Pulse contour cardiac output derived from non-invasive arterial pressure in cardiovascular disease.

Pulse contour methods determine cardiac output semi-invasively using standard arterial access. This study assessed whether cardiac output can be determined non-invasively by replacing the intra-arterial pressure input with a non-invasive finger arterial pressure input in two methods, Nexfin CO-trek and Modelflow , in 25 awake patients after coronary artery bypass surgery. Pulmonary artery thermodilution cardiac output served as a reference. In the supine position, the mean (SD) differences between thermodilution cardiac output and Nexfin CO-trek were 0.22 (0.77) and 0.44 (0.81) l.min(-1) , for intra-arterial and non-invasive pressures, respectively. For Modelflow, these differences were 0.70 (1.08) and 1.80 (1.59) l.min(-1) , respectively. Similarly, in the sitting position, differences between thermodilution cardiac output and Nexfin CO-trek were 0.16 (0.78) and 0.34 (0.83), for intra-arterial and non-invasive arterial pressure, respectively. For Modelflow, these differences were 0.58 (1.11) and 1.52 (1.54) l.min(-1) , respectively. Thus, Nexfin CO-trek readings were not different from thermodilution cardiac output, for both invasive and non-invasive inputs. However, Modelflow readings differed greatly from thermodilution when using non-invasive arterial pressure input.

A comparison of cardiac output derived from the arterial pressure wave against thermodilution in cardiac surgery patients.

In three clinical centres, we compared a new method for measuring cardiac output with conventional thermodilution. The new method computes beat-to-beat cardiac output from radial artery pressure by simulating a three-element model of aortic input impedance, and includes non-linear aortic mechanical properties and a self-adapting systemic vascular resistance. We compared cardiac output by continuous model simulation (MF) with thermodilution cardiac output (TD) in 54 patients (18 female, 36 male) undergoing coronary artery bypass surgery. We made three or four conventional thermodilution estimates spread equally over the ventilatory cycle. In 490 series of measurements, thermodilution cardiac output ranged from 2.1 to 9.3, mean 5.0 litre min(-1). MF differed +0.32 (1.0) litre min(-1) on average with limits of agreement of -1.68 and +2.32 litre min(-1). Differences decreased when the first series of measurements in a patient was used to calibrate the model. In 436 remaining series, the mean difference became -0.13 (0.47) litre min(-1) with limits of agreement of -1.05 and +0.79 litre min(-1). When consecutive measurements were made, the change was greater than 0.5 litre min(-1), on 204 occasions. The direction of change was the same with both methods in 199. The difference between the methods remained near zero during surgery suggesting that a single calibration per patient was adequate. Aortic model simulation with radial artery pressure as input reliably monitors changes in cardiac output in cardiac surgery patients. Before calibration, the model cannot replace thermodilution, but after calibration the model method can quantitatively replace further thermodilution estimates.

Hemodynamic effects of intermittent manual lung hyperinflation in patients with septic shock.

