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Biomedical subjects

L L Huntsman

Publications and source records attributed to L L Huntsman.

At least 19 recordsLinked to original sources
PubMed1986

Determination of the stenotic aortic valve area in adults using Doppler echocardiography.

The severity of aortic stenosis was evaluated by Doppler echocardiography in 48 adults (mean age 67 years) undergoing cardiac catheterization. Maximal Doppler systolic gradient correlated with peak to peak pressure gradient (r = 0.79, y = 0.63x + 25.2 mm Hg) and mean Doppler gradient correlated with mean pressure gradient (r = 0.77, y = 0.59x + 10.0 mm Hg) by manometry. The transvalvular pressure gradient is flow dependent, however, and associated left ventricular dysfunction was common in our patients (33%). Thus, of the 32 patients with an aortic valve area less than or equal to 1.0 cm2 at catheterization, 6 (19%) had a peak Doppler gradient less than 50 mm Hg. To take into account the influence of volume flow, aortic valve area was calculated as stroke volume, measured simultaneously by thermodilution, divided by the Doppler systolic velocity integral in the aortic jet. Aortic valve areas calculated by this method were compared with results at catheterization in the total group (r = 0.71). Significant aortic insufficiency was present in 71% of the population. In the subgroup without significant coexisting aortic insufficiency, closer agreement of valve area with catheterization was noted (n = 14, r = 0.91, y = 0.83x + 0.24 cm2). Transaortic stroke volume can be determined noninvasively by Doppler echocardiographic measures in the left ventricular outflow tract, just proximal to the stenotic valve. Aortic valve area can then be calculated as left ventricular outflow tract cross-sectional area times the systolic velocity integral of outflow tract flow, divided by the systolic velocity integral in the aortic jet.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1986

Cardiovascular response to rapid infusion of lactated Ringer's.

Cardiovascular response to rapid infusion of lactated Ringer's was investigated in 5 adult dogs (average body weight = 21.1 kg) under 1% halothane anesthesia. Following implantation of aortic flow probe and left atrial line, the chest was closed and splenectomy was performed prior to the experiment. Warmed lactated Ringer's was administered at five different infusion rates (2.5, 5, 10, 15 and 20 ml/kg/min in random sequence) to each dog until left atrial pressure (LAP) reached 20 mmHg or a maximum of 50 ml/kg had been infused. Subsequent infusions were done after stroke volume (SV) spontaneously returned to the control level. Cardiac output (CO), SV, heart rate (HR), mean arterial pressure (MAP), LAP and central venous pressure (CVP) were monitored simultaneously during infusions. HR was stable during infusions, whereas MAP increased by 39% of control. Response of LAP to volume infused was nearly linear at fast infusion rates (10, 15 and 20 ml/kg/min). Response of LAP to slow infusion rates (2.5 and 5 ml/kg/min) was curvilinear (decelerating curve). The relationship between CVP and volume infused was similar to LAP vs. volume infused. Ventricular function curves (SV, CO and stroke work vs. LAP) were also influenced by the rate of infusion with steeper curves at slow infusion rates than curves derived from fast infusion rates. However, initial changes in SV and CO curves were not significantly affected by the rate of infusion. We conclude that the cardiovascular response to rapid infusion of lactated Ringer's is rate dependent but initial changes in SV and CO curves are not significantly affected at infusion rates of 2.5, 5, 10, 15 or 20 ml/kg/min.

Animals↗
PubMed1984

The dependence of force and velocity on calcium and length in cardiac muscle segments.

