Intro to Resp Medicine

• TLC - Total lung capacity = total volume of air in the lung during maximum effort of inspiration

• VC - Vital capacity = Greatest Vol of air that can be expelled from lung anger taking deep breath

• RV - Residual volume = remaining Vol of air after maximum expiration

• FRC - functional residual capacity = normal vol of air left in the lungs after expiration during normal breathing

• VT - tidal volume = Vol of air exchanged between normal insp and expiration

• IRV - inspiratory reserve volume = max amount of air that can be inspired after normal inspiration (on top of whats already inspired)

• IC - inspired capacity = max vol of air that can be inspired after normal expiration

• ERV - Expiratory reserve vol = volume of air that can be expired after natural expiration.

• Height (taller has greater volumes)

• Sex (males have greater volumes)

• Age

• Race (European>Asian)

• Respiratory diseases - this will give a reduced volume and flow rate

Volume of inspired air in which oxygen and carbon dioxide gases are not exchanged across the alveolar membrane in the respiratory tract.

It is the exchange of gas between alveoli and external evironement.

Alveolar ventilation (mL/min) = (Tidal volume (mL) - Dead Space (mL)) x Frequency of breaths (breaths/min) 

Dead space = area where no gas exchange due to lack of alveoli e.g. trachea

Respiration, olfaction, filtration, humidification, warming of air, and secretion handling

The nasal septum (medial wall)

Palantine process of Maxilla and horizontal plate of palantine bone

Cribriform plate of the ethmoid, frontal bone and sphenoid bone

Charecterised by 3 bones (conchae) - Superior, middle and inferior conchae

• The inferior concha is a separate bone while the superior and middle conchae are parts of the ethmoid bone

• The superior, middle and inferior meatus lie beneath the conchae

Perpendicular plate of ethmoid bone and Vomer

To create turbulence and warm, humidify, and slow inspired air

Increase surface area lined with pseudostratified columnar epithelium with goblet cells to secere mucus. This helps to trap dust / pathogen from the air inhaled and then get excreted.

Posterior nasal apertures connecting the nasal cavity to the nasopharynx

Cribriform plate of the ethmoid

Paranasal sinuses are hollow spaces filled in air within the bony structures of the face and they drain into nasal cavity.

• Frontal sinus - located within the frontal bone

• Ethmoidal sinus (ear cells) - located in the ethmoid bone

• Maxillary sinuses - located in the maxillary bone

• Sphenoidal sinuses - located in the sphenoid bone

• Allow skull to be lighter in weight

• Add resonance to the voice

• Absorbs shock during trauma

• Lined with mucosal cells which secrete mucus.

Sphenoidal sinuses

The paranasal sinuses drain into the nasal cavity via the meatus

• Superior meatus - drains posteior ethmoid sinus

• Middle meatus - drains maxillary, frontal and anterior ethmoid sinuses

• Inferior meatus - drains nasolacrimal duct

• Spheno-ethmoidal recess - drains sphenoid sinus

Drainage canal is higher up > Drainage is against gravity > prone to build-up of infected material.

Kiesselbach’s plexus

Trigeminal nerve (CN V)

Facial vein

Nasopharynx, oropharynx, laryngopharynx

Pharyngotympanic (Eustachian) tube

A ring of lymphoid tissue in the naso- and oropharynx

Stylopharyngeus

To propel the bolus toward the oesophagus during swallowing

The oesophagus

Has only one bone - Hyoid bone

Has 9 cartilages:

• 3x single (thyroid, cricoid & epiglottis)

• 3x paired (arytenoid, corniculate & cuneiform).

Thyroid cartilage (hyaline)

• superior thyroid notch is the laryngeal prominence = ‘adam’s apple’

• Inferior horn articulates with cricoid cartilage

• Superior horn runs towards hyoid bone but get attached to it by lateral thyroid ligaments

• Cricoid cartilage is signet ring shape

• the articular facet laterally articulates with inferior horn of thyroid.

• The tracheal ring is incomplete posteriorly = no cartilage = semicircle shape

• Thyrohyoid membrane - Attaches thyroid cartilage to hyoid bone. Runs between superior border of thyroid to inferior border of hyoid.

• Cricotracheal ligaments - attaches cricoid cartilage to superior border of 1st tracheal cartilage

Epiglottis is attached anteriorly to thyroid cartilage by thyro-epiglottic ligament.