OBJECTIVE: The purposes of this study were to investigate the hemodynamic changes induced by intermittent manual lung hyperinflation (MHI) and to assess if these changes are adverse enough to warrant prohibition of MHI as a routine procedure in the care of patients with septic shock. DESIGN: The study's design was experimental prospective. SETTING: The settings were university hospital intensive care units. PATIENTS: Subjects included 13 consecutive mechanically ventilated patients with septic shock who met the inclusion criteria. MEASUREMENTS AND RESULTS: Phasic MHI-related increments in mean inspiratory airway pressure were concordant to changes in mean pulmonary artery pressure (MPAP) (r(2) = 0.67) with a 0.6 mm Hg rise in MPAP per cm H(2)O airway pressure. The magnitude of MPAP changes was not reflected in magnitude of stroke volume index (SVI) (r(2) = 0.06). On average, MHI did not induce statistically significant hemodynamic changes and mean values returned to baseline level within 15 minutes. SVI during MHI increased slightly in 9 patients, from 37 +/- 15 (mean +/- SD) to 41 +/- 17 mL/m(2) (P <.05), and decreased in 4, from 60 +/- 10 to 50 +/- 14 mL/m(2) (not significant). Patients with an increase in SVI had lower baseline values for SVI, cardiac index, and left ventricular stroke work index (P <.05) and higher values for systemic vascular resistance index compared with patients with a decrease in SVI (P <.05). Left ventricular stroke work index was higher in patients with a decrease in SVI than in patients with an increase in SVI (52 +/- 9 vs 34 +/- 8; P <.05). Tidal volume increased from 499 +/- 176 mL before MHI to 587 +/- 82 mL, 5 minutes after MHI (P <.05) with a return to baseline values within 15 minutes after the procedure. CONCLUSION: The hemodynamic effects of intermittent MHI in patients with septic shock are relatively small and insignificant and seem to be related to the cardiovascular state before the procedure. The risk of inducing hemodynamic changes with MHI should not be considered as a contraindication in patients with septic shock who are mechanically ventilated.

Cardiac and hemodynamic effects of hemodialysis and ultrafiltration.

Imbalance between cardiac oxygen supply and demand may trigger cardiac events in already vulnerable hemodialysis (HD) patients. We studied the effect of ultrafiltration (UF) and HD in nine chronic HD patients by continuously measuring blood volume (BV; by Critline), blood pressure (BP; by Portapres), and changes in hemodynamics (Modelflow) during isolated UF (iUF) of 500 mL in 30 minutes and subsequent HD combined with UF (HD + UF). Aortic pressure was reconstructed from finger pressure. Changes in cardiac oxygen supply were assessed by calculating the area under the aortic pressure curve during diastole (diastolic pressure time index [DPTI]). Changes in cardiac oxygen demand were assessed by calculating systolic pressure time index (SPTI). BV decreased 4.0% +/- 1.8% during UF and 7.3% +/- 3.3% during HD + UF (both P < 0.01). Systolic BP did not change; diastolic and mean BP increased 11 +/- 7.4 and 11 +/- 8.4 mm Hg during iUF, respectively (both P < 0.01), and stabilized during HD + UF. Overall pulse pressure decreased 19 +/- 11.1 mm Hg (P < 0.01). Heart rate increased 13 +/- 11 beats/min (P < 0.01) and systemic vascular resistance increased 59% +/- 51% (P < 0. 01), whereas stroke volume and cardiac output (CO) decreased by 40% +/- 17% and 30% +/- 13%, respectively (both P < 0.01). Both cardiac oxygen supply (DPTI) and demand (SPTI) increased during iUF, and both decreased during HD + UF. By the end of the procedure, DPTI/SPTI ratio had increased 9% +/- 8% (P < 0.05). Changes in CO correlated closely to changes in BV. Despite large changes in hemodynamics during uncomplicated UF and HD, the balance between cardiac oxygen supply and demand (DPTI/SPTI ratio) did not decrease, but improved slightly.

Estimation of beat-to-beat changes in stroke volume from arterial pressure: a comparison of two pressure wave analysis techniques during head-up tilt testing in young, healthy men.

