Practice Problems 1-5

With an RC circuit in series with a voltage source, what is the value of I if the capacitor is fully charged?

0 amps

Which one is not advantage of surface EMG? a. Quick, easy to appy b. No medical supervision, required certification c. Minimal discomfort d. Little cross-talk concern

d

The flat section in an ECG trace between the P-wave and QRS complex is caused by: a. A pause in Bachmann's bundle b. Arterial fibrillation c. Caused by rapid depolarization of the ventricles d. A group of electrically active enzymes e. A pause in the electrical depolarization of the heart at the AV node

e

Calculate the theoretical cut off frequency where the gain of the signal is down 3dB, R= 22kOhm, C=10nF

fc= 1/2piRC fc=1/(2*pi*22kOhm*10nF) fc=723.41 Hz

How can an engineer effectively remove random errors: e) by calibration f) by using twisted pair cables g) by taking multiple measurements and averaging the results h) by using an amplifier circuit

g

ECG signals were used to collect the heart rate from 5 subjects before and after physical exercise. (a) What is the appropriate statistical analysis tool? (b) is it two tailed, upper tailed, or lower tailed? (c) state null and alternative hypothesis

(a) paired t Test (b) two tailed) (c) Ho= there is no differences u1=u2 Ha= There is a difference, u1 =/= u2

(a) For a circuit with an initially discharged capacitor, if an input voltage of 10V is applied, what is Vo? (b) What is the time constant if R=100kOhm and C=10uF? (c) What is the voltage equation? (d) What is the shape of the graph Vo vs Time?

(a) t=0, Vo=0V; t=infinity, Vo=10V (b) 𝜏=RC=1 second (c) V=Vmax(1-e^-t/RC) (d) at 𝜏 seconds, V=0.63*Vmax, it is similar to a square root graph until you hit 10V, then it is flat line

What does ECG/EKG stand for? What is it used for?

Electrocardiogram It is a test that detects heart problems by measuring the electrical activity generated by the heart.

What does EEG stand for? What is it used for?

Electroencephalogram It is a test used to find problems related to electrical activity of the brain.

What does EMG stand for? What is it used for?

Electromyogram It is a test that measures and graphs the electrical activity in your muscle.

At a given point in time a patient's ECG trace for Lead I reads 0.9 mV and Lead III reads 0.4 mV. Based on Einthoven's Law what will be the reading on Lead II?

Lead I + Lead III = Lead II 0.9mV+0.4mV=1.3mV

A pressure transducer has a sensitivity of 10 mV per MPa and a zero offset = 0.1 V. What is the output voltage at a pressure of 200 MPa? S=deltaQo/deltaQi Qo=S*Qi+Zo

Qo=10mV/MPa*200MPa+0.1V=2.1V

A pressure transducer has a sensitivity of 50 mV per MPa and a zero offset = 0 V measured at a temperature of 0°C. What is the output voltage at a pressure of 200 MPa? Show the instrument response curve S=deltaQo/deltaQi Qo=S*Qi+Zo

Qo=50mV*200MPa=10V 10V on Y axis, 200MPa on X axis, 50mV/MPA as slope

What type of circuit is a lowpass filter?

RC circuit in series with an AC source. Zr=R, Zc=1/jwC

What is the voltage divider equation for resistors in parallel?

V1=(R1/(R1+R2))*Vi

A defibrillator is a medical Bio-Instrument that is used to deliver therapeutic doses of electrical energy to reset the heart after suffering from life-threatening cardiac arrhythmias. The basic electrical circuit for a defibrillator is given below. Given a 2kV source in series with a 20kΩ resister, calculate the time required to charge a 100 μF defibrillator capacitor to 1.9 kV. Equations: V=IR, 𝜏=RC, i=(VsR)∙𝑒^(−𝑡/𝜏), 𝑉𝑅=𝑉𝑆∙𝑒^(−𝑡/𝜏), 𝑉𝐶=𝑉𝑠(1−𝑒^(−𝑡/𝜏))

Vc=Vs(1-e^-t/RC) 1900=2000(1-e^-t/RC) 100=2000e^-t/RC ln(100/2000)=ln(0.05)=-t/RC t=-(ln(0.05))*(20*10^3)(100*10^-6) t=5.99 seconds

Calculate the output voltage when the source voltage is 3.3V, the gauge factor is 2, and applied strain is 10^-4 Vo=[(epsilon*Gf)/4]*Vex

Vo=10^-4*2*3.3/4=0.165mV

On an Elvis Board, when are resistors in series?

