Cardiac output in man (1951)

this film demonstr Ates two methods of estimating the output of the heart in man the volume of blood ejected by this living pump has long been the subject of Interest one early attempt to measure its output was made by the Reverend Steven hailes soon after he became Vicor of Teddington in 1710 having bled a sheep to death I fixed a musket Barrel to the pulmonary vein near its entrance into the left Oracle then placing the Barrel in a perpendicular posture with a funnel on the top of it I poured in melted beeswax this perpendicular height of melted wax which was near 4T would not have filled the oricle and ventricle if I had not at the same time taken care to pass a small brass pipe through one of the ascending branches of the aorta into the left ventricle through which the air passed off as the wax entered into the ventricle the brass pipe being at the same time gradually drawn up by an assistant I was by this means assured of the force with which the injected cavity of the heart was dilated which is more uncertain with a syinge this dilating Force continued acting uniformly until the wax was grown stiff and hard then taking out the wax which was formed in the shape of The ventricle this is the proper cavity of the left ventricle just before its contraction this piece of wax thus formed May reasonably be taken to be near commensurate to the quantity of blood received into this ventricle at each diaster and is then propelled into the aota at the subsequent cites the Sheep was 3 years old and weighed 91 a its pulses beat 65 times in the minute the capacity of the left ventricle of its heart was equal to 1.85 cubic in there seemed however to be no way in which the problem could be solved in intact man until Fick outlined a possible method of approach in 1870 all the blood pumped by the right side of the heart passes through the lungs where it becomes fully oxygenated and bright red in any individual resting man the rate of oxygen uptake is fairly uniform say 240 cubic cm per minute when bright red fully oxygenated blood is Flowing quickly through the tissues each unit volume of blood will give up a little oxygen represented here by one tiny bubble per corple as it does so it becomes slightly dark in color this Blood returns to the right heart and then passes through the lungs where each unit volume will only take up a similar small amount of oxygen in becoming saturated this is shown again as one tiny bubble of oxygen to each corple if we imagine that this small uptake of oxygen is 40 cubic cm to each liter of blood and the lungs are in fact taking up 240 cubic C M of oxygen per minute then 6 L of blood must be flowing through the lungs in a minute and this is of course the cardiac output if the blood is flowing through the tissues at half this rate the oxygen needs of the tissues would only be met if each unit of blood gave up twice as much oxygen diagrammatically each corple gives up two Tiny Bubbles of oxygen and in doing so the blood becomes much darker in color each unit of blood now arriving at the lungs takes up twice as much oxygen as before in becoming fully saturated diagrammatically each corple takes up two Tiny Bubbles in becoming fully oxygenated which is 80 Cub cm per liter instead of 40 as in the previous example the oxygen needs of the resting man are still 240 cubic cm per minute and the lung blood flow or cardiac output is thus 240 over 80 or 3 L per minute therefore in order to estimate the output of the heart in man we have to measure the rate of oxygen absorption in the lungs and the arterio Venus oxygen difference which is the amount of oxygen taken up by mixed Venus blood on its way through the lungs in practice the subject on whom the estimation is required lies comfortably on a padded x-ray couch in order to measure his oxygen uptake a spirometer is used the air in the bell of which is enriched with oxygen from a cylinder the spirometer mouthpiece is fitted in front of the subject's teeth and behind his lips while the nostrils are closed by a comfortable sponge rubber spring clip to make an airtight connection the absence of leakage at the nose and mouth is ensured by testing the tap is then turned enabling the subject to breathe to and from the spirometer the spirometer Bell Rises and falls with each respiration and these movements are written by an attached pen on a revolving drum as all the exhaled carbon dioxide is absorbed by soda lime the volume of the spirometer decreases owing to the absorption of oxygen in the lungs the rate at which oxygen is absorbed is represented by the upward slope of the respiratory tracing on the paper on which the tracing has been been made minute intervals are marked by vertical lines the changes in volume are measured on a vertical scale a line is ruled corresponding exactly to the slope of the tracing 10 minutes are counted and the scale volumes are read at the beginning and end of this period the difference is the volume of oxygen consumed in 10 minutes hence oxygen consumption by this individual in a minute is 235 cubic cm we now proceed to sample mixed Venus blood forcan responsible for developing the technique of direct sampling of blood from the right side of the heart in the summer of 1920 9 I conceived the idea that a thin flexible urar catheter could be inserted along the veins into the heart without harm in the austa Victoria Hospital at abas Val near Berlin I myself Expos exposed a vein at my left elbow and inserted this small catheter he then walked to the X-ray room and arranged a mirror in front of the screen so that he could follow the passage of the catheter into his own heart here is the actual radiograph taken at the time he felt nothing and there were no ill effects later on I passed the thicker catheter and on two occasions I tried to obtain pictures of my heart outlined by radioopaque injections during the following two years I catheterized my heart nine times through different veins without any unpleasant Sensations or other trouble this seemed adequate proof of the safety of the method Dr forsman was aged 25 when he conducted these experiments on himself in the process of which he used all the available superficial veins on both elbows and the seenus veins in both thighs now let us return to our demonstration catheterization of the heart must be carried out with all sterile precautions a sterilized catheter is taken from its storage tube a syringe is attached and the catheter is flushed through with saline solution it is then ready for insertion and is placed in an accessible position on the sterile instrument tray we uh proceed to prepare the arm of our patient for the insertion of the catheter the possibility of leaving a cardiac catheter in position for a sufficient length of time to make serial observation on the behavior of the heart was first realized by Dr Andre Kang and his colleagues who published their method in 1941 a local anesthetic in this case 2% procaine solution is injected into the skin and subcutaneous tissues over and around the median basilic vein at the bend of the elbow when the skin has been made insensitive a small transverse cut is made over the vein the incision being opened up with forceps the vein is picked up and two ligatures are passed around it the lower ligature is tied firmly while the upper is simply a loop by which about half an inch of vein is supported while an opening is made into it with scissors the catheter with saline dripping from its tip is then inserted with its concave curve facing medially once the catheter has entered the vein the wound is covered by sterile swabs and the catheter passed gently along until about 20 cm have entered the vein a saline monometer may now be connected to the catheter and a slow drip of heiz saline maintained for demonstration purposes the saline is stained with Evan's blue dye further manipulation of the catheter into the desired position is controlled by the X-ray screen as we get dark adapted the catheter comes into view in the upper part of the thorax it is now seen passing through the left innominate vein down through the superior vena until it enters the right atrium while it is in the atrium the saline shows relatively small pulsations at a level opposite the middle of the heart the catheter can now be manipulated through the tricuspid valve into the right ventricle as it enters the ventricle pulsations at once become more vigorous and Rise about 10 cm higher than the right atrial pressure with further manipulation the catheter tip will pass upwards into the pulmonary artery and in this case it enters the right branch in this position pressures rise a further 5 or 6 cm pulsations remaining vigorous for cardiac output estimations samples may be withdrawn from any of these three positions in the right heart right atrium right ventricle or pulmonary artery in taking samples the monometer connection is detached from the catheter and enough blood is withdrawn by a syringe to clear the catheter of salite A Change Is then made to a special sampling syringe containing liquid paraffin into which right heart blood is drawn the catheter is then cleared by washing through with saline and the monometer is reattached an indwelling needle and stilet have meantime been inserted through the anesthetized skin into the opposite brachial artery simultaneously with sampling of blood from the right heart an arterial sample is withdrawn the blood Rises into the syringe under arterial pressure and very little traction is required on the plunger each sample is ejected from the syringe into a bottle containing dry sodium oxalate and significant contact with the atmosphere is prevented by adding a layer of gas-free liquid paraffin the sample is is then stirred under the paraffin to ensure that the oxalate goes into solution and thus prevent clotting of the blood the samples are numbered and kept on Ice until analysis can take place these samples are analyzed in a hold in blood gas apparatus a measured