Hunting arrow and method

A hollow shaft hunting arrow carries a small volume of liquified carbon dioxide which is released by flash expansion upon penetration into the thorax of a game animal. The thorax is pressurized with carbon dioxide gas at sub-zero temperature to cause collapse of the lungs and fibrillation of the heart, so that the animal can be harvested on the spot, thus avoiding escape and uncertain recovery. The liquified carbon dioxide is carried in an internal reservoir and is released by flash expansion upon opening actuation of a valve closure member. The arrowhead includes a freely movable center core which is attached to an actuator shaft that is engagable with a release valve. The release valve is actuated by either piercing a metallic membrane, fracturing a glass or ceramic lens or unseating the ball closure of a ball valve assembly. A small amount of fluorescent dye is introduced into the liquified carbon dioxide which provides a marker in the blood trail left by a wounded animal which will fluoresce or glow when exposed to ultraviolet light.

FIELD OF THE INVENTION
 This invention is related generally to hunting arrows for harvesting large
 game animals such as elk and deer, and in particular to a hollow shaft
 hunting arrow which carries liquid carbon dioxide that is released by
 flash expansion to produce tension pneumothorax upon penetration.
 BACKGROUND OF THE INVENTION
 The traditional bow hunting method for harvesting large game animals is to
 kill by exsanguination. The design of conventional hunting arrows has been
 optimized to produce the most effective method for draining the animal's
 blood from its circulatory system, thus interrupting the animal's ability
 to provide adequate tissue profusion. Without an adequate blood supply in
 the circulatory system, the exchange of oxygen and carbon dioxide at the
 tissue level cannot continue. The oxygen level then drops and the carbon
 dioxide level rises until the balance between the two are incompatible
 with life and the animal expires, achieving the primary goal of harvesting
 the animal.
 However, because the kill is not instantaneous, the game animal has the
 ability to travel quickly and far from the position it is standing when
 first struck by the arrow. During the course of its wounded flight,
 especially in larger animals such as deer or elk, the animal quickly
 disappears from sight, and the hunter is then burdened with the task of
 tracking the wounded animal, aided primarily by the blood trail. The blood
 trail is difficult to follow and so the animal may not be found. The
 mortally wounded animal may endure unnecessary suffering and may escape to
 an inaccessible location.
 Consequently, improvements in modern hunting arrows for large game animals
 have been directed to achieving a rapid kill. Some improvements have been
 directed to maximizing the cutting effect of the arrow head to improve the
 chance of severing a major blood vessel, thus promoting a quick kill, for
 example as shown in U.S. Pat. No. 4,762,328. In that patent, a game
 arrowhead consists of a fixed broad head point with splines that deform
 and expand upon impact, thus creating greater tissue displacement and
 trauma effect upon penetration.
 U.S. Pat. No. 4,277,067 discloses a hollow arrow shaft which has drainage
 apertures to promote exsanguination.
 U.S. Pat. Nos. 4,252,352; 3,993,311 and 5,314,196 disclose arrows that have
 a hollow shaft which contain components for enhancing bleeding in a
 wounded animal and for facilitating tracking the wounded animal.
 U.S. Pat. No. 4,277,069 discloses an arrow for blood tracking which
 includes a tubular shank which is perforated with drainage holes along its
 length.
 Another hunting arrow improvement that represents a departure from the
 conventional exsanguination technique is disclosed in U.S. Pat. No.
 3,617,060. The hollow shaft hunting arrow includes a longitudinal passage
 which communicates with the atmosphere. When the arrowhead pierces the
 thoracic wall of the animal, the thoracic cavity is connected directly in
 communication with the atmosphere by the longitudinal passage. When this
 occurs, the internal pressure of the thoracic cavity rises from below
 atmospheric to atmospheric, thus resulting in collapse of the animal's
 lungs.
 Yet another hunting arrow improvement includes apparatus for releasing
 pressurized air upon penetration, where the pressurized air enhances the
 cutting effectiveness of the arrowhead, for example as disclosed in U.S.
