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Egan Ch 10
Ventilation
| Question | Answer |
|---|---|
| What are the 2 primary functions of the lungs? | supply the body with O2, remove CO2 |
| Ventilation | process of moving gas in and out of the lungs |
| What are the 2 phases of ventilation? | inspiration and expiration |
| Tidal volume | volume of air that is inhaled or exhaled from the lungs during effortless breathing |
| Equation for determining ventilation | Pressure=Volume -------+(Resistance*Flow) compliance |
| What is a positive pressure? | one that is greater than atmospheric pressure |
| What is a negative pressure? | subatomic pressures less than 1 atmosphere |
| Pressure gradient | difference between 2 pressures |
| What are the 3 important pressure gradients involved in ventilation? | transrespiratory, transpulmonary, transthoracic |
| What does the transrespiratory pressure represent? | the difference btw the atmosphere (body surface) and the alveoli |
| What does the transrespiratory pressure cause to happen? | gas to flow in and out of the alveoli during breathing |
| What does the transpulmonary pressure represent? | the pressure difference btw the alveoli and the pleural space |
| What does the transpulmonary pressure cause to happen? | mintains alveolar inflation. Transpulmonary pressure results from the opposing elastic recols of the thorax and lungs themselves. |
| What does the transthoracic pressure represent? | difference in pressure btw the pleural space and the body surface. It is the pressure across the chest wall. It represents the total pressure needed to expand or contract the lungs and chest wall together. |
| Before inspiration waht is the pleural pressure at in cm of H2O? | -5 |
| Before inspiration what is the alveolar pressure in cm of H2O? | 0 |
| Describe the what happens as inspiration begins. | Muscular effort expands the thorax. This causes a decrease in pleural pressure. Transpulmonary pressure gradient widens, causing alveoli to expand. Causing a negative transrespiratory pressure and air enters |
| Describe what happens as expiration begins | Thorax recoils and transpulmonary pressure starts to rise. Alveolar pressure rises. Transpulmonary pressure narrows and alveoli deflate. Alveolar pressure exceed that at the airway opening. |
| To generate pressure gradients the lungs must be? | distended |
| What are the two categories of forces opposing lung inflation? | elastic forces, frictional forces |
| Elastic forces? | involve tissures of the lungs and thorax and surface tension in alveoli |
| Frictional forces? | resistance caused by gas flow and tissure movement during breathing |
| Elasticity | physical tendency of an object to return to an initial state after defomation |
| In the lung inflation is equivalent to? | stretching |
| What opposes inflation? | lung elastic forces |
| To increase lung volume what must be applied? | pressure |
| The amount of inflation or stretch is measure as a volume by a? | spirometer |
| What happens to the inflation vurve as the lung is stretched to it's maximum? | becomes flat |
| What does the flattening indicate? | increasign opposition to expansion |
| hysteresis | difference btw the inflation and deflation curves |
| What does hysteresis indicate? | factors other than simple elastic tissure forces are present |
| Part of the hysteresis exhibited by the lung is a result of? | surface tension forces in the alveoli |
| Less or more pressure is needed to inflate a fluid filled lung to a given volume? | Less pressure is needed |
| The recoil of the lung is a combination of what 2 things? | tissue elasticity, and suface tension forces in the alveoli |
| During inflation additional pressure is needed to overcome what? | surface tension forces |
| Pulmonary surfactant | phospholipid that lowers surface tension in the lung |
| What type of cells produce pulmonary surfactant? | Alveolar type II cells |
| Compliance | volume changed per unit in applied pressure. |
| What does compliance measure? | distensibility of the lung |
| Formula for compliance | CL=change in the volume (Liters) ----------------------- change in the pressure (cm H20) |
| Compliance of a healthy adult lung averages? | 0.2L/cm H2O or 200ml/cm H2O |
| Compliance is measured under what conditions? | static (no airflow) |
| Measurement of pulmonary compliance in a patients requires the placement of what? | balloon tipped catheter in the espohagus |
| What does the compliance curve of a patient with emphysema look like? | steeper and displaced to the right. large changes in volume for small pressure changes (increased compliance due to loss of elastic fibers) |
| What does the compliance curve of a patient with pulmonary fibrosis look like? | flatter than normal curve and shifted down to the right. smaller volume change for any given pressure(decreased compliance, lungs become stiffer with a reduced volume) |
