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[IEEE Annual International Conference of the IEEE Engineering in Medicine and Biology Society Volume..
[IEEE Annual International Conference of the IEEE Engineering in Medicine and Biology Society Volume 13: 1991  Orlando, FL, USA (31 Oct.3 Nov. 1991)] Proceedings of the Annual International Conference of the IEEE Engineering in Medicine and Biology Society Volume 13: 1991  An Analysis Of The Mechanical Work Of Breathing Based On A Respiratory Impedance Model
Gomis, P., Gonzalez, C.H., Lew, M.N., Medrano, G.Bạn thích cuốn sách này tới mức nào?
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Năm:
1991
Ngôn ngữ:
english
DOI:
10.1109/iembs.1991.684995
File:
PDF, 190 KB
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Physiological Modeling 29.34 AN ANALYSIS OF THE MECHANICAL WORK OF BREATHING BASED ON A RESPIRATORY IMPEDANCE MODEL Gomis P . , Gonzalez C . H . , L e n M.N.', Medrano G... Crupo de Bloingenieria y Biofisica Apliuda. Universidad SiBolivar Apartado 89000 Carace.$ 1080A Venezwla * CAtedra de Tisiologia CAtedra de Namonologia lacultad de Medicinn Universidad Central de Yenoruela ABSTRACT An analysis of mechanical work of breathing during inspiration is presented, based on calculation of ventilatory work obtained from experimental data of 3 normal subjets and 3 chronic obstructive pulmonary disease (COPD) patients, and from computer simulation of a non linear lumped model of respiratory,impedance. Using this model for normal and COPD subjects, elastic and dynamic (resistive) work was computed for different patterns in a wide range of breathing frequencies. These results were compared with experimental data. The use of this model may allow us to pronose different ventilatory patterns in patients with respiratory disease according to optimal ventilatory work. INTRODUCTION The mechanical work of breathing done by the respiratory system during the inspiratory time is related to ventilatory parameters: alveolar ventilation (V,) and respiratory frequency (f), and to the impedance load: respiratory resistance and reactance 111. The aim of this work is to measure the work of breathing in normal and diseased subjects (COPD) at rest by two methods: i. with experimental data, and ii. by values estimated by a computer simulation of the respiratory impedance mode 1. The respiratory system is characterized by nonhomogeneous and nonlinear elements and they are related by distributed parameters. Generally, the oscillatory mechanics of the system is studied by linear lumped parameters models of the respiratory impedance [2,3,4]. Our model however uses nonlinear parameters to represent the airway resistance (Raw) and the pulmonary compliance, due to our interest in computing the inspiratory mechanical work for differe; nt extents of respiratory pressure and volumes. The. Raw was described by Rohrer's equation: P, = K, V t K, Vz where K, and K, are viscous and turbulents constants, P, is the pressure.difference between mouth and alveolar region and V is the flow. The nonlinear compliance characteristic of the lung was expressed by the equation proposed by Salazar et al. [5]: V = V, {l  ek where V is the tidal volume, Vo is the maximal pulmonary volume from the resting position, Pap is the difference between the alveolar and pleural pressures and k is a constant proportional to the halfinflation pressure. 2268 "HODS The respiratory work calculations were done by means of experimental data and from the simulation of the respiratory impedance model described. Experimental values were obtained from the records of pulmonary studies of six subjects ( 3 normals and 3 with COPD). Traces of mouth and esophageal pressures, flow and volume at the mouth were trasmitted to a multichannel recorder HP7054 and the elastic and dynamic work of breathing were computed using esophageal pressurevolume XY graph. [Fig. 1). Total work is represented by the sum of elastic and dynamic work. The simulation of the respiratory work during inspiratory time using the nonlinear respiratory impedance model was performed by a standard PCAT 286 microcomputer and the simulation language SIMNONl". The same ventilatory pattern (9,: f, Vt) obtained from each patient was considered in order to run the simulation program. The inspiratory flow patterns used in the model consisted of a pure sine wave (0 a sin wt) and a wave shape formed by the sum of oddharmonics sine waves = a(sin wt t O.2sin 3wt t O.Olsin 5wt)). The latter is closer to the physiological flow pattern and was proposed by Lafortuna et a1.