6.10: Cardiorespiratory mechanics Flashcards
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
What anatomical adaptations do the airways have to mitigate against this collapsing?
Extrapulmonary airways are supported with cartilage to support the vessels
What is compliance
Tendency to distort under pressure (change in: volume/pressure)
What is elastance
Tendency to recoil to its original column
How is diastolic flow created
Aortic valve closes, ejection ceases but due to recoil of elastic arteries, pressure falls slowly and diastolic flow in downstream circulation
As arterial compliance decreases, what happens to blood pressure?
Systolic pressure increases
Diastolic pressure decrease
How does the skeletal muscle pump facilitate venous return
Effect of contraction of muscles in lower limbs compresses against the veins in presence of patent and apply pressure so blood cannot be pushed back down to foot
How does the respiratory pump facilitate venous return
I’m thorax, diaphragm contracts to create negative intra-thoracic pressure
Pulling IVC outwards creating reduced pressure in thorax than in abdomen
Blood travels down pressure gradient
What condition does an increase in the incompetent valves in veins lead to?
Dilated superficial veins in leg (varicose veins)
What is oedema in feet caused by?
Prolonged elevation of venous pressure
What happens in aneurysmal disease?
Over time vessel walls weaken
Cause balloon like distension
Vascular aneurysms incr. radius of vessel so inward force incr.
If muscle fibres weaken, force cannot be produced so aneurysm continues to expand until rupture
What gender is aneurysmal disease more common in
Men
What law is an aneurysmal disease a pathological example of
Law of Laplace
Wall tension should be proportional to radius of vessel
Diverticula are
Small bulges or pockets that can develop in the lining of the intestine with age
What is the relationship between transmural pressure and vessel volume called
Compliance
Is ve our or arterial compliance higher
Venous compliance is z 10/20higher
What effect does incr. smooth muscle contraction have on venous pressure and volume
Increases venous pressure
Decreases venous volume
What class of drugs can be taken to increase venous pressure
Venoconstrictors
Why is there more ventilation in the base of the lung as opposed to the apex
At bottom, alveoli are smaller and more compliant due to gravity increasing abundance lower down
Pleural pressure is less negative at the bottom and so the transmural gradient is lower as well, increasing ventilation
Why is there more perfusion in the base of the lung as opposed to the apex
More recruitment, less resistance and higher flow rate the lower down the lung you go
Also due to gravity pulling down tissue and Extracellular fluid
Is perfusion or ventilation more affected by location in the lung and why
Perfusion because blood is denser than air
What is wasted perfusion
More blood going past respiratory exchange surface than can participate in gas exchange
Occurring at base of lung where more perfusion than ventilation
What is wasted ventilation
More ventilation than perfusion
Gas is moved into parts of the lung that are not getting sufficient pulmonary circulation supply
How are compliance and resistance affected by COPD
Increased compliance and increased resistance
Emphysemic breakdown of structural lung tissue increases compliance and bronchitic swelling of the airways and mucus hypersecretion increases resistance to airflow
