Measurement of Cardiac Output and Blood Volume During Hemodialysis with Fluorescent Dye Dilution Technique.

Intradialytic hypotensive events (IDH) accompanied by deleterious decreases of the cardiac output complicate up to 25% of hemodialysis treatments. Monitoring options available to track hemodynamic changes during hemodialysis have been found ineffective to anticipate the occurrence of IDH. We have assembled opto-electronic instrumentation that uses the fluorescence of a small bolus of indocyanine green dye injected in the hemodialysis circuit to estimate cardiac output and blood volume based on indicator dilution principles in patients receiving hemodialysis. The instrument and technique were tested in 24 adult end-stage renal failure subjects during 64 hemodialysis sessions. A single calibration factor could be used across subjects and across time. Intra-subject variability of the measurements over time was <10%. Stroke volume index (SVI) (mean ± SEM = 34 ± 1 vs. 39 ± 2 mL m-2) and central blood volume (CBV) index (783 ± 36 vs. 881 ± 33 mL m-2) were lower at the beginning of the sessions in which IDH eventually occurred. Cardiac index, SVI, and CBV index decreased with hemodialysis in all treatment sessions but the decrease was more intense in the IDH sessions. We conclude that hemodynamic monitoring can be implemented in patients receiving hemodialysis with minimal disruption of the treatment and could help understand intradialytic hypotension.

Fluorescence dilution technique for measurement of cardiac output and circulating blood volume in healthy human subjects.

BACKGROUND: The authors previously validated in an animal model a new indicator dilution technique for measuring cardiac output and circulating blood volume by recording transcutaneously the fluorescence of circulating indocyanine green with an optical probe placed on the skin surface. The current study compared fluorescence dilution recordings recorded from several locations on the human face in terms of signal intensity and stability and estimated the subjects' cardiac output and circulating blood volume from the recordings. METHODS: Fluorescence dilution traces were recorded transcutaneously in six healthy human volunteers after rapid intravenous injection of 1 mg indocyanine green. Three placements of the optical probe were tested: the nose ala, the ear lobe, and the temple area. In three subjects, the recordings were calibrated in terms of circulating indocyanine green concentration to estimate cardiac output and circulating blood volume. RESULTS: Fluorescence dilution traces had the same duration for the three locations, but the recordings obtained from the nose ala and the ear lobe were twice as intense as those from the temple. The fluorescence intensity at each site was linearly related to the local laser Doppler perfusion index. The coefficient of variation for the area under the first pass curve (inversely proportional to cardiac output) was approximately 6% for triplicate measurements at the same location. Cardiac output and circulating blood volume derived from the fluorescence recordings were in the normal range. CONCLUSIONS: The study demonstrates that intense and reproducible fluorescence dilution signals can be measured transcutaneously in healthy humans and could potentially be used to measure cardiac output and circulating blood volume minimally invasively.

Reduction of compartment compliance increases venous flow pulsatility and lowers apparent vascular compliance: implications for cerebral blood flow hemodynamics.

The global compliance of a fixed-volume, incompressible compartment may play a significant role in determining the inherent vascular compliance. For the intracranial compartment, we propose that the free-displacement of the cerebral spinal fluid (CSF) directly relates to cerebral vascular compliance. To test this hypothesis, an in vivo surrogate intracranial compartment was made by enclosing a rabbit's kidney within a rigid, fluid-filled container. Opening/closing a port atop the box modulated the free flow of box fluid (open-box state). We observed that the pulsatility of the renal venous outflow increased in response to hampering the free flow of fluid in-and-out of the container (closed-box state). To associate the observed pulsatility changes with the compliance changes, a parametric method was proposed for the computation of the apparent compliance (C(app)) of the whole renal vascular system. The calculated C(app) for each experiment's closed-box state was favorably compared to a time-domain compliance assessment method at the mean heart rate. In addition, it was revealed that C(app) in the open-box state was greater than that in the closed-box state only when the calculations were performed at frequencies lower than the heart rate and closer to the ventilation rate. These experimental results support the concept that the vessel compliance of vascular systems enclosed within a rigid compartment is a function of the global compartment compliance.

Transcutaneous fluorescence dilution cardiac output and circulating blood volume during hemorrhagic hypovolemia.

BACKGROUND: Cardiac output and circulating blood volume are important parameters for assessing cardiac function in the intensive care setting and during major surgeries. The authors tested in an animal model of hemorrhagic hypovolemia the feasibility of measuring these parameters simultaneously by transcutaneous fluorescence monitoring of an intravenous bolus injection of indocyanine green. METHODS: Fluorescence dilution cardiac output was measured in seven anesthetized rabbits and compared to thermodilution cardiac output. The optical probe used to excite the indocyanine green fluorescence was in contact with the skin above the ear artery. Local heating enhanced blood perfusion of the measurement site. Cardiac output was measured during baseline conditions, during hemorrhagic hypovolemia, and after partial restoration of the blood volume with reinfused blood. Estimates of the circulating blood volume were simultaneously obtained from the analysis of the fluorescence dilution traces. RESULTS: Cardiac output measured by fluorescence dilution (thermodilution) averaged 455 +/- 16 (450 +/- 13) ml/min in baseline conditions and 323 +/- 15 (330 +/- 13) ml/min during hypovolemia. Fluorescence dilution cardiac output was linearly related to thermodilution cardiac output (slope = 1.13 +/- 0.05, ordinate = -50 +/- 19 ml/min, R = 0.92). Interanimal differences explained most of the variance between cardiac output estimates obtained with the two techniques. Circulating blood volume decreased from 204 +/- 5 ml in baseline conditions to 174 +/- 8 ml after bleeding and reflected blood volume changes in this acute bleeding-reinfusion model. CONCLUSIONS: The study extends the applicability of the fluorescence dilution technique for cardiac output measurement to hypovolemic conditions and demonstrates its ability to produce accurate estimates of the circulating blood volume in experimental animals.

Measurement of cardiac output with indocyanine green transcutaneous fluorescence dilution technique.

BACKGROUND: Cardiac output is an essential parameter for the hemodynamic assessment of patients with cardiovascular disease. The authors tested in an animal model the feasibility of measuring cardiac output by transcutaneous fluorescence monitoring of an intravenous bolus injection of indocyanine green. METHODS: Fluorescence dilution cardiac output was measured in 10 anesthetized rabbits and compared with cardiac output measured with a pulmonary thermodilution catheter and to aortic velocity measured by Doppler ultrasound. Indocyanine green fluorescence was excited with a near-infrared laser and measured with an optical probe positioned on the central ear artery. Measurements were obtained during baseline conditions as well as during short-term decreases and increases of the cardiac output. RESULTS: The fluorescence of circulating indocyanine green detected transcutaneously varied proportionally to that of arterial blood samples, which allowed for calibration in terms of blood concentration of indocyanine green. Average values of fluorescence dilution cardiac output and thermodilution cardiac output measured in baseline conditions were 412 (+/- 13) and 366 (+/- 11) ml/min, respectively. Fluorescence dilution cardiac output showed a close, one-to-one linear relation with thermodilution cardiac output in each animal and in the pooled data from all animals (slope = 0.95 x 0.03; R = 0.94). Fluorescence dilution cardiac output overestimated thermodilution cardiac output by an average of 46 (+/- 6) ml/min during baseline conditions. Fluorescence dilution cardiac output was tightly correlated with aortic velocity. CONCLUSIONS: The proposed technique yielded accurate estimates of the cardiac output in experimental animals. This study should provide an initial framework for clinical testing of this new minimally invasive method for measuring cardiac output.