Canine skeletal muscle ventricles: functional assessment using the pressure-volume plane

In five dogs, skeletal muscle ventricles (SMVs) were constructed from the latissimus dorsi muscle, and placed within the thoracic cavity. After a 3-week delay period, SMVs were electrically preconditioned with 2-Hz continuous stimulation for 6 weeks. At a second procedure, SMVs were connected to a mock-circulation system, and performance was evaluated according to pressure-volume relationships at three different SMV contraction rates (33, 54, and 97 per min) and three stimulation protocols (25, 43, and 85 Hz) under varying loading conditions. Under appropriate conditions of afterload, the end-diastolic pressure-volume relation of SMVs was comparable with that of the cardiac ventricles, although SMVs were less compliant. At higher burst stimulation frequencies, SMV compliance was increased. Compliance was not affected by varying the rate of SMV contraction. End-systolic elastance, a reflection of contractility, appeared to be constant for each SMV, in contrast to cardiac ventricles, and was not influenced by changes in burst stimulation frequency or contraction rate. In this study, SMVs were capable of a level of stroke work 180% of that of the native right ventricle (RV) at rest (0.397 +/- 0.047 x 10(6) ergs) and 37% of that of the left ventricle (LV) at rest (0.298 +/- 0.61 x 10(6) ergs), at 33 contractions per minute (CPM), 25-Hz burst frequency, and physiological preload, but this level could not be sustained at higher contraction rates. Nevertheless, power output (SMV stroke work x contraction rate) was maximal at 97 CPM. These findings demonstrate important function differences between pumping chambers constructed from conditioned skeletal muscle, and those composed of cardiac muscle, which must be considered when using skeletal muscle ventricles for cardiac support or replacement.

Logistic time constant of isovolumic relaxation pressure-time curve in the canine left ventricle. Better alternative to exponential time constant

BACKGROUND

The time constant of left ventricular (LV) relaxation derived from a monoexponential model has been widely used as an index of LV relaxation rate or lusitropism, although this model has several well-recognized problems. In the present study, we proposed a logistic model and derived a "logistic" time constant (TL) as a better alternative to the conventional "exponential" time constant (TE).

METHODS AND RESULTS

A total of 189 beats (147 isovolumic and 42 ejecting beats) were investigated in seven canine excised cross-circulated heart preparations. We found that the logistic model fitted much more precisely all the observed LV isovolumic relaxation pressure-time [P(t)] curves than the monoexponential model (P < .05). The logistic model also fitted well both the time curve of the first derivative of the observed P(t) (dP/dt) and the dP/dt-P(t) phase-plane curve. Like TE, TL indicated that volume loading depressed LV lusitropism and that increasing heart rate and ejection fraction augmented it. TL was independent of the choice of cutoff point defining the end of isovolumic relaxation; TE was dependent on that choice.

CONCLUSIONS

We conclude that the logistic model better fits LV isovolumic relaxation P(t) than the monoexponential model in the present heart preparation. We therefore propose TL as a better alternative to TE for evaluating LV lusitropism.

Cardiac function of an acute ischemic heart failure model produced by microsphere injection into the left coronary artery. Pressure-volume relationship as determined by a conductance catheter

The authors produced an acute canine heart failure model by injecting microspheres (phi 15.5 +/- 0.1 mm, 5 x 10(5)) into the left coronary artery, and characterized the model in terms of the pressure-volume relationship obtained by the conductance catheter method. Cardiodynamics of the microsphere injection group (M group: n = 10) and control group (C group: n = 12) were studied with 1) heart rate, 2) aortic pressure, 3) cardiac output (CO), 4) maximal ventricular elastance, 5) effective arterial elastance/maximal ventricular elastance, and 6) external work/pressure-volume area efficiency. With microsphere injection, CO and external work/pressure-volume area efficiency significantly decreased. With administration of dobutamine (5 mg/kg/min), CO and maximal ventricular elastance recovered to normal and aortic pressure became higher than normal. These changes in heart rate, aortic pressure, CO, maximal ventricular elastance, and external work/pressure-volume area efficiency in the M group were comparable in percentage to those in the C groups. Cardiodynamics of this heart failure model generally were stable for 3 hrs after microsphere injection. The authors concluded that this model would be an excellent acute heart failure model for investigating hemodynamic effects of circulatory assist devices.

