The use of electrochemically activated saline as a uterine instillation in pony mares.

Twelve pony mares were randomly assigned to either a control or a treatment group and inseminated with fresh, raw semen from a single stallion of known fertility in a cross-over trial design. Pregnancy was diagnosed by transrectal ultrasound 12-14 days post-ovulation and then terminated by administration of a luteolytic dose of cloprostenol. Treatment mares received a uterine instillation of 100 ml of electrochemically activated (ECA) saline 4-12 hours post-insemination. Control mares received no treatment post-insemination. Per cycle pregnancy rate was 58.3 % in the control group and 50 % in the treatment group. There was no statistical difference (P = 1.000) in pregnancy rate between the 2 groups. The principles of ECA and applications of ECA saline are discussed.

Dynamic myocardial contractile parameters from left ventricular pressure-volume measurements.

A new dynamic model of left ventricular (LV) pressure-volume relationships in beating heart was developed by mathematically linking chamber pressure-volume dynamics with cardiac muscle force-length dynamics. The dynamic LV model accounted for >80% of the measured variation in pressure caused by small-amplitude volume perturbation in an otherwise isovolumically beating, isolated rat heart. The dynamic LV model produced good fits to pressure responses to volume perturbations, but there existed some systematic features in the residual errors of the fits. The issue was whether these residual errors would be damaging to an application where the dynamic LV model was used with LV pressure and volume measurements to estimate myocardial contractile parameters. Good agreement among myocardial parameters responsible for response magnitude was found between those derived by geometric transformations of parameters of the dynamic LV model estimated in beating heart and those found by direct measurement in constantly activated, isolated muscle fibers. Good agreement was also found among myocardial kinetic parameters estimated in each of the two preparations. Thus the small systematic residual errors from fitting the LV model to the dynamic pressure-volume measurements do not interfere with use of the dynamic LV model to estimate contractile parameters of myocardium. Dynamic contractile behavior of cardiac muscle can now be obtained from a beating heart by judicious application of the dynamic LV model to information-rich pressure and volume signals. This provides for the first time a bridge between the dynamics of cardiac muscle function and the dynamics of heart function and allows a beating heart to be used in studies where the relevance of myofilament contractile behavior to cardiovascular system function may be investigated.

Nonlinear myofilament regulatory processes affect frequency-dependent muscle fiber stiffness.

To investigate the role of nonlinear myofilament regulatory processes in sarcomeric mechanodynamics, a model of myofilament kinetic processes, including thin filament on-off kinetics and crossbridge cycling kinetics with interactions within and between kinetic processes, was built to predict sarcomeric stiffness dynamics. Linear decomposition of this highly nonlinear model resulted in the identification of distinct contributions by kinetics of recruitment and by kinetics of distortion to the complex stiffness of the sarcomere. Further, it was established that nonlinear kinetic processes, such as those associated with cooperative neighbor interactions or length-dependent crossbridge attachment, contributed unique features to the stiffness spectrum through their effect on recruitment. Myofilament model-derived sarcomeric stiffness reproduces experimentally measured sarcomeric stiffness with remarkable fidelity. Consequently, characteristic features of the experimentally determined stiffness spectrum become interpretable in terms of the underlying contractile mechanisms that are responsible for specific dynamic behaviors.

Myofilament kinetics in isometric twitch dynamics.

To better understand the relationship between kinetic processes of contraction and the dynamic features of an isometric twitch, studies were conducted using a mathematical model that included: (1) kinetics of cross bridge (XB) cycling; (2) kinetics of thin filament regulatory processes; (3) serial and feedback interactions between these two kinetic processes; and (4) time course of calcium activation. Isometric twitch wave forms were predicted, morphometric features of the predicted twitch wave form were evaluated, and sensitivities of wave form morphometric features to model kinetic parameters were assessed. Initially, the impulse response of the XB cycle alone was analyzed with the findings that dynamic constants of the twitch transient were much faster than turnover number of steady-state XB cycling, and, although speed and duration of the twitch wave form were sensitive to XB cycle kinetic constants. parameters of wave shape were not. When thin filament regulatory unit (RU) kinetics were added to XB cycle kinetics, the system impulse response was slowed with only little effect on wave shape. When cooperative neighbor interactions between RU and XB were added, twitch wave shape (as well as amplitude, speed and duration) proved to be sensitive to variation in cooperativity. Importantly, persistence and shape of the falling phase could be strongly modified. When kinetic coefficients of XB attachment were made to depend on sarcomere length, changes in wave shape occurred that did not occur when only sliding filament mechanisms were operative. Indeed, the force-length relationship proved to be highly sensitive to length-dependent XB attachment in combination with cooperative interactions. These model findings are the basis of hypotheses for the role of specific kinetic events of contraction in generating twitch wave form features.

