in the drawings , fig1 and 2 illustrate generally at 10 a portable infusion pump according to a preferred embodiment of the invention . infusion pump 10 provides an ambulatory system which enables health care professionals to infuse patients directly from single dose container bags which are pre - filled with iv solutions . infusion pump 10 of the invention is suitable for use in homes , hospitals or clinics . it is also readily adapted for operation in any position , such as resting on a table with the patient in bed , or it could be carried by the patient . infusion pump 10 is comprised of a box - shaped housing 12 having a lid 14 which pivots open and closed about a hinge 16 . the interior of the housing is divided into an upper compartment 18 and lower compartment 20 by a horizontal flat plate 22 . the upper compartment is sized and shaped commensurate with the size and shape of a standard large ( 115 cc ) iv bag 24 , and the compartment can also contain a standard small ( 50 cc ) iv bag . an inflatable bladder 26 is mounted across the upper surface of plate 22 within the upper compartment . the opposite walls of the bladder are hermetically sealed together about their periphery to provide a closed internal volume for containing a fluid under pressure . in the present embodiment , the fluid is a gas , preferably air , although liquid fluids could also be employed , such as a low viscosity , non - toxic oil . lower compartment 20 of the housing mounts an air pump 28 , a two - position solenoid valve 30 , a battery compartment 32 and a printed circuit board , not shown , which contains components of the electric control circuit 34 shown schematically in fig5 . a pressure sensor 36 is mounted from plate 22 and depends downwardly into the lower compartment . the pressure sensor includes a moveable pressure pad 38 which extends upwardly through a central opening 40 in plate 22 into juxtaposed relationship with the lower wall of bladder 26 . expansion and contraction of the bladder as its internal fluid pressure increases and decreases correspondingly causes up and down movement of the pressure pad . the pressure sensor generates an electric pressure signal responsive to movement of the pressure pad , and this signal is directed through line 42 into control circuit 34 . the control circuit is powered by suitable dry cells , not shown , mounted in the battery compartment . control circuit 34 is also connected through line 44 to operate the air pump . the pump inlet draws atmospheric air through inlet tube 46 and filter 48 , with pressurized air being directed out through tube 50 into the solenoid valve 30 . this valve has a normally closed inlet 52 connected with air pump 28 , and a normally open outlet 54 is connected via tube 56 through filter 48 and tube 58 to atmosphere . an outlet 60 leads through tube 62 to the bladder . in the normally open position of the valve , the inner volume of the bladder is opened through outlet 54 to atmospheric air so that the iv bag cannot be pressurized . at the same time , inlet 52 blocks out pressurized air from the pump . when the control circuit sends a signal through the line 42 to the valve , inlet 52 is opened so that the valve directs pressurized air from the pump into the bladder while outlet 54 is closed . with lid 14 in its open position shown in fig1 iv bag 24 is inserted so that it lies flat across the upper wall of the bladder . in this solution - dispensing position of the bag , the bag &# 39 ; s dispensing port 64 and filling port 66 extend toward the right of the compartment , as viewed in fig1 and 2 . fig4 illustrates dispensing spike 68 in accordance with the invention which provides means for releasably interconnecting the iv tubing with the iv bag . dispensing spike 68 is comprised of a tubular body 70 having a proximal end adapted for receiving the end of iv tubing 72 . the distal end of the tubular body is formed into a piercing spike 74 which is adapted to pierce through the closed end of dispensing port 64 . this opens the inner channel of the spike to solution within the bag . the dispensing spike thereby interconnects the end of the iv tubing in fluid communication with the solution in the bag . dispensing spike 68 includes an annulus 76 formed about the tubular body . the annulus has a diameter which is sufficiently large to enable the hand of the user to apply a force along the longitudinal axis of the body for inserting and removing the spike into and from the dispensing port . a diameter in the range of 0 . 6 &# 34 ; to 1 . 0 &# 34 ;, and preferably 0 . 