Suppression of myocardial mitochondrial respiratory function in acute failing hearts made by a short-term Ca2+ free, high Ca2+ coronary perfusion

We made acute cardiac failure in excised cross-circulated canine hearts by a new coronary perfusion protocol consisting of Ca2+ free Tyrode perfusion for the first 10 min, high Ca2+ (16 mmol/l) Tyrode perfusion for the next 5 min, and normal Tyrode perfusion for the last 5 min interrupting blood cross circulation. After 50 min from the blood recirculation, left ventricular contractility was stably depressed to 60% of control. We studied mechanoenergetics of these acute failing hearts for the next 1-3 h. Then, we prepared mitochondria from these excised failing hearts and the support dogs' normal hearts to examine their mitochondrial respiratory function by the respiratory control index (RCI) and the oxygen consumption rate in state III (State III O2). RCI and State III O2 were significantly smaller in the failing hearts than in the normal hearts. However, sham protocol consisting of normal Tyrode coronary perfusion for 20 min did not affect RCI and State III O2. These results revealed that the mitochondrial respiratory function was moderately impaired in these acute failing hearts made by the new short-term Ca2+ intervention. However, no ultrastructural injuries of mitochondria were detected in these failing hearts.

Preventive effect of pirfenidone against experimental sclerosing peritonitis in rats

We investigated the preventive effect of pirfenidone (PFD), a newly developed anti-fibrotic agent, on experimental sclerosing peritonitis (sp) which we had established in rats. Male Wistar rats (150-250 g) were divided into the following two groups; 7 rats were treated with daily intraperitoneal (i.p.) injection of 0.1% chlorhexidine gluconate (CH) and 15% ethanol solved in 2 ml of saline for 26 days as a control of SP model (CH group) and 6 rats were treated daily with peroral (p.o.) administration of 350 mg/kg of PFD in addition to the daily i.p. injection of aforementioned CH-ethanol-saline solution for 26 days (CH + PFD group). Macroscopic intraperitoneal changes and histological fibrotic changes were graded by scoring in a blind manner. Actual subserosal thickness was measured by observation under light microscope. Body weight gain was significantly greater in CH + PFD group than in CH group (P < 0.05). Macroscopic intraperitoneal adhesion changes in CH + PFD group were significantly fewer than in CH group (P < 0.05). Fibrotic changes were fewer and subserosal thickness in liver and intestine were smaller in CH + PFD group with statistical significance (p < 0.1). We concluded that PFD markedly inhibited or prevented fibrotic changes in the experimental sclerosing peritonitis induced by CH.

Heterogeneity of rice ragged stunt oryzavirus genome segment 9 and its segregation by insect vector transmission

Genomic heterogeneity of genome segment 9 (S9) of rice ragged stunt virus (RRSV) was investigated and a point mutation was found to be responsible for an electrophoretic mobility shift of S9 on polyacrylamide gel electrophoresis (PAGE). A new form of S9 (S9L) which migrated slightly faster than natural S9 (S9U) had the same length with A-->C transversion at nt 843. Synthetic S9 with a C:G pair at nt 843 migrated slightly faster than that with an A:U pair. Therefore, we conclude that the single point mutation shifts the electrophoretic mobility. Using polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP), we could detect S9U and S9L alone or mixture in insect vectors after acquisition as well as in infected rice plants.

Cardiac quick-release contraction mechanoenergetics analysis using a cardiac muscle cross-bridge model

Huxley's sliding filament cross-bridge muscle model coupled with parallel and series elastic components was simulated to examine the conflicting reports on the amount of energy saved by quick release at the peak contraction time. Cross-bridge energy utilization was determined by considering the ATP hydrolysis for the cross-bridge cycling. The quick-release cases were simulated by letting the muscle fiber suddenly shorten to the resting fiber length at peak systole, and then the contraction was allowed to continue at the resting length. Simulation results demonstrated that, using realistic parameter values, typically approximately 15% of the muscle fiber energy is used after peak systole (and approximately 30% of the cross-bridge energy), but this is also a function of the muscle fiber properties characterized by cross-bridge association and dissociation rate constants. Increasing the kinetic rate constants, the series elasticity, the initial fiber length, or the time of peak intracellular calcium will increase the amount of energy left, which may explain some of the discrepancies in the literature. Cardiac muscle hypertrophy will increase the fraction of muscle fiber energy left after peak systole to approximately 30%. The strongest indicator of the percent energy left at peak systole was the time the fiber reached peak systole, and as the fiber reached peak systole faster, the amount of energy saved by quick release increased.

Rice ragged stunt Oryzavirus genome segment 9 encodes a 38 600 Mr structural protein

The complete nucleotide sequence of rice ragged stunt virus genome segment 9 (S9) was determined. The S9 segment is 1132 nucleotides long and has a long open reading frame starting from the first AUG codon at nucleotide position 14-16 and terminating at a UAG codon located at 1028-1030, which could encode a polypeptide with an Mr of 38 600 (P9). The encoded polypeptide has no sequence homology to polypeptides of any other plant reoviruses published previously. An immunological study demonstrated that P9 was the smallest of the structural proteins. The P9 polypeptide was expressed as a fusion protein with maltose binding protein in Escherichia coli. Antisera to purified virions and to the fusion protein reacted with both the bacterially expressed polypeptide and the smallest polypeptide of the purified virus in immunoblotting analyses.

Cardiodynamic conditions for the linearity of preload recruitable stroke work

Studies reported in the literature show that the stroke work (SW) versus end-diastolic volume (Ved) relationship, namely, the preload recruitable stroke work relation (PRSW), is experimentally linear in closed-chest dog hearts and its slope reflects left ventricular contractility. We considered the theoretical cardiodynamic conditions necessary for the linearity of the SW-Ved relation by utilizing ventricular end-systolic elastance, Emax (ventricular contractility), and effective arterial elastance, Ea (arterial afterload). We simulated the SW-Ved relation, using four theoretical models of the left ventricle, as follows: Ea is constant and the end-systolic pressure-volume relation (ESPVR) is linear (model 1), or nonlinear (model 2), and Ea is variable and ESPVR is linear (model 3), or nonlinear (model 4). The results show that the SW-Ved relation can be linear in both linear and nonlinear ESPVR models (models 3 and 4) only when Ea is variable. In these models, end-systolic pressure (Pes) and Ea should gradually fall, maintaining the stroke volume (SV) relatively constant with decreases in Ved until the low end of the physiological Ved range. Then, Ea should rise sharply so that Pes does not fall below the critical level. These results suggest that the autoregulation mechanisms of an intact animal operate to adapt the arterial afterload against acute changes in LV preload, maintaining cardiac output and coronary artery pressure. Such mechanisms may thus produce a linear SW-Ved relation over a wide range of conditions.

The effect of total blood exchange with PHP solution on cardiac xenotransplantation

Prevention of hyperacute rejection is a difficult and unsolved problem in xenotransplantation. Natural antibodies and complement activation have been known to play an important role in the xenotransplantation between discordant species pairs. In the present study, total blood exchange (TBE) was performed with pyridoxalated-hemoglobin-polyoxyethylene conjugate (PHP) solution (Ajinomoto Co., Inc., Kawasaki, Japan) before cardiac xenotransplantation in order to remove the immunoglobulins and prolong xenograft survival time. Guinea pigs and rats were used as the discordant species combination for donor and recipient. Two groups were established: Group 1, untreated control (n = 8) and Group 2, TBT with PHP solution (n = 8). The exchange blood transfusion was carried out at the rate of 15-20 ml/h utilizing PHP solution using a blood pump. After the blood exchange was processed, hematocrit (Ht) levels dropped to 4 or 5%, and a cardiac xenotransplantation was performed within 24 h. The levels of serum IgA, IgM, and IgG were decreased to less than 25, 25, and 10% of the base line, respectively, after blood exchange. A mean xenograft survival time in Group 2 was prolonged to 472 +/- 74 min and to 10.4 +/- 1.8 min in Group 1 (p < 0.01). A titer of the anti-guinea pig lymphocytotoxic antibody in rat serum was decreased to almost nil. The data from this study suggest that total blood exchange with PHP solution may be useful in preoperative removal of xenograft antibodies in xenotransplantation.