The segment length (SL) dependence of force (F) and light load shortening velocity (VL) was determined for central segments of ferret papillary muscles at different extracellular calcium concentrations. Muscles were maintained at 27 degrees C in a physiological solution which contained in mM: NaCl 140; KCl 5.0; MgSO4 1.0; NaH2PO4 1.0; acetate 20; the pH was 7.4. Calcium concentrations were 1.125, 2.25, 4.5 and 9.0 mM. Total force-segment length relations were determined from both muscle length isometric ( auxotonic ) and segment isometric contractions, and were found to be the same for each contraction mode. The peak force generated at a particular segment length was independent of both the amount of shortening during a contraction and the initial SL. Increasing extracellular Ca2+ shifted the F-SL relation toward greater force and the SL axis intercept toward shorter SL. Maximum peak twitch tension was achieved in 9.0 mM Ca2+. Calcium variations also changed the shape of the total F-SL relation from linear in high Ca2+, to concave in low Ca2+. In order to estimate the active F-SL relations, corrections were made for passive force by two methods. The first assumed that passive force was related to SL, and yielded F-SL relations which were nearly identical to those found for total force. This similarity included the curvature changes observed in different Ca2+ concentrations, a finding which is consistent with the hypothesis that length dependent activation is the cause of force decline at short SL. The second method assumed passive force to be related to muscle length, an approach which would be appropriate if, for example, a connective tissue sheath on the muscle dominated passive behavior. These F-SL curves displayed a plateau above 90% SLmax and appeared to be vertically shifted versions of each other. Such characteristics are consistent with the possible role of an internal load in causing the decline of force at short SL. VL-SL relations were obtained from load clamps to 1 mM, imposed at various times during a segment isometric twitch. The results indicate that 1) VL declines linearly with SL below 90% SLmax and 2) VL-SL relations are shifted to higher velocity and shorter SL axis intercepts by increasing Ca2+. The slopes of the VL-SL relations obtained in different calciums are similar. Although an internal load could explain the calcium dependence of VL, it would not explain the similarity of the slopes of the VL-SL relations found in different calciums .

Animals↗
PubMed1983

Force-length relations in cardiac muscle segments.

Using a new technique that measures the length of a segment in the central region of isolated papillaries, we have determined the force-segment length relation for ferret papillary muscles at 27 degrees C. The muscles contracted under muscle length isometric (auxotonic) and segment isometric conditions in physiological solutions containing 9.0, 4.5, 2.25, and 1.125 mM Ca2+. Force-segment length relations obtained from auxotonic and segment isometric contractions were identical in a given Ca2+ concentration. Calcium variations, however, changed the position, shape, and segment length intercept of the force-segment length relation. Force, at a given segment length, increased with increasing Ca2+ up to 9.0 mM Ca2+. The force-segment length relation changed shape from linear, in 4.5 mM Ca2+, to concave in 1.125 mM Ca2+. The segment length intercept was found by extrapolation to be 68, 69, and 74% SLmax in 4.5, 2.25, and 1.125 mM Ca2+, respectively. Two passive force corrections were used to calculate the developed force-segment length relations. Assuming passive force to be related primarily to segment length yields curves that change shape with Ca2+ concentration, suggesting length-dependent activation. On the other hand, assuming passive force to be related to muscle length results in curves for different Ca2+ concentrations that are nearly vertically shifted versions of each other, suggesting the influence of internal loads.

Animals↗
PubMed1983

Myocardial segment velocity at a low load: time, length, and calcium dependence.

The length and time dependence of shortening velocity (VL) at a very light load (1 mN) was determined for central segments of ferret papillary muscle at 27 degrees C. A recently developed technique that measures the cross-sectional area of the chosen segment was used to assess segment length. Segment length (SL) or force could be used as a feedback control signal. VL was determined by releasing the muscle to a 1-mN load (less than or equal to 3% maximum force) at various times during a segment isometric twitch. Segment isometric twitches were typically performed at 95-98% SLmax, SLmax being the longest segment length attainable in the preparation. VL, as a function of time and SL, was determined from SL shortening during the load clamp. Muscle responses were sampled, stored, and analyzed with an on-line digital computer. The data indicate that 1) at a given SL, VL declines from 20 to 50% of its peak value by the time of peak force production, 2) VL declines linearly with SL below 90% SLmax in 1.125, 2.25, and 4.5 mM extracellular Ca2+, 3) VL exhibits a dependence on extracellular Ca2+, having peak values at 90% SLmax of 3.32 +/- 0.33, 2.66 +/- 0.17, and 1.89 +/- 0.17 SL/s in 4.5, 2.25, and 1.125 mM extracellular Ca2+, respectively.

Animals↗
PubMed1983

Onset of relaxation in cardiac muscle segments.

The onset of relaxation has been studied in undamaged central segments of isolated ferret papillary muscles at 27 degrees C, 12 beats/min. A technique that provides a signal proportional to the length of a chosen segment was used to assess segment velocity and length. Feedback control was employed to obtain segment isometric contractions. At a variety of times during segment isometric twitches, rapid load clamps were imposed using a range of loads from resting force to greater than half peak developed force. For the purposes of this study, the onset of relaxation was defined as occurring when active segment shortening ceased and elongation began (i.e., Vseg = 0). Early load clamps to low loads resulted in V = 0 at comparatively short segment lengths and early times. Later load clamps caused zero velocity to occur at longer segment lengths and later times. The V = 0 points in fact formed a line in the segment length-time plane. Contractions clamped to higher loads exhibited reduced shortening and a prolonged time course so that the V = 0 points showed the same dependence on length and time. Remarkably, all the variations of load-clamp load, time, and initial length yielded V = 0 points that were intermixed along a single line. Increasing or decreasing extracellular Ca2+ caused the V equal to O points to shift to later times and shorter segment lengths or earlier times and longer segment lengths, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1983

Noninvasive Doppler determination of cardiac output in man. Clinical validation.

A noninvasive technique for assessing cardiac output (CO) was evaluated by comparing it with thermodilution determinations in patients in the intensive care unit. The new method uses pulsed ultrasound to measure aortic diameter and continuous-wave Doppler ultrasound to obtain aortic blood velocity. An initial study evaluating just the velocity measurement showed that changes of the Doppler index of output (DI) correlated well with those of thermodilution cardiac output (TDCO). Linear regression analysis yielded delta DI = 0.87 delta TDCO + 0.14 (r = 0.83, n = 95). Using a university research instrument these measurements were possible in 54 of 60 patients (90%). A second study using a prototype commercial device incorporated the diameter measurement. Ultrasonic cardiac output (UCO), calculated as the time integral of velocity multiplied by the aortic area, was compared to TDCO. The data, obtained from 45 of 53 patients (85%), are described by the linear regression UCO = 0.95TDCO + 0.38 (r = 0.94, n = 110) over a range of 2-11 l/min. Patients with aortic stenosis, aortic insufficiency or a prosthetic valve have been excluded from the second study due to conditions likely to violate the assumptions upon which the calculation of absolute cardiac output is based. These results indicate that accurate CO can be measured by noninvasive ultrasound in most patients. The technique may be useful for extended CO monitoring in acute care patients and for CO assessment in many other types of patients undergoing diagnostic studies and therapeutic interventions.

Aorta↗
PubMed1979

Auxotonic contractions in cardiac muscle segments.

The dynamics of segment shortening have been measured in the central regions of isolated papillary muscles during muscle isometric and after-loaded isotonic contractions. Segment lengths are inferred from muscle cross-sectional area using an assumption that the segments remain isovolumic. Area is assessed with a magnetic induction technique. Infused microspheres have been used as visual markers to corroborate the segment length measurement. The results confirm the existence of major segmental shortening during muscle isometric conditions. However, the time course of shortening is not the same as that of force development. Rather, the segments remain shortened until after force has fallen significantly from its peak value. This behavior appears in the force-segment length plane as counterclockwise loops. The relationship of peak force to segment length has been determined and found to depend on the mechanical conditions under which the muscle is equilibrated. These results demonstrate the utility of the new technique and indicate central segment behavior that is substantially different from that observed for the whole muscle.

Animals↗
PubMed1977

Nonuniform contraction in the isolated cat papillary muscle.

