lec 6 Flashcards
explain bronchial circulation
-bronchial arteries from aorta (oxygenated)
-supply the large airways to small bronchii
-some deoxy bronchial blood leaves airways -> pulmonary veins (oxy) = forms shunt (bypasses gas exchange)
-addition of bronchial blood to pulmonary veins decrease PO2 slightly
-pulmonary veins to left atrium
-venous return to left atrium > venous return to right atrium
explain pulmonary blood volume
-average volume of blood in the lungs- 12% of total blood volume
-high thoracic pressure can expel 250ml of blood from pulmonary circulation
-loss pf blood from systemic circulation (e.g. hemorrhage) may cause automatic shift of blood
-for efficient gas exchange: blood should be directed to area of the lung with best airflow
define hypoxia + hypoxic
hypoxia refers to lack of oxygen reaching tissues
so to increase blood flow,
in systemic circulation, blood vessels dilate (increase oxygen delievery)
in pulmonary circulation, blood vessels constrict (to optomise oxygen uptake)
explain hypoxic pulmonary vasoconstriction (HPV)
-blood vessels constrict (e.g. due to a blockage)
-decrease in PaO2- adjacent blood vessels constrict for 3-10 minutes
-increase vascular R to hypoxic lung areas + increase in rate of cardiac output to areas of the lung that are better ventilated
-hypoxic areas may be: patchy depending on local O2 + widespread
how is PaO2 + PaCO2 determined
-‘Va + rate if alveolar gas exchange (‘Vgas)
-but we assume that all the alveoli have adequate ‘Va + Q
Va/Q conc.
explain the ventilation-perfusion ratio
- ‘Va = normal, ‘Q = normal, rate = ‘Va/’Q = 0.8-1 (is healthy lung, more O2 then CO2 in lungs)
-‘Va = 0, Q = normal, rate = ‘Va/’Q = 0 (shunt = no airflow but normal blood flow, more CO2 then O2 in lungs, decreased ‘Va/Q’ ratio)
-‘Va = normal, Q = 0, rate = ‘Va/’Q = infinity (alveolar dead space = normal airflow, in blood flow, zero CO2, increase ‘Va/Q’ ratio)
how does Q’ increase to allow for increased blood flow (when exercising + 3 methods)
when exercising, ‘Q increase by x4-7 to lungs, extra flow allowed by
-recruit capillaries = increase no. of open capillaries (up to 3x increase)
-distend (swell) capillaries= more then x2 increase in flow through each capillary
-increase pressure= (as a last resort)
-note: the pulmonary vessels large capacity for recruitment + distension prevent a significant increase in pulmonary capillary pressure
if have pneumonia and place person with AFFECTED lung positioned upward, what happens to blood flow + gas exchange VS when AFFECTED lung positioned downward
- decrease blood flow + poor ventilation of the affected lung
-gravity increases blood flow to unaffected lung, leading to adequate gas exchange
-good ventilation but blood flow decreases
-gravity increases blood flow, but pneumonia causes decrease gas exchange
explain the effect of gravity on bloodflow and ‘Va/’Q matching
-when a person is standing, gravity pulls lung tisssue down, top of lung has larger, stiffer alveoli = decreased Cl, so air directed to alveoli with increase Cl
-gravity also directs blood to bottom of lungs (BP= 23mmHg across the lung, -15mmHg top of lung when standing, and +8mmHg at the bottom of the lung)
-so ‘Va/’Q ratio higher at top of lung, lower at bottom of lung
explain capillary transit time
-alveolar walls lined with many capillaries- like a continous sheet of blood
-capillary transit time is 0.8sec at rest, and as low as 0.3 when increase Q
-but if capillary transit time is less then 0.25sec, Hb will not equilibrate with O2 = decrease in PaO2 (0.25sec is fastest u can move blood through capillaries + get oxygenated)
-recruiting + distending capillaries when increase ‘Q prevents large increase in blood velocity + decrease in capillary transit time
-if pulmonary artery pressure increases = 1st option during exercise, transmit time would increase much faster + greater decrease in PaO2