 Pat. No. 5,762,574. The hunting arrow has a hollow shaft which is
 pressurized with compressed air. Upon penetration into the animal, the
 compressed air is released through vents at a pressure of about 150 psi as
 a release valve opens. The pressurized air exacerbates the localized wound
 inflicted by the arrow head, thus accelerating trauma to soft tissue.
 Further improvements have included an arrow that is fitted with a
 cylindrical cartridge containing a chemical drug material that will
 paralyze, incapacitate or kill a game animal by injecting a drug into the
 body of the animal upon impact. For example, U.S. Pat. No. 4,463,953
 includes a pod carried on an arrow shaft which releases a drug within the
 body of the game animal upon penetration. A similar arrangement is shown
 in U.S. Pat. No. 4,726,594 in which a cylindrical cartridge containing a
 drug is dispensed by a detonator which explodes on impact and injects the
 drug from the cartridge through a needle into the game animal.
 BRIEF SUMMARY OF THE INVENTION
 The conventional technique of draining blood from an animal's circulatory
 system is not efficient and results in unnecessary suffering. Therefore,
 there is a continuing interest in providing a more humane and effective
 method for harvesting a game animal with a hunting arrow.
 A hollow shaft hunting arrow constructed according to the present invention
 carries a small volume of liquified carbon dioxide which is released by
 flash expansion to produce tension pneumothorax upon penetration. The
 thorax of the game animal is pressurized with carbon dioxide gas at
 sub-zero temperature to cause collapse of the lungs and fibrillation of
 the heart, so that the animal can be harvested on the spot, thus avoiding
 escape and uncertain recovery.
 In the preferred embodiment, the arrow is tubular and includes a reservoir
 which is pressurized with approximately 10 cc of liquified carbon dioxide.
 The contents of the charged reservoir are released by flash expansion upon
 penetration into the animal's thorax and opening actuation of a valve
 closure or fracture of a seal. A flow passage connects the reservoir with
 at least one discharge orifice in or adjacent the arrow point, so that
 upon release, the liquid carbon dioxide expands in the gaseous state and
 compresses the lungs and freezes the thorax of the game animal.
 The expansion of the liquid carbon dioxide occurs at sub-zero temperatures,
 which flash-chills the thorax, the lungs and the heart. This immediately
 induces bilateral pneumothorax and also causes fibrillation of the heart.
 Because of this sudden heart and lung failure, the game animal will be
 immobilized almost immediately, and the animal will expire quickly, with
 minimal suffering.

DETAILED DESCRIPTION OF THE INVENTION
 Preferred embodiments of the invention will now be described with reference
 to various examples of how the invention can best be made and used. Like
 reference numerals are used throughout the description and several views
 of the drawing to indicate like or corresponding parts.
 The most rapid and effective method for rendering a game animal's lungs
 ineffective is to design the hunting arrow to collapse both lungs, i.e.
 produce bilateral pneumothorax, and simultaneously arrest the heartbeat.
 With both lungs collapsed and heart failure, the game animal will be
 unable to provide adequate exchange of oxygen and carbon dioxide.
 Therefore, even if the circulatory system were still intact, the game
 animal would be unable to maintain oxygen levels high enough and/or carbon
 dioxide low enough to support life at the tissue level.
 During respiration, the diameter of the game animal's thorax and rib cage
 is increased by flexing the intercostal muscles. The length of the
 intrathoracic cavity is increased by flexing the diaphragm, which causes
 it to change shape. In the relaxed state, the diaphragm is dome-shaped,
 and in its flexed state, it is flat. These two mechanism increase the
 intrathoracic volume of the game animal. This effort allows the
 atmospheric pressure to force air through the game animal's airway from
 the lungs, causing the lungs to inflate. When the intercostal muscles and
 diaphragm relax, the thorax returns to its original shape with much
 smaller intrathoracic volume, thus forcing the inhaled air out, which
 allows the oxygen-depleted and carbon dioxide-enriched air to be forced
 from the animal's lungs into the atmosphere.
