Impedance Threshold Device

The term Inspiratory Impedance Threshold Device has somewhat confused the EMS community. It sure confused me, particularly after I looked up each word individually and assembled them together. What this product really is – is a one-way pressure actuated valve.

The ResQPod works sort of like a PEEP valve only backwards – after you ventilate through the ResQPod and compress the chest forcing all the air out, air is prevented from re-entering the lungs passively between breaths. No more gas can enter the lungs again until the next delivered ventilation. PEEP holds pressure in while the ResQPod holds pressure out.

The ventilatory device used with most studies of the ResQPod, are those using it with BVM’s. BVM’s have some well documented problems generating positive pressure where you need it. While notorious for delivering high airway pressures, BVM’s typically deliver very low pressures in the lung. In one recent study of ventilation using a BVM, “The average percentage of time a positive pressure was recorded in the lung was 47.3%.” The BVM type device when used for CPR typically produces very little if any pressure changes in the thorax.

What really moves blood around during CPR is not just a negative pressure as often claimed by some Sales Reps, it is PRESSURE CHANGES. Since the BVM does not produce much positive pressure the ResQPod really helps by creating a negative pressure, thereby producing pressure changes that did not exist before. The ResQPod has demonstrated that it improves blood flow by creating negative intrathorasic pressures. It has been shown to produce -7.3 +/- 4.5 mm Hg which relates to cmH20 as shown below.

-7.3 mmHg = 9.9cm H2O

Remember that during the active phase of chest compression, the ventilation gas you deliver is forced back out under your hands, returning the lung to a low or zero pressure state (atmospheric). Most ventilators typically use between at least 25-30cm H2O of pressure when ventilating an adult patient. When you do CPR with a good EMS type Ventilator, you will go from a high pressure of at least 25-30cm down to a low of 0cm. With the ResQPod on a BVM you go from about 0cm down to –9.9cm.

What if you could improve minute volumes, control inspiratory pressures, and go from 25-35cm down to -9.9? In other words, what would happen if you combined the superior control of a volume constant ventilator WITH the hemodynamic enhancement of the ResQPod?


About Dan White

I'm a retired Paramedic and EMS Instructor with 35 years EMS and emergency medical product experience. I love canoes, cars and EMS. I have written a lot about EMS Technology on the Paramedic Blog, the Insights on Innovation column for, on and I can be reached directly at 573-240-0002.
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6 Responses to Impedance Threshold Device

  1. Eric says:

    Are you going to EMS Today in March?  If so, perhaps some of us EMS bloggers could gather for… communion one evening…

  2. Dan says:

    sounds like a great idea! I just booked my booth, flight, & hotel
    not 1 hour ago :>) You want me to see if I can hit up JEMS for a meeting space at
    the show, or just a bar deal one evening?

  3. Eric says:

    Well, I know of at least one other blogger thats going to be there, and perhaps we can coordinate something on his blog.  He\’s got a post to that effect dated 1.16.07.  I\’m thinking bar…

  4. Eric says:

    Alright, Dan.  I have an equipment question for you.  My agency is looking to upgrade thermometers.  What would you recommend?  We\’re still using mercury thermometers for hypothermia, and have very cheap electronic ones for otherwise.  I want a durable, quality thermometer that will read low temps, and be able to do oral & rectal.  Thanks!

  5. Dan says:

    Bloggers at JEMS;

    Which day sounds better, Thursday or Friday?

    Thursday evening at the Aquarium Party where AJ Heightman of JEMS says
    "there will be a bar and tables at the end of the exhibit/tour in the
    aquarium where we could gather for a few minutes."- or on Friday right
    across the street from the Convention Center at a sports bar called
    DSX, at 6:30PM after the exhibits close.

    On thermometers;

    There are five ways to take temperatures.
    The simple mercury (and
    non-mercury) thermometer
    The adhesive colorimetric
    Simple electronic digitals
    Tympanic Thermometers
    High end diagnostic quality
    electronicI’ve had some issues with tympanic thermometers in the
    field. They take a while to temperature stabilize. I don\’t think they render accurate reading on initial patient contact (particularly in winter). But, I really like the speed
    of them when doing Firefighter Rehab. The adhesives tend to read surface skin temperatures. The
    simple digitals are OK, but you get what you pay for accuracy wise. Of all, I would tend
    to lean either towards the simplest (a real thermometer), or a real high-end
    diagnostic quality digital device. Frankly, the way you do it now makes a lot of sense to me.

  6. Pingback: SNPeCPR |

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