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1

A method for quantification of lung resistive and compliant properties for spirometry interpretation support -Tests on a virtual patient

Gólczewski T., Pałko K. J.

Biocybernetics and Biomedical Engineering

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2013

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Vol. 33, no. 3

136--144

EN

The forced expiratory volume in one second (FEV1), the fundamental index in obstructive lung disease diagnosis, depends on both resistive (RP) and compliant (CP) properties of the respiratory system (RS). The study aim was to test initially a method that could differentiate their influence to aid spirometry interpretation during screening examinations. Tests were done on a virtual RS elaborated previously. After respiratory muscle relaxation, a part of air was exhaled passively to an added compliance (Cad) or through an added resistance (Rad). The CP and RP were estimated from mouth pressure changes under different conditions of RS and measurement (different obstruction severities, various Cad and Rad values, etc.). Measurements had to be performed after maximal inspiration to avoid dependence of results on the lung volume. The Cad maneuver enabled to estimate the CP properly. Inertances and bronchi collapse caused pressure fluctuations, whereas bronchi reopening modified pressure rise after airflow interruption. Rad > 0.8 kPa s/L eliminated these problems and made the RP estimation independent from the Rad value and the CP. The calculated value of resistance depended on both airway resistance and parenchyma viscosity (like FEV1) and viscosity of other tissues. Since collapse instantaneous observation in real patients is impossible, initial but extensive tests illustrating influence of the collapse on measurement could be done only on a virtual RS.

2

Influence of ventilation mode on blood oxygenation - investigation with Polish Virtual Lungs and Italian Model of Circulation

Gólczewski T., Zieliński K., Ferrari G., Pałko K. J., Darowski M.

Biocybernetics and Biomedical Engineering

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2010

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Vol. 30, no. 1

17-30

EN

Positive alveolar (PA) and thoracic (Pr) pressures during artificial ventilation disturb pulmonary circulation, and might influence arterial blood oxygenation (PaO2). Initial analysis of such influence of different artificial ventilation modes is the goal of this paper. Previously elaborated virtual respiratory system (IBIB PAS, Warsaw, Poland) and cardiovascular system model (ICP CNR, Rome, Italy) were connected with two files-buffers to work as one virtual cardio-pulmonary system. Dependence of PaO2 on two methods (continuous inspiratory airflow (VCV) or pressure (PCV)), two ventilatory frequencies (fV = 15 or 7.5/min), and two values of the minute ventilation (Vmin = 6 or 8L/min) was investigated. Perfusion dependence on gravity was neglected as the virtual patient was in the supine position. Simulations showed that when fV = 15/min, neither the used method nor Vmin influence pulmonary blood flow significantly, whereas they influence the flow during expiration when fV = 7.5 (blood flow falls more for PCV and Vmin = 8 L/min). Vmin more significantly influences alveolar partial pressure of oxygen (P02) when fV = l5/min. P02 was greater for PCV. As effects on the flow and PO2 were contradictory, Pa02 was almost independent of the used method and fV. It depended on Vmin more significantly if fV = 15/min.

3

A hybrid model of the respiratory system

Michnikowski M., Glapiński J., Guć M., Gólczewski T., Darowski M.

Biocybernetics and Biomedical Engineering

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2009

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Vol. 29, no. 1

71-80

EN

The aim of this work is building a hybrid model of the human respiratory system which enables connecting the real clinical devices (respirators) with the computerized virtual lungs. A simulation of the artificial ventilation of lungs, with the use of the hybrid model and the Siemens Servo 900 respirator, was made. Waveforms of pressure inside the lungs, flow in the respiratory tract, and the lung volume during the simulated artificial ventilation were recorded. The compliance and resistance of the hybrid model of the respiratory system were calculated on the basis of the inspiratory pause algorithms and compared to the values set in the model. The initial tests have shown that the calculated values of the parameters differ by 20% (worst result) from the values set in the model. The model will enable the investigation of the different modes of lung ventilation, as well as educational presentation of the respirator-patient interaction.