| FRC | resting volume of the lungs. point at which alveolar pressure equals atmospheric pressure. |
| Normal FRC | 40% of total lung capacity |
| What happens if the normal relationship of the chest wall is disrupted? | the lung tents to collapse to a volume less than FRC, and the thorax expand to a volume larger than the FRC |
| The tendency of the chest wall to expand is offset by what? | the contractile force of the lungs |
| Diseases that alter the compliance of either the chest wall or lung often disrupt the balance point usually with a change in what? | lung volume |
| Inhalation occurs when the balance btw the lungs and the chest wall do what? | shifts |
| At the beginning of the breath the tendency of the chest wall to expand facilitates what? | lung expansion |
| What diseases can reduce chest wall compliance and lung volumes? | obesity, kyphoscoliosis, ankylosing spondylitis |
| The total compliance of the respiratory system equals? | lung compliance plus the compliance of the thorax |
| What are 2 ways to measure lung thorax compliance? | placing a relaxed or anesthetized subject in a body respirator. OR In an intubated patient with a cuffed endotracheal tube by using positive pressures. |
| How can the total compliance of the respiratory system be altered? | By the position of the patient as well as disorders affedting compliance of the lungs, chest wall or both. |
| Frictional (nonelastic) opposition to ventilation has the following 2 components? | tissue viscous resistance, and airway resistance |
| What is tissure viscous resistance? | impedance of motion caused by displacement of tissues during ventilation |
| In tissue viscous resistance what tissues are displaced? | lungs, rib cage, diaphragm, and abdominal organs |
| Tissue viscous accounts for how much total resistance to lung inflation? | 20% |
| What diseases can alter tissue viscous resistance, increasing total impedance to ventilation? | obesity, fibrosis, ascites |
| What is airway resistance? | impedance to ventilation by movement of gas through airways |
| Airway resistance accounts for how much of the frictional resistance to ventilation? | 80% |
| what is the formula for airway resistance? | Raw=Palv-Pao -------- V |
| What is the range for airway resistance in healthy adults | 0.5-2.5cm H2O |
| How is airway resistance measured (Flow)? | pneumotachometer |
| Hw are alveolar pressures determined in the body? | plethysmograph |
| How much of the resistance to gas flow occurs in the nose, mouth , and large airways? | 80% |
| How much of the total resistance to flow is attributed to airways smaller than 2 mm in diameter where flow is mainly laminar? | 20% |
| Airway caliber is determined by what factors? | anatomic support provided to the airways, and pressure differences across their walls |
| What do the larger airways mainly depend on for support? | cartilage |
| What do the smaller airways mainly depend on for support? | surrounding lung parenchyma |
| transmural pressure gradient | difference between the pleural pressure and the pressure inside the airway |
| Equal pressure point | pressure inside equals the pressure outside in the pleural space |
| dynamic compression of the airways | narrowing of the airways due to an increase in surrounding pressures |
| When does dynamic airway compression occur in a healthy adult? | only at lung volumes well below the resting expiratory level |
| Destruction of elastic tissure does what to the compliance of the lung? | increases compliance of the lung |
| Assessment of mechanical work of breathing involves measurement of? | physical parameters of force and distance as they relate to moving air in and out of the lung |
| Assessment of metabolic work involves meaurement of? | oxygen cost of breathing |
| How to calculate mechanical work of breathing? | WOB=change in pressure*change in volume |
| When can total mechanical work be measured? | during artificial ventilation if respiratory muscles are completely at rest. |
| How much of the WOB can be attributed to elastic forces opposing ventilation? And the remaing? | two thirds. is a result of frictional resistance to gas and tissue movement |
| In the presence of pulmonary disease th WOB can? | increase dramatically |
| In restrictive lung disease the area of the volume pressure curve is? | greater because the slope of the static component is less than normal |
| The area of the voume pressure curve in obstructive lung disease is? | increased because the portion associated with frictional resistance is markedly widened. |
| The meachanical WOB depends on teh pattern of? | ventilation |
| Large tidal do what to the elastic component of work in mechanical WOB? | increase the elastic component of work |