Overall cardiac functional effect of positive inotropic drugs with differing effects on relaxation.

Recent interest in so-called calcium-sensitizing positive inotropic drugs has highlighted the potential problem of a positive effect on force development being offset, at least partially, by the negative effect that many of these drugs have on relaxation. The purpose of this study was to examine the interplay of contraction and relaxation in determining the overall cardiac effect of different positive inotropic drugs. Using a buffer-perfused isolated rabbit heart preparation, we studied four drugs (calcium, dobutamine, EMD 57033, and CGP 48506) that were given at doses sufficient to increase similarly left ventricular pressure-generating capability by approximately 20%. We show that, even though they produce equivalent changes in pressure-generating capability, these four agents produce dissimilar changes in relaxation capability, with dobutamine speeding relaxation, EMD 57033 slowing relaxation, and calcium and CGP 48506 having little effect of relaxation. Similar relative effects were observed for drug-induced changes in the timing of pressure-generation events. These effects combine to produce different drug-induced changes in overall cardiac pump function judged by the relation between cardiac output and heart rate. Dobutamine shifted the maximal cardiac output to a higher heart rate. In contrast, both calcium sensitizers shifted the maximum in cardiac output to a lower heart rate, whereas calcium had no effect. Thus even though positive inotropic drugs may have similar effects on left ventricular pressure generation, the overall benefit of such drugs on ventricular pump function will depend on how the drug also affects ventricular relaxation and ejection capabilities.

Secophalloidin and phalloidin-(S)-sulfoxide as contraction modifiers for comparative study of skeletal and cardiac muscles.

Phalloidin, a toxic product of the mushroom Amanita phalloides, binds specifically to F-actin resulting in strong stabilization of F-actin structure (for review, see; Wieland, 1986). Binding to a specific site on the muscle thin filament F-actin, phalloidin modifies contraction in a tissue specific manner. Phalloidin induced changes depend on functionally important parameters (thin filament activation, cross-bridge kinetics), indicating changes in essential steps of the contractile mechanism. Moreover, there is a different action with different phalloidin derivatives. Such properties make phallotoxins (phalloidin and its derivatives) powerful modifiers for muscle research (for review, see: Bukatina, 1996). Phalloidin-induced changes vary qualitatively with muscle types. In all types of skinned skeletal muscle preparations that have been studied (fast and slow muscles from evolutionarily distant animals), the most general effect of phalloidin is to cause a decrease in tension (Bukatina, Morozov, 1979; Alievskaya et al., 1987; Bukatina et al., 1993). In mammalian skeletal muscles, this decrease in tension may be followed by a slowly developing increase in tension. The resulting tension may considerably exceed the tension before phalloidin administration. In contrast, skinned cardiac muscle responds to phalloidin only by increasing isometric tension from the onset of the response. Moreover, the phalloidin response is completed in approximately one-tenth the time in cardiac muscle that it takes in skeletal muscle. These phalloidin effects in cardiac muscle result in an enhanced Ca2+ responsiveness (Boels, Pfitzer, 1992) with an increase in both the force at maximum Ca2+ activation and the Ca2+ sensitivity (Bukatina et al., 1995).

Dethiophalloidin increases Ca2+ responsiveness of skinned cardiac muscle.

Phalloidin, an F-actin stabilizing peptide, is known to enhance Ca2+ responsiveness in skinned cardiac muscle. Here we studied the effects of dethiophalloidin (DTPH), a phalloidin derivative which, binding much more weakly to F-actin, on skinned bovine left ventricle muscle. When added to activated skinned muscle, DTPH (15-80 micron), similarly to phalloidin, caused a rapid (within several minutes) enhancement of active force; the relative force enhancement by DTPH became greater as Ca2+ concentration was decreased. Unlike phalloidin, DTPH effects were reversible. Using a value of the force enhancement at 15 micron DTPH (76% of maximum), an apparent equilibrium constant for DTPH binding to myofilaments was estimated at about 5 micron. Force-pCa plots showed that DTPH (80 micron) brought about a 10% increase in the maximal Ca(2+)-activated force and a 0.34 pCa units increase in the Ca2+ sensitivity. Both changes are stronger than those caused by phalloidin in similar conditions (6% and 0.2 pCa units, respectively). As with phalloidin, DTPH did not change the value of the Hill coefficient in the fit tothe force-pCa curve. DTPH and phalloidin interacted as follows: (1) pre-treatment with phalloidin entirely prevented the response to DTPH, indicating the absence of any non-specific DTPH action; and (2) when added after DTPH, phalloidin decreased the force enhancement due to DTPH, reflecting a stronger effect of DTPH to increase force. In conclusion, the stabilization of F-actin structure is not a major factor in the mechanism by which phalloidin modifies contraction.

