$596 Journal o f Biomechanics 2006, Vol. 39 (Suppl 1)

6215 We-Th, no. 14 (P64) Evaluation of nasal airway patency by analysis of breathing sounds U. Zaretsky 1 , D. Elad 1 , A. Primov-Fever 2, M. Wolf 2,3. 1Department of Biomedical Engineering, Tel Aviv University, Tel Aviv, Israel, 2Department of Otorhinolaryngology, Sheba Medical Center, Tel HaShomer, Israel, 3 Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel

Acoustic signals have been used in medicine since early days, especially in the respiratory system. These signals represent the summation of sound waves which originate from the respiratory turbulent air flow and are also modified by the airway geometry and tissue characteristics. In a previous investigation we demonstrated the correlation between the energy of high frequency content and the degree of vessel obstruction. The goal of this study was to examine whether the content of nasal acoustic signals contains structures that may provide parameters to differentiate between obstructed and open nasal passageways. We developed a simple device with two condenser microphones that could be positioned on the external sides of the nostrils nearby the nasal nares. The subject was instructed to breathe through the nose for several cycles and efforts. Nasal decongestant was applied to the nose that yielded lower amplitudes and after 5 minutes the maneuver was repeated. The signals were amplified and digitized into the PC for off-line processing. Data processing was performed on the expiratory phase only and included averaging over three selected cycles, noise reduction and evaluation of the ratios of the sum of amplitudes (kPSD) and the sum of square amplitudes (kAMP) between the two sides of the nasal passageways. The data was recorded from 20 healthy volunteers who signed an informed consent. The analysis revealed that the kPSD parameter correlated well with the expected (i.e., treated) side in 14 out of the 20 examinees. Non-significant changes were noted in 4 examinees and changes in the opposite direction were found in 2 examinees. Subjective sensation was also recorded and have shown good correlation with the objective parameters in 45-65% of the subjects. In conclusion, a simple non-invasive test revealed a potential for quick and objective evaluation of differences between the nasal passageways patency.

6696 We-Th, no. 15 (P64) Mechanics of respiratory muscles in s ingle- lung transplanted emphysematic patients A. Ratnovsky 1, M.R. Kramer 2, D. Elad 1. 1Department of Biomedical Engineering, Tel Aviv University, Tel Aviv, Israel, 2pulmonary Institute, Rabin Medical Center, Petach Tikva, Israel

The efficiency of respiration depends on the coordinated movement of the respiratory muscles in generating sufficient pressure gradients for air flow in and out of the lungs. In hyperinflated lungs, such as in emphysema, the alteration in the geometry of the respiratory muscles decreases their ability to drive the respiratory pump. Single-lung transplantation (SLT) improves the qualify of life and exercise capacity of emphysematic patients, but it may induce asynchronous performance between the respiratory muscles on the two sides of the chest. Recently, we demonstrated that the electromyography (EMG) signals of four main respiratory muscles were without substantial differences between the healthy and emphysematic groups, and between the side of the transplanted lung and that of the native lung. However, the global strength of respiratory muscles as measured by mouth pressure was found to be significantly lower in the emphysematic group. In this study we investigated the effect of SLT in emphysema patients upon respiratory muscles mechanics. The forces and powers generated by three main respiratory muscles were calculated for a range of respiratory maneuvers in emphysematic patients with a single transplanted lung and were compared with the results of healthy sub- jects. The control group demonstrated significantly higher averaged maximal forces, work and power. The total work done by each respiratory muscle on the side of the transplanted lung was higher compared with that of the native lung side and compared with the control group. Taken together, these results suggested that he asynchrony between the lungs after single-lung transplant leads to asynchronous muscle forces and work as well as lesser muscle strength compared to healthy subjects.

6911 We-Th, no. 16 (P64) Surface tension distribution in lungs with surrfactant deficiency S. Ben-Zaken 1 , A. Marmur 2, Z. Weintraub 3, E. Kimmel 1 . 1Biomedical Engineering Department, Technion liT, Haifa, Israel, 2Chemical Engineering Department, Technion liT, Haifa, Israel, 3Neonatal Department, Western Galilee Hospital Nahariya, Medicine Department, Technion liT, Haifa, Israel

Lung surfactant is a surface active agent which appears in the liquid films that coat surfaces in the lung. Deficiency of surfactant in the lung induces pathological functioning such as in respiratory distress syndrome (RDS) in pre- mature newborns. Some 15 years ago, the dodecahedron model (Kimmel, E., and Budiansky, B.(1990): ASME J. Biomech. Eng. 112: 160-167) provided a theoretical framework that related mechanical properties of homogeneous lung

