Non-invasive Stroke Volume Measurement Research Articles

Noninvasive Beat-To-Beat Stroke Volume Measurements to Determine Preload Responsiveness During Mini-Fluid Challenge in a Swine Model: A Preliminary Study.

Cardiac output (CO) is an important parameter in fluid management decisions for treating hemodynamically unstable patients in intensive care unit. The gold standard for CO measurements is the thermodilution method, which is an invasive procedure with intermittent results. Recently, electrical impedance tomography (EIT) has emerged as a new method for noninvasive measurements of stroke volume (SV). The objectives of this paper are to compare EIT with an invasive pulse contour analysis (PCA) method in measuring SV during mini-fluid challenge in animals and determine preload responsiveness with EIT. Five pigs were anesthetized and mechanically ventilated. After removing 25% to 30% of the total blood from each animal, multiple fluid injections were conducted. The EIT device successfully tracked changes in SV beat-to-beat during varying volume states, i.e., from hypovolemia and preload responsiveness to target volume and volume overload. From a total of 50 100-mL fluid injections on five pigs (10 injections per pig), the preload responsiveness value was as large as 32.3% in the preload responsiveness state while in the volume overload state it was as low as -4.9%. The bias of the measured SV data using EIT and PCA was 0 mL, and the limits of agreement were ±3.6 mL in the range of 17.6 mL to 51.0 mL. The results of the animal experiments suggested that EIT is capable of measuring beat-to-beat SV changes during mini-fluid challenge and determine preload responsiveness. Further animal and clinical studies will be needed to demonstrate the feasibility of the EIT method as a new tool for fluid management.

Improvement of Left Ventricular Ejection Time Measurement in the Impedance Cardiography Combined with the Reflection Photoplethysmography.

Cardiac stroke volume (SV) is an essential hemodynamic indicator that can be used to assess whether the pump function of the heart is normal. Non-invasive SV measurement is currently performed using the impedance cardiography (ICG). In this technology, left ventricular ejection time (LVET) is an important parameter which can be determined from the ICG signals. However, the ICG signals are inherently susceptible to artificial noise interference, which leads to an inaccurate LVET measurement and then yields an error in the calculation of SV. Therefore, the goal of the study was to measure LVETs using both the transmission and reflection photoplethysmography (PPG), and to assess whether the measured LVET was more accurate by the PPG signal than the ICG signal. The LVET measured by the phonocardiography (PCG) was used as the standard for comparing with those by the ICG and PPG. The study recruited ten subjects whose LVETs were simultaneously measured by the ICG using four electrodes, the reflection PPG using neck sensors (PPGneck) and the transmission PPG using finger sensors (PPGfinger). In each subject, ten LVETs were obtained from ten heartbeats selected properly from one-minute recording. The differences of the measured LVETs between the PCG and one of the ICG, PPGneck and PPGfinger were −68.2 ± 148.6 ms, 4.8 ± 86.5 ms and −7.0 ± 107.5 ms, respectively. As compared with the PCG, both the ICG and PPGfinger underestimated but the PPGneck overestimated the LVETs. Furthermore, the measured LVET by the PPGneck was the closest to that by the PCG. Therefore, the PPGneck may be employed to improve the LVET measurement in applying the ICG for continuous monitoring of SV in clinical settings.

Echocardiographic Evaluation of Hemodynamics in Patients With Decompensated Systolic Heart Failure

Doppler echocardiography is currently applied for the assessment of left ventricular and right ventricular hemodynamics in patients with cardiovascular disease. However, there are conflicting reports about its accuracy in patients with unstable decompensated heart failure. The objective of this study was to evaluate the accuracy of the technique in patients with unstable heart failure. Consecutive patients with decompensated heart failure had simultaneous assessment of left ventricular and right ventricular hemodynamics invasively and by Doppler echocardiography. In 79 patients, the noninvasive measurements of stroke volume (r=0.83, P<0.001), pulmonary artery systolic (r=0.83, P<0.001) and diastolic pressure (r=0.51, P=0.009), and mean right atrial pressure (r=0.85, P<0.001) all had significant correlations with invasively acquired measurements. Several Doppler indices had good accuracy in identifying patients with pulmonary capillary wedge pressure >15 mm Hg (area under the curve, 0.86 to 0.92). The recent American Society of Echocardiography/European Association of Echocardiography guidelines were highly accurate (sensitivity, 98%; specificity, 91%) in identifying patients with increased wedge pressure. In 12 repeat studies, Doppler echocardiography readily detected the changes in mean wedge pressure (r=0.75, P=0.005) as well as changes in pulmonary artery systolic pressure and mean right atrial pressure. Doppler echocardiography provides reliable assessment of right and left ventricular hemodynamics in patients with decompensated heart failure.