 The integrity of the game animal's respiratory system is maintained by a
 partial vacuum within its thorax which allows the lungs to remain
 inflated. The atmospheric pressure of inhaled air expands the volume of
 the lungs as the volume of the thorax is increased by the animal's
 intercostal (between the rib) muscles, as well as the animal's diaphragm.
 According to the present invention, a quick kill is achieved by inducing
 bilateral pneumothorax and fibrillation of the heart by discharging a
 large volume of carbon dioxide gas at sub-zero temperatures which
 flash-chills the thorax, the lungs and the heart. When the heart is
 suddenly chilled, it stops beating and begins fibrillating (twitching)
 which is more effective than piercing the heart. Moreover, the thoracic
 cavity is suddenly pressurized, thus compressing and collapsing both
 lungs, which immediately terminates respiration and the flow of oxygen.
 When both lungs are compressed and collapsed, this state in the game
 animal is referred to as "tension pneumothorax." The mechanism of death is
 still the interruption of the animal's ability to adequately exchange
 oxygen and carbon dioxide at the tissue level. However, the present
 invention renders the animal's lungs and heart ineffective rather than
 draining blood from its circulatory system.
 A hunting arrow capable of producing tension pneumothorax and flash
 chilling the thorax and surrounding organs is described below.
 Referring now to FIG. 1 and FIG. 2, a hunting arrow 10 has a hollow shaft
 12 made of tubular material. The length of the arrow shaft may vary,
 typically extending 25 inches-35 inches from its trailing or aft end 12A
 to its leading or forward end 12B, and is made from commercially available
 materials such as fiberglass tubes, hollow plastic shafts and thin-walled
 aluminum shafts.
 Conventional stabilizers 14 are attached to the aft end 12A of the shaft
 and are secured by an adhesive such as epoxy resin. The stabilizers 14 are
 preferably made of a plastic material, but other materials such as
 feathers and paper may be used. A conventional nock 16 is fitted to the
 aft end of the arrow shaft for receiving the bow string.
 The forward end of the arrow 12B is fitted with a compound arrow head 18
 which consists of a stationary broad head 20 with fixed splines 22 and a
 movable chisel point piercing member 24 that is mounted for axial movement
 within a tubular receiver barrel 26. The receiver barrel 26 is secured to
 the forward end 12B of the arrow shaft by a threaded end fitting 28.
 According to an important feature of the invention, multiple vent holes or
 discharge apertures 30 are formed in a fenestrated shaft section 12C near
 the arrowhead. The vent apertures 30 are drilled through a hollow sidewall
 portion 12C of the shaft 12 at a distance of from about six inches up to
 twelve to twenty inches from the arrowhead 18, depending on the size of
 the thorax of the animal being hunted. The number and the size of the
 discharge apertures 30 are selected to afford rapid and complete discharge
 of pressurized CO.sub.2 into the thorax upon penetration.
 In this exemplary embodiment, the diameter of each vent aperture 30 is in
 the range of 1/16 inch-3/32 inch. The number of vent apertures 30 is
 selected to provide an effective discharge cross-section area which is at
 least as large as and preferably larger than the flow discharge outlet
 area of the release valve. Preferably, eight flow discharge apertures are
 provided, each having a diameter of 3/32 inch, and are substantially
 equally spaced on three inch centers in four rows along the length of the
 arrow shaft sidewall section 12C.
 As shown in FIG. 2 and FIG. 3, the vent holes 30 are located between the
 arrow point 18 and a release valve 32, thus providing vent ports for
 discharging CO.sub.2 gas from the release valve into the thorax of the
 game animal. In the preferred embodiment, the fenestrated shaft section
 12C containing the multiple discharge vent ports 30 is approximately
 twelve inches in length, as measured from the arrowhead 18, thus defining
 a vent chamber C.