OBJECTIVE: The aim of this study was to compare beat-to-beat changes in stroke volume (SV) estimated by two different pressure wave analysis techniques during orthostatic stress testing: pulse contour analysis and Modelflow, i.e., simulation of a three-element model of aortic input impedance. METHODS: A reduction in SV was introduced in eight healthy young men (mean age, 25; range, 19-32 y) by a 30-minute head-up tilt maneuver. Intrabrachial and noninvasive finger pressure were monitored simultaneously. Beat-to-beat changes in SV were estimated from intrabrachial pressure by pulse contour analysis and Modelflow. In addition, the relative differences in Modelflow SV obtained from intrabrachial pressure and noninvasive finger pressure were assessed. RESULTS: Beat-to-beat changes in Modelflow SV from intrabrachial pressure were comparable with pulse contour measures. The relative difference between the two methods amounted to 0.1+/-1% (mean +/- SEM) and was not dependent on the duration of tilt. The difference between Modelflow applied to intrabrachial pressure and finger pressure amounted to -2.7+/-1.3% (p = 0.04). This difference was not dependent on the duration of tilt or level of arterial pressure. CONCLUSIONS: Based on different mathematical models of the human arterial system, pulse contour and Modelflow compute similar changes in SV from intrabrachial pressure during orthostatic stress testing in young healthy men. The magnitude of the difference in SV derived from intrabrachial and finger pressure may vary among subjects; Modelflow SV from noninvasive finger pressure tracks fast and brisk changes in SV derived from intrabrachial pressure.

Continuous stroke volume monitoring by modelling flow from non-invasive measurement of arterial pressure in humans under orthostatic stress.

The relationship between aortic flow and pressure is described by a three-element model of the arterial input impedance, including continuous correction for variations in the diameter and the compliance of the aorta (Modelflow). We computed the aortic flow from arterial pressure by this model, and evaluated whether, under orthostatic stress, flow may be derived from both an invasive and a non-invasive determination of arterial pressure. In 10 young adults, Modelflow stroke volume (MFSV) was computed from both intra-brachial arterial pressure (IAP) and non-invasive finger pressure (FINAP) measurements. For comparison, a computer-controlled series of four thermodilution estimates (thermodilution-determined stroke volume; TDSV) were averaged for the following positions: supine, standing, head-down tilt at 20 degrees (HDT20) and head-up tilt at 30 degrees and 70 degrees (HUT30 and HUT70 respectively). Data from one subject were discarded due to malfunctioning thermodilution injections. A total of 155 recordings from 160 series were available for comparison. The supine TDSV of 113+/-13 ml (mean+/-S.D.) dropped by 40% to 68+/-14 ml during standing, by 24% to 86+/-12 ml during HUT30, and by 51% to 55+/-15 ml during HUT70. During HDT20, TDSV was 114+/-13 ml. MFSV for IAP underestimated TDSV during HDT20 (-6+/-6 ml; P<0.05), but that for FINAP did not (-4+/-7 ml; not significant). For HUT70 and standing, MFSV for IAP overestimated TDSV by 11+/-10 ml (HUT70; P<0.01) and 12+/-9 ml (standing; P<0.01). However, the offset of MFSV for FINAP was not significant for either HUT70 (3+/-8 ml) or standing (3+/-9 ml). In conclusion, due to orthostasis, changes in the aortic transmural pressure may lead to an offset in MFSV from IAP. However, Modelflow correctly calculated aortic flow from non-invasively determined finger pressure during orthostasis.

Broad-band spectral analysis of 24 h continuous finger blood pressure: comparison with intra-arterial recordings.

The present study compares the spectral characteristics of 24-h blood pressure variability estimated invasively at the brachial artery level with those estimated by measurement of blood pressure at the finger artery using the non-invasive Portapres device. Broad-band spectra (from 3x10(-5) to 0.5 Hz) were derived from both finger and intra-brachial pressures recorded simultaneously for 24 h in eight normotensive and twelve hypertensive ambulant subjects. At frequencies lower than 0.07 Hz, higher spectral estimates were obtained by Portapres than by intra-brachial measurements. The maximum overestimation occurred in systolic pressure at around 10(-2) Hz, where the amplitude of the oscillations was two times greater when measured by Portapres. A less pronounced overestimation was found for diastolic pressures. The maximum overestimation was greater during daytime than during night-time. At around 0.1 Hz, invasive and non-invasive spectra were similar. At the respiratory frequencies (0.15-0.50 Hz), the power spectra were overestimated by Portapres during daytime, and underestimated at night. These results provide reference information for the correct interpretation of Portapres data in the estimation of 24-h blood pressure spectral power.

