Roles of Clinician and Engineer in Design and Evaluation of Autonomous Critical Care

Devices

What are the knowledge gaps?

1University of Maryland

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Lex Schultheis, M.D., Ph.D.Research Professor, Fischell Dept .of Bioengineering

2University of Maryland

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When a clinician identifies a pattern that could be managed the same way each time,

Mayo Clinic spin-off’s softwareK143372

a machine may be used to aid clinical management.

http://ambientclinical.com/aware/

http://graphics8.nytimes.com/images/2008/11/13/health/chen_600.jpg

3University of Maryland

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Components of a Simple PCLCThe goal is to make the Response match the Command

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Command (C)

Response (R)+

Disturbance (D)

Controller

Sensor

Plant

Gain(multiplication factor)

error R

R = C{G/1 +G} + D/(1 + G)Closed loop control makes R » C,Despite changes in G or an external disturbance.

How Do Clinicians Think About PCLC?

5University of Maryland

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Meaningful “Sensors” Are Often Qualitative Rather Than Quantitative

A clinical sensor does a whole lot of interpretation…by Frank Netter

6University of Maryland

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“Actuator” Success Is Also Often Qualitative

http://sports.yahoo.com/highschool/blog/prep_rally/post/Tennis-star-returns-from-arm-amputation-to-reach?urn=highschool-wp2374

7University of Maryland

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Clinicians Can Be Suggestible, But HaveLearned To Be Wary Of Surrogate Markers.

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Routine use of pulmonary artery catheters in heart surgery is no longer widespread.

Monitoring processed EEG in uncomplicated cases of general anesthesia has declined in acceptance.

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http://www.covidien.com/rms/products/oem-monitoring-solutions/bis-brain-monitoring-technology-oem-solutions/bis-loc-2-channel-oem-module

http://www.nytimes.com/health/guides/test/swan-ganz-right-heart-catheterization/overview.html

8University of Maryland

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Even A Common Quantitative Variable Like Blood Pressure Is Interpreted Differently By Various

Clinicians, Depending On Context.

http://ec.pond5.com/s3/010687752_prevstill.jpeg

http://www.medicine.virginia.edu/clinical/departments/anesthesiology/education/copy_of_portalresidency/resident-life/day-tee

http://images.wisegeek.com/surgeons-performing-open-surgery.jpg

9University of Maryland

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Physicians Follow Multiple Inputs And Sometimes Perform Many Tasks Simultaneously.

Could PCLC help managethe workload?

We are MIMO PCLCs

Me

http://www.unmc.edu/anesthesia/echo/advanced/index.html

10University of Maryland

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Physicians Internalize An Encyclopedia Of Experience That We Can Match To The Condition Of A New Patient.

No machine algorithm processes as complex information, filters data and improvises as well as human being in the loop.

However, clinicians can also be dogmatic…

http://i1.mirror.co.uk/incoming/article4736848.ece/ALTERNATES/s615/Cancer-Treatment.jpg

http://www.physiciansweekly.com/wp-content/themes/twentyten/timthumb.php?src=http://www.physiciansweekly.com/wp-content/uploads/2013/03/anger-management.1.86541190.png&w=620&

11University of Maryland

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Clinicians Are Tool Users—They Expect That Their Tools Will Work And Be Easy To Use.

http://www.flyheight.com/videos/doctors-try-to-hammer-out-surgical-instrument-that-got-stuck-in-a-patients-kneegraphic/

How Do Engineers Think About PCLC?

13University of Maryland

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Engineers Will First Want To Characterize The Relevant Signals.

Signals are the quantitative energies that propagate through a System.

The System is , the device that processes or controls signals.

Signals are either Energy signals (finite) or Power signals (infinite in duration).

Systemcommand response

https://s17-us2.ixquick.com/cgi-bin/serveimage?url=http%3A%2F%2Ftse2.mm.bing.net%2Fth%3Fid%3DOIP.M6f03c1f6916c4cbe2533da88e752003co0%26pid%3D15.1%26f%3D1&sp=1a0645b7c031b15af624d2b7cd9966eb

14University of Maryland

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• Power signals may be reconstructed from mathematically simple, periodic functions as components (orthogonal basis set).

• Sinusoids are the most widely used orthogonal basis set, e.g. Fourier methodology.

• Physiologic signals may be described as a sum of sinusoids characterized by amplitude, period and phase.

Engineers Always Manipulate Signals Quantitatively, More Often The Frequency Domain Than As Time

Functions.

15University of Maryland

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• Real world signals are composed of information and noise.

• Finite signals may be approximated with an arbitrary degree of resolution.

• Bandlimiting a signal may reduce noise and is essential when using sampled data (digital processing) to avoid aliasing.

Engineer designers know:

16University of Maryland

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Engineers Will Want Quantitative Specifications Before Designing A PCLC.

* Specifications may be defined in the time domain, but in general should be able to be transformed into the frequency domain.

• What are the maximum allowed transient and steady state errors?

• What is the maximum speed of response needed?

System

Command Response

17University of Maryland

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Engineers Use High Gain To Minimize Error and Compensators to Improve Response.

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Command (C)

Response (R)+

Disturbance (D)

Controller

Sensor

• Open-loop failure can cause saturation!• Processing delay in the loop can cause

oscillation!!!

PatientActuator

Plant

Compensator

Gaine R

18University of Maryland

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If A PCLC Is Linear, Stationary And Causal, System Performance Is Completely Characterized By The Impulse Response And Transfer Function.

System(t)

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0.5

1Time history

Time (secs)

5 10 15 20 25 30

0.005

0.01

0.015

Power Spectral Density

Frequency (rads/sec)

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Power Spectral Density(phase)

Frequency (rads/sec)

Degre

es

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Time history

Time (secs)

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0.1

0.2

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Power Spectral Density

Frequency (rads/sec)

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Power Spectral Density(phase)

Frequency (rads/sec)

Degre

esSystem(s)

19University of Maryland

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PCLC May Also Be Designed Around State Variables Meet Some Prespecified Optimum Of Performance.

• The internal state variables are the smallest possible subset of system variables that can represent the entire state of the system at any given time for all commands.

• This approach is equivalent to design by transfer function provided that all of the state variables are observable and controllable.

20University of Maryland

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• Patient state variables may not be either observable or controllable.

• The patient will also change (non-stationary).

• An “optimum” system response may vary with the patient’s condition.

• Clinical signals are noisy.

• Patients may appear similar, but they are all different, so a compensator design may not be comprehensive.

Challenges to Analytical Design of PCLC

21University of Maryland

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Rule-based control: a simple example

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Command (C)

Response (R)+

Disturbance (D)

Sensor

• Tends to oscillate around the decision point• Works best for slowly changing environments

PatientActuator

PlantBang-bangcontroller

PatientActuator

Plant

22University of Maryland

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Model-based control example: The physiologic sensor is not in the tissue of interest.

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Disturbance (D)

Sensor in Blood

SignalIn Blood

Command (C)

SignalIn Blood

Response (R)

Signalin Blood

Signalin

Target Tissue

Relational Model

Accuracy and stability of the PCLC depends on the relevance of the signal where it is measured compared to the signal in the tissue of interest.

PatientActuator

Plant

23University of Maryland

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Another model-based control example: A pharmacodynamic sensor is used to control drug delivery.

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Disturbance (D)

PharmacodynamicSensor

Desired PD

Command (C)

PD Outcome

Response (R)

ADMEModel

Accuracy and stability of the PCLC depends on the completeness of PK/PD in terms of predicting clinical outcome and the quality of ADME models for the patient population to be exposed.

How Can Clinicians and Engineers Think

About PCLP Together?

25University of Maryland

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Clinicians must • Understand the clinical outcomes that are worthwhile from the

patient’s perspective • Validate surrogate markers against clinical outcomes • Identify clinical consequences of system failure

Engineers must• Describe how component failure will affect machine signal

processing • Develop mitigations against failure that do not rely on human

intervention so they do not introduce new risks.• Keep systems simple and robust to meet conditions of actual use.

Thank you!