Simple and accurate way for estimating total and segmental arterial compliance: The pulse pressure method

We derived and tested a new, simple, and accurate method to estimate the compliance of the entire arterial tree and parts thereof. The method requires the measurements of pressure and flow and is based on fitting the pulse pressure (systolic minus diastolic pressure) predicted by the two-element windkessel model to the measured pulse pressure. We show that the two-element windkessel model accurately describes the modulus of the input impedance at low harmonics (0–4th) of the heart rate so that the gross features of the arterial pressure wave, including pulse pressure, are accounted for. The method was tested using a distributed nonlinear model of the human systemic arterial tree. Pressure and flow were calculated in the ascending aorta, thoracic aorta, common carotid, and iliac artery. In a linear version of the systemic model the estimated compliance was within 1% of the compliance at the first three locations. In the iliac artery an error of 7% was found. In a nonlinear version, we compared the estimates of compliance with the average compliance over the cardiac cycle and the compliance at the mean working pressure. At the first three locations we found the estimated and “actual” compliance to be within 12% of each other. In the iliac artery the error was larger. We also investigated an increase and decrease in heart rate, a decrease in wall elasticity and exercise conditions. In all cases the estimated total arterial compliance was within 10% of mean compliance. Thus, the errors result mainly from the nonlinearity of the arterial system. Segmental compliance can be obtained by subtraction of compliance determined at two locations.     

Computing total arterial compliance of the arterial system from its input impedance

The total arterial compliance of the arterial system was computed from its input impedance by expressing the impedance in terms of its frequency-response vector diagram (f.r.v.) The f.r.v. plot of a 3-element windkessel subjected to random pacing follows, theoretically, a circular path. Since the windkessel model serves as a good approximation for the arterial system, we have used the simple properties of its f.r.v. plot to obtain the compliance, which is otherwise normally determined from the peripheral resistance and the time constant of the diastolic pressure decay. The arterial compliance can also be determined from the impulse response function of the arterial system. Data obtained from dog experiments during no intervention, aortic occlusion and during occlusion of both carotid arteries have been analysed.     

Estimation of arterial compliance in aortic regurgitation: three methods evaluated in pigs

Three methods for measuring arterial compliance when aortic regurgitation is present are examined. The first two methods are based on a Windkessel model composed of two elements, compliance C and resistance R. Arterial compliance was estimated from diastolic pressure waveforms and diastolic regurgitant flow for one method, and from systolic aortic pressure waveforms and systolic flow for the other method. The third method was based on a three-element Windkessel model, composed of characteristic resistance r, compliance C and resistance R. In this method arterial compliance was calculated by adjusting the model to the modulus and phase of the first harmonic term of the aortic input impedance. The three methods were compared and validated in six anaesthetised pigs over a broad range of aortic pressures. The three methods were found to give quantitatively similar estimates of arterial compliance at mean aortic pressures above 60 mm Hg. Below 60 mm Hg, estimates of arterial compliance varied widely, probably because of poor validity of the Windkessel models in the low pressure range.     

Use of non-invasive finger blood pressure monitoring in the estimation of aortic pressure at rest and during the Mueller manoeuvre.

The aim of this investigation was to evaluate whether reliable estimates of aortic pressure can be derived using non-invasive finger blood pressure monitoring. Finger blood pressure (Ohmeda 2300 Finapres device; Finapres, Englewood, CO) was compared with simultaneous ascending aortic pressure measured with a catheter-transducer system both at rest and during acute negative intrathoracic pressure (the Mueller manoeuvre). Thirty-eight patients aged 17-73 years were studied. All were undergoing routine diagnostic or therapeutic cardiac catheterization. Beat-to-beat values of systolic, diastolic and mean non-invasive finger and invasive aortic blood pressure were measured at rest and factors which might have an influence on the difference between methods were examined. The mean finger-aortic difference was +5 +/- 14 mmHg for systolic, -2 +/- 7 mmHg for diastolic, -5 +/- 8 mmHg for mean and +6 +/- 13 mmHg for pulse pressure. In multivariate linear regression analysis, the difference in systolic pressure was related to aortic systolic pressure (standardized coefficient beta = -0.33, P = 0.01), heart rate (beta = 0.49, P < 0.000), age (beta = -0.29, P < 0.025) and height (beta = 0.40, P < 0.005). The linear regression equations to derive resting aortic pressures from the non-invasive finger pressure readings had correlation coefficients between 0.83 and 0.87 and standard errors of estimate between 6 and 14 mmHg. During the Mueller manoeuvre, Finapres reproduced average pressure changes reliably compared with intra-aortic pressure. Due to moderate inter-individual variation in the finger-aortic differences the correlation coefficients ranged from 0.83 to 0.93 and the standard errors of estimate from 3 to 6 mmHg. Non-invasive finger blood pressure monitoring could be used to estimate central aortic mean and diastolic blood pressure fairly reliably at rest, but with respect to systolic pressure the variance in finger-aortic difference was marked. The average intra-aortic pressure changes caused by the Mueller manoeuvre were reliably reproduced by the Finapres device.     

