Mathematical modelling of non-invasive oscillometric finger mean blood pressure measurement by maximum oscillation criterion

A mathematical study is performed to assess how the arterial pressure-volume (P-V) relationship, blood pressure pulse amplitude and shape affect the results of non-invasive oscillometric finger mean blood pressure estimation by the maximum oscillation criterion (MOC). The exponential models for a relaxed finger artery and for a partly contracted artery are studied. A new modification of the error equation is suggested. This equation and the results of simulation demonstrate that the value of pressure estimated by the MOC does not exactly agree with the value of the true mean blood pressure (the latter being defined as pressure corresponding to maximum arterial compliance). The error depends on the arterial pressure pulse amplitude, as well as on the difference between the arterial pressure pulse shape index and the arterial P-V curve shape index. In the case of contracted finger arteries, the MOC can give an overestimation of up to 19 mmHg, the pressure pulse shape index being 0.21 and the pulse amplitude 60 mmHg. In the case of relaxed arteries, the error is less evident.     

Theoretical analysis of non-invasive oscillometric maximum amplitude algorithm for estimating mean blood pressure

A theoretical analysis is performed to evaluate the effect of arterial mechanical and blood pressure pulse properties on the accuracy of non-invasive oscillometric maximum amplitude algorithm (MAA) estimates of the mean blood pressure obtained using air-filled occlusive cuffs. Invasively recorded blood pressure pulses, selected for their varied shapes, are scaled to simulate a wide range of blood pulse pressures (diastolic blood pressure minus systolic blood pressure). Each scaled blood pressure pulse is transformed through an exponential model of an artery to create a series of blood volume pulses from which a simulated oscillometric waveform is created and the corresponding MAA estimate of the mean blood pressure and error (mean blood pressure minus MAA estimate) are determined. The MAA estimates are found to depend on the arterial blood pressure. The errors are found to depend on the arterial mechanical properties, blood pressure pulse shape and blood pulse pressure. These results suggest that there is no direct relationship between the mean blood presure and MAA estimate, and that multiple variables may affect the accuracy of MAA estimates of the mean blood pressure obtained using air-filled occlusive cuffs.     

New oscillometric method for indirect measurement of systolic and mean arterial pressure in the human finger. Part 2: correlation study

With a new oscillometric method equipped with a transmittance infrared photoelectric plethysmograph, indirect systolic, and mean arterial pressures were measured in 12 normotensive and hypertensive subjects with systolic and mean arterial pressures ranging from 55 to 163 mmHg and from 95 to 200 mmHg, respectively. The pressure values obtained by this method were compared with direct measurements of the brachial intra-arterial pressure recorded simultaneously. A fairly good correlation between the pairs of simultaneous data from these two methods were obtained.     

Continuous mean arterial pressure measurement in the fingers: The influence of local arm cooling

Two different methods were studied for non-invasive beat-to-beat finger mean arterial pressure (MAP) measurement in 14 healthy volunteers during local arm cooling to 17°C. Fingertip skin blood flow was recorded by a laser Doppler instrument. The difference between the oscillometric beat-to-beat blood pressure measurement device (UT9201) and volume clamp monitor (Finapres) before cooling was −1.5±1.1 mmHg, and, although statistically significant, (p<0.01), this difference cannot be considered clinically meaningful. The results obtained using the two devices during arm cooling showed a systematic disagreement in the continuously recorded MAP. After a 30s period of cooling, the group-averaged difference of UT9201 minus Finapres, calculated as change from the baseline, reached (mean±SD) 8.8±6.3 mmHg (statistically significant, p<0.01).     

Characterization of the oscillometric method for measuring indirect blood pressure

In this study, human subjects and dogs were used to determine the ability of the oscillometric method to indicate systolic and diastolic pressure. In the human studies, the auscultatory method was used as the reference. In the animal studies, directly recorded blood pressure was used as the reference. The ability of the sudden increase in cuff pressure oscillations during cuff deflation to indicate systolic pressure was examined and found to overestimate systolic pressure slightly in man, but more in animals. Systolic pressure was encountered when the cuff pressure oscillations were about one half of their maximum amplitude. However, in both man and animals the ratio was not constant; although the range was less in man than in animals. Diastolic pressure was encountered when cuff-pressure oscillation amplitude was about 0.8 of the maximal amplutide. This ratio for diastolic pressure was not constant over a range of diastolic pressure. The range of variability was less for man than for the dog. Supported by Grant #HL8947-03; National Heart, Lung, and Blood Insitute, Bethesda, Maryland. C.F. Babbs was supported by Career Development Award HL-00587; National Heart, Lung, and Blood Institute, Bethesda, Maryland.     

