Yoshifumi Okamoto

Right ventricular function evaluated by volumetric analysis during left heart bypass in a canine model of postischemic cardiac dysfunction

Right ventricular function during left heart bypass was evaluated by volumetric analysis with a conductance catheter in 12 dogs with postischemic cardiac dysfunction. The conductance catheter was used to assess the volumetric status of the right ventricle and thereby allowed a right ventricular pressure-volume curve to be obtained, in which transient volume loading on the right ventricle was applied. The following right ventricular properties during left heart bypass were assessed and compared with properties measured without left heart bypass, by means of load-independent parameters: maximum elastance, stroke work/end-diastolic volume relation, end-diastolic pressure/volume relation, and stroke work/end-diastolic pressure relation. The stroke volume derived from the conductance catheter and the electromagnetic flow probe showed good linear correlation (r2 = 0.733 to 0.975). After initiation of left heart bypass, maximum elastance did not change significantly, although volume intercept significantly increased, from 1.2 +/- 7.3 to 3.6 +/- 7.9 ml (p < 0.05). End-diastolic pressure/volume relation was well fitted to the exponential curve (EDP = e(k1.EDV+k2)) and was shifted to the right and downward during left heart bypass; the slope k1 significantly decreased, from 0.12 +/- 0.06 to 0.10 +/- 0.07 (p < 0.01). Stroke work/end-diastolic volume relation and stroke work/end-diastolic pressure relation were closely fitted to the linear regression, and their slopes were significantly increased during left heart bypass, from 0.14 +/- 0.08 to 0.18 +/- 0.08 (p < 0.05) and from 0.22 +/- 0.15 to 0.34 +/- 0.19 (p < 0.01), respectively. These results suggest that the decompression of the left ventricle and septal shifting by left heart bypass provide good diastolic compliance and good systolic performance because of afterload unloading of the right ventricle. Thus the left heart bypass improved the overall right ventricular performance, particularly at higher end-diastolic pressures, in dogs with postischemic cardiac dysfunction.

Skeletal Muscle Powered Ventricle: Comparison of Double-Layered Small Ventricle and Single-Layered Large Ventricle

Canine left latissimus dorsi (LD) muscles were used to construct two kinds of skeletal muscle powered ventricles (SMPV): a double layered small size (10‐17 mL) SMPV (A), and a single‐layered large size (40–70 mL) SMPV (B). The same muscle was used sequentially for the construction of both SMPV. A mock circulation system was used for testing. This allowed for change of the preload (10–60 mmHg) and afterload (40–160 mmHg) independently. The peak developed pressure (PDP) and stroke volume (SV) were measured, and the stroke work (SW) was analyzed on line by a computer. The isovolumic PDP was 93.3 ± 11.8 mmHg at 10 mmHg preload, and 157.7 ± 20.2 mmHg at 60 mmHg for A, and 37.8 ± 5.5 mHg and 107.8 ± 8.5 mmHg for B. The SV and SW at 50 mmHg preload and 80 mmHg afterload were 18.30 ± 1.25 mL and 1.06 ± 0.10 × 106 erg for A, and 34.18 ± 2.36 mL and 2.51 ± 0.28 × 106 erg for B. The SV and SW at 20 mmHg preload and 160 mmHg afterload were 2.65 ± 0.31 mL and 0.27 ± 0.05 × 106 erg for A, and 1.03 ± 0.23 mL and 0.04 ± 0.01 × 106 erg for (B). The SW generated by the large single‐layered SMPV is similar to that reported for the canine left ventricle but requires a high preload. The large single‐layered SMPV showed a higher dependence on pre‐ and afterload changes than the double layered small SMPV, which generates a higher pressure even at low preloads.