Continuous cardiac output in septic shock by simulating a model of the aortic input impedance: a comparison with bolus injection thermodilution.

BACKGROUND: To compare continuous cardiac output obtained by simulation of an aortic input impedance model to bolus injection thermodilution (TDCO) in critically ill patients with septic shock. METHODS: In an open study, mechanically ventilated patients with septic shock were monitored for 1 (32 patients), 2 (15 patients), or 3 (5 patients) days. The hemodynamic state was altered by varying the dosages of dopamine, norepinephrine, or dobutamine. TDCO was estimated 189 times as the series average of four automated phase-controlled injections of iced 5% glucose, spread equally over the ventilatory cycle. Continuous model-simulated cardiac output (MCO) was computed from radial or femoral artery pressure. On each day, the first TDCO value was used to calibrate the model. RESULTS: TDCO ranged from 4.1 to 18.2 l/min. The bias (mean difference between MCO and TDCO) on the first day before calibration was -1.92 +/- 2.3 l/min (mean +/- SD; n = 32; 95% limits of agreement, -6.5 to 2.6 l/min). The bias increased at higher levels of cardiac output (P < 0.05). In 15 patients studied on two consecutive days, the precalibration ratio TDCO:MCO on day 1 was 1.39 +/- 0.28 (mean +/- SD) and did not change on day 2 (1.39 +/- 0.34). After calibration, the bias was -0.1 +/- 0.8 l/min with 82% of the comparisons (n = 112) < 1 l/min and 58% (n = 79) < 0.5 l/min, and independent of the level of cardiac output. CONCLUSIONS: In mechanically ventilated patients with septic shock, changes in bolus TDCO are reflected by calibrated MCO over a range of cardiac output values. A single calibration of the model appears sufficient to monitor continuous cardiac output over a 2-day period with a bias of -0.1 +/- 0.8 l/min.

Effects of arteriovenous fistulas on cardiac oxygen supply and demand.

BACKGROUND: Arteriovenous (AV) fistulas used for hemodialysis access may affect cardiac load by increasing the preload while decreasing the afterload. In dogs, AV fistulas have also been shown to affect coronary perfusion negatively. We investigated the net effect of AV fistulas on cardiac oxygen supply and demand. METHODS: Aortic pressure waves were reconstructed from finger pressure recordings obtained on the nonfistula arm using a wave-form filter. Changes in systolic, mean, and diastolic aortic pressure were calculated, together with changes in heart rate (HR), stroke volume (SV), cardiac output (CO), and systemic vascular resistance (SVR) during a 60-second compression of AV fistulas in 10 patients. Changes in cardiac supply and demand were estimated by calculating the area under the aortic pressure curve during diastole [diastolic pressure time index (DPTI)] and systole [systolic pressure time index (SPTI)], respectively. RESULTS: During fistula compression, systolic, mean and diastolic pressure increased by 4.2 +/- 4.3, 2.6 +/- 3.0, and 2.8 +/- 2.9 mm Hg (mean +/- SD, all P < 0.05). The HR decreased by 3.8 +/- 2.5 beats per minute (P < 0.01), and SV decreased 3.7 +/- 6.1% (NS). CO decreased 9.4 +/- 8.6%, and SVR increased 14.3 +/- 11.7% (both P < 0.05). The SPTI increased by 1.5 +/- 1.5 mm Hg.sec (P < 0.01), and the DPTI increased by 7.6 +/- 8.1 mm Hg.sec (14.8% increase, P < 0.05) during compression. The ratio of supply and demand (DPTI/SPTI) improved by 13.5 +/- 13.0% (P < 0.01) when the fistula was compressed. CONCLUSION: AV fistulas have a small effect on left ventricular oxygen demand, but decrease cardiac oxygen supply considerably.

Fifteen years experience with finger arterial pressure monitoring: assessment of the technology.

