Earl H. Wood

Comparison of Simultaneously Recorded Central and Peripheral Arterial Pressure Pulses During Rest, Exercise and Tilted Position in Man

Central (aortic or subclavian), brachial, radial and femoral pressure pulses were recorded simultaneously in 12 healthy subjects during conditions of rest, exercise and 70 degree head-up tilt. Peripheral systolic pressure at rest uniformly exceeded the central systolic pressure generated by the same heartbeat. The average radial pulse pressure was 146, 146 and 165 per cent of central pulse pressure during rest, exercise and tilt while radial mean pressures were 94, 93 and 98 per cent of central mean pressures respectively. Summation of the incident pulse wave with reflected waves from the periphery and resonance effects in the peripheral arterial systems may produce these changes in pressure and contour.

Inotropic Effects of Electric Currents

I. Tension was recorded from a segment of a thin bundle of calf or sheep ventricular fibers in which the membrane potential could be changed electrically, using a sucrose-gap technique. After reversal of membrane potential and consequent contracture for 2 to 3 seconds, a positive inotropic effect 2 to 12 times that which occurred during paired-pulse stimulation was obtained. The decay of this potentiated state was slow in resting preparations (average half-life, 95 seconds), but was determined by the number of beats in driven preparations (about eight beats to return to control amplitude). Lengthening consecutive action potentials by subthreshold constant depolarizing currents or 5-mv shifts in the membrane potential by 50-msec current pulses during the plateau phase of successive action potentials caused positive inotropic effects, attaining a steady state in about eight beats. Reversing the polarity of such currents (hyperpolarization) caused negative inotropic effects with the same phase dependency as for depolarizing currents. These negative inotropic effects attained a steady state in six to eight beats. The first action potential after cessation of these currents was close to normal, whereas return to control tension required six to eight beats. The half-life of decay of these negative inotropic states at rest was similar to that of positive inotropic states. Decay of inotropic states in contracting preparations was phase dependent, occurring only during the rapid depolarization and plateau phases of the action potential. II. These and other strength-interval effects on cardiac contractility in a constant chemical and physical environment are consistent with two hypotheses. (1) The presystolic level of intracellular calcium bound to specific (rapid release) sites on the sarcoplasmic reticulum, the inner surfaces of the sarcolemma and T tubules, is a major determinant of the level of [Ca2+]1 attained during the initial phase of an action potential and hence the tension developed by mammalian cardiac muscle (that is, its inotropic state) at that particular instant. (2) The amount of intracellular calcium present at these sites at any instant after an action potential (that is, the moment-to-moment inotropic state of the muscle) is predetermined in the inverse direction of the intersystolic intervals of prior systoles and in the positive direction by the duration and magnitude of the plateau phases of prior action potentials and (for rest periods as long as 10 seconds) the elapsed time, in an exponentially decreasing fashion, since termination of the last absolute refractory period.

Applications of the Lagged Normal Density Curve as a Model for Arterial Dilution Curves

1. Indicator dilution curves (concentration versus time) were recorded from the femoral and dorsalis pedis arteries of normal men after injections of indocyanine green into the superior vena cava or thoracic aorta. A four-parameter mathematical model, the lagged normal density curve, adequately described the form of the portion of these curves representing indicator passing by the sampling site for the first time. 2. The curves were observed to be of constant shape, the spread of the curve being approximately linearly related to the mean transit time t¯. The spread was dependent on the injection site; dispersion was shown to be greatest in the central circulation, less in the aorta, and still less in the arteries of the leg. For the latter segment, the mean transit time t¯. The spread was dependent 0.3 t¯, the square root of the variance was 0.18 t¯, and the parameters of the lagged normal density curve, σ and τ, were 0.09 t¯ and 0.16 t¯, respectively. 3. The linear relationships between parameters of the recorded curves and the mean transit times indicate that the effect of rate of flow, over a range from resting values to four to six times above resting values, has almost no influence on the dispersion. This suggests that the flow characteristics are essentially unchanged over this range. Such linear relationships always occur with laminar flow but cannot prove its existence because turbulent flow can also produce this result. The similarity of the linear relationships at low flow rates to those at high flow rates, where turbulence almost certainly is present, suggests that arterial flow is usually turbulent. Turbulence may be expected at relatively low flow rates in nonhomogeneous fluids driven by a pulsatile head of pressure through elastic, branched, tapering, curved tubes.

The Presence of Venoarterial Shunts in Patients with Interatrial Communications

Evidence is presented which indicates that shunting of small amounts of blood from right to left occurs frequently through interatrial communications. Such right-to-left shunts are of small magnitude in the usual case of atrial septal defect, but it appears that of the fractions of blood shunted, a greater proportion has originated from the inferior vena cava than from the superior vena cava.

Continuous determination of beat to beat stroke volume from aortic pressure pulses in the dog.

Present methods for measurement of stroke volume from die aortic pressure pulse are not suitable for beat-to-beat determinations during non-steady state conditions because these methods assume that each systolic ejection is equal to the peripheral runoff during the same beat We bare tested a new method which allows determination of an aortic pressure-volume conversion factor over a wide range of pressures during transient changes in stroke volume and infusions of vasoactive drugs in 6 dogs with chronically implanted aortic electromagnetic flowmeters. Each aortic diastolic pressure decay is approximated by an exponential the time constant of which is used to calculate the pressure loss during systole due to blood flow into the periphery. The total increment in aortic pressure due to systolic ejection, if there were no flow from the aorta during systole, then is calculated. The total systolic increment (Delta;Psv) is assumed to describe the pressure-volume characteristics during systole and is related to stroke volume by a constant multiplier that is derived from the indicator-dilution measurements of cardiac out put. The values for beat-to-beat variations that were determined by use of the aortic electromagnetic flowmeter and by this aortic pres sure pulse method were found to be within the range of measurement errors of stroke volume determined from individual aortic electro magnetic flow pulses.

