Breathing of Humans and its Simulation

Transcription

1 Breathing of Humans and its Simulation Mina Nishi LSTM-Erlangen Institute of Fluid Mechanics Friedlich-Alexander-University Erlangen-Nuremberg Cauerstr.4, D Erlangen June 14, 2004

2 Abstract In this thesis, a breathing flow rate monitoring system and a mechanical breathing simulator are developed, constructed and tested for the experimental investigation of human breathing. Human breathing is a combination of three lung functions, ventilation, diffusion and circulation. In the present thesis, ventilation functioning is focused for the measurment and simulation. One of the most interesting features of ventilation functioning is its time varying volume flow rate. To measure this, the breathing mask which covers nose and mouth are used with cooperating with the thermal sensor. The sensor is called Time of Flight sensor, which is environmental condition, like temperature or humidity, independent and direction sensitive. The sensor gives two different information, one is the direction signal and the other signal is proportional to the mass flow rate. With this system, the ventilation volume flow rate can be precisely measured so that the exact human ventilation simulation will be realized. The sampled raw data of human ventilation will be analyzed to obtain the typical ventilation curve which is used for diagnosis of lung functioning defection. The second important part of this thesis is to simulate human ventilation with certain equipment which can reproduce any kind of ventilation curve. The simulation system is constructed with the mass flow contoroller which is applied for the exhalation simulation and for the inhalation simulation, volume flow controller, a proportional valve which is operated with vacuum pump and chamber. The whole ventilation simulation system is constructed and the result of the simulation is presented in this thesis. This work need to be developed further to make the breathing dummy or precise model of the human oropharynx so that it will provide the various possibilities, for example, to examine the particle deposition inside the human trachea etc.

3 Contents 1 Introduction 2 2 A Brief Literature Survey Breathing System of human being Measurement of the Human Breathing Parameters of Ventilation functioning tests Measurement Techniques of the Human Ventilation Analyzing Technique of the Human Ventilation Breathing Simulator Development of a Breathing Measurement System Construction and Equipment for Breathing Flow Rate Measurements Geometry of the breathing Mask Incorporation of Flow Sensors Calibration and Time response of the Sensor Signal Processing Final Measurements Realization of a Ventilation Simulator Construction of ventilation Simulator Instrumentations Volume Flow Control System for Exhalation Volume Flow Control System for Inhalation Calibration of Combined Values Verification Test of the Simulator Application of mass flow rate control system as an exhalation unit 45 5 Conclusions, Final Remarks and Outlook 47

4 CONTENTS ii A numerical calculation of the three time components of the time of flight sensor 50 A.1 principle of Operation A.1.1 Response of the sending wire A.1.2 Time-of-flight calculations A.1.3 Response of the receiving wire A.2 Discussion of Responses of Sending and Receiving Wires

5 List of Figures 2.1 Respiratory System Schematic Representation of Lung volumes Volume-Displacement Spirometer Various Spirometers Flow Volume Loop Classification of Abnormal Ventilation Functioning Mechanical Ventilator Digital Image of Active Servo Lung Experimental setup of the flow field in Humans Oropharynx Idealized Model geometry of human oropharynx Schematic aerosol experimental setup with Humans Inhaler D views of the oral airway model and bifurcation airway model Velocity and Non-dimensional temperature profiles Digital image and Schematic Figure of the mask with the sensor CTA Ventilation measurement Configuration of the Time of Flight Sensor Digital Image of the Time of Flight Sensor Schematic description of Time of Flight Sensor Measurement of time difference Time difference and the summation versus the flow velocity Calibration set up of the sensor for high velocity flow Calibration set up of the sensor for Low velocity flow Calibration curve of the extreme low velocity region Calibration curve of the Time of Flight Sensor Frequency response of the Time-of-Flight sensor Human Ventilation measurement with Time-of-Flight sensor... 38

6 LIST OF FIGURES Configuration of the ventilation simulation system Digital image of the proportional valve Calibration Curve for the Exhalation Simulation Calibration Curve for the Inhalation Simulation Averaged Calibration Curve for Combined Condition Simulation of the Human Ventilation Simulation of the Human Ventilation with Mass Flow Controller. 46 A.1 Sketch of the time of flight wires of sensor A.2 Theoretical prediction of sending wire time constant A.3 Theoretical prediction of fluid time of flight A.4 Fluid time of flight plotted on log scales A.5 Theoretical prediction of fluid time of flight as a function of Peclet number A.6 Detected time of flight versus the flow velocity A.7 Theoretical prediction of receiving wire time constant

