2.19 - Alveolar Ventilation Flashcards
What are the two components of Total Pulmonary Ventilation?
Physiological Dead Space Ventilation & Alveolar Ventilation
What is the formula for total ventilation (Vt)?
Vt = f (frequency; bpm) x TV (L)
What are the two components of physiological dead space?
Anatomical dead space: airways (nose –> bronchiole) Functional dead space: ventilated parts of lungs that are not perfused (~0 for a healthy person). But can increase in some patients
What are the roles of anatomical dead space?
Preparation for gas exchange: cleaning of air, water saturation, temperature control Modulation of airway resistance Sets alveolar gas concentrations
Describe the concentration of CO2 during the breathing cycle
At beginning of expiration, [CO2] is 0: absolute dead space [CO2] increases after delay [CO2] increases linearly towards the end of expiration At end of expiration [CO2] = PACO2 During inspiration, rapid drop of [CO2] to 0
What is the formula for alveolar ventilation (Va)?
Va = total ventilation (Vt) - dead space ventilation (Vd)
There is a slow replacement of air in the alveoli per breath (3-4 half lives to fully replace air; t=23sec). What is the benefit of this?
Prevents sudden changes in the partial pressures of oxygen and co2. It also stabilises feedback mechanisms for respiratory control
Which areas of the lung are most ventilated?
Upper lung areas are least ventilated, the lower lung areas are most ventilated
What proportion of total ventilation does alveolar ventilation make up?
Approximately 70%
What two factors determine the extent of ventilation?
RAW and CL determine extent of ventilation: if increased, exchange is longer and vice versa
During strenuous exercise, O2 consumption and CO2 formation can increase up to 20-fold. Ventilation increases almost exactly in step with this increase in O2 consumption. Which of the following statements best describes the changes of PaO2, PaCO2 and arterial pH in a healthy athlete during such exercise