We review the Finapres technology, embodied in several TNO-prototypes and in the Ohmeda 2300 and 2300e Finapres NIBP. Finapres is an acronym for FINger Arterial PRESsure, the device delivers a continuous finger arterial pressure waveform. Many papers report on the accuracy of the device in comparison with intra-arterial or with noninvasive but intermittent blood pressure measurements. We compiled the results of 43 such papers and found systolic, diastolic and mean accuracies, in this order, ranging from -48 to 30 mmHg, from -20 to 18 mmHg, and from -13 to 25 mmHg. Weighted for the number of subjects included pooled accuracies were -0.8 (SD 11.9), -1.6 (8.3) and -1.6 (7.6) mmHg respectively. Subdividing the pooled group according to criteria such as reference blood pressure, place of application, and prototype or commercial device we found no significant differences in mean differences or SD. Measurement at the finger allows uninterrupted recordings of long duration. The transmission of the pressure pulse along the arm arteries, however, causes distortion of the pulse waveform and depression of the mean blood pressure level. These effects can be reduced by appropriate filtering, and upper arm 'return-to-flow' calibration to bring accuracy and precision within AAMI limits. For the assessment of beat-to-beat changes in blood pressure and assessment of blood pressure variability Finapres proved a reliable alternative for invasive measurements when mean and diastolic pressures are concerned. Differences in systolic pressure are larger and reach statistical significance but are not of clinical relevance. Finger arteries are affected by contraction and dilatation in relation to psychological and physical (heat, cold, blood loss, orthostasis) stress. Effects of these phenomena are reduced by the built-in Physiocal algorithm. However, full smooth muscle contraction should be avoided in the awake patient by comforting the patient, and covering the hand. Arterial state can be monitored by observing the behaviour of the Physiocal algorithm. We conclude that Finapres accuracy and precision usually suffice for reliable tracking of changes in blood pressure. Diagnostic accuracy may be achieved with future application of corrective measures.

Estimation of blood pressure variability from 24-hour ambulatory finger blood pressure.

Portapres is a noninvasive, beat-to-beat finger blood pressure (BP) monitor that has been shown to accurately estimate 24-hour intra-arterial BP at normal and high BPs. However, no information is available on the ability of this device to accurately track ambulatory BP variability. In 20 ambulatory normotensive and hypertensive subjects, we measured 24-hour BP by Portapres and through a brachial artery catheter. BP and pulse interval variabilities were quantified by (1) the SDs of the mean values (overall variability) and (2) spectral power, computed either by fast Fourier transform and autoregressive modeling of segments of 120-second duration for spectral components from 0.025 to 0.50 Hz or in a very low frequency range (between 0.00003 and 0.01 Hz) by broadband spectral analysis. The 24-hour SD of systolic BP obtained from Portapres (24+/-2 mm Hg) was greater than that obtained intra-arterially (17+/-1 mm Hg, P<0.01), but the overestimation was less evident for diastolic (3+/-1 mm Hg, P<0.01) and mean (3+/-1 mm Hg, P<0.01) BP. The BP spectral power <0.15 Hz was also overestimated by Portapres more for systolic than for diastolic and mean BPs; similar findings were obtained by the fast Fourier transform, the autoregressive approach, and focusing on the broadband spectral analysis. BP spectral power >0.15 Hz obtained by the Portapres was similar during the day but lower during the night when compared with those obtained by intra-arterial recordings (P<0.01). No differences were observed between Portapres and intra-arterial recordings for any estimation of pulse interval variabilities. The overestimation of BP variability by Portapres remained constant over virtually the entire 24-hour recording period. Thus, although clinical studies are still needed to demonstrate the clinical relevance of finger BP variability, our study shows that Portapres can be used with little error to estimate 24-hour BP variabilities if diastolic and mean BPs are used. For systolic BP, the greater error can be minimized by using correction factors.