Experimental study of nutating centrifugal blood pump in vivo

The nutating centrifugal pump, dubbed the teaspoon pump (TS pump), was developed by Bauermeister and Affeld [1]. Later, it was improved by Akamatsu and colleagues at Kyoto University Faculty of Technology [2–4]. We have recently performed experimental studies in vivo with the TS pump, and examined its safety and efficacy. Five male sheep, weighing 48–64 kg, were used in this study. Drainage and return cannulae were inserted into the left atrium and the descending aorta, respectively. The TS pump was then driven in totally assisted circulation in first four experiments, and in partial assist (almost 50%) in the last experiment. In all cases, the entire circulation was easily maintained, and the mean arterial pressure was maintained at over 65 mmHg. Blood samples showed no remarkable abnormality concerning hemolysis; the values of free hemoglobin 48 hours after the initiation of total assist circulation were 12–13 mg/dl. Blood cell counts and total bilirubin values were within normal limits. The antithrom bogenicity of the system remained satisfactory. However, some problems were observed: (1) when ventricular fibrillation occurred while the animal was in a hypovolemic state, the drainage was found inadequate; (2) none of the sheep were able to maintain a standing position postoperatively. In order to achieve more reliable results, we need to resolve these problems.

Dual Chamber Skeletal Muscle-Powered Pump: Performance at Low Filling Pressure

The skeletal muscle powered pump (SMPP) has been reported to require a high preload (>30mmHg) to eject against a systemic range of afterload [1–3]. In recent studies we found that a small (15-ml) single layered pump had an optimal diastolic chamber volume/muscle mass ratio (V/M ratio) close to a normal left ventricular V/M ratio and that it was the most suitable to work under physiologic pre- and afterload conditions [3]. The aim of this study was to test the hypothesis that two small single layered cylindrical pumps (dual chamber single layered pump; DCSLP) in parallel would have sufficient performance to support the left ventricle (LV) in parallel, that is, at low (physiologic) preloads.

Reperfusion injury in dog hearts with permanent occlusion of a coronary artery, probably due to reperfusion via collateral vessels

To clarify whether or not reperfusion injury occurs in the permanent occlusion of a coronary artery, we analyzed quantitatively contraction band necrosis as an indicator of early recanalization, coagulation necrosis, infarct size and measured regional blood flow in dog hearts with collateral circulation. Fifty mongrel dogs were divided into four groups: 15 dogs with a 24-hour occlusion of the left anterior descending coronary artery just distal to the first diagonal branch (permanent occlusion group): 15 dogs a with 3-hour occlusion followed by 24-hour recanalization (recanalization group); 10 dogs with a 2-hour occlusion without recanalization (transient occlusion group); 10 dogs with a 4-hour occlusion without recanalization (transient occlusion group). The regional blood flow in the subepicardium and subendocardium determined by the generated hydrogen gas clearance method was greatly decreased 30 minutes after occlusion (14 + 8%/12 +/- 9%) and was relatively restored from 180 minutes (31 +/- 21%/21 +/- 14%) to 24 hours later (41 + 19%/26 + 16%) in spite of complete occlusion of the coronary artery. The percentage infarct area in the risk area was significantly greater in the permanent occlusion group (60 +/- 26%) than in the recanalization group (35 +/- 31%). Although most of the infarct was occupied by contraction band necrosis in the recanalization group (86 +/- 12%), contraction band necrosis was diffusely seen even in the permanent occlusion group (54 +/- 27%). In both the permanent and recanalization groups, contraction band necrosis was the main histological feature of small infarcts occupying less than 30% of the risk area, while coagulation necrosis was the main feature in very large infarcts occupying more than 80% of the risk area. In the occlusion groups without recanalization, the percentage area of contraction band necrosis in the risk area was 6 +/- 8% after the 2-hour occlusion, 23 +/- 17% after the 4-hour occlusion and 31 +/- 21% after permanent occlusion; the difference between the 4-hour and permanent occlusion groups was not significant. In the permanent occlusion group, the percentage infarct area in the risk area was inversely correlated with regional blood flow during occlusion, an indicator of collateral flow. It was concluded that reperfusion injury occurs even in hearts without recanalization. The pathogenesis may involve reperfusion in the risk area via collateral circulation. Protection against reperfusion injury is important to minimize the infarct size even in hearts with permanent occlusion, although the presence of collateral flow is an important factor in limiting infarct size.