7 Chapter 1 Introduction In various fields of medicine like physiology or Aerosol medicine, investigations related to the breathing of human beings have gained an increasing interest. Mainly this work is concentrated on the instantaneous volume flow rate through the mouth and nose of different individuals. Breathing is a physiological function which is a combination of three functions, ventilation, perfusion (diffusion) and circulation. For this thesis work, the ventilation function is the target of the monitoring and simulation. The monitoring ventilation is interesting especially for the people who work in medical field to diagnose the lung disease etc. as well as the people who try to simulate the human ventilation mechanically or numerically. There are two different kinds of Human Breathing simulator; one is used for the patients who have the breathing problem, this can be called mechanical ventilator (Machine aided breathing system) and the other is the pure breathing simulator for the measurements in e.g., Human Toxicology field. Some researchers[13] have already developed the mechanical model of human oropharynx to investigate the deposition of the particulate matters on the wall of it. Once one develops the mechanical ventilation system and it is possible to cooporate with such oropharynx system so that one can examine the particle deposition. In Chapter 2, the measurement of the breathing in the clinics or medical laboratory is mainly discussed. The purpose of the measurement for the medical doctors is, for example, diagnosis of the disease. In the first section of this chapter, the breathing system of humans is briefly explained and in the second section, the measurement technique for the Human breathing, how to analyze the result of the measurement and the parameter of them are introduced. The human breathing simulator which is available in the world is introduced in the

8 3 last section. In chapter 3, the monitoring system of the human ventilation volume flow rate is discussed. The monitoring system including the breathing mask with mass flow rate sensor is developed so that time varying human ventilation of different individuals will be accurately sampled. For the sampling, firstly CTA is applied, however, the result has considerable error thus the time of flight sensor is applied for the necessity since it is not sensitive of the environmental condition like temperature and humidity of the exhaled air. In chapter 4, the experimental investigation of a mechanical ventilation simulator is described. Firstly, two proportional valves, which are incorporated either with vacuum chamber for the inhalation simulation or with pressurized air for the exhalation simulation, are operated by the program of the soft ware Lab view with data acquisition card to simulate the human ventilation. However, the exhalation simulation does not suit the original ventilation curve because the ventilation is time varying flow and simple proportional valve is not suitable for that simulation. Thus a mass flow controller with pressure transducer is applied for the ventilation simulation. The data line of real human ventilation curve is applied for this mechanical simulation. The whole simulation system and the result are presented in this chapter. The conclusions and final remarks are written in chapter 5.

9 Chapter 2 A Brief Literature Survey In this chapter, the work which is relevant to the breathing monitoring and simulation, is briefly explained in three sections as human breathing system, the measurement of the human ventilation and the human breathing simulator. Human breathing is a combination of the lung functions of ventilation, perfusion and circulation. There are many kinds of breathing functioning test, however, one of the test, ventilation functioning test is a great interest for the medical doctors and researchers since it gives the direct diagnosis of the lung disease. In the second section of this chapter, the measurement technique for the ventilation function which is mainly used in the clinics are referred and anlysing technique of the sampled data are briefly explained. In the third section, the breathing simulators are introduced. The fields of interest in developing a breathing simulator are various. Particularly to develop the breathing support machine(mechanical Ventilator) is required for the patients who are suffered from various respiration diseases. Not only for the patients, but also once the breathing simulator is developed, it will be easy to make bench test of the breathing mask filter etc. For example, influence of the contamination of the environment for humans, namely the deposition of the particulate matter in the oropharynx, which field is called Human Toxicology (inhalation toxicology of air pollution) is one of the most promising fields with developing the breathing simulator.

10 2.1 Breathing System of human being 5 Figure 2.1: Respiratory System [5] 2.1 Breathing System of human being Humans are the only mammal which breathes not only with the nose but also with the mouth. Normally humans breathe in through the nose because it allows humans to chew food and breathe at the same time since the nose is separated from the mouth by a bone called palate. And the other reason is that the nose works as a biological air conditioning unit and also it contains hairs which traps large dust particles so that if there is a lot of dust in the air one may also sneeze to remove it from the nostrils. In Fig.2.1 the human respiratory system is shown. After taking the air through nose or mouth then it passes into the throat and down the windpipe(trachea). The entrance of the trachea is protected by a valve, the epiglottis, which closes when one swallows food or drink. And then the air goes to the lungs. The lungs are found inside humans chest or thorax surrounded by the rib cage which protects them. The ribs also support the lungs and help to pump air in and out when humans breathe. This function is called ventilation which flow is monitored and simulated in this thesis. The other part of the thorax (chest) which helps to pump air in and out is the diaphragm. The diaphragm is a sheet of fiber and muscle which rises and falls as

11 2.1 Breathing System of human being 6 Gas Inspired air (% ) Expired air (% ) Nitrogen Oxygen Carbon Dioxide Water Vapor varies saturated Table 2.1: Contents of the air of inhalation and exhalation Temperature ( C) Inspired air Expired air Table 2.2: Temperature of the air of inhalation and exhalation[1] humans breathe. During breathing in (inhalation), skeletal muscles such as the diaphragm and external intercostals contract thereby increasing volume within the thorax and lungs. As volume within the air spaces of the lung (intrapulmonic volume) increases, air pressure within the lung (intrapulmonic pressure) falls below atmospheric pressure and air rushes into the lung. During breathing out (exhalation), the inspiratory muscles relax causing the volume of the thorax and lungs to be reduced. The reduction in intrapulmonic volume is accompanied by an increase in intrapulmonic pressure above atmospheric pressure, forcing pulmonary gas back into the atmosphere. Normally, unlabored expiration at rest is a passive event resulting from relaxation of inspiratory muscles. When an increase in pulmonary ventilation is required, such as during exercise, expiration becomes an active event dependent upon contraction of expiratory muscles that pull down the rib cage and compress the lungs. On average an adult human inspires and expires 10 to 20 cycle/min (the breathing frequencies or respiratory rate is 0.17 to 0.33 Hz) during normal quiet breathing (eupnea). This can increase to 25 cycle/min ( 0.42Hz ) during heavy exercise. Each time humans breathe the air 5 to 7 L/min which is inspired and expired, about 0.5 L of air moves into and out of the respiratory system. This volume is known as tidal volume (cf ). The product of tidal volume and respiratory rate is equal to the rate of