A sensitivity analysis of a personalized pulse wave propagation model for arteriovenous fistula surgery. Part A: Identification of most influential model parameters

Previously, a pulse wave propagation model was developed that has potential in supporting decision-making in arteriovenous fistula (AVF) surgery for hemodialysis. To adapt the wave propagation model to personalized conditions, patient-specific input parameters should be available. In clinics, the number of measurable input parameters is limited which results in sparse datasets. In addition, patient data are compromised with uncertainty. These uncertain and incomplete input datasets will result in model output uncertainties. By means of a sensitivity analysis the propagation of input uncertainties into output uncertainty can be studied which can give directions for input measurement improvement. In this study, a computational framework has been developed to perform such a sensitivity analysis with a variance-based method and Monte Carlo simulations. The framework was used to determine the influential parameters of our pulse wave propagation model applied to AVF surgery, with respect to parameter prioritization and parameter fixing. With this we were able to determine the model parameters that have the largest influence on the predicted mean brachial flow and systolic radial artery pressure after AVF surgery. Of all 73 parameters 51 could be fixed within their measurement uncertainty interval without significantly influencing the output, while 16 parameters importantly influence the output uncertainty. Measurement accuracy improvement should thus focus on these 16 influential parameters. The most rewarding are measurement improvements of the following parameters: the mean aortic flow, the aortic windkessel resistance, the parameters associated with the smallest arterial or venous diameters of the AVF in- and outflow tract and the radial artery windkessel compliance.     

Implication of the systolic hump in systemic arterial pressure waves

The systolic hump in the aortic blood pressure wave is defined as the aorticresistance component proportional to the aortic blood flow superimposed on the windkessel component. An electrical analogue comprising a series resistance (aortic resistance) plus a resistance (peripheral resistance) and capacitance (aortic compliance) in parallel (i.e. windkessel component) is used for analysis. Curve fitting using the leastsquares method is performed on calculated and measured blood pressure waves from dogs under haemodynamical conditions induced by infusion of three drugs (noradrenaline, isoproterenol and acetylcholine). The curve fitting RMS (root mean square) errors are <3% for blood pressure waves and <30% for blood flow waves, with good agreement between measured and calculated blood flow waveforms. Infusion of noradrenaline and acetylcholine is found to induce a significant decrease and increase in the aortic resistance, respectively. Although only a small fraction of the blood pressure wave, the systolic hump has a marked effect on the systolic pressure waveform.     

Arterial compliance is an independent factor predicting acute hemodynamic performance of intra-aortic balloon counterpulsation

Data concerning the effect of arterial compliance (AC) on hemodynamics during intraaortic balloon counterpulsation (IABC) are lacking. This study examines the effect of AC on acute hemodynamics induced by IABC in 15 patients with post-infarction cardiogenic shock. AC was estimated by aortic pulse wave analysis using the reflection time index (RTI). Measurements were obtained once per day during IABC. The % reduction in systolic aortic pressure (ASAP), end-diastolic aortic pressure (AEDAP) and the peak aortic diastolic augmentation (PADA) were used as performance indices of IABC; 107 sets of measurements were obtained. Multivariate analysis indicated an independent association of each IABC performance index with AC (p<0.05). A high AC group (RTI< or =20.6%, n=40) and a low AC group (RTI>20.6%, n=67) were obtained. DeltaSAP deltaEDAP and PADA were significantly higher in the low AC group by almost 75%, 54.6% and 11.3% (p<0.03), while arterial blood pressure did not significantly differ. Arterial compliance is an independent factor affecting hemodynamics during IABC. RTI values higher than 20.6% may predict a better acute hemodynamic response to IABC.     

