Patent Publication Number: US-2009223460-A1

Title: Bioactive gas supply chamber for animal research such as hypoxia studies on non-anesthetized small animals with direct physiologic monitoring

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/035,220, entitled “Bioactive Gas Supply Chamber for Animal Research such as Hypoxia Studies on Non-Anesthetized Small Animals with Direct Physiologic Monitoring”, filed on Mar. 10, 2008. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a bioactive gas supply chamber, such as a hypoxia chamber, for use in animal research conducted on non-anesthetized small animals with physiologic monitoring. 
     2. Description of Related Art 
     Researchers who conduct experiments using rats and mice often require that their research animals be un-anesthetized during the experiment in order to avoid any effects from anesthesia that might skew the results. The primary difficulty associated with conducting tests on un-anesthetized subjects is their mobility. Some direct measurements, such as pulse oximetry, are very dependent on immobility of the subject. 
     Within the meaning of this application physiologic measurements will be classified as direct measurements and indirect measurements. Direct measurements are those physiologic parameters that require a sensor to be in direct contact with the subject and include as representative examples, pulse oximeters, blood pressure monitors, internal temperature measurements and the like. Indirect measurements include full body plethysmographic measurements of tidal volume. 
     One method commonly used for immobilizing subjects is a restraining device such as a restraint tube. Animal restraint tubes most often used in research are constructed generally of a clear plastic and have a slit that runs the entire length along the top of the tube. The tube is open on one end, and is closed on the other end, but the slit described above is joined on the closed end by a slit that runs to the center of the end cap. 
     To use the tube, one grabs the animal&#39;s tail, and pulls it through the slit from the open end of the tube, toward the closed end. Once the animal is pulled all of the way into the tube, a restricting ring or plate is slid into the open end of the tube to allow the user to push the animal farther into the tube and restrict its motion. With the securing of the restricting ring the animal is effectively immobilized and the research can proceed. The majority of animal restraint tubes allow certain access to the animal with the animal being fully conscious, and the restraint tubes have been used in a wide variety of research applications. 
     Hypoxia literally translate as a deficiency in oxygen. The medical definition of Hypoxia is a shortage of oxygen in the body. Hypoxaemia is the reduction of oxygen specifically in the blood; anoxia is when there is no oxygen available at all. Biomedical research into hypoxia requires atmospheric control system. The pulminary research solutions offered by Buxco (www.Buxco.com) are also relevant to this field, although not expressly disclosed for hypoxia studies, see for example. These include unrestrained whole body chambers, specialized sealed restraint tubes, and even a head out chamber device for monitoring respiratory and related functions in small animals. 
     These devices are generally associated with what is called full body plethysmography generally for assessing lung function. This approach to assess lung function involves placing the subject into a small closed box and measuring the pressure changes within the box that occur as the animal breathes. The animal is conscious and unrestrained. This technique currently enjoys wide popularity because 1) it is simple and 2) the subject, such as a mouse, remains unharmed after the experiment. The endpoint is the heuristic variable known as Penh, which stands for ‘enhanced pause’. Some publications draw into serious question the validity of using Penh to measure lung function. Regardless these systems are not well suited for monitoring other physiologic parameters that require the sensors to be in intimate contact with the subject, such as pulse oximetry, blood pressure, internal temperature, etc. 
     The limitation in the existing systems is that they hinder the ease and types of research that are conducted. As a representative illustration see the 2003 study from University of Washington Medical Center regarding “Oxygen regulation and limitation to cellular respiration in mouse skeletal muscle in vivo” in which the researchers describe the development of “novel” methodology for measuring oxygen consumption in the subject mice. See also the 1998 study from Case Western Reserve regarding the “Altered respiratory responses to hypoxia in mutant mice deficient in neuronal nitric oxide synthase” wherein the experiments were conducted on awake and anaesthetized mutant and wild-type control mice. For the study of the un-anesthetized subjects the physiologic parameters were limited to the whole body plethysmograph described above and monitoring of oxygen consumption and carbon dioxide production from gas monitoring of the chamber vent. 
     There is a need to assist researchers for conducting respiratory research on animals, such as hypoxia studies, to provide bioactive gas supply mechanisms that allow for studies on conscious animals and which allow for direct measurements of physiologic parameters. It is an object of the present invention to provide a wider variety of easily utilized tools to the animal researcher. 
     SUMMARY OF THE INVENTION 
     The inventors of the present invention provides a bioactive gas supply chamber that may be used in a hypoxia chamber system provided for use in animal research conducted on non-anesthetized small animals with direct physiologic monitoring of the animals. 
     These and other advantages of the present invention will be clarified in the detailed description of the preferred embodiments taken together with the attached figures wherein like reference numerals reference like elements throughout. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a hypoxia chamber system provided for use in animal research conducted on non-anesthetized small animals with direct physiologic monitoring in accordance with one aspect of the present invention; 
         FIG. 2  is a schematic view illustrating the easy insertion and removal of a animal restraint tube from the hypoxia chamber of the hypoxia chamber system of  FIG. 1 ; and 
         FIG. 3  is a schematic perspective view of a hypoxia chamber of the hypoxia chamber system of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     It is noted that, as used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless expressly and unequivocally limited to one referent. The various embodiments and examples of the present invention as presented herein are each understood to be non-limiting with respect to the scope of the invention. 