12 2.2 Measurement of the Human Breathing 7 pulmonary ventilation, also known as minute respiratory volume. A value within normal range is 7.5 L/min. This, however, is when humans are resting. If one begins to exercise, not only one breathes faster but also breathes deeper. An adult human has an extra 2.5 L of breath to call upon if needed. When taking heavy exercise a man could be breathing the air in and out up to 120 L/min. The air that one inspires and expires is a mixture of gases as it is shown in Table2.1. The most important of these are nitrogen, oxygen, carbon dioxide and water vapor. The air that one expires is not the same as the air of atmosphere as the water vapor in the atmosphere varies a lot depending upon the weather, for example, the air is saturated with water vapor if it is raining, instead, the air that one expires is always saturated with water vapor. The temperature of the air of the humans inhalation and exhalation may also change as it is shown in Table2.2. One breathes in cold air, the air is warmed up to body temperature by the blood in the many capillaries which are found close to the walls of the nasal cavity. These blood vessels also provide water which humidifies the air if it is too dry so that it does not harm the lungs. 2.2 Measurement of the Human Breathing In this section, the measurement of the breathing in the clinics or medical laboratory is mainly discussed. Medical doctors and researchers test the breathing functions for the following purposes: 1. Diagnosis of known or suspected lung disease 2. Treatment of lung disease, monitoring the effect of preventive measures or diagnostic procedures 3. Establishing a prognosis 4. Pre-operative assessments 5. Evaluation of pulmonary disablement 6. Monitoring the respiratory health of populations 7. Interpretation of other volume dependent lung function tests

13 2.2 Measurement of the Human Breathing 8 Breathing is a physiological function which is a combination of three functions, ventilation, perfusion (diffusion) and circulation. The breathing functioning test can be categorized into 10 different tests [2]: 1. Ventilation functioning tests e.g., Lung Volume test, Flow Volume curve analysis, Residual Volume Measurement, Air way resistance test, Lung Compliance test 2. Exercise load test e.g., Tredmill stress test 3. Sleeping respiration test e.g., Polysomnography 4. Air way sensitive test e.g., Astograph method, Body Plestymograph 5. Blood gas Analysis e.g., Artery blood test, Mixed blood test 6. Lung diffusion test e.g., DLCO (Diffusing Capacity for Carbon Monoxide Method) 7. Alveoli Gas diffusion test e.g., Gas Dilution method, Closing Volume method 8. Respiration regulation test, Ventilation response test e.g., CO2 ventilation response test, P0.1(Occlusion pressure test) 9. Circulation test 10. Others In all these ten different kinds of breathing functioning test, the first three tests are most relevant topic for this thesis work and especially the first one, ventilation tests are most commonly used method in the clinics to detect different kinds of diseases. Thus, the Ventilation functioning tests is mainly discussed in the following.

14 2.2 Measurement of the Human Breathing Parameters of Ventilation functioning tests In Ventilation functioning tests, there are for example, airway resistance test and lung compliance test. The former measures the pressure difference developed per unit flow, measured as the difference in pressure between the mouth and that in alveoli. The latter measures the lung volume change per unit of pressure change. Since both are less related to the present thesis work no more details is given in this thesis. There are many parameters for the Lung Volume Test which can be divided in two parts, one is the volume of air when humans breathe in relaxed manner (unlabored respiration) and the other is the volume of the air of Labored respiration. All of them are recorded in liters and reported at Body Temperature, Pressure, and Saturated with water vapor (BTPS). Lung Volume of Unlabored Respiration The volume parameters of unlabored respiration, which is performed in a relaxed manner without haste or deliberately holding back is shown in Fig.2.2. The curve in that Figure is called Spirogram which presents a graphic display of inspired and expired air volume against time. Lung Volume of labored Respiration Secondly the volume parameters of labored respiration which is performed when humans respirate as forcefully and rapidly as possible. These parameters are important for the volume flow loop analysis which is discussed in section Forced Vital Capacity (FVC) The maximum volume of gas that can be expired, after a maximal inspiration to total lung capacity. forced inspiratory vital capacity (FIVC) A maneuver performed similarly beginning at maximal expiration and inspiring. Forced Expiratory Volume (FEV T ) The volume of gas expired during a given time interval (T second) from the beginning of the FVC maneuver. Of the various FEVT measurements the FEV1 is the most widely used. Forced Expiratory Flowx-y (FEF x y ) The average flow rate during a given interval (percent) of the FVC maneuver. The index x y is used to denote the portion of the FVC for which