Poster Presentations

parenchyma, such as viscoelastic moduli, with surface tension, transpulmonary pressure and tensile forces in the tissue components. In this study we measure alveolar size and shape distribution in rat lungs using microscope pictures taken through the pleura by means of CSD camera which is mounted over an opening in the chest. The rat is intubated and ventilated and tracheal pressure is measured as well. Image analysis, using Image-pro +© software, provides size and shape distribution of alveoli in normal lung (n = 20); in washed lung (n = 15) that suffers from lack of surfactant (BAL); and in a lung (n = 10) that was first washed and then treated by exogenous surfactant (SRT). Images of alveoli were grouped and associated with inflation and deflation limbs. Dimensions such as maximal and minimal sizes, aspect ratio, area and average diameter of each alveolus were calculated. A novel method is suggested to estimate local surface tension in each alveolar size group, using the dodecahedron model. Increased level of spoil to lung surfactant is typified by: (i) a wider range of alveolar sizes where most of the open and active alveoli are greater in size than normal; ( i i ) increased surface tension from below 30dyne/cm in normal lung to about 70dyne/cm in BAL and (iii) decreased differences between inflation and deflation curves and therefore decreased hysteresis. The increased respiratory effort in RDS is probably not connected to the reduced hysteresis-like differences between inflation and deflation in the BAL lung compared to normal.

6981 We-Th, no. 17 (P64) The experimental evaluation of asymmetric ventilation waveforms on surfactant transport during airway reopening J.E. Pillert, D.P. Gaver II1. Biomedical Engineering Department, Tulane University, New Orleans, LA, USA

Acute Respiratory Distress Syndrome (ARDS) can be described as a decrease in pulmonary compliance with an accumulation of alveolar edema, leading to airway occlusion. Mechanical ventilation, while a common treatment for ARDS, is also known to result in low-volume ventilator-induced lung injury. The large mechanical stresses associated with ventilator-induced injury can lead to epithelial cell damage, further damaging a diseased lung. Our goal is to use this information to experimentally study the mechanics and surfactant adsorption at the air-liquid interface and identify optimized ventilation parameters. In this study, a rigid model of airway reopening, consisting of a narrow-bore (1 mm ID) glass tube maintained at 37°C, is utilized to explore the effects of an asymmetric ventilation waveform at an air-liquid interface on surfactant transport. A finger of air is oscillated and progressed through purified H20 or a surfactant-doped solution and the capillary pressure drop across the a i r - liquid interface is determined. This simplified model of an airway provides a means of evaluating waveform parameters (frequency, amplitude, mean flow, and degree of asymmetry) to reduce mechanical stresses that may damage the lungs during ventilation. Two general waveform asymmetries are studied: a fast-reverse flow, where the interface moves slower into the liquid occlusion relative to its faster motion back into the finger of air, and a fast-forward flow, where the asymmetric motion is reversed. The specific waveform parameters listed above are investigated with multiple values for both the fast-reverse and fast-forward degrees of asymmetry. A fast-reverse ventilation waveform is determined to be more successful at lowering capillary pressures than a fast-forward waveform. We hypothesize that during fast-reverse flow, surfactant builds up on the interface, providing a reservoir as the interface expands during its slow-forward flow. It is anticipated that identifying optimized waveforms will reduce low-volume ventilator-induced lung injury in patients with ARDS and other respiratory diseases. Supported by NASA grant NAG3-2734 and NIH P20-EB001432

6991 We-Th, no. 18 (P64) A computational model of the effects of airway reopening on the integrity of pulmonary epithelial tight junctions A.-M. Jacob, D.P. Gaver. Biomedical Engineering Department, Tulane University, New Orleans, LA, United States of America

Normal lung physiology is characterized by an intact, selective barrier function that permits the communication only of essential gases between the lungs and surrounding vessels. This is due in large part to the extremely low permeability of the pulmonary epithelial cell layer, which is established and maintained by the diffuse expression of tight junctions (TJs) between adjacent epithe- lial cells. Acute respiratory distress syndrome (ARDS) is the life-threatening pathology initiated by damage to the epithelium that causes the breakdown of this barrier and the flooding of the airways and alveoli with protenaceous edema fluid. Mechanical ventilation, though in most cases a necessary medical intervention, typically exacerbates this condition. Our analysis computationally examines this effect by determining the mechanical stresses that the epithelial cell layer experiences as air is forced into a liquid-filled edematous airway. Using finite element analysis, we examine how the apical fluid stresses - determined using the boundary element method - are transduced to the TJs