Mechanics of ventilation

Respiration refers to two integrated processes which are?

External respiration

Internal/cellular respiration

What is external respiration?

•Exchange of oxygen and carbon dioxide between the body and the external environment

What is internal respiration?

Uptake, utilisation of oxygen by cells and release of carbon dioxide

What are the 4 steps of external respiration?

1. Ventilation between the atmosphere and air sacs (alveoli) in the lungs

2. Exchange of O2 and CO2 between air in the alveoli and the blood in the pulmonary capillaries

3. Transport of O2 and CO2 by the blood between the lungs and the tissues.

4. Change of O2 and CO2 between the blood in the systemic capillaries and the tissue cells

What is cellular metabolic process ?

Intracellular metabolic process carried out in mitochondria which uses oxygen and produces carbon dioxide while deriving energy (ATP) from nutrient molecules

What is the formula of cellular metabolic processes?

food + O2 --> CO2 + H2O + ATP

What are the nutrient molecules used in cellular respiration?

•generally carbohydrates or fatty acids

What type of respiration is cellular respiration?

Aerobic

What is anaerobic respiration?

•when cells lack oxygen:

foodàlactic acid + ATP

What is apart of the extra-thoracic anatomy?

Nasal passages

Mouth

Pharynx

Larynx

What is apart of the intra-thoracic anatomy?

Trachea

Cartilaginous ring

Right bronchus

Bronchiole

Terminal bronchiole

How many alveoli are there in the lungs?

300 million

What is gas exchange driven by?

•Gas exchange driven by diffusion along concentration gradients (passive)

What is ventilation driven by?

Mechanical forces

•Air is moved into and out of the lungs along ?

pressure gradients

What is gas pressure?

Force that the gas exerts on the walls of its container

What is Boyle's law?

"For a fixed mass of enclosed gas at constant temperature, the product of the pressure (P) and volume (V) remains constant."

What is the equation for Boyle's law?

PV = k

or

P1V1=P2V2

Decreasing volume increases collisions and does what to pressure?

Increases pressure

If you relax, open your mouth, and don't breathe, the pressure in your lung/alveoli =?

Atmospheric pressure

A pressure differential exists only between?

•pulmonary and pleural pressure

Which is largerL pleural or pulmonary pressure?

•Pleural pressure < Pulmonary pressure

What is the. transmural pressure gradient =?

Intra-aveolar pressure - intrapleural pressure

What is the thoracic wall pressure?

Same as atomspheric

What separates the lung from the thoracic wall?

Pleural sac

Why is the pulmonary pressure larger than the pleural pressure?

-The lungs are stretched and under tension (pulling inwards)

-The chest wall is under tension (pulling outwards)

What happens in a pneumothorax?

The intrathoracic pressure equalizes with atmospheric pressure, collapsing the lung.

What are the two conditions at which we leave the pressure equilibrium ?

Inspiration and expiration

What establish pressure differentials?

Mechanical forces

What happens in inspiration?

Size of thorax on contraction of inspiratory muscles increases and lungs as they are stretched to fill the expanded thorax, drawing in more air.

What happens on expiration?

Size of thorax on relaxation of inspiratory muscle. Size of lungs decrease as they recoil

What is the 1st event of inspiration?

1.Inspiratory muscles contract

What is the 2nd event of inspiration?

The diameter of the thoracic cage increases

What is the 3rd event of inspiration?

Intrapleural pressure (PPL) becomes more negative

What is the 4th event of inspiration?

Transmural pressure (PTM) increases and causes alveoli to swell or open

What is the 5th event of inspiration?

Intra-alveolar pressure falls relative to atmospheric pressure

What is the 6th event of inspiration?

.Air flows down pressure gradient from atmosphere to alveoli

What is the 7th event of inspiration?

Tidal volume (VT) of about 500 mls is added to resting volume or FRC

What is the 8th event of inspiration?

At end of inspiration - no airflow and intra-alveolar pressure = atmospheric pressure.

What are the 3 types of inspiratory muscles?

Primary

Accessory

Airway

What are the primary inspiratory muscles?

diaphragm and external intercostals

What are the accessory inspiratory muscles?

sternocleidomastoid, scalenes

What are the airway inspiratory muscles?

Laryngeal

Pharyngeal

Genioglossus

What is a diaphragm?

•dome shaped; flattens upon contraction and descends (1-10 cm); causing 75% of inspiration

What do external intercostals do?

: Lift ribs upwards and outwards

What do the scalene do?