sample of blood is placed in the bottle under an alkaline solution which will absorb any carbon dioxide after various precautions this blood is shaken and exposed to atmospheric air in the bottle during this shaking oxygen is absorbed and the absorption of oxygen is shown by a rise of the fluid level in a calibrated pet the amount of oxygen which is absorbed by the sample is thus measured directly any changes in temperature and pressure which take place during the procedure are automatically compensated by a control bottle exposed to identical conditions in the water bath in actual practice 3 cubic cm of alkaline borate solution are introduced into the holdan bottle the blood sample is again stirred to avoid errors resulting from sedimentation three cubic cm of blood are sucked into a stoppered ostwald pipet and the pipet is wiped clean at the tip the measured sample is gently introduced into the bottle where it lies in a layer under the covering alkaline solution a special bottle holder with an airtight screw cap is fitted and the whole device which is attached to a pivoted lever is put into position in the water bath where it is left to come to temperature equilibrium for a few minutes when temperature equilibrium is ensured by testing during temporary closure of the Taps of the apparatus the Taps are finally closed for the analysis the reading on the scale of the calibrated pipet is exactly .50 Cub CM the bottle is then shaken automatically by engaging a clutch and the absorption of oxygen by the sample is indicated by the rising fluid level in the measuring tube complete saturation with oxygen is indicated by censation of upward movement of this fluid column leveling tubes then adjust the pressure conditions to atmospheric and the final reading of 350 cubic cm indicat that this 3 Cub CM sample of right heart blood had absorbed 50-35 that is15 cubic cm of oxygen when an arterial sample has been similarly analyzed we can calculate the cardiac output the oxygen absorption in the spirometer tracing was 235 cubic cm per minute the oxygen absorbed by the right heart sample was 50 cubic cm per liter while the corresponding arterial sample took up 11 Cub cm per liter subtracting 11 from 50 we obtain the arterio Venus oxygen difference which is 39 cubic cm per liter therefore the cardiac output is 235 divided by 39 or approximately 6 L per minute as both oxygen uptake and arterovenous oxygen difference are measured at room temperature no significant error arises from omission of the usual temperature and pressure Corrections in addition to permitting measurement of cardiac output the catheter enables us to take Optical records of pressures within the heart one satisfactory recording device is called a strain gauge this consists essentially of a special type of wire which Alters its electrical resistance when stretched the stretching movements are of course grossly exaggerated in this illustrative diagram changes in resistance produced by pressure are used to deflect the galvanometer mirror using the wheatstone bridge principle these deflections are recorded on moving photographic paper the apparatus is mounted on a wheeled trolley The Strain gauge is contained in an oblong box with arrangement for fluid transmission of pressures from the heart a three-way tap permits easy switching to either the saline monometer or the strain gauge a similar strain gauge may be connected to the indwelling arterial needle in the other arm it is seen here with its connections mounted on a stand beside a pressure bottle containing sterile saline when everything is ready the switches on the recording trolley are turned on and the beams of light from the galvanometers may be observed through a tunnel while they record on moving photographic paper when the record in is complete the switches are turned off and the paper is removed from the camera for development studies May then be made of the pressure recordings here is a developed photographic record showing from Above Down tracings of respiration arterial pulse and the lowermost record is the recording of pressures from the right ventricle with the calibrated scale of pressures drawn alongside the peak of pressure in the right ventricle is the same as the systolic pressure in the pulmonary artery this record shows what happens when the catheter is drawn back from the pulmonary artery into the right ventricle the dotted line shows the identity of systolic pressure levels while the filling pressure of The ventricle is recorded at the end of Di nasly now here is a second method of estimating cardiac output if a measured quantity of dye is injected into the fluid flowing through a model system representing the right heart lungs and left heart the dye will be diluted as it is washed through by the flowing fluid and it will appear in the effluent first as a highly stained fluid from followed by a slowly fading tail in timed samples from an exit tube the concentration of dye will rise steeply at first and then