Ca(2+)-free, high-Ca2+ coronary perfusion suppresses contractility and excitation-contraction coupling energy

We studied the mechanoenergetic effects of a short-term Ca(2+)-free, high-Ca2+ Tyrode solution coronary perfusion in eight excised, cross-circulated canine hearts. The perfusion protocol consisted of coronary perfusion with Ca(2+)-free Tyrode solution for 10 min followed by high-Ca2+ (16 mM) Tyrode solution for 5 min. This new protocol successfully induced acute contractile failure in seven hearts, without myocardial ultrastructural changes. We studied the end-systolic pressure-volume relation (slope = Emax, a contractility index) and the relation between oxygen consumption per beat (VO2) and systolic pressure-volume area (PVA) in these failing hearts. These hearts had no increase in end-diastolic pressure at a given volume, a 40% decrease in Emax and a proportional decrease in the PVA-independent VO2 for 1-4 h, but no decrease in the oxygen cost of PVA, defined as the slope of the VO2-PVA relation. The oxygen cost of Emax for Ca2+ handling, defined as the slope of the relation between PVA-independent VO2 and Emax, was unchanged in the failing hearts. We conclude that the present protocol induced left ventricular contractile failure, primarily involving the suppression of Ca2+ handling energy for excitation-contraction coupling.

Logistic characterization of left ventricular isovolumic pressure-time curve

Although some investigators have attempted to express the left ventricular pressure-time curve by mathematical functions such as exponential and sinusoidal functions, none of them reasonably fits the left ventricular pressure-time curve. In the present study, we hypothesized that a ventricular isovolumic pressure-time curve could be expressed as the difference between two S-shaped curves for pressure rising and falling, and proposed a new "hybrid logistic" function to express the left ventricular isovolumic pressure-time curve. We investigated how well this hybrid logistic function fits left ventricular isovolumic pressure curves experimentally observed under physiological preload and contractility in the excised cross-circulated left ventricles of 10 dogs. The new function precisely fitted the isovolumic pressure curves regardless of preload and contractility with correlation coefficients above 0.9996, much better than the previously proposed functions. The observed values characterizing the magnitude and time course of the isovolumic pressure curve such as peak +/- dP/dt also closely correlated with the corresponding theoretical values calculated by the present best-fit function. We conclude that our new hybrid logistic function reasonably characterizes the canine left ventricular isovolumic pressure-time curve within physiological ranges of preload and contractility. The present results indicate that this hybrid logistic function is useful to evaluate left ventricular contraction and relaxation comprehensively.

Left ventricular mechanoenergetics under altered coronary perfusion in guinea pig hearts

Coronary perfusion pressure (CPP) is well known to affect left ventricular (LV) mechanoenergetics (Gregg's phenomenon). The garden hose effect via the Frank-Starling mechanism caused by coronary distension has long been considered to be the underlying mechanism of this phenomenon. However, recent studies have revealed a close correlation between CPP and the excitation-contraction coupling in myocytes. The aim of this study was to investigate the mechanoenergetic aspects of Gregg's phenomenon by the ventricular contractility (Emax) dependency of the myocardial oxygen consumption (VO2)-total mechanical energy (PVA, systolic pressure-volume area) relationship. Experiments were performed in the excised, cross-circulated guinea pig heart preparation. The protocol consisted of LV volume loading (VOL run), changing coronary perfusion pressure at a fixed LV volume (CPP run) and intracoronary calcium (Ca) infusion also at the same LV volume (Ca run). In all seven hearts, we obtained a linear VO2-PVA relation in VOL run. The VO2-PVA relations in CPP and Ca runs, which equally enhanced Emax, were highly linear and had no significant difference in their slopes, both significantly steeper than in VOL run. These findings suggest no significant difference in the oxygen cost of Emax between CPP and Ca runs. The enhanced LV mechanoenergetics under increasing CPP is characterized by increases in the VO2 component primarily for the excitation-contraction coupling to a greater degree than expected from the mechanical (garden hose) effect.

Sinusoidal and exponential decays of postextrasystolic transient alternans in excised blood-perfused canine hearts

We have recently reported that the postextrasystolic contractile potentiation decays in alternans after a compensatory pause in canine left ventricles even under normal coronary and contractile conditions. The transient alternans appears to consist primarily of a small-magnitude exponential decay and a large-magnitude sinusoidal decay. We, therefore, hypothesized that the contractility (y) of the postextrasystolic alternans beats (beat number x) could be expressed as y = a x exp[-(x-1)/b] + c x exp[-(x-1)/d] x sin[pi(x-0.5)] + yo, where a and c are the normalized magnitudes (relative to the preceding regular beat) of the two exponential terms in the first postextrasystolic beat, b and d are their time constants, and yo is the normalized magnitude of the post-alternans regular beat (approximately 1). The first exponential term represents the monotonic decay. The sine term multiplied by the second exponential term represents the alternating decay. Mathematical curve-fitting indicated: 1) the above equation very closely fitted the alternans data with a squared correlation coefficient of 0.9996 on average, 2) c was 7 times on average greater than a, indicating dominance of the sine component, 3) b and d were 2.5 and 1.0 beats on average, indicating a faster decay of the sine component, and 4) this b was comparable to the time constant of the exponential decay of the postextrasystolic potentiation after no compensatory pause. This study suggests that myocardium has a mechanism to switch the postextrasystolic potentiation between the exponential and alternans decays depending on the first postextrasystolic interval.

[Home terminal care for terminal gastric cancer patients--case of epidural morphine injection]

Pain management at home for a terminal gastric cancer patient unable to take medications orally was made possible by a combination of serial morphine drip infusion and epidural anesthesia with morphine on a continuing basis using a disposal syringe. Before the patient was discharged, a conference was held to prepare for home care. Besides the patient and family, it was attended by the primary care doctor, ward nurse, home nurse, pharmacy staff, pain clinic doctor and hospital office personnel. The patient was duly informed of the disease by name and, thanks to fine cooperation from the medical staff, had achieved a good understanding, and spent his remaining time meaningfully. Morphine dosages upon discharge were 80 mg/day by drip infusion and 90 mg/day epidurally. For times of increased pain, the patient was instructed in how to self-administer 0.5% Mepivacaine (5 ml/time) with a syringe using an epidural catheter equipped with a 3-way stopcock. When this proved insufficient to control the pain, the patient was instructed to come for outpatient treatment on an emergency basis. With one visit per week to the hospital and home visits by a nurse once or twice a week, the patient managed at home for 82 days before increased pain resulted in rehospitalization. After the pain was brought under control and the patient was discharged, he was again hospitalized 5 days later. The pain control up until the time of death was by drip infusion of up to 1,200 mg/day morphine.

Effects of capsaicin on mechanoenergetics of excised cross-circulated canine left ventricle and coronary artery

Capsaicin selectively acts on sensory nerve endings in cardiac muscles and coronary arterial smooth muscles. Capsaicin at high doses has cell-nonselective effects including both inhibition of cardiac muscle exciteability and enhancement of vascular smooth muscle tone. We studied whether and how intracoronary infusion of capsaicin affects mechanoenergetics of the excised blood-perfused canine heart and coronary vascular resistance. We found that capsaicin at low concentrations increased Emax (a contracility index) and oxygen consumption (VO2) possibly due to a specific action on capsaicin-sensitive sensory nerves in left ventricular muscles, though in a small number of hearts (3/10). This result coincides with the reported histochemical observations that the distribution of capsaicin-sensitive sensory nerves in the canine left ventricle is not dense. Capsaicin at high doses dose-dependently decreased Emax and proportionally decreased coronary flow. It also lowered the linear VO2-PVA (pressure-volume area; total mechanical energy) relationship without a change in the slope, decreasing unloaded VO2 (VO2 intercept of the VO2-PVA relation). These effects of high-dose capsaicin seem to be direct negative inotropic action on cardiac muscles associated with enhancement of coronary arterial smooth muscle tone, since these effects were not desensitized. No morphological changes of myocardial cells or mitochondria were detected. Therefore, the negative inotropic action is not due to the toxic effect of capsaicin.

