Physiological Monitoring and Recording, part II

In this second physio-centric post I'll be discussing the sensors and equipment used to record pulse and respiration data from our subjects, as well as offer advice regarding their placement. Setting up the pulse oximeter and respirator belt takes only a couple minutes, meaning very little extra effort is needed in order to capture this valuable data. There's literally no excuse not to do it!

Pulse oximeter

Although the Biopac system we use does have a pulse oximeter unit available for purchase, we use an MRI-compatible Nonin 8600FO (see Note 1) and feed the analog signal to a UIM100C add-on module. The UIM100C has multiple analog input channels, so we use a separate one for the TTL signal input from the MRI equipment as well.

Figure 1 - Nonin 8600 FO pulse ox unit

Placement of the fiber optic sensor can be tricky, especially if your subject has a weak pulse, but generally speaking the sensor should be placed on the subject's index finger and secured firmly with medical tape. If you wrap it too tight then the sensor can have trouble getting consistent readings.

Figure 2 - Pulse oximeter sensor on finger

If using a button box or one of our other response devices then you'll want the subject to use the hand that doesn't have the pulse ox attached to it. The more they move the more likely the sensor could slip and give faulty readings. The image below shows a sample of the data we've recorded using this setup.

Figure 3 - Pulse data and TTL pulses recorded in Acknowledge 

Respirator belt

For acquiring respiration data we use the DA100C module along with a transducer that then attaches to a pneumogram sensor. The module attaches directly to our MP150 and UIM100C units thanks to the piecewise nature of the Biopac system.

Figure 4 - Biopac pneumogram sensor

Figure 5 - Respiratory sensor and elastic belt

The sensor is a self-inflating pressure sensing pad that connects to the transducer on the DA100C unit via plastic tubing and measures changes in the abdominal circumference of the subject during respiration. The unit should be placed on the subject's body at the location of maximum respiratory expansion. Speaking from experience, I typically find that to be around the subject's lower ribs and slightly off to the side (see Figure 5). The elastic belt keeps the sensor in place but care must be taken so as not to make the subject too uncomfortable (See Note 2). Below are two examples of data collected with this setup. The first image is normal respiration while the second shows a subject holding their breath and then inhaling. The pressure sensor is sensitive enough to pick up even the slightest fluctuations in respiration, which is why its placement and the tightness of the elastic strap are critical for successfully acquiring data.

Figure 6 - Respiratory data and TTL pulses in Acqknowledge

Figure 7 - Breath hold and recovery data with TTL pulses in Acqknowledge

Hopefully these last two posts have convinced you to incorporate acquiring physio data into your scanning protocol. It's easy to set up and well worth the effort. Even if you're not sure you'll end up using the data, it's better to have it stored away in a hard drive somewhere than not have it at all.

Note 1: Our Nonin unit has been discontinued for several years. It is a legacy device that's at least a decade old. We've purchased several newer pulse oximeters, even another one from Nonin, and none of them worked as effectively as the 8600FO. We currently have another pulse oximeter on order and I plan on updating this post once we fully test it.

Note 2:The adjustable elastic band did not come with the Biopac system but with the Siemens 3T Trio instead.