RESPIRATORY PHYSIOLOGY PDF

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respiratory control centre in medulla oblongata (Brain stem). PRESSURE- VOLUME RELATIONSHIPS: In the pulmonary physiology absolute pressure means. Respiratory Physiology. Jesús Armando Sánchez-Godoy. J.A. Sánchez-Godoy. Departamento de Ciencias Fisiológicas, Pontificia Universidad. Javeriana. PDF | On Oct 1, , Nicholas Lees and others published Respiratory Physiology.


Respiratory Physiology Pdf

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𝗣𝗗𝗙 | This textbook describes the physiological function of the respiratory system which includes mechanics of breathing, lung function test. FRC is the lung's physiological reserve/reservoir (resting volume of the lung) for IN ARDS, lung compliance is reduced (lungs are stiffer and more difficult to. Respiratory System Physiology. Mimi Jakoi, PhD. Jennifer Carbrey, PhD. The underlined headings correspond to the eight Respiratory System videos. 1.

Introduction

Each year millions of patients undergo surgical procedures, with a non-negligible mortality rate and incidence of postoperative pulmonary complications PPCs 1 , 2. In this context, even small improvements can translate to a relevant reduction of morbidity and improved outcome after surgery.

The last decade has seen a great interest on the possibility to reduce the incidence of PPCs through the adoption of ventilatory strategies aimed at minimising the potential damage induced by mechanical ventilation, namely using protective ventilation 3 , similarly to what was previously proposed in patients with the acute respiratory distress syndrome 4.

However, the optimal setting of the ventilator during general anaesthesia is still under debate.

There is consensus that tidal volume VT reduction to 6—8 mL per kg of predicted body weight improves the respiratory function 5 and reduces the incidence of PPCs 6.

The role of positive end-expiratory pressure PEEP is more debated, with several authors proposing the use of higher PEEP levels but trials reporting inconsistent results 7 , 8. Monitoring tools during general anaesthesia are increasingly at the cutting edge, providing to clinicians the opportunity to gather in real-time several respiratory parameters, allowing the clinician to assess the patient comprehensively 9.

However, there are often conflicting results concerning the optimal intraoperative ventilation settings, and translating into clinical action the different parameters available on the ventilator might not be straightforward.

The aims of this review are: I to provide a basic introduction to the respiratory physiology applied to intraoperative mechanical ventilation; II to resume the most recent evidence in the field; and to help the clinician interpreting respiratory physiology in the operating room. Basic physiology and mechanical ventilation The knowledge of respiratory system and lungs mechanics is essential to understand as well as to better interpret correctly the interaction between ventilator and patient.

Respiratory system mechanics is the result of a complex interaction between the chest wall and the lungs.

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In physiologic conditions, respiratory muscles, elastic properties of chest wall and lungs play a central role in the generation of the airflow, creating a pressure gradient from the airway opening to the pleural cavity. In the intraoperative settings, due to the use of neuromuscular blockade and drugs reducing the respiratory drive, the muscular component is markedly reduced or, as occurs in most cases, completely abolished.

As a consequence, the ventilator must create the airflow, to generate a positive pressure and consequently a tidal volume, independently from the action of respiratory muscles.

The interpretation of all ventilator-derived parameters in the operating room is fundamental because they provide an early and simple way to optimize mechanical ventilation setting, recognize and manage intraoperative issues 10 , In the next paragraphs we provide a concise overview to measure and to interpret physiology monitoring inside the operating room.

Elastic and resistive components of the respiratory system The ratio between volume variation during the respiratory cycle, namely VT, and the pressure gradient generated to achieve such VT, i.

Introduction

Respiratory system compliance CRS is given by the addition in parallel of chest wall CCW and lung compliance CL , resulting in a total compliance value inferior to the single ones. Flow Q encounters a resistance, generating a pressure increase proportional to Q. The resistance of the airways R is estimated dividing the pressure drop by the flow that generated it.

Therefore, the peak airway pressure Ppeak is both influenced by the elastic and resistive properties of the respiratory system. To eliminate the resistive component, the airflow must be interrupted by using an end-inspiratory pause. Indeed, the most accurate value of compliance is calculated in condition of zero-flow; in this way, the pressure component related to resistance is abolished, allowing to calculate a value of pressure in static conditions at end-inspiration reflecting the elastic properties of the respiratory system or the lung alone.