[6] who obtained it from Fourier analysis. By simulation, also, the total, elastic and dynamic (viscous and turbulent) wor! were computed for different ventilatory patterns: V, from 4 to 12 L/min and f from 6 to 60 breathshin in normals and COPD patients. The parameters of the respiratory impedance model were [l]: k 0.022 cmHzOl, V 5L, K, = 1.36 cnH,O/L/s and K, = 4.69 cnH,O/Lz/sq in normal subjects and K, = 2.3 cmH20/L/s and K, = 10.04 cmH20/LZ/sZ in COPD patients. {v RESULTS Figure 1 shows the way to obtain the mechanical work values from experimental data. The values of mechanical work obtained from experimental records and those computed with the model using a pure sine wave flow pattern are listed in Table 1. A close relationship is observed between work values gotten experimentally from patients and those estimated through the model used. Aditionally, we observed that the elastic and dynamic work values in normal subjects are similar, whereas, in COPD subjects the dynamic work is significantly greater than the elastic one. Annual International Conference of the IEEE Engineering in Medicine and Biology Society, Vol. 13. No. 5. 1991 CH30684/91/00002268 601.00 8 1991 IEEE VOLUME (L) I 6 1.4 7 8 9 1 0 1 1 1 1 E S O P H M E M PRESSURE (cm H201 1 3 1 4 Figure 1 . Esophageal pressurevolume relation in a normal subject ( A . T . ) . A area: Elastic work, B area: Dynamic work. TABLE I: Ventilatory work in different patients: Experimental and model data. EXPERIMENTAL MODEL SUBJECT f Vt Pel qdyn Wtot ire1 M.C. 28 20 25 0.57 0.56 0.20 0.58 0.44 0.34 0.84 edyn Qtot normal A.T. L.G. 0.69 0.69 1.00 0.40 0.54 1.42 0.27 0.53 0.60 0.33 1.13 1.00 0.60 1.66 COPD B.C. A.F. P. v. 32 25 20 0.52 0.76 0.72 0.60 2.16 0.19 0.76 0.26 1.07 2.76 0.95 1.33 0.40 0.24 0.42 2.35 0.78 1.23 2.75 1.02 1.65 f:breaths/minute; Vt: Tidal Volume (L) Pel: Elastic workminute (Kgf.m/min) Hdin: Dynamic workminute (kgf.m/min) k o t : Total workminute (Kgf.m/min) Figure 2 shows the result? of the simulation for a ventilatory pattern of V, = 6 L/min in a normal subject. The variations of work per minute (total, elastic, viscous and turbulent) are related with diferent respiratory frequencies, noting a minimal value of total work for an optimal frequency. DISCUSSION Preliminary results showed a close relationship between experimental data and the values resulting from the simulation procedure. Total mechanical work in normal subjects was found to be very similar to the minimal work obtained through the model. In COPD patients at rest, the data of respiratory work are greater than the minimal one estimated by the model. This suggests that in COPD patients their ventilatory pattern produces a respiratory work above the optimum one estimated by the model. If the ventilatory pattern of these patients could be modified, then a IWorklmln Kghlmln I 0.41 '' 0 10 ,/ ., h / . a 20 30 40 SO Frequency br4ilh l mlnuto Vlrcou8 Turbulenl Elritlc ' + Bo 70 Total Figure 2 . Breathing work rates vs. respiratory frequency for a normal subject at PA = 6 L/min. reduction of the total mechanical work rate could be obtained in order to reach the values proposed by the model and then achieve a better respiratory performance and a therapeutic approach. Furthermore, our work is oriented to the optimization of the respiratory impedance model by means of the estimation of the nonlinear R, and compliance parameters for each patient and their validation by the model proposed. BEPEBENCBS [l] Macintyre, N.R,, Leatherman, N.E. "Mechanical loads on the ventilatory muscles: A theoretical analysis". Am. Rev. Respir. Dis. 139: 968973,1989. [2] Eyles, J . G . , Pimmel, R.L. "Estimating respiratory mechanical parameters in parallel compartment models". IEEE Trans. Biomed. Eng. 28: 313317, 1981. [31 Lutchen, K.R., Costa, K.D. "Physiological interpretations based on lumped elements models fit to respiratory impedance data: Use of forwardinverse modeling". IEEE Trans. Biomed. Eng. 37: 10761086, 1990. [41 Navajas, D., Far&, R., Canet, J., Rotger,M., Sanchis, J . "Respiratory input impedance in anesthetized paralyzed patients". J . Appl. Physiol. 69: 13721379, 1990. [ 5 1 Salazar, E., Knowles, J . H . "An analysis of pressurevolume characteristics of the lung". J . Appl. Physiol. 19: 97104, 1964. [61 Lafortuna, C., Minetti, A.E., Mognoni, P. "Inspiratory flow pattern in humans". J. Appl. Physiol. 57: 11111119, 1984. Prof. Pedro Gomis Universidad Simdn Bolivar, Nlicleo del Litoral Apdo. Postal 314, La Guaira, Venezuela. Phone: 5831722911; Fax: 5831722315 This work was supported by Decanato de Investigacibn y Desarrollo  Universidad Simdn Bolivar, by Fundacidn Instituto de Ingenieria and by Consejo de Desarrollo Cientffico y Humanfstico U.C. V . (Venezuela) Annual International Conferenceof the IEEE Engineering In Medicine and Biology Society,Vol. 13, No. 5, 1991 CH30684/91/00002269 $01.00 0 1991 IEEE 2269