Myocardial contractile depression from high-frequency vibration is not due to increased cross-bridge breakage.

Experiments were conducted in 10 isolated rabbit hearts at 25 degrees C to test the hypothesis that vibration-induced depression of myocardial contractile function was the result of increased cross-bridge breakage. Small-amplitude sinusoidal changes in left ventricular volume were administered at frequencies of 25, 50, and 76.9 Hz. The resulting pressure response consisted of a depressive response [delta Pd(t), a sustained decrease in pressure that was not at the perturbation frequency] and an infrequency response [delta Pf(t), that part at the perturbation frequency]. delta Pd(t) represented the effects of contractile depression. A cross-bridge model was applied to delta Pf(t) to estimate cross-bridge cycling parameters. Responses were obtained during Ca2+ activation and during Sr2+ activation when the time course of pressure development was slowed by a factor of 3. delta Pd(t) was strongly affected by whether the responses were activated by Ca2+ or by Sr2+. In the Sr(2+)-activated state, delta Pd(t) declined while pressure was rising and relaxation rate decreased. During Ca2+ and Sr2+ activation, velocity of myofilament sliding was insignificant as a predictor of delta Pd(t) or, when it was significant, participated by reducing delta Pd(t) rather than contributing to its magnitude. Furthermore, there was no difference in cross-bridge cycling rate constants when the Ca(2+)-activated state was compared with the Sr(2+)-activated state. An increase in cross-bridge detachment rate constant with volume-induced change in cross-bridge distortion could not be detected. Finally, processes responsible for delta Pd(t) occurred at slower frequencies than those of cross-bridge detachment. Collectively, these results argue against a cross-bridge detachment basis for vibration-induced myocardial depression.

Left ventricular pressure response to small-amplitude, sinusoidal volume changes in isolated rabbit heart.

The objective was to determine the dynamics of contractile processes from pressure responses to small-amplitude, sinusoidal volume changes in the left ventricle of the beating heart. Hearts were isolated from 14 anesthetized rabbits and paced at 1 beats/s. Volume was perturbed sinusoidally at four frequencies (f) (25, 50, 76.9, and 100 Hz) and five amplitudes (0.50, 0.75, 1.00, 1.25, and 1.50% of baseline volume). A prominent component of the pressure response occurred at the f of perturbation [infrequency response, delta Pf(t)]. A model, based on cross-bridge mechanisms and containing both pre- and postpower stroke states, was constructed to interpret delta Pf(t). Model predictions were that delta Pf(t) consisted of two parts: a part with an amplitude rising and falling in proportion to the pressure around that which delta Pf(t) occurred [Pr(t)], and a part with an amplitude rising and falling in proportion to the derivative of Pr(t) with time. Statistical analysis revealed that both parts were significant. Additional model predictions concerning response amplitude and phase were also confirmed statistically. The model was further validated by fitting simultaneously to all delta Pf(t) over the full range of f and delta V in a given heart. Residual errors from fitting were small (R2 = 0.978) and were not systematically distributed. Elaborations of the model to include noncontractile series elastance and distortion-dependent cross-bridge detachment did not improve the ability to represent the data. We concluded that the model could be used to identify cross-bridge rate constants in the whole heart from responses to 25- to 100-Hz sinusoidal volume perturbations.

Relaxation effect of CGP-48506, EMD-57033, and dobutamine in ejecting and isovolumically beating rabbit hearts.