4

The virtual cardio-respiratory system: a sub-model of gas exchange and transfer

Gólczewski T., Darowski M.

Biocybernetics and Biomedical Engineering

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2008

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Vol. 28, no. 1

29-40

EN

A virtual cardio-respiratory system (CRS) is proposed for testing ventilatory support and scientific hypothesis. It may appear more convenient than experiments on animals or limited investigations on patients. In particular, there are no limitations for manipulation of virtual CRS parameters while such manipulation is difficult or impossible in the case of real CRS. The virtual CRS architecture: The proposed virtual CRS consists of: (a) the sub-model of respiratory system mechanics (RSM) previously used as the stand-alone virtual respiratory system, (b) a sub-model of gas exchange and transfer in the respiratory and circulatory systems (GET), which is constituted with three modules: gas transfer in respiratory system, gas exchange in lungs, and gas transfer in circulation. The GET utilizes airflows and pressures supplied by the RSM whereas the RSM utilizes volumes of gases supplied by the GET. Results: the CRS gave proper results for both respiration and respiratory arrest. In particular, if the CRS 'respired' with pure oxygen then arterial blood saturation with oxygen remained high for tens of minutes after respiratory halt when airways were open; otherwise atelectasis developed during 8-10 minutes. Like for real patients, carbon dioxide tension in blood decreased quickly when ventilation increased and it increased slowly when the ventilation fell.

5

Spirometry: quantification of the shape of the maximal expiratory flow-volume curve

Gólczewski T., Lubiński W.

Biocybernetics and Biomedical Engineering

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2008

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Vol. 28, no. 3

17-25

EN

The relationship between Forced Expiratory Volume in one second (FEV1) and the Forced Vital Capacity (FVC) is intensively used in diagnosing because of its quantitative description with the index FEV1/FVC. There is not such index for the relationship between airflows (Peak Expiratory Flow (PEF) and Maximal Expiratory Flow at xx% of FVC (MEFxx, where xx = 75, 50, 25%)). Our aim was to describe that relationship quantitatively with the angle alfa between the 4-dimensional vector F = [PEF, MEF75, MEF50, MEF25] and the plane determined by two reference vectors: the mean of such vectors for the young and elderly. The reference vectors were found with data for 1,120 males and 1,625 females - Polish (white) population, healthy, never-smoking, aged 18 - 85 yrs, who performed a technically adequate spirometry maneuver. Upper Limit of Normal (ULN) was determined with the linear regression of the 5th percentiles of alfa on age (0.074*age + 2.76). Such an ULN seems to well indicate both improper examination and non-healthy persons.

6

Choice of proper lung ventilation method

Darowski M., Gólczewski T., Michnikowski M.

Biocybernetics and Biomedical Engineering

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2006

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Vol. 26, no. 1

21-37

EN

In the article three different methods of lung ventilation have been analyzed: Continuous Positive Airways Pressure (CPAP), Proportional Assist Ventilation (PAV) and Pressure Support Ventilation (PSV). The aim of these analyses was to predict clinical situations when the considered modes of ventilation would play their role in the best, optimal way. The study on effective ventilatory support by CPAP, PAV and PSY was conducted using virtual respiratory system - a new, but yet verified model of the system, recently developed by our group. Computer simulation, done on a healthy lung model and on a pathologically changed lung model, has clearly shown the conditions under which CPAP, PAV or PSY could be really effective. CPAP is worth using in patients with a high airways resistance, in which case this mode of ventilatory support ensures breathing with normal frequency and less energy-consuming inspiration. PAV usually results in a smaller peak and the mean alveolar pressure than PSY which decreases a potentially harmful effect of the positive pressure ventilation on the cardiovascular system. On the other hand, PAV may be used safely when estimation of the parameters such as the lung/thorax compliance and the airway resistance is reliable, since the setting of the supporting pressure is based on this estimation.