15 2.2 Measurement of the Human Breathing 10 Abbr. Full name Short description of the volume of the gas VC Vital Capacity full inspiration after a maximal expiration FRC Functional Residual Capacity remained in the lungs at the average the FRC level RV Residual Volume present in the lung at the end of a full expiration ERV Expiratory Reserve Volume maximally expired from the level of the FRC level TV Tidal Volume inspired or expired during a normal respiratory cycle IRV Inspiratory Reserve Volume inspired from the FRC level IC Inspiratory Capacity maximal volume which is inspired from the FRC level TLC Total Lung Capacity present in the lung at the end of a full inspiration Figure 2.2: Schematic Representation of Lung volumes [3]

16 2.2 Measurement of the Human Breathing 11 this average flow is measured (mostly used as FEF25%-75%: the average flow rate for the liter of gas expired after the first 25% of FVC during an FVC maneuver). Forced Inspiratory Flow (FIF x y ) The average flow rate during a given interval (volume) of the FIVC maneuver. Maximum Voluntary Ventilation (MVV) The largest volume that can be breathed during a 10- to 15- second interval with voluntary effort. Normal values of healthy young men average between 150 to 200 L/min. (slightly lower in healthy women) and decreases with age in both men and women. Peak Expiratory Flow Rate (PEFR) The maximum flow rate attained during an FVC maneuver. Normal values for healthy young adults may exceed 600 L/min Measurement Techniques of the Human Ventilation For the measurement of human ventilation functioning, spirometer is most commonly used in medical field. As it is shown in Fig.2.3, Usually nose clip and mouthpiece are used for this measurement. There are various spirometers which can be divided in two groups. One is volume displacement spirometers and the other one is flow-sensing spirometers. The Volume-Displacement spirometers provide a direct measure of respired volume for example, displacement of a bell, piston or bellows spirometer. Fig.2.3 is an example of the spirometer with displacement of a bell. They are recorded in the spirogram (cf, Fig.2.2) and the parameters like FEV 1, FVC and VC are calculated including correction to BTPS which is necessary for the accurate measurement since Expired air is at body temperature and saturated with water vapor but the air cools down in the spirometer. The problem of the Volume-Displacement spirometers is the poor dynamic characteristics. The response characteristics of them is faithful only for the recording of events occurring over seconds (FVC, FEV 1 ) and they are not usually sufficiently fast to accurately record rapid events (e.g. PEF measurements). On the other hand, flow-sensing spirometers generally utilize a sensor that measures

17 2.2 Measurement of the Human Breathing 12 Figure 2.3: Volume-Displacement Spirometer [8] flow as the primary signal and calculate volume by electronic (analog) or numerical (digital) integration of the flow signal. The most commonly used flow-sensing spirometers are with: 1. Pneumotachmeter, 2. Hot Wire Anemometer or 3. turbine blade as shown in Fig.2.4. However, the accuracy of each new sensor may need to be established. Accuracy and reproducibility depend on the stability and calibration of the electronic circuitry and appropriate correction of flow and volume to BTPS conditions. For example, a small error when detecting 0 flow rate can cause these devices to produce large errors in the measurement of FVC, as the error is continually added during the time needed to complete the exhalation. With heavy use, the sensor may also change its calibration due to the condensation of water vapor.

18 2.2 Measurement of the Human Breathing 13 Figure 2.4: Various Spirometers[7] upper:fleischpneumotachometer, middle:hot wire spirometer, bottom:turbine spirometer

19 2.2 Measurement of the Human Breathing 14 The pneumotachograph derives the volume flow rate from the measurement of pressure drop over a fixed resistance, consisting of a bundle of parallel capillary tubes (Fleisch type pneumotachometer). The apparatus is designed in such a way that the air flowing through the resistance has a laminar profile, ensuring a direct proportionality between pressure drop over the resistance and flow. This condition is met only within a given range of flows. When this range is exceeded, the relationship between pressure drop and flow becomes nonlinear in the sense that the pressure drop increases progressively more for a given increase in flow. The limits of linearity should be known. Volume is obtained from analog or digital integration of the flow signal. It has its own error as it can be explained with the acceleration. Since the calibration is made under steady conditions, whereas ventilation is a time varying Pulsating flow. This will cause also the decelerations from the actual values especially for fast breathing measurement. The ventilation measurement with constant temperature anemometry his also inaccurate as the human ventilation is temperature varying and saturated with water vapor. This problem is discussed in detail in Section 3.3 with the actual ventilation measurement with CTA. The turbine spirometer measures inaccurately the flow rate of time varying Pulsating flow because of its inertia Analyzing Technique of the Human Ventilation A hard copy of the spirogram(e.g. Fig.2.2) or flow volume curve (Fig.2.5) gives valuable information of the ventilation functions. The factors which determine the size of normal lungs are: age, height, weight, stature, gender, posture, habits, ethnic group, reflex factors and daily activity pattern. The evaluation is, for example, predicted vital capacity which is calculated by the subject s age, height, weight etc. is compared to the measured vital capacity. This is an example equation [4] of the predicted vital capacity: Male: ( age) height (ml) Female: ( age) height (ml) But only for 17 < age < 70 Reduction in VC (e.g., less than 80%) can be caused by a loss of lung tissue. In general this may be the result of tissue destruction or resections (lobectomy), space-occupying lesions (tumors), or changes in the composition of the

