Frequently Asked Questions
Promethion does not require sealed cages because it uses pull mode respirometry. This reduces stress, allows the use of bedding and home cages, and ensures animal safety in the event of a power failure.
Promethion generates a complete raw data file for each recording from which all analytical details can be extracted with better accuracy, traceability and detail than other systems, giving you greater analytical flexibility and statistical power.
How rapidly does Promethion sample metabolic data (VO2, VCO2, RER, EE) from multiple cages?
We offer two performance levels.
Our continuous systems sample from all cages in a system simultaneously, giving you a record-breaking 1-second temporal resolution for all metabolic data, 10-60x superior to the competition.
Our multiplexed systems sample metabolic data all cages in 8, 16, 24 or 32 cage systems in as little as 2.5 minutes, independent of the number of cages and of the length of tubing from the cages to our analyzers. This provides you excellent temporal resolution for fine-grained activity data.
How rapidly does Promethion sample non-metabolic data?
One second, for all variables in for all cages (up to 128 cages) in a system simultaneously. This gives you unprecedented detail for food and water intake, plus body mass, wheel running, position and coarse and fine activity.
Is the running wheel an external add-on to the cage?
The optional running wheels are internal to the cage, so the leaks and other issues that plague bolt-on competitive products are not a concern. And leaks are never a concern anyway, thanks to Promethion’s pull-mode indirect calorimetry.
Is it true that Promethion doesn’t use desiccants?
Water vapor dilutes O2 and CO2 concentrations in air pulled from the cage, making metabolic measurements inaccurate if it is not removed – or measured and accounted for. Promethion measures water vapor pressure and barometric pressure directly, and compensates for the dilution effect of water vapor mathematically using basic physics. This is more accurate and it allows measurement of metabolic water production and respiratory water loss, and can compensate for variable hydration of food, leading to more accurate energy equivalents.
Other systems use desiccants and chiller systems to remove water vapor from sampled air. These systems are inefficient, unreliable and wasteful. In addition, they discard valuable data about water loss from the experimental animals.
Why are Sable Systems gas analyzers unique?
We design and make them in-house and unlike gas analyzers intended for process control, our analyzers are designed from the ground up with the uncompromised stability and resolution required for flow-through respirometry. They are not affected by the presence of water vapor (unless, of course, they measure it). Sable Systems analyzers are widely regarded as among the best available in the world. Our customer list includes climatologists, virtually every major research institution world-wide, NIST and NASA.
A: MetaScreen is our easy-to-use data acquisition and control software for multiplexed metabolic and behavioral phenotyping.
Q: What is SableScreen?
A: SableScreen is roughly equivalent to MetaScreen, except that it allows continuous metabolic measurement.
Q: Do these packages provided real-time information during the recording, so that I can determine if everything is working as it should?
A: Yes, the packages provide real-time information on metabolic and other parameters.
Q: What is Expedata?
A: Expedata is our flagship data analysis package, which takes raw data files recorded by either MetaScreen or SableScreen and extracts the data that you need. It can be operated manually, but most researchers use automated analytical scripts (macros). Macros are readable and editable. Each Promethion system comes with a wide variety of macros to cover most common data extraction scenarios. Custom macros are included with each new system purchase. Sable Systems also provides courses to learn the macro language. [links to education page]
Q: If I upgrade the system at a future date, do I need to pay additional per- sensor licensing fees for the additional sensors in the system?
A: Unlike other metabolic phenotyping system manufacturers, we do not charge per-sensor licensing fees.
Q: I have several associates and graduate students, and I would like them all to have unrestricted access to the analytical environment, Expedata. What is the licensing fee for additional copies of Expedata?
A: There are no licensing fees for additional copies of Expedata used by personnel in the same laboratory.
Q: If we decide to upgrade our Promethion system, do we have to purchase aggregators or computer cards to handle the additional sensors?
A: Promethion does not use aggregators or computer cards at all. All data transfer in Promethion uses digital technology, and the only interface required is a USB port. Upgrading the system is fast and effortless.
Q: Do I need a powerful computer to acquire Promethion data?
A: Any modern desktop or laptop computer with at least 2 GB of RAM will work for data acquisition. Our data acquisition and analysis software requires a PC operating system. Windows 7, Windows 8 and Windows 8.1 all work well.
Q: Do I need a powerful computer for data analysis?
A: We recommend a multi-core computer with at least 8 GB of RAM and a 64-bit operating system. Our data analysis software requires a PC operating system. Windows 7, Windows 8 and Windows 8.1 all work well.
Q: What happens if there is a power outage during data acquisition?
A: Data are spooled to disk as they are acquired. A prematurely interrupted file can easily be recovered. We recommend that you use either a laptop computer or a computer with a UPS for data acquisition so that momentary power outages will have no effect.