There is consensus that tidal volume VT reduction to 6—8 mL per kg of predicted body weight improves the respiratory function 5 and reduces the incidence of PPCs 6.

The role of positive end-expiratory pressure PEEP is more debated, with several authors proposing the use of higher PEEP levels but trials reporting inconsistent results 7 , 8. Monitoring tools during general anaesthesia are increasingly at the cutting edge, providing to clinicians the opportunity to gather in real-time several respiratory parameters, allowing the clinician to assess the patient comprehensively 9.

However, there are often conflicting results concerning the optimal intraoperative ventilation settings, and translating into clinical action the different parameters available on the ventilator might not be straightforward.

Respiration (physiology)

The aims of this review are: I to provide a basic introduction to the respiratory physiology applied to intraoperative mechanical ventilation; II to resume the most recent evidence in the field; and to help the clinician interpreting respiratory physiology in the operating room.

Basic physiology and mechanical ventilation The knowledge of respiratory system and lungs mechanics is essential to understand as well as to better interpret correctly the interaction between ventilator and patient.

Respiratory system mechanics is the result of a complex interaction between the chest wall and the lungs. In physiologic conditions, respiratory muscles, elastic properties of chest wall and lungs play a central role in the generation of the airflow, creating a pressure gradient from the airway opening to the pleural cavity.

In the intraoperative settings, due to the use of neuromuscular blockade and drugs reducing the respiratory drive, the muscular component is markedly reduced or, as occurs in most cases, completely abolished. As a consequence, the ventilator must create the airflow, to generate a positive pressure and consequently a tidal volume, independently from the action of respiratory muscles. The interpretation of all ventilator-derived parameters in the operating room is fundamental because they provide an early and simple way to optimize mechanical ventilation setting, recognize and manage intraoperative issues 10 , In the next paragraphs we provide a concise overview to measure and to interpret physiology monitoring inside the operating room.

Elastic and resistive components of the respiratory system The ratio between volume variation during the respiratory cycle, namely VT, and the pressure gradient generated to achieve such VT, i. Respiratory system compliance CRS is given by the addition in parallel of chest wall CCW and lung compliance CL , resulting in a total compliance value inferior to the single ones.

Flow Q encounters a resistance, generating a pressure increase proportional to Q. The resistance of the airways R is estimated dividing the pressure drop by the flow that generated it.

Therefore, the peak airway pressure Ppeak is both influenced by the elastic and resistive properties of the respiratory system. To eliminate the resistive component, the airflow must be interrupted by using an end-inspiratory pause.

Indeed, the most accurate value of compliance is calculated in condition of zero-flow; in this way, the pressure component related to resistance is abolished, allowing to calculate a value of pressure in static conditions at end-inspiration reflecting the elastic properties of the respiratory system or the lung alone.

In particular, airway pressure measured in condition of zero-flow is called Pplat that differs from Ppeak that is measured in presence of flow, thus carrying the effect of airway resistances. Pplat is the closest estimation of pressure inside the alveoli that can be measured non-invasively. At the end of inspiration, the expiratory valve is released to allow passive expiration, and a PEEP can be applied.

Usually, a clearly sign of PEEPi is when the flow starts from a negative value at end-expiration; in this case setting a prolonged I:E ratio and decreasing respiratory rate with the help of a neuromuscular blockade and sedation reduce the air-trapping, thus dropping the total airway pressure during expiration.When metabolizing macronutrients carbon dioxide and water are produced.

Exposure to second-hand smoke can cause lung cancer in individuals who are not tobacco users themselves. By definition, airways with no cartilage are termed bronchioles. The other ends of these muscle fibers converge to attach to the fibrous central tendon, which is also attached to the pericardium on its upper surface Figure 2—3. To eliminate the resistive component, the airflow must be interrupted by using an end-inspiratory pause.

Pulmonary Physiology, 9e

Once it diffuses by osmosis it combines with the hemoglobin to form oxyhemoglobin. Successful treatment depends on restoring the proper drainage of the sinuses. Anaizi DOI: