Ventilation and Lung Volumes Gas Transport Flashcards
How do you calculate Tidal volume?
Tidal volume is dead space + volume of air entering alveoli.
How do we calculate pulmonary ventilation?
Pulmonary ventilation is respiratory rate x tidal volume (RR x TV)
How do we calculate the alveolar ventilation?
RR X (TV-DS) (minus the dead space, usually about 150ml)
What is minute volume?
The volume of air entering and leaving the lungs each minute (or pulmonary ventilation)
What is Tidal volume?
The air taken in and out with each breath
How are respiration rates varied throughout life?
Newborn - 30-60 breaths ber minute
Young Children - 20-30 breaths per minute
Adults - 12-20 breaths per minute
How do you work out minute volume?
MV = Respiratory Rate (RR) x Tidal Volume (TV)
At what point does conducting airways become respiratory airways?
Ventilation is classified as…
Pulmonary ventilation = moving gases in/out of lungs
Alveolar ventilation = volume of air participates in gas exchange
So alveolar ventilation is less than pulmonary ventilation
Why is alveolar ventilation less in volume than pulmonary ventilation?
Because not all the air that’s in the lungs gets exchanged.
This is called ‘dead space’
What are the two types of dead space?
Anatomical dead space
Physiological dead space - is the part of the respiratory system where gaseous exchange
Generally speaking in normal the dead space volume is about the same in both components.
How would you calculate tidal volume?
Tidal volume = dead space + volume of air entering alveoli
Label the parts of the Spirometer
Label the parts of a Spirogram.
What makes up the functional residual capacity?
The expiratory reserve volume + residual volume
What are the typical lung volume capacities?
What is inspiratory capacity?
Tidal volume + inspiratory reserve volume
What’s the functional residual capacity?
expiratory reserve volume + reserve volume
How can residual volume and functional residual capacity be measured?
- They cannot be measured by spirometry.
- They helium hilution method or plethysmography are used instead.
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What is the helium dilution method?
- Get them to first breathe normally until reaching equilibrium
- Then something or other
What happens to residual volume and forced viral capacity in diseased states?
- Increased RV occurs in emphysema and COPD and sometimes in asthma
- Respiratory muscles have a greater resting length
- Respiratory movements are less efficient
- Work of breahting is increased
What are the tests of ventilatory function?
In respiratory diseases it is important to measure degree to which airflow is limited.
A couples of useful measures are:
Forced expiratory volume in 1 second (FEV1 ) and Forced Vital Capacity (FVC) and its ratio FEV1/FVC is expresses as a %.
FEV1 and FVC are measured against predictive values.
Peak Expiratory Flow Rate (PEFR) also used: PEFR is a person’s maximum speed of expiration as measured with a peak flow meter
A good way to monitor COPD/Asthma is to monitor at home.
How would time-volime graph be different in obstruction and restriction?
What is a flow volume loop?
The flow-volume loop (also called a spirogram) is a plot of the inspiratory and expiratory flow (on the Y axis) against volume (X axis) during the performance of maximally forced inspiratory and expiratory maneuvers.
What moves oxygen into blood and Co2 into air from blood?
Pressure gradient
- Negative intrathoracic pressure –> ventilation (breathe in, volume gets bigger, pressure drop in lungs, becomes sub-atmospheric, air rushes in)
- Partial pressure differences (in alveoli, oxygen leaves, co2 is low in inspired air, so co2 leaves)
What is Boyl’es law?
A law stating that the pressure of a given mass of an ideal gas is inversely proportional to its volume at a constant temperature.
What is Avogadro’s Law?
Volume of gas at the same temperature & pressure contain the same number of molecules
What is Charle’s Law?
At a constant pressure the volume of gass is proportional to its absolute temperature
What is the ideal gas law?
The volume occupied by n moles of any gas has a pressure (P) at temperature (T).
PV = nRT
P × V = n × (R) × T,
What are the Graham and Henry’s law of gases?
Give an overview of Dalton’s Law of partial pressure
The Pressure exerted by a mixutre of gases is equal to the sum of the individual partial pressure exerted by each gas in the same volume.