       FIG. 1  is a schematic view of a hypoxia chamber system provided for use in animal research conducted on non-anesthetized small animals, such as mice  5 , with direct physiologic monitoring in accordance with one aspect of the present invention. 
     A key component of the hypoxia chamber system is a hypoxia chamber  10 . The chamber  10  can also be referenced as a bioactive gas chamber within the meaning of the present invention as it can be used with any combination of bioactive gases and is not limited to hypoxia studies. 
     The chamber  10  may be formed of any gas impermeable material, such as plastic and may be formed from clear plastic to aid in viewing the subject  5  throughout the experiment. Alternatively, a dark color with windows, or dark tinted or transparent material may be used to form the chamber  10 , as such construction has been found to be soothing for mice and may be helpful for conducting experiments. 
     The chamber  10  is constructed to receive a restraint tube  20  therein. The restraint tube  20  illustrated is the STARR-GATE™ brand restraint tube from Starr Life Sciences, but other tubes can be utilized. The STARR-GATE™ brand restraint tube is preferred as it more easily accommodates a variety of direct measurement sensors  40 , such as a tail mounted pulse oximeter sold under the brand name MOUSE OX™ by Starr Life Sciences. 
     The chamber  10  includes an open end  12  that receives the tube  20  therein and includes a notch  14  that make it easier to receive the locking nut  22  of the adjustable nose cone  24  of the tube  20 . The chamber  10  includes at least one inlet  16  for the introduction of the bioactive gasses into the chamber  10  as described below. The chamber  10  includes a ledge  18  for receipt and support of the forward end of the tube  20  that will maintain the tube  20  and animal  5  substantially level. 
     The end of the chamber  10  with the opening  12  and notch  14  will abut the end plate  26  of the tube  20 , but it is not intended for this to be an airtight seal. The gap between the opening  12  (including notch  14 ) and the end plate  26  serves to form a vent in the functioning chamber  10 . 
     The shape of the chamber  10  is shown as generally rectangular, but any shape that can receive the tube  20  is acceptable. The opening  12  should conform to the shape of the back plate  26 , in general. The ledge  18  is formed with a leading ramp to allow the user to easily slide the tube  20  into position as generally represented in  FIG. 2 . 
     The chamber  10  accommodates the tube  20  which allows for direct measurement through a direct physiologic sensor monitor shown generally at  40 . The monitor  40  includes a tail mounted sensor  42  coupled to an associated controller, recorder and display device  44 . The Mouse OX™ brand pulse oximeter from Starr Life Sciences is one type of direct measurement physiologic sensor. Tail cuff blood pressure monitors represent another illustrative direct measurement sensor that is accommodated with the tube  20 . Rectal temperature monitors represent another illustrative direct measurement sensor that is accommodated with the tube  20 . Any of a wide variety of animal contacting sensors can be used depending upon the needs of the researcher. 
     A bioactive gas supply  60  is coupled to the inlet  16  and adapted to selectively supply the needed gas to the subject  5 . The Oxydial™ gas supply device from Starr Life Sciences represents one type of bioactive gas supply system that can be used to form the supply  60 . In the supply  60  a plurality of distinct gasses are supplied from gas sources  62  to a blender valve  64  which can selectively combine the gases to the desired mix and supply these to the inlet  16  via blender outlet  66 . The gas sources  62  may be, for example, oxygen and nitrogen, whereby the researcher can selectively mix these to have any combination of the two gasses from 0% oxygen to 100% oxygen. The gas sources  62  may be, for example, air and nitrogen, whereby the researcher can selectively mix these to have any combination of effectively oxygen and nitrogen from 0% oxygen (100% nitrogen) to 21% oxygen (i.e. 100% air), and this embodiment will give the researcher a greater precision in the blender between the 0-21% marks. Further, there is nothing preventing the supply  60  from including a mixture of 3 or more gasses to form the desired bioactive gas that is supplied to the subject  5 . 
     Further it is anticipated that more than one sealable inlet  16  is provided so that separate supplies  60  can be coupled directly to the chamber  10  if desired. Functionally, the chamber  10  would operate the same. It is preferred if the inlet  16  is opposed from the vent formed by the opening  12  to form a flow through the entire chamber  10  in operation. 
     The chamber  10  of the present invention is very easily used by researchers as they merely utilize existing restraint tubes  20  and slide them into the chamber  10 . The system  10  can be used with any bioactive gas combination that can be vented to atmosphere. An overriding containment or hood vent may be required for some bioactive gases that have venting restrictions. The present invention intends to open up a whole world or research possibilities for rapid, cost effective animal research. 
     The present invention has been described with reference to specific details of particular embodiments thereof. It is not intended that such details be regarded as limitations upon the scope of the invention except insofar as and to the extent that they are included in the accompanying claims. A number of variations to the present invention will be apparent to those of ordinary skill in the art and these variations will not depart from the spirit and scope of the present invention. The scope of the invention is defined by the appended claims and equivalents thereto.