Respiratory Physiology Flashcards
What occurs in quiet breathing?
Diaphragm used for quiet breathing
Inspiratory muscles contract
Thoracic volume- increases, Thoracic pressure decreases
-> Air pushed in along pressure gradient
Expiration is passive
What muscles are used in forceful breathing?
intercostal and accessory muscles
What happens when alveolar pressure is greater than atmospheric pressure?
Inspiration
-> expiration is the opposite
What happens to intrapleural pressure during breathing?
falls during inspiration and increases during expiration
What is tidal volume?
air moving in and out of lung during quiet breathing
What occurs when you forcibly inhale to the maximum amount?
You reach the inspiratory reserve volume
-> exhalation to its maximum is the expiratory reserve volume
What is the residual volume?
Volume left in lung even after ERV
What is the vital capacity?
Sum of ERV, IRV, TV
How is total lung capacity calculated?
Sum of VC and RV
Why does posture affect breathing?
Abdominal cavity and its contents can obscure or complicate breathing
-> This can be further complicated by obesity
What is the FEV1?
Forced expiratory volume in 1 sec
What occurs when patients suffer from restrictive/obstructive pulmnory diseases?
vital capacity is reduced
What are examples of restrictive pulmonary diseases?
obesity, TB, fibrosis, pneumonia, pneumoconisus
What is the affect of restrictive pulmonary diseases on VC/FEV1?
Reduced VC is close to FEV1 (smaller volumes of air are exchanged but it occurs at a similar rate to healthy patient)
What is the affect of obstructive pulmonary diseases on VC/FEV1?
Vital capacity is reduced and exchange is reduced due to a smaller FEV1 value
What are examples of obstructive pulmonary diseases?
COPD, Emphysema, asthma, bronchitis
What are the different zones in the airways?
Conducting zone (no gas exchange = anatomical dead space)
Respiratory zone (region of gas exchange)
What parts make up the conducting zone?
Trachea, bronchi, bronchiole terminals (+ oral/nasal cavity)
-> 150ml reaches here out of 450ml tidal volume
What parts make up the respiratory zone?
Respiratory bronchiole, alveolar duct, alveolar sac (gas exchange)
-> 300ml of air actually reaches lungs
Where does gas exchange occur in the lungs?
Gas exchange occurs between the alveolar air and the pulmonary capillary blood
-> Gases (oxygen and CO2) move across alveolar wall by diffusion which is determined by PARTIAL PRESSURE gradients
What do gases have to cross in order to reach alveolus/blood?
Gases cross T1 pneumocytes , endothelial cells, basement membrane (0.5-2micrometers)
What happens to different substances in air as they pass from atmosphere into alveoli?
Atmospheric oxygen concentration drops from 21% to 13.2% in alveoli
PPs of oxygen is the same in alveoli as articular blood due to equilibrium of exchange
N drops too
In air there is no CO2 but it increases to 5.3% in alveoli
Water exists in air but increases in alveoli
What are ventilation and perfusion?
Ventilation (V)- amount of gases passing through the lung
Perfusion (Q)- amount of gases travelling your pulmonary circulation
-> these are matched
How do V and Q relationship vary in different parts of the lung in an upright/prone person?
V and Q are greater at the base of the lung
-> The V:Q varies at different levels in the lung
These differences are less marked in a prone subject
How are CO2 and O2 transported?
In the blood:
O2- by Haemoglobin
-> Iron from haem group reversibly binds to oxygen (affinity differs depending on PP)
CO2- RBCs/plasma
What are the features of haemoglobin?
Globular metalloprotein
MW = 68,000
2 alpha & 2 beta protein chains
4 haeme groups: Porphyrin ring/Iron atom
200-300 Hb molecules / RBC
How is oxygen transported when breathing normal air?
Attached to haemoglobin (97%)
Dissolved in plasma (3%)
How is oxygen transported when breathing pure/hyperbaric oxygen?
If o2 given to a patient- haemoglobin is saturated so excess oxygen becomes available dissolved in blood
What occurs in the oxygen dissociation curve when it reaches 60mmhg?
Low concentration- low saturation of Haemoglobin
As this increases past 60mmHg the curve for saturation becomes more horizontal
What are Bohr shifts?
When dissociation curve shifts to the right or left
What would cause a left shift to occur, what happens?
Hypothermia and alkalosis (increases affinity for o2)- easier to harvest oxygen into lung but more difficult to lose o2 in tissues
What would cause a right shift to occur, what happens?
Increased temp, acidosis, increased 2, 3 DPG (reduced haemoglobin affinity for oxygen)
-> Hb gives away o2 in tissues
What is 2,3 DPG?
By-product of glycolysis (part of feedback group which can limit tissue hypoxia)
What happens when CO2 binds to Hb?
limits its ability to carry o2 to tissues
What occurs as a result of CO poisoning or anaemia?
Venous PO2 is reduced in CO poisoning and anaemia- therefore the oxygen in tissues will be very low and can cause anaemic hypoxia
In what forms is CO2 transported?
Dissolved CO2 (10% of total)
Combined to protein: carbamino compounds (20% of total)
Bicarbonate ions (70% of total)
How is control of breathing achieved?
Breathing is automatic process controlled by voluntary muscles
Not autonomic- rhythm created in brainstem
What can cause breathing rate to increase?
Cerebral cortex (conscious change)
Peripheral chemoreceptors in artery (triggered by low oxygen and high CO2)
Central chemoreceptors (when triggered by low pH or high CO2 in CSF)
Joint receptors (triggered by movement/exercise)
What can cause breathing rate to decrease?
If breathing is consciously increased- Lung stretch receptors can recognise increased inflation and reduce respiratory centres rhythm
What is Hypoxia?
reduction of o2 delivery to tissues
What occurs in hypoxic hypoxia?
Decreased O2 reaching alveoli
Decreased diffusion of O2 into blood
What occurs in Anaemic hypoxia?
Decreased oxygen transport in blood
-> Due to low Hb or reduction in Hb ability to be an oxygen carrier (as in CO poisoning)
What occurs in ischaemic hypoxia (stagnant)?
Decreased O2 transport in blood due to low blood flow
What occurs in cytotoxic hypoxia?
Decreased O2 utilisation by cells
What is the main sign of cyanosis?
Blue colouring of skin and mucous membranes
What are the types of cyanosis?
Peripheral- localised
Central- affects whole body (can be evident in oral tissues)
-> Due to >5gm de-oxygenated haemoglobin / dl of blood (deoxyhaemoglobin)
How is oxygen levels monitored clinically?
Saturation not PP of oxygen is measured in clinical setting
-> Pulse oximeter measures this- arterial oxygen PP (PaO2)
-> Evaluates wavelength in oxygenated and deoxygenated Hb in pulsing arterial blood
-> Warning when it drops past 90% value (cyanosis would be detected at around 40%)
What are the causes of central cyanosis?
Generally due to decreased O2 delivery to blood, hypoxic hypoxia:
low atmospheric PO2
airflow in airways (obstruction)
O2 diffusion into blood
pulmonary blood flow
‘shunting’ (‘venous’ blood into arteries)
What are the causes of peripheral cyanosis?
Often due to decreased blood flow to tissues - stagnant/ischaemic hypoxia
-> Peripheral vascular diseases