20 2.2 Measurement of the Human Breathing 15 Figure 2.5: Flow Volume Loop [3] parenchyma itself (fibrosis). The VC is often reduced in obstructive lung disease. Other causes of a decreased VC can also be: depression of the respiratory centers or neuromuscular diseases, reduction of available thoracic space (pneumothorax, cardiac enlargement) and limitations of thoracic (kyphoscoliosis) or diaphragmatic (pregnancy, ascites) movement, brain obstacle and the deformation of the thorax. The Volume Flow Loop (Fig.2.5) is a graphic analysis of the flow generated during the FVC maneuver plotted against volume change (maximal expiratory flow-volume MEFV) and is usually followed by the FIV maneuver, plotted similarly (maximal inspiratory flow volume MIFV). In a volume Flow Loop instantaneous flow at any lung volume over the VC can be read directly from its tracing.flows at 75%, 50% and 25% of the VC are commonly reported as the V max75, V max50, and V max25 respectively (the subscript referring to the percentage of the lung volume (VC) remaining). Flow is also reported as FEF25%, FEF50%, and FEF75% (the subscript referring to the portion of the lung volume

21 2.3 Breathing Simulator 16 a: Normal subjects b: Obstructive Ventilatory defect c: Asthma d: Restrictive Ventilatory Defect e: Various Restrictive Ventilatory Defects Figure 2.6: Classification of Abnormal Ventilation Functioning [6] (VC) that has been exhaled). If automatic timing is available the FEVT and FEV T % can be determined for specific intervals. There are many interpretations from the shape of the curve as it is shown in Fig Breathing Simulator There are two different kinds of Human Breathing simulator; one is used for the patients who have the breathing problem, this can be called mechanical ventilator (Machine aided breathing system) and the other is the pure breathing simulator for the measurements in e.g., Human Toxicology field. There are various breathing support system or mechanical ventilator available

22 2.3 Breathing Simulator 17 Figure 2.7: Mechanical Ventilator[22] in the market which works in the way that a Patient is connected to the ventilator by a endotracheal tube passed through the nose or mouth into the trachea. The mechanical ventilator delivers inspiratory gases directly into the person s airway. Fig.2.7 is an example of mechanical ventilator. The other type of simulator Active Servo Lung 5000 [12] shown in Fig.2.8 is an example. This can not be connected to the patients as mechanical ventilator but it is used for the education of the medical students etc. Similar mechanism has the ventilation simulators are used by the researchers who study about the human toxicology. For example, Dr. Heenan et. al have constructed very precise human oropharynx model which is connected to the ventilation simulator[13] (Fig.2.9, Fig2.10 to study particle deposition. Dr. Matida et al constructed the

23 2.3 Breathing Simulator 18 Figure 2.8: Digital Image and Schematic description of Active Servo Lung 5000

24 2.3 Breathing Simulator 19 experimental setup to test the efficiency of aerosol deposition together with a commercial dry powder inhaler as it is shown in Fig.2.11 It is also interesting to simulate the particle deposition, or mass transfer in the human oropharynx. Several reserches[18][19][20] have made the models (Fig.2.12,Fig.2.13) and obtained interesting results.

25 2.3 Breathing Simulator 20 Figure 2.9: Oropharynx[13] Schematic experimental setup of the flow field in Humans Figure 2.10: Idealized Model geometry of human oropharynx[13]

26 2.3 Breathing Simulator 21 Figure 2.11: Schematic aerosol experimental setup with Humans Inhaler[21]

27 2.3 Breathing Simulator 22 Figure 2.12: 3-D views of the oral airway model and bifurcation airway model[18] Figure 2.13: Velocity and Non-dimensional temperature profiles[18]

28 Chapter 3 Development of a Breathing Measurement System In this chapter, the human ventilation measurement system which is cooperated with the time of flight sensor is described. The geometry of the designed measurement mask is shown in the first section and in the second section, the principle of the measurement sensor, time-of-flight sensor is briefly explained. In the third section, some verification experiments are shown and in the last section, the final measurement and the results are presented. 3.1 Construction and Equipment for Breathing Flow Rate Measurements Geometry of the breathing Mask It is necessary to construct the breathing measurement mask carefully to measure the volume flow rate of human ventilation accurately. There are two types of masks which are available in the market such as nose mask and the mask for mouth and nose. Human beings breath usually with nose, however, it is also true that it is the only mammal which breaths not only with the nose but also with the mouth because it has the ability of speaking. Thus it is required to use the mask which covers both properly. Medical researchers use commonly the equipment to measure the functioning of lung, such as spirometer (cf, chapter 2), which requires to use nose clips and subjects breathe only with mouth. In this thesis work, the mask which covers nose and mouth is selected to make

