In our recent article evaluating portable oxygen systems (see Aviation Consumer, August 2001) we mentioned that one reason that more pilots are using supplemental oxygen is the availability of affordable portable pulse oximeters.
A pulse oximeter measures blood oxygenation level in real time. Introduced to the GA community by Dr. Brent Blues Aeromedix.com in 1998, this tool has convinced all but the most hardheaded that hypoxia is a threat and often at altitudes lower than is traditionally taught to pilots.
We think that an oximeter is must-have equipment for any owner using supplemental oxygen on a regular basis and even if you dont use it much, borrow an oximeter, try your own tests and make up your mind. Many pilots have discovered that they werent in nearly as good shape at altitude as they previously thought, with or without oxygen.
How It Works
A pulse oximeter shines a beam of red and infrared light, generated by an LED, through the skin. By measuring the ratio of red and infrared light thats absorbed by the blood, the device can calculate the percentage of hemoglobin in the blood thats carrying oxygen. This percentage is expressed as the percent of blood oxygen saturation (%SpO2). Typical sea level readings for a healthy person are in the range of 96 percent.
Oximeters also measure your pulse, which can be interesting information at times, especially on a tricky IFR approach in heavy weather. But for oxygen monitoring, pulse rate is generally irrelevant. All these units attach to the end of a finger, but other locations-such as an ear lobe-are also used in medical applications.
We tested three units in the process of evaluating the portable oxygen systems covered in the previous article. Two, the Nonin FlightStat and Palco Aero are currently sold for aviation use. The third, the Datex-Ohmeda TuffSat is being introduced into the aviation market by Aeromedix.com and should be available by the time you read this. We also crosschecked these non-FDA-approved pulse oximeters with a hospital grade FDA-approved unit that served to confirm that all three gave accurate readings.
The first pulse oximeter introduced to the aviation market was the FlightStat ($395). Its the smallest and lightest of the three (1.3 x 1.3 x 2.2 inches, 2 ounces) and is widely available from numerous sources, including all the portable oxygen system suppliers, as well as at a discount from others such as Aeromedix.com.
Its entirely self-contained; theres no switch or wires. Just slip it over your index finger and read both %SpO2 and pulse rate on the red LED display. Remove your finger and it goes to sleep. A spot LED flashes at your pulse rate and displays different colors depending upon the quality of the signal. The FlightStat is designed to be read with your palm up, bending your finger over towards you, so if you prefer leaving the finger extended, or to grip the wheel or stick, it must be read upside down. This didnt present much of a problem, in our experience.
According to the manufacturer, the pair of AAA-cell batteries provides 18 hours of operation, equivalent to 1600 40-second spot checks. Unfortunately, the batteries run down over a period of months when not in use, so keep that in mind if you use it infrequently. The digits flash when the batteries are low. Rechargeable batteries can be used, but wont last as long.
Installing new batteries requires removing and replacing an end cap held in place with a captured screw (a coin will work). The small cap is easily dropped and slightly awkward to reinstall; not something youd want to be doing in flight in most circumstances.
Given how often the batteries need changing, a thumbscrew would seem to make more sense than a coin slot. It comes with a long neck lanyard including a cord lock to secure it, a nylon belt carry case and an extra spring, since that seems to be the units weak point. (The spring provides clamping pressure on the finger.)
On the down side, its bulky enough to be uncomfortable and cumbersome on your finger for long periods of time and the digits are small. In bright sunlight, the LED digits can be difficult to read and youll have to interrupt your scan to read the data.
The Aero ($395) is a larger unit (4.5 x 1.8 x 1 inch 3.4 ounces with adapter) exclusively available from Aeromedix.com. It comes with a remote finger sensor on a 28-inch lead.
This allows you to place the unit where you can see it in your normal scan while the lightweight flexible rubber fingertip sensor doesnt encumber your finger nearly as much as the FlightStat or the hard clip of the Tuffstat. The red LED display alternates between %SpO2 and pulse rate, with numbers about 30 percent larger and much easier to read than the FlightStats. The single AAA-cell battery, easily exchanged via a slide out panel on the backside, gives only six hours of continuous use.
A low-battery indicator comes on when there are 30-minutes of power left. An acceptable pulse reading is shown via an orange pulse indicating single-point LED.
Theres a switch to turn the unit on; it turns itself off after the finger sensor is removed from your finger and the battery doesnt run down in storage, partially offsetting the lesser battery life. Still, youll be feeding the Eveready bunny fairly often so always carry spares.
Our biggest beef with the Aero is that the body is at least twice as big as it needs to be, and it could probably be made even smaller than that. This is partly a function of its basic design that allows for a variety of modular sensor attachments, all of which are irrelevant for GA use. A smaller unit would make it easier to find a place for in your scan, making it more useful. Longer battery life would also be nice.
The TuffStat (estimated $400 when available from Aeromedix.com) is a much bulkier unit (5.8 x 2.8 x 1.2 inches, 9 ounces) with a remote sensor.
A large LCD readout provides larger, easy-to-read numbers with a switchable backlight for night use. Its quite bright, however; youll do better for your night vision using some other means to illuminate it.
The remote fingertip sensor, looking something like a plastic clothespin, is attached via a 36-inch lead. You can use it for continual monitoring, though the sensor isnt nearly as unobtrusive as the Aeros and the bright night light could pose a problem.
Four AA-cell batteries will power it for 17 hours. It appears more rugged than the other two units and comes with a protective neoprene foam rubber case for even more protection. All three pulse Oximeters are covered by one-year limited warranties.
Our favorite oximeter was the Aero. It most easily allows for constant monitoring with minimal fuss in the cockpit. Using some Velcro to attach it somewhere convenient makes for the best combination of ease of use and ergonomics.
The short battery life is a bother, but at least its easy to change the battery. Also, it seems far larger than necessary, but it isnt so large as to make size a serious drawback.
The FlightStat works fine, but the small digits and cumbersome design dont lend themselves to continual monitoring, which we prefer. For intermittent checking, its small size and quick slip-on design make it an acceptable choice.
The TuffSat is best for those with less perfect vision or who tend to be tough on their equipment. We like the long run time, but its otherwise too large for our tastes.
All of the units lack one feature wed like to see: An alarm with adjustable %SpO2 setting so you dont have to continuously monitor the readings.
With hypoxia as insidious a condition as it is, this could be a real lifesaver and we think it might convince more pilots to own these devices.
Contact- Aeromedix.com, 982 West Broadway, Jackson Hole, WY 83002; 888-362-7123; www.aeromedix.com. Nonin Medical, Inc., 2605 Fernbrook Lane North, Plymouth, MN 55447-4755; 800-356-8874; www.nonin.com.
-by Douglas S. Ritter
Doug Ritter is an Aviation Consumer contributing editor and publisher of www.equipped.org.