New oscillometric method for indirect measurement of systolic and mean arterial pressure in the human finger. Part 1: Model experiment

To analyse the mechanism of the occurrence of the maximum volume pulsation in an artery during the application of counterpressure, the static, and dynamic pressure-volume (P-V) relationship was measured in excised arterial segments placed in a compression chamber. Teh volume change caused by perfusing the segment with a sinusoidal pump was detected by an infrared photoelectric plethysmograph during the application of counterpressure. It was revealed that the characteristic change in the amplitude of volume pulsation in response to the gradual change in the counterpressure was due to the nonlinearity of the P-V relation of the artery, and that the value of the counterpressure showing the maximum pulsation amplitude was coincided with the mean arterial pressure. From this evidence it was concluded that the maximum volume pulsation occurs when the transmural pressure was equal to zero, i.e. the arterial wall isunloaded. Based on the results a new oscillometric method for the indirect measurement of systolic and mean arterial pressure in an arterial segment was designed. Through the comparison of data with the actual pressure produced by perfusing the segment, it was demonstrated that systolic and mean arterial pressure can be indirectly measured by this technique within ±3 mm Hg error.     

Vibration plethysmography: A method for studying the visco-elastic properties of finger arteries

Vibration plethysmography records changes in vascular volume produced by fast vibrations of cuff pressure. From these, waveforms of dynamic vascular compliance (DVC) are obtained. A total of 46 recordings of DVC, photo-electric plethysmogram (PG), cuff pressure (CP), and indirect blood pressure (BP) are performed on two adjacent fingers (third and fourth) in 23 healthy subjects. The shape and polarity of the DVC waveform markedly depends upon CP or transmural pressure (TP) (TP=BP-CP). The correlation coefficient between DVC and PG waveforms is nearly −1 at negative mean TP, near zero at zero TP, and approaches +1 at positive TP. For CP moving between systolic and diastolic BP, the DVC waveform shows a diastolic peak, with its maximum close to the zero value of instantaneous TP. xy-diagrams of PG against TP and of DVC against TP plotted for the diastolic phase of single pulses reveal a close coincidence of the DVC peak with the maximum slope of the PG/TP curve. A similar relationship appears when slow changes in PG and the amplitude of PG pulse waves are plotted against mean TP.     

基于奇异值矩阵分解的腕式示波法血压测量算法

为了减小因手腕部生理结构导致腕式示波法测量中存在的内在干扰,本文提出一种基于奇异值矩阵分解(SVD)的新型曲线拟合算法(SCFA),用于提高测量精度。该方法是通过对腕式示波法测量的波形数据进行SVD,提取出主要特征成分,并对该波形成分应用曲线拟合算法(CFA)计算出血压值。根据对45例样本的测量和数据分析,以听诊法(AM)测量值为参照,基于新算法计算的血压值与测量值之间的相关系数为0.96。对比传统的曲线拟合算法(TCFA)计算值,新算法的结果更为准确。实验结果表明,SCFA能够部分消除腕式示波法血压测量过程中的内在干扰,有效的提高腕式血压测量的准确度。     

Analysis for the non-invasive determination of arterial properties and for the transcutaneous continuous monitoring of arterial blood pressure

Analyses are developed for the procedures of (i) the noninvasive determination of the arterial elastic properties and (ii) the transcutaneous continuous monitoring of arterial blood pressure. Expressions for the pulse wave velocity and arterial pressure are derived, separately, in terms of (1) the nonlinear arterial elastic properties (the coefficients of the strain energy density function), the internal and external diameters of the deformed pressurised artery and the ratio of the unpressurised arterial internal and external diameters, and (2) the nonlinear arterial elastic properties, unpressurised tube diameters and the external diameter of the pressurised artery. It is then shown that if the values of the pulse velocities at an arterial section and of the corresponding arterial diameters are obtained (say, by transcutaneous ultrasonic monitoring) at three instants, then adequate equations are obtained (from the above pulse velocity expressions) which can be solved to yield the values of the arterial properties and the undeformed arterial internal and external diameters. These values are substituted in the expression for arterial pressure, to yield an expression for the arterial pressure, solely in terms of the external arterial diameters. Hence, by continuously transcutaneously ultrasonically monitoring the external arterial diameter, the arterial pressure can be monitored continuously and noninvasively. The feasibility and the required accuracy of making these measurements are currently under investigation.     

