Alveolar ventilation Flashcards
minute ventilation
tidal volume x respiratory rate
conducting airways volume
150ml
anatomical dead space
500ml flows into alveoli, but 150ml of it is air from the airways that wasn’t exhaled. moved in and out of airways
don’t allow gas exchange with blood
alveolar ventilation
total volume of fresh air entering alveoli per minute - more important in gas exchange
factors affecting alveolar ventilation
increasing depth of breathing more effective in increasing alveolar ventilation than increasing rate
taking short, shallow breaths decreases alveolar ventilation because the anatomical dead space ventilation is increased, so no fresh air flows in
fixed volume goes to dead space
if tidal volume decreases, fraction of tidal volume going to dead space increases
alveolar dead space
alveoli with little or no blood supply are unable to perform gas exchange, so some fresh air isn’t used
physiological dead space
sum of alveolar and anatomical dead spaces
rates of gas exchange
rate at which oxygen enters body cells and leaves tissue capillaries is equal to volume of oxygen added to blood in the lungs in same time
rate at which carbon dioxide is produced by cells and enters systemic blood is same as rate of removal and expiration
what does balance of oxygen consumed and carbon dioxide produced depend on?
nutrients used for energy - enzymatic pathways for metabolising carbohydrates, fats and proteins generate different amounts of co2
respiratory quotient
ratio of co2 produced to o2 consumed
respiratory quotients for diff. things
carbohydrates - 1
fat - 0.7
protein - 0.8
respiratory quotient for mixed diet
0.8 - 8 molecules of co2 produced per 10 molecules of oxygen consumed
% oxygen in atmospheric air
21
79 nitrogen
partial pressure of gases
rapidly moving gas molecules collide and exert pressure - increased by increased temp and conc.
independent of pressure other gases exert (Dalton’s law) - molecules os far apart they don’t affect eachother
diffusion
from high partial pressure to low
total pressure
sum of partial pressures - atmospheric pressure is 760 mmHg
Henry’s law
when a liquid is exposed to air containing a gas, molecules of gas will enter liquid and dissolve in it
amount of gas dissolved is directly proportional to the partial pressure of the gas with which liquid is in equilibrium
at equilibrium, partial pressures of gas molecules in liquid and gaseous phases must be identical
concentration and solubility
conc of a gas in liquid is proportional to partial pressure and solubility
more solubility -> greater conc at any partial pressure
partial pressures will be same at equilibrium, but concs differ
what determines systemic arterial partial pressures?
alveolar partial pressures
typical alveolar gas pressures
Po2 = 105 mmHg Pco2 = 40 mmHg
nitrogen in alveoli
biologically inert under normal conditions
doesn’t undergo net exchange
most abundant gas in alveoli
typical atmospheric gas pressures
Po2 = 160 mmHg Pco2 = 0.3 mmHg
why are alveolar and atmospheric pressures different?
oxygen is lower in alveoli because some oxygen leaves alveoli to enter pulmonary capillaries
carbon dioxide is higher in alveoli because some oxygen enters alveoli from pulmonary capillaries
factors determining alveolar Po2
Po2 of atmospheric air
rate of alveolar ventilation
rate of total-body oxygen consumption
effects of factors determining alveolar Po2
decrease of Po2 in atmospheric air decreases alveolar Po2
decrease in alveolar ventilation decreases alveolar Po2
increased consumption of O2 by cells decreases Po2 in blood returning to the lungs - increases conc gradient from lungs to pulmonary capillaries - increases diffusion rate. if alveolar ventilation doesn’t change, alveolar Po2 is reduced, as more fresh air leaves alveoli to enter tissues
effects of factors determining alveolar Pco2
decreased alveolar ventilation increases alveolar Pco2]
increased production of co2 increases alveolar Pco2
determinants of alveolar Po2 and Pco2
ratio of oxygen consumption to alveolar ventilation - higher the ratio, lower alveolar Po2
ratio of carbon dioxide production to alveolar ventilation - higher the ration, higher alveolar Pco2
hypoventilation
occurs in increased ratio of co2 production to alveolar ventilation - can’t keep pace. Pco2 increases
hyperventilation
occurs in decreased ratio of co2 production to alveolar ventilation - Pco2 decreases
increased ventilation relative to metabolism
partial pressures in systemic venous blood
Pco2 46mmHg
Po2 40mmHg
difference in partial pressures in alveolar-capillary membrane -> net diffusion of oxygen from alveoli to blood and carbon dioxide from blood to alveoli
when does net diffusion of gases cease?
when capilllary partial pressures become equal to alveolar partial pressures
rates of diffusion in a healthy person
high enough and blood flow slow enough that complete equilibrium is reached before blood reaches the end of capillaries
pulmonary circulation at rest vs exercise
capillaries at apex of lung are usually closed due to resting blood pressure being too low to keep them open, but the increased cardiac output in exercise increases pressure and opens them
pulmonary edema
filling of alveoli with fluid
increases diffusion barrier
diffuse interstitial fibrosis
alveolar walls become v thickened with connective tissue (fibrotic) - fibrosis arises from infection, autoimmune disease, hypersensitivity to inspired substances, exposure to toxic airborne chemicals, etx
symptoms of diffusion disease
shortness of breath
poor oxygenation of blood
don’t affect elimination of co2 as it diffuses more rapidly than oxygen