8 &# 34 ;, is suitable for this purpose . it is another important feature of the invention that annulus 76 , in cooperation with housing end wall 78 and lid 14 , is releasably captured and securely held in place when the bag is in its proper solution - dispensing position . toward this objective , a notch 79 ( fig3 ) is formed along the upper side of housing end wall 78 . a u - shaped groove 80 is formed in the notch at a position for seating about the lower portion of tubular body , as best shown in fig4 . in this position , annulus 76 fits within the upper compartment with its outer surface seated against the housing end wall . outward forces on the tubular body , such as when the iv tubing is pulled , are resisted by the annulus which thereby holds the spike against displacement from the iv bag as long as the lid is closed . the corresponding end of the lid is formed with a downwardly projecting ridge 82 which matches the shape of the notch . u - shaped groove 84 ( fig1 ) is formed in the lower side of the ridge , and this groove seats against the upper portion of tubular body 70 when the lid is closed . lid 14 is releasably held in its closed position by means of a plurality , shown as three , of latches 86 which are mounted at spaced positions on a slidebar 88 . the slidebar is mounted for back and forth movement across the upper edge of housing front wall 90 . a spring 92 is mounted at one end of the slidebar to urge it toward the right , as viewed in fig1 . with the slidebar urged to the right , the latches engage lid notches 94 ( fig3 ) to hold the lid down . a manually operated latch release button 96 carried on the slidebar projects through an opening in the front of the housing to permit the user to move the slidebar to the left so that the latches release from the lid . another important feature of the invention is the provision of an on - off switch 98 which , in combination with dispensing spike annulus 76 , generates a bag - in - place signal when the bag is in its proper solution - dispensing position . the bag - in - place signal is directed through line 100 into the control circuit for controlling the infusion procedure . the end of horizontal plate 22 is formed with a slot 102 ( fig3 ) through which spike annulus 76 projects downwardly into the lower compartment . switch 98 is provided with an actuating arm 104 , and the switch is positioned in the lower compartment so that the arm projects into an interference relationship with the portion of annulus which extends downwardly through slot 102 . when the dispensing spike is out of the position shown in fig1 such as when the iv bag is either out of the compartment or improperly positioned , then annulus 76 cannot fit fully down through the slot . this permits the actuating arm to move upwardly so that switch 98 is operated to a position in which the bag - in - place signal is disabled . while an air filter 48 is shown for filtering air from the atmosphere into pump 28 , the invention contemplates that the filter could be eliminated with the pump drawing inlet air directly from the atmosphere , and with exhaust air from the bladder being sent through outlet 54 directly to atmosphere . the invention also contemplates an arrangement in which the outlet from pump 28 directs air through a line leading directly into bladder 26 . in such an arrangement , the solenoid valve 30 would have one inlet connected with the bladder and one outlet which directs air to the atmosphere either directly or through an air filter . the valve would be operated by a control circuit of the type shown in fig5 between one position in which the valve inlet is closed while the pump fills the bladder with pressurized air , and in another position in which the valve inlet is opened so that pressurized air from the bladder is discharged through the valve to atmosphere . housing 12 includes a control panel 106 having a power - on pushbutton 108 , an infuse pushbutton 112 . the pushbutton 112 . the panel also includes a light 114 providing a battery low condition signal , and a light 116 providing a check status signal . pushbutton 108 is provided with a light 118 for indicating a power - on condition , pushbutton 110 is provided with a light 120 indicating an infuse condition , and pushbutton 112 is provided with a light 122 for indicating a stop condition . the flow chart comprised of fig6 a and 6b illustrates the steps in the method of operation of diffusion pump 10 . with air pump 28 turned off , the iv bag is placed into its solution - dispensing position within the upper compartment of the housing at step 124 . the lid is then closed at step 126 , which is followed by the patient , or health care professional , pushing the power button at step 128 . this turns on the power light at step 130 , and the control circuit runs its system checks at step 132 . if the spike annulus properly actuates switch 98 at light step 134 , a &# 34 ; yes &# 34 ; indication is directed into the &# 34 ; system okay &# 34 ; logic step 136 . if not , the check status light is turned on and an automatic alarm sounds at step 139 . if the &# 34 ; system okay &# 34 ; condition exists , the infuse button is pushed at step 138 . if the lid is accidentally opened prior to completion of infusion , switch 98 is deactivated at step 140 . the control circuit responds and turns the air pump off at step 142 , valve 30 is deactivated at step 144 so that air is exhausted from the bladder through the filter to atmosphere , the check status light is turned on at step 146 , and the infuse light is turned off at step 148 . the signal generated from the infuse button being turned on is directed into line 150 which : turns on pressure sensor 36 at step 152 , turns the air pump on at step 154 , activates valve 30 at step 156 which directs pressurized air from the pump into the bladder , and turns the infuse light on at step 158 . next , the logic checks whether the pressure sensor senses a bladder pressure of a greater than a predetermined level , for example greater than 6 . 