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