7

Wirtualny układ oddechowy i jego wykorzystanie w testowaniu metod sztucznej wentylacji i wspomagania oddychania

Gólczewski T., Darowski M.

Bio-Algorithms and Med-Systems

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2005

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Vol. 1, no. 1/2

65--71

PL

Problemy techniczne, ekonomiczne oraz wzrastające znaczenie kwestii etycznych powodują, że wykorzystanie w badaniach naukowych wirtualnych organów może okazać się bardziej wygodne niż eksperymenty na zwierzętach czy ograniczone możliwości wykorzystania pacjentów w badaniach. W szczególności wirtualny układ oddechowy (WUO) może być użyteczny w testowaniu respiratorów i nowych metod wspomagania, w edukacji i treningu personelu, a także we wstępnym testowaniu hipotez naukowych. W pracy przedstawiono: (1) ideę WUO, (2) weryfikację za pomocą standardowej spirometrii (wyników symulacji nie można odróżnić od wyników otrzymanych dla realnych pacjentów), (3) przykłady wykorzystania WUO w: (a) porównaniu zagrożeń dla zdrowia podczas różnych trybów sztucznej wentylacji, (b) analizie konieczności stosowania niezależnej wentylacji płuc, (c) analizie skuteczności wspomagania oddychania metodą CPAP w obturacyjnej chorobie płuc.

EN

Economic, technical and ethical problems may render the use of virtual organs in investigations more convenient than experiments on animals or limited investigations on patients. In particular, Virtual Respiratory System (VRS) may be useful for tasks such as respirator and support methods testing, education, staff (medical & technical) training, (initial) testing of scientific hypotheses, etc. The paper presents: (1) the VRS idea, (2) verification with standard spirometric examination (it is impossible to distinguish between results for real patients and VRS, which confirms VRS reliability), (3) examples of the use of VRS in: (a) comparison of health hazard in ventilation of different modes, (b) analysis of necessity of differential ventilation, (c) analysis of efficiency of support with CPAP in obstructive lung disease.

8

Nowe spojrzenie na genezę pierwotnego nadciśnienia tętniczego - hipoteza cybernetyczna

Gólczewski T.

Bio-Algorithms and Med-Systems

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2005

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Vol. 1, no. 1/2

73--80

PL

Nowa, biocybernetyczna teoria genezy pierwotnego nadciśnienia tętniczego została zaproponowana w 1992 r. Wyniki eksperymentalne ostatnich lat otrzymane przez innych autorów wypełniły ją biochemiczną treścią. Najważniejsze z tych wyników dotyczą wpływu pulsacyjności przepływu krwi na wydzielanie przez śródbłonek takich substancji wazoaktywnych, jak: wazodylatory prostacyklina i tlenek azotu (NO) oraz np. endotelina (ET-1) obkurczająca naczynia. W pracy pokazano, jak pętle ujemnego sprzężenia zwrotnego (SZ), które stabilizują ciśnienie tętnicze, są skomponowane z oporu obwodowego (PR), dynamiki zmian przepływu krwi (DA) oraz sekrecji NO lub ET-1. DA zależy od wielkości odbić fal przepływu determinowanej przez różnicę między PR i impedancją tętniczą. W normalnych warunkach mamy pętle: PR→+DA+NO→-PR oraz PR→+DA→-ET-1→+PR (gdzie →+/- oznacza sprzężenie dodatnie/ujemne, np. NO→-PR znaczy, że wzrost ilości NO powoduje spadek PR). Jednakże, jeśli ze wzrostem ciśnienia impedancja zacznie rosnąć szybciej niż PR (np. z powodu starzenia), to dodatnie sprzężenie PR→+DA zamieni się w ujemne PR→-DA. W efekcie ujemne SZ zamienią się w dodatnie i tylko nieliniowości układu krążenia (np. ograniczona wydolność serca) limitują zmiany PR i P. Te dodatnie SZ powodują albo nadciśnienie, albo hipotonię, co zależy od znaku wyjściowego uchybu, który ulega wzmocnieniu przez dodatnie SZ. Prezentowana teoria dotyczy tego typu pierwotnego nadciśnienia, które jest związane z uczuciem zmęczenia, a nie pobudzenia. Teoria tłumaczy negatywny lub pozytywny wpływ większości czynników wiązanych z nadciśnieniem, np. dziedziczność, starzenie się, ćwiczenia fizyczne itd.

