6.10: Cardiorespiratory mechanics

Question 1

Changes in volume and pressure during inspiration

Answer 1

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

Question 2

Why doesn’t resistance continue to increase as airways get smaller?

Answer 2

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

Question 3

Poiseuilles law

Answer 3

Emphasises importance of arterial diameter as determinant of resistance as relatively small changes in vascular tone can produce large changes in flow

Question 4

Why is there a lower proportion of systemic blood in the arteries

Answer 4

Blood pumped at higher pressure here so pumped faster
Blood in veins pumped at lower pressure so spends more time in veins

Question 5

How much of the blood at any one time do veins hold

Answer 5

70%

Question 6

What makes veins “compliant”

Answer 6

Less muscular epithelium so more able to dilate according to blood being pumped

Question 7

Why does pulmonary circulation operate only around 10-20% of pressure at systemic circulation

Answer 7

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

Question 8

How to estimate mean arterial pressure

Answer 8

Cardiac output x total peripheral resistance

Question 9

3 assumptions when calculating mean arterial pressure

Answer 9

Rigid vessels
Steady flow
Right atrial pressure negligible

Question 10

What is regulation flow achieved by

Answer 10

Variation in resistance in vessels while BP remains relatively constant

Question 11

How does cardiac output to skeletal muscle change from rest to exercise

Answer 11

From 0.75L to 6L
Rest of organs have similar supply

Question 12

Laminar flow is

Answer 12

Velocity of fluid is constant at any one point and flows in layers
Blood flows fastest closest to centre of lumen

Question 13

Turbulent flow is

Answer 13

Blood flows erratically forming eddys, prone to pooling

Question 14

What is turbulent flow associated with

Answer 14

Pathophysiological changes to endothelial lining of blood vessels (thrombosis)

Question 15

When measuring blood pressure manually in the upper arm, what kind of flow does slow deflation of cuff cause?

Answer 15

Turbulent flow, heard w stethoscope

Question 16

What is pulse pressure

Answer 16

Difference between diastolic and systolic blood pressure
Allows the risk of heart events such as strokes and attacks to be calculated

Question 17

Calculating pulse pressure

Answer 17

Systolic BP - Diastolic BP

Question 18

How to calculate mean arterial pressure from pulse pressure

Answer 18

MAP = diastolic BP + 1/3PP

Question 19

Unit for mean arterial pressure

Answer 19

mmHg

Question 20

What word describes positive transmural pressure

Answer 20

Patent

Question 21

During inspiration why does alveolar pressure decrease

Answer 21

Diaphragm contracts and thoracic cavity increases in volume, which decreases the intra-alveolar pressure

Question 22

During inspiration why does pleural pressure decrease

Answer 22

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

Question 23

How does transmural pressure change during inspiration

Answer 23

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

Question 24

During hard-expiration why is there the chance that airways collapse?

Answer 24

Pleural and airway pressure considerably increased
Pleural pressure exceeds airway pressure causes flow to cut off

Question 25

What anatomical adaptations do the airways have to mitigate against this collapsing?

Answer 25

Extrapulmonary airways are supported with cartilage to support the vessels

Question 26

What is compliance

Answer 26

Tendency to distort under pressure (change in: volume/pressure)

Question 27

What is elastance

Answer 27

Tendency to recoil to its original column

Question 28

How is diastolic flow created

Answer 28

Aortic valve closes, ejection ceases but due to recoil of elastic arteries, pressure falls slowly and diastolic flow in downstream circulation

Question 29

As arterial compliance decreases, what happens to blood pressure?

Answer 29

Systolic pressure increases
Diastolic pressure decrease

Question 30

How does the skeletal muscle pump facilitate venous return

Answer 30

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

Question 31

How does the respiratory pump facilitate venous return

Answer 31

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

Question 32

What condition does an increase in the incompetent valves in veins lead to?

Answer 32

Dilated superficial veins in leg (varicose veins)

Question 33

What is oedema in feet caused by?

Answer 33

Prolonged elevation of venous pressure

Question 34

What happens in aneurysmal disease?

Answer 34

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

Question 35

What gender is aneurysmal disease more common in

Answer 35

Men

Question 36

What law is an aneurysmal disease a pathological example of

Answer 36

Law of Laplace
Wall tension should be proportional to radius of vessel

Question 37

Diverticula are

Answer 37

Small bulges or pockets that can develop in the lining of the intestine with age

Question 38

What is the relationship between transmural pressure and vessel volume called

Answer 38

Compliance

Question 39

Is ve our or arterial compliance higher

Answer 39

Venous compliance is z 10/20higher

Question 40

What effect does incr. smooth muscle contraction have on venous pressure and volume

Answer 40

Increases venous pressure
Decreases venous volume

Question 41

What class of drugs can be taken to increase venous pressure

Answer 41

Venoconstrictors

Question 42

Why is there more ventilation in the base of the lung as opposed to the apex

Answer 42

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

Question 43

Why is there more perfusion in the base of the lung as opposed to the apex

Answer 43

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

Question 44

Is perfusion or ventilation more affected by location in the lung and why

Answer 44

Perfusion because blood is denser than air

Question 45

What is wasted perfusion

Answer 45

More blood going past respiratory exchange surface than can participate in gas exchange
Occurring at base of lung where more perfusion than ventilation

Question 46

What is wasted ventilation

Answer 46

More ventilation than perfusion
Gas is moved into parts of the lung that are not getting sufficient pulmonary circulation supply

Question 47

How are compliance and resistance affected by COPD

Answer 47

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