Postextrasystolic transient contractile alternans in canine hearts

We found that postextrasystolic potentiated contractility after a spontaneous extrasystole most frequently decayed as a transient alternans over several beats in excised, cross-circulated, atrially paced canine hearts. This type of heart preparation; which we have been using consistently in mechanoenergetic studies, had normal coronary blood perfusion pressure as well as flow and mechanoenergetic performance. Spontaneous atrial and ventricular extrasystoles occurred occasionally in every heart. Arrhythmic changes in left ventricular (LV) pressure at a fixed volume reflected corresponding changes in contractility. We analyzed nearly 3,600 cases of postextrasystolic potentiation in 68 hearts; 84% decayed as transient alternans, 6% decayed exponentially, and 10% belonged to neither type. We found that a postextrasystolic compensatory pause always preceded the transient alternans after either an atrial or ventricular extrasystole at any constant atrial pacing rate (85-188 beats/min). The decay was either exponential or nonalternating when the pause did not exist after an atrial extrasystole during occasional pacing failure. Therefore, the compensatory pause after either an atrial or ventricular extrasystole seems essential for the postextrasystolic transient alternans of LV contractility in the type of canine heart preparation we have been using.

Genomic heterogeneity of rice dwarf phytoreovirus field isolates and nucleotide sequences of variants of genome segment 12

Electrophoretic profiles of the dsRNAs of field isolates of rice dwarf virus (RDV) were compared with those of an isolate maintained at Hokkaido University (RDV-H). Unexpectedly, the genomic dsRNAs of most of the field isolates showed distinct electrophoretic mobility profiles. This was the case even among isolates from the same region. Genome segment 12 (S12) from some variants migrated faster than S12 from RDV-H. These RNAs were converted to full-length cDNAs and sequenced. S12 from all the variants had the same length of 1066 nucleotides with nucleotide sequence identities of 96 to 99%. Three open reading frames previously reported were present in all the variants, and the sequence identities were 95 to 99% for P12, 98 to 100% for P12OPa, and nearly 100% for P12OPb. A comparison of the nucleotide and amino acid sequences of the variants with sequences of the RDV-H and Akita isolate showed that there are two genomic types, one represented by RDV-H and the other by the Akita isolate.

Paul Dudley White International Lecture: cardiac performance as viewed through the pressure-volume window

Viewing canine left ventricular performance through the pressure-volume (P-V) window, I proposed a new index of ventricular contractility (Emax: end-systolic P-V ratio or maximum elastance) in my doctoral thesis at the University of Tokyo in 1969. After I joined Dr. Kiichi Sagawa (deceased in 1989) at Johns Hopkins University, we firmly established the Emax concept during 1971-1978. The concept was extended to derive the systolic P-V area (PVA) as a new measure of the total mechanical energy generated by ventricular contraction in 1978. Experiments have revealed that PVA closely correlates with cardiac oxygen (O2) consumption (VO2) under various loading conditions at a constant Emax, the VO2-PVA relation changes its elevation with Emax, and the O2 costs of PVA and Emax characterize the mechanoenergetics of cardiac contraction under various normal and abnormal conditions in an innovative manner (Suga: Physiol Rev 70: 247-277, 1990). Emax and PVA can also evaluate the ventriculo-arterial hydraulic and energetic matching in normal and failing hearts. Emax and PVA have thus widely opened the P-V window to the extent that human and animal normal and failing cardiac performance can be characterized in a physiologically sound manner.

Ejecting activation differs in energetics from ordinary positive inotropism in the canine left ventricle

Ventricular ejection is known to have dual effects on the end-systolic pressure: the ejecting deactivation by a relatively large ejection against a low afterload versus the ejecting activation by a relatively small ejection against a high afterload. We studied how the increase in contractility index (Emax) by the ejecting activation would affect myocardial oxygen consumption (VO2). To this end, left ventricular steady-state ejecting contractions were produced with various stroke volumes from a fixed end-diastolic volume in an excised cross-circulated canine heart. The effect of the ejection-activated Emax on VO2 was assessed by the relation between VO2 and pressure-volume area (PVA). PVA is the total mechanical energy generated by ventricular contraction. In contrast to the elevation of the linear VO2-PVA relation in a parallel manner with an enhanced Emax by ordinary positive inotropic agents such as catecholamines and calcium, the ejection-activated Emax did not elevate the VO2-PVA relation. This result indicates that the ejecting activation enhances Emax in an energetically different manner from ordinary positive inotropism in the canine left ventricle.

