Hallowell EMC: Hallowell Engineering & Manufacturing Corporation

Part Description: 000A3760 - MicroVent 1

000A3760 MicroVent 1

A ventilator capable of providing ventilatory support for the smallest animals you are capable of intubating.

If you don't think you can intubate mice, just look into our recently released Rodent WorkStand and Intubation Packs.  The WorkStand holds the animal in a stable, position that is comfortable for your technician.  The intubation packs, a Rat Pack and a Mouse Pack, hold everything you need to directly visualize and quickly intubate with a minimum amount of trauma.  A short instructional video is also provided along with numerous still photos for clarification of the procedure.

The MicroVent 1 is a dual mode ventilator. It will operate to deliver standard intermittent positive pressure ventilation (IPPV) or it will operate to deliver high frequency oscillatory ventilation (HFOV). The entire breathing system has a volume of less than 1cc.  There are just four parameters to control, Oxygen flow, Frequency (breaths per minute), Amplitude (tidal volume) and Mean Airway Pressure (Mean Paw).

In operation a small flow of fresh gas, in the range of 50-100ml/min, is set.  This gas can be oxygen as provided by the built-in flow meter or any mixture of gases you provide from an external source.  This gas may flow through an anesthetic vaporizer if you desire using gas anesthetics, then on to the breathing system where it passes the patient connection, flows through an open needle valve and on to your scavenging system as required.  The animal may breathe spontaneously from this stream of gas as it passes the patient connection at all times.  The needle valve is used to adjust Mean Paw as seen on the pressure manometer.  As the valve is closed, gas flow is restricted causing pressure in the breathing system and thus in the animal's lungs to increase. This Mean Paw will maintain the expanded lungs permitting continuous gas exchange with a minimum of atelactatic alveoli.

The breathing system is also connected to a glass cylinder containing a floating puck, which is set in motion as per the settings for frequency and amplitude.  In IPPV mode the frequency selectable ranges from 75 to 240 breaths per minute (BPM).  The tidal volume (TV) deliverable is from zero to 10ml. This does not limit the usefulness of the MicroVent 1 to extremely small animals.  A switch to HFOV mode changes the frequency range to 750 to 2400 "breaths" or more accurately cycles per minute.  The "tidal volume" during HFOV is generally an order of magnitude less than it would be during IPPV and is now used to set up an oscillation of the molecules of gas from the breathing system down to the alveoli.  This oscillation helps promote the diffusion of the different gasses in the system.  There is a gradient in the partial pressures of oxygen and anesthetic gas in the system from a peak where the fresh gas flows past the patient connection to a low in the alveoli where the concentrations have been decreased by patient uptake.  There is also a gradient in the partial pressure of carbon dioxide in the system from a high in the alveoli to a low in the fresh gas stream.  The oxygen and anesthetic molecules continually migrate toward the alveoli while the carbon dioxide continually migrates toward the fresh gas stream as they all seek to come into equilibrium within the system.

The oscillations are superimposed on the set Mean Paw, "all" the alveoli are held open in virtually a steady state as the frequency is very high and volume of the oscillations is minuscule.  The animal now only vibrates slightly.  Gas exchange is accomplished by the diffusion of molecules as motivated by the difference in pressure gradients.  No longer do you have the gross movement of the respiratory cycle so distracting to the microsurgeon.  The animal just lays there as gas exchange proceeds and the operation proceeds uninhibited by movement within the patient.

In addition, depending on the amplitude of each cycle, a value of resulting continuous positive airway pressure, CPAP, can be observed on the pressure manometer.  This feature naturally allows and virtually assures that the operator will be implementing lung protective strategies as described by Amato and Ranieri, et al.  The alveoli are no longer collapsing on expiration then snapping open again as they expand with each breath.  This condition has been shown to cause damage to the alveolar epithelium and endothelium.

Incorporated into the MicroVent 1 is a system that allows you to connect it either directly to vacuum or an active or a passive scavenging system.  Placing the Scavenger Select switch in the Active/Passive position directs the waste gasses directly to the scavenging port where you can connect a charcoal canister or an active system that already has a scavenging interface valve in place.  Switching to the Vacuum position directs the gasses into an internal open interface system allowing you to connect a vacuum line directly to the scavenging port.  In this case the scavenging flow rate is then adjusted on the flow meter on the front panel.
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Pittsfield, MA 01201
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