Non-invasive measurement of pulmonary arterial pressure: II. A radionuclide method

Pulmonary artery pulse pressure (PP) and diastolic pressure (Pd) may be obtained by applying a haemodynamic model of blood flow kinetics and wall mechanics to the pulmonary artery: Pp = rho(ws/(Ss/Sd-1))2log(Ss/Sd)-1/2 rho w2s Pd = (Sd/Ss)1/2Pp where rho is blood density, ws is peak ejection velocity, and Ss and Sd are peak maximal and end diastolic cross-sectional areas of the main pulmonary artery. The different parameters of the equations were measured from radionuclide first pass and equilibrium studies. Radionuclide first pass studies were performed in 24 patients with intravenous injection of 20 mCi of 99Tcm red blood cells with a gamma camera in a 20 degrees right anterior oblique position: data were collected in list mode, i.e. a continuous sequence of spatial and temporal coordinates of each photon. Pulmonary arterial pressure was recorded simultaneously with a microtip catheter during the first pass study. Gated first pass images of the right side of the heart were reconstructed, regions of interest drawn over the right ventricle and the main pulmonary artery (MPA) and time-activity curves generated. Peak systolic (Cs) and end diastolic (Cd) counts obtained from the MPA curve were proportional to the cross sections Ss and Sd of the MPA and Ss/Sd = Cs/Cd. The diameter (D) of the pulmonary artery was calculated as the distance between the two zeros of the second derivative of a cross-sectional profile. The averaged cross-sectional area was S = pi D2/4. ECG gated blood pool studies were performed in a LAO 40 degrees position when the tracer was at equilibrium; they were processed automatically and the right ventricular end diastolic counts (EDC) converted into volume (EDV) using an aortic volume/count ratio. Right ventricular peak ejection rate (PER) was obtained from the RV time-activity curve and the instantaneous peak ejection velocity was calculated, ws = PER X EDV/S X EDC. PP and Pd were calculated in mmHg and the radionuclide method yielded pressure values that correlated reasonably with catheterisation values: PP(rad) = 0.99 PP(cath)-0.55, r = 0.84 and Pd(rad) = 0.67 Pd(cath) + 4.91, r = 0.74. We conclude that radionuclide techniques can provide a non-invasive method based on a haemodynamic model for measuring pulmonary arterial pressure.     

Assessment of aortic pressure power components and their link to overall elastic and resistive arterial properties

This paper reviews the analytical expressions for in-phase and quadrature aortic power components associated with the real and imaginary parts of aortic input admittance, respectively. It is shown that active power Wact, and its steady, Wstdy, and pulsatile, Wpuls, components logically follow from in-phase power. Reactive power follows from quadrature power only for sinusoidal signals. The definition of reactive power indexes for real aortic pressures and flows requires extreme care. The link between overall arterial properties and pressure power components (and indexes) is investigated, making use of a three-element windkessel model and ascending aortic pressure and flow data taken from eight anaesthetised dogs, under basal state and after treatment with a vasoconstrictor (methoxamine). Seven dogs are normotensive in the baseline state (NBA cases, n = 7), the average (+/- SE) of mean pressure being 86.5 +/- 5.2 mmHg. The eighth dog has a baseline mean pressure of 134 mmHg and is considered to be hypertensive. The two experimental cases from this dog are grouped with those from the other seven dogs after vasoconstriction, to form the NVC + H group (n = 9). On average, fitting the model to the experimental data yields a 100% increase (p < 0.05) in total peripheral resistance, a 63% decrease (p < 0.01) in total arterial compliance and a 10% decrease (p > 0.05) in aortic characteristic impedance, from the NBA group to the NVC + H. Correspondingly, the peak-to-peak amplitude of quadrature power shows a 69% increase (p < 0.02). Wact, Wstdy, and Wpuls show a 28% increase (p > 0.05), a 40% increase (p < 0.02) and a 43% decrease (p > 0.05), respectively. Energetic efficiency of the arterial system, Eart = 1 - (Wpuls/Wact), increases by 8% (p < 0.02). From analysis of the estimates of power components and arterial parameters in relation to low-frequency phase angles of aortic impedance, it is concluded that the decrease in total arterial compliance with increasing pressure reduces the power lost in pulsation. This happens at the expense of an increase in quadrature power and absolute values of related reactive power indexes.     

