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Karel H Wesseling

Publications and source records attributed to Karel H Wesseling.

14 recordsLinked to original sources
PubMed2006

Arterial pressure transfer characteristics: effects of travel time.

We investigated the quantitative contribution of all local conduit arterial, blood, and distal load properties to the pressure transfer function from brachial artery to aorta. The model was based on anatomical data, Young's modulus, wall viscosity, blood viscosity, and blood density. A three-element windkessel represented the distal arterial tree. Sensitivity analysis was performed in terms of frequency and magnitude of the peak of the transfer function and in terms of systolic, diastolic, and pulse pressure in the aorta. The root mean square error (RMSE) described the accuracy in wave-shape prediction. The percent change of these variables for a 25% alteration of each of the model parameters was calculated. Vessel length and diameter are found to be the most important parameters determining pressure transfer. Systolic and diastolic pressure changed <3% and RMSE <1.8 mmHg for a 25% change in vessel length and diameter. To investigate how arterial tapering influences the pressure transfer, a single uniform lossless tube was modeled. This simplification introduced only small errors in systolic and diastolic pressures (1% and 0%, respectively), and wave shape was less well described (RMSE, approximately 2.1 mmHg). Local (arm) vasodilation affects the transfer function little, because it has limited effect on the reflection coefficient. Since vessel length and diameter translate into travel time, this parameter can describe the transfer accurately. We suggest that with a, preferably, noninvasively measured travel time, an accurate individualized description of pressure transfer can be obtained.

Aorta↗
PubMed2006

Time course analysis of baroreflex sensitivity during postural stress.

Postural stress requires immediate autonomic nervous action to maintain blood pressure. We determined time-domain cardiac baroreflex sensitivity (BRS) and time delay (tau) between systolic blood pressure and interbeat interval variations during stepwise changes in the angle of vertical body axis (alpha). The assumption was that with increasing postural stress, BRS becomes attenuated, accompanied by a shift in tau toward higher values. In 10 healthy young volunteers, alpha included 20 degrees head-down tilt (-20 degrees), supine (0 degree), 30 and 70 degrees head-up tilt (30 degrees, 70 degrees), and free standing (90 degrees). Noninvasive blood pressures were analyzed over 6-min periods before and after each change in alpha. The BRS was determined by frequency-domain analysis and with xBRS, a cross-correlation time-domain method. On average, between 28 (-20 degrees) to 45 (90 degrees) xBRS estimates per minute became available. Following a change in alpha, xBRS reached a different mean level in the first minute in 78% of the cases and in 93% after 6 min. With increasing alpha, BRS decreased: BRS = -10.1.sin(alpha) + 18.7 (r(2) = 0.99) with tight correlation between xBRS and cross-spectral gain (r(2) approximately 0.97). Delay tau shifted toward higher values. In conclusion, in healthy subjects the sensitivity of the cardiac baroreflex obtained from time domain decreases linearly with sin(alpha), and the start of baroreflex adaptation to a physiological perturbation like postural stress occurs rapidly. The decreases of BRS and reduction of short tau may be the result of reduced vagal activity with increasing alpha.

Adaptation, Physiological↗
PubMed2006

Heterogeneity and prediction of hemodynamic responses to dobutamine in patients with septic shock.

OBJECTIVE: To establish the heterogeneity of hemodynamic responses to dobutamine in patients with septic shock and to identify the predictive factors of these hemodynamic responses. DESIGN: Prospective study. SETTING AND PATIENTS: A total of 12 patients with septic shock in a tertiary medical intensive care unit. INTERVENTIONS: A 20-min dobutamine infusion at 5 microg.kg(-1).min(-1) with subsequent increments to 8, 12.6, and 20 microg.kg(-1).min(-1), on two consecutive days. Responses were dichotomized into changes in heart rate (HR) or stroke volume index (SVI) of >10% and < or =10% at the maximal dobutamine infusion. MEASUREMENTS AND MAIN RESULTS: No differences were found in survival, Acute Physiology and Chronic Health Evaluation II score, maximal dobutamine doses, or pharmacokinetics of dobutamine between HR and SVI groups. In DeltaHR > 10% vs. DeltaHR < or = 10%, baseline HR was lower, and baseline mixed venous oxygen tension and saturation were higher. During dobutamine infusion, mean arterial pressure decreased in DeltaHR > 10%. Cardiac index and the systemic oxygen delivery index increased and the systemic vascular resistance index decreased at unchanged SVI. Pressure work index increased and the ratio of the diastolic to systolic aortic pressure time indices decreased but not to <0.6. In DeltaHR < or = 10%, systemic vascular resistance index and the ratio of the diastolic to systolic aortic pressure time indices decreased (but remained >0.6) without changes in SVI or cardiac index. Baseline hemodynamic and metabolic variables did not differ between SVI groups. In DeltaSVI > 10%, cardiac index increased with dobutamine, but Pao2 and the systemic oxygen delivery index decreased. In DeltaSVI < or = 10%, HR and the systemic oxygen delivery index increased; mean arterial pressure, left ventricular stroke work index, systemic vascular resistance index, and the ratio of the diastolic to systolic aortic pressure time indices decreased. CONCLUSIONS: Patients with a positive chronotropic response to dobutamine had lower baseline HR values, and a chronotropic rather than inotropic response predicted an increase in cardiac index and systemic oxygen delivery index. Incremental dosages of dobutamine did not compromise indirectly measured myocardial oxygen balance.

Adult↗
PubMed2005

Endothelial function and baroreflex sensitivity according to the oral glucose tolerance test in patients with coronary artery disease and normal fasting glucose levels.

Endothelial dysfunction and reduced BRS (baroreflex sensitivity) may be present in patients with CAD (coronary artery disease). The normal fasting glucose level does not exclude abnormal glucose metabolism in patients with CAD. The aim of present study was to evaluate endothelial function and BRS according to glucose metabolism in patients with normal fasting plasma glucose and stable CAD subjected to PTCA (percutaneous transluminal coronary angioplasty). Forty-six consecutive patients who underwent elective PTCA were studied (37 men; mean age 56 years). Endothelial function was assessed non-invasively using the arterial vasodilator response to salbutamol (albuterol). BRS was measured using a cross-correlation method. The extent of coronary narrowing was estimated by calculation of the Gensini score. All patients underwent a 75 g OGTT (oral glucose tolerance test). IGT (impaired glucose tolerance) or diabetes was present in approx. 60% of patients. The vasodilator response to salbutamol, as a measure of endothelial dysfunction, was significantly impaired in patients with IGT or diabetes compared with those with normal glucose tolerance (-0.5+/-1.6% compared with -7.9+/-2.2; P=0.01). Glucose metabolism and age were significant predictors of endothelial dysfunction (R(2)=35.2%, P=0.02). BRS did not differ significantly between patients with normal glucose tolerance and those with IGT or diabetes (6.9+/-1.2 compared with 6.1+/-0.6 ms/mmHg respectively; P=0.669). BRS was negatively correlated with age (r=-0.34, P=0.021) and the Gensini score (r=-0.34, P=0.022). The significant predictors of BRS were Gensini score, age and past myocardial infarction (R(2)=37.02%, P=0.002). Patients with established CAD, normal fasting glucose and IGT or diabetes demonstrated impaired endothelial function which did not correlate with the extent of coronary artery involvement. Conversely, BRS in the study population was not affected by glucose metabolism, but showed an interaction with the extent of coronary narrowing.

Adult↗
PubMed2004

Sublingual nitroglycerin used in routine tilt testing provokes a cardiac output-mediated vasovagal response.

OBJECTIVES: We set out to determine the effect of sublingual nitroglycerin (NTG), as used during routine tilt testing in patients with unexplained syncope, on hemodynamic characteristics and baroreflex control of heart rate (HR) and systemic vascular resistance (SVR). BACKGROUND: Nitroglycerin is used in tilt testing to elicit a vasovagal response. It is known to induce venous dilation and enhance pooling. Also, NTG is lipophilic and readily passes cell membranes, and animal studies suggest a sympatho-inhibitory effect of NTG on circulatory control. METHODS: Routine tilt testing was conducted in 39 patients with suspected vasovagal syncope (age 36 +/- 16 years, 18 females). Patients were otherwise healthy and free of medication. Before a loss of consciousness set in, oncoming syncope was cut short by tilt-back or counter-maneuvers. Finger arterial pressure was monitored continuously (Finapres). Left ventricular stroke volume (SV) was computed from the pressure pulsations (Modelflow). Spontaneous baroreflex control of HR was estimated in the time and frequency domains. RESULTS: During tilt testing, 22 patients developed presyncope. After NTG administration but before presyncope, SV and cardiac output (CO) decreased (p < 0.001), whereas SVR and HR increased (p < 0.001) in all patients. Arterial pressure was initially maintained. Baroreflex sensitivity decreased after NTG. On Cox regression analysis, the occurrence of a vasovagal response was related to a drop in SV after NTG (hazard ratio 0.86, p = 0.005). CONCLUSIONS: The cardiovascular response to NTG is similar in vasovagal and non-vasovagal patients, but more pronounced in those with tilt-positive results. The NTG-facilitated presyncope appears to be CO-mediated, and there is no evidence of NTG-induced sympathetic inhibition.

Administration, Sublingual↗
PubMed2004

Reconstruction of brachial pressure from finger arterial pressure during orthostasis.

INTRODUCTION: In patients with recurrent syncope, monitoring of intra-arterial pressure during orthostatic stress testing is recommended because of the potentially sudden and rapid development of hypotension. Replacing brachial arterial pressure (BAP) by the non-invasively obtained finger arterial pressure (FinAP) has advantages because catheterization in itself may provoke a syncope. OBJECTIVE: To investigate whether reconstruction of the brachial pressure curve (ReBAP) from FinAP can account for systolic and diastolic offset in the recorded pressure on the transition from a supine to an upright position and during maintained postural stress. METHODS: In nine healthy young subjects BAP and FinAP were recorded in the supine position, during 8 min of standing and during 20 min of 70degrees passive head-up tilt (HUT70) whereafter three of the subjects fainted within 20 min of HUT. The FinAP signal was modeled off-line into a reconstructed brachial pressure curve. RESULTS: For FinAP but not for ReBAP, systolic (P < 0.05) and diastolic (P < 0.001) bias increased in the transition from the supine to the HUT position. Bias for the systolic pressure in the supine position and after 7.5 and 20 min of HUT were 2, 7 and 11 mmHg for FinAP but only 0, -2 and 1 mmHg for ReBAP (P < 0.05 for HUT). For the diastolic pressure these values were -2, 5 and 8 mmHg for FinAP and 4, 5 and 6 for ReBAP (P < 0.01 for supine). CONCLUSIONS: Brachial pressure reconstruction from the finger arterial pressure waveform accounts for the bias from the supine to the upright position, eliminates the bias for the systolic but not for diastolic finger pressure and reduces the trend in diastolic bias with increased tilt duration.

Adult↗
PubMed2004

Time-domain cross-correlation baroreflex sensitivity: performance on the EUROBAVAR data set.

OBJECTIVE: To test a new method (cross-correlation baroreflex sensitivity, xBRS) for the computation of time-domain baroreflex sensitivity on spontaneous blood pressure and heart interval variability using the EUROBAVAR data set. METHODS: We applied xBRS to the 42 records in the EUROBAVAR data set, obtained from 21 patients in the lying and standing positions. One patient had a recent heart transplant and one was diabetic with evident cardiac autonomic neuropathy. xBRS computes the correlation between beat-to-beat systolic blood pressure and R-R interval, resampled at 1 Hz, in a sliding 10 s window, with delays of 0-5 s for interval. The delay with the greatest positive correlation is selected and, when significant at P = 0.01, slope and delay are recorded as one xBRS value. Each 1 s of the recording is the start of a new computation. Non-parametric tests are used. RESULTS: With patients in the lying position, xBRS yielded a value of 12.4 ms/mmHg compared with the EUROBAVAR sequential 16.2 ms/mmHg, and for the standing positions the respective values were 6.2 and 6.7 ms/mmHg, giving lying to standing ratios of 1.96 and 2.10, respectively. xBRS yielded results for all files, with 20 values per minute on average at a lower within-patient variance. Best delays were 0, 1 and 2 s, and the delay increased by 102 ms when the patient was in the standing position. The xBRS method was successful in the patients with diabetes and the heart transplant. CONCLUSION: The xBRS method should be considered for experimental and clinical use, because it yielded values that correlated strongly with and were close to the EUROBAVAR averages, yielded more values per minute, had lower within-patient variance and measured baroreflex delay.

Adult↗
PubMed2003

Beat-to-beat noninvasive stroke volume from arterial pressure and Doppler ultrasound.

The proper understanding of the cardiovascular mechanisms involved in complaints of short-lasting dizziness and the evaluation of unexplained recurrent syncope requires continuous monitoring of cardiac stroke volume (SV) in addition to blood pressure and heart rate. The primary aim of the present study was to evaluate a pulse wave analysis method that calculates beat-to-beat flow from non-invasive arterial pressure by simulating a non-linear, time-varying model of human aortic input impedance (Modelflow; MF), by comparing MF stroke volume (SV(MF)) to Doppler ultrasound (US) flow velocity SV (SV(US)). A second purpose was to compare the two methods under two different conditions: the supine and head-up tilt (30 degrees ) position. SV(US) and SV(MF) with non-invasive arterial pressure (Finapres) as input to the aortic model were measured beat-to-beat during spontaneous supine breathing and in the passive 30 degrees head-up tilt (HUT30) position in six normotensive healthy humans [three females, mean age 24 (21-26) years]. There were variations in supine SV track between the two methods with zero difference and a SD of the beat-to-beat difference (MF-US) of 4.2%. HUT30 induced a systematic difference of 10.5% and an increase in SD to 6.9%, which was reproducible. Beat-to-beat changes in SV in the supine resting condition were equally well assessed by both methods. Systematic differences appear during HUT30 and show opposite signs. The difference between the two methods upon a change in body position may be attributed to limitations in each method.

Adult↗
PubMed2003

Finometer, finger pressure measurements with the possibility to reconstruct brachial pressure.

OBJECTIVE: To evaluate three methods aimed at the reconstruction of brachial pressure from non-invasive finger arterial pressure measurements as implemented in the Finometer trade mark, (FMS, Finapres Measurement Systems, Arnhem, Netherlands), the successor to the Finapres trade mark (TNO Biomedical Instrumentation, Amsterdam, Netherlands). METHODS: Finger arterial pressure (FinAP) may differ from intra-brachial pressure (BAP). Pulse shape differences are removed by applying a generalized waveform filter. Pressure level differences are corrected by a generalized level correction equation using filtered systolic and diastolic levels and by level calibration, which uses an additional return-to-flow (RTF) systolic pressure measurement on the ipsilateral upper arm for an individual calibration of the reconstructed brachial pressure. VALIDATION: These methods were validated in 37 subjects, aged 41 to 83 years after a cardiac catheterization procedure. Intra-brachial and Finometer pressures were recorded simultaneously. Finometer pressures were compared after application of waveform filtering and level correction (flcAP), and after an additional RTF calibration (reBAP). RESULTS: Finger arterial systolic, diastolic and mean pressures for the group differed from BAP by -9.7 +/- 13.0, -11.6 +/- 8.0 and -16.3 +/- 7.9 mmHg (mean +/- SD) respectively. Similarly flcAP differed by -1.1 +/- 10.7, -0.2 +/- 6.8 and -1.5 +/- 6.6 mmHg and reBAP differed by 3.1 +/- 7.6, 4.0 +/- 5.6 and 2.7 +/- 4.7 mmHg. CONCLUSION: Reconstruction of BAP from FinAP as implemented in the Finometer reduces the pressure differences, with an individual RTF calibration to well within AAMI requirements.

Adult↗
PubMed2002

Thoracic sympathectomy: effects on hemodynamics and baroreflex control.

UNLABELLED: Endoscopic thoracic sympathectomy at T2-T4 is an effective and safe treatment for primary axillary and palmar hyperhidrosis and facial blushing refractory to conventional treatment. T2 and T4 ganglia however are in the direct pathway of sympathetic innervation of the heart and part of the vasomotor nerves. In this study we investigate possible changes in steady-state hemodynamics as well as in beat-to-beat cardiovascular control after thoracoscopic sympathectomy of T2-T4. In 12 patients we measured continuously heart rate (HR) and blood pressure (BP) (non-invasively with Finapres) during rest and during deep inspiration, in supine and sitting position as well as during a change from lying to standing. Stroke volume (SV) and total peripheral resistance (TPR) were estimated from the BP recordings by the Modelflow method. Markers for cardiovascular control were obtained from power and cross-spectra of BP and HR. After sympathectomy, only in the sitting position was mean HR decreased, while TPR and BP (diastolic and mean) were lower in the supine as well as sitting positions. SV clearly increased. Low frequency power in HR and BP was significantly decreased, just like the max/min ratio in HR after standing up, indicating a diminished capacity in sympathetic vasomotor control. High frequency power of HR as well as baroreflex sensitivity, both parasympathetic markers, did not change in a statistically significant manner. CONCLUSION: Besides altering steady-state hemodynamics, a thoracic sympathectomy causes relatively small, though measurable changes in cardiovascular control, in particular of peripheral vasomotion.

Adult↗
PubMed2002

In vivo interaction of endotoxin and recombinant bactericidal/permeability-increasing protein (rBPI23): hemodynamic effects in a human endotoxemia model.

The cardiovascular derangement that results from the administration of endotoxin in healthy subjects is qualitatively similar to what is observed in patients in septic shock. The biological response to endotoxin is attributed in part to cytokine release. In experimental endotoxemia, recombinant bactericidal/permeability increasing protein (rBPI(23)) has shown a protective effect by binding endotoxin with the subsequent inhibition of the endotoxin-induced cytokine release and of neutrophil activation. In a controlled, blinded crossover study the early cardiovascular effects of rBPI(23) were investigated in an experimental endotoxemia model in humans. The beat-to-beat changes in arterial pressure and cardiac output following infusion of endotoxin (40 EU/kg body weight) and rBPI(23) (1 mg/kg) or placebo (human serum albumin, 0.2 mg/kg) were studied for 2 hours in 8 healthy male adults. Endotoxin or rBPI(23) alone did not induce significant cardiovascular changes. Endotoxin following rBPI(23) infusion elicited a fall in total peripheral resistance with its nadir after 4 minutes to 40% (range 16-53; P <.001) of control level. Mean arterial pressure showed little change, and the fall in total peripheral resistance was associated with a reflex increase in heart rate and cardiac output (32%; range 43-106). Changes in cardiovascular variables in the subsequent 2 hours were not significant. In vitro activation of the contact system by, respectively, rBPI(23), LPS, and LPS-rBPI(23) complexes was assessed. Following incubation with rBPI(23), LPS, and LPS-rBPI(23) complexes, complex levels were generated at levels comparable to those observed in the buffer control. The rapid vasodilatation by endotoxin administered concomitantly with rBPI(23) is not mediated by complement or contact system activation. The early vasodilatation is compensated by an increase in cardiac output, which therefore does not result in arterial hypotension. The monitoring of continuous cardiac output allows for the detection of rapid effects on systemic flow and conductance that go unnoticed in a recording of arterial pressure.

Adult↗
PubMed2002

Variable day/night bias in 24-h non-invasive finger pressure against intrabrachial artery pressure is removed by waveform filtering and level correction.

BACKGROUND Twenty-four-hour finger arterial pressure (FAP) recordings show a negative bias against intrabrachial artery pressure (BAP) and the bias is greater during the night, thereby overestimating the nocturnal blood pressure dip. We have available a methodology with which to reconstruct BAP from FAP by waveform filtering (transfer function) and generalized level (bias) correction that reduces the bias for short-term blood pressure records. OBJECTIVE To investigate if this methodology also decreases the extra bias during the night, thereby yielding a better estimate of the nocturnal dip. METHODS Twenty-four-hour FAP and BAP blood pressure recordings were simultaneously obtained in eight healthy normotensive volunteers and 14 patients with hypertension (ages 19-60 years), during standardized scheduled activities. The data were analysed off-line, applying the brachial reconstruction technique (reBAP) consisting of a waveform filter and level correction. Simultaneous beats yielded systolic, diastolic and mean pressures that were averaged per 30 min, per day, per night, per activity, over the 24-h period, and for volunteers and patients separately. RESULTS Over the full 24 h, FAP systolic, diastolic and mean values for the total group differed from BAP by +1 +/- 10, -8 +/- 7 and -10 +/- 8 mmHg (mean +/- SD), respectively. Similarly, reBAPs differed by +1 +/- 11, -2 +/- 7 and -2 +/- 7 mmHg. BAPs dipped by 20 +/- 8, 13 +/- 6 and 15 +/- 6 mmHg, respectively, during the night. These dips were overestimated by +8, +4 and +4 mmHg by FAP, but not by reBAP: -1, +1 and +1 mmHg. The volunteer and the patient groups showed slight differences in results, but these were not statistically significant. CONCLUSIONS The generalized reconstruction technique to obtain near-brachial pressure from non-invasive FAP almost completely removed bias over the full 24-h day-night period and improved tracking of diurnal changes for all three blood pressure values.

Adult↗