the apparatus shown in use in fig1 is very simple . it comprises a face mask ( 11 ) to which an oxygen - enriched air mixture is fed along a first tube ( 12 : from a source not shown ) and a nitric oxide / nitrogen mixture ( no / n 2 ) is fed along a second tube ( 13 ) from a cylinder ( 15 ) thereof . the nitric oxide supply is controlled by a regulator ( 16 ) which itself is controlled by a suitably programmed box of electronics ( 17 ) driven by signals obtained from a sensor ( 18 ) in the mask 11 ( the sensor is a thermistor that is cooled by , and so detects , airflow ). in this particular case the system is arranged to note the end of an exhalation , and to trigger the operation of the regulator 16 so as to have the pulse of nitric oxide fed into the mask ready for the beginning of the next inhalation . fig2 shows the progress of a bolus ( 21 ) of nitric oxide / air mixture down the patient &# 39 ; s windpipe ( 22 ) and on deep into his lungs ( 23 ). though at first sight it looks as though there are several bolus preceding one after the other , in fact there is only one , shown at different times on its journey , and the object of the figure is to show how the bolus remains as an entity , and does not disperse as it progresses ( and so reaches the deepest part of the lungs as a concentrated burst of nitric oxide with the full therapeutic effect required ). the timing of the bolus delivery is shown graphically in fig3 . airflow in and out of the lungs takes place at regular intervals , as the patient breathes , and just as the flow starts a pulse of nitric oxide is delivered , and &# 34 ; washed down &# 34 ; with the remaining inhaled air . the nitric oxide spike delivery system shown in fig4 and 5 involves respectively a valve operating system ( shown in fig4 ) and a cylinder containing 100 ppm nitric oxide in a carrier gas diluent such as nitrogen and having a two - stage regulator ( fig5 ). the regulator , which may be of any conventional design , drops the pressure of the 100 ppm nitric oxide / nitrogen mixture so that with a valve - open flow rate of 12 litres per minute opening the valve for 0 . 5 seconds causes a volume of 100 cc to be delivered . after the main pressure reducing regulator , it is the valve orifice that offers the greatest resistance to flow ; therefore it is possible to specify the flow rate from the inlet pressure delivered to this valve . fig5 also shows joined to the valve and cylinder the calibration study equipment ; this is used to measure the volume of gas mixture emitted from the valve with various opening times . the results of this study are shown in fig6 a / b , and are discussed below ( the actual volumes obtained are there compared with the volumes expected on the basis of the valve having a &# 34 ; square wave &# 34 ; opening form ). valve operation may be triggered either manually via an external pressure pad switch or automatically . the manual switch acts on the switch shown in fig4 triggering a pulse of predetermined width which then acts on the drive of the valve . the automatic trigger is synchronised to the airway pressure signal shown also in fig4 . once triggered , the period that the valve is open is specified electronically . a trigger output signal is available from the gas switch unit so that the instant that the nitric oxide spike is delivered during the respiration cycle can be monitored and recorded on the data acquisition system . where necessary , signals have been optically isolated to avoid circumvention of the physiological monitoring system electrical isolation barrier . the actual gas valve switch used in the apparatus has been designed specifically for use in the operating theatre , and accordingly is housed in a fully sealed box ( shown by the dashed outline ) to prevent the ingress of fluids and permit easy cleaning . the unit operates from a single pp3 style 9 v battery down to a level of 6 v ( a low battery indicator is provided ). the valve utilised is a 1 . 6 mm orifice miniature solenoid valve with stainless steel base block , tube and plunger assembly , and is fitted with an epdm seal ( all of these are as recommended for use with nitric oxide ). the coil is operated from a 6 v direct current supply , and has a power rating of 5 watts . minimum operating time is 10 ms . in order to maximise battery life , the valve coil is energised at a peak current of 400 ma for 7 . 