Application of art,science and gumption in the care of the disabled

Non-invaswe oscillometric blood pressure and pulse measured by an Omron HEM-703CP monitor were compared with arterial values obtained from direct measurements of the radial artery. An excellent correlation and agreement was found between the two methods (systolic r=0.99; diastolic r=0.97; pulse r=0.99), although there was some variability among individual subjects. The range of difference between them was 0 to l. mmHg for systolic and—6 to + 5mmHg for diastolic pressures. When tested on the bench using the Metron QA-1280 non-invasive blood pressure analyser the HEM-703CP monitor rarely exhibited errors exceeding 2–3 mmHg over a measurement range of 50–200 mmHg.     

Systolic Hypertension Mechanisms: Effect of Global and Local Proximal Aorta Stiffening on Pulse Pressure

Decrease in arterial compliance leads to an increased pulse pressure, as explained by the Windkessel effect. Pressure waveform is the sum of a forward running and a backward running or reflected pressure wave. When the arterial system stiffens, as a result of aging or disease, both the forward and reflected waves are altered and contribute to a greater or lesser degree to the increase in aortic pulse pressure. Two mechanisms have been proposed in the literature to explain systolic hypertension upon arterial stiffening. The most popular one is based on the augmentation and earlier arrival of reflected waves. The second mechanism is based on the augmentation of the forward wave, as a result of an increase of the characteristic impedance of the proximal aorta. The aim of this study is to analyze the two aforementioned mechanisms using a 1-D model of the entire systemic arterial tree. A validated 1-D model of the systemic circulation, representative of a young healthy adult was used to simulate arterial pressure and flow under control conditions and in presence of arterial stiffening. To help elucidate the differences in the two mechanisms contributing to systolic hypertension, the arterial tree was stiffened either locally with compliance being reduced only in the region of the aortic arch, or globally, with a uniform decrease in compliance in all arterial segments. The pulse pressure increased by 58% when proximal aorta was stiffened and the compliance decreased by 43%. Same pulse pressure increase was achieved when compliance of the globally stiffened arterial tree decreased by 47%. In presence of local stiffening in the aortic arch, characteristic impedance increased to 0.10 mmHg s/mL vs. 0.034 mmHg s/mL in control and this led to a substantial increase (91%) in the amplitude of the forward wave, which attained 42 mmHg vs. 22 mmHg in control. Under global stiffening, the pulse pressure of the forward wave increased by 41% and the amplitude of the reflected wave by 83%. Reflected waves arrived earlier in systole, enhancing their contribution to systolic pressure. The effects of local vs. global loss of compliance of the arterial tree have been studied with the use of a 1-D model. Local stiffening in the proximal aorta increases systolic pressure mainly through the augmentation of the forward pressure wave, whereas global stiffening augments systolic pressure principally though the increase in wave reflections. The relative contribution of the two mechanisms depends on the topology of arterial stiffening and geometrical alterations taking place in aging or in disease.     

Non-invasive measurement of pulmonary arterial pressure: I. A haemodynamic modelling approach

In order to monitor pulmonary arterial pressure (P) by any non-invasive imaging technique, a haemodynamic model of blood flow kinetics and wall mechanics has been developed. It is a one-dimensional model of pulsatile flow in an elastic pulmonary arterial trunk, assuming that blood is an incompressible fluid and viscous effects are negligible. The equations are P(t)-Pd = rho c2lnS(t)/Sd-1/2pw-2(t) Pd = (Sd/Ss)1/2Pp where, at any time of the ejection phase of systole, P(t), S(t) and w(t) are the pulmonary arterial pressure, cross-sectional area of the pulmonary artery and blood velocity averaged on the cross section S, respectively, PP is the pulse pressure, the difference between the peak systolic pressure and the diastolic pressure Pd; rho is blood density, c pulse wave velocity, and Ss and Sd are maximum (systolic) and minimum (diastolic) values of the cross-sectional area S. Using these equations, P(t) can be calculated if the three parameters, i.e. c, S(t) and w(t) are measured. So far, it has been impossible to measure the pulse wave velocity c non-invasively. We have investigated the calculation of c from S(t) and w(t) using the equation of continuity in the absence and presence of reflected pressure waves. The hypotheses of the haemodynamic model are discussed.     