| High breathing rates do what to the frictional work in mechanical WOB? | increase the frictional work |
| Patients with pulmonary fibrosis often assume what breathing pattern? | rapid shallow, this pattern minimizes the mechanical of distending the lungs but at the expense of more energy to increase breathing rate. |
| Patients with obstructive disease often assume what breathing pattern? | breathing slowly using pursed lip breathing during exhalation to minimize airway resistance |
| When increased work of breathing occurs with respiratory muscle weakness what happens to the inspiratory muscles? Tidal volume & RR | they fatigue. Tidal volume decrease, RR increases. |
| How is the oxygen cost of breathing assessed? | by measuring the rate of oxygen consumption at rest and at increased levels of ventilation. |
| What is the average of ocygen cost of breathing in an individual? | 0.5-1.0 mL of oxygen per liter of increased ventilation |
| The rate of oxygen consumtion by the respiratory muscles is closely related to? | the inspiratory pressures generated by the diaphragm |
| How is diaphragmatic pressure measured? | (similar to intrapleural)thin catheter is placed into the esophagus. One balloon remains in the esophagus and the other at the tip of the stomach. This measures the difference in pressures. |
| In the presence of pulmonary diseas teh oxygen cost of breathing does what? Ventilation? | increase. increase |
| Abnormally high oxygen cost of breathing is one factor that limits exercise in what type of patients? | patients with obstructive disease such as emphysema |
| Increased oxygen consumption by the respiratory muscles may also contribute to what when dealing with mechanical ventilation? | failure to wean patients off the ventilator |
| Is ventilation distributed evenly in the lungs? | no |
| What 2 factors account for the unevenness in the distribution of ventilation? | regional and local factors |
| What are the regional factors in the distribution of ventilation? | relative differences in thoracic expansion, and regional transpulmonary pressure gradients |
| (Thorax expansion) The thorax and respiratory muscles cause greater expansion at the lung bases or apices? | bases |
| (Transpulmonary pressure gradients)The transpulmonary pressure is directly relates to what at a given level of alveolar inflation? | pleural pressure |
| Changes in transpulmonary pressure gradient are greatest in what type of alveoli? Do these alveoli expand more or less? | peripheral alveoli. More |
| Pleural pressure increases how much for ech centimeter form the lung apex to its base for th average adult? | it increases 0.25cm H2O |
| What does the increase in pressure in the pleural space from the lung apex to its base result from? | weight of the lung an the effect of gravity |
| How much is pleural pressure at the apex? | -10 cm H2O |
| How much is the pleural pressure at the bases of the lungs? | -2.5 cm H20 |
| The bases of the upright lung receive how my ventilation compaired to the apices? | 4 times as much at the bases |
| (Local factors in Distribution of ventilation) Alveolar filling and ventilation are affected by? What determines the filling and emptying? | Local factors. compliance and resistance |
| Each respiratory unit has an elastic element which is? and a resistive element which is? | alveolus. Airway |
| Change in alveolar volume and the time required fro the change to occur depend on? | compliance and resistance of each respiratory unit |
| The more distensible the lung unit the greater will be the? | volume change at a given transpulmonary pressure |
| Lung units with high compliance(distendablilty) have less what? How does this affect the filling and emptying? | elastic recoil than normal. They fill and empty more slowly |
| Lung units with low compliance(high elastic recoil)do what? How does this affect the filling and emptying? | increase their volume less. They fill and empty faster than normal |
| What does the alveolar surfactand help to do in filling and emptying? | helps stabilize alveoli of different sizes and evens out filling and emptying |
| What also affects the emptying and filling? | airway resistance |
| The relationship btw the compliance and resistance of a lung unit is measured and this property of each lung unit is called? | time constant |
| Time constant equals? | compliance times resistance |
| What causes a lung unit to have a long time constant? how long do they take to fill and empty? | If resistance or compliance is high. Take longer to fill and empty |
| What causes a lung unit to have a short time constant? How long do they take to fill and empty? | when resistance or compliance is low. Takes faster than normal to fill and empty. |
| Time constants affect local or regional distribution of ventilation in the lungs? | local |
Created by:
blh