Why use Finapres or Portapres rather than intra-arterial or intermittent non-invasive techniques of blood pressure measurement?

In the clinic, blood pressure is measured almost exclusively using non-invasive intermittent techniques, of which the auscultatory (Riva-Rocci/Korotkoff, RRK) and the computerized oscillometric method are most often used. However, both methods only provide a momentary value. In addition, the accuracy is hampered by phenomena such as cuff response and white coat hypertension, thus providing artefactually increased values. The vascular unloading technique of Penáz together with the Physiocal criteria of Wesseling provide reliable, non-invasive and continuous estimates of blood pressure. This technique is thus an alternative to the invasive intra-arterial measurements in many cases, without the risks and ethical questions inherent to invasive measurements. Since the pressure waveform is available continuously, computations such as pulse contour and Modelflow cardiac output, spectral analysis and baroreflex sensitivity provide further information on the dynamics of the cardiovascular system on a beat-to-beat basis, similar to intra-arterial measurements.

Compressed storage of arterial pressure waveforms by selection of significant points.

Continuous records of arterial blood pressure can be obtained non-invasively with Finapres, even for periods of 24 hours. Increasingly, storage of such records is done digitally, requiring large disc capacities. It is therefore necessary to find methods to store blood pressure waveforms in compressed form. The method of selection of significant points known from ECG data compression is adapted. Points are selected as significant wherever the first derivative of the pressure wave changes sign. As a second stage recursive partitioning is used to select additional points such that the difference between the selected points, linearly interpolated, and the original curve remains below a maximum. This method is tested on finger arterial pressure waveform epochs of 60 s duration taken from 32 patients with a wide range of blood pressures and heart rates. An average compression factor of 4.6 (SD 1.0) is obtained when accepting a maximum difference of 3 mmHg. The root mean squared error is 1 mmHg averaged over the group of patient waveforms. Clinically relevant parameters such as systolic, diastolic and mean pressure are reproduced with an offset error of less than 0.5 (0.3) mmHg and scatter less than 0.6 (0.1) mmHg. It is concluded that a substantial compression factor can be achieved with a simple and computationally fast algorithm and little deterioration in waveform quality and pressure level accuracy.

Variability of near-fainting responses in healthy 6-16-year-old subjects.

1. Fainting is a common phenomenon in young subjects, but the final events before the actual faint are not well known. The aim of the present study was to study the inter-individual variability of haemodynamic events associated with near-fainting in children and teenagers. 2. Sixty-eight healthy subjects (aged 6-16 years) performed a 70 degrees tilt-up test with intravascular instrumentation for 5 min. Responses in 29 near-fainting subjects were analysed and compared with 39 non-fainting subjects. Arterial pressure was measured by Finapres. Left ventricular stroke volume was computed from the pressure pulsation waveform. 3. Inability to maintain vasomotor tone was the mechanism underlying near-fainting in the vast majority of near-fainting subjects. The three classical haemodynamic responses (vasovagal, vasodepressor and vagal) could be recognized, but large individual differences were found. After tilt back, blood pressure in near-fainters showed a mirror response to the stage before tilt-back; blood pressure gradually increased and was normal at 1 min after tilt-back. 4. The variability in haemodynamic responses on approach of an orthostatic faint is wide in the young.

The Valsalva manoeuvre as a cardiovascular reflex test in healthy children and teenagers.

