Miniature transport respirator performance evaluation for ventilatory support

Abstract. In the face of the coronavirus pandemic (COVID-19), in hospital and emergency units, there is low availability of mechanical respirator for patients in need of this support, greatly improving the survival rate. In these situations, there is a need for simpler equipment, easy access, low cost, and fast manufacturing. In this study, a 3D prototype transport respirator was developed using as a model the Takaoka 600 Mini Respirator, national technology from the 1950s. The influence of adjustable parameters of the respirator was evaluated to understand it is functioning: maximum and minimum lung pressure; respirator intake pressure; respiratory rate; inspiratory and expiratory time according to the sensitivity of the mini respirator; and pressure and flow of O2 line intake. The increase in sensitivity led to an increase in maximum and minimum pulmonary pressure, decreased inspiratory and expiratory time, with margins of 1/1, 1/2, 1/3 inspiratory/expiratory time ratio (I/E ratio). The intake flow of O2 varied proportionally with the pressure of air intake into the respirator, with its increase leading to an increase in respiratory rate, without major influences on lung pressure and the I/E ratio. The O2 line intake pressure without major influences on lung pressure, showing and I/E ratio >1 in values below 3.5 kPa x 100. In conclusion, it was possible to obtain a pulmonary ventilator-dependent only on positive O2 flow, compact and effective for patient transport, and in cases of emergencies with control of maximum pressure and respiratory rate offered to the patient. Among the parameters evaluated for this respirator, an line pressure of O2 from 3.5 kPa x 100, sensitivity between 3 and 5, a flow of 5 to 15 L/min is recommended.

Auxiliary total artificial heart: A compact electromechanical artificial heart working simultaneously with the natural heart.

Leading international institutions are designing and developing various types of ventricular assist devices (VAD) and total artificial hearts (TAH). Some of the commercially available pulsatile VADs are not readily implantable into the thoracic cavity of smaller size patients because of size limitation. The majority of the TAH dimensions requires the removal of the patients' native heart. A miniaturized artificial heart, the auxiliary total artificial heart (ATAH), is being developed in these authors' laboratories. This device is an electromechanically driven ATAH using a brushless direct current (DC) motor fixed in a center metallic piece. This pusher plate-type ATAH control is based on Frank-Starling's law. The beating frequency is regulated through the change of the left preload, assisting the native heart in obtaining adequate blood flow. With the miniaturization of this pump, the average sized patient can have the surgical implantation procedure in the right thoracic cavity without removing the native heart. The left and right stroke volumes are 35 and 32 ml, respectively. In vitro tests were conducted, and the performance curves demonstrate that the ATAH produces 5 L/min of cardiac output at 180 bpm (10 mmHg of left inlet mean pressure and 100 mm Hg of left outlet mean pressure). Taking into account that this ATAH is working along with the native heart, this output is more than satisfactory for such a device.

Flow visualization studies to improve the spiral pump design.

The spiral pump (SP) uses centrifugal and axial pumping principles simultaneously, through a conical shaped impeller with threads in its surface. Flow visualization studies were performed in critical areas of the SP. A closed circuit loop was filled with glycerin-water solution (40%). Amberlite particles (80 mesh) were illuminated by a planar helium-neon laser light (7 mW). The particle velocities were recorded with Kodak (TMAX-400) black and white film, and the flow behavior was studied with a micro video camera and color video printer. The flow visualization studies showed no turbulence or stagnant areas in the inlet and outlet ports of the SP. When using the impeller with one lead, at the top of the threads some recirculation appeared when the total pressure head increased. Two new impellers were made. One of them had the same conical shape with a thread having 2 leads. The second had a thread with 2 leads, but it also had a bigger cone angle. These modifications improved the pump hydrodynamic performance, decreasing the recirculation in pumping conditions that require pressures over 200 mm Hg.

Characteristics of a blood pump combining the centrifugal and axial pumping principles: the spiral pump.

