iWorx TA command module (IX-TA-220) teaching kits and the SP-304 spirometer come with the A-FH-300 flowhead (also available as a set of three as A-FH-300-3), which has a linear range of -300 to +300 liters/minute and is suitable for most measurements on human subjects. Other flowheads with different ranges of linearity are also available.
The A-FH-1000, with a linear range of -1000 to +1000 liters/minute, is suitable for performing certain lung function tests and measuring respiratory volumes from human subjects that are exercising.
Three smaller flowheads, the A-FH-100, the A-FH-10, and the A-FH-1, are more suitable for measuring volumes from small animals that range in size from dogs to mice.
The common feature of all these models of flowheads is that they all have good linearity in their respective normal range because the flow of air through each model of flowhead is laminar. If a flowhead has laminar flow (low turbulence), the back pressure that develops in the flowhead from the presence of fine stainless gauze across the stream of air, is related to the velocity of the air (or its viscosity) in a linear manner. When this velocity-dependent pressure contacts a sensitive differential pressure transducer like the one built into the SP-304, the voltage output created by the transducer is also velocity dependent. So, the volume respired can be accurately derived from the voltage output of the transducer. Another feature of all these flowheads is the minimal amount of condensation that develops in the flowhead. Because the fine stainless steel gauze in the flowhead is mounted between plastic rings, the gauze rapidly equilibrates with the passing air and condensation is prevented. Each model of flowhead can be easily calibrated, especially if a 1 liter syringe and the calibrate function from the LabScribe recording software are used. Also, each model of flowhead can be easily cleaned or sterilized.
The A-FH-1000 flowhead is molded in ABS plastic, like the A-FH-300, so it is light. Unlike the A-FH-300, the A-FH-1000 can be easily dismantled for replacement of the gauze assembly.