Influence of central and peripheral changes on the hydraulic input impedance of the systemic arterial tree

The input impedance of the systemic arterial tree of the dog has been computed by Fourier analysis. It was shown that a distance between pressure and flow transducers of less than 2 cm results in appreciable errors which manifest themselves mainly in the phase of the input impedance. The input impedance for controls, occlusions at various locations in the aorta, and an increase and decrease of peripheral resistance were studied. For the same experiments, the total arterial compliance was calculated from the peripheral resistance of the diastolic aortic-pressure curve. The characterstic impedance of the ascending aorta was also estimated. The impedance in the control situation may be modelled by means of a 3-element Windkessel consisting of a peripheral resistance and (total) arterial compliance, together with a resistance equal to the characteristic impedance of the aorta. The occlusions of the aorta show that blockage at (and beyond) the trifurcation do not result in a detectable change in input impedance, except for a slight increase of the peripheral resistance. The more proximal an aortic occlusion, the more effect it has on the pattern of the input impedance. When the aorta is occluded at the diphragm, or higher, the single (uniform) tube appears to be a much better model than the Windkessel. Occlusion of one or both carotid arteries increases the mean pressure; consequently not only the peripheral resistance increases but also the total arterial compliance decreases. The Windkessel with increased peripheral resitance and decreased compliance is again a good model. After a sudden release of occlusion of the aorta, the arterial system has a low peripheral resistance and may also be modelled by the Windkessel.     

Noninvasive determination of arterial compliance

When the cuff pressure exerted on the upper arm is released from suprasystolic pressure to diastolic pressure, a group of changing pulse waves can be recorded by an experimental apparatus. Using pulse wave analysis, information on the volume change together with the pressure increments can be obtained, and then the arterial compliance index can be calculated. The arterial compliance index is used to express the arterial compliance. Clinical trials show that the arterial compliance index of the hypertensive patient group is much lower than that of the normal subject group (P<0·001). The decrease of the arterial compliance is consistent with the worsening condition of retinal arteriosclerosis lesions in hypertensive patients. The increases in age and systolic pressure are accompanied by a decrease of the arterial compliance. This method is very simple, noninvasive and ready for clinical application.     

基于示波法和光电容积脉搏波描记法的动脉顺应性动态检测仪

目的针对目前静态检测方法血压依赖性造成的敏感性不足和需要血压校正的问题，找到一种对动脉亚临床病变引起的弹性减退更敏感且无需血压校正的指标。并设计一种适用于家庭和社区诊所的新型动脉顺应性动态检测仪器。方法对动脉加压导致了透壁压减小和顺应性非线性增加，同时也导致了脉搏波传递时间（pulse transitt ime，Prr）非线性增大。基于示波法血压测量和光电容积脉搏波描记法（photoelectric plethysmography，PPG）设计了检测仪器,实现了对肱动脉加压动态检测。并在不同透壁压下对高血压组和对照组脉搏波传递时间增量进行测量。结果由高到低预设3个透壁压。即8．00、6．67、5．33kPa（60、50、40mmHg），加压所导致的高血压组PTT增量总体均值和标准差分别为（3．7±2．1）、（8．5±3．2）、（13．1±3．5）ms，而对照组相应的总体均值和标准差分别为（5．4±2．2）、（12．5±2．8）、（19．3±3．1）ms。在相同透壁压下，两组之间差异有统计学意义（P〈0．01）。实验结果表明，随着透壁压的减小，虽然两组脉搏波传递时间均增加。但两组的差异也越来越大。选择透壁压为5．33kPa（40mmHg）时脉搏波传递时间增量△PTY40为更敏感的动脉弹性指标，它与收缩压负相关（r=-0．73，P〈0．01），与舒张压负相关（r=-0．54，P〈0．01），与脉压负相关（r=-0．49，P〈0．01）。结论虽然△PTT40具有明显的血压相关性，但它是动态检测的结果，通过对动脉施加外在作用力，拉大了高血压中、低危险患者与健康人之间的组间统计学差异．能够更敏感地分辨动脉亚临床病变引起的动脉弹性减退,比较好地解决了静态检测方法血压依赖性造成的敏感性不足和需要血压校正的问题。所设计的仪器操作简便，有望在早期的动脉亚临床病变的诊断及监测方面发挥作?     

