Ventilation Flashcards
Tidal volume
. Vt = VD + alveolar ventilation
. VD = dead space
. 500 mL of air that enters body w/ each inspiration
. Volume of gas inspired or expired in a single respiratory cycle
Respiratory quotient
. Ratio of CO2 produced to O2 consumed . RQ = VCO2/VO2 . Varies w/ the foods consumed . Average VO2: 250 ml/min . Average VCO2: 200 ml/min . Average RQ: 0.8
Minute volume
. Amount of air exhaled per minute
. VE = Vt x n
. Vt: tidal volume
.n= respiratory rate
Dead space
. Within each tidal volume there is a volume of gas that does not participate in gas exchange
. Nonfunctional air in terms of diffusion of O2 and CO2
. Primarily is the volume of air contained in the conducting airways that do not do gas exchange
. Every pound of weight gives 1 ml of dead space
Alveolar ventilation
. Alveolar ventilation = VA x n
Alveolar ventilation = VE - VD
. Alveolar ventilation = VCO2/PaCO2
. VA = alveolar volume: amt. of air entering lungs w/ each inspiration that participates in gas exchange
. VE = minute ventilation
. VD = dead space
.n= respiratory rate
. VCO2 = volume of CO2 expired per unit time
. PaCO2= partial pressure of CO2 in arterial blood
T/F the partial pressure of CO2 of alveolar gas and arterial blood CO2 are identical
T
T/F changing alveolar ventilation via hyper or hypoventilation will change arterial blood gases
T
Anatomic dead space
. Volume of air contained w/in pharynx, larynx, and conducting airways
. Much greater than alveolar dead space
. Normally 150 ml
Alveolar dead space
. Volume of air w/in unperfused alveoli
Physiologic dead space
. Anatomic dead space + alveolar dead space
. Functional measurement
. In normal subject the anatomic and physiologic dead space is usually the same, but physiologic dead space can be much greater than anatomic in someone w/ lung disease
Fowler’s method
. Measure of anatomic dead space
. Single breath pure O2 inspired to total lung capacity
. Then conc. Of N2 gas of subsequent exhalation is measured w/ rapid nitrogen analyzer
. Initial portion of exhaled air has anatomic dead space and contains no N2
. As exhalation continues the N2 conc. Rises and is mix of anatomic dead space and alvolar gas
. Plateau at uniform N2 conc. Represents our alveolar gas
. Plotted on graph w/ phase II divided w/ vertical line, anatomic dead space is phase I plus volume of phase II up to vertical line
Bohr’s equation function
. Measured physiologic dead space
. Determines fraction of tidal volume that doesn’t participate in gas exchange and contributed to “washed” ventilation
. Normal physiologic dead space to tidal volume ration os 0.2- 0.35
How to examine static lung volume
. . Spirometer
. Measures volume of air breathed out
. Can’t measure RV, FRC, TLC, and anatomic dead space
Inspiratory reserve volume (IRV)
. Max volume of gas that can be inspired starting at the end of normal inspiration
. Typically 3000 ml
Expiratory reserve volume (ERV)
. Max volume of gas that can be expired starting from the end of normal expiration
. Normally 1100 ml
Residual volume (RV)
. Volume of gas that remains in lungs after a max expiration
. Normally 1200 ml
Forced expiratory volume (FEV1)
. Max amount of gas that can be expired in the 1st second of a FVC following a max inspiration
. Typically 3800 ml
. Can be expressed as percentage of FVC (FEV1/FVC)
. Normally 0.8
Total lung capacity (TLC)
. Total amount of gas in lungs at end of maximum inspiration (sum of all 4 lung volumes)
. RV+ ERV+ Vt+ IRV
. Typically 5800 ml
Vital capacity (VC)
. Max volume of gas that can be expired after max inspiration (ERV +Vt + IRV)
. Typically 4600 ml
Functional residual capacity (FRC)
. Amount of gas in lungs at end of normal expiration
. ERV+RV
. Typically 2300 ml
Forced vital capacity (FVC)
. Amount of gas that can be expelled from the lungs by expiring as forcibly possible after a maximum inspiration
. Typically under 4600 ml
Measurement of FRC
. Spirometer w/ He dilution
. Can then determine RV and TLC
. When He is inspired, it remains in lungs bc it is blood insoluble
. Measure FRC: patient breathes in air w/ known air volume and known He conc.