5 ms , and then the current is reduced to a holding level of 100 ma for the remaining period that the valve is maintained open . constant current drive is employed to exploit the full discharge range of the battery . a minimum of one thousand operations with a pulse width of 625 ms should be possible from a high performance alkaline manganese ( i . e . duracell procell ) battery . the valve - open time may be set to one of twelve intervals in the range of 10 ms to 2 s . an led is provided to indicate the state of the valve . the system may be manually triggered from a pneumatic pressure pad switch which permits easy operation either by hand or foot . alternatively , triggering can be performed automatically , as described below . in its automatic mode the apparatus includes an automatic trigger that is fed a suitable trigger stimulus derived from the repeated airway pressure output of the physiological pressure monitoring system . the repeated output is an amplified and stabilised version of the sensor signal . however , to ensure reliable detection of a respiratory event ( in the tests described hereinafter , this is the onset of expiration ) some further signal conditioning is required . this latter takes the form of a second - order low pass filter ( to remove mains interference ), zero - offset cancellation , and amplification . the expiration event is then used to initiate a delayed time interval which , once this has elapsed , generates a trigger pulse to the gas valve switch . the delay time is adjustable in the range of 0 to 5 seconds , enabling the automatic trigger to be positioned at any desired point in the respiration cycle . this unit derives its operating power from the + 12 v and - 12 v rails of the data acquisition system . in the physiological studies described below the valve assembly was connected to the intratracheal tube use to ventilate the test animal with a manley mechanical ventilator . airway pressure was measured by an air - filled transducer ( spectromed p20 , coventry , uk ). the valve was triggered by a fall in the airway pressure on expiration . the switch provided a burst of 100 ppm nitric oxide / nitrogen gas mixture at the start of the inhalation ( the start was judged from direct observation of the pressure wave form and an electrical signal from the valve ). by way of contrasting the invention &# 39 ; s treatment against that conventionally used in the field , the effects of different times of opening of the switch according to the invention were compared with the situation and results obtaining when the whole of the inhaled volume being made up of nitric oxide in air at a concentration of 40 ppm . the first study was to determine the volume of gas delivered by the cylinder / valve assembly used in the fig1 apparatus of the invention . this was measured spirometrically ; as shown in fig5 a measurement device was constructed to measure the volume displaced from a &# 34 ; floating bell &# 34 ; on a water container . the volume displaced by a series of open times of the valve ( from 10 ms to 1 sec ) are shown graphically in fig6 a & amp ; b ( 6b shows the 10 to 100 ms range at a larger scale ), together with the calculated ( expected ) volumes delivered by the valve if it operated with total efficiency ( i . e . it opened with a &# 34 ; square wave &# 34 ; form ). the observed volumes were used to provide the amount of gaseous nitric oxide delivered to the ventilation system in the actual test experiments discussed further below . the experiments providing the desired test results were carried out on pigs which weighed between 35 and 60 kg ( mean : 45 . 2 kg ). the animals were obtained from a commercial breeding centre , and were pathogen - free . they were initially sedated with 0 . 5 mg / kg droperidol ( dropleptan , from janssen pharmaceutical ltd , oxon , uk ) and 0 . 3 mg / kg midazolam ( hypnovel , from roche , welwyn , uk ). a 19 - 21 gauge intravenous cannula was placed in a peripheral vein of their ear , and sodium pentobarbital ( sagatal , from rhone - polenc , uk ) was infused in ( at a dose of up to 15 mg / kg ) to induce anaesthesia . the infusion was maintained at 9 - 11 ml / hr up to a maximum of 30 mg / kg . the animal was then intubated through a tracheotomy , and then paralysed with 0 . 2 mg / kg alcuronium ( alloferin , from roche , welwyn , uk ). the ventilator was run at a tidal volume of 500 ml and 15 breaths per minute , and air was used . the left carotid or femoral artery was cannulated in order to measure systemic arterial pressure . the adequacy of anaesthesia was assessed by monitoring the responses of the heart rate and systemic blood pressure to noxious stimuli . access to the thoracic organs was achieved by a midline sternotomy . the pericardium was opened and 1 , 000 u / kg heparin ( from paynes & amp ; byrne , greenford , uk ) was administered into the right atrium . two cannulae ( id 5 mm , from portex , uk ) were placed respectively in the inferior vena cava and in the right ventricle through an incision in the right atrium . the animal was exsanguinated via the cannula in the inferior vena cava while 1 - 2 l of buffered krebs - ringers solution containing 40 gm / l dextran 70 were concurrently infused into the right ventricle . the rate of infusion was adjusted to keep the systemic arterial blood pressure stable until 3 litres of blood were obtained . the heart was then stopped by an intracoronary injection of 10 - 3 potassium chloride , and a stiff