The unknown shown by numerical tools: application to right dysfunction

Funding Acknowledgements

Type of funding sources: Public Institution(s). Main funding source(s): Ph.D. Research Grant

Introduction. Numerical modelling of cardiovascular flows is emerging as a powerful tool when applied to clinical practice, thanks to its capability of describing hemodynamics non-invasively. Among the different approaches, lumped parameters (0D) models present the advantage of describing the complete circulation at low computational cost, with strong stress on cause-effect relationships between the different functional elements and flow/pressure waveforms. 0D models fully express their potentiality when applied to complex physio-pathological conditions. This work applies such an approach to the right ventricular (RV) dysfunction, modelling the case of an equal systolic and diastolic percentage dysfunction, i.e., 60%. The model highlights how the right dysfunction affects the left performances, despite the unaltered left ventricular (LV) functionality.

Purpose. Numerical tools may help clinicians in understanding the characteristic features of physio-pathological conditions, clearly differentiating the contributions of single functional elements.

Methods. We develop a 0D model of both left and right circulation, in which heart chambers are simulated with the time-varying elastance concept. Ideal diodes associated with resistances are adopted for the heart valves, and the dissipative effects for the vascular beds and elastic properties for the great vessels are considered. The healthy and the RV dysfunction cases are considered, and, for the pathological condition, we impose a 60% right systolic and diastolic dysfunction.

Results. Fig. 1 shows an example of the outputs calculated by our model e.g., the pressure-volume (pV) loops which, in the clinical practice, are obtained with invasive measurements. On the right heart, the simulated dysfunction reduces systolic pressures, augments diastolic pressures and causes an enlargement of the ventricle (Fig. 1a). Interestingly, the pathology reflects also on the LV: the left pV loop exhibits a left/downward shift, despite the unaltered functionality (Fig. 1b). Overall hemodynamic variables reported in Fig. 1c confirm that RV dysfunction causes a deterioration of the global hemodynamics, i.e., CVP increases and, SV and CI decrease. Moreover, RV dysfunction reduces not only the RV performances (EFrv), but the well-functioning LV activities (EFlv) as well. These findings strengthen the arising clinical practice of checking the LV performance to understand when it is necessary to intervene, e.g., in the presence of the Tetralogy of Fallot.

Conclusion. Numerical models are powerful tools that can help clinicians in understanding the featuring element of a physio-pathological condition. Here, we have shown that RV dysfunction reduces LV functionalities, thus corroborating the emerging idea that optimal timing for intervention in right diseases requires that also the left side circulation is considered.

Abstract Figure. Fig. 1.

Work of breathing-tidal volume relationship: analysis on an in vitro model and clinical implications

OBJECTIVE

Work of breathing (WoB) is currently employed to assess the afterload on the respiratory muscles and to estimate the energy expenditure for breathing. Since WoB depends on the ventilated tidal volume (TV), WoB*L(-1), the indicized form of WoB has been employed as a measure of WoB which is independent of TV. Actually, the independence of WoB*L(-1) from the ventilated TV has never been demonstrated. The aim of this study was to verify the predicted TV-independence of WoB*L(-1) on an in vitro model.

METHODS

Our experimental model was constituted as follows: two endotracheal tubes, with internal diameter measuring respectively 6.5 and 8.5 mm, were alternatively connected with two rubber balloons whose compliance was respectively 0.02 and 0.06 L/hPa; the system was mechanically ventilated at ten different tidal volumes, ranging from 0.3-1 l. Flow rate was kept constant (35 l/m) during the whole experiment.

RESULTS

Both elastic components of the model showed a static volume-pressure relationship which was linear in the experimental range of TV. In all combinations of resistance and compliance WoB increased quadratically whereas WoB*L(-1) increased linearly with the growing TV (p < 0.001).

CONCLUSIONS

These results demonstrate the TV-dependence of WoB*L(-1) and suggest that WoB*L(-1), if TV changes, cannot be considered as an index of respiratory muscle afterload and should not be used as a guide for weaning patients from the mechanical ventilation. Finally, we introduced a new parameter (WoB1L) which seems to be a more TV-independent measure of respiratory work.

Evidence for alpha-melanocyte-stimulating hormone (alpha-MSH) receptors on human malignant melanoma cells

The presence of alpha-MSH receptors on human melanoma has so far been suggested in the literature but not proved. We describe a reproducible and specific binding assay of alpha-MSH on human melanoma cells, using a high-specific-activity 125I-labelled hormone (1.5 to 2 mCi/micrograms) with consistent receptor binding (usually exceeding 2 pg/10(6) cells) and stable for 3 weeks. Asynchronized cells in suspension were incubated for 15 min at 37 degrees C with the tracer and various concentrations of unlabelled hormones. Synthetic alpha-MSH was compared to beta-MSH, ACTH1-24, ACTH4-10, beta-LPH, CLIP, CRF, MIF I, A8VP and beta-endorphin. Out of a panel of 8 human melanoma cell lines, 3 showed specific and reproducible alpha-MSH binding curves. No significant binding to human fibroblast and human carcinoma cells was seen. alpha-MSH, beta-MSH and, to a lesser extent ACTH4-10 (a part of the alpha-MSH sequence) were the only peptides able to displace labelled alpha-MSH from its binding sites, indicating the high specificity of the MSH receptor. Affinity constants (Ka) ranged from 10(8) to 10(9) l/mole and the estimated receptor number was 1,000 to 2,000 per cell. We conclude that some human melanoma cell lines expressed specific MSH receptors with stable affinity but which are low in number.