Lecture 3 Flashcards
Define Pulmonary (Minute) ventilation
total air movement into/out of lungs (relatively insignificant in functional terms) L/min
Define Alveolar ventilation
fresh air getting to alveoli and therefore available for gas exchange (functionally much more significant!) L/min
Of 500ml fresh atmospheric air inhaled, how much reaches alveoli?
350ml as first 150ml is “stale air” from dead space.
What is tidal volume and resp rate of healthy man\/
500ml, 12 breaths/min
What is tidal vol (Ml) and resp rate of anxious man?
300ml and 20 (rapid)
What is tidal vol and resp rate of chilled out man?
750ml, 8 (slow)
Therefore what is alveolar ventilation of anxious man?
Tidal vol 300ml, resp 20 breaths/min
3000 (hypOventilation, normal is 4200). tidal vol = 300, -150ml dead space = 150 ml x 20 breaths per min = 3000ml/min
Alveolar ventilation of chilled out man (750 tidal vol, 8 breaths/min) ?
air to alveoli = 750-150 = 600ml x 8 = 4800 (hypERventilation). Normal is 4200
Define Partial Pressure
The pressure of a gas in a mixture of gases is equivalent to the percentage of that particular gas in the entire mixture multiplied by the pressure of the whole gaseous mixture
What is the partial pressure of O2 we breathe? Atmospheric Pressure = 760mmHg
160mmHg BUT only 100mmHg (13.3kPa) in alveoli due to dead space and residual volume (volume that never leaves alveoli) and also becomes saturated with water. And air is in equilibrium (pressure of gas in blood with gas in alveoli)
Atmospheric Pressure = 760mmHg
Pressure of air we breathe therefore = 760mmHg
21% of air we breath = O2
Partial pressure of O2 in air we breath = 21% x 760mmHg
= 160mmHg
What is “normal” alveolar ventilation (L/min)
4.2L/min (4200ml/min)
What is the partial pressure of Oxygen and CO2 during normal ventilation?
13.3kPa p02 (around 100mmHg), 5.3kPa CO2(around 40mmHg). In healthy lungs the partial pressures found in the alveoli are the same as the partial pressures in the blood as equilibrium is reached.
What happens to P02 during Hypo and hyper ventilation?
Hypoventilation decreases PO2, hyper ventilation increases PO2
What is the pressure in the pulmonary circulation?
25/10 mmHg. systolic P ~25mm Hg, diastolic P ~8 mmHg. High flow, low pressure circuit is more susceptible to the effects of gravity and this gives rise to a great degree of variability in blood flow within the lung.
What enters the right atrium and leaves the right ventricle
Superior Vena Cava enters, Pulmonary Artery leaves.
What enters the left atrium and leaves the left ventricle
Pulmonary vein enters, leaves =Aorta
Where does nutritive bronchiole circulation (2% systemic circulation) drain to?
Left atrium.
What is the alveolar pO2 and pCO2?
pO2 100mmHg, pCO2= 40mmHg
What is the pO2 and pCO2 in pumonary Arterys?
pO2 = 40mmHg, CO2 =46mmHg
What is the pO2 and pCO2 in pulmonary Veins?
pO2 = 100mmHg, pCO2= 40mmHg
What do these abbreviations mean? A, a, ṽ
A – alveolar
a – arterial blood
ṽ – mixed venous blood (e.g. in pulmonary artery)
what are these values on kPa: 100mmHg, 40mmHg
100mmHg =13.3kPa, 40mmHg=5.3kPa
What factors affects rate of diffusion across the membrane
partial pressure gradient.
gas solubility
the available surface area
(all directly proportional)
inversely proportional to the thickness of the membrane
most rapid over short distances
What is the diffusion distance alveolar air space to capillary?
0.1-1.5micrometers
Why does CO2 diffuse more rapidly?
CO2 diffuses more rapidly because of its greater solubility. Nevertheless the overall rates of equilibrium between O2 & CO2 are similar because of the greater pressure gradient for O2.
What happens in emphysema?
Destruction of alveoli leading to reduced surface area for gas exchange causing low pO2 in pulmonary vein. High compliance (big change in volume for small change in pressure) but has lost elasticity (often through smoking) due to activation of an enzyme elastase which breaks down the elastic tissue within the lungs. Therefore no resistance to stretching the lungs and so expiration becomes v difficult (use internal intercostal and abdominal muscles on every expiration) as well as the loss of surface area.
What happens in fibrotic lung disease?
Thickened alveolar membrane slows gas exchange. Loss of lung compliance may decrease ventilation. Low pO2 in circulation. increases the thickness of the tissues across which gas has to diffuse
Pulmonary edema
Fluid in interstitial space increasing diffusion distance. Usually due to pulmonary hypertension (increase in blood pressure in pulmonary capillaries forcing plasma out of capillaries which pools in interstitial space).
Low PO2 in circulation. Arterial PCO2 may be normal due to CO2 solubility in water (the edema).
Asthma
Increased airway resistance decreasing airway ventilation. PO2 low in alveolar and circulation. Lower partial pressure gradients and so less diffusion from alveoli to blood etc
characteristics of obstructive lung diseases
Obstructive Obstruction of air flow, especially on expiration. Asthma,
COPD (Chronic Obstructive Pulmonary Disease) eg
Chronic bronchitis - Inflammation of the bronchi
Emphysema -Destruction of the alveoli, loss of elasticity.
Obstructive diseases increase the work of expiration
Obstructive = Out, increases work of expiration
how can spirometry can be used to identify abnormal lung function
Static – where the only consideration made is the volume exhaled (FVC)
Dynamic – where the time taken to exhale a certain volume is what is being measured (FEV1)
Describe and explain the characteristic results you would observe following lung function tests in patients with obstructive lung diseases
Decreased FEV1/FVC. Eg. FEV1=1.3, FVC = 3.1. % = 42% In Obstructive diseases the impact on air flow is greater than the impact on lung capacity so the FEV1:FVC ratio is significantly reduced
Describe and explain the characteristic results you would observe following lung function tests in patients with restrictive lung diseases
Increased FEV1/FVC despite absolute values lower. eg. 2.8/3.1 = 90%. In Restrictive diseases the impact on lung capacity can be huge, meaning there is simply less air to flow (which reduces FEV1) but the air that does flow is not obstructed. As such both FEV1 and FVC reduce in proportion and the ratio remains normal or may even increase.
What is FEV1/FVC and healthy values (spirometary)
FEV1 = Forced expiratory volume in 1 second (FEV1) FVC = Forced vital capacity (FVC)
Healthy young males: FEV1 = 4L , FVC = Forced Vital Capacity = 5L
So FEV1/FVC = 80% young healthy males. Absolute values vary but rati should remain the same even if other values decline.
Is alveolar ventilation greater at the base or apex of the lungs?
Alveolar ventilation and complience is greater at the base of the lung and declines with height from base to the apex because we get a bigger change in volume at the base of the lung compared with the closer to the apex of the lungs because the lungs are kind of “hanging” and so squash the lower alveoli and expand the top ones. Therefore the lower ones have more capacity to expand. Will change if patient is lying down etc as due to gravity,
What is bronchial circulation (nutritive)?
Supplying nutrients to the bronchioles. Approx. 2% systemic circulation and drains back into left atrium so therefore dilutes minorly the oxygenated blood in the aorta.
Does the same amount of blood flow through pulmonary circulation compared to systemic circulation?
Yes, because it is in series! Like a one way road the whole way around. This is why the pulmonary circulation is high flow low pressure.
What blood represents the same pp O2 and CO2 as within the peripheral tissues?
Venous blood (in systemic circulation)
What is the rate of diffusion of CO2 and O2 across the alveolar wall?
O2 = 250ml/min CO2 = 200ml/min
Why can CO2 diffuse across at a similar rate compared to O2 despite the partial pressure gradient being much smaller?
Because it is much more soluble in water compared to o2 which isn’t as easily absorbed.
What volume can spirometry not measure?
Residual volume (and therefore anything that has residual volume as a component)
Characteristics of restrictive lung diseases and examples.
Restrictive Restriction of lung expansion, Loss of lung compliance.:
RestrINtive - increase work of Inspiration
Fibrosis: formation of excess fibrous connective tissue creates a “stiff” lung.
Idiopathic (cause unknown); 50:100,000 new cases per year UK
Asbestosis (and other occupational origins e.g. coal dust)
Infant Respiratory Distress Syndrome: (insufficient surfactant production)
Oedema (pressure resists inflation of alveoli)
Pneumothorax
Restrictive diseases increase the work of inspiration
Can FRC (functional residual capacity) be increased in obstructive lung diseases?
Yes! Eg COPD as harder to exhale all of air.
What happens in restrictive lung diseases to air flow and total lung volume?
Airflow = reduced (but only because total lung volume is reduced as limitations to lung expansion). Rate is same.
Is FEV1/FVC always indicative of health?
No. Restrictive lung disease often present normal %
Is compliance increased or decreased in fibrosis?
decreased
Do FEV1 and FVC reduce in restrictive lung disease?
Yes, they both reduce similarly so the ratio remains the smae/simelar
Is compliance increased in restrictive lung diseases?
No
