery - MFV Mean flow velocity - pCO₂ Carbon dioxide tension - R Index de résistance=Pourcelot index - TCD Transcranial Doppler Supported by the DFG (SFB 330)     

Continuous and noninvasive measurement of systolic and diastolic blood pressure by one mathematical model with the same model parameters and two separate pulse wave velocities

There is keen interest in continuous and noninvasive blood pressure (BP) measurement. However, many technologies have a shortcoming of complex mechanical structure. In our study, two arterial pulses are acquired by photoplethysmography (PPG) at ear and toe in order to explore a new method of measuring BP by pulse wave velocity (PWV). We previously validated and reported a BP-PWV mathematical model with measurements from humans with no evidence of cardiovascular disease, but were only able to determine PWV related to diastolic blood pressure (DBP). In this paper, we propose methods of identifying pulse transmit time (PTT) in low, normal and high systolic blood pressure (SBP) conditions. By averaging the PTT’s of incident wave and reflected wave for non-systematic error reduction, we obtain a PWV that is suitable for estimating SBP. SBP and DBP are estimated by two separate PWV’s based on the previously calibrated models. Experimental measurements are conducted on 26 subjects (age 19 ± 1 and 60 ± 1) with no evidence of cardiovascular disease. The measurement errors (Mean Deviation = 2.16 mmHg (SBP) and 1.49 mmHg (DBP); Standard Deviation = 6.23 mmHg (SBP) and 6.51 mmHg (DBP)) satisfy the accuracy criteria of Association for the Advancement of Medical Instrumentation. The results verify that SBP and DBP can be estimated by one mathematical model with the same model parameters and two separate PWV’s.     

ICP measurement control: laboratory test of 7 types of intracranial pressure transducers

Intracranial pressure (ICP) monitoring has become an important parameter in the assessment of comatose patients, with raised intracranial pressure. The transducers in use have to fulfill the criteria of measurement accuracy, practicability and cost-effectiveness. However, these requirements are not always met in clinical practice. The need for ongoing quality control through independent laboratories remains. We have developed a laboratory set-up for the evaluation of intracranial pressure probes. Seven different types of currently used transducers have been tested for measurement accuracy. Under in vitro conditions 3 parameters were assessed: measurement accuracy, a 24 h drift and 10 day drifts. Tests for measurement accuracy were performed at increasing pressure levels of up to 80 mmHg. They were repeated 10 times per probe. This test allowed the simultaneous assessment of 5 different ICP probes. Drift was evaluated for 24 h and 10 days, at 6 pressure levels between 0 and 50 mmHg. Seven different types of ICP probes were tested (HanniSet®, Camino®, Codman®, Spiegelberg®, Medex®, Epidyn® and Gaeltec®). Measurement accuracy was best with HanniSet® probes. The maximum errors with this transducer were 3 mmHg. Camino® and Codman® showed similar results. Spiegelberg® had slightly larger deviations. With Epidyn® and Gaeltec® the highest errors were noted, up to 10 mmHg in the high pressure range. The 24 h drift was lowest with HanniSet® (0.2 mmHg) and Camino® (0.8 mmHg). The largest drifts were seen with Medex®, Spiegelberg® and Gaeltec® (1.8 mmHg). Ten day drift was lowest with HanniSet® (0.1 mmHg/day) and Codman® (0.2 mmHg/day). The highest long-term drifts were found with Epidyn® and Gaeltec® (1.5 mmHg/day). Drift did not exhibit a linear pattern. After an initial rise in drift during the first 24-72 h, it decreased slowly during the next 7 days. Most ICP probes revealed measurement inaccuracy and drift. These results emphasize the necessity for ongoing evaluations of ICP probes. Therefore, tests for quality assurance are essential to establish a consistent standard of proficiency of ICP transducers.     