Median cricoid ligament

• The arytenoid cartilages - (pointy bits) have apex at the top, Vocal process anteriorly and muscular process posteriorly.

  • The Vocal process attaches vocal ligaments

• Corniculates and cuneiform cartilages sits above arytenoid cartilages.

For gas exchange - to move air into the lungs to extract O2 to oxidise food which contains energy. This energy can be converted to ATP, used for bodily function.

This generates CO2 which must be exchanged out.

> Defence = filters air partilces and removes pathogens in mucus

> Metabolic = synthesise surfactants, prostaglandins and angiotensin II

> Endocrine = as above

> Haematologic = filtration of small clots, fat / cancer cells by pulmonary capillaries

> immunologic = alveolar macrophages secrete cytokines for protection

> Thermoregulatory and water elimination

> Phonation = coverts sound to speech

Assessed as the metabolic rate = how much O2 is needed at a time. Measured as O2 consumption (VO2) or CO2 production (VCO2).

• Basal metabolic rate = amount of O2 needed for basic survival ~250ml/min. In exercise it inc to ~3L/min. Daily average is ~1L/min

  
  

Metabolic rate can also be measured through CO2 production (VCO2).

RQ is the ratio of CO2 produced to O2 consumed - it indicates th type of substrate being metabolised. Used to estimate energy expenditure.

• RQ = VCO2 / VO2

RQ values (Carbs 1.0, Fats 0.7, protein 0.8, mixed diet 0.8) —> if a substrate has lower RQ = more O2 is required to metabolise it.

RQ > 1.0 = lipogenesis (excess carbs being converted to fat)

RQ < 0.7 = ketosis or starvation

• Movement of gases from environment and lung occurs through series of bifurcating airways.

• Each generation of airways (Z) is numbered (total of 23) - Trachea is Z0 > bifurcate to 2 bronchi Z1

• 1st 16 generation is known as conducting zone - no gas exchange due to thick surface.

  • Air moves by convection (bulk) in conducting zone.

• Generation 17 to 23 are transitional and respiratory zones. - the membrane gets thinner down the generation = gas exchange occurs at an increasing rate.

  • The surface area also increases beyond gen 17

The relationship between airway generation (Z) and surface area is what determines speed at which air moves through the lungs:

• Flow (cm3/sec) = Speed (cm/sec) x Area (cm2)

As we move down the airway, overall SA increases = air is spread over wider area = speed reduced.

• Z17 onwards, gas speed is determined by speed of diffusion (as opposed to convection / bulk movement in the conducting zone Z0-Z16).

Partial pressure gradients

• Gas diffuse down the gradient from high to low.

• To increase O2 flow across patient’s lung, the diffusion gradient need to be increased = increase pO2 within respiratory zones > high gradient > increase rate of diffusion.

• Can’t just increase convection!

• PB = atmospheric pressure = pressure exerted by weight of gas molecule in the atmosphere at given location. Measured in kpa

• At sea level PB is ~100kpa and this decreases with high altitude (every 5450m above sea level, PB is halved)

• Partial pressure = pressure of any particular gas (O2/CO2) which depends on no of molecule of that gas in given volume

  • Related by Dalton’s Law of PP which states total pressure is the sum of partial pressures.

  • Partial pressure = Fractional concentration of a gas in a mixture x Total pressure

Dead space is the vol of gas within the respiratory system in which gas exchange does not occur

• Anatomic dead space = present in everyone

  • It is air in the conducting zone which is not available for gas exchange due to thick membrane + some inspired air doesnt reach alveoli. In adult its ~150ml.

  • depends on size of pt - larger pt > greater ADS

• Alveolar dead space = present in patient with resp disease

  • It is vol of gas within respiratory zone where gas exchange does not occur (it would in normal patient so its 0ml)

• Physiological dead space = anatmical dead space + alveolar dead space.

  • Increase in physiological is mainly due to alveolar dead space as anatomical dead space is constant

• Increases significantly in certain lung diseases - primarily due to under perfusion of affected alveoli

  • e.g PE, pumonary hypotension due to blood loss.

• An increase in physiological dead space will decrease alveolar ventilation > impacts blood oxygenation, CO2 and pH

• Total (minute) ventilation is defined as volume of gas brethed in one minute. Calculated as:

  • Minute/total ventilation = Tidal volume x RR

• Due to anatomical dead space, not all of this ventilation reaches respiratory zone. AV is calculated as:

  • Alveolar ventilation = (Tidal Volume - Anatomic Dