Introduction
Materials and methods
Animals
Anesthesia
Multi-electrode method to separate ventricular from atrial filling
Electrode # | Position X (in mm) Horizontal position (left-right) with respect to Gauge Point (GP). Orientation: The left-lateral side of the thorax has positive X values | Position Y (in mm) Vertical position (cranial-caudal) with respect to Gauge Point (GP). Orientation: The cranial end of the thorax has positive Y values |
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1 | 24.5 | 9.1 |
2 | -28.1 | 34.2 |
3 | -36.0 | -16.2 |
4 | 64.9 | 28.8 |
5 | -59.5 | 46.8 |
6 | -27.0 | -81.1 |
7 | -41.4 | 158.7 |
8 | -9.0 | -131.6 |
9 | -86.5 | 61.3 |
Measuring equipment
Manipulation of cardiac output
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Decrease in venous return induced by a vena cava obstruction. For this purpose, a 3-0 prolene wire (Ethicon Inc., Somerville, New Jersey, USA) was placed around the vena cava. A step-wise decrease of cardiac output, as monitored by the ultrasonic flow-probe, could be obtained by step-wise tightening of the prolene wire.
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Increase in heart rate by external cardiac pacing (Q-stim, Biosense Webster Inc., Diamond Bar, California, USA) connected to the stimulator output of a Physio-control Lifepack 9 defibrillator (Physio-control Inc., Redmond, Washington, USA.)
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Inotropic stimulation by administration of dobutamine (5 μg/kg/minute b.w. i.v.)
Data acquisition and averaging
Initial calibration
Statistical analysis
Results
Animal # | Type | Gender | Weight (kg) | Age (weeks) |
---|---|---|---|---|
1 | Dalland Pig | Female | 45,. | 12 |
2 | Dalland Pig | Female | 45 | 12 |
3 | Dalland Pig | Female | 44 | 12 |
4 | Dalland Pig | Female | 42.6 | 12 |
5 | Dalland Pig | Female | 33 | 10 |
6 | Dalland Pig | Female | 82 | 19 |
Measured cardiac output data
Baseline | Vena cava constriction (maximal) | Pacing (140 bpm) | Dobutamine (7 minutes) | |
---|---|---|---|---|
HR (bpm) | 54 ± 8 | 63 ± 11 | 140 ± 1 | 89 ± 14 |
MAP (mmHg) | 118 ± 17 | 96 ± 27 | 113 ± 23 | 138 ± 26 |
Type of manipulation | Number of changes > SD | Concordant* | Discordant* | False positive* | False negative* |
---|---|---|---|---|---|
Vena cava constriction | 46 | 42 (91.3%) | 1 (2.2%) | 2 (4.3%) | 1 (2.2%) |
Cardiac pacing | 4 | 3 (75.0%) | 0 | 1 (25.0%) | 0 |
Dobutamine | 8 | 7 (87.5%) | 0 | 1 (12.5%) | 0 |
All manipulations combined | 58 | 52 (89.6%) | 1 (1.7%) | 4 (6.9%) | 1 (1.7%) |
Discussion
Comparison between HCP and ICG
Conclusions
Key messages
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In an animal model we demonstrated that the new technique of cardiac output monitoring (HCP) is able to track changes in cardiac output.
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In contrast to impedance-based methods, the new system (HCP) enables specific measurement of changes in ventricular volume, instead of changes in total heart volume.
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The HCP produces eight independent and simultaneous voltage input streams, connected to eight independent voltage demodulator units. This enables recognition of the effect of ventricular volume changes in the applied field on the thoracic skin.
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An Ultrasonic Flow Probe (FP) around the aorta was used as the gold standard.
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In a study on six pigs, Pearson's correlation between the CO-HCP and the CO-FP was r = 0.978. Bland-Altman analysis showed a bias of - 0.114 L/minute, and variability of the bias (2SD) of 0.55 L/minute.