Subject-specific pulse wave propagation modeling: Towards enhancement of cardiovascular assessment methods.

Cardiovascular diseases are the leading cause of death worldwide. Pulse wave analysis (PWA) technique, which reconstructs and analyses aortic pressure waveform based on non-invasive peripheral pressure recording, became an important bioassay for cardiovascular assessment in a general population. The aim of our study was to establish a pulse wave propagation modeling framework capable of matching clinical PWA data from healthy individuals on a per-subject basis. Radial pressure profiles from 20 healthy individuals (10 males, 10 females), with mean age of 42 ± 10 years, were recorded using applanation tonometry (SphygmoCor, AtCor Medical, Australia) and used to estimate subject-specific parameters of mathematical model of blood flow in the system of fifty-five arteries. The model was able to describe recorded pressure profiles with high accuracy (mean absolute percentage error of 1.87 ± 0.75%) when estimating only 6 parameters for each subject. Cardiac output (CO) and stroke volume (SV) have been correctly identified by the model as lower in females than males (CO of 3.57 ± 0.54 vs. 4.18 ± 0.72 L/min with p-value < 0.05; SV of 49.5 ± 10.1 vs. 64.2 ± 16.8 ml with p-value = 0.076). Moreover, the model identified age related changes in the heart function, i.e. that the cardiac output at rest is maintained with age (r = 0.23; p-value = 0.32) despite the decreasing heart rate (r = -0.49; p-value < 0.05), because of the increase in stroke volume (r = 0.46; p-value < 0.05). Central PWA indices derived from recorded waveforms strongly correlated with those obtained using corresponding model-predicted radial waves (r > 0.99 and r > 0.97 for systolic (SP) and diastolic (DP) pressures, respectively; r > 0.77 for augmentation index (AI); all p-values < 0.01). Model-predicted central waveforms, however, had higher SP than those reconstructed by PWA using recorded radial waves (5.6 ± 3.3 mmHg on average). From all estimated subject-specific parameters only the time to the peak of heart ejection profile correlated with clinically measured AI. Our study suggests that the proposed model may serve as a tool to computationally investigate virtual patient scenarios mimicking different cardiovascular abnormalities. Such a framework can augment our understanding and help with the interpretation of PWA results.

Changes of peritoneal transport parameters with time on dialysis: assessment with sequential peritoneal equilibration test.

BACKGROUND: Sequential peritoneal equilibration test (sPET) is based on the consecutive performance of the peritoneal equilibration test (PET, 4-hour, glucose 2.27%) and the mini-PET (1-hour, glucose 3.86%), and the estimation of peritoneal transport parameters with the 2-pore model. It enables the assessment of the functional transport barrier for fluid and small solutes. The objective of this study was to check whether the estimated model parameters can serve as better and earlier indicators of the changes in the peritoneal transport characteristics than directly measured transport indices that depend on several transport processes. METHODS: 17 patients were examined using sPET twice with the interval of about 8 months (230 ± 60 days). RESULTS: There was no difference between the observational parameters measured in the 2 examinations. The indices for solute transport, but not net UF, were well correlated between the examinations. Among the estimated parameters, a significant decrease between the 2 examinations was found only for hydraulic permeability LpS, and osmotic conductance for glucose, whereas the other parameters remained unchanged. These fluid transport parameters did not correlate with D/P for creatinine, although the decrease in LpS values between the examinations was observed mostly for patients with low D/P for creatinine. CONCLUSIONS: We conclude that changes in fluid transport parameters, hydraulic permeability and osmotic conductance for glucose, as assessed by the pore model, may precede the changes in small solute transport. The systematic assessment of fluid transport status needs specific clinical and mathematical tools beside the standard PET tests.

Peritoneal fluid transport: mechanisms, pathways, methods of assessment.

