Critical care patients are often connected to ventilators, to support or replace their breathing. The ventilators deliver a mixture of gas to the patient by applying a specific volume or pressure, and then the patient exhales passively. This thesis is based of the hypothesis that a slower reduction of the expiration pressure could benefit intensive care patients connected to a ventilator. To enable research within the area, a device which can control the expiration is needed. In this thesis project, an expiration valve was controlled to create different pressure patterns during expiration. To facilitate the research and the usage of the expiration control, an application software was created with the purpose to simulate relevant pressure, flow and volume curves. The prototype is an expiration cassette created for the ventilator Servo-i by Maquet Getinge Group. To enable flexibility, the prototype is external and no information is transmitted from or to the ventilator. The prototype has its own flow and pressure sensors. The different pressure patterns which the prototype uses are designed as a linear decrease and as if a constant resistance was added to the system. The user can also create their own pressure pattern, by deciding 20 pressure points in the duration of two seconds. The simulation application was designed with the ability to simulate the same pressure patterns available with the prototype. By using a lung model, it is possible to simulate the ideal pressure, flow and volume in the lungs which can be expected from the chosen expiration control. During the implementation, two different types of lung models were evaluated in order to determine the specificity required. The prototype was tested with settings which were chosen to challenge the performance of the control. Some problematic areas were detected, such as high pressures or large volumes. However, the prototype was judged to perform well enough to be used in animal trials. The lung model used for the simulation application was a simple model of the lung, consisting of a resistor and a capacitor in series. The simulations were compared with the real system with the purpose to get an indication on the difference between theory and reality. The application presents the expected behavior when using the expiration control. However, it should be kept in mind by the user that the application represents a theoretical model.

Em condições basais a inspiração é um fenômeno ativo enquanto a expiração é um fenômeno passivo. Em condições de desafios metabólicos, como aumento da pressão parcial de CO2 e da [H+] no sangue arterial (hipercapnia/acidose), ocorre aumento da atividade inspiratória, a expiração passa a ser ativa, produzindo aumentos da atividade dos músculos abdominais, e a resistência das vias aéreas superiores reduz. O Locus Coeruleus (LC) contém neurônios noradrenérgicos (NE) que aumentam sua frequência de potenciais de ação quando expostos a elevados níveis de CO2/[H+] e se comunicam com os neurônios respiratórios do tronco encefálico para fazer ajustes compensatórios na ventilação pulmonar durante a hipercapnia/acidose. Utilizando preparações in situ de ratos avaliamos a contribuição dos neurônios NE do LC na geração central das atividades inspiratória e expiratória e no controle da resistência das vias aéreas superiores em condições basais e em resposta a hipercapnia/acidose. Neurônios NE do LC foram seletivamente silenciados de maneira aguda e reversível pela aplicação do peptídeo de inseto alatostatina (Alst) após a transfecção celular utilizando um vetor lentiviral para expressão de receptores de Drosophila para a Alst acoplados a proteína G inibitória (AlstR). Dez a doze dias após, realizamos a abordagem dorsal da preparação in situ de ratos. Os nervos frênico (PN), abdominal (AbN), hipoglosso (HN) e vago cervical (cVN) foram registrados e analisados em diferentes fases do ciclo respiratório. Registros extracelulares single unit dos neurônios do LC também foram realizados. A frequência respiratória (fR), a duração da inspiração (DI) e da expiração (DE), a expiração ativa, a magnitude da modulação respiratória e a frequência de potenciais de ação dos neurônios do LC também foram avaliadas. A inibição seletiva dos neurônios NE do LC usando Alst não provocou alterações significativas na atividade dos motores nervos respiratórios, na fR, DI e DE em normocapnia. A inibição desses neurônios antes e/ou durante à hipercapnia/acidose reduziu significantemente a amplitude do AbN e em alguns momentos, eliminou a expiração ativa, além de reduzir as respostas inspiratórias do PN e HN (amplitude) e a atividade pós-inspiratória (adução da glote) do cVN. Quandoda ausência da expiração ativa após a inibição dos neurônios NE do LC, a DI, DE e a duração da atividade pré-inspiratória do cVN (abdução da glote) e HN (protusão da língua) foram normalizadas. A adição de Alst em preparações in situ de ratos que não expressavam o AsltR durante a hipercapnia/acidose não causou alterações no padrão dos nervos motores respiratórios registrados, na incidência da expiração ativa e na fR, DI e DE. Entre os neurônios do LC registrados, encontramos três populações com diferentes padrões de modulação pela respiração e uma com atividade tônica. A hipercapnia/acidose aumentou a magnitude da modulação respiratória e a frequência de potenciais de ação destas populações neuronais. Esses dados demonstram que os neurônios NE do LC exercem importante papel modulatório excitatório na geração central da inspiração, expiração ativa e no controle da resistência das vias aéreas superiores evocados pela hipercapnia/acidose em preparações in situ de ratos / In basal conditions, inspiration is an active phenomenon while expiration is a passive phenomenon. Under conditions of high metabolic demands, such as increased in partial pressure of CO2 and [H+] in arterial blood (hypercapnia/acidosis), there is an increase in inspiratory activity, expiration becomes active, producing increases in abdominal muscle activity, and the resistance of the upper airways reduces. The Locus Coeruleus (LC) contains noradrenergic (NE) neurons that increase their firing frequency when exposed to elevated CO2/[H+] levels and communicate with respiratory brainstem neurons to make compensatory adjustments in lung ventilation during hypercapnia/acidosis. Using in situ preparations of rats, we evaluated the contribution of LC NE neurons in the central generation of inspiratory and expiratory activities, as well as in the control of upper airway resistance in basal conditions and in response to hypercapnia/acidosis. LC NE neurons were selectively acutely and reversibly silenced by application of the insect allatostatin peptide (Alst) after cellular transfection using a lentiviral vector for expression of Alst Drosophila receptors coupled to inhibitory G protein (AlstR). Ten to twelve days after, we performed the dorsal approach of the in situ preparation of rats. The phrenic (PN), abdominal (AbN), hypoglossal (HN) and cervical vagus (cVN) nerves were recorded and analyzed in different phases of the respiratory cycle. Single unit extracellular records of LC neurons were also performed. Respiratory frequency (fR), duration of inspiration (DI) and expiration (DE), active expiration, the magnitude of respiratory modulation and the firing frequency of LC neurons were also evaluated. Selective inhibition of LC NE neurons using Alst did not produce significant changes in the activity of respiratory motor nerves, fR, DI and DE in normocapnia. Inhibition of these neurons before and/or during hypercapnia/acidosis significantly reduced AbN amplitude and its incidence, as well as the inspiratory responses of PN and HN (amplitude) and post-inspiratory activity (glottal adduction) of the cVN. In the absence of active expiration after the inhibition of LC NE neurons, the DI, DE and the pre-inspiratory activity of cVN (glottal abduction) and HN (tongue protrusion) were normalized. The perfusion of Alst in in situ preparations of rats withoutthe expression of the AsltR during hypercapnia/acidosis did not change the pattern of the recorded respiratory motor nerves, the incidence of active expiration, fR, DI and DE. Among the registered LC neurons, we found three populations with different patterns of respiratory modulation and one with tonic activity. Hypercapnia/acidosis increased the magnitude of the respiratory modulation and their firing frequency. These data demonstrate that LC NE neurons exert an important excitatory modulatory role in the central generation of inspiration, active expiration and in the control of upper airway resistance evoked by hypercapnia/acidosis in in situ preparations of rats