**7. Valve-less Biomechanical Hearts**

9

**989 ml/min 1 Hz n=6**

Group B

A C T C T C T C T C T

B C T C T C T C T C T

**Figure 10.** Gel electrophoresis of myosin heavy chains MHC I and MHC IIa from group A with a mean pulse frequency of 5 Hz. Control (C) was the non stimulated contra-lateral LDM. In group B with a mean stimulation frequency of 1 Hz,

**6. Stroke volume of SMVs with 100% type-I-fiber (A) vs. SMVs with 50%**

As an example one fast, relatively fatigue resistant SMV delivered a maximal pump volume of about 3 L/min. It could be maintained over two minutes. Thereafter it decreased to 1,5 L/min after 5 minutes. This dynamic adaptation of stroke volume per minute in that high level of pumping volume up to 3 L/min was solely possible in the 50% type IIa fibre muscle. 100 % type

**A B**

**Figure 11.** Stroke volumes evaluated in a Frog surrounded by a goat's SMV of a latissimus dorsi muscle of 330g up to 200 days postoperatively. In group A with 100% type I fibres stroke volume per minute was at 405 ml and in the fast, relatively fatigue resistant muscle with about 50% type IIa fibres stroke volume per minute was at 888 ml per minute.

I fibre ventricles did enhance its pumping capacity however only up to 1 L/min.

**405 ml/min 5 Hz n=6**

This amount of stroke volume per minute could be maintained over months.

Group A

**0**

**200**

**400 600**

**800**

**1000**

**1200**

**Volume [ml/min]**

type IIa MHC is well preserved and about 50% after several months in all stimulated SMVs.

**type-IIa fiber (B)**

350 Regenerative Medicine and Tissue Engineering

Biomechanical Hearts, constructed in adult Boer goats (n=5), are blood pumps, consisting of a pumping chamber with clinically relevant stroke volumes [11]. They can be integrated into the circulation in a one-step operative procedure during pharmacological stimulation with the β-2-stimulator Clenbuterol (5 x150μg/wk). This experimental pumping chamber, made of PTFE, was anastomosed to the descending aorta by two ring armoured PTFE-prostheses (Impra Medica GmbH, München), as shown in Figure 13. The pumping chamber was used mainly for three reasons: firstly, to stabilize the ventricular pump cavity with improved flow characteristics to minimize thrombo-embolic complications; secondly, to prevent muscle damage by overstretch-induced ischemia; and thirdly, to prevent a ventricular chamber rupture.

During surgery, the mean stroke volume of BMHs was 53.8±22.4 ml. One month after surgery, in peripheral pressure, the mean and minimal diastolic pressure of BMH-support‐ ed heart cycle differed significantly from unsupported ones (Figure 14). After BMHsupported heart contractions, the subsequent maximal rate of pressure generation, dP/dt max increased by 20.5±8.1% (p<0.02). One BMH, catheterized 132 days after surgery, shifted a volume of 34.8 mL per beat and 1.4 L/min with a latissimus dorsi muscle of 330 g (Figure 14, top).

**Figure 13.** Scheme of an experimental setting in a big animal model in an aorto-aortic configuration. The thoracic aorta is ligated between the two anastomoses. Two muscular stimulation electrodes activate the LDM and an epicar‐ dial sensing electrode enables the syncronization with the heart cycle.

**Figure 14.** Stroke volume determination with a conductance catheter, placed within the pumping chamber of the BMH (left, top). Pressure-volume-loop of a BMH on postoperative day 132 with a stroke volume of 34.8 ml and an output of 1400ml per minute (right, top). ECG with stimulation bursts, a pressure trace from a peripheral artery where the BMH is in a 1:2 mode and synchronized with the heart (bottom).

**Figure 15.** Explanted BMH without valves after 414 days of pumping within a Boer goat. The pumping chamber was made of a double layered polyurethane membrane including steel springs and it was connected to the aorta by ring armoured PTFE prostheses.