Effect of room temperature on percentage finger systolic blood pressure response to finger cooling

Percentage finger systolic blood pressure (%FSBP) in response to finger cooling is used to assess vascular components of the hand-arm vibration syndrome and the measurement method is under discussion for standardization. It has been suggested that measurement circumstances including room temperature may affect %FSBP. We investigated the effect of room temperature on %FSBP response to finger cooling in healthy subjects. Six healthy male subjects who were medical students volunteered for the study. Multi-channel plethysmograph was used for simultaneous multi-finger FSBP measurements. The examination room was kept at 21±1°C and 25±1°C, and the subjects were randomly assigned. Percentage finger systolic blood pressures for the index, middle, ring and little fingers at 15°C and 10°C cuff-water temperatures were calculated. Four-way analysis of variance was performed to determine the independent effect of subject, room temperature, finger and cuff-water temperature factors on %FSBP. The room temperature as an independent factor affecting %FSBP was statistically significant (P<0.01). From the results, it can be concluded that %FSBP response to finger cooling in healthy subjects may be affected by room temperature. Therefore, room temperature is expected to be controlled when assessing peripheral vascular components of the upper extremities using %FSBP response to finger cooling.     

Removal of cardiac beat artifact in oesophageal pressure measurement by frequency analysis

Oesophageal pressure (P_es) measurements are important in medical research and useful in clinical diagnosis. Measurements, however, are contaminated heavily by cardiac artifacts. The spectrum and waveform of the P_es signal is obtained from the oesophageal balloon. Adaptive finite impulse response (AFIR) filter and modified adaptive noise cancellation (MANC) methods are adopted to filter out cardiac beat interference. These results are compared. In the frequency domain, frequency variations and spectral overlap between the P_es components and cardiac beat signal components impact on the performance of the filter. From our experimental results on power strength, the fourth or higher harmonics did not have any significant effect on the filter performance. However, the second harmonics of these signals had a significant effect on the filtering result. Thus, in the design of AFIR filters, attention is needed to minimise these effects. In frequency analysis, these harmonics or overlapping frequencies do not affect MANC. MANC was the better method for eliminating cardiac beat artifact in P_es measurement. The dynamic compliance (C_dyn) was also used to evaluate the performance of MANC and AFIR. The standard deviation of C_dyn was less than 0.15 using MANC, compared with standard deviations as high as 0.57 for AFIR. We conclude that MANC performs better than AFIR.     

Removal of cardiac beat artifact in oesophageal pressure measurement by frequency analysis

Oesophageal pressure (Pes) measurements are important in medical research and useful in clinical diagnosis. Measurements, however, are contaminated heavily by cardiac artifacts. The spectrum and waveform of the Pes signal is obtained from the oesophageal balloon. Adaptive finite impulse response (AFIR) filter and modified adaptive noise cancellation (MANC) methods are adopted to filter out cardiac beat interference. These results are compared. In the frequency domain, frequency variations and spectral overlap between the Pes components and cardiac beat signal components impact on the performance of the filter. From our experimental results on power strength, the fourth or higher harmonics did not have any significant effect on the filter performance. However, the second harmonics of these signals had a significant effect on the filtering result. Thus, in the design of AFIR filters, attention is needed to minimise these effects. In frequency analysis, these harmonics or overlapping frequencies do not affect MANC. MANC was the better method for eliminating cardiac beat artifact in Pes measurement. The dynamic compliance (Cdyn) was also used to evaluate the performance of MANC and AFIR. The standard deviation of Cdyn was less than 0.15 using MANC, compared with standard deviations as high as 0.57 for AFIR. We conclude that MANC performs better than AFIR.