6.10: Cardiorespiratory mechanics Flashcards
(47 cards)
Changes in volume and pressure during inspiration
Diaphragm contracts, increased volume and decreased pressure
Gas exchange down conc. gradient in alveoli leads to incr. pressure and volume
Diaphragm relaxes and lung recoils decreasing volume and increasing pressure
Expiration leads to both decrease in pressure and volume
Why doesn’t resistance continue to increase as airways get smaller?
No. Of airways increases to point where resistance decreases in terms of flow of air through these
Cartilaginous discs on airway reduce ability to dilate due to pressure changes, creating larger resistant effect
Poiseuilles law
Emphasises importance of arterial diameter as determinant of resistance as relatively small changes in vascular tone can produce large changes in flow
Why is there a lower proportion of systemic blood in the arteries
Blood pumped at higher pressure here so pumped faster
Blood in veins pumped at lower pressure so spends more time in veins
How much of the blood at any one time do veins hold
70%
What makes veins “compliant”
Less muscular epithelium so more able to dilate according to blood being pumped
Why does pulmonary circulation operate only around 10-20% of pressure at systemic circulation
Doesn’t take much pressure to pump blood between heart and lungs as they are close, lungs have low resistance circuits so no much pressure needed to overcome
How to estimate mean arterial pressure
Cardiac output x total peripheral resistance
3 assumptions when calculating mean arterial pressure
Rigid vessels
Steady flow
Right atrial pressure negligible
What is regulation flow achieved by
Variation in resistance in vessels while BP remains relatively constant
How does cardiac output to skeletal muscle change from rest to exercise
From 0.75L to 6L
Rest of organs have similar supply
Laminar flow is
Velocity of fluid is constant at any one point and flows in layers
Blood flows fastest closest to centre of lumen
Turbulent flow is
Blood flows erratically forming eddys, prone to pooling
What is turbulent flow associated with
Pathophysiological changes to endothelial lining of blood vessels (thrombosis)
When measuring blood pressure manually in the upper arm, what kind of flow does slow deflation of cuff cause?
Turbulent flow, heard w stethoscope
What is pulse pressure
Difference between diastolic and systolic blood pressure
Allows the risk of heart events such as strokes and attacks to be calculated
Calculating pulse pressure
Systolic BP - Diastolic BP
How to calculate mean arterial pressure from pulse pressure
MAP = diastolic BP + 1/3PP
Unit for mean arterial pressure
mmHg
What word describes positive transmural pressure
Patent
During inspiration why does alveolar pressure decrease
Diaphragm contracts and thoracic cavity increases in volume, which decreases the intra-alveolar pressure
During inspiration why does pleural pressure decrease
Due to adhesive force of the pleural fluid, the expansion of the thoracic cavity forces the lungs to stretch and expand as well
This increase in volume leads to decrease in pleural pressure
How does transmural pressure change during inspiration
It will increase due to a decrease in both pleural and alveolar pressure
Continues to increase at end inspiration because pleural pressure remains same as mid-inspiration but alveolar pressure decreases so difference between them also increases
During hard-expiration why is there the chance that airways collapse?
Pleural and airway pressure considerably increased
Pleural pressure exceeds airway pressure causes flow to cut off
