Canine latissimus dorsi muscle: an apparatus for isometric force measurements.

This paper describes a device used to measure the isometric forces generated during electrical stimulation of the canine latissimus dorsi muscle in vivo with a preserved neurovascular supply. This device uses 2 strain gauge force sensors linked to a movable alignment frame to which the muscle is attached. The muscle length is controlled by the application of known weights to the system. The device has a frequency of response of 17.5 Hz and compliance of approximately 0.1 mm N(-1), and its experimental performance was tested in the anesthetized mongrel dog.

Extracorporeal circulation with autogenous oxygenation: hemodynamic and gasometric parameters.

Ten experimental perfusions with autogenous oxygenation were performed in mongrel dogs to evaluate the efficacy of the procedure in maintaining normal hemodynamic the efficacy of the procedure in maintaining normal hemodynamic conditions and adequate blood gases for 1 h. Blood was drained from the right and left atria and pumped to the pulmonary artery and aorta, respectively. Two closed circuits containing compliant chambers and roller pumps were utilized. Artificial ventilation with an FiO2 of 50% were used in 5 animals and with an FiO2 level of 30% in the other 5. EKG, cardiac output, aortic, pulmonary artery, and left atrium pressures were registered. Pulmonary tissue was biopsied after perfusion. The heart was electrically fibrillated after perfusion was established and defibrillated at the end of the bypass. The procedure was able to maintain blood gases and pulmonary, aortic, and left atrial pressures within normal ranges during the perfusion. The mobility of the heart and the access to all coronary arteries was excellent. Clinical central nervous system evaluation, EKG tracings, and pulmonary histological exams showed no adverse effects of perfusion. We conclude that the technique employed may present a suitable proceeding for extracorporeal circulation in closed heart surgeries, and its clinical application should be evaluated as a safe and economical alternative.

Design, manufacturing, and testing of a paracorporeal pulsatile ventricular assist device: São Paulo Heart Institute VAD.

This paper describes the design of a ventricular assist device (VAD), its manufacturing, and testing. The VAD presented is pulsatile, with a free-floating membrane, smooth internal surfaces, and pericardial valves. It comprehends also a pneumatic driving unit capable of operating in the "full to empty," EKG synchronized or asynchronous modes. In vitro tests were performed to assess its mechanical durability, hydrodynamic performance, and hemolysis. To optimize cannulas and implant techniques, we performed in vivo tests in 22 sheep and 8 calves. In these tests, we also evaluated hemolysis and the device's capacity to normalize hemodynamic parameters during induced cardiac failure. The VAD worked for 4,000 h without failure in a mock circulatory loop. In full to empty mode, it displayed a rate-mediated "Starling-like" performance. Optimum output was achieved with a systole duration of 40% of the cycle. The in vitro hemolysis index (IH) was 6.7 +/- 2.1. Hemolysis in animal experiments was clinically nonsignificant. In calves with induced cardiac failure, the VAD was able to normalize hemodynamic parameters within 120 min.

[Design, manufacturing, and testing of a pulsatile ventricular assist device]. / Projeto, construção e testes de um dispositivo de assistência ventricular pulsátil.

PURPOSE: To describe the design of a ventricular assist device (VAD), its manufacturing and testing. METHODS: The VAD is pulsatile, with a free floating membrane, smooth internal surfaces, and pericardium valves. It comprises also a pneumatic driving unit capable of operating in the "full to empty", EKG synchronized or asynchronous modes. The system was tested "in vitro" to assess its mechanical durability, hydrodynamic performance and hemolysis. "In vivo" tests were performed in 22 sheep and 8 calves aiming at optimizing cannulas and implant techniques. In these experiments, hemolysis and the device's capacity of restoring to normal hemodynamic parameters during induced cardiac failure were evaluated. RESULTS: The device was worked 4,000 hours without failure in a mock circulatory loop. Hydrodynamic performance was satisfactory for adult circulatory support. In "full to empty" mode it displayed a frequency mediated "Starling like" performance. Optimum output was achieved with a systole duration of 40% of the cycle. "In vitro" hemolysis index was 6.7 +/- 2.1. Hemolysis in animal experiments was clinically non significant. In calves under induced cardiac failure the VAD was able to normalize hemodynamic parameters within 120 minutes. CONCLUSION: This VAD is capable to circulatory assist for cardiogenic shock in conditions needed for an adult patient and the average time span anticipated for bridge to transplantation or post cardiotomy cardiogenic shock.

A pathway for information transmission to the inner ear. Application to cochlear implants.

The use of cochlear implants as an aid to neurosensory deafness is becoming an established procedure. The transmission of a processed speech signal is accomplished either transcutaneously via radiofrequency or percutaneously by connector coupling. Whereas the former is sensitive to electromagnetic interference, the latter increases the risk of infection. To overcome these disadvantages, an infrared (IR) system for transmission through the tympanic membrane was devised and tested. The transmitter/receiver consisted of an IR light emitting diode (LED; 920 nm) and a photovoltaic cell. The LED was placed inside the auditory canal of four dogs and the photovoltaic cell in the tympanic cavity over the cochlear promontory. A sinusoidal signal modulation was applied to the LED. The emitted signal was detected undistorted after crossing the tympanic membrane, with an average absorbance of 20%. High frequency cut-off was adequate for cochlear implant purposes and audio prosthetic devices in general. The authors conclude that the tympanic membrane may be used as a translucent sealed interface to transmit data in the audio range to the middle and inner ears, with small power loss, good frequency response, and immunity to interference.

Mechanical support of the circulation and the Frank-Starling law: a physiological approach

The performance curves of an external pulsatile flow pump for temporary circulatory mechanical support are analyzed with special attention to the "fill to empty" control mode and an analogy with the Frank-Starling law is established

Biomechanical circulatory assistance. Importance of aerobic capacity of normal and conditioned skeletal muscles.

To define more efficient use of biomechanical circulatory assistance, the contracting and fatigue characteristics of normal and conditioned latissimus dorsi of seven adult mongrel dogs were analyzed. The conditioned muscles underwent vascular adaptation and electrical stimulation with burst frequency of 50 Hz in rates of 60 and 120 contractions per minute for 6 to 8 weeks. They were compared with unconditioned contralateral controls by isometric force measurements. Normal and transformed muscles exhibited the same optimum pacing parameters (burst frequencies from 50 Hz up and train durations from 150 msec) with supramaximal amplitude stimulation. Conditioned muscles showed initial smaller forces (-27%) and longer contraction times (+32%). Fatigue curves of unconditioned muscles for different duty cycles showed marked initial decreases and proportional stable values of force after some minutes, with equal final tension time indexes under these conditions (20 +/- 3 KgF seg/min 100 g). Conditioned muscles maintained stable force for same duty cycles and a greater tension time index during prolonged conditions (68 +/- 6 KgF seg/min 100 g). This study revealed that normal and conditioned skeletal muscles are capable of maintaining steady state work depending upon their aerobic capacity and suggests that these muscles may undergo adaptive transformation while contracting in a synchronous fashion with the heart during variable duty cycles.

Measurements of renal sympathetic nerve activity in conscious sinoaortic denervated rats.

The increase in renal sympathetic nerve activity (RSNA) produced in freely moving rats by sinoaortic denervation was analyzed both by counting the neural spikes and integrating the recorded electroneurogram. The percent increase was found to be greater when activity was calculated considering spike frequency (71%) rather than integrated voltage (54%). The different values obtained by the two methods suggests that after SAD, in addition to the increase in the nerve impulse frequency, there is an alteration in the pattern of nerve discharge.