Three-dimensional visualization of the intact thorax and contents: A technique for cross-sectional reconstruction from multiplanar X-ray views☆

Abstract A method is described for obtaining the three-dimensional spatial distribution of roentgen opacity within the intact canine thorax. Video recordings of multiple roentgenographic projections are digitized during rotation of the dog in the X-ray field to provide the data required for the reconstruction of a sequence of parallel spatially adjacent cross-sectional images of the thorax or heart over their entire anatomic extent at 1 60 second intervals in time. The accuracy of the technique is demonstrated with test objects and excised canine hearts, and the capability for high temporal resolution is illustrated by the cross-sectional reconstruction of a metabolically supported, isolated working canine left ventricle at different phases of the cardiac cycle. These data, along with simultaneous measurement of intracardiac and transmural pressures, provide the determinants required for estimations of dynamic myocardial length/tension relationships that are necessary for the quantitative assessment of cardiac contractility and reserve.

Intrapericardial, Intrapleural, and Intracardiac Pressures during Acute Heart Failure in Dogs Studied without Thoracotomy

Pressures at multiple sites in the thorax of supine anesthetized dogs were recorded simultaneously with fluid-filled catheters inserted percutaneously. Pleural and pericardial pressures were corrected to the level of their respective recording catheter tips as determined by roentgenograms. Intracardiac pressures were referred to the midthoracic coronal plane or to the vertical level of the pericardial catheter tip. Pericardial pressures at end-expiration averaged −5.0 cm H2O (range 0 to − 13) and varied with the vertical position of the catheter tip, becoming less negative as the height above the midthoracic coronal plane diminished. Acute right heart failure was produced by partial obstruction of the pulmonary artery by a catheter-tip balloon. Although mean right atrial pressure increased by an average of 26 cm H2O, consistent increases in pericardial pressure did not occur. Similarly, during acute obstruction to left ventricular outflow by inflation of a balloon within the thoracic aorta, left atrial end-diastolic pressure increased by an average of 14.5 cm H2O, but no consistent increase in pericardial pressure was recorded. No systematic changes in pleural pressure were detected in either case. Thus there was no evidence of pericardial restriction of cardiac dilatation during acute heart failure under these experimental conditions.

Indicator-Dilution Curves in Acyanotic Congenital Heart Disease

Dye dilution and cardiac catheterization technics were used to study 36 patients with a central left-to-right shunt due to patent ductus arteriosus, atrial septal defect or ventricular septal defect. The configuration of dilution curves following injection of dye into an antecubital vein was similar in all instances. Principal abnormalities of the curve were a prolongation of its disappearance slope and a relative reduction in the peak concentration of dye. Quantitatively expressed, these abnormalities could be correlated with the magnitude of the left-to-right shunt. Curves of normal contour were observed following surgical closure of the ductus arteriosus, and in patients with isolated pulmonary stenosis.

Diagnostic applications of indicator-dilution technics in congenital heart disease.

In summarizing the diagnostic value of the indicator-dilution technics in the study and investigation of congenital heart disease, perhaps a simple listing of the advantages and disadvantages of the technics will suffice. The advantages are as follows: 1. The technics have a high degree of safety. In the more than 3000 cardiac patients in whom they have been utilized there have been no deaths and little or no morbidity. 2. The sensitivity of the technics for the detection and localization of right-to-left and left-to-right shunts is much superior to that of the conventional blood-gas methods. 3. Quantitative determinations of systemic and pulmonary blood flow and intrathoracic shunts by indicator-dilution methods can be made simultaneously over periods of less than 1 minute; when indicator dyes are used, these technics do not require manometrie analyses, accessory respiratory exchange studies, or active cooperation of the patient; and they are independent of foreign (anesthetic) gases in the blood. 4. The technics are versatile and can be extremely useful either for the detection and diagnosis of minimal, relatively simple defects or for the elucidation of the extremely complex types of congenital malformations. 5. The information obtained is of both a qualitative and a quantitative nature; that is, the nature and location of defects can be determined and, in addition, the magnitude and direction of flow through the defects in question as well as the levels of systemic and pulmonary blood flows can be estimated. The disadvantages of the technics are as follows: 1. Rather complicated and sensitive recording equipment is essential. 2. Considerable technical skill is required of the persons carrying out the procedure in the placement of the necessary needles and catheters and in the proper selection of the multiple possible injection and sampling sites reached by these instruments in order to obtain the information needed to establish the diagnosis in question. 3. Correct interpretation of the diagnostic significance of the dilution curves obtained requires careful study and considerable experience by the person responsible for this phase of the investigation. In other words, these technics entail relatively little discomfort and little danger for the patient, but require good equipment and, more important, considerable time, effort and skill on the part of the investigator and his assistants in order to obtain highly successful results.

Biplane roentgen videometric system for dynamic (60-sec) studies of the shape and size of circulatory structures, particularly the left ventricle.

An operator interactive video system for the measurement of roentgen angiographically outlined structures is described. Left ventricular volume and three-dimensional shapes are calculated from up to 200 pairs of diameters measured from ventriculograms at the rate of 60 pairs of biplane images per second. The accuracy and reproducibility of volumes calculated by the system were established by analysis of roentgenograms of inanimate objects of known volume and by comparison of left ventricular stroke volumes calculated by the system with the stroke volumes calculated by indicator-dilution technique and aortic root electromagnetic flowmeter. Computer-generated display of the large amounts of data obtained by the videometry system is described.