E.g. in alveoli
PB = pn2 + po2+ pc02 + p520
Ph20 = water vapour pressure
What is the partial pressure of O2 in air?
Air contains 21% O2
PiO2 = partial pressure of inspired O2
in mmHG = 21% of 760 = 159
in kPa = 21% of 101 = 21
What is the difference in pressure of atmospheric air vs alveolar air?
What does the rate of diffusion of O2 and Co2 from aqueous lining of alveoli to blood depend on?
- The partial pressure of the gas
- The solubility of the gas in the liquid: solubility of Co2 > x20 of O2
- Area available for gas exchange
- Thickness of alveolar membrane
Ability of gas to diffuse betwen alveolar air and blood is measured by its diffusing capacity (or transfer factor) DL
Describe the ultrastructure of the respiratory membrane
- Gaseous exchange due to pressure differences
Give some facts about oxugen exchange
- Dissolves slightly in H20
- Forms a reversible combination with Hb
- The amount of O2 carried by the blood can be expressed as:
1) Arterial oxygen content CaO2 (ml/100ml)
2) The arterial oxuygen content (CaO2) is the amount of oxygen bound to Hb + the amount of oxygen dissolved in arterial blood - % saturation of Hb with O2, SaO2 (%)
- The relationship of PaO2 to SaO2 and CaO2 is not linear.
- It is the O2 dissociation curve for Hb
Explain the diffusion gradient from the capillaries to the alveoli and the tissues
Describe the structure of haemoglobin
- 1 molecule of oxygen binds 4 oxygen molecules
- Each heme group has a porphyrin ring with an iron atom in the center
- Fetal haemoglobin is slightly different (2 alpha and 2 gamma globulin chains)
Explain Haemoglobin & Oxygen transport
Explain the haemoglobin-oxygen dissociation curve
What is the haemoglobin-oxygen dissociation curve?
What would happen if the oxygen-haemoglobin curve shifted to the left?
Hb’s O2 affinity increases and the Hb-O2 dissociation curve shift lefts when there is a decrease in
- body temperature
- PCO2
[2,3-BPG}
[H+} an increase in pH
Explan the differences seen in the foetal and adult HbO2 dissociation curves
- Higher affinity for oxygen
- So adult can give off oxygen to fetal blood supply via placenta
What are the dangers of carbon monoxide?
CO binds stronger than O2
How is CO2 transported in the blood?
Explain the Co2 Dissociation Curve
Haldane Effect: removing O2 from Hb incrfeases ability of Hb to pick up CO2 and CO2 generated H+
The Bohr effect and the Haldane effect work in synchrony to facilitate: O2 liberation and uptake of CO2 & Co2 generated H+ at tissues
Explain gas exchange a thte tissues
Haemoglobin binds to H+ ions causing chloride shift
Explain gas exchange in the lungs
What is the acid-base balance?
What is the principal equation?
What is the Henderson-Hasselbalch Equation?
What are the causes of pH changes in the blood?
Respiratory
Hypoventilation –> Acidosis
Hyperventilation –> Alkalosis
Metabolic (including renal)
- Diabetic Ketoacidosis –> acidosis
Vomiting - Alkalosis
- Renal failure - Acidosis
What are the Physiological responses to pH changes?
- Buffering by chemicals, including HCO3-, Hb and other blood proteins (rapid response, limited capacity)
- Changes in ventilation (rapid response, impossible if primary cause is respiratory)
- Changes in renal excretion of H+ and HCO3- (slower response, limited if the -primary cause is renal)
What happens in respiratory acidosis?
- Lungs retain Co2
- HCO3- rises and pH falls
- Kidney compensates by retaining HCO3- and excreting H+ (slow)
- This resotres pH towards normal
- But HCO3- and PCo2 remain high
What happens in respiratory alkalosis?
- Lungs lose excess Co2
- HCO3- falls and pH rises
- Kidney compensated by retaining H+ and excreting HCO3- (slow)
- This restores pH towards normal
- But HCO3- and PCO2 remain low
What is a davenport diagram?
