Pulmonary Ventilation Flashcards
Explain the airway anatomy?
The conducting airways consist of a series of rapidly branching tubes (conduits) that become narrower, shorter, and more numerous as they penetrate deeper into the lung. After about 23 to 25 orders of branching, the airways terminate in alveoli. Starting at the trachea, the airways branch in a dichotomous fashion both symmetrically and asymmetrically. Each generation of airway branching is assigned a number, with the trachea assigned zero (0). The gas exchange airway may be reached in as few as 10 levels of branching, but around the 16th level of branching is more typical. From the trachea, the airway diameter decreases with each new generation of branching. However, the total cross-sectional area increaseswith each level of branching. As a result, the linear velocity of airflow decreases with each order of branching, an important consideration in determining the distribution of airway resistance.
Explain the where does air go chart?
Explain in general airflows, air resistance and area as you move down the respiratory system?
From the trachea, the airway diameter decreases with each new generation of branching. However, the total cross-sectional area increaseswith each level of branching. As a result, the linear velocity of airflow decreases with each order of branching, an important consideration in determining the distribution of airway resistance.
What is the tidal volume?
Tidal volume is the air that passes the mouth with each breath. Only some of that air reaches the alveolus. Only some of that air participates in gas exchange.
Tidal volume is the air that passes the mouth with each breath and equals approximately 450 ml. Airway volume (anatomical dead space volume is the air in the conducting zone) equals approximately 150 ml. Therefore, 450 ml minus 150 ml = 300 ml reach the alveoli (alveolar volume)!!
What is the physiologic dead space?
While a portion of each inspired tidal volume is obligated to the conducting airways (ANATOMICAL DEAD SPACE), another portion may end up in alveoli that are NOT perfused with pulmonary capillary blood (ALVEOLAR DEAD SPACE). In both cases, this air does not participate in gas exchange with the capillary blood. The volume of air occupying the conducting airways AND non-perfused alveoli is referred to as the physiologicdead space volume.
Physiological dead spaceis defined as the portion of each tidal volume that does not participate in gas exchange with pulmonary capillary blood. It includes the anatomical dead space and alveolar dead space. The latter is represented by alveoli that are ventilated but NOT adequately perfused with pulmonary capillary blood. These alveoli contribute to dead space volume because gas exchange with pulmonary capillary blood does not occur. Hence, physiological dead spaceis equal to the sum of the anatomicaland alveolardead space.
What is anatomic dead space?
Fresh air does not go directly to the terminal respiratory units. Fresh air first flows through the conducting airways (nose, mouth, pharynx, larynx, trachea, bronchi and bronchioles). In the conducting airways, O2 and CO2 do not exchange between gas and blood. Therefore, that portion of the fresh inspired air is called ANATOMICAL DEAD SPACE, VD.
What is the alveolar dead space?
TIDAL VOLUME = 450 ml
ANATOMICAL DEAD SPACE VOLUME =150 ml
ALVEOLAR VOLUME = 300 ml
However, some of the alveolar volume does not participate in gas exchange (alveolar dead space)
The volume of air occupying the non-perfused alveoli OR The volume of air occupying the under-perfused alveoli. In a perfect lung, all alveoli receive
ventilation and blood flow in the same proportion. The perfect lung does not exist even in the healthiest individuals and may be markedly abnormal in diseased lungs. The concept of alveolar dead space is used clinically to describe the deviation of ventilation relative to blood flow.
What is alveolar ventilation?
Alveolar ventilation -is the volume of fresh air introduced into the gas exchanging regions of the lungs per minute.
At the end of a normal expiration (just before the next inspiration) the conducting airways are filled with alveolar gas. Thus, as a tidal inspiration begins, the alveoli must first receive the gas that was in the anatomical dead space from the last exhalation. This gas does not raise alveolar PO2 or lower alveolar PCO2 very much because it has the same composition as the alveolar gas. After the dead space volume is inspired, the alveoli receive fresh air until the tidal volume is completed. The last portion of the fresh air, of course, remains in the conducting airways.
During inspiration tidal volume is? What is the alveolar volume then?
During inspiration, tidalvolume is 450 ml. Since dead space is 150 ml, this means that the alveolar volume (the volume of fresh air reaching the airspaces is 300 ml. Alveolar Volume = Tidal Volume MINUS Dead Space Volume VA = VT-VD (450 ml -150 ml =300 ml) In this example, 67% of gas entering alveoli is fresh air.
What are the equations and difference between minute ventilation, dead space ventilation, and alveolar ventilation?
Minute ventilation= tidal volume x frequency VE = VT x f
Dead space ventilation= dead space volume x frequency VD = VD x f
Alveolar Ventilation= minute ventilation -dead space ventilation VA = VE -V D OR VA= (VT-V D) x f
Alveolar ventilation affects what? What other factors influence this?
Alveolar ventilation affects alveolar gas partial pressures. Factors that influence alveolar gas partial pressures include:
x Balance between ventilation and blood flow.
x Ventilation rate, hypoventilation vs. hyperventilation.
x Respiratory cycle.
x Functional residual capacity.
Explain the balance between blood flow and ventilation? if ventilation to an alveolus is blocked what happens?
If perfusion reduces relative to ventilation what happens?
explain the alveolar partial pressure in hypoventilation and hyperventilation?
What is the Functional residual capacity?
FRC acts as a buffer against extreme changes in alveolar PO2 with each breath.