A: Our continuous systems sample from all cages in a system simultaneously, giving you a record-breaking 1-second temporal resolution for all metabolic data, 10-60x superior to the competition.
Our multiplexed systems sample metabolic data all cages in 8, 16, 24 or 32 cage systems in as little as 2.5 minutes, independent of the number of cages and of the length of tubing from the cages to our analyzers. This is two samples for each cage time constant of ~5 minutes, giving you excellent temporal resolution for fine-grained activity data.
Q: In Promethion multiplexed metabolic measurement systems, it obtains new metabolic samples from each cage every 2.5 minutes. However, it is also obtaining data from all of the sensors in the system (food intake, water intake, body mass, position, beam-breaks and so on) every second. How does it synchronize the metabolic data with the other data acquired from the other sensors?
A: The unique analytical environment interpolates between the metabolic measurements made on each cage, yielding a full set of metabolic data re-sampled to the same effective acquisition rate as the other sensors. This ensures that the metabolic and sensor data are perfectly synchronized. You will never have to face the headache of reconciling different sets of data acquired in different ways with different sampling and binning intervals again!
Q: What about the synchronization between metabolic and sensor data in your continuous systems?
A: Because our continuous systems sample metabolic and sensor data at the same frequency (1 Hz), our continuous systems are intrinsically perfectly synchronized.
Q: What corrections does Promethion make to the raw data for water vapor dilution and barometric pressure changes? And what equations do you use for calculating metabolic parameters from your raw data?
A: “Water vapor pressure and barometric pressure are measured directly, and the necessary corrections are made according to Dalton’s law of partial pressures.
The equations are described in the world’s only textbook of metabolic measurement, “Measuring Metabolic Rates: A Manual for Scientists”, by John R. B. Lighton, published by Oxford University press in 2008. Unlike like all other metabolic phenotyping systems, Promethion’s data analysis is totally transparent. The data analysis scripts can be readily examined to show all the steps in the transition from raw data to final, publication-quality extracted data.
Q: Have your equations, and especially your technique for mathematical compensation for water vapor dilution, been rigorously validated?
A: The equations are described in the world’s only textbook of metabolic measurement, “Measuring Metabolic Rates: A Manual for Scientists”, by John R. B. Lighton, published by Oxford University press in 2008. Dr. Lighton is our President and chief scientist. He has over 80 scientific publications using metabolic measurement as a central methodology, is recognized as one of the world’s leading and most innovative experts in metabolic measurement, and is responsible for much of the design of all Sable Systems equipment and associated. Validation of the calculations employed by Promethion were made using the “gold standard” of quantitative propane combustion and demonstrate practically perfect performance (Malanson et al.)
Q: Promethion appears to have very fast cycle times relative to the competition. Why is this?
A: Cycle time is how rapidly the system can sample cage one through cage X and back to cage one. In most systems, there may be several meters of tubing between the gas-switching systems and the cages which requires long equilibration times – up to several minutes before gas concentrations stabilize after switching to a given cage.
Promethion’s advanced plumbing and gas switching design eliminates long equilibration requirements, so its real-world performance is exactly as stated. Moreover with Promethion, each group of eight cages operates gas switching and analysis independently, so the cycle time does not increase with the number of cages being monitored.
Often competitive systems cycle times are based on zero tubing length between the cages and their gas-switching and gas analyzer systems.
Q: I have heard of power failures causing the pumps of a metabolic phenotyping system to shut down, asphyxiating a whole group of expensive transgenic animals. Can this happen with the Promethion system?
A: No, because it is a pure, native pull-mode system, it does not require a tight seal for the cages. If a prolonged power failure occurs, sufficient diffusion will occur to keep the animals alive. Your animals, your science and your budget are safe with Promethion.
Q: Our IACUC states that cages should be ventilated with at least 15 air exchanges per hour. Most metabolic phenotyping systems struggle to meet even a third of that figure. Can Promethion meet the specification, or do we have to spend time and effort requesting an exemption?
A: Promethion can use higher flow rates than many (most?) other systems. Promethion’s gas analyzers are specifically designed for flow-through respirometry and are among the most stable and precise in the world. Higher flow rates reduce the magnitude of the gas concentration signals, but thanks to the stability and resolution of the analyzers, this does not affect accuracy. The high flow rates allow IACUC regulations to be met without requiring exemptions.
Q: Are there any additional benefits to the higher flow rate?
A: The high flow rate translates to a lower concentration of CO2 in the cage. With many metabolic phenotyping systems, CO2 concentrations within the cage can easily reach 0.5%. Because of the high flow rate, CO2 concentrations within the cages of a Promethion system will seldom exceed 0.1 – 0.2%. This means that in a Promethion system, animals are close to normocapnia (ambient CO2 concentrations). Animals exposed to incipient hypercapnia (excessive CO2 concentrations) can have a panoply of negative physiological and cognitive effects.
