Exam 2 - Topic 4 - Monitoring Equipment

Question 1

ECG

Answer 1

• developed in late 19th century
• NASA advanced it fast to measure astronauts
• most universities now have biomedical engineering

Question 2

Biometrics

Answer 2

• the measurement of physiological variables and parameters

Question 3

What do we measure?

Answer 3

• Bioelectric potentials
• Cardiovascular
• Temperature
• Respiratory

Question 4

How can measurements be obtained?

Answer 4

• passively
• applying energy to obtain data
• reflection or refraction of light

Question 5

Performance characteristics of Medical Intrumentation

Answer 5

• Sensistivity
• Range
• Frequency response
• Accuracy
• Signal to noise ratio
• Stability
• Isolation
• Simplicity

Question 6

Linearity

Answer 6

• degree to which variations in output follow variations in input
• reflects that output is proportional to input
• Something you want over as much range as possible

Question 7

Frequency response

Answer 7

• variation in sensitivity over frequency range

Question 8

Hysteresis

Answer 8

• measurement is different when read in a ascending manner versus a descending manner
• due to friction in system
• do not want lots of this

Question 9

Signal to noise ratio

Answer 9

• Want as high as possible
• noise can produce errors in measurement and obscure data
• noise caused by power lines / electromagnetic interference
  - electrocautery knife

Question 10

Isolation

Answer 10

• necessary for electrical safety

- may need to make a measurement when there is no connection between patient and ground

Question 11

Man-instrument system

Answer 11

• Electrical system is input
• electrode or transducer captures physiologic parameter as resistance/voltage/or current
• electronic signal sent to signal conditioning equipment to get modified and processed
• new signal is sent to display

Question 12

Transducer

Answer 12

• converts non-electrical signal (pressure/temp) to electrical
• uses strain gauge and Wheatstone bridge to make pressure signal into electrical signal

Question 13

Strain gauge

Answer 13

• detects mechanical displacement
• when compressed ….resistance goes down
• when stretched…. Resistance goes up
• this can change voltage across device which is sent as signal

Question 14

Wheatstone bridge

Answer 14

• measures unknown electrical resistance

- made of four resistors…three are known and can be used to find the fourth or unknown

Question 15

Bioelectric potential

Answer 15

• potential created in body due to ionic voltage gradients in certain types of cells (muscle, heart, nerve)

Question 16

Biopotential electrodes

Answer 16

• Microelectrodes : measure near or within cell
• Skin electrodes : measure from surface of skin - popular
• Needle electrodes : measure via penetration of skin

Question 17

Characteristics of electrode

Answer 17

• Non-polarized (should not hold a charge)
• long term stability
• good signal acquisition
• reproducible parameters
• convenience of application
• non-toxic

Question 18

Issues with electrodes

Answer 18

• motion artifact
• lead slippage
• electrical interference
• electrode slippage
• gel drying out
• skin surface changes (touch, sweat, motion)

Question 19

Fluid filled monitoring system

Answer 19

• Catheter insertion
• extension tubing (hard tubing aka low compliance)
• pressure transducer
• flush system (small pressurized bag of crystalloid - 300mmHg)
  +prevents clotting and back flow of blood through catheter
• signal conditioning system (amplifier) / Monitor

Question 20

Factors affecting waveform in fluid monitoring system

Answer 20

• Inertia: causes lag in response to pulse wave

- Natural frequency: Underdamping (exaggerated response) or overdamping (blunted response)

Question 21

Natural frequency

Answer 21

• natural oscillation based on mass and stiffness
• will decrease with increased mass
• will decrease with decreased stiffness
• Natural frequency of all components must be greater than highest harmonic in order to avoid under/over damping

Question 22

1 Hertz

Answer 22

• 1 cycle per second

- so…. 120 bps = 2 Hz

Question 23

Orientation of catheter tip

Answer 23

• should face into blood flow to be more accurate

Question 24

Guidelines for fluid-filled monitoring

Answer 24

• simple system
• large bore catheters
• low compliance and short tubing (3-4 ft max)
• tight connectors
• continuous flush device (3 ml/hr)
• check for air bubbles
• keep tubing away from movement
• MUST be leveled (catheter and transducer same height)
• MUST be zeroed (take away effects of atmospheric pressure)
• MUST be calibrated (usually by manufacturer)

Question 25

Snap test

Answer 25

• close flush valve really fast
• creates waveform that tells us:
  - dampening of system
  - frequency response time