cannula ( id 13 mm ) was placed in the main pulmonary artery . through an incision in the left ventricle , another cannula ( id 16 mm ) was retrogradely inserted into the left atrium and secured by heavy silk ties which prevented ballooning of the atrial appendage . the cannulae were then connected to an external perfusion system . time from cardiac arrest to the start of perfusion was never more than 20 minutes . the perfusion circuit used a heated jacketed reservoir which received autologous blood from the left atrium . from the reservoir , the perfusate was pumped into the pulmonary artery by means of a roller pump ( watson marlow model 5001r , uk ). a 150 ml reservoir with a small cushion of air was interposed between the pump and the arterial cannula ; this acted as a pulse damper as well as a bubble trap . perfusate temperature was monitored with a thermistor in the inflow cannula . the height of the venous reservoir could be adjusted to the desired venous pressure . perfusion was instituted at 10 ml / min / kg , and slowly increased by 10 ml / min / kg steps over an hour until a flow rate of 100 ml / min / kg was reached . the variables recorded throughout the experiments were cardiac output ( pulmonary blood flow ) ( q ), pulmonary artery pressure ( pap ), left atrial pressure ( pwp ), systemic arterial pressure ( sap ), and central venous pressure ( cvp ). the pulmonary vascular resistance ( pvr ) was calculated from q /( pap - pwp ). for the purposes of analysis the analogue outputs of the transducers and ultra - sonic flow metres and , where required , the nitric oxide analyser were sampled on demand by a personal computer ( macintosh se 30 , apple computer inc ., cupertino , calif ., usa ) using a 16 bit adc interface at a sample rate of 500 hz ( mp100 , biopac system , inc ., goleta , calif ., usa ). the inhibition of vascular endothelial nos was achieved by adding to the perfusion solution the analogue for l - arginine called n g - nitro - l - arginine methyl ester ( l - name ) ( at a rate of 1 - 2 mg / kg ). this causes a rise in both pvr and the systemic vascular resistance ( svr ). the constrictor was an analogue of thromboxane called u46619 ; 10 pmol / min was infused to elevate the pvr some twofold . in the first protocol the nitric oxide / nitrogen cylinder contained 40 ppm . the valve was activated to give in random order ( 10 , 20 , 40 , 80 , 160 , 320 , 640 and 1000 ms ) from the start of the breath . there were four measurements of the pvr over five minutes , and a total of five pigs were studied . in the second protocol a period of ventilation of the lungs with 40 ppm of nitric oxide in air was compared with the spike . the spike was set at different times of opening of the valve ( 10 , 80 , 160 and 320 ms ) and the nitric oxide source was a cylinder of 100 ppm of nitric oxide / nitrogen . as can be seen from the results shown graphically in fig7 a , the pulmonary vascular resistance ( pvr ) is raised using l - name at time 0 . then , with nitric oxide / nitrogen pulses , or spikes , of duration varying from 1 sec down through 240 , 120 , 80 , 40 , 20 to 10 msec , it can be seen how the pvr fell to a level below baseline ( the zero line ). the results show the mean values and the standard deviation . it will be seen that the 10 msec burst of nitric oxide / nitrogen was just as effective as the 1 sec burst . in fig7 b the pvr value after administration of u46619 is shown as 100 %. the percentage fall in pvr with &# 34 ; spikes &# 34 ; of nitric oxide / nitrogen is compared with continuously - inhaled nitric oxide ( shown as c ). the control full breath is of nitric oxide at 40 ppm in air whiles the bursts are 100 ppm . here it can be seen that 10 msec of 10 ppm nitric oxide / nitrogen is as effective as 40 ppm of nitric oxide / air throughout the entire inhalation ( ie , as long as one to two seconds ). in the pig lungs where the pulmonary vascular resistance ( pvr ) is elevated with u46619 and the nos inhibitor , spiked nitric oxide is as effective as 1 sec or continuous full inhalation of nitric oxide in reducing the pvr . in other words , as little as a 10 ms burst of nitric oxide is equivalent to a whole breath of nitric oxide . it can be calculated that spiked 0 . 74 ppm nitric oxide can give the same effect as 40 ppm in the whole breath . thus , toxicity risk is lessened , there is no need for complex gas mixing , and potentially any breathing pattern can be used .
the invention is a method and apparatus for treatment in which nitric oxide is supplied from a source to a patient for inhalation incorporating a regulator to control the flow of nitric oxide from the source to the patient , a monitoring apparatus to monitor the patient &# 39 ; s respiration , and a controller to cause the regulator to permit the egress of a very short pulse of nitric oxide of a known , predetermined volume at a predetermined time during the patient &# 39 ; s inhalation .