5 psi , at step 160 . if that level or above is not sensed , then the air pump remains on at step 162 . when the bladder pressure reaches or exceeds that level , then the air pump is turned off at step 164 . the circuit logic next determines at step 166 whether the bladder pressure is below a lower predetermined level , for example 5 . 5 psi . if it is below that level , then the air pump is turned on at step 168 . if not , then the logic at step 170 determines if the time elapsed since the pump was on is greater than 5 minutes . if so , then the air pump remains off at step 172 . next , the infuse light is turned off at step 174 , valve 30 is deactivated to exhaust air from the bladder at step 176 , the check status light is on and the alarm sounds at step 178 . the method then proceeds to step 180 where the patient or health care professional checks the status of infusion . if the infusion is complete , the power button is turned off at step 182 . this turns all systems off at step 184 so that the patient can open the lid at step 186 , and remove the iv bag at step 188 . if the infusion is not complete , then the patient can correct the problem at step 190 and press the infuse button at step 192 . this turns the check status light off at step 194 , and the logic proceeds through line 196 to repeat the infusion process . if at any time during the infusion process the patient presses the stop button at step 198 , then the infuse light is turned off at step 200 , the stop light is turned on at step 202 , the solenoid valve is deactivated at step 204 and the air pump is turned off at step 206 . the logic then determines at step 208 if infusion is complete . if so , the logic proceeds to step 182 so that the power button can be turned off . if the infusion is not complete , then the patient can correct the problem at step 210 and then press the infuse button at step 212 which turns the stop light 122 off at step 214 . the logic then proceeds through line 216 to repeat the infusion procedure . fig7 illustrates another embodiment providing a modified dispensing spike 218 for releasably holding the spike in a pump housing 220 when a lid 222 is closed . dispensing spike 218 is formed about its proximal end with an annular groove 224 . the annular recess portion within the groove releasably fits on its lower side into a matching u - shaped seat 226 which is formed on the upper edge of the housing end wall . the lid has a downward protecting portion 227 at its front end which is formed with a similar u - shaped seat 228 which moves into register with and fits into the top side of the spike groove when the lid is closed . the sharpened end 230 of the spike penetrates into the iv bag dispensing port 232 . a tubular body 234 of the spike is formed with an internal bore 236 which receives the end of the iv tubing , not shown . an annulus 238 formed about the body provides a push surface against which force can be applied by the user &# 39 ; s hand to insert and remove the spike into and from the dispensing port . with the lid closed , the upper and lower seats 226 and 228 fit about the spike groove so that the spike is locked against unintended removal from the housing during the infusion process . while the foregoing embodiments are presently considered to be preferred , it is understood that numerous variations and modifications may be made therein by those skilled in the art and it is intended to cover in the appended claims all such variations and modifications as fall within the true spirit and scope of the invention .
an infusion pump for infusing solutions from iv bags through tubing to patients . the pump comprises a housing having a compartment which receives an iv bag in a solution - dispensing position . the bag is placed over a bladder within the compartment , and the bladder is expanded by a pressurized fluid to apply a pushing force against the bag which collapses to infuse solution through the tubing . a pump in the housing pumps a fluid such as air into the bladder under influence of a control circuit . a pressure sensor indirectly senses pressure of fluid in the bladder through a pressure of pad which contacts the bladder wall . a control circuit generates a pressure signal responsive to movement of the pressure pad for operating a valve which directs fluid between the pump and bladder . a dispensing spike is provided for interconnecting a dispensing port of the bag in fluid communication with the tubing . the spike is formed with an annulus which cooperates with a wall of the housing to prevent unintended withdrawal of the spike from a dispensing port while infusion takes place . the annulus also operates a switch which is connected in the control circuit to ensure that infusion proceeds only when the bag is in its proper solution - dispensing position in the housing .