 The fenestrated sidewall portion 12C of the arrow shaft encloses a tubular
 cannister 34 which is pressurized with a small volume of a liquified gas
 L, preferably liquid carbon dioxide. The canister 34 is a thin-walled
 aluminum container which is sealed on one end by the release valve 32. It
 is sealed on its opposite end by a refill valve assembly 36 which includes
 a threaded refill fitting 38 and a movable plug seal 40. The canister 34
 encloses a reservoir 35 which contains a predetermined volume of liquified
 gas L, for example 10 cc of liquified carbon dioxide in this exemplary
 embodiment.
 Referring to FIG. 2, FIG. 3 and FIG. 4, in the preferred embodiment the
 release valve 32 is a ball valve assembly which includes an annular seal
 collar 42, an annular valve seat 44 and ball closure member 46.
 Preferably, the ball closure member 46 is an aluminum ball, and the valve
 seat 44 is coated with Teflon.TM. TFE or FEP fluorocarbon polymer. The
 seal collar 42 is attached by small set screws 48 to the tubular sidewall
 12C. The valve closure ball 46 is sized for fluid sealing engagement
 against the annular valve seat 44 (FIG. 3) which is concentric with the
 discharge bore of the release valve.
 The discharge bore of the release valve 32 provides an outlet flow port 32A
 through the seal collar 42 and through the valve seat 44. The closure ball
 46 seals the outlet flow port in a valve closed position (FIG. 2) and is
 movable to a valve open position (FIG. 3) in which the outlet flow port
 32A is opened and the valve seat is uncovered, thus providing a flow
 passage from the reservoir 35 into the discharge chamber C in the valve
 open position.
 The canister 34 is charged with five to fifteen cubic centimeters of liquid
 carbon dioxide and is inserted into the hollow arrow shaft section 12C.
 The leading end of the canister 34 is engagable with a release actuator 60
 which opens the release valve 32 immediately upon penetration, thus
 releasing the expanding CO.sub.2 gas through the outlet flow port 32A into
 the vent chamber C for discharge into the game animal's thoracic cavity.
 The canister 34 is attached to the inside sidewall of the arrow shaft
 section 12C by small set screws 48. The refill fitting 36 is threaded to
 engage a fill nozzle through which liquid carbon dioxide is supplied. The
 liquid carbon dioxide L is produced by compressing and cooling carbon
 dioxide gas to -37.degree. C. The liquified carbon dioxide is introduced
 into the canister 34 through the fill port 38A which temporarily displaces
 the rubber plug 40 as the canister fills. The rubber plug 40 is
 automatically driven into a sealing position against a valve seat 38B on
 the recharge fitting 38 as the canister 34 becomes fully pressurized.
 After the canister 34 has been completely charged with liquified CO.sub.2,
 the plug 40 seats and the refill port 38A is sealed. The canister 34 is
 locked in place by a stop disc 54, which is secured to the aft end 12A of
 the arrow shaft by small set screws 48.
 Approximately 2 liters of CO.sub.2 gas are required to collapse the lungs
 of a small deer and 4-6 liters for an elk. Each cubic centimeter of liquid
 CO.sub.2 produces approximately one-half liter of gas. The length of the
 CO.sub.2 canister 34 and its diameter are sized appropriately, and in this
 exemplary embodiment, the canister 34 is sized to hold approximately 10 cc
 of liquid CO.sub.2 (L).
 In an alternative embodiment, shown in FIG. 7, the canister 34 is not
 utilized, and instead the CO.sub.2 reservoir 35 is formed by a length of
 the tubular sidewall 12, in which the arrow shaft itself holds the liquid
 CO.sub.2. An aluminum plug 54 is first inserted through the bore of the
 arrow shaft 12, and is anchored in place by set screws 48. The location
 and spacing distance of the aluminum plug 54 relative to the release valve
 32 is determined by the amount or volume of liquid CO.sub.2 desired. The
 valve seat in this embodiment is formed by a resilient O-ring seal 50,
 which is received within a concave pocket 52 that is machined into the
 collar 42. The valve closure member 46 in this embodiment is an aluminum
 ball 46 that is sized for sealing engagement against the O-ring seal 50,
 shown in the valve closed position in FIG. 7.