29 3.1 Construction and Equipment for Breathing Flow Rate Measurements 24 it sure the natural human ventilation will occur during the measurement, unlike the conventional spirometry. The mask is incorporated with the time of flight sensor, whose functioning principle explained in the next subsection. The breathing mask and measuring set up is described in Fig.3.1. To connect the breathing mask to the sensor, glass nozzle with the angle of 7 is applied to avoid the flow separation during the respiration. To homogenize the incoming flow and to protect the sensor wires from large aerosols which can cause measurement errors and even can destruct the wires, flow straightening mesh is placed at the exit of the breathing mask (the point A) and at the both entrance of the sensor (B and C). The volume flow rate is calculated based on that the cross sectional area where the thermal sensors are located and the velocity profile is 90% flat [9] Incorporation of Flow Sensors In this section, the incorporation of the sensor with the ventilation measurement is described. First sub section shows the measurement of the human ventilation with conventional Constant Temperature hot wire anemometry(cta) is applied. The result shows the difference between the sums of the air volume of inhalation and exhalation in 5min-long measurement more than 10%, this difference is the measurement error because of the exhaled air variation in temperature and humidity. Thus, it is concluded that the new sensor must be used for the measurement of human ventilation. The second sub section will briefly explain about the principle of the time-of flight sensor and some verification experiments are described Human ventilation Measurement with CTA The first measurement of the human ventilation is done with CTA sensor. The result of the human ventilation measurement with the CTA sensors shown in Fig.3.2. The duration of the inhalation and the breathing frequency is correctly measured, however, the summation of the air volume of the inhalation and exhalation in 5min measurement contains more than 10% difference such as the inhalation is always more than that of exhalation due to the CTA sensor s dependency on the temperature. Since the conventional Constant Temperature Hot Wire Anemometry (CTA) or Constant Current Hot Wire Anemometry (CCA) [10] are the measurement technique which is based on using the heat loss from

30 3.1 Construction and Equipment for Breathing Flow Rate Measurements Figure 3.1: Digital image and Schematic Figure of the mask with the sensor 25

31 3.1 Construction and Equipment for Breathing Flow Rate Measurements 26 Sensor parameter Wire diameterd w Wire lengthl w Wire spacing x Excitation frequencyf Value 12.5µm 5mm 1.5mm 30Hz Table 3.1: The parameter of the time of flight sensor the wire for the velocity calculation thus their accuracy is highly sensitive to the variation of the flow temperature. It gives less output signal if the temperature of the measured material is increased even though one calibrates the output signal of the CTA sensor with the temperature correction factor. This error is not only because of the temperature varying but also of the humidity in the flow. The exhaled air is saturated with water vapor since the heat transfer of the hot wire increases with increasing humidity[11]. Since the conventional hot wire anemometry does not measure the ventilation accurately, a new sensor had to be utilized instead of CTA sensor. One needs a sensor which is temperature independent and sensitive to the direction of the flow since breathing has basically tow directions. According to the principle of the time-of-flight sensor, the atmospheric temperature and the humidity do not effect on the accuracy of the measurement [9]. In the next sub section, the principle of time-of-flight is briefly explained The principle of Time-of-Flight sensor The thermal sensor is chosen for the measurement because of its temperature independence and its directional sensitivity. (Figure 3.3) There are three parallel wires which are placed in the throat area. The middle one is the sending wire which is heated by an oscillating current at 30Hz frequency. The rest two wires are receiving wires, which detect the temperature variation in the wake of the sending wire, are located at a distance 1.5mm each from the sending wire. The length of all these heated wires, which are made of platinum, is 5mm and its diameter is 12.5µm. The sensor geometry is designed by the company Draeger[14] so that the form of the velocity profile is formed always turbulent velocity profile. Fig.3.3 depicts the configuration of the sensor. The throat inner diameter is 12.5mm and the volumetric flow rate can be calculated with the cross sectional

32 3.1 Construction and Equipment for Breathing Flow Rate Measurements 27 - Inhalation Exhalation duration Sum of Inhaled air Sum of Exhaled air error% 18sec sec sec Figure 3.2: CTA Ventilation measurement area and atmospheric temperature. The cross section, where the thermal sensor is located is slightly thinner than the opening of the sensor and the angle is 7. Since the breathing measurement will be two directional measurements, the geometry of the sensor must be symmetry. The principle of the sensor function is the following. For simplicity, only one directional sensor (two wire sensor) is discussed. In Fig.3.5 it is described two wires mounted perpendicular to the flow to carry out time of flight measurements which yield velocity information. The wire located in the upstream (wire A)

33 3.1 Construction and Equipment for Breathing Flow Rate Measurements 28 Figure 3.3: Configuration of the Time of Flight Sensor is electrically heated device providing time varying thermal signal to the flow. This resultant thermal signal is flown downstream to the receiving wire (wire B) which operates as a resistant thermometer, and detects the delayed arrival of the thermal signal. The measured time of flight and known distance between the sending and receiving wires permit the flow velocity to be calculated with the following equation. t f = x U Where x is the distance between the hot wires and U is the flow velocity. Fig.3.6 shows the example of the time difference which are obtained from the sending wire and receiving wire signal. The signal which is given to the sending wire is sinusoidal varying electrical current and the receiving wire detects the temperature oscillation. This total time difference contains three different components, 1. the time of flight(convection by the fluid in the wake of the sending wire) 2. the thermal lag of the receiving wire