Chronic intracranial pressure monitoring by telemetry: Clinical experience

Intracranial pressure (ICP) monitoring is a critical measure for avoiding severe brain dysfunction or brain death by directing supportive therapy so as to prevent ICP increase severe enough to reduce cerebral blood perfusion. Such situations occur with brain swelling, increased cerebral vascular volume, and increase in cerebrospinal fluid (CSF) volume. Causes include ischemic stroke, subarachnoid bleeding, brain contusion, encephalitis (as in Reye's syndrome), and hydrocephalus from meningitis or neoplasm. When several days of ICP monitoring can direct resolution of the pressure crisis, the invasive direct connection of an intracranial sensor with external recording device carries only minimal infection risk. Prolonged ICP monitoring for weeks or months demands telemetry and becomes desirable in a number of chronic disease problems including both congenital and acquired hydrocephalus where enlarged and pressurized cerebral ventricles develop with reduced absorption of continuously secreted CSF. Although the primary disturbance in CSF circulation can remain incurable, its palliation by valve-regulated CSF diversions or shunting can restore normal brain function and in infants permit normal brain development. Missing this goal can result from failure to maintain a sufficiently normal pattern of CSF dynamics and ICP. Monitoring of the CSF pressure fluctuations transmitted through an intraventricular catheter provides the most accurate record of ICP pulsations. Therefore, a pressure sensing module can be “T'd” into an existing shunt system in continuity with the already placed ventricular tube. The capacity to monitor ICP accurately by telemetry was first established in dogs made hydrocephalic to assure free CSF pulse through a ventricular catheter (1,2,3, 4,5). The subsequent use of ICP monitoring by telemetry in three patients will be described.     

Impact of age on critical closing pressure of the cerebral circulation during dynamic exercise in humans

Limited information is available regarding cerebral vascular responses to dynamic exercise in older adults. We examined the influence of age on exercise-induced changes in the critical closing pressure (CCP) of the cerebral vasculature. Twelve young and twelve older subjects performed two bouts of steady-state cycling at low and moderate intensities (30 and 50% heart rate reserve). Mean arterial pressure (MAP), middle cerebral artery blood velocity (MCA V) and partial pressure of end-tidal carbon dioxide ( ) were measured. The CCP was estimated by linear extrapolation of pairs of systolic and diastolic blood pressure and MCA V waveforms. Exercise-induced increases in MAP were greater in older subjects (P < 0.01), while mean MCA V (MCA V(mean)) responses to exercise were similar between groups (P = 0.59). The CCP was elevated from rest during low- and moderate-intensity exercise in both groups (moderate exercise: young, +13 ± 2 mmHg and older, +22 ± 2 mmHg; P < 0.01), with the older subjects exhibiting greater increases in CCP during both exercise intensities (moderate exercise: young, +43 ± 9% rest versus older, +153 ± 45% rest; P = 0.04). In contrast, cerebral vascular conductance index (MCA V(mean)/MAP; CVCi) was only decreased during moderate exercise in older subjects (P < 0.01) and CVCi was not altered from rest in young subjects during low- or moderate-intensity cycling. No age-group differences were observed in at rest or during two intensities of exercise (P = 0.40). These data demonstrate that older subjects exhibit larger exercise-induced increases in CCP and decreases in CVCi. Thus, ageing is associated with greater increases in cerebral vascular tone during low- and moderate-intensity dynamic exercise.     

A new method for processing of continuous intracranial pressure signals

This paper describes a new method for processing of continuous pressure signals. Continuous intracranial pressure (ICP) signals were sampled at 100 Hz, converted into digital data and processed during 6s time windows. According to a new algorithm, cardiac beat-induced single ICP waves were identified; pressure waves caused by noise in the signal were rejected for further analysis. The amplitude and latency values of the accepted single ICP waves were determined. For accepted 6s time windows, the mean ICP wave was computed as mean ICP wave amplitude and mean ICP wave latency. Mean ICP for every time window was computed according to current practice as sum of pressure levels divided by number of samples. The mean ICP wave parameters provide information about the single ICP waves that is not given by mean ICP. The method has been implemented in software to be used during online ICP monitoring, revealing mean ICP wave amplitude, mean ICP wave latency and mean ICP as numerical values every 6s. The values are presented in trend plots. Verification of correct single ICP wave identification can be done during online ICP monitoring. The clinical significance of the method was illustrated in four patients by observations that mean wave amplitudes corresponded better to the acute clinical state than the mean ICP; mean wave amplitudes could be elevated despite a normal mean ICP. In one patient with ICP and arterial blood pressure (ABP) signals monitored simultaneously with identical time reference, there was a weak correlation between mean ICP and ABP wave amplitudes. It is tentatively suggested that the mean ICP wave parameters are related to intracranial pressure-volume compensatory reserve capacity (compliance).     