Because it is not known whether ejection influences the negative effect of the Ca(2+)-sensitizing drugs on ventricular relaxation, we extended our previous analysis of stress-dependent relaxation in isovolumic beats to encompass ejecting beats and evaluated the relationships between both the time of onset of relaxation and the rate of relaxation and wall stress in a broader analysis framework. Furthermore, because the sites of action of the Ca(2+)-sensitizing drugs CGP-48506 and EMD-57033 may be different, and thus CGP-48506 may have fewer adverse effects on resting muscle length or force, we compared these two drugs to test the hypothesis that CGP-48506 would have less effect than EMD-57033 on relaxation in the isolated buffer-perfused rabbit heart. This analysis of stress-dependent relaxation in both ejecting and isovolumic beats readily differentiates between the negative lusitropic effect of 2 x 10(-6) M EMD-57033, the negligible lusitropic effect of 6 x 10(-6) M CGP-48506, and the positive lusitropic effect of 1.25 x 10(-6) M dobutamine. Furthermore, comparison of the effect of the two Ca(2+)-sensitizing drugs in ejecting versus isovolumic contractions shows that CGP-48506 affects relaxation differently in ejecting contractions than it does in isovolumic contractions, whereas EMD-57033 affects relaxation similarly in both ejecting and isovolumic contractions.

A primary health care approach to an outbreak of cutaneous larva migrans.

Primary health care (PHC) has been defined by the World Health Organisation as essential health care made universally accessible to community members, with their full participation, at a cost affordable to the community. PHC could therefore be used in the prevention and treatment of zoonotic diseases in humans, as such diseases are more prevalent in disadvantaged communities. The successful use of PHC principles in the treatment and control of cutaneous larva migrans in children in a semi-rural, low-income community is discussed in this paper. Constraints to implementation of PHC principles were identified as resistance from health care professionals, lack of interdepartmental cooperation and bureaucratic delays. It is concluded that PHC principles can be used successfully for the prevention and treatment of specific zoonoses provided that an aetiological diagnosis is made and the epidemiology of the condition understood. The results also confirmed the relevance of the veterinarian in the control of zoonotic diseases as part of the PHC team.

Functional effects of EMD-57033 in isovolumically beating isolated rabbit hearts.

The results of isolated myocyte and cardiac muscle experiments indicate that inotropic agents that increase responsiveness of myofilaments to Ca2+ (so-called Ca2+ sensitizers) may prolong myocardial contraction and increase diastolic tone, but the importance of these effects in the whole heart is unclear. Therefore, we studied the effects of the Ca2+ sensitizer EMD-57033 (EMD) on left ventricular (LV) contractile events and passive properties in isovolumically beating isolated rabbit hearts that were buffer perfused at 30 degrees C. Several LV pressure and timing variables were evaluated, including the passive pressure-volume relationship, the Frank-Starling relationship, and the wall stress dependence of the duration of relaxation during perfusion with 0, 2, and 4 microM EMD. EMD (2 microM) increased average peak developed pressure of the Frank-Starling relationship by approximately 18%. In contrast, the peak developed pressure of the Frank-Starling relationship decreased toward control with 4 microM EMD, and therefore all the results presented pertain to 2 microM EMD. The maximum developed pressure at baseline volume was increased by approximately 19% by 2 microM EMD, and this was accompanied by an increase in contraction duration of approximately 13%, due exclusively to slowed relaxation. The relative contributions of maximal wall stress (sigma max) versus an independent negative lusitropic effect of EMD were determined at three LV volumes. At baseline volume, just less than one-half of the effect to slow relaxation was ascribable to an increase in sigma max, whereas the remainder was due to an independent EMD effect. LV passive properties were unchanged by perfusion with 2 microM EMD. We conclude that EMD is a potent inotrope in our isolated rabbit heart preparation, which has no effect on diastolic tone and causes a modest prolongation of contraction duration due to slowed relaxation. At baseline volume, approximately 50% of the slowed relaxation was ascribable to positive inotropy leading to increased sigma max, whereas the remaining approximately 50% was ascribable to a direct negative lusitropic effect of EMD. We discuss our results in terms of the current hypotheses regarding the mechanism of action of the Ca2+ sensitizers.

Mechanical determinants of left ventricular relaxation in isovolumically beating hearts.

