Assessment of atrial contribution to left ventricular filling during cold pressor test by M-mode echocardiography in patients with coronary artery disease

To determine whether temporarily increased afterload causes changes in left ventricular (LV) diastolic properties, we examined 19 patients with coronary artery disease (CAD) and 14 healthy subjects by M-mode echocardiography during immersion of the left hand in ice water. The M-mode echocardiograms were digitized to assess the percentage of atrial contribution (%AC) to LV filling as a marker of diastolic properties. Six patients and 5 controls had to be excluded owing to inability to clearly define the endocardium in the left ventricle throughout the entire heart cycle. In the control situation, the %AC did not differ significantly between the two groups. During the cold pressor test, the mean %AC at peak systolic and peak diastolic pressures was significantly higher in the CAD group than in the control group (p less than 0.05). Thus, by using M-mode echocardiography during the cold pressor test it is possible to document an increased atrial contribution to LV filling in patients with CAD. It is suggested that the mechanism is increased myocardial stiffness evoked by ischaemia with a resultant increased role of atrial contraction.     

Excitation and contraction in atrial and ventricular myocardium of the guinea-pig

Several parameters of excitation-contraction coupling were compared in two types of muscle, using thin strips from the left atria and papillary muscles from the right ventricles of guinea-pigs. (1) The duration of the action potential and twitch is much longer in ventricular than in atrial muscle. (2) Mechanical restitution can usually be described by a monoexponential function in ventricular and biexponential function in atrial muscle. (3) Post-extrasystolic potentiation, when related to the steady state force, is greater in ventricular muscle. (4) When priming with paired-pulse stimulation, mechanical restitution can be studied after the short interval and after the long interval. In atrial muscle, mechanical restitution is very similar after the short and long intervals but in ventricular muscle they are different in size. (5) Ryanodine (10^-6 M) can decrease the steady state force to about 10% of control in atrial but only to about 35% in ventricular muscle. Ryanodine (10^-8 M) causes the slow phase of restitution in atrial muscle to disappear but in ventricular muscle only increases the rate of mechanical restitution. (6) Ca-antagonists (Cd²⁺ 0.2 mM) can decrease the steady state force to zero in atrial and ventricular muscle. Ca-antagonists, in low concentrations (Cd²⁺ 0.01 mM), mainly affected the fast phase of mechanical restitution. (7) The recirculation fraction of calcium was about 0.64 in atrial and 0.27 in ventricular muscle. The findings are discussed in the light of known ultrastructural differences between atrial and ventricular myocardium.     

Model analysis to investigate the contribution of ground substance to ligament stiffening

In our previous study, tensile tests on ligament and fascicle from swine hind limbs revealed that the tangent modulus in the stress–strain curve of the ligaments, i.e. stiffness, was higher than that of the fascicles. Since the ligament is a composite of fascicles and ground substance whose stiffness is almost negligible, our finding was contrary to a current notion about the strength of materials that a composite can never be stronger than its constituent elements. To answer this puzzling question, we hypothesized that the fascicles’ stiffness is not uniform along the longitudinal axis, and that because the weaker portions are mainly elongated during tensile tests, their stiffness is underestimated. During tensile testing on ligament, the weaker portions of fascicles are reinforced by the stronger portions of the adjoining fascicles. In this study, to confirm that our hypothesis hold, we performed tensile tests on fascicles, thereby finding that fascicles do not elongate uniformly. Next, we developed a continuous elastic model, by taking into account a fascicle's kinematic non-uniformity along its longitudinal direction and mechanical interaction between fascicles and the ground substance. Simulation results demonstrated the inverse characteristics between ligaments and fascicles. Furthermore, the results helped us to understand ligament's failure mechanism.     

Numerical modeling of ventricular filling

The fluid dynamical and physiological assumptions underlying general mathematical modeling of ventricular filling are outlined. We then describe the use of a lumped parameter model and computer simulation to study how the early transmitral velocity profile is affected by isolated changes in ventricular compliance and relaxation, atrial pressure and compliance, and valvular morphology. We show that the transmitral velocity is fundamentally affected by twophysical determinants: the transmitral pressure difference and the net compliance of the atrium and the ventricle. These physical determinants in turn are specified by the variousphysiologic parameters of interest. This approach has shown that peak velocity is most strongly affected by initial left atrial pressure, lowered somewhat by prolonged relaxation, low atrial and ventricular compliance, and systolic dysfunction. Peak acceleration is directly affected by atrial pressure and inversely affected by the time constant of isovolumic relaxation, with little influence of compliance, whereas the deceleration rate is almost purely given by mitral valve area divided by instantaneous atrioventricular compliance at the end of the rapid filling wave.     