The objective of this study was to determine whether the Valsalva manoeuvre is applicable as a test for neurocardiovascular control in healthy children and teenagers. Sixty-eight 6- to 16-year-old children and teenagers performed two Valsalva manoeuvres in the sitting position. They were instructed to maintain airway pressure (strain) for 15 s at 30 mmHg in the first and at 40 mmHg in the second manoeuvre. Finger arterial pressure and heart rate were monitored continuously. In three of the 68 subjects it was not possible to obtain a reliable blood pressure recording due to movements of the finger and/or hand. Only 10 subjects were able to reach a strain of 30 mmHg and to maintain this strain constant during 15 s; in the others the level or the duration of the strain varied substantially. Nine subjects kept strain at 40 mmHg during 15 s. With a Valsalva manoeuvre of 30 mmHg, control values of blood pressure and heart rate in the last 5 s prior to the manoeuvre increased in 11 subjects. Notwithstanding the large range in straining (15-55 mmHg), on visual inspection blood pressure and heart rate responses known from studies in adults could be recognized in 57 of the 65 subjects. In the other eight subjects atypical heart rate responses were observed. Forty-four of the 65 subjects could perform a Valsalva manoeuvre with a higher airway pressure compared to the first manoeuvre: range 35-55 mmHg. The higher airway pressure resulted in more pronounced blood pressure and heart rate responses. There was no correlation between age and gender versus airway pressure. It was concluded that the Valsalva manoeuvre generated blood pressure responses as found in adults. Heart rate responses were sometimes atypical, and needed underlying blood pressure measurement for full interpretation. For quantitative analysis the test was hampered by the inability of the majority of our young subjects to produce the exact strain during the 15-s period. Qualitatively, however, the Valsalva manoeuvre seems applicable as a cardiovascular reflex test to assess neurocardiovascular control in children and teenagers.

Models of brachial to finger pulse wave distortion and pressure decrement.

OBJECTIVE: To model the pulse wave distortion and pressure decrement occurring between brachial and finger arteries. Distortion reversion and decrement correction were also our aims. METHODS: Brachial artery pressure was recorded intra-arterially and finger pressure was recorded non-invasively by the Finapres technique in 53 adult human subjects. Mean pressure was subtracted from each pressure waveform and Fourier analysis applied to the pulsations. A distortion model was estimated for each subject and averaged over the group. The average inverse model was applied to the full finger pressure waveform. The pressure decrement was modelled by multiple regression on finger systolic and diastolic levels. RESULTS: Waveform distortion could be described by a general, frequency dependent model having a resonance at 7.3 Hz. The general inverse model has an anti-resonance at this frequency. It converts finger to brachial pulsations thereby reducing average waveform distortion from 9.7 (s.d. 3.2) mmHg per sample for the finger pulse to 3.7 (1.7) mmHg for the converted pulse. Systolic and diastolic level differences between finger and brachial arterial pressures changed from -4 (15) and -8 (11) to +8 (14) and +8 (12) mmHg, respectively, after inverse modelling, with pulse pressures correct on average. The pressure decrement model reduced both the mean and the standard deviation of systolic and diastolic level differences to 0 (13) and 0 (8) mmHg. Diastolic differences were thus reduced most. CONCLUSION: Brachial to finger pulse wave distortion due to wave reflection in arteries is almost identical in all subjects and can be modelled by a single resonance. The pressure decrement due to flow in arteries is greatest for high pulse pressures superimposed on low means.

Aortic and peripheral blood pressure during isometric and dynamic exercise.

The purpose of this study was to compare aortic blood pressure (AOR) to peripheral measurements by the Riva-Rocci/Korotkov (RRK) and Finapres continuous finger pressure (FIN) methods during dynamic and static exercise. A tip manometer was introduced in the ascending aorta after coronary angiography in 7 cardiac patients with good exercise capability. Static exercise was of moderate intensity and led to an increase of average diastolic and systolic AOR of 20 and 18 mmHg, respectively. The corresponding RKK values were 20 and 30 mmHg and the FIN values were 16 and 14 mmHg, respectively. In maximal cycle ergometry the discrepancies were larger, especially in the 4 subjects who reached 80% or more of predicted maximal work load. Diastolic and systolic increases in AOR in these 4 subjects were 12 and 38 mmHg, respectively. The RRK values were 17 and 76 mmHg. Increases in FIN values of 17 and 74 mmHg for diastolic and systolic measurements, respectively, were found. The peripheral FIN and RRK measurements give a systolic increase that is twice as large as that for AOR. It is concluded that RRK and FIN greatly overestimate the load to the cardiovascular system in dynamic exercise. When the cardiovascular load is estimated by the rate-pressure product, RRK produces an increase of 197%, FIN of 181%, while AOR gives an increase of only 133%. This suggests that the present criteria for blood pressure in exercise testing should be critically examined.