34 3.1 Construction and Equipment for Breathing Flow Rate Measurements Figure 3.4: Digital Image of the Time of Flight Sensor 29

35 3.1 Construction and Equipment for Breathing Flow Rate Measurements 30 Figure 3.5: Schematic description of Time of Flight Sensor 3. the thermal lag of the sending wire All time components can be numerically calculated as it is described in the Appendix[9]. Although there are three different components, Fig.3.7 shows that in the low velocity range, the range of human ventilation measurement (0.15m/s to 2m/s), the thermal lag of the wires are negligible and only time of flight is dominant Calibration and Time response of the Sensor Calibration of the thermal sensor For high volume flow rate such as more than 10L/min, Mass flow controller has been used and for the low volume flow rate such as less than 10L/min the calibration is done with the water chamber calibration since Mass flow controller has its own error if the volume flow rate is too less. The calibration of the sensor for high volume flow rate is done with the experimental set up which is shown in Fig.3.8. It is connected to the mass flow controller[15] with 6m pipe and connector so that the flow will be fully developed. In the connector the mesh is equipped thus the velocity profile of the cross section of the measuring point in the sensor will be turbulent (90%flat). The

36 3.1 Construction and Equipment for Breathing Flow Rate Measurements 31 Figure 3.6: Measurement of time difference[9] Figure 3.7: The three components of the time difference and their summation versus the flow velocity [9]

37 3.1 Construction and Equipment for Breathing Flow Rate Measurements 32 Figure 3.8: Calibration set up of the sensor for high velocity signal will be transferred from the computer to the Mass flow controller through Data Acquisition (DAQ) card and the signal from the sensor is acquired and stored in the computer through the DAQ card. As it is described in the Fig.3.9, the low volume flow rate calibration is done by water chamber. The way of calibration is the following. There is a water chamber with no leakage, except the upper part, where the sensor is connected. When the valve located the bottom of the chamber is opened, water comes out from the outlet and the surrounding air which volume is same as water, comes into the chamber from the upper side through the sensor. The procedure of the calibration is; firstly open the valve, take the water from the valve outlet of the chamber and measure the mass of the water. Simultaneously the duration time is also measured with stopwatch so that one can obtain the mean mass flow rate of the water. The atmospheric pressure and temperature are measured by the pressure gauge and thermocouple respectively for the calculation of the density of the air and finally the mass flow rate of the air is obtained. The lowest velocity less than 0.017m/s can be realized with this test rig, however, it is found that as it is shown in Fig.3.10 the thermal sensor has free convection problem, it can not measure the velocity less than 0.15m/s. The calibration curve for the thermal sensor is shown in Fig The Calibration is done totally two times in different days on which temperature difference is 3 degree centigrade. Since the thermal sensor is atmospheric temperature insensitive, the calibration curves are

38 3.1 Construction and Equipment for Breathing Flow Rate Measurements 33 Figure 3.9: Calibration set up of the sensor for Low velocity flow Figure 3.10: Calibration curve of the extreme low velocity region

39 3.1 Construction and Equipment for Breathing Flow Rate Measurements 34 Figure 3.11: Calibration curve of the Time of Flight Sensor obtained the difference between two calibrations is less than 5 % Frequency response of the sensor Human breathing is two directional pulsating flow whose frequency ranges approximately from 0.17Hz to 0.33Hz in normal condition and can reach more

40 3.2 Final Measurements 35 than 0.42Hz after a heavy exercise. The frequency response test is proceeded with such experimental set up as the combination of the signal generator and mass flow controller connected with the TOF sensor for both direction. The sinusoidal signal is given to the mass flow controller from the signal generator so that it can produce the sinusoidal time varying volume flow rate with different frequencies but only one direction. The result of the frequency response is shown in fig.3.12 as the given signal is the signal given to the mass flow controller and detected signal is the acquired from the measurement electronics of the TOF sensor. It is in principle same time responce characteristic is observed for both direction, he is shown only for one directional frequency responce test results with different frequencies. There is a time lag of 0.05sec in each frequency test. This is due to the response of the mass flow controller, however, it is sufficiently responding for the measurement of the Human ventilation Signal Processing In the measurement, two signals from the measurement electronics of the sensor are obtained; one corresponds to the mass flow rate and the other corresponds to the flow direction. The signal for the mass flow rate is represented from 0 to 10 volt, on the other hand, signal for the direction is represented 0 or 5 volt. In the actual measurement, 0 volt for the direction signal represents inhalation and 5 volt does exhalation. According to the directional signal, inhalation and exhalation is differentiated as inhalation is described negative volume flow rate and exhalation is positive volume flow rate by the calculation with FORTRAN program whose scheme is the following; firstly the noise signal like too high volume flow rate signal is cut off since the normal quiet breathing does not reach more than 35L/min and also the signal of the free convection range of the sensor is replaced 0L/min since the sensor cannot measure less than 1.17L/min. After cutting the noises, the signal is converted into the volume flow rate according to the direction signal. 3.2 Final Measurements The ventilation curve is sampled by the system which is described in Fig.3.1. Fig.3.13 is the typical ventilation curve in normal quiet condition. This ventilation measurement is done with 5 different individuals (different height, weight,

41 3.2 Final Measurements 36 Figure 3.12: Frequency response of the Time-of-Flight sensor upper 0.1Hz middle 0.5Hz below 1Hz

42 3.2 Final Measurements 37 age and sex) taking summation of the volume of inhalation and exhalation respectively for 5min normal quiet breathing, the volume difference between sum of the in- and exhalation is always less than 2% whereas with the CTA sensor measurement can not reach less than 10%.