Two well-known centrifugal and axial pumping principles are used simultaneously in a new blood pump design. Inside the pump housing is a spiral impeller, a conically shaped structure with threads on the surface. The worm gears provide an axial motion of the blood column through the threads of the central cone. The rotational motion of the conical shape generates the centrifugal pumping effect and improves the efficiency of the pump without increasing hemolysis. The hydrodynamic performance of the pump was examined with a 40% glycerin-water solution at several rotation speeds. The gap between the housing and the top of the thread is a very important factor: when the gap increases, the hydrodynamic performance decreases. To determine the optimum gap, several in vitro hemolysis tests were performed with different gaps using bovine blood in a closed circuit loop under two conditions. The first simulated condition was a left ventricular assist device (LVAD) with a flow rate of 5 L/min against a pressure head of 100 mm Hg, and the second was a cardiopulmonary bypass (CPB) simulation with a flow rate of 5 L/min against 350 mm Hg of pressure. The best hemolysis results were seen at a gap of 1.5 mm with the normalized index of hemolysis (NIH) of 0.0063 +/- 0.0020 g/100 L and 0.0251 +/- 0.0124 g/100 L (mean +/- SD; n = 4) for LVAD and CPB conditions, respectively.

[Artificial respiration with extracorporeal membrane oxygenator in arteriovenous position without pump. Experimental study]. / Respiração artificial com oxigenador de membrana extracorpóreo em posição artério-venosa sem bomba. Estudo experimental.

PURPOSE: To test the hypothesis of respiratory support and to study the consequent hemodynamic alterations, we performed pumpless A-V ECMO using a 1.2m2 polipropylene hollow fiber membrane oxygenator, specially adapted from conventional model utilized in routine cardiac surgery. METHODS: Two canine groups of six dogs each were studied. Group 1 had normal lungs and group 2 acute respiratory failure induced by 0.035ml/kg intravenous oleic acid. The dogs were anesthetized and maintained in apnea with curare. Heparin was given in a single dose of 400U/kg. Gasimetric and hemodynamic parameters were monitored each 30 minutes during a 3 hour period. Then the oxygenator was discontinued and after 15 minutes a final arterial blood gas sample was taken for analysis. RESULTS: Blood samples at 3 hours have shown a mean PaO2 of 260.6mmHg in group 1 and 114.4mmHg in group 2 and PaCO2 of 54.3 and 56.2mmHg, respectively. After the oxygenator was discontinued PaCO2 levels increased to 161.6 and 193.7mmHg, respectively. The hemodynamic parameters shown few alterations. CONCLUSION: In both groups pumpless A-V ECMO was able to maintain gasimetric parameters within acceptable patterns and compatible with life, with few hemodynamic alterations. However, an adequate mean arterial blood pressure is needed to provide flow through membrane oxygenator.

Autotransfusao intra-operatoria. Novo dispositivo para sua realizacao. / Intraoperative autotransfusion. A new device for its conduction

E apresentado um dispositivo para realizacao de autotransfusao intra-operatoria, constituido por um recipiente de acrilico, descartavel e capaz de coletar, anticoagular e filtrar o sangue. A autotransfusao foi praticada em 12 casos, sendo 8 em cirurgia de emergencia e 4 em cirurgia seletiva. O dispositivo mostrou-se simples e de facil utilizacao, mas elevada frequencia de contaminacao em amostra de sangue aspirado indica a necessidade de aprimoramento na manipulacao do mesmo

Nutricao enteral atraves de sondas nasojejunais. Apresentacao de uma nova sonda feita de borracha de silicone. / Enteral nutrition through naso-jejunal intubation. Presentation of a new tube made of silicone elastomers

Os autores apresentam um novo modelo de sonda para alimentacao enteral, inteiramente feito de silastic radiopaco e provido, na sua extremidade distal, de um pequeno balao contendo mercurio. Suas vantagens em relacao as sondas de alimentacao tradicionais sao: menor calibre, extraordinaria flexibilidade e biocompatibilidade e facilidade de migracao espontanea para o duodeno ou jejuno, quando desejada. Sua utilizacao em dez pacientes que dependiam de alimentacao enteral para manutencao ou melhora das suas condicoes nutritivas, revelou resposta satisfatoria ao tratamento, com ausencia de fenomenos irritativos e excelente tolerancia por parte dos enfermos propiciando uma infusao mais constante e mais segura da dieta