Fluid removal during peritoneal dialysis is controlled by many mutually dependent factors and therefore its analysis is more complex than that of the removal of small solutes used as markers of dialysis adequacy. Many new tests have been proposed to assess quantitatively different components of fluid transport (transcapillary ultrafiltration, peritoneal absorption, free water, etc.) and to estimate the factors that influence the rate of fluid transport (osmotic conductance). These tests provide detailed information about indices and parameters that describe fluid transport, especially those concerning the problem of the permanent loss of ultrafiltration capacity (ultrafiltration failure). Different theories and respective mathematical models of mechanisms and pathways of fluid transport are presently discussed and applied, and some fluid transport issues are still debated.

Sequential peritoneal equilibration test: a new method for assessment and modelling of peritoneal transport.

BACKGROUND: In spite of many peritoneal tests proposed, there is still a need for a simple and reliable new approach for deriving detailed information about peritoneal membrane characteristics, especially those related to fluid transport. METHODS: The sequential peritoneal equilibration test (sPET) that includes PET (glucose 2.27%, 4 h) followed by miniPET (glucose 3.86%, 1 h) was performed in 27 stable continuous ambulatory peritoneal dialysis patients. Ultrafiltration volumes, glucose absorption, ratio of concentration in dialysis fluid to concentration in plasma (D/P), sodium dip (Dip D/P Sodium), free water fraction (FWF60) and the ultrafiltration passing through small pores at 60 min (UFSP60), were calculated using clinical data. Peritoneal transport parameters were estimated using the three-pore model (3p model) and clinical data. Osmotic conductance for glucose was calculated from the parameters of the model. RESULTS: D/P creatinine correlated with diffusive mass transport parameters for all considered solutes, but not with fluid transport characteristics. Hydraulic permeability (L(p)S) correlated with net ultrafiltration from miniPET, UFSP60, FWF60 and sodium dip. The fraction of ultrasmall pores correlated with FWF60 and sodium dip. CONCLUSIONS: The sequential PET described and interpreted mechanisms of ultrafiltration and solute transport. Fluid transport parameters from the 3p model were independent of the PET D/P creatinine, but correlated with fluid transport characteristics from PET and miniPET.

[Extended assessment of peritoneal transport kinetics of substances and water as an important element of integrated dialysis care]. / Rozszerzona ocena kinetyki transportu przezotrzewnowego czqsteczek i wody jako wazny element koncepcji zintegrowanej opieki dializacyjnej.

UNLABELLED: The concept of integrated dialysis care is based on the choice of the most optimal method of renal replacement therapy for particular patient in particular period of disease. In many cases peritoneal dialysis (PD) is the initial therapy. PD modalities and regimens are modified according to values of parameters of ultrafiltration and adequacy. The routinely used methods of analysis of peritoneal transport are very useful for general assessment of properties of peritoneum as a dialysis membrane. However, the application of these methods do not guarantee the full assessment of peritoneal transport kinetics of water and substances. Therefore, the capabilities of the most adequate modification are limited. The tests based on mathematical models taking into account the kinetics of intraperitoneal dialysate volume seem to be the right supplement of standard methods. MATERIALS AND METHODS: To illustrate the problem mentioned above, the aim of this study was comparison of peritoneal transport of substances and water in two groups of patients: group I with negative ultrafiltration (UF) (n=14) and group II with positive UF (n=6). In the studied groups peritoneal equilibration test (PET) was done, then the assessment of peritoneal water transport was performed using 125I-HSA as dialysate volume marker, and finally the velocity of peritoneal transport of small molecules expressed by solute mass transport rate (SMTR) coefficient was measured. Patients from both groups belonged to the same category of high-average transporters according to PET criteria. RESULTS: On the base of broaden assessment of peritoneal transport of water and substances it was proved that different, "therapeutic approach" should be applied in studied groups to reach the adequate dialysis. Although in group II the minor modification of continuous ambulatory peritoneal dialysis (CAPD) regimen was desired, the radical change of CAPD schedule or transfer to automated peritoneal dialysis was necessary in cases of patients from group I. CONCLUSIONS: The results of the study indicate that the extended assessment of peritoneal transport kinetics of water and substances increases the capabilities of individualisation of PD program. Therefore, it should be treated as an important element of integrated dialysis care.