EN

A new, biocybernetic theory of primary arterial hypertension was proposed in 1992. Experimental results of last years obtained by other authors have filled the theory with biochemical facts. Most important of these facts concern influence of pulsatile blood flow on endothelial secretion of several vasoactive substances as: vasodilators, e.g. prostacyclin, nitric oxide (NO), and vasoconstrictors, e.g. endothelin (ET-1). The paper shows how loops of negative feedback, which stabilize arterial pressure (P), are composed of peripheral resistance (PR), dynamics of blood flow alteration (DA) and NO or ET-1 secretion. DA depends on blood flow wave reflections, which are determined by difference between PR and arterial impedance. Normally, there are the loops: PR→+DA→+NO→-PR and PR→+DA→-ET-1→+PR (where '→+', '→-' means positive or negative connection, respectively, e.g. NO→-PR means that increase of NO amount causes decrease of PR). However, if the impedance starts to increase with P more quickly than PR (e.g. because of ageing), the positive connection PR→+DA changes into PR→-DA. As the consequence, the negative feedbacks change into the positive ones, and only nonlinearity of the cardiovascular system (e.g. limited heart efficiency), bounds alteration of PR and P. These positive feedbacks cause either hypertension or hypotonia, which depends on the sign of the initial deviation that is amplified by the feedbacks. The presented theory concerns rather the primary hypertension type that is connected with fatigue than other types. The theory explains negative or positive influence of almost all factors connected with hypertension, as heredity, ageing, physical exercises, etc.

9

Na autonomiczny układ nerwowy wpływa dynamika zmian przepływu krwi

Gólczewski T.

Bio-Algorithms and Med-Systems

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2005

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Vol. 1, no. 1/2

81--86

PL

CEL: Określenie, która cecha pulsacyjnego przepływu krwi oddziałuje na autonomiczny układ nerwowy (AUN): czy sam fakt pulsacyjności, wyrażany za pomocą powszechnie znanego Pulsatility Index (PI), czy też dynamika zmian przepływu, wyrażana przez Waveform Age (WA) - indeks opracowany przez autora. METODA: rytm serca (HR) jest traktowany jako wskaźnik napięcia AUN. Znormalizowanej funkcji korelacji wzajemnej użyto do analizy zmian HR, WA i PI wywołanych kontrolowanym oddychaniem (okres 8-24 s, próba Valsalvy). MATERIAŁ: Prędkość przepływu krwi w tętnicy ramiennej u 10 osób. WYNIKI: Zmiany HR i WA są silnie skorelowane (R=-0.9), WA zmienia się wcześniej o 1.7-0.7s niż HR (dla konkretnej osoby przesunięcie w czasie jest stałe i całkowicie niezależne od sposobu oddychania). PI również koreluje z HR (R=-0.9), ale tylko podczas rytmicznego oddychania z mniejszymi częstościami i wówczas zmienia się po HR. WNIOSEK: Nie sam fakt pulsacyjności przepływu, a dynamiczność zmian przepływu zdaje się wpływać na AUN.