The functional residual capacity (FRC) of the lungs is the amount of air remaining in the lungs at the end of normal expiration. The FRC is approximately 2300 ml. Only approximately 350 ml of new air is brought into the alveoli with each normal respiration, and the same amount of old alveolar air is expired. Therefore, the amount of alveolar air replaced by new atmospheric air with each breath is only one seventh of the total, so that many breaths are required to exchange most of the alveolar air. This slow replacement of alveolar air makes the respiratory control mechanisms much more stable.
Explain regional differences in ventilation in the lungs?
The lungs are like a slinky, hanging from the ceiling. The coils closest to the ceiling are wide apart while the coils at the bottom are very close together. How does this effect where air flows during inspiration? An important concept for you to understand about ventilation is the effect of gravity on the distribution of ventilation within the lung. As you will see in subsequent topics, this has implications for the matching of ventilation to perfusion in both normal and pathological lungs, as well as duringone lung ventilation for thoracotomy procedures.
What is the effect of gravity on ventilation?
The figure above illustrates compliance for different alveoli ranging from the base to the apex of the upright lung. Remember that compliance is change in volume divided by change in pressure (∆V/∆P, or dV/dP), so the compliance in this figure is the slope of the sigmoid curve at anypoint.
While it may be counterintuitive, the alveoli at the top of the lung are ventilated less than those at the bottom. The reason is that the alveoli at the top are on a less compliant part of the curve – i.e., they are already “stretched,” and for any given pressure change, they will expand less than their counterparts at the base.
With the introduction of a pneumothorax (for instance, during surgical thoracotomy), the entire lung tends to settle down to a lower volume because it is no longer surrounded by negative intrapleural pressure. As this happens, the highest regions of lung “slide down” to the steeper (more compliant) portion of the curve, and the bottom regions of lung move to the less compliant part of the curve at the bottom of the graph. This will cause a reversal in the distribution of ventilation within the lung (see below).
What does a pneumothorax do to air distribution?
What is the forced expiration flow rate?
Forced expiratory volume (FEV) measures how much air a person can exhale during a forced breath. The amount of air exhaled may be measured during the first (FEV1), second (FEV2), and/or third seconds (FEV3) of the forced breath. Forced vital capacity(FVC) is the total amount of air exhaled during the FEV test. In conjunction with the FVC, useful information can also be obtained from calculating the average flow rate for a specified volume of the FVC. The average rate of flow for the middle two quarters of the FVC is often used for this purpose. This is referred to as the mid-expiratory flow rate or forced expiratory flow (FEF) between 25% to 75% of the FVC, abbreviated as FEF25-75%. The FEF25-75% can be computed from the mid portion of FVC. This measurement will help determine if the patient has any obstructive or restrictive diseases of the airways. To calculate FEF 25-75% 1) Determine the volume of air expelled between 25% and 75% of the FEV trace (i.e. from 25% to 75%). 2) Determine the time required to expel the volume of air between 25% and 75% of the FEV 3) Divide the volume (step 1) by the corresponding time to exhale this volume (step 2).
A normal individual can expire about 80% of their FVC in the first second, termed FEV1.0. In other words, the FEV1.0/FVC is normally 80% or more. About 94% of the FVC is normally expelled by 2 seconds (FEV2.0) and 97% by 3 seconds (FEV3.0). Obstructive impairments are characterized by increased airway resistance causing reduced expiratory airflow rates. Obstructive disorders are always associated with airway dysfunction. With obstructive impairments, the actual (recorded) FEV1.0/FVC is less than 80% and the FEV1.0 and FEF25-75% are 75% or less of the predicted values. How obstructive disordersaffect other lung volumes, including the FVC, depends upon theseverity or stage of the disease. Restrictive impairments are characterized by limited lung expansion, reduced lung volumes, and usually decreased expiratory flow rates from predicted values. Thus, the recorded FVC and FEV1.0 are below the predicted normal. However, with a strictly restrictive disorder, airway resistance is normal, so the ratio of the actual FEV1.0 to the FVC of the subject is normal (i.e., FEV1.0/FVC> 80%). The loss of lung volume with restrictive disorders is reflected by reductions in other lung volumes (RV, FRC) and a reduced FEF2575% from predicted values.
Describe obstructive impairments seen on spirogram? what are some? what characterizes them?
Obstructive impairments are characterized by increased airway resistance causing reduced expiratory airflow rates. Obstructive disorders are always associated with airway dysfunction. Examples of obstructive diseases include asthma, chronic bronchitis, and emphysema. However, even a severe cold with pulmonary congestion might be manifested as an obstructive disorder
Explain the restrictive disorders seen in spirogram?
Restrictive impairments are characterized by limited lung expansion, reduced lung volumes, and usually decreased expiratory flow rates from predicted values. Thus, the recorded FVC and FEV1.0 are below the predicted normal. However, with a strictly restrictive disorder, airway resistance is normal, so the ratio of the actual FEV1.0 to the FVC of the subject is normal (i.e, FEV1.0/FVC> 80%). The loss of lung volume with restrictive disorders is reflected by reductions in other lung volumes (RV, FRC) and a reduced FEF2575% from predicted values. include pulmonary fibrosis, sarcoidosis, pleural effusion, spinal cord injury that affects innervation to the respiratory muscles, or spinal nerve paralysis such as with polio. Injury or disease to the respiratory control centers of the brain stem might also be reflected as a restrictive impairment.
Explain obstructive and normal breathing on a flow volume loop.
explain what restrictive airway disorders look like on a flow volume loop?