 In this alternative embodiment, the outlet flow port 32A of the release
 valve collar 42 is enlarged by a threaded bore T which is sized to mate
 with the filling nozzle from the liquid CO.sub.2 source. The CO.sub.2
 reservoir 35 is filled and pressurized with liquid carbon dioxide L before
 the arrowhead 18 is fitted. That is, before the arrowhead 18 and actuator
 shaft 60 are inserted, the threaded fill port 32A is engaged by the
 threaded end of a supply tube which is connected to a source of liquid
 carbon dioxide. After a threaded union is made up, liquid carbon dioxide
 is pumped into the reservoir 35. As the reservoir is filled, the ball
 closure member 46 is driven into seated engagement against the O-ring seal
 50. The supply tube is then removed after the reservoir 35 is fully
 charged and sealed. Next, the actuator shaft 60 is inserted through the
 vent passage C of the arrow until it is received within the throat of the
 release valve outlet port 32A, as shown in FIG. 7. The barrel 26 of the
 arrowhead 18 is torqued until the arrowhead is firmly secured in place,
 with the end 60A of the actuator shaft positioned immediately adjacent the
 ball closure member 46.
 Referring now to FIG. 5 and FIG. 6, an alternative release valve embodiment
 is disclosed. In this arrangement, the valve sealing element is a
 frangible glass or ceramic lens 56 or metallic membrane which is held in
 sealing engagement against a seal gasket 58, thus closing the release
 valve outlet port 32A. The seal gasket, the sealing element and the seal
 collar 42 are bonded together by adhesive deposits.
 Because of the extremely low temperature (about-37.degree. C.) of the
 liquid carbon dioxide L, the glass, ceramic or metallic material of the
 sealing element 56 will be relatively brittle, and easy to penetrate or
 shatter in response to a high intensity impact. A high intensity impact
 sufficient to move, break or rupture the sealing element 56 is transmitted
 by an actuator shaft 60 which is attached to the movable arrow point 24.
 According to this arrangement, the actuator shaft 60 functions generally
 as a valve actuator, and in particular as a firing pin mechanism.
 The actuator shaft 60 is attached on its forward end to a movable arrow
 core 62. The movable arrow core 62 is dimensioned and formed for a sliding
 fit within the inside bore 26A of the receiver barrel 26. The tubular
 shank portion 64 is threaded externally and is coupled in a threaded union
 T with the end fitting 28 as shown in FIG. 2. The actuator shaft 60 is
 guided for retracting movement by a narrow diameter, tubular shank portion
 64 which is integrally formed with and extends aft of the retainer barrel
 26. The actuator shaft 60 is dimensioned for a sliding fit within the
 inner bore 64B of the tubular shank portion 64.
 The aft end portion 60A of the actuator shaft is positioned immediately
 adjacent the closure member within the throat of the outlet flow port as
 shown in FIG. 2, FIG. 3, FIG. 5 and FIG. 7, but not touching the valve
 closure member. According to this arrangement, the actuator end portion
 60A is properly positioned for thrust transmitting engagement against the
 valve closure member in response to retraction movement of the arrow point
 piercing member 24.
 Upon penetration, the chisel point 24 and arrowhead core 62 are retracted,
 thus driving the actuator shaft end portion 60A into the lens or membrane
 56, which shatters the lens into fragments F (FIG. 6) or ruptures the
 membrane, thus releasing high pressure CO.sub.2 into the vent chamber C.
 Prior to impact, the chisel point 24 extends forward of the arrowhead 18,
 as shown in FIG. 1, FIG. 2 and FIG. 5. However, upon impact, the chisel
 point 24 and the arrow core 62 are retracted into the retainer barrel 26,
 thus driving the actuator shaft 60 into the release valve closure member.