Changes in intracranial pressure during machine and continuous haemofiltration

Nine consecutive patients with both fulminant hepatic failure and acute oliguric renal failure were treated either by daily machine haemofiltration (MHF), or by continuous arterio-venous haemofiltration (CAVHF). Six patients received a total of twenty treatments by MHF and four CAVHF, mean duration of treatment 56 hours, range 24-160. Intracranial pressure (ICP) was measured using a subdural catheter. During treatment with MHF, the mean ICP increased from 8.9 +/- 1.4 mmHg at the start of filtration to 14.8 +/- 2.1 mmHg at the end of treatment (p less than 0.05), whereas there was no corresponding increase during the same period of time with CAVHF treatment, the mean ICP fell, but not significantly from 19.4 +/- 4.8 mmHg to 11.2 +/- 2.3 mmHg. The mean ICP increased to greater than 25 mmHg on eleven occasions during treatment with MHF, requiring treatment with bolus mannitol or propofol, during the same period of treatment with CAVHF no such surges in ICP were recorded. This suggests that continuous haemofiltration is to be preferred to intermittent machine haemofiltration in the management of patients with acute hepatorenal failure.     

Non-invasive estimation of cerebrospinal fluid pressure waveforms by means of retinal venous pulsatility and central aortic blood pressure

Current techniques used for cerebrospinal fluid pressure (CSFp) measurements are invasive. They require a surgical procedure for placement of a pressure catheter in the brain ventricles or in the brain tissue. The human eye provides direct visualisation of its physiological structures and due to its anatomical connection with CSF via the retrolaminar optic nerve it may provide accessible information about CSFp. A total of 25 subjects were included in this study. 15 subjects were used to characterise the relationship between intraocular pressure (IOP), spontaneous retinal venous pulsatility (SRVP), and CSFp. IOP was manipulated and SRVP amplitudes recorded dynamically using the dynamic vessel analyzer (DVA). The relationship between IOP and SRVP amplitude was established to estimate CSFp. Additionally Doppler blood flow velocity of the middle cerebral artery and arterial blood pressure (ABP) were acquired for all subjects. This was to compare and validate our findings with an alternative approach (ICM+) which uses these values to estimate CSFp. A CSFp waveform was extracted from central blood pressure (CBP) waveform by removing its cardiac component frequency. Furthermore to calibrate the CSFp to CBP waveform ratio, invasive CSFp, and ABP was measured from 10 subjects with brain tumours who had a range of normal to elevated CSFp (i.e., 0-30 mmHg). Results show good agreement between the two methods (correlation r (2) = 0.55) Mean estimated CSFp for the two techniques did not show any significant difference (p > 0.05). A significant correlation between CBP pulse (CBPp) and invasive CSFp pulse (CSFpp) was observed (i.e., CSFpp = 0.0654CBBp + 3.91, p < 0.01). Estimated CSFpp was calibrated to CBPp according to this relation. In conclusion, the study demonstrated a good correlation between two different methods of estimating CSFp non-invasively and may provide a novel method to estimate CSF waveforms non-invasively.     

Long-term pressure monitoring with arterial applanation tonometry: a non-invasive alternative during clinical intervention?

Arterial tonometry is a non-invasive technique for continuous registration of arterial pressure waveforms. This study aims to assess tonometric blood pressure recording (TBP) as an alternative for invasive long-term bedside monitoring. A prospective study was set up where patients undergoing neurosurgical intervention were subjected to both invasive (IBP) and non-invasive (TBP) blood pressure monitoring during the entire procedure. A single-element tonometric pressure transducer was used to better investigate different inherent error sources of TBP measurement. A total of 5.7 hours of combined IBP and TBP were recorded from three patients. Although TBP performed fairly well as an alternative for IBP in steady state scenarios and some short-term variations, it could not detect relevant long-term pressure variations at all times. These findings are discussed in comparison to existing work. Physiological alterations at the site of TBP measurement are highlighted as a potentially important source of artifacts. It is concluded that at this point arterial tonometry remains not enough understood for long-term use during a delicate operative procedure. Physiological changes at the TBP measurement site deserve further investigation before tonometry technology is to be considered as an non-invasive alternative for long-term clinical monitoring.     

