Biomedical subjects

J R Jansen

Publications and source records attributed to J R Jansen.

At least 19 recordsLinked to original sources

PubMed2001

The volume-dependency of parallel conductance throughout the cardiac cycle and its consequence for volume estimation of the left ventricle in patients.

OBJECTIVE: To study the hypothesis that the electrical conductance of tissues and fluids (parallel conductance (G(p))) around the ventricle depends on left ventricular volume throughout the cardiac cycle. METHODS: We extended a recently developed method to determine G(p) throughout the cardiac cycle. First, we compared the estimates of parallel conductances obtained with the new method (G(a)(p)) with those of the conventional one (G(1)(p)), both averaged over the cardiac cycles. Secondly, G(a)(p) was determined throughout the cardiac cycle and its volume dependency was assessed. Thirdly, the factor alpha was calculated as the ratio between stroke volume, obtained by the conductance method using G(1)(p), and that obtained by a thermodilution method. Because the non-homogeneous field was indicated to be the reason for the dependency of G(p) on left ventricular volume as well as for the need for alpha, we tested whether the hypothesis implies that a correction with alpha is not needed if G(p) is determined throughout the cardiac cycle. RESULTS: We found a negative linear relation between G(p) and left ventricular volume. This relation appeared to be reproducible within each patient. Furthermore, we found that alpha deviates from 1 primarily due to the dependency of G(p) on left ventricular volume. CONCLUSION: To obtain stroke volume or to determine absolute left ventricular volume continuously within a cardiac cycle, G(p) should be determined throughout each cardiac cycle and if a constant G(p) throughout the cardiac cycle is used a correction with the factor alpha should be made to correct for a possible influence of electrical field heterogeneity.

Cardiac Output↗

PubMed2001

Computer control versus manual control of systemic hypertension during cardiac surgery.

BACKGROUND: We recently demonstrated the feasibility of computer controlled infusion of vasoactive drugs for the control of systemic hypertension during cardiac surgery. The objective of the current study was to investigate the effects of computer controlled blood pressures on hemodynamic stability when compared to conventional manual control. METHOD: Systemic artery blood pressures were managed either by computer (80 patients) or by a well-trained anesthesiologist (80 patients). The vasodilator drugs sodium nitroprusside and nitroglycerin were used. Hemodynamic stability was determined from the standard deviation of the mean arterial pressure samples and from the percentages of time that arterial pressure was hypertensive or hypotensive. RESULTS: The average standard deviation of the mean arterial pressure samples was smaller for the computer controlled than for the manually controlled group: 7.5+/-2.2 (mean+/-SD) versus 8.9+/-2.3 mmHg (P<0.0001). The systemic artery pressure was less hypertensive and less hypotensive in the computer controlled than in the manually controlled group: 9.4+/-5.7 versus 13.1+/-6.0% (P<0.0001) and 8.0+/-5.9 versus 11.8+/-7.4% (P<0.0001), respectively. CONCLUSION: We conclude that, compared with manual control, computer control of systemic hypertension significantly improved hemodynamic stability during cardiac surgery.

Adult↗

PubMed2001

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.

Adult↗

PubMed2001

Mean cardiac output by thermodilution with a single controlled injection.

OBJECTIVE: A new method to estimate mean cardiac output by thermodilution with a single duration-controlled injection was evaluated in patients. DESIGN: Prospective criterion standard study. SETTING: University hospital cardiac surgical intensive care unit and cardiac operation room. PATIENTS: Of 33 patients, 24 underwent coronary bypass graft surgery, four had a valve replacement, and five were treated in the intensive care unit. INTERVENTIONS: Interventions consisted of thermodilution cardiac output measurements. One single duration-controlled injection of cold fluid was used to calculate cardiac output. This controlled injection was performed with a duration equal to one whole ventilation cycle of the ventilator. An algorithm adapted to this duration-controlled injection calculated cardiac output. Moreover, this algorithm has properties to reduce errors caused by artificial ventilation and thermal noise. MEASUREMENTS AND MAIN RESULTS: In 33 patients, the averaged values of four measurements equally spread over the ventilatory cycle (phase-controlled) were compared with the values of two single duration-controlled measurements. The measurements were performed during periods of stable respiration and circulation. No significant difference was observed between the mean of four phase-controlled measurements and the mean of the two duration-controlled measurements. The cardiac output values in the intensive care patients were significantly higher compared with the two other patient groups (p <.05). The difference between the two methods could not be subdivided for the three patient groups (p >.05). The coefficient of variation of the single duration-controlled thermodilution measurements was significantly lower than the single phase-controlled measurements, 3% vs. 6% (p <.01). CONCLUSIONS: One single duration-controlled injection thermodilution measurement is as accurate and repeatable as the mean of four phase-controlled measurements and is clinically feasible.

Adult↗

PubMed2000

A new approach to determine parallel conductance for left ventricular volume measurements.

OBJECTIVES: To determine absolute ventricular volume with the conductance catheter technique, the electrical conductance of tissues and fluids (parallel conductance) around the ventricle should be determined precisely. METHODS: A new objective method to estimate parallel conductance based on analysis of the dilution curve of hypertonic saline was investigated. The parallel conductances obtained with the new method (G(a)(p)) were compared to those obtained with the conventional method (G(l)(p)). The study was performed in the left ventricle of 12 patients. RESULTS: G(a)(p) was not significantly different from G(l)(p). For the G(l)(p) method the average percentage difference between duplicate values, both taken as absolute values, was 15.06% and for the G(a)(p) method it was 4. 01%. Thus the reproducibility of the method is a factor four better than that of the method. This difference appeared to be significant. CONCLUSION: We conclude that a smaller number of injections will be required to obtain the same precision using our method.

Cardiac Catheterization↗

PubMed2000

Automated cardiac output measurements by ultrasound are inaccurate at high cardiac outputs.

OBJECTIVE: The sonographic technique of automated cardiac output measurement (ACM) is a promising new method to measure cardiac output and could be of use in a high-risk obstetric unit in the treatment of pre-eclamptic patients. The aim was to determine the accuracy of the ACM method. DESIGN: Comparative study of the sonographic technique of ACM versus cardiac output measured by thermodilution (TD). METHODS: The study included 39 intensive care patients, 21 men, 13 non-pregnant women and five severely pre-eclamptic pregnant patients, with a wide range of cardiac outputs, in whom TD catheters had been inserted for clinical reasons. Two separate experienced observers, blinded to the results obtained with the other method, performed four successive measurements in each patient with either the ACM or TD technique. The averaged cardiac output value per patient and method was used for comparison. RESULTS: Cardiac output was successfully measured with ACM and TD in 85 and 100% of patients, respectively. Mean cardiac output measured by ACM (6.77 +/- 1.90 L/min) was significantly lower than that measured by TD (9.12 +/- 3.06 L/min). Although cardiac output values obtained with ACM were significantly correlated with those measured by TD, the ACM values were consistently lower than TD values in the higher cardiac output range; the relationship was represented by ACM = 0.35 TD + 3.55 L/min (r = 0.57, P < 0.001). The (ACM - TD) difference increased significantly with cardiac output, through a difference in stroke volume, not in heart rate. CONCLUSION: The ACM is not an accurate tool to measure cardiac output in patients with a high cardiac output, including treated pre-eclamptic women.

Adult↗

PubMed1999

Automated infusion of vasoactive and inotropic drugs to control arterial and pulmonary pressures during cardiac surgery.

OBJECTIVE: To evaluate the feasibility of a closed-loop system for simultaneous control of systemic arterial and pulmonary artery blood pressures during cardiac surgery. DESIGN: Feasibility study. SETTING: The cardiac surgery operating room. PATIENTS: The performance of the multiple-drug closed-loop system was evaluated during cardiac surgery in 30 patients who required treatment with more than one vasoactive or inotropic drug. INTERVENTIONS: A multiple-drug closed-loop system integrated five single-drug blood pressure controllers. Arterial hypertension was controlled using sodium nitroprusside or nitroglycerin, arterial hypotension was controlled using noradrenaline or dobutamine, and pulmonary hypertension was controlled using nitroglycerin. The anesthesiologist selected target pressures and single-drug blood pressure controllers. The multiple-drug closed-loop system had a set of priority rules that automatically activated from the selected single-drug controllers the optimum single-drug controller for each hemodynamic state. Drug infusion rates of the nonactive controllers were kept constant. The initial knowledge that was used to construct the priority rules was obtained from standard anesthetic protocols on perioperative management of cardiac surgical patients. A supervisory computer program defined the actions to be taken in cases of infusion pump problems, invalid pressure measurements, and during unexpected increases and decreases in systemic arterial pressure. MEASUREMENTS AND MAIN RESULTS: The activation of single-drug controllers by the priority rules was accurate and fast. On average, a different single-drug controller was activated once every 7.2 mins. As a measure of variability, the average deviation of mean arterial pressure and mean pulmonary artery pressure from their target values was evaluated and was 8.6+/-4.0 and 4.4+/-4.0 mm Hg, respectively, before cardiopulmonary bypass and 8.0+/-3.6 and 2.4+/-0.9 mm Hg, respectively, after cardiopulmonary bypass. None of the single-drug controllers showed any signs of unstable response. CONCLUSION: Closed-loop control of both arterial and pulmonary pressures using multiple drugs is feasible during cardiac surgery.

Adult↗

PubMed1998

The compliance of the porcine pulmonary artery depends on pressure and heart rate.

1. The influence of mean pulmonary arterial pressure (mean Ppa) on dynamic (Cd) and pseudo-static compliance (Cps) of the pulmonary artery was studied at a constant and a changing heart rate. Cd is the change in cross-sectional area (CSA) relative to the change in Ppa throughout a heart cycle. Cps is the change in mean CSA relative to the change in mean Ppa. If Cd is known, pulmonary blood flow can be computed from the Ppa using a windkessel model. We investigated whether Cps can be interchanged with Cd. 2. In nine anaesthetized pigs, we determined the mean CSA and Cd of the pulmonary artery at various Ppa levels, ranging from approximately 30 to 10 mmHg, established by bleeding. Two series of measurements were carried out, one series at a spontaneously changing heart rate (n = 9) and one series at a constant heart rate (n = 6). To determine CSA a conductance method was used. 3. Cps depended on pressure. The mean CSA versus mean Ppa curves were sigmoid and steepest in the series with the increasing heart rate (established by bleeding). The CSA versus Ppa loop during a heart cycle, giving Cd, was approximately linear and almost closed. The Cd versus mean Ppa relationship was bell shaped. Its width was smaller if the heart rate increased during the series of measurements. The pressure, where Cd was maximum, was higher at higher heart rates. Furthermore, the maximum Cd was not affected by the heart rate. 4. Because the pulmonary artery constricts with increasing heart rate, Cps will be overestimated during procedures where heart rate increases. Cd should be determined on a beat-to-beat basis to calculate flow because it changes with mean pulmonary arterial pressure and heart rate.

Algorithms↗

PubMed1998

Tracing best PEEP by applying PEEP as a RAMP.

OBJECTIVE: The aim of this study was to show the feasibility of a slow, continuously increasing level of positive end-expiratory pressure (PEEP) (ramp manoeuvre) in selecting best PEEP and to evaluate whether best PEEP, as defined by maximal oxygen transport, coincides with best systemic arterial oxygenation or best compliance. DESIGN: In 11 anaesthetized piglets, PEEP was increased between 0 cmH2O (zero end-expiratory pressure; ZEEP) and 15 cmH2O (PEEP15) with a constant rate of 0.67 cmH2O x min(-1). This ramp manoeuvre was performed both under normal conditions and after induction of an experimental lung oedema. During the ramp manoeuvre, haemodynamic and pulmonary variables were monitored almost continuously. RESULTS: During the rise in PEEP, cardiac output declined in a non-linear way. In the series with normal conditions, best PEEP was always found at ZEEP. In the series with experimental lung oedema, best PEEP, as defined by maximum oxygen transport, was found at PEEP1-6, as defined by maximal compliance, at PEEP7.5 and by maximal arterial oxygen tension (PaO2) at PEEP10-14. CONCLUSIONS: Best PEEP according to oxygen transport is lower than best PEEP according to compliance and PaO2; the use of PEEP as a ramp might prevent unnecessarily high levels of PEEP.

Animals↗

PubMed1997

Left ventricular pressure-volume relationships before and after cardiomyoplasty in patients with heart failure.

BACKGROUND: The aim of this study was to elucidate whether beneficial effects of cardiomyoplasty (CMP) in patients with dilated cardiomyopathy are the result of a decrease in existing ventricular dilatation or a prevention of further dilatation. METHODS AND RESULTS: Combined micromanometer-conductance catheters were used to evaluate left ventricular pressure-volume relationships in six patients with dilated cardiomyopathy before and at 6 and 12 months after CMP. Acute changes in preload and afterload were induced by a standardized leg-tilting intervention and a bolus infusion of nitroglycerin. After CMP, end-diastolic volume (EDV) decreased from 138+/-10 to 103+/-18 mL/m2 (P<.01) at 6 months and to 83+/-17 mL/m2 (P<.01) at 12 months. End-diastolic pressure (EDP) decreased from 20.2+/-6.4 to 13.9+/-7.7 mm Hg (P<.01) at 6 months after CMP. Peak ejection rate and ejection fraction increased at 6 months after CMP from 594+/-214 to 799+/-214 mL/s (P<.05) and from 26.6+/-4.7% to 40.1+/-8.3% (P<.05), respectively. Peak dP/dt decreased at 12 months after CMP from -842+/-142 to -712+/-168 mm Hg/s (P<.05). Leg-tilting before CMP increased EDP from 20.2+/-6.4 to 25.6+/-5.2 mm Hg (P<.01), end-systolic pressure (ESP) from 118+/-17 to 122+/-17 mm Hg (P<.05), and tau from 50.8+/-2.8 to 53.8+/-2.3 ms (P<.05). Six months after CMP, leg-tilting also increased EDV from 103+/-18 to 110+/-22 mL/m2 (P<.05) and ESV from 62+/-14 to 66+/-14 mL/m2 (P<.05). Before CMP, nitroglycerin decreased EDP from 20.2+/-6.4 to 10.4+/-3.8 mm Hg (P<.01), ESP from 118+/-17 to 96+/-11 mm Hg (P<.05), ESV from 100+/-11 to 89+/-7 mL/m2 (P<.05), and tau from 50.8+/-2.8 to 44.5+/-3.7 ms (P<.05). Six months after CMP, nitroglycerin decreased EDP, ESP, and tau to similar values. CONCLUSIONS: Our findings show that up to 1 year after CMP, marked decreases in left ventricular volume are present. Our measurements suggest that CMP actively reduced the dilated ventricle but did not prevent a higher EDV on an increased venous return. The latissimus dorsi muscle wrap contraction results in better synchronization of contraction and more rapid emptying of the left ventricle.

Cardiomyopathy, Dilated↗

PubMed1997

Near continuous cardiac output by thermodilution.

A new thermodilution method for frequent (near continuous) estimation of cardiac output, without manual injection of fluid into the blood, was tested. The method utilizes a pulmonary artery catheter equipped with a fluid filled heat exchanger. The technique is based on cyclic cooling of the blood in the right atrium and measurement of the temperature changes in the pulmonary artery. Using this technique, a new estimate of cardiac output can be obtained every 32 s. Cardiac output estimates, obtained for a running mean of three measurements with this method, were compared to the mean of three conventional thermodilution measurements. The measurements were obtained during short periods of stable respiration and circulation. In six pigs, we made 46 paired measurements of conventional thermodilution (TD) and near continuous (TDc) thermodilution. The cardiac output (COTD) ranged from 2.4-13.7 l/min (mean 5.4 l/min). The best linear fit through the paired data points was COTDc = -0.57 + 1.01 COTD. The mean difference between the methods was -0.50 l/min (S.D. = 0.39). The mean coefficient of variation of repeated measurements with the near continuous thermodilution was 3.6%. Considering changes of more than 0.25 l/min to be significant, all changes in cardiac output measured by conventional thermodilution were followed by the running mean of three near continuous thermodilution estimates. This study demonstrates the feasibility of the new method to monitor cardiac output, and to detect all changes greater than 0.25 l/min.

Animals↗

PubMed1997

Detection of dicrotic notch in arterial pressure signals.

OBJECTIVE: A novel algorithm to detect the dicrotic notch in arterial pressure signals is proposed. Its performance is evaluated using both aortic and radial artery pressure signals, and its robustness to variations in design parameters is investigated. METHODS: Most previously published dicrotic notch detection algorithms scan the arterial pressure waveform for the characteristic pressure change that is associated with the dicrotic notch. Aortic valves, however, are closed by the backwards motion of aortic blood volume. We developed an algorithm that uses arterial flow to detect the dicrotic notch in arterial pressure waveforms. Arterial flow is calculated from arterial pressure using simulation results with a three-element windkessel model. Aortic valve closure is detected after the systolic upstroke and at the minimum of the first negative dip in the calculated flow signal. RESULTS: In 7 dogs ejection times were derived from a calculated aortic flow signal and from simultaneously measured aortic flow probe data. A total of 86 beats was analyzed; the difference in ejection times was -0.6 +/- 5.4 ms (means +/- SD). The algorithm was further evaluated using 6 second epochs of radial artery pressure data measured in 50 patients. Model simulations were carried out using both a linear windkessel model and a pressure and age dependent nonlinear windkessel model. Visual inspection by an experienced clinician confirmed that the algorithm correctly identified the dicrotic notch in 98% (49 of 50) of the patients using the linear model, and 96% (48 of 50) of the patients using the nonlinear model. The position of the dicrotic notch appeared to be less sensitive to variations in algorithm's design parameters when a nonlinear windkessel model was used. CONCLUSIONS: The detection of the dicrotic notch in arterial pressure signals is facilitated by first calculating the arterial flow waveform from arterial pressure and a model of arterial afterload. The method is robust and reduces the problem of detecting a dubious point in a decreasing pressure signal to the detection of a well-defined minimum in a derived signal.

Algorithms↗

PubMed1997

Components of carbon monoxide transfer at different alveolar volumes during mechanical ventilation in pigs.

We studied the effect of increasing alveolar volume on pulmonary carbon monoxide transfer (DLCO) and its components, i.e. membrane diffusing capacity (DM) and capillary blood volume (Qc), during mechanical ventilation in eight anaesthetized and paralysed healthy pigs (mean weight 11.2 kg). We used an inspiratory pause procedure for simulation of the single-breath technique, and inflated 15, 20, 25 and 30 ml kg-1 in random order. DM and Qc were derived using the Roughton-Forster equation. Per litre BTPS increase in effective VA, DLCO (inspiratory oxygen fraction 0.30) decreased on average by 11.8 mumol s-1 kPa-1, DM slightly increased by 2.7 mumol s-1 kPa-1 and Qc decreased by 241 ml. The increase in DM was much smaller than might be expected from the increase in VA, which we ascribe to a loss of the alveolar capillary membrane for gas transfer because of the concomitant decrease in Qc. The decrease in Qc may be explained by a squeezing effect of the intrapulmonary pressure rise on the alveolar wall and by stretching of lung tissue.

Animals↗

PubMed1996

A stable model of respiratory distress by small injections of oleic acid in pigs.

OBJECTIVE: Development of a stable model of respiratory distress in pigs with oleic acid, fulfilling clinical criteria of the adult respiratory distress syndrome (ARDS). DESIGN: Eight pigs (9.1 +/- 0.7 kg) were anesthetized with pentobarbital, paralyzed with tubocurarine and mechanically ventilated with an FIO2 of 0.6, an I:E ratio of 2:3 and a PEEP of 0.2 kPa. Oleic acid (dissolved 1:1 in 96% alcohol) was administered in a series of multiple injections of 0.1 ml until PaO2 was lower than 8 kPa. MEASUREMENTS AND RESULTS: Careful titration of the oleic acid injections on guidance of the PaO2 established a reproducible respiratory distress (PaO2 = 7.3 +/- 0.8 kPa), in which gas exchange and hemodynamic variables were stable for at least 4 h. The number of oleic acid injections (22 +/- 11, mean and SD) varied between the animals. CONCLUSIONS: With the use of multiple injections of oleic acid, a stable model of early respiratory distress in pigs can be achieved, in spite of individual differences in sensitivity. Such a stable model allows for a diversity of studies on early respiratory distress.

Animals↗

PubMed1996

Haemodynamic and respiratory conditions during alternating and synchronous ventilation of both lungs.

OBJECTIVE: We tested the hypothesis that mean thoracic expansion (and mean lung volume) is lower during alternating ventilation (AV), i.e. ventilation of both lungs with a phase shift of half a ventilatory cycle, compared to synchronous ventilation (SV) of both lungs. As a consequence, intrathoracic pressure will be lower, causing lower, central venous pressure and higher cardiac output. DESIGN: In eight anaesthetized and paralysed piglets, differential ventilation was established by fixation of an endobronchial tube in the left main bronchus. SV and AV were sequentially applied for four and three periods, respectively, of 10 minutes each. Minute ventilation was the same during AV and SV and adapted to normocapnia. Two series of observations were performed: series 1 with intact thorax and monitoring of oesophageal pressure; series 2 after perforation of the sternum, airtight closure of the thorax and monitoring of pericardial pressure. RESULTS: In both series, mean lung volume was 16 +/- 4% lower and central venous, oesophageal (series 1) and pericardial pressures (series 2) were 0.5-0.7 mmHg lower during AV compared to SV (all p < 0.001). In series 1, aortic pressure was 5 mmHg and cardiac output 8% higher (both p < 0.001). In series 2, cardiac output was 5% higher during AV (p < 0.001), but aortic pressure did not change (p = 0.07). CONCLUSION: Our data verified the hypothesis. The lower oesophageal (series 1), pericardial (series 2) and central venous pressures during AV compared to SV could be explained by the smaller thoracic expansion due to the lower mean lung volume, which was attributed to compression of the opposite lung by the, expansion of the inflated lung.

Animals↗

PubMed1996

Correction for respiration artifact in pulmonary blood pressure signals of ventilated patients.

OBJECTIVE: To develop an algorithm that corrects pulmonary artery pressure signals of ventilated patients for the respiration artifact. The algorithm should test the validity of the pulmonary pressure signal and differentiate between the cyclic respiration artifact and true measurement artifacts. METHODS: The shape of each pulmonary pressure beat is described by eight characteristic features, including mean pressure value and the systolic and diastolic timing and pressure values. The features are corrected for the respiration artifact by fitting them in a least-squares sense on the first and second harmonics of the ventilator frequency. The corrected features are used by a signal validation algorithm, which adds a validity flag to each pressure beat. The validation algorithm rejects pressure beats with sudden changes in their shape but adapts itself when the changes persist. RESULTS: The performance of the correction and validation technique was evaluated using pulmonary artery pressure signals of 30 patients who were scheduled for open heart surgery. The algorithm correctly recognized as invalid data those pressure signals disturbed by coagulation, surgical manipulations, or flushes of the pressure line. The algorithm marked on average 77 +/- 11% of the pulmonary pressure beats as valid. CONCLUSIONS: The validation algorithm marked sufficient pressure beats as valid to update a trend display every 5 sec. The correction algorithm enabled the validation algorithm to differentiate between true measurement artifacts and the respiration artifact.

Algorithms↗

PubMed1996

Effects of endotoxin infusion on mean systemic filling pressure and flow resistance to venous return.

Mean systemic filling pressure (Psf) is an indicator of the filling state of the systemic circulation. Cardiac output (Q') is related linearly to the difference between Psf and central venous pressure (Pcv), according to: Q' = (Psf - Pcv)/Rsf, where Rsf is the flow resistance downstream from the sites where blood pressure is equal to Psf. In 16 anaesthetized pigs we evaluated Psf, Rsf and Q' during baseline conditions, continuous endotoxin infusion and after subsequent fluid loading. Psf and Rsf were determined from simultaneous measurements of Q' and Pcv at seven levels of lung inflation. The following results were obtained. Psf was 8.1 +/- 1.8 mm Hg (mean +/- SD) during baseline conditions, increased after endotoxin infusion to 9.9 +/- 3.2 mm Hg (P = 0.04) and remained the same after infusion of 18 ml kg-1 of Ringer s lactate. Rsf increased from 0.34 +/- 0.07 to 0.80 +/- 0.34 mm Hg ml-1 s by endotoxin and decreased after fluid infusion to 0.58 +/- 0.14. Q' changed inversely proportional to Rsf (P = 0.001). Rsf changes were highly correlated with the changes in total systemic flow resistance (Rs) (P < 0.001). Endotoxin caused haemoconcentration and a decrease in plasma volume. The stability of Psf during endotoxin infusion and after volume loading indicate that the stressed volume was well maintained and changes in blood volume are compensated by changes in non-stressed volume. The increase in Rsf can be attributed to arteriolar vasoconstriction, venous vasoconstriction and haemoconcentration.

Animals↗

PubMed1996

Systemic filling pressure in the intact circulation determined with a slow inflation procedure.

In eight mechanically ventilated, anaesthetized pigs weighing 10.3 +/- 0.8 kg (mean +/- SD) we studied the effect of the inflation time of the lung on the estimation of the mean systemic filling pressure (Psf) from the changes in venous return and central venous pressure during inflation of the lung. For this purpose we applied slow inflation procedures (SIP) to the lung with inflation times of 2.4, 4.8, 7.2, 9.6 and 12 s at tidal volumes (VT) of 15 and 30 ml/kg. The data were compared with the values of Psf obtained from inspiratory pause procedures (IPPs). A linear regression between venous return and central venous pressure applied during a SIP underestimated Psf compared with the value obtained with IPPs. An exponential fit through the values of Psf obtained from the different SIPs predicted an inflation time of about 15 s for an estimation of Psf that is not different from the Psf (IPP). The advantage of the SIP method is that the Psf can be determined much faster than with the method based on IPPs. However, due to the rather long inflation time needed, the method may be only applicable under circumstances where neurohumoral control mechanisms are suppressed as during intensive care and anaesthesia.

Anesthesia↗