# Shared Flashcard Set

## Details

lecture 4
physiological signals and systems
34
Physics
09/06/2010

Term
 Ohms Law
Definition
 E=I*R   or   V=I*R   E= electromotive force or voltage (V) (volts) I=electric current or flow of electrons (Amperes) R=resistance (Ohms)
Term
 signal sources
Definition
 provide the energy to operate the circuit   may take the form of a battery or a time varying constant voltage or a constant current source
Term
 conventional flow
Definition
 travels down the voltage gradient from + to -
Term
 electron flow
Definition
 from the source of electrons to the deficit from - to +
Term
 direct current (DC) source   (time invariant)
Definition
 no changes in voltage with time   ex: output of a battery
Term
 constant current source
Definition
 delivers the specified current irrespective of whatever voltage it takes to produce the current
Term
 constant voltage source
Definition
 produces the specified voltage regardless of the current that must flow
Term
 Alternating current (AC) sources
Definition
 produce voltages or currents that are time varying   V(t)=A*sin(ωt+Φ)   V=voltage A=peak amplitude (Vp) ω=radian frequency (frequency in Hz f=ω/(2*π) or      ω=2*π*f) t=time (seconds) Φ= phase delay (radians) usually 0
Term
 current source
Definition
 I(t)=A*sin(ωt+Φ)   the source driving the circuit is a current rather than a voltage   useful when modeling the cardiovascular system if you need the CO to remain constant
Term
 mixed sources
Definition
 combinations of alternating current (time varying) and direct current (time invariant)   the mean goes from 0 to the value of the time invariant signal   ex: V(t)=10*sin(12.566*t)+8 the mean is 8 volts
Term
 ECG signal
Definition
 measurement is one of voltage (electrical potential) vs. time     mean contains no clinical info.
Term
 Blood Pressure waveform
Definition
 signal generated by the mechanical action of the myocardium squeezing blood into the hydraulic impedance of the vasculature     example of a mixed (AC+DC) signal source
Term
 systolic pressure
Definition
 useful when the maximum stress on the blood vessel wasll is an important consideration, as in patients with aneurysms, intracranial hypertension
Term
 mean blood pressure   (systolic/diastolic)
Definition
 useful determinant of organ perfusion especially when considered as perfusion pressure (mean arterial pressure minus venous pressure)
Term
 diastolic pressure
Definition
 important when considering perfusion of the left ventricle (majority of the left ventricular blood flow occurs during diastole)
Term
 pulse pressure
Definition
 systolic-diastolic
Term
 pulse ox plethysmogram
Definition
 measurement of the change in volume of the pulsatile blood vessels as detected by light passing through the tissue of interest   most useful info derived is the amplitude of the volume signal
Term
 DC components
Definition
 mean values of blood pressure and mean values of CO   used to calc. systemic vascular resistance SVR=(MAP-MCVP)/(mean CO)
Term
 AC components
Definition
 diastolic and systolic pressure
Term
 system response
Definition
 has signal amplitude on the Y axis which is the ratio of output signal amplitude to the amplitude of the input signal and frequency on the X axis
Term
 ideal system response
Definition
 has an amplitude ratio of 1:  output and input amplitudes are the same=perfect reproduction
Term
 curve above ideal response
Definition
 output signal is greater than input signal and at that frequency the input signal is artifically amplified and the output signal is distorted from the input signal
Term
 curve lower than ideal response
Definition
 the amplitude of the output signal at that frequency is artifically attenuated or less than the amplitude of the input signal.  indicates that the output signal is a distorted form of the input signal
Term
 a frequency of 0 corresponds to...
Definition
 the mean or DC component, which is reproduced exactly because the amplitude of the system response at zero frequency is 1
Term
 Fourier Analysis
Definition
 a method for describing complex waveforms in terms of more manageable sine an cosine waves   sine waves can be added together in order to produce a more complex waveform   as higher and higher order odd harmonics are added to the fundamental, the waveform becomes a better approximation to the goal of producing a perfect square wave
Term
 fundamental frequency
Definition
 the basic period of the waveform
Term
 harmonic
Definition
 an integer number times the fundamental frequency
Term
 1st term of the Fourier series
Definition
 represents the mean of the waveform and it is a term that has no frequency associated with it   by definition the mean is a constant, independent of frequency   even a system with inadequate frequency response is still capable of accurately measuring the mean of the waveform
Term
 filters
Definition
 electronic methods for removing unwanted frequencies from signals
Term
 low pass filter
Definition
 frequencies below the cutoff are allowed to pass through but frequencies above the cutoff are removed
Term
 high pass filter
Definition
 high frequencies are permitted to move through the filter and low frequencies are removed
Term
 bandpass filter
Definition
 small region where only certain frequencies can pass through   there is a low pass cutoff frequency at f1 and a high pass cutoff frequency at f2 with a center frequency for the pass band
Term
 band reject filter
Definition
 passes all low and high frequency signals but rejects the frequencies that are above the lower cutoff f1 and below the upper cutoff f2   used in ECG monitoring to eliminate the 60 Hz interference
Term
 standard ECG frequency response
Definition
 0.05-100 Hz
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