synchronize Arduino with [metro] initialization

Hallo all

I have the following code running in Arduino, which detects force from multiple FSRs and assigns each a unique ID so I can parse the sensors in Max:

//read 12 FSRs, convert force value to LED brightness

int inVal;
int brightness;

void setup(){
Serial.begin(9600);
//multiple LED pins/////////
for(int x=2; x
pinMode(x, OUTPUT);
}
}

void loop(){
//multiple FSR pins
for(int i=0; i
inVal = analogRead (i);
inVal/=3;
inVal=constrain(inVal, 0, 255);

brightness=inVal;
//prepend sensor value with pin# ident
Serial.write(i);
Serial.write(brightness);
analogWrite((i+2), brightness);
}
delay(10);
}

My problem is the fact that the Arduino code is continually running, sending sensor ID and value - for example, at any time it could be sending "5, 0; 6, 0; 7, 143; 8, 0; when I begin polling the serial port I might get EITHER the sensor value first followed by sensor ident, OR ident then value. I thought that a solution might be to only send the data to MaxMSP when a sensor is pressed. Would the following result in jittery data?

if sensorVal >0{
send all the data;
}
else{
blank space here;
}

Or is another solution to get Arduino to listen to the serial port and wait for a keystroke or ascii value (from MaxMSP). I know how to send stuff from Arduino to Max, but have no idea how to do this the other way round. What I wish to achieve is a guarantee that whenever I begin polling the serial port I will always get sensor ident FIRST, followed by the associated sensor value.

Any suggestions?
Thanks
Brendan