Biomedical Instrumentation

Transcription

1 University of Zagreb Faculty of Electrical Engineering and Computing Biomedical Instrumentation Measurement of respiration prof.dr.sc. Ratko Magjarević November 2016

2 Respiratory system Consists of the lungs, airways and the chest wall Function of respiratory system is gas exchange (O 2 and CO 2 ) between the blood and the atmosphere Gas exchange is passive due to diffusion

3 Respiration rate Respiration rate is an important vital sign. It is, the number of breaths taken within a set amount of time. Tachypnea /Bradypnea / Apnoea, is a sensitive indicator of physiologic distress that requires immediate clinical intervention. Normal breathing rate

4 Gas exchange a) Oxygen diffusion from air to blood b) Carbon dioxude (CO 2 ) diffusion from blood to alveoli (lungs) The partial pressure of gas in the different parts of the respiratory and circulatory system (mmhg) Location po2 (mmhg) pco2 (mmhg) ph2o (mmhg) pn2 (mmhg) Inhaled air 158,0, 0,3 5,7 596,0 Alveolar air 100,0 40,0 47,0 573,0 Exhaled air 116,0 32,0 47,0 565,0

5 Respiratory measurements - instrumentation Imaging x-ray, CT, MRI Lung volume change estimation or detection Fluoroscopes Electrical, mechanical or pneumatic devices placed around torso Nasal temperature sensors Transthoratic electrical impedance meters Force plates for movement detection associated with breathing

6 Characteristic respiratory values The following five static lung volumes can be measured: VT (tidal volume), IRV (inspiratory reserve volume), ERV (expiratory reserve volume), IC (inspiratory capacity) and VC (vital capacity).

7 Breathing waveform

8 Spirometers Most digital spirometers display the following graphs: A volume-time curve, showing volume (liters) along the Y-axis and time (seconds) along the X-axis A flow-volume loop, which graphically depicts the rate of airflow on the Y-axis and the total volume inspired or expired on the X-axis

9 The shape of the flowvolume loop can indicate the location of airflow limitation, such as the large upper airways or smaller distal airways

10 Spirometers Pneumotachometer This type of spirometer is also referred to as a differential pressure transducer (DPT) and measures the flow of air by detecting pressure differences across the two sides of a fine wire-mesh within a flow head. One advantage of this spirometer is that the subject under investigation can breathe in fresh air during the experiment. However, a DPT does not provide an output reading of absolute pressure within the system. Whole body plethysmograph The whole body plethysmograph provides a more accurate measurement for the components of lung volumes compared to conventional spirometers. In this technique, the subject is enclosed in a small airtight chamber when the measurement is taken. This method obtains the absolute volume of air within the subject s lungs.

11 Respiratory rate measurement Spirometry is a non-invasive method of lung function testing, which measures the amount (volume) and/or speed (flow) of air that can be inhaled and exhaled. Most lung function tests involve fairly simple breathing tasks and are usually not uncomfortable. Breathing requirements for some test measurements may be normal and quiet. Other tests require forced inhalation or exhalation after a deep breath. Spirometry can be used for assessing lung conditions such as asthma, emphysema, pulmonary fibrosis and cystic fibrosis. methodes

12 Respiratory rate measurement methods Pneumotachometer is a device that measures the flow of respiratory gases. The pressure gradient is directly related to flow, thus allowing a computer to derive a flow curve measured in liters per minute. Lung function can be determined by measuring airflow and the corresponding changes in lung volume.

13 Measurement and visualization in real time mode both quiet (spirometry), and forced (pneumotachometry) breathing, measurements of maximal breathing capacity; Simultaneous review of several curves of forced expiration and self-acting (or hand-held) choice of best test; Construction of spirometry graphs (volume-time) and pneumotachometries (flowvolume, volume-time) in real time,

14 Forced expiratory flow (FEF) a) Measurement of forced vital capacity (FVC) and expiratory capacity as well as the expiratory flow at mid range expiration (FMEF 25% - 75%) b) Air flow versus volume (Q - V)

15 Forced expiratory flow (FEF) Forced expiratory flow (FEF) is the flow (or speed) of air coming out of the lung during the middle portion of a forced expiration. Forced vital capacity (FVC) is the volume of air that can forcibly be blown out after full inspiration, measured in liters. FVC is the most basic maneuver in spirometry tests. Forced expiratory volume in 1 second (FEV1) represents the proportion of a person's vital capacity that they are able to expire in the first second of expiration Forced expiratory flow 25 75% (FEF25 75%) a mean of the flow during an interval

16 Forced expiratory flow (FEF) Measurement Approximate value Male Female Forced vital capacity (FVC) 4.8 L 3.7 L Tidal volume (Vt) 500 ml 390 ml Total lung capacity (TLC) 6.0 L 4.7 L Average values for forced vital capacity (FVC), forced expiratory volume in 1 second (FEV1) and forced expiratory flow 25 75% (FEF25 75%), according to a study in the United States 2007 of 3,600 subjects aged 4 80 years. Y-axis is expressed in litres for FVC and FEV1, and in litres/second for FEF25 75%.

17 A plethysmograph is an instrument for measuring changes in volume within an organ (e.g.lungs) or whole body Pulmonary plethysmographs are commonly used to measure the functional residual capacity (FRC) of the lungs the volume in the lungs when the muscles of respiration are relaxed and total lung capacity.

18 Water-sealed spirometar

19 Peak expiratory flow The peak expiratory flow (PEF), or peak expiratory flow rate (PEFR) is a person's maximum speed of expiration, as measured with a peak flow meter, a small, hand-held device used to monitor a person's ability to breathe out air. It measures the airflow through the bronchi and thus the degree of obstruction in the airways.

20 Impedance pneumography Impedance pneumography is a commonly-used technique to monitor a person s respiration rate, or breathing rate. It is implemented by either using two electrodes (Figure 6.4a) or four electrodes (Figure 6.4b). The objective of this technique is to measure changes in the electrical impedance of the person s thorax caused by respiration or breathing.

21 Impedance pneumography Equvalent circuit for two electrode measurement two electrodes and four electrodes measurement models

22 Impedance pneumography Waveshape of the respiratory signals measured by impedance pneumography

23 Impedance pneumography Block diagram of the respiratory measurement chain

24 Impedance pneumography Block diagram of the respiratory measurement chain

25 Piezoelectric sensors Mounted on a belt the piezoelectric device that responds linearly to changes in length It measures changes in thoracic or abdominal circumference during respiration. These measurements can indicate inhalation, expiration and breathing strength and can be used to derive breathing rate.

26 Piezoelectric sensors Respiration belt Sleep Sense 1387-kit From:

27 Measurement of respiration gases composition 1 A mass spectrometer generates multiple ions (2) from the gas sample under investigation (1), it then separates them according to their specific mass-to-charge ratio (m/z) (3), and then records the relative abundance of each ion type (4). 2 3 A mass spectrum of the molecule is thus produced. It displays the result in the form of a plot of ion abundance versus mass-tocharge ratio. 4 Mass spectrometer block diagram and measurment of gass components in exhaled air

28 Literature Weber, J., Medical Instrumentation, Chapter 9, Measurement of the Respiratory System (A. Šantić, Biomedicinska elektronika, poglavlje 7.5 Mjerenje karakterističnih veličina respiracije )