Changes in central artery blood pressure and wave reflection during a cold pressor test in young adults

The relative contribution of sympathetic nervous system (SNS)-induced increase in peripheral vascular resistance on central artery blood pressure (BP) and aortic wave reflection (augmentation index; AIx) is not completely understood. Central BP and wave reflection characteristics were measured using radial artery applanation tonometry before, during a 3-min cold pressor test (CPT), and 90 and 180-s post-CPT in 15 young, healthy adults (25 +/- 1 years). The CPT resulted in a greater magnitude of change in the estimated aortic systolic (31 vs. 23%, P < 0.05) and pulse (31 vs. 13%, P < 0.05) BP compared with the change in brachial artery BP. Additionally, the CPT resulted in an increased mean arterial pressure (MAP) (P < 0.05) and AIx (10 +/- 2 vs. 26 +/- 2%, P < 0.05). The change in MAP during the CPT was correlated to the change in AIx (r = 0.73, P < 0.01) and inversely related to roundtrip duration of the reflected wave to the periphery and back (r = -0.57, P < 0.05). The present study suggests that cold pressor testing results in a significant increase in arterial wave reflection intensity, possibly due to an increased MAP. However, the greater increase in systolic and pulse BP in the central compared with the peripheral circulation suggests that increased central artery wave reflection intensity contributes to increased left ventricular myocardial oxygen demand during CPT-induced hypertension.     

Identification of the three-element windkessel model incorporating a pressure-dependent compliance

A new one-step computational procedure is presented for estimating the parameters of the nonlinear three-element windkessel model of the arterial system incorporating a pressure-dependent compliance. The data required are pulsatile aortic pressure and flow. The basic assumptions are a steadystate periodic regime and a purely elastic compliant element. By stating two conditions, zero mean flow and zero mean power in the compliant element, peripheral and characteristic resistances are determined through simple closed form formulas as functions of mean values of the square of aortic pressure, the square of aortic flow, and the product of aortic pressure with aortic flow. The pressure across as well as the flow through the compliant element can be then obtained so allowing the calculation of volume variation and compliance as functions of pressure. The feasibility of this method is studied by applying it to both simulated and experimental data relative to different circulatory conditions and comparing the results with those obtained by an iterative parameter optimization algorithm and with the actual values when available. The conclusion is that the proposed method appears to be effective in identifying the three-element windkessel even in the case of nonlinear compliance.     

Validation of a new noninvasive method to measure blood pressure and assess baroreflex sensitivity in preterm infants during sleep

STUDY OBJECTIVES: Accuracy and precision of a noninvasive device for continuously measuring blood pressure (BP) (Finometer, FMS, The Netherlands) during sleep was assessed in preterm infants. DESIGN: Absolute BP beat-to-beat values, interbeat changes, measurement precision, and baroreflex sensitivity were compared with BP measurements from intraarterial catheters. PARTICIPANTS: Ten preterm infants (gestational age 27-36 weeks; birth weight 964-2620 gm) were studied in the neonatal intensive care unit. MEASUREMENTS AND RESULTS: The 2 modes of BP measurement were compared in 2-minute epochs (n = 10-12/infant). Mean arterial pressure, systolic arterial pressure, and diastolic arterial pressure were analyzed beat to beat, and baroreflex sensitivity was assessed using spontaneous sequence analysis. Mean differences for absolute BP (mm Hg) were as follows: mean arterial pressure, 3 (limits of agreement, -1 to 8); systolic arterial pressure, -4 (-8 to 1); and diastolic arterial pressure, 7 (4 to 10). Mean differences and limits of agreement for interbeat changes were essentially 0 for mean arterial pressure, systolic arterial pressure, and diastolic arterial pressure. Precision (+/- 95% confidence intervals, mm Hg) for the Finometer were mean arterial pressure +/- 7, systolic arterial pressure +/- 8, and diastolic arterial pressure +/- 6. Precision was greater for the arterial catheter (mean arterial pressure +/- 3, systolic arterial pressure +/- 4, and diastolic arterial pressure +/- 4). Baroreflex sensitivity calculated from the Finometer BP was (mean +/- SEM, ms/mm Hg) 1.74 +/- 0.23 and, from the catheter system, BP was 1.56 +/- 0.21 (p value NS). CONCLUSIONS: The Finometer provides accurate measurements of beat-to-beat BP and baroreflex sensitivity. The ability to continuously measure BP and baroreflex sensitivity during sleep in infants may provide vital clues into pathologic conditions associated with impaired autonomic control during sleep.     