. Patient breathes a few breathes, the He molecules are contained Volume w/in spirometer plus volume w/in lungs
. This causes He to have new concentration
. FRC = (V1C1)/C2 - V1
Airflow
. Airflow in a tube is equal to the pricing pressure in the tube divided by resistance (Ohm’s)
. Vdot = P/R
. Driving pressure of airflow during respiration is generated by muscles of inspiration working in conjunction w/ recoil forces of lung
Poiseuille’s Equation
. Vdot = (P(pi)r^4)/8nl . Vdot: airflow . P: driving pressure . R: tube radius .n: viscosity .l: length of tube . Airflow directly proportional to 4th power of tube radius . Directly proportional to driving pressure . Inversely proportional to viscosity . Inversely proportional to length
Equation for resistance in respiratory system
R = P/V = 8nl/(pi)r^4
. Directly proportional to viscosity
. Directly proportional to length
. Inversely proportional to the 4th power of tube radius
Turbulent flow of air
. Disorganized flow w/ no smooth sheets of flow
. Needs greater driving pressure
. May occur in trachea, esp. when flow velocities are high
Laminar flow in respiratory system
. Parabolic profile
. Smooth flow
. Only occurs in very small airways
Transitional flow in respiratory system
. Mix of turbulent and laminar flows
. Occurs in most of the bronchial tree
Resistance to airflow down the bronchial tree
. Airway resistance peaks w/in medium sized bronchi
. Very small bronchioles contribute little airway resistance due to total cross sectional area of airways inc. very rapidly w/ airway branching
. As total airway cross sectional area inc., air resistance dec.
Effect of volume of dynamic airway resistance
. During inspiration, lung volume inc. towards TLC and lung tissue exerts radial traction forces on airways to stretch them open and airway resistance dec. (opposite at low lung volumes)
Parasympathetic control on airway smooth muscle
. Bronchocontriction
. Inc. airway resistance
. Has greatest influence on airway smooth muscle tone
Sympathetic control of airway smooth muscle
. Produces bronchodilation
. Dec. airway resistance
. Use E and NE reacting w/ beta-2 adrenergic receptors
.
Mast cell control of airway smooth muscle
. Located in CT underlying smooth muscle
. Release histamine and leukotrienes that constrict muscles producing bronchoconstriction
. Histamine binds to H1 receptors
. Both histamine and leukotrienes inc. prostaglandin production
Psotaglandin effect on airway smooth muscle
. E causes dilation
. F-2alpha causes contraction
How does smoke, dust, and SO2 effect airway smooth muscle
. Initiates release of ACH from efferent parasympathetics to cause constriction
. Binds to irritant receptors w/in airway submucosa
FEV1 in restricted lung diseases
. Pulmonary fibrosis
. Both FEV and FVC are reduced
. FEV1/FVC may be normal or increased
FEV1 in obstructive diseases
. Bronchial asthma
. FEV1 is reduced much more than FVC
. Dec. FEV1/FVC
. If less than 0.6 then it indicated moderate airway obstruction
. Less than 0.4 indicates severe airway obstruction
Forced expiratory flow rate (FEF)
. Measured over middle half of FVC (btw 25-75% of vital capacity)
FEF in obstructive lung diseases
. Deceased
. Decrease is proportional to severity of obstruction
. Time required to expel vital capacity is prolonged
Obstructive lung disease
. Inc. in airway resistance
. Asthma, bronchitis, emphysema CF, sarcoidosis(granulomas of airway) seen below carina
. Above carina: foreign body, croup/tracheitis, epiglottitis, tumors, neuromuscular disease/parkinson)
Asthma
. Inc. responsiveness of airway smooth mm. To stimuli causing widespread narrowing of airways
. Bronchoconstriction is reversible spontaneously or after treatment
Bronchitis
. Prolonged exposure to bronchial irritants that leads to airway obstruction
. May involve hypersecretion of mucous and/or hypertrophy of smooth mm.
Emphysema
. Destruction of lung parenchyma
. Results in reduction of radial traction w/in small airways and enlargement of alveoli
Restrictive diseases
. Expansion of lung is restricted from alterations in lung parenchyma of pleura disease, chest wall, or neuromuscular apparatus
. Reduced VC but airway resistance is not inc.
. Examples: MG, guillain barre, pleural effusion, flail chest/broken ribs, massive obesity, diaphragm paralysis
Pulmonary fibrosis
. Thickening of interstitial spaces
. Cause inc. radial traction w/in small airways
.dec. airway resistance