Both pressure and volume have been proposed to determine the speed of left ventricular (LV) relaxation, but their relative importance is not known. Accordingly, we used isolated, buffer-perfused, isovolumically beating ferret hearts to study the effects of maximal developed pressure (Pdmax) and LV volume (V) on the speed of LV relaxation. Experiments were performed at 30 degrees C, and the hearts were paced at a baseline interbeat interval (BI) of 800 ms. Pdmax was varied independently of V by use of seven BI (75 to 133% of baseline BI), which resulted in test beats that developed a range of Pdmax due to varying degrees of restitution. Pdmax was also varied by setting V at five levels (80 to 120% of baseline V) during the test beats. Speed of relaxation was quantified as the time period of pressure decay from 75 to 25% Pdmax (T75-25). Data were analyzed by multiple linear regression. Increases in both Pdmax and V independently prolonged T75-25, and T75-25 was 1.45 times more sensitive to Pdmax than to V. However, when Pdmax and V were combined to estimate maximal wall stress (sigma max), the effects of Pdmax and V, as well as relative circumferential muscle length (estimated by V1/3), were not important determinants, and T75-25 depended on sigma max alone. Thus we conclude that 1) Pdmax and V are both determinants of the speed of LV relaxation and that Pdmax is approximately 1.5 times more important than V, and 2) the effects of Pdmax and V on relaxation act via the common mechanism of sigma max.

Series coupled non-contractile elements are functionally unimportant in the isolated heart.

OBJECTIVE: In order to evaluate possible artefact in interpretations of contractile behaviour in isolated heart experiments, the relative elastances of series coupled non-contractile and contractile components of the left ventricle of the isolated heart were evaluated. METHODS: Hearts were isolated from ferrets and rabbits and mounted on a servo-controlled volume regulation device. These hearts were made to beat isovolumetrically until a selected volume perturbation was introduced. Constant flow volume withdrawals at two flow values were performed over a period of < 20 ms centred around the time of peak isovolumetric pressure. Three levels of isovolumetric pressure were produced using basal, extrasystolic, and potentiated beats. Pressure responses to volume withdrawals at two flows and three isovolumetric pressures were then analysed using a mathematical model to evaluate relative values of series coupled contractile and non-contractile elastances. To validate the analysis procedure, a non-contractile series artefact with known elastance was coupled to the left ventricle; volume perturbations were then applied to the coupled left ventricle-artefact system; responses were analysed and the estimate of series coupled non-contractile elastance was compared to the known elastance of the added artefact. RESULTS: A wide range of isovolumetric pressures [208(SD 40) mmHg] was produced in the ferret with basal, extrasystolic, and potentiated beats. A lesser range of isovolumetric pressures [50(15) mmHg] was produced in the rabbit. The mathematical model fitted the data very well in both the ferret and rabbit. The elastance of the series coupled non-contractile component could be estimated only in some ferrets. When estimated in the ferret, the elastance of the series coupled non-contractile component was never less than 4x that of the contractile component. When a series artefact of sufficiently low value was coupled with the native left ventricle, the elastance of the non-contractile component could be reliably estimated in both ferrets and rabbits and the estimated value approximated that of the added artefact. This indicated that the elastance of the series coupled non-contractile component of the native left ventricle was much higher than that of the added artefact. CONCLUSIONS: The series coupled non-contractile component of the isolated heart possesses a very much higher elastance than the contractile component. In fact, the elastance of the non-contractile component is so great that it contributes very little to the dynamic behaviour of the left ventricle. Virtually all of the elastance of the left ventricle of the isolated heart is due to the contractile component.

Similarities between dynamic elastance of left ventricular chamber and papillary muscle of rabbit heart.

The frequency-dependent dynamic elastance of the left ventricle (LV) of isolated rabbit heart was determined and compared with dynamic stiffness of excised rabbit papillary muscle. Comparison was made in three states: 1) relaxed, 2) BaCl2 contracture, and 3) rigor. Dynamic chamber elastance was determined by pressure-to-volume ratio at 12 frequencies of sinusoidal volume variation between 0.1 and 30 Hz. Dynamic elastance during BaCl2 contracture was distinctly different from that during either relaxed or rigor states. Characteristics of BaCl2 contracture were 1) as frequency increased, polar plot of real and imaginary elastance showed a progressively opening clockwise spiral that tended eventually to become tangent to the apogee of a semi-circle by 30 Hz; 2) modulus spectrum exhibited asymptotes at low and high frequencies with an intervening dip to a minimum at 1.25 Hz; and 3) phase showed a sharp transition at dip frequency from small negative values at lower frequencies to large positive values at intermediate frequencies and then declined at highest frequencies. There was little dependence of dynamic elastance on frequency in both relaxed and rigor states. Dynamic muscle stiffness exhibited all features of dynamic chamber elastance in all three states. We concluded that dynamic elements responsible for myofiber stiffness were also responsible for LV chamber elastance. Furthermore, it was possible to describe and interpret dynamic chamber elastance and muscle stiffness with a common model based on muscle cross-bridge theory. This model did a reasonable job of reproducing all important features of experimentally observed LV chamber elastance and muscle stiffness. Thus dynamic homologies between chamber and muscle were established in experimental data and in the fact that a single interpretive model served equally well for both chamber elastance and muscle stiffness.