Finger-to-brachial comparability of 'modelflow' stroke volume improves after pulsewave reconstruction.

Modelflow is a method that determines stroke volume (SV) from central or peripheral continuous blood pressure signals. Pulsewaves are changed along the arterial tree; distortion occurs as the mean pressure level gradually declines. These changes might jeopardize the determination of SV from a distal measurement site. Techniques have been assessed to reconstruct brachial artery pressures (BAPs) from non-invasive finger blood pressure (FIN) waveforms. In this study, we determined the effect of different forms of brachial reconstruction techniques on the comparability of modelflow SV from FIN and BAP. Supine resting FIN and BAP were measured simultaneously in 57 subjects, covering a wide range of blood pressures and degrees of vascular disease. SV from the two sites were compared before correction and after correction for pulsewave distortion or pressure gradient. The latter was determined by a regression formula and by a return to flow (RTF) method, using the brachial cuff pressure at the moment of reappearance of FIN during cuff deflation. SV from unfiltered FIN exceeded BAP-derived SV by 4.6 (SD 11) ml. This difference was positively related to the subjects' age. Correction for pulsewave distortion increased the average difference to 13 (12) ml (P < 0.05 to the unfiltered condition). Adjustment for the pressure gradient reduced the difference to -2.5 (7) ml (P < 0.01). RTF had no additional effect. We concluded that the FIN-to-BAP comparability can be increased by brachial reconstruction techniques, which correct for the pressure gradient. This can be adequately performed without additional measurements, allowing its application to measurements already taken.

Reconstruction of brachial artery pressure from noninvasive finger pressure measurements.

BACKGROUND: Pulse wave distortions, mainly caused by reflections, and pressure gradients, caused by flow in the resistive vascular tree, may cause differences between finger and brachial artery pressures. These differences may limit the use of finger pressure measurements. We investigated whether brachial artery pressure waves could be reconstructed from finger pressure measurements by correcting for the pressure gradient in addition to correction for pulse wave distortion with a previously described filter. METHODS AND RESULTS: Finger artery pressure (with Finapres), intra-arterial brachial artery pressure (BAP), Riva-Rocci/ Korotkoff (RRK), oscillometric, and return-to-flow (RTF) measurements were simultaneously performed in 57 healthy elderly subjects and patients with vascular disease and/or hypertension. A generalized waveform filter was used to correct for pulse wave distortions. Correction equations for the pressure gradient, based on finger pressure, RRK, RTF, or oscillometric measurements, were obtained in 28 randomly selected subjects and tested in 29. Before reconstruction, Finapres underestimated mean and diastolic BAP (finger pressure minus BAP: systolic, -3.2 +/- 16.9 mm Hg; mean, -13.0 +/- 10.5 mm Hg; diastolic, -8.4 +/- 9.0 mm Hg [mean +/- SD]). After filtering, reconstructed BAP waves were similar to actual BAP in shape but not in pressure level. Optimal correction for the pressure gradient with an equation based on RTF measurements reduced the pressure differences to meet American Association for the Advancement of Medical Instrumentation criteria (reconstructed finger pressure minus BAP: systolic, 3.7 +/- 7.0 mm Hg; mean, 0.7 +/- 4.6 mm Hg; and diastolic, 1.0 +/- 4.9 mm Hg). CONCLUSIONS: BAP waves can be reconstructed from noninvasive finger pressure registrations when finger pressure waves are corrected for pulse wave distortion and individual pressure gradients.