EN

GOAL: To determine which feature of the pulsatile blood flow influences autonomic nervous system (ANS): whether the pulsation degree quantified with commonly used Pulsatility Index (PI) or dynamics of flow changes quantified with Waveform Age (WA) - an index proposed previously by the author. METHOD: Heart rate (HR) was treated as an index of ANS function. The normalized cross-correlation function was used for analysis of PI, WA, and HR changes induced by controlled breathing (with 8 - 24 sec periods, and Valsalva maneuver). MATERIAL: 10 persons - blood flow velocity in the brachial artery. RESULTS: Changes of WA and HR were strictly correlated (R=-0.9), and WA altered sooner than HR (1.7-0.7sec - but for a particular person, this time-shift was exactly constant for all breathing modes). PI correlated with HR (R=-0.9), but it changed later than HR (1 heart period). The dependence exists only for breathing with greater frequency. CONCLUSION: It seems the dynamics influences ANS.

10

The respirator as a user of virtual lungs

Gólczewski T., Kozarski M., Darowski M.

Biocybernetics and Biomedical Engineering

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2003

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Vol. 23, no. 2

57-66

EN

The virtual respiratory system (VRS) is proposed for testing physical respirators, new methods of ventilatory support, and scientific hypotheses. VRS may be also helpful in students education and staff training. Method: VRS simulates the relationship between the air flow and the pressure. The main features of the model are: separation of the lungs and the chest, division of the lungs into five lobes, closing bronchi, gravity influence. Real-to-virtual converter is based on the gas flow source, which is controlled by the calculated value of the air flow that should exist, for the measured pressure being the VRS input. Results: several phenomena are discussed, e.g. the influence of compliance nonlinearity and resistance changeability on ventilation, the CPAP efficiency, differences in lobes ventilation, breathing frequency determination.

11

Influence of ventilatory mode on respiration parameters - investigation on virtual lungs

Gólczewski T., Darowski M.

Biocybernetics and Biomedical Engineering

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2003

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Vol. 23, no. 3

63-72

EN

In the paper influence of different artificial ventilation modes (pressure-controlled, volume-controlled with constant and with decelerating flow, and power-controlled, i.e. adaptive) on chosen respiratory parameters (peak and mean pressure in lungs, peak gas flow, distribution of lungs ventilation) were analyzed in cases of permanent and sudden obstruction. The comparison has proved that the adaptive mode generally has some advantages over routinely used ventilatory modes, if influence on all the respiratory parameters together is taken into account: all the parameters achieve moderate values for the adaptive mode, while at least one parameter achieves a big value for each other mode. Thus, the adaptive mode causes the smallest total health hazard.

12

Model studies on respiratory parameters for different lung structures. Part I. Theoretical consideration

Darowski M., Kozarski M., Gólczewski T.

Biocybernetics and Biomedical Engineering

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2000

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Vol. 20, no. 2

67-77

EN

A computer model of lungs mechanics has been developed to simulate changes of basic respiratory variables during spontaneous breathing and mechanical ventilation. This non-homogeneous lungs model can be used as a part of hybrid, gyrator model of the respiratory system, which enables to transform static and dynamic properties of the modelled lungs into pneumatic impedance connected to the respirator. The proposed computer model may be presented as a quasi-electrical network, built out of RLC-like elements, in which non-linear mechanical properties of the human respiratory system have been taken into account. Computer simulation showed on-line changes on p-V pIane as a function of tidal volume during spontaneous breathing.

PL

Zaproponowano komputerowy model mechaniki płuc do symulacji zmian podstawowych zmiennych oddechowych podczas oddychania spontanicznego i sztucznej wentylacji. Ten niehomogeniczny model płuc może być użyty jako część hybrydowego, żyratorowego modelu układu oddechowego, który umożliwia trasformację statycznych i dynamicznych własności mechanicznych płuc w impedancję pneumatyczną dołączoną do respiratora. Zaproponowany model komputerowy może być zobrazowany jako quasi-elektryczna sieć zbudowana z elementów odpowiadających w przybliżeniu elementom RLC, w której uwzględniono nieliniowe własności układu oddechowego. Pokazano, jako przykład możliwości modelu, zmiany on-line ciśnień i objętości w klatce piersiowej podczas oddechu spontanicznego o różnej głębokości wdechu.