Non-invasive stroke volume measurement by cardiac magnetic resonance imaging and inert gas rebreathing in pulmonary hypertension

Right ventricular function determines the prognosis of pulmonary hypertension (PAH). Measurement of stroke volume (SV) non-invasively could be a promising method to monitor disease progression. Cardiac magnetic resonance (CMR) imaging is recognized as an accurate and reproducible method to measure SV. Inert gas rebreathing (IGR) using acetylene is a validated but cumbersome method for pulmonary blood flow (PBF) measurement in PAH. A more convenient rebreathing technique using rapid photoacoustic analysis of nitrous oxide has been introduced and validated in left heart failure. We investigated the accuracy of CMR imaging and IGR using photoacoustic analysis to measure SV in patients under investigation for PAH. Thirty-three patients (16♀:17♂) with suspected PAH following echocardiography had SV measured by CMR imaging (using pulmonary arterial{CMR PA} and aortic {CMR Ao} flow methods) and IGR. The results were compared with our reference standard: thermodilution (TD) measured during right heart catheterization (RHC). All methods showed similar correlation for SV. Bland-Altman analysis confirmed acceptable levels of agreement between the four techniques. TD versus CMR Ao flow had bias (limits of agreement) of -5.41 ml (-22.37 to 11.56 ml), TD versus CMR PA flow 0.12 ml (-20.13 to 20.37 ml) and TD versus IGR 6.25 ml (-16.01 to 28.51 ml). Cardiac magnetic resonance imaging and IGR using photoacoustic analysis in patients with suspected PAH provided non-invasive measurements of SV that agreed closely with those obtained from TD measured during RHC.

Non-invasive stroke volume measurement and passive leg raising predict volume responsiveness in medical ICU patients: an observational cohort study

IntroductionThe assessment of volume responsiveness and the decision to administer a fluid bolus is a common dilemma facing physicians caring for critically ill patients. Static markers of cardiac preload are poor predictors of volume responsiveness, and dynamic markers are often limited by the presence of spontaneous respirations or cardiac arrhythmias. Passive leg raising (PLR) represents an endogenous volume challenge that can be used to predict fluid responsiveness.MethodsMedical intensive care unit (ICU) patients requiring volume expansion were eligible for enrollment. Non-invasive measurements of stroke volume (SV) were obtained before and during PLR using a transthoracic Doppler ultrasound device prior to volume expansion. Measurements were then repeated following volume challenge to classify patients as either volume responders or non-responders based on their hemodynamic response to volume expansion. The change in SV from baseline during PLR was then compared with the change in SV with volume expansion to determine the ability of PLR in conjunction with SV measurement to predict volume responsiveness.ResultsA total of 102 fluid challenges in 89 patients were evaluated. In 47 of the 102 fluid challenges (46.1%), SV increased by ≥15% after volume infusion (responders). A SV increase induced by PLR of ≥15% predicted volume responsiveness with a sensitivity of 81%, specificity of 93%, positive predictive value of 91% and negative predictive value of 85%.ConclusionsNon-invasive SV measurement and PLR can predict fluid responsiveness in a broad population of medical ICU patients. Less than 50% of ICU patients given fluid boluses were volume responsive.

Evaluation of Impedance Cardiography during Anesthesia in Extremely Obese Patients

In three anesthetized markedly obese patients, non-invasive stroke volumes (the transthoracic electrical impedance method) were compared to simultaneously obtained invasively measured stroke volumes (dye-dilution method). Close correlations were obtained (r = 0.90--0.98) between the two methods, although constant lower impedance stroke volumes were found in these patients when the values usually employed for the electrical resistivity of the blood (zeta) were used for calculation of the impedance stroke volume. No statistically significant difference (P greater than 0.10) between the two methods was found when a zeta of 175 ohm X cm was used for the calculations, or when the percentage changes in stroke volumes were analyzed. The impedance method is safe and reliable; it also permits non-invasive measurements of stroke volume during anesthesia in markedly obese patients.