Energetics of the negative and positive inotropism of pentobarbitone sodium in the canine left ventricle

OBJECTIVE

Pentobarbitone (sodium) is an anaesthetic widely used in animal experiments. It is known to be a cardiovascular depressant and a coronary dilator, but its effects on myocardial energetics in relation to its negative and positive (due to Gregg's phenomenon) inotropism have not been studied. The aim of this study was therefore to determine whether and how pentobarbitone affects cardiac mechanoenergetics compared with other negative inotropic agents for which data are already available.

METHODS

The effects of graded doses of intracoronary pentobarbitone on mechanoenergetics were studied in the excised cross circulated left ventricles of 12 dogs. The framework of the Emax (a contractility index)--VO2 (myocardial oxygen consumption)--PVA (systolic pressure-volume area, a measure of total mechanical energy) relationships was fully utilised.

RESULTS

Pentobarbitone increased Emax at low doses in five of the 12 hearts. In two of these five hearts, a marked coronary dilatation was found. Pentobarbitone decreased Emax dose dependently at high doses in all the hearts and lowered the VO2 intercept but not the slope (oxygen cost of PVA) of the VO2-PVA relation. There was no difference in oxygen cost of Emax between pentobarbitone and CaCl2, although they have opposite inotropism. These findings suggest that pentobarbitone depresses myocardial mechanoenergetics via suppression of total calcium handling in the excitation-contraction-relaxation coupling.

CONCLUSIONS

Pentobarbitone at low doses partly acts as a positive inotropic agent, but at high doses it acts as a negative inotropic agent like beta blockers and calcium antagonists on cardiac mechanoenergetics in canine blood perfused hearts.

The effects of dynamic cardiac compression on ventricular mechanics and energetics. Role of ventricular size and contractility

The purpose of this study was to determine the role of ventricular size or contractility in the effectiveness of dynamic cardiac compression in terms of the pressure-volume relationship and myocardial oxygen consumption. In 10 isolated cross-circulated dog hearts, the ventricle was directly compressed during systole. For the volume run, measurements for slope of the end-systolic pressure-volume relation, pressure-volume area, external work, coronary blood flow, and myocardial oxygen consumption were achieved before and during a fixed amount of dynamic cardiac compression. Left ventricular volume was then increased while stroke volume was kept constant, and measurements were repeated. For the contractility run, after the control measurements were taken, left ventricular contractility was significantly increased or decreased by infusion of either dobutamine or propranolol into the coronary circulation. Measurements were repeated before and during dynamic cardiac compression at the control level of end-diastolic and stroke volumes. Dynamic cardiac compression significantly increased slope of the end-systolic pressure-volume relation, pressure-volume area, and external work (p < 0.01), whereas coronary blood flow and myocardial oxygen consumption were not affected. The increase in pressure-volume area caused by dynamic cardiac compression was greater with the larger volume. Despite the significant differences in the native left ventricular contractility, the increases in slope of the end-systolic pressure-volume relation, pressure-volume area, and external work did not differ among the three groups. We conclude that dynamic cardiac compression enhances left ventricular systolic function independent of ventricular contractility and without affecting coronary blood flow or myocardial oxygen consumption. Mechanical enhancement is more effective in the dilated heart.

Estimation of total carbon dioxide contents in canine coronary arterial and venous whole blood samples

We examined whether total carbon dioxide content (CCO2) estimation equations for human whole blood in the literature are applicable to canine coronary arterial and venous blood samples. PCO2 of the tested blood samples covered 19-52 mmHg; PO2 19-398 mmHg. Three CCO2 estimation equations developed by Kelman, Godfrey, and Douglas et al yielded CCO2 values over a range of 26.7-54.9 vol%, where plasma CCO2 values calculated by the Henderson-Hasselbalch equation ranged over 27.7-62.2 vol%. The estimated blood CCO2 values were almost identical among the three equations. They also closely correlated with plasma CCO2 values measured after hemolysis with saponin. We conclude that the human whole blood CCO2 estimation equations are applicable to canine coronary arterial and venous blood samples. These CCO2 equations may be used for canine cardiac metabolic studies.