Microspheres infused into the coronary microcirculation were used as markers to define segments within isolated cat papillary muscles. Video recording and analysis provided measurements of the variations of segment lengths as the muscles contracted at lengths of 76-100% Lmax. In all muscles, segments in the center region were found to shorten during muscle isometric contraction while those in the end regions lengthened. Central shortening was typically 10-15%. In the passive state, segment lengths varied directly with muscle length over a broad range characterized by low force. Segments in the center region, however, displayed an abrupt transition to high stiffness at a certain length while end regions continued to stretch. Force-length relationships obtained for the presumably healthy center segment are significantly different from those obtained for the whole muscle. These results suggest that there may be major difficulties with the interpretation of mechanical measurements on papillary muscles unless contractile inhomogeneity is eliminated or taken into account.

Animals↗
PubMed1977

Estimation of stroke volume changes by ultrasonic doppler.

The purpose of this study was to conduct a controlled evaluation of the continuous-wave Doppler technique for the estimation of stroke volume changes. Six anesthetized dogs were studied. Aortic blood velocity was recorded from the suprasternal notch by a special continuous-wave Doppler unit. Cardiac output was varied by fluid infusion and exsanguination, and over 300 simultaneous records of aortic blood velocity and thermodilution cardiac output were taken. Average stroke volume and average systolic velocity integral (SVI), the area under the Doppler velocity curve were calculated. The relationship of SVI to stroke volume was evaluated for each animal using linear regression. Average results were: correlation coefficient 0.95 +/- 0.04 SD; y-intercept 0.38 +/- 0.14 cm(SD); standare error of fit 0.29 +/- 0.03 cm (SD). These data show that the systolic integral of aortic blood velocity was essentially directly proportional to stroke volume, even over a six-fold range. Thus, this technique will provide an accurate non-invasive estimate of changes in stroke volume.

Animals↗
PubMed1977

Length-dependent calcium inotropism in cat papillary muscle.

We studied changes in the relationship of isometric developed force to muscle length when extracellular calcium concentration was altered in isolated cat papillary muscles. In two series of experiments at temperatures of 30 degrees C and 32 degrees C, and rates of 12 and 30 beats/min, 21 muscles were exposed to calcium concentrations of 1.125, 2.25 and 4.5 mM. Muscle lengths were varied between 80% and 100% of the length at which maximum developed force occurred (Lmax). Peak developed force and the time from stimulus to peak were measured. The data indicate that force is not altered proportionately at all lengths when calcium concentration is changed. Rather, we found that a substantially greater modification of force occurs at short lengths than at long lengths. Similarly, the time to peak force increases with length at a rate which is more than 4 times greater at the low calcium concentration than it is at the high concentration. Small but consistent shifts of Lmax also are seen. We observed that Lmax is longer when inotropic changes reduce force and shorter when force is increased. These results indicate that the inotropic effect of extracellular calcium concentration changes is dependent on muscle length.

Animals↗
PubMed1975

Trancutaneous determination of aortic blood-flow velocities in man.

A transcutaneous ultrasonic Doppler technique for measurement of aortic blood-flow velocities has been developed and compared to more established techniques in order to evaluate its potential usefulness. It is possible by this method to quantitate blood velocity in both the ascending aorta and the aortic arch with ease and reliability. Ultrasonic access to the aorta from the suprasternal notch proved adequate in more than 90 per cent of the normal subjects examined. If further clinical trials prove as encouraging, this technique may be of significant value for patient monitoring and cardiac diagnosis.

Aorta↗
PubMed1975

Correlation of peak aortic and carotid flow acceleration during coronary occlusion in conscious baboons.

1. Peak blood flow acceleration measured in the common carotid artery was compared with peak flow acceleration measured in the ascending aorta of three baboons. 2. The response to occlusion for 60s of the circumflex branch or the anterior descending branch of the left coronary artery was investigated. 3. Both accelerations decreased approximately to the same extent. Peak aortic flow velocity, stroke volume and cardiac output also decreased but to a smaller extent. 4. It is concluded that peak aortic flow acceleration is a sensitive index of myocardial function during acute coronary occlusion in conscious primates and that peak carotid flow acceleration is an indirect measure of myocardial performance under the same conditions.

Animals↗