Thirty-minute compared to standardised office blood pressure measurement in general practice

Background

Although blood pressure measurement is one of the most frequently performed measurements in clinical practice, there are concerns about its reliability. Serial, automated oscillometric blood pressure measurement has the potential to reduce measurement bias and white-coat effect''

Aim

To study agreement of 30-minute office blood pressure measurement (OBPM) with standardised OBPM, and to compare repeatability

Design and setting

Method comparison study in two general practices in the Netherlands

Method

Thirty-minute and standardised OBPM was carried out with the same, validated device in 83 adult patients, and the procedure was repeated after 2 weeks. During 30-minute OBPM, blood pressure was measured automatically every 3 minutes, with the patient in a sitting position, alone in a quiet room. Agreement between 30-minute and standardised OBPM was assessed by Bland–Altman analysis. Repeatability of the blood pressure measurement methods after 2 weeks was expressed as the mean difference in combination with the standard deviation of difference (SDD)

Results

Mean 30-minute OBPM readings were 7.6/2.5 mmHg (95% confidence interval [CI] = 6.1 to 9.1/1.5 to 3.4 mmHg) lower than standardised OBPM readings. The mean difference and SDD between repeated 30-minute OBPMs (mean difference = 3/1 mmHg, 95% CI = 1 to 5/0 to 2 mmHg; SDD 9.5/5.3 mmHg) were lower than those of standardised OBPMs (mean difference = 6/2 mmHg, 95% CI = 4 to 8/1 to 4 mmHg; SDD 10.9/6.3 mmHg).

Conclusion

Thirty-minute OBPM resulted in lower readings than standardised OBPM and had a better repeatability. These results suggest that 30-minute OBPM better reflects the patient''s true blood pressure than standardised OBPM does.     

Bayesian fusion algorithm for improved oscillometric blood pressure estimation

A variety of oscillometric algorithms have been recently proposed in the literature for estimation of blood pressure (BP). However, these algorithms possess specific strengths and weaknesses that should be taken into account before selecting the most appropriate one. In this paper, we propose a fusion method to exploit the advantages of the oscillometric algorithms and circumvent their limitations. The proposed fusion method is based on the computation of the weighted arithmetic mean of the oscillometric algorithms estimates, and the weights are obtained using a Bayesian approach by minimizing the mean square error. The proposed approach is used to fuse four different oscillometric blood pressure estimation algorithms. The performance of the proposed method is evaluated on a pilot dataset of 150 oscillometric recordings from 10 subjects. It is found that the mean error and standard deviation of error are reduced relative to the individual estimation algorithms by up to 7 mmHg and 3 mmHg in estimation of systolic pressure, respectively, and by up to 2 mmHg and 3 mmHg in estimation of diastolic pressure, respectively.     

Non-invasive,minute-to-minute estimates of systemic arterial pressure and pulse pressure variation using radial artery tonometry

Abstract

The Tensys T-line uses tonometry to reproduce the arterial blood pressure tracing non-invasively. The purpose of this study was to assess the agreement between estimates of the T-line and an intra-arterial catheter (for both mean arterial pressure [MAP] and pulse pressure variation [PPV]) in the setting of spine surgery. Continuous blood pressure data were collected for 7507 minutes from 25 patients. Five increasingly aggressive T-line filters were applied. The mean bias for mean, diastolic and systolic blood pressure ranged from 3.4–6.4, 3.1–7.1 and 0.1–0.8?mmHg and 6.5–11.8% for PPV. Ninety-five per cent confidence intervals for mean, diastolic and systolic blood pressure ranged from 24–28, 23.1–24.7 and 33.4–35.6?mmHg for 14–21% for PPV. The limits of agreement preclude the use of the T-line for reliable estimation of MAP or PPV in spine surgery.