Biomedical subjects
Publications and source records attributed to T Akutsu.
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This paper describes the implementation of a microcomputer based P-wave synchronization system for the artificial heart. This system provides for synchronization of the cardiac prosthesis pump with P-wave signals from electrodes implanted in the remnant of the natural atrium. The device carries out the functions of P-wave detection and determines the duration of systole based upon a moving average of the time intervals between successive pulses. The system has been tested both on a mock circulatory system and in vivo on calves. The purpose of the paper is to provide details of the circuitry and algorithms used.
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Cardiovascular regulatory mechanisms are implemented by means of a very complex control system involving neural, humoral, and mechanical agents. The state of the art in TAH today reveals that we have passed a stage where we can be satisfied with a 6 or 9 mo survival. Development and implementation of a versatile control theory must be another milestone before a TAH can really serve the prospective patient population requiring such a device. This study reveals the vital role and merits as well as the feasibility of incorporating such a control theory into the device.
For HR in the range of 70--110 beats/min, and same driving conditions, the pump with rigid housing produced a maximum of 15% greater CO than that with the soft housing, against an arterial pressure of 125/75 mm Hg. All 3 pumps exhibited greater sensitivity in function curves for HR in the range of 90--110 beats/min. The greatest sensitivity point in the function curve, for the rigid housing pump was found to be independent of HR change in the range of 90--110 beats/min. However, with an increase in HR the function curves shifted to the right in the case of soft housing pumps. In other words, greater atrial pressure was required to obtain the same CO with an increase in HR. The linear relationship found between CO and HR in flexible and soft housing pumps was very advantageous for controlling CO, whenever such change was required. In all 3 hearts there was a decrease in pulse pressure with an increase in HR. The decrease in pulse pressure was primarily due to the increase in diastolic pressure, while systolic pressure remained almost constant at all HRs. Since these experiments were conducted in a test circulatory system using an aqueous-glycerin solution, information on the degree of hemolysis was not addressed in this report.
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Three vasoactive drugs--glucagon, acetylcholine and dopamine were used in calves with an implanted TAH to study their mere vascular effects. We noticed that glucagon, besides being a potent vasodilator, affected the vascular system gradually rather than instantly. Also, it allowed for the gradual recovery of the system, thus avoiding sudden fluctuations in systemic and pulmonary blood pressures. Glucagon was found to have a unique capability of decreasing vascular resistance with only a slight drop in systolic pressure. Acetylcholine action was rather instant, exhibiting a sudden fall in both systolic and diastolic blood pressures. In animals with a TAH, dopamine seemed to work differently from that in subjects with an intact natural heart. While many investigators failed to see any change in pulmonary vascular resistance due to dopamine injection in subjects with an intact natural heart, we noticed about 20% increase in pulmonary vascular resistance (with a dose of 10 muGm/Kg). However, at low dosages of dopamine, we did not notice any appreciable change in pulmonary vascular resistance, which suggests that its action is dose dependent. We tend to believe that glucagon offers promising results in controlling the pulmonary hypertension in calves with a TAH. It is, also, our opinion that further investigation on the vascular effects of dopamine would reveal more pertinent and interesting results and solve the existing discrepancies.