Raise the first 2 ribs

What does the sternomastoid do?

Raise the sternum

When are the accessory muscles used?

Used during exercise and respiratory disease

•Examples for respiratory diseases associated with the requirement of accessory muscle activity include?

•Chronic bronchitis

•Asthma

•Emphysema

--> Chronic obstructive pulmonary diseases (COPD)

•Bronchiolitis (e.g. respiratory syncytial virus (RSV) in infants)

What are the roles of airway muscles?

--> Enlarging of the airway --> Reduced flow resistance

--? Stabilisation of the airway (esp. pharynx) --? Preventing collapse

What are the 2 types of expirations?

Passive and active expiration

What is passive expiration?

-Passive process, when at rest

-Relaxation of inspiratory muscles sufficient

What is active expiration?

-Contraction of abdominal muscles (push up diaphragm)

-Contraction of internal intercostals

When is active expiration required?

Coughing, Sneezing, Exercise, Resp. disease, Screaming, Singing, Vomiting...

What are spirometers composed of?

lof two vessels

-One contains water, the other floats upside down in the first.

As the subject breathes through the attached tube of the spirometer what happens?

air flows in and out of inner vessel which moves up and down

What are different about modern spirometers?

lSame operating principle

lCan link to computer via USB for generation of spirograms etc.

What are readings of lung volumes and capacities obtained using?

Spirometer

Reading of lung volume and capacities is thorugh what?

Spirogram

Capacity of lung volume and capacities is what?

Sum of volumes

What can the spirometer not measure?

RV, FRC, TLC

What is TV?

tidal volume (500ml)

What is IRV?

inspiratory reserve volume(3000)

What is IC?

inspiratory capacity (3500)

What is ERV?

expiratory reserve volume (1000)

What is RV?

residual volume (1200)

What is FRC?

functional residual capacity (2200)

What is VC?

vital capacity (4500)

WHat is TLC?

total lung capacity (5700)

What is FEV1?

-Forced expiratory volume in one second (FEV1)

FEV1 is usually expressed in?

-% of the (forced) vital capacity ((F)VC)

FVC is determines in?

pulmonary function test

What is the FEV1/FVc ratio in a. healthy person?

80%

What is PEFR?

peak expiratory flow rate

What is PEFR used alongside?

Spirometry

What are PEFR used as?

Measure of airway resistance

What are the benefits of PEFR?

-Cheap and easy to use

-Very useful in Asthma

What happens in obstructive diseases to FEV1 and FEV1/FVC?

Reduced

What are some obstructive diseases?

asthma, COPD, chronic bronchitis, emphyse

What are obstructive diseases?

•Airflow rate (vol/time) reduced due to airway obstruction

What is higher in obstructive diseases?

RV

What happens in restrictive diseases to FEV1 and FEV1/FVC?

FEV1 decreased, but FEV1/FVC normal or increased

What are some restrictive diseases?

pulmonary fibrosis, asbestosis

Why are airways free in restrictive diseases?

•Due to lungs being less compliant; airways free

what happens to RV in restrictive diseases?

Normal

What is the total lung capacity in obstructive disease?

Normal

What is the total lung capacity in restrictive disease?

Decreased

What is the residual volume in obstructive diseases?

INcerased

What is the residual volume in restritive diseases?

Nromal

What is the forced vital capacity in obstructive diseases?

Normal or only slightly decreased

What is the forced vital capacity in restritictive diseases?

Decreased

What is the FEV1 in obstructive disease?

Decreased

What is the FEV1 in restrictive disease?

Decrease

How can you measure the functional residual capacity (FRC) ?

by the Helium Dilution Technique

What is a helium dilution technique?

lHelium/oxygen mixture in spirometer

How does Helium dilution technique work?

lPatient starts breathing at FRC

lNew volume of the system now V2 = V1 + FRC

lHelium diluted accordingly

lBut total amount of Helium cannot change (closed system)

Helium dilution technique is inappropriate in which patients?

lInappropriate in patients with obstructive pulmonary disease

Why does the helium dilution technique work?

BC helium is insoluble

What is a body plethysmography?

lPatients sits in a "body box" (airtight chamber) and breathes through a mouthpiece

lAt FRC, the mouthpiece is closed

lPatient tries to breathe in

What are the consequence of body pleuthysmogrpahy?

- Chest and lungs expand, pressure in lungs drop as volume increases

- Expanding chest compresses the air inside the chamber, air volume in chamber decreases, pressure in chamber increases