容积型指脉波图监测及评价体外反搏效果的对照研究

对２０ 名男性健康志愿者采用经桡动脉穿刺置管主动脉根部测压的方法,分别研究不同反搏工作参数对主动脉压力和指脉波的影响。结果反搏时主动脉舒张压随储气罐压力的增加升高（最高可达１６８．５６ ｍ ｍ Ｈｇ）;主动脉舒张波的ｄｐ／ｄｔ值均逐渐上升,但收缩波的ｄｐ／ｄｔ值则呈下降趋势;指脉舒张波起点与主动脉舒张波起点比较平均滞后（１０８．２０±２５．７０） ｍ ｓ,而指脉收缩波起点则平均滞后（９６．６９±３８．７０） ｍ ｓ;指脉波的Ｄ／Ｓ比值与主动脉压力波的Ｄ／Ｓ比值随反搏储气罐压力的增加而同步增加,并由直线回归分析得出动脉Ｄ／Ｓ比值（Ｙ）与指脉Ｄ／Ｓ比值（Ｘ）的回归方程式Ｙ＝ ０．３７６＋ ０．４５７Ｘ。本研究指示体外反搏对动脉压力波的Ｄ／Ｓ比值、舒张压及其ｄｐ／ｄｔ值均有显著影响,指脉波仍然是目前调节反搏工作参数及监测反搏效果的较为安全、可靠的方法     

Pulse Oximetry Wave Variation as a Noninvasive Tool to Assess Volume Status in Cardiac Surgery

OBJECTIVE:

To compare variations of plethysmographic wave amplitude (ΔPpleth) and to determine the percent difference between inspiratory and expiratory pulse pressure (ΔPp) cutoff values for volume responsiveness in a homogenous population of postoperative cardiac surgery patients.

INTRODUCTION:

Intra-thoracic pressure variations interfere with stroke volume variation. Pulse pressure variations through arterial lines during mechanical ventilation have been recommended for the estimation of fluid responsiveness. Pulse oximetry may offer a non-invasive plethysmographic method to evaluate pulse pressure; this may be useful for guiding fluid replacement.

METHODS:

Controlled, prospective study in cardiac surgery patients under controlled ventilation. Simultaneous digital recordings of arterial pressure and plethysmographic waves were performed. ΔPp, systolic pressure (ΔPs), ΔPpleth, and systolic component (ΔSpleth) were calculated. A ΔPp ≥ 13% identified fluid-responsive patients. Volume expansion was performed in responsive subjects. Systolic and amplitude components of pressure and plethysmographic waves were compared.

RESULTS:

In 50 measurements from 43 patients, ΔPp was correlated with (Ppleth (r=0.90, p<0.001), (Ps (r=0.90, p<0.001), and (Spleth (r=0.73, p<0.001). An aArea under ROC curve (AUC) identified the fluid responsiveness thresholds: (Ppleth of 11% (AUC = 0.95±0.04), (Ps of 8% (AUC=0.93±0.05), and (Spleth of 32% (AUC=0.82±0.07). A (Ppleth value ≥ 11% predicted (Pp ≥ 13% with 100% specificity and 91% sensitivity. Volume expansion, performed in 20 patients, changed (Pp, (Ppleth, (Ps and (Spleth significantly (p<0.008).

CONCLUSIONS:

ΔPpleth is well correlated with ΔPp and constitutes a simple and non-invasive method for assessing fluid responsiveness in patients following cardiac surgery.