When one end of each resistor fall in the same horizontal (number) row. The other end of each resistor are not in the same number rows.

A voltmeter with a full scale value of 12 V is used to measure a true voltage of 1.5 V. The measured value is 1.2 V. The percent error of this measurement is: a. 20.0 % b. 13.3 % c. 25.0 % d. 1.67 %

a

Accuracy of an instrument is: a. The difference between its true output and its measured value b. The standard deviation of its measured output c. The smallest measurable increment in its output d. The largest signal that it can measure without distortion e. The measure it takes in calibrating itself

a

The P-wave in the ECG trace is caused by a. Atrial depolarization b. Atrial repolarization c. Ventricular depolarization d. Atrioventricular node

a

There is a false statements about EMG and skeletal muscles. Which of following is false? a. Action potentials between skeletal muscle cells and cardiac muscle cells have very similar patterns. b. Lengths of thin filaments and thick filaments are not changed during the muscle contraction. c. Action potentials in skeletal muscles do not act directly on the muscle contraction. Rather, they causes an increase of Ca2+ ions in myofibril that allows the skeletal muscles contract. d. The central nervous system can increase the strength of muscle contraction by increasing the number of active motor units.

a

The following figure below is the Wheatstone bridge circuit with a strain gauge at R1. What is the Wheatstone bridge circuit (select all correct answers to get points)? a. When resistances of resistors are all same, the output voltage should be zero. b. The circuit measures resistance itself of the strain gauge. c. It is a sensor whose electrical resistance varies by the amount of strain applied on the device. d. It is a circuit with negative temperature coefficient. e. The output voltage is proportional to the gauge factor and the source voltage. f. The circuit can be integrated with other types of sensors. g. The circuit converts the small resistance change to measurable voltage change.

a, e, f, g

A sensor is defined as: a. A physical quantity measured by the instrument b. A device that converts measurements to an electrical signal c. A device that converts one form of energy to another

b

Resolution of an instrument is: a. The standard deviation of its measured output b. The smallest measurable increment in its output c. The difference between its true output and its measured value d. The largest signal that it can measure without distortion e. The measure it takes in calibrating itself

b

There is a false statements about EMG and skeletal muscles . Which of following is false a. Motor neuron is a nerve cell delivering nervous impulses from the brain to a muscle. b. Based on size principle, largest motor units are always recruited first before smallest ones. c. The central nervous system can increase the strength of muscle contraction by increasing the number of active motor units and increasing the firing rate of individual motor units. d. The main function of sarcoplasmic reticulum in muscle is to store Ca2+ ions.

b

There is a false statements about EMG and skeletal muscles. Which of following is false? a. EMG is the superposition of the evoked action potentials of all the active motor units in a muscle. b. One motor unit have a muscle fiber. c. Muscle fibers contract fully or not at all. d. Stimulated motor neurons release neurotransmitters at neuromuscular junctions.

b

Which of the following are typically not a constraint for a Biomedical instrument: a. Stochastic nature of signals b. High magnitude of signals c. Impedance matching d. Simplicity and ease of use

b

EMG: a. Measures the electromagnetic signals generated by the brain b. Is related to the angular direction of the ocular dipole c. Can be used to analyze biopotentials of skeletal muscle d. Is a DC signal recorded in striated muscle

c

The QRS complex is: a. The flattest section of the ECG b. Eliminated during arterial fibrillation c. Caused by rapid depolarization of the ventricles d. A group of electrically active enzymes e. Between 0.6 and 0.75 seconds long

c

Which of the following best define "Precision": a) The smallest incremental quantity that can be measured with certainty b) The ease of accessibility of the measurand c) The ability of an instrument to give the same output repeatedly for a given input d) The ease of use of an instrument for the operator

c

What is the approximate frequency range of the ECG biopotential: a. 25 - 1250 Hz b. 0.1 - 10 Hz c. 0.1 - 90 Hz d. 0.1- 175Hz

d

With a yd bar of 2.8, ud=0, sd of 3.56, and a n of 5, alpha 0.05, critical t value of 2.776, state whether to accept the null hypothesis.

t=(2.8-0)/(3.5637/sqrt5)=1.757 Accept Ho since 1.757 does not exceed our critical t value

Explain each term for a paired t test t= [(yd bar) - (ud)]/[sd/sqrt(n)]

yd= difference in the two samples (ie heart rate before - heart rate after) yd bar= mean of yd ud= expected differences sd= standard deviation = sqrt(sum(x-xbar)^2/n-1) n= number of samples