 In the embodiment shown in FIG. 2, FIG. 3 and FIG. 7, the release valve
 closure member is the closure ball 46. As the actuator shaft end portion
 60A is driven into the closure ball 46, it unseats the closure ball and
 permits high pressure CO.sub.2 to vent into the vent chamber C. Upon
 penetration, the aft end 60A of the actuator shaft is retracted into the
 reservoir 35, as shown in FIG. 3 and FIG. 6. Because of the interference
 imposed by the actuator shaft, and since the actuator shaft cannot move
 forward upon penetration, the sealing ball 46 cannot re-engage the valve
 seat 44, thus permitting all of the pressurized CO.sub.2 contents to be
 delivered into the vent chamber C. Likewise, after the frangible seal 56
 is ruptured or shattered, all of the CO.sub.2 contents are delivered
 immediately into the vent chamber C for flash discharge through the
 apertures 30 into the game animal's thorax.
 The compound arrowhead 18 is designed with a freely movable center core 62.
 When the arrow point 24 makes contact, the center core retracts, providing
 the energy needed to drive the release valve 32 to the open position.
 Opening actuation of the release valve 32 is accomplished as the center
 core 62 of the arrowhead retracts through the retainer guide barrel 26 of
 the arrowhead. The center core 62 of the arrowhead consists of the arrow
 point 24 at one end tapering to the actuator shaft end portion 60A at the
 aft end which engages the release valve closure member. The release valve
 32 is actuated open by either piercing a metallic membrane, fracturing a
 glass or ceramic lens 56 or moving and unseating the closure ball 46 of
 the ball valve assembly.
 The design of the arrowhead 18 with a retractable core 62 not only provides
 the mechanism for releasing the liquified carbon dioxide, but also allows
 the arrowhead 18 to change its configuration after penetrating the wall W
 of the thoracic cavity. After the arrow point 24 has retracted inside the
 receiver barrel 26 of the arrowhead, the end of the arrow is reconfigured
 into a blunt end. The blunt end will arrest the arrow as it engages the
 opposite wall W of the thorax, thus opposing pass-through, and ensuring
 proper placement of the fenestrated arrow section 12C within the thoracic
 cavity as the low temperature CO.sub.2 gas is completely discharged.
 The release of the low temperature CO.sub.2 gas into the thorax of the
 animal will produce two effects. The first effect will be to produce a
 bilateral pneumothorax--the collapse of both lungs. Secondly, because the
 CO.sub.2 is being converted from a liquid state into a gas, the gas being
 introduced into the game animal's thorax will be at a very low
 temperature, 83.degree. F. below zero (-37.degree. C.). This chilling
 effect produces an interruption of the electrical activity of the heart.
 An occurrence known as fibrillation takes place in the heart at
 temperatures below +35.degree. F. During fibrillation, the heart muscles
 cease to contract in a coordinated effort and instead merely twitch.
 During this time the heart is not pumping blood and the game animal's
 blood pressure drops to zero.
 Collapsing both lungs will prevent the game animal from exchanging oxygen
 and CO.sub.2 with the environment. Death occurs when either the oxygen
 tension is not high enough or the CO.sub.2 tension is too high to support
 normal tissue function. The presence of pressurized CO.sub.2 inside the
 thorax will also enhance the increase in CO.sub.2 tension in the animal's
 blood, thus accelerating the death process. The increase of CO.sub.2
 tension in the game animal kills primarily by the production of carbonic
 acid forcing the pH of the blood down. A low pH in the game animal also
 makes its heart susceptible to fibrillation.
 A small amount of fluorescent dye may be introduced in the liquified
 CO.sub.2 which will provide a marker in the blood trail left by the
 wounded animal. At night the blood trace will then fluoresce or glow when
 exposed to ultraviolet light from a small portable UV lantern.
 Although the invention has been described with reference to certain
 exemplary arrangements, it is to be understood that the forms of the
 invention shown and described are to be treated as preferred embodiments.
 Various changes, substitutions and modifications can be realized without
 departing from the spirit and scope of the invention as defined by the
 appended claims.