the intensity of color will fall away an estimation of the concentration of the dye in each timed sample permits the construction of a Time concentration curve suppose capital I represents the amount of Dy injected from mathematical analysis of our curve we can estimate the mean concentration of the Dy C the amount of injected Dy divided by its mean concentration will be the volume of fluid passing through the system during the time T the volume flow per second will therefore be I over CT and the cardiac output per minute will be over CT multiplied by 60 in practice this method is applied in the following manner the amount of injected dye is carefully measured by weighing the syringe before and after the injection meantime the patient is made comfortable and his right arm is placed on a pillow his figma monometer cuff is wound around his left arm the position of the left arm is then fixed by strapping to a board passing under the mattress the heparinized serum tubes in which blood is to be collected are mounted on a drum which revolves at a uniform speed a piece of plastic tubing H cut to a suitable length passes through an angled glass Bend just above the collecting tubes the arm is prepared by swabbing with iodine and injecting a local anesthetic over the brachial artery simultaneously the right arm is prepared for the inen injection through a locally anesthetized area a needle is now inserted through the anesthetized skin into the brachial artery and the plastic tubing is connected to the hub of the needle the blood is at first directed into a large boiling tube a blank sample of Venus blood is withdrawn from the right arm the syringe containing the dye is then attached as the injection is made the time is marked by a signal on the revolving drum and the collection of samples of arterial blood is begun these samples are accurately timed by reference to the time marker scale when a suitable number of samples has been obtained as judged from experience of the type of case collection is stopped and the arterial needle closed by a stilet here are the centrifuged tubes the timing of each sample is marked on graph paper round round the drum the graph paper taken off the drum is marked for subsequent plotting of Dy concentrations against the time scale to obtain adequate amount for colorimetry the dyed plasma is mixed with equal quantities of saline the rising and falling concentrations of dye may be seen in the upper row of tubes two hematocrite tubes are seen on the right standard concentrations of dye made up in the same way are shown in the lower row it will be noted in the upper row that Dy appears sample reaches its maximum about the sixth tube and then the concentration Falls away more slowly while after the 11th tube there is a secondary rise in D concentration due to recirculation of blood containing the Dy Dy concentrations are red in a sensitive photoelectric Colorimeter and the reading noted the exact concentration of each sample is now plotted to make a Time concentration curve in this case the recirculation causes a secondary rise before the Baseline is reached if however the concentrations are plotted on a logarithmic scale the falling concentrations form a straight straight line which may be extended to the base line giving the curve representing one circulation only the formula for estimation of flow I over CT multiplied by 60 gives of course the volume of dyed plasma flowing through the system this has to be corrected by the hematocrit in order to give blood flow or cardiac output the output in this case was 6 L per minute suppose the flow through our model is 6 l a minute and the mean time spent in Passage through the system is 1/3 of a minute then at any moment the volume of fluid in the system will be 13 of 6 L that is 2 L in the time concentration curve a vertical line balancing the area to its right and left cuts the time scale at the mean circulation time Mt in man this permits a calculation of the volume of the circulatory system between the point of injection and the sight of arterial sampling the major part of this volume is contained in the heart and lungs and can be called the intrathoracic blood volume the two methods of estimating cardiac output are each subject to small uncontrollable errors charting simultaneous determinations by the direct F and the die methods a diagonal would represent complete agreement of the answers the actual results in a series of such paired determinations cluster closely around this diagonal indicating excellent agreement since the standard error of any single measurement is about 6% these new techniques have a special place in the study of difficult problems and patients in whom surgical operations on the heart are to be considered in the course of such investigations valuable knowledge on the behavior of the heart in health and disease is being built up further technical Improvement will take place in the future and we shall glean new for the better management of heart disorders