43 3.2 Final Measurements 38 - Exhalation Inhalation duration sum of exhaled air sum of inhaled air error% 18sec sec sec sec sec sec Figure 3.13: Human ventilation measurement with Time-of-Flight sensor

44 Chapter 4 Realization of a Ventilation Simulator In this chapter, the realization of a breathing simulation system is described. There is a brief explanation of the volume flow control system in the first two sections. In the third section, the final ventilation simulation result is shown. 4.1 Construction of ventilation Simulator In this section, the way how to construct the ventilation simulator is described. The proportional volume control valve is selected to simulate the human ventilation and the application for the valves is described in the following subsections Instrumentations The configuration of the ventilation simulation system is shown in Fig.4.1. The pressurized air is supplied up to 6bar. The vacuum chamber which capacity is more than 80 m 3 is connected to the vacuum pump manufactured by the company Busch[?]. The vacuum pump type is GRV2000 and has the vacuuming ability of 2000m 3 /h. For volume flow rate controlling, two proportional valves with measurement electronics which are manufactured by the company Buerkert[?] (Fig.4.2) are used. The proportional valves change the opening (cross sectional area) according to the electrical signal which ranges from 0 to 10 volt so that it controls the volume flow rate. The proportional valve of type 6021 for the exhalation simulation,

45 4.1 Construction of ventilation Simulator 40 Figure 4.1: Configuration of the ventilation simulation system

46 4.1 Construction of ventilation Simulator 41 Figure 4.2: Degital image of the proportional valve Type 6022 for the inhalation simulation and type 1094 for the measurement electronics are used. The norminal width of the opening of the type 6021 valve is maximum 1.6mm and that of type 6022, 4mm. To use the small opening valve, the controlling capacity is bigger, however, it is necessary to employ the bigger opening valve especially for the inhalation simulation because the pressure difference can not reach more than 1bar as it is operated with negative pressure with vacuum chamber and it can not give the sufficient amount of volume flow rate for the inhalation simulation. The frequency response of the valve is set to 1000Hz in the measurement electronics. The computer gives the ventilation curve to the data acquisition card (DAQ), which is sampled from different individuals (cf. chapter 3) and DAQ card gives the signal for opening and closing to the proportional valves and additionally, obtaining the velocity and the flow direction signal from the TOF sensor simultaneously Volume Flow Control System for Exhalation For the simulation of exhalation, the proportional valve is connected to the pressurized air supply. Since the volume flow rate depends not only on the electrical signal but also on the pressure of the high-pressure side, it is necessary to calibrate the valve with fixed inlet pressure.

47 4.1 Construction of ventilation Simulator 42 Figure 4.3: Calibration Curve for the Exhalation Simulation with opening and closing The calibration curve of the proportional valve with pressurized air is taken for opening and closing of the valve in steady condition shown in fig.4.3. There is output strain between opening and closing of the valve thus, for the ventilation simulation, the averaged curve is taken as it is described in the next section Volume Flow Control System for Inhalation For the simulation of inhalation, the same type of the proportional valve as for simulation of exhalation is used with sub-pressure operation. Since the volume flow rate is not sufficient with the opening size of the proportional valve operated by the pressure difference between vacuum chamber and the atmospheric pressure unlike the system with pressurized air. Hence a bigger opening proportional valve is used. This valve is connected to the vacuum chamber which is vacuumed by the pumps up to 0.04bar. The high-pressure side of the system of this simulation is atmospheric pressure which is different from the system of exhalation simulation with positive pressurized air. The atmospheric pressure remains constant and independent on the opening of the valve unlike the exhalation simulation setup. When the absolute pressure ratio between the high pressure side and low pressure side is less than 0.528, the flow velocity at the valve opening reaches sonic velocity

48 4.2 Calibration of Combined Values 43 Figure 4.4: Calibration Curve for the Inhalation Simulation with opening and closing then the velocity and mass flow rate will remain constant. And it is required to reach choked flow to get the constant volume flow rate. It is only possible in the vacuum atmosphere as the pressure of the higher pressure side remains constant. In this regard, since the opening of the valve does not affect the inlet pressure (atmospheric pressure), inhalation simulation system can control the volume flow rate more accurately than exhalation simulation system. The calibration curve of the proportional valve with negative pressure operation is taken for opening and closing of the valve in steady condition shown in Fig Calibration of Combined Values After the connection of the two valves and completing the construction of the whole set up, the calibration curve for both proportional valves are taken since the back pressure affects the volume flow rate of the valves and the calibration curves for the single connected setup are not any more valid. The final averaged calibration curve is shown in Fig.4.5.