Short time-scale LV systolic dynamics: pressure vs. volume clamps and effect of activation.

We recently proposed a new model-based approach to quantifying short time-scale left ventricular (LV) systolic dynamics. In this study we examine the hypothesis that the quantitation of LV dynamics using the proposed approach is independent of external mechanical perturbations and the level of activation. Mechanical perturbation independence was assessed in seven isolated ferret hearts in which controlled changes in pressure (pressure clamp) or volume (volume clamp) were introduced at the time of peak isovolumetric pressure (protocol 1), and responses to these clamps were analyzed over the first 16 ms. The model described both pressure- and volume-clamps responses equally well. Model parameters were not different among various pressure clamps, and parameters estimated from volume clamps could accurately predict responses to pressure clamps [r2 range: 0.993-0.999; normalized root-mean-square error (NRMSE) range: 2.35-5.86%]. To examine activation independence, volume- (4 hearts) and pressure-clamp (4 hearts) responses were obtained and analyzed for baseline and postextrasystolic potentiated beats in a manner similar to protocol 1. The model parameter values estimated from the baseline state accurately predicted responses for the postextrasystolic potentiated state (r2 and NRMSE range for volume-clamp data: 0.989-0.998 and 3.35-6.88%, respectively; r2 and NRMSE range for pressure-clamp data: 0.992-0.996 and 4.26-5.23%, respectively). Thus the proposed approach can dissect the contributions of changes in activation from those due to changes in contractile unit properties on the function of the intact LV.

A qualitative study of the attitudes of members of a developing community towards their dogs and veterinary services.

A university-based hospital serving mainly a developing community readily appreciated that its clientele was from a very different sociological and cultural background than that of the professional staff and that developed and developing communities and their pets exhibit different patterns in their health status, with most diseases being predominantly related to socio-economic predicament. The need for a community-orientated service was recognised. From 1987 to 1988, the small animal outpatient clinic was used for an informal, unstructured sociological observation and interview-based study of the clientele and their pets. During this period, an informal educational programme was implemented to teach basic pet health care, and the efficacy of this programme was empirically gauged by comparing the knowledge and attitudes of first-time clients with those of regular clients. Regular clients appeared to become increasingly concerned about the health and management of their pets and the condition of their animals appeared to improve, with a corresponding decline in the degree of parasitism. The majority of clients however, still regarded the main reason for keeping dogs as the provision of some form of security. It also appeared as if improved attitudes towards household pets paralleled improvements in socio-economic status.

Single perturbed beat vs. steady-state beats for assessing systolic function in the isolated heart.

Single-beat and steady-state techniques for evaluating end-systolic pressure-volume relationship (ESPVR) and Frank-Starling mechanism (FSM) in the crystalloid-perfused isolated rabbit heart were compared. In the single-beat technique, a train of stable isovolumic beats was interrupted with a single perturbed beat that either ejected against various levels of imposed isobaric load (ESPVR protocol) or beat isovolumically against various levels of end-diastolic volume (V(ED); FSM protocol). In steady-state technique, sustained beating was established, isobarically, at each of various loads (ESPVR protocol) or, isovolumically, at each of various V(ED) values (FSM protocol). ESPVR from steady-state technique lay above and to the left of that from single-beat technique. Contractile state was not uniform within steady-state technique, whereas it was uniform within single-beat technique. In the FSM protocol, single-beat technique exhibited the following features relative to steady-state technique: 1) greater range of developed pressures, 2) steeper ascending limb and more sharply defined maxima, 3) higher maximal developed pressure (Pdmax), and 4) greater volume at Pdmax(Vmax). Again. a common contractile state existed within single-beat technique but not within steady-state technique. It was concluded that single-beat technique was preferable to steady-state technique for evaluating ESPVR and FSM because 1) single-beat technique required less time for obtaining data, 2) single-beat technique allowed identification of uncomplicated values of Pdmax and Vmax, and 3) single-beat technique provided a common contractile-state reference for all data, whereas steady-state technique did not.