持续性心房颤动心室律的昼夜节律变化

目的从持续性心房颤动心电图的心室律变化动力学的角度,探讨心房颤动的心电信号中心室律昼夜节律的变化规律,为心房颤动的治疗提供有意义的思路。方法用时域、近似熵和分形分析对31份24h的心房颤动Holter心电图和18份正常人的24h Holter心电图的心室律及其昼夜节律进行了分析。结果心房颤动患者的心室率的SDA、RMSSD和近似熵的24h均值显著地高于正常组,但是都表现出冥想的类似的昼夜节律。心房颤动的心室率的分形指数显著低于正常人,而表现出近似白噪的动力学特性,并且失去了昼夜节律。结论心房颤动的心室律在时域和近似熵上具有和正常人类似的昼夜节律,而其分形特性则不具有正常人所具有的昼夜节律。     

Response of left ventricular diastolic filling to graded exercise relative to the lactate threshold

Summary During incremental exercise, the left ventricular ejection fraction increases up to the intensity of the anaerobic threshold and tends to level off at higher exercise intensities. Since there is a correlation between the response of peak filling rate and ejection fraction to exercise, this study was conducted to determine whether the response of left ventricular diastolic function is similar to the response of systolic function relative to lactate threshold. Twelve healthy men performed two exercise tests on a cycle ergometer. In the first test, lactate threshold and maximal power output were determined. In the second exercise test, gated radionuclide ventriculography was performed at rest, at the lactate threshold intensity, and at peak exercise to measure ejection fraction and peak filling rate. Ejection fraction increased significantly from rest [mean (SD): 62 (5)%] to lactate threshold [76 (7) %] and did not change significantly from lactate threshold to peak exercise [77 (7)%]. Likewise, peak filling rate (normalized for stroke counts) increased from resting [6.1 (0.9)V _s · s^–1] to lactate threshold [9.4 (1.8)V _s · s^–1] and did not change significantly from lactate threshold to peak exercise [9.6 (2.9)V _s · s^–1]. There was no correlation between the change in peak filling rate and the change in ejection fraction from rest to lactate threshold. Thus, during incremental exercise, left ventricular diastolic function responds qualitatively similar to systolic function.     

Barium inhibition of the tonic component of frog atrial contraction

Barium ions are able to substitute for calcium as charge carriers for the slow inward current of cardiac membrane. The effects of such a substitution on the mechanical activity of voltage-clamped frog atrial trabeculae have been investigated using the double mannitol gap device coupled with a mechanoelectric transducer. In the presence of barium, the tonic phase of the contraction is suppressed and the remaining contraction is correlated to the influx of barium ions via the slow inward channel. Since a Na–Ca exchange regulates the tonic contraction, the present results suggest that barium ions cannot substitute for calcium in this mechanism.     

Left ventricular function after long-term treatment with ventricular inhibited compared to atrial triggered ventricular pacing

The long-term effect of ventricular inhibited (VVI) and atrial triggered ventricular (VAT) pacing on cardiac performance was determined by cardiac catheterization at rest and during exercise in 9 patients with high-degree AV block. Cardiac output (Q) increased at rest by 22% during VAT vs. VVI (5.5 vs. 4.5 l/min, p less than 0.01). An increased stroke volume constituted the difference (75 vs. 63 ml, p less than 0.05). Mean working capacity increased by 12% in the supine position with VAT vs. VVI (p less than 0.05). During exercise Q increased by 40% with VAT vs. VVI (10.2 vs. 7.3 l/min, p less than 0.01) due to an increase in heart rate. Most pressures were largely unchanged. Stroke work and atrial rate decreased during VAT vs. VVI, which may indicate a lower sympathetic activity with VAT vs. VVI. The study demonstrated that hemodynamics advantages of VAT are still obtainable after several years of VVI pacing.     

Independent regulation of atrial coronary blood flow by atrial contraction rate in conscious dogs

Summary The effects of separate increases in atrial and ventricular contraction rates on the distribution of coronary flow within the heart were determined in conscious dogs with chronic heart block. Atrial tachycardia increased atrial blood flow and did not change ventricular blood flow. Ventricular tachycardia increased ventricular blood flow but not atrial blood flow. The results are consistent with the concept of local regulation of coronary perfusion by local myocardial energy turnover. The results also call attention to a potential adverse impact of atrial tachyarrhythmia in patients with underlying coronary ischemia.     

An attempt to quantitate the contribution of antidiuretic hormone to the diuresis of left atrial distension in conscious dogs

In order to quantitate the contribution of the antidiuretic hormone (ADH) to the diuresis of left atrial distension 52 experiments have been performed in 12 conscious, chronically instrumented beagle dogs. Left atrial pressure was increased by a reversible mitral stenosis by about 10 cm H₂O (1.0 kPa) for 60 min. Plasma ADH concentration (range between 1.3 and 6.0 pg·ml^?1) (radioimmunoassay) decreased in every experiment, the average decrease being about 50%. An i. v. infusion of vasopressin (0.05 mU ·min^?1·kg^?1) abolished the diuretic effect of left atrial distension or decreased the urine volume below control values; natriuresis was not affected. The magnitude of the vasopressin effect was dependent on the concurrent sodium excretion: when sodium excretion was low during left atrial distension, vasopressin was more effective in reducing the urine volume than when sodium excretion was high. It is concluded that the diuresis of left atrial distension is mediated (a) by a suppression of ADH and (b) by factors controlling sodium excretion, the contribution of these two mechanisms being dependent on the concurrent sodium excretion.     

Videodensitometric determination of left ventricular ejection and filling characteristics

Left ventricular ejection fraction and values proportional to mitral and aortic flow were measured throughout the cardiac cycle by videodensitometric analysis of left ventricular roentgen angiograms. The technique was used simultaneously with measurement of the dimensions of the ventricle to provide absolute values for comparison. Sensitivity of the technique was tested by the ability to detect the atrial contribution to mitral flow and left ventricular chamber volume. Roentgen videodensitometry has the advantages that much information can be extracted from videoangiograms in real-time (on-line, if need be), it requires relatively low concentration of contrast medium, and it is self-calibrating.     

Sarcomere length during contraction of isolated guinea-pig ventricular myocytes

 An improved method was developed for measuring sarcomere length (SML) during twitch contractions of single cardiac ventricular myocytes, using a charge-coupled photodiode array self-scanning at a rate of 1.5 ms/element. The average resting SML of 111 cells was 1.88±0.04 μm (mean ±SD). When contractions were triggered by action potentials under perforated-patch conditions, the time course of SML shortening closely followed changes in cell length. A large variation was observed in contraction time course between myocytes, some cells having a phasic component with a duration at 50% shortening (full-width at half-maximum; FWHM) of approximately 40 ms, while others shortened more slowly (FWHM of phasic component @100 ms). FWHM was highly correlated with relaxation half-time, but with neither action potential duration nor resting SML. The kinetics of slowly contracting cells could not be converted to the rapid type by using conditioning trains or applying isoprenaline. The steady-state SML/pCa relation in ventricular myocytes was measured by applying solutions of various pCa immediately after localized punctures of the surface membrane using a focal laser beam. The Hill coefficient, n _H, was @4–5 and K _1/2@400–500 nM, but there was no evidence of two populations of cells with different Ca²⁺ sensitivities. Received: 28 September 1998 / Received after revision: 11 December 1998 / Accepted: 14 December 1998     

Application of static muscular contraction to the analysis of the mechanism of vomiting

Summary Static muscular work which consisted in holding a load on the back inhibited the act of vomiting which was induced by apomorphine or by stimulation of the stomach receptors by a solution of potassium chloride. The act of vomiting was inhibited by placing the dog under conditions in which the experiment was formerly conducted (following several experiments with the load, i.e., by way of conditioned reflex). Various components of the act of vomiting were inhibited differently. The mildest depression was found in the activity of somatic musc les (abdominal press). The autonomic component of the act of vomiting (secretion of saliva, dyspnea, stomach contraction, increased rate of cardiac contractions) was only slightly inhibited. With increase of inhibition (anesthesia) the reactions of blood pressure and respiration were found to be the most stable components out of the whole autonomic complex of vomiting reactions. A definite sequence of introduction of various components of the act of vomiting was established in experiments without the load. Several new suggestions are made concerning the regulation of the act of vomiting.Presented by V. N. Chernigovskii, Active Member Acad. Med. Sci. USSR     

Separate contribution of ventricular · pumping and load impedance on ventricular power output

The heart is a rather special type of fluid pump in the sense that it is an $\text{organic}$ pump. In this paper, however, it is postulated that the heart behaves like any other mechanical pump whose power output may assume, for a primary change in load, values bounded by two limits which are power output values obtained had the pump been a pressure generator and a flow generator respectively. A power output value outside the limits would imply a definite alteration in ventricular pump function concomitant with the load change. A nomogram to illustrate the proposal is included. The hypothesis may be developed into a powerful tool for assessing the pumping capability of the left ventricle, and this has significant clinical and physiological implications.