Novel non-invasive techniques for hemodynamic monitoring

The monitoring of hemodynamic parameters is crucial for optimal patient management and treatment. However, established methods are often invasive and possibly inapplicable to sensitive age groups. Novel, non-invasive techniques have the potential to transform cardiovascular (CV) assessment, offering reduced hospitalization periods, lower infection risk and decreased staff-to-patient ratio. Cardiac output (CO) monitoring provides valuable insight on global tissue perfusion. To overcome limitations of traditional methods, a novel technique was proposed. Taking into account the basic principles of CV physiology we derived an equation where the required variables can be extracted non-invasively. The novel technique was validated in a controlled, in silico, environment against previously established wave analysis methods. Subsequent data analysis showed that the new method yielded superior accuracy and precision. The new method was further evaluated in vivo using a 2D transthoracic echocardiography protocol for CO estimation. The corresponding comparison showed that the SVB method provides highly reproducible and accurate estimates of CO when compared to ultrasound. The estimation of pulse transit time (PTT) affects critically the accuracy and precision of pulse wave velocity (PWV) measurements. We proposed the "Diastole-Patching" method (DPm), which estimates PTT based on a signal region in the diastolic foot of the wave and is more robust against noisy arterial waveforms. DPm and previously established techniques were tested with a computational model of the arterial tree where the "real" values of PWV are known. The novel method yielded the highest agreement, accuracy and precision even when the waves were distorted with noise. The technique was further evaluated against the corresponding â"reference" algorithm of a commercially available device with in vivo acquired waves. DPm yielded more precise and reproducible measurements of PWV. Total Systemic Compliance (CT) expresses the ability of the arterial system to dilate and store blood during cardiac ejection. Our aim was to develop a relationship between aPWV and CT. The proposed, generalized Bramwell-Hill model of the systemic arterial tree estimates CT by a single non-invasive measurement of PWV. The proposed scheme was found to accurately estimate CT from aPWV. The mechanical properties of woven Dacron grafts differ significantly from the human aorta. As a result, aortic graft implantation changes the aortic geometry and mechanical properties, thus affecting blood pressure and wave reflections. A dedicated cardiovascular model was developed to include graft geometry and in vitro measured Dacron properties. It was found that aortic reconstruction affected aortic hemodynamics. For the proximal graft, the primary reason for pulse pressure rise is augmentation of the forward wave. For the distal graft, the pulse pressure rise is associated with augmented wave reflections resulting from the compliance mismatch between the aorta and the distal graft. To conclude, this body of work has shown that given the current computational tools and biosensors, it is possible to design and validate a set of non-invasive techniques that will provide valuable clinical insight for a wide gamut of cardiovascular diseases.

The "systolic volume balance" method for the noninvasive estimation of cardiac output based on pressure wave analysis

Nikolaos Stergiopulos, Orestis Vardoulis

Papaioannou TG, Vardoulis O, Stergiopulos N. The "systolic volume balance" method for the noninvasive estimation of cardiac output based on pressure wave analysis. Am J Physiol Heart Circ Physiol 302: H2064-H2073, 2012. First published March 16, 2012; doi: 10.1152/ajpheart.00052.2012.-Cardiac output (CO) monitoring is essential for the optimal management of critically ill patients. Several mathematical methods have been proposed for CO estimation based on pressure waveform analysis. Most of them depend on invasive recording of blood pressure and require repeated calibrations, and they suffer from decreased accuracy under specific conditions. A new systolic volume balance (SVB) method, including a simpler empirical form (eSVB), was derived from basic physical principles that govern blood flow and, in particular, a volume balance approach for the conservation of mass ejected into and flowed out of the arterial system during systole. The formulas were validated by a one-dimensional model of the systemic arterial tree. Comparisons of CO estimates between the proposed and previous methods were performed in terms of agreement and accuracy using "real" CO values of the model as a reference. Five hundred and seven different hemodynamic cases were simulated by altering cardiac period, arterial compliance, and resistance. CO could be accurately estimated by the SVB method as follows: CO = C x PPao/(T - P-sm x T-s/P-m) and by the eSVB method as follows: CO = k x C x PPao/T, where C is arterial compliance, PPao is aortic pulse pressure, T is cardiac period, P-sm is mean systolic pressure, T-s is systolic duration, P-m is mean pressure, and k is an empirical coefficient. SVB applied on aortic pressure waves did not require calibration or empirical correction for CO estimation. An empirical coefficient was necessary for brachial pressure wave analysis. The difference of SVB-derived CO from model CO (for brachial waves) was 0.042 +/- 0.341 l/min, and the limits of agreement were -0.7 to 0.6 l/min, indicating high accuracy. The intraclass correlation coefficient and root mean square error between estimated and "real" CO were 0.861 and 0.041 l/min, respectively, indicating very good accuracy. eSVB also provided accurate estimation of CO. An in vivo validation study of the proposed methods remains to be conducted.

2012

Noninvasive estimation of aortic hemodynamics and cardiac contractility using machine learning

Vasiliki Bikia, Stamatia Zoi Pagoulatou, Georgios Rovas, Nikolaos Stergiopulos

Cardiac and aortic characteristics are crucial for cardiovascular disease detection. However, noninvasive estimation of aortic hemodynamics and cardiac contractility is still challenging. This paper investigated the potential of estimating aortic systolic pressure (aSBP), cardiac output (CO), and end-systolic elastance (E-es) from cuff-pressure and pulse wave velocity (PWV) using regression analysis. The importance of incorporating ejection fraction (EF) as additional input for estimating E-es was also assessed. The models, including Random Forest, Support Vector Regressor, Ridge, Gradient Boosting, were trained/validated using synthetic data (n = 4,018) from an in-silico model. When cuff-pressure and PWV were used as inputs, the normalized-RMSEs/correlations for aSBP, CO, and E-es (best-performing models) were 3.36 +/- 0.74%/0.99, 7.60 +/- 0.68%/0.96, and 16.96 +/- 0.64%/0.37, respectively. Using EF as additional input for estimating E-es significantly improved the predictions (7.00 +/- 0.78%/0.92). Results showed that the use of noninvasive pressure measurements allows estimating aSBP and CO with acceptable accuracy. In contrast, E-es cannot be predicted from pressure signals alone. Addition of the EF information greatly improves the estimated E-es. Accuracy of the model-derived aSBP compared to in-vivo aSBP (n = 783) was very satisfactory (5.26 +/- 2.30%/0.97). Future in-vivo evaluation of CO and E-es estimations remains to be conducted. This novel methodology has potential to improve the noninvasive monitoring of aortic hemodynamics and cardiac contractility.

2020

Coronary waves during valsalva maneuver measured during catheterization

Maria Cristina Rolandi

The mechanical interactions between heart contraction and perfusion of the heart are difficult to study in humans because of the restrictions in inducing changes in hemodynamic and cardiac mechanics parameters during catheterization. We hypothesize that the Valsalva maneuver can induce such alterations in the cardiac-coronary mechanical interaction and that these variations can be studied with the Wave Intensity Analysis. In order to interpret eventual changes in the wave intensity, a deep understanding of the effect of the Valsalva maneuver on the coronary circulation is needed. A particular attention has to be payed on the effect of the control of the microvascular resistance that is known to compensate for eventual alterations in the surrounding hemodynamic conditions when vessel tone is intact. In the catheterization laboratory, coronary pressure and flow velocity signals were recorded simultaneously by a new guidewire developed by Volcano Corporation. Aortic pressure, left ventricular pressure and ECG were acquired by the catheterization laboratory setup and recorded together with coronary hemodynamic signals. Left ventricular performance parameters were derived per beat from the noninvasive recording of the finger pressure using the Nexfin monitor developed by BMEYE B.V. In order to match the output data of coronary hemodynamic and left ventricular performance parameters, a dedicated program has been written in Delphi. An analysis of the per-beat data was performed in order to study the relative dependence of the parameters during the Valsalva maneuver. Pilot results of the Wave Intensity Analysis were obtained with an existing custom-made program also written in Delphi. Our study shows that the Valsalva maneuver caused a profound stress in the whole cardiovascular system. The well-known changes of the aortic pressure were transmitted also to the left ventricle and the coronary microcirculation. The data show that this stress caused a small but significant decrease in the flow velocity. As expected, the microvascular resistance varied with the same pattern as the coronary pressure trying to keep the flow constant. With respect to the decrease in stroke volume, cardiac output and contractility, the left ventricular performance was strongly compromised: pulse pressure generation and cardiac contraction were almost annulled. The decrease in systolic left ventricular pressure of almost 40% and the 2 fold increase in the end-diastolic left ventricular pressure confirm the decrease in the pumping action. Consequentially, the oxygen consumption of the heart decreased to 40% of the baseline level but only after an initial increase at the onset of the strain by 10%. The results also show that the timing of variation of the parameters was not the same. Especially the left ventricular end-diastolic pressure changed more rapidly than the perfusion pressure. Pilot results on Wave Intensity Analysis (WIA) show that the Valsalva maneuver gave rise to changes in the Wave Intensity pattern suggesting that the speed of the reflected waves has indeed been altered. Our results agree with previous studies that reveal a slight decrease in the flow velocity due to the Valsalva maneuver. Nevertheless, our results contradict the belief that ascribes the decrease in flow velocity to the decrease in oxygen consumption. We assume that the flow decrease is due to mechanical factors, especially the rise of left ventricular end-diastolic pressure. The results shown on WIA are pilot results and some work is still needed in this direction to obtain more information on the coronary-cardiac interaction. However, these results give confidence about the use of the Valsalva maneuver as an intervention affecting external parameters and thus they are useful in the study of coronary-cardiac interaction in humans.