Design of a System that Transfers Ventilator Information

to the Internet

Lauren Sims

Advisor: Dr. Bill Walsh

Background

Mechanical neonatal respirators play an important role….

Ensuring adequate respiration in infants is difficult– involuntary mechanism

– the tongue is proportionally larger than in an adult

– trachea is very flexible (easy to kink)

– lungs have proportionally less volume and compliance

– large head/body ratio requires care to maximize airway

Ensuring adequate respiration is very important– primary cause of cardiac arrest is respiratory failure

– risk of long term (i.e., brain) damage from abnormal breathing

Typical Flow Time Waveform

This Flow Time Waveform is from a full term infant. The lungs are essentially normal. The normal decelerating flow time waveform consists of the following:

*Rapid rise to peak inspiratory flow with the initiation of inspiration.

*Inspiratory flow decays rapidly to baseline and smoothly transitions to expiratory flow. The decay becomes exponential as it approaches the baseline.

*Rapid rise to peak expiratory flow.

*Exponential decay of expiratory flow back to baseline.

Background

.... but careful monitoring of respiration is not efficient !

Respirator has a built in monitoring system, but...– screen is local to respirator

– controls are local to respirator

– requires dedicated personnel presence at all times

Respirator also has the capability for remote monitoring– built-in data collection via internal microprocessor

– built-in RS-232C data transmission capability

– built-in software command set for microprocessor data retrieval

Remote monitoring capability is currently unused

Siemens SV300 Servo Ventilator

My Project

Investigate the possibility of moving monitoring function to the web

– Is it possible to get at performance data via the serial port?

– Is it possible to post the data to a web page on a server?

– Would web enabled monitoring bring better care or lower costs?

Results

Good performance data is available on the SV300 via an RS-232 interface.....

– Curve

– Trend

– Alarm

– Breath

– Settings

– Technical (battery state, etc.)

.... but RS-232 is difficult and code is computer Operating System dependent.

('ServoVentilator 300/300A ReferenceManual', Siemens-Elema AB, 1997).

Some Parameters and Scaling FactorsChannels 00-99: Basic

• Airway Flow 5V/l/s

• Insp. Tidal Volume 5V/L

• Airway Pressure 50mV/cm H2O

• Exp. Tidal Volume 5V/L

• O2 Concentration 50mV/%

• Barometric Press. 4.883 V/Bar

• Aux Code 4.883 mV/bit

• Pause Pressure 50mV/cm H2O

• Resp. Rate calc 50mV/breaths/minute

• Peak Pressure 50mv/cm H2O

• Exp. Minute vol. 0.2V/l/min

• Airway pressure 50mV/cm H2O

• CI Battery Voltage 1mV/mV

• End exp. Pressure 100mV/cm H2O

Channels 100-199: Extended

• Airway Flow and Pressure• AUX Channels 1-8• CI battery voltage• Measured & CMV frequency• Exp/Insp Tidal Volume and minute volume• Peak Pressure• O2 concentration• Barometric & Gas supply pres. (air, O2) • Inspiration and pause times• Alarm Reset/2 min off & option• SIMV frequency• PEEP, set; Pressure limits, set• Exp. Minute vol; upper/lower alarm limit• Ventilation mode, Set• Valve slots 1-3, binary codes• Alarms: apnea, power failure, mode switch error,

Mains failure, overrange, CI internal communication error, O2 concentration levels, gas supply, battery, etc.

Results• An example RS-232 communications program for DOS is available.

– printed in the ventilator technical manual

– around 1200 lines of 'C' code

– uses the Greenleaf CommLib version 3.2 'C' libraries for DOS ($400)

– has some 'C' functions that are peculiar to DOS compiler ($400) (e.g., delay(), kbhit(), getch(), itoa(), etc.)

• I am trying to port this code to Linux (with help).– linux is free

– linux has a C compiler (also free)

– I have access to a free serial library for Linux (serial.c)

– linux has equivalent function calls (i.e., usleep() instead of delay())

– linux has a built-in web server

Results

• I have obtained a unix serial library (corcordt@cs.purdue.edu)

• I have typed in all of the example 'C' code from the manual

(see: <http://www.virtualdave.com/~lauren/bme272>)

• I am working on porting the example code to unix (linux); i.e., replacing all the DOS Greenleaf library calls in the example code (e.g., asigetc(), aisputc(), etc.) with unix serial calls (e.g. IO_Read(), IO_Write, etc.) with Prof. J. M. Fitzpatrick.

• Only three functions left to port over (asigets_timed(), asigetc_timed() and isrxempty()) which are all similar

• Should have a RS-232 communication executable by Wednesday, April 4

Resources Needed

• I need access to an SV300 ventilator to test/debug (weekend?)

• I need a laptop that I can install linux on for testing/debugging

Future Work

• Once communications are established and access to the data from the respirator is obtained, it shouldn't be too hard to pipe the data to a web page and serve it.

• Finalize poster presentation for April 11th.