We use load cell technology, the same technology that is used in laboratory balances. This provides excellent linearity, and we have developed proprietary electronic methods for improving the resolution of this technology to an unprecedented level. Our mass monitors, the basis of our food intake measurements, have a range of 0-1 kg and a resolution of 0.002 gram, corresponding to a dynamic range of an incredible 1:500,000 – better than a standard lab balance.
Impressive technology, but does it bring any practical benefits?
The wide mass measurement range allows the load cell technology to monitor food intake, water intake, and rat and mouse body mass measurements. This saves money and time as the mass monitor can be used for all of the above measurements. There is no need to purchase multiple models of mass monitors, and no need to keep track of which type is being used for which application.
Second, the very high resolution translates to detecting micro-intake events, which are invisible to other systems. For example, mice often pause at the food hopper and nibble at food, taking only a few milligrams before moving on. This is a legitimate intake event, but is completely missed by systems which can only detect 10 to 20 times that amount.
Each micro-intake event represents a decision by the experimental animal to ingest food. It is up to you to decide whether to ignore that behavior, or to be aware of it.
How do you know whether a food intake event is real, or simply the result of random noise?
With Promethion, each food intake event is analyzed in the following way. First, a period of stable food hopper mass is determined prior to the feeding event, and second, an equivalent stable hopper mass is determined after the feeding event. The two masses and their associated standard deviations are compared using a statistical test, and the intake event is only scored if the probability of the mass change having occurred by chance is below a settable threshold, P <= 0.05 by default.
These calculations are done automatically by macros under the full control of the user. Of course, you have full control over all parameters and plenty of technical and scientific support if you have questions.
Do your food hoppers swing from chains, as with some other systems? It seems that would add several seconds of uncertainty to the timing of intake bouts.
Promethion food hoppers are rigidly mounted to ultra-precise load cells with no ringing, swinging or instability, giving you precise timing and intake measurements.
Are your food hoppers mounted in large tubes? Would tubes have an unacceptable amount of dead volume for metabolic measurements?
Such tubes certainly distort metabolic response times. Our mass measurement modules are designed to have negligible interior volumes. They have no effect on metabolic measurements. Moreover, they are only 1 cm high. They also add no significant height to the cage.
Do your mass measurement devices need a half-day of stabilizing prior to starting measurements?
No, you can get reliable data from them immediately because they are based on load cells, rather than drifty force transducers.
What binning interval do you use for food intake measurements?
Promethion captures the food intake at one second intervals. During analysis, the scientist can specify any binning interval that is a multiple of one second, and the system will calculate food intake parameters based on the binning interval set. This gives unprecedented flexibility in food intake analysis.
With other systems, it may be necessary to re-book the metabolic phenotyping center and re-run the animals with a different binning interval at huge inconvenience and expense.
Do you offer full intake pattern analysis?
We offer several standard analytical protocols for extracting intake and meal patterns. And because all of the raw data are retained we can implement any imaginable intake analysis protocol with greater intake mass and temporal precision than is available anywhere else. The only limit is your imagination.
I need accurate conversion of food intake masses to energy equivalents. How do you compensate for the variable contribution of hydration to food mass and its effect on energy conversion accuracy?
Promethion records the water vapor pressure within the cage. This allows food masses to be corrected for variable hydration levels, yielding more accurate food mass to energy equivalent conversions. No other system offers this capability, which we suspect will soon become a requirement for reproducible research.
A: Simply choose the kind of access control to implement (paired feeding, yoked feeding, time and duration limited feeding, or quantity limited feeding), and enter the parameters. The rest is automatic.
Q: What happens if the mouse is in the way of the access control door as it closes?
A: The access control unit knows the door position, and if any resistance is encountered before the door is fully closed, the unit diagnoses an obstruction and opens the door. After a settable interval (default 10 seconds) the door will attempt to close again.
Q: How can I tell what the status of the food access control was during a recording?
A: The position of the food access door is recorded every second and saved as part of Promethion’s deep data field.
Q: Do you have food access control models for both rats and mice?
A: Yes, we have two models, one for mice and one for rats.
Q: Is the access control part of the food intake measurement system, or can it be used separately if I do not have a requirement for measuring food intake, but only for controlling it?
A: The AC-2 access control system is independent of the food intake measurement system.
A: No error is introduced from evaporation because the intake measurement is strictly differential. A disturbance of the hopper or dispenser is sensed and the mass change from before to after the disturbance is measured. Thus, slow changes in hopper or dispenser mass are ignored. This makes Promethion’s intake measurement technique more accurate than simple weighing of the hopper or dispenser at intervals.
Q: if the temperature of the cage increases, gas at the top of the water dispenser can expand and force drops of water from the dispenser spout. Are drops incorrectly counted as intake events because they must cause a disturbance in the mass measurements?
A: By default, intake events must last longer than a user-settable duration in order to be counted as true intake events. The disturbance caused by a drop falling from the dispenser, which is a rare event, is extremely brief and does not resemble a genuine intake event, so it is ignored.
A: An enrichment habitat is suspended from a mass monitor, and the mass of the habitat is recorded every second and added to Promethion’s deep data field. Every time an animal climbs into the habitat, the mass readings become unstable and then stabilize again when the animal settles down in the habitat. Conversely, when an animal leaves the habitat, there is a brief period of unstable mass measurement followed by the mass of the empty habitat. Thus, the animal essentially tares the habitat and weighs itself with each entrance and exit. During analysis, a sophisticated algorithm extracts each accurate body mass measurement and interpolates between them to yield a “continuous” body mass recording.
Q: What if the animal doesn’t enter the habitat?
A: Most animals use the enrichment habitat frequently. In our experience, at least 95% of animals will use it often enough to yield excellent data. The side benefit is not causing stress effects by manual weighing.
Q: Can you get any additional information from the mass measurement sensors in this application?
A: Yes. For example, it is easy to detect grooming and scratching episodes that take place in the mass measurement habitat. Also, it is sometimes possible to detect whether an animal has eaten cached food. If an animal leaves the habitat and then re-enters it without having accessed the food or water hoppers, but if its body mass has nevertheless increased, it is likely to have eaten from a cached food store.
A: 1 cm. That is the finest beam spacing in the metabolic phenotyping field. Because the open field monitor contains considerable built-in intelligence (without requiring connection to cards inside a computer!) it is capable of analyzing the shape of objects and calculating their centroid, which it does to an effective resolution of 0.25 cm.
Q: Do you have both mouse and rat models of the open field array?
A: Yes, and the beam spacing is identical for each model, though the rat model is physically larger. This means that the rat open field array can be used to monitor either mouse or rat cages, saving money without sacrificing resolution.
Q: Does the open field array monitor beam breaks, or actual position?
A: Both. You have a full second-by-second record of the animal’s position in the cage, and any beam-breaks that it causes.
Q: Can you distinguish coarse and fine activity?
A: Coarse activity is primarily directed pedestrian locomotion, while fine activity is a more sedentary group of behaviors, including grooming and scratching. Promethion has default distinctions between coarse and fine activity and they can be fine-tuned. Because the system records all of the data in one second inervals, there is total analytical flexibility to create data sets that show the practical effect of incremental changes in the coarse/fine distinction.
Q: Can I export the position data to other programs in order to create heat maps or do other, more detailed analyses?
A: Yes. All raw and processed data acquired by Promethion can be exported, either directly to Excel or as a .CSV file.
A: By sensing the proximity of a magnet mounted on the wheel. The magnet is detected using a sensitive reed switch.
Q: Does the reed switch have a limited lifetime?
A: The estimated lifetime of our Reed switch is at least 1,000,000,000 (10^9) operations. Each turn of the running wheel constitutes an operation.
Q: Aren’t optical methods better in terms of reliability and lifetime?
A: We decided against using optical methods because they are less reliable. First, they are vulnerable to dirt buildup that blocks the optical beam. Second, their alignment is critical and they can easily become knocked out of alignment. Third, the light source of an optical gate is a light emitting diode with a lifetime of about 5 to 11 years of continuous use (50,000 to 100,000 hours). That is only about a third of the operating lifetime of our magnetic switch even under worst-case conditions.
Q: Are wheel rotations easily converted to actual distance run and running speed?
A: Our analysis environment (Expedata) can quickly and automatically accumulate wheel revolutions and multiply them by the running wheel circumference to yield cumulative distance traveled. Dividing distance by time yields running speed.
With our continuous metabolic measurement systems, energy expenditure can be correlated with running speed to derive important physiological parameters, such as cost of transport, that otherwise require expensive and time-consuming use of treadmills with dedicated instrumentation and trained personnel – all on a free-moving, unimpeded animal that is voluntarily running rather than being forced to run using electric shock!
Q: Do you have a way of automatically blocking access to the wheel?
A: Yes, we have an automatic wheel-block for our mouse cages. The wheel can be locked on a schedule, or based on other user-enterable parameters. A rat wheel-block is under development, but bear in mind that rats responded extremely negatively to having their running wheels blocked and it is generally considered better to remove them entirely from the cage to prevent the rat from using them.
Citations: Melanson, E.L., Ingebrigtsen, J.P., Bergouignan, A.,Ohkawara, K., Kohrt,W.M., Lighton, J.R.B. (2010). A new approach for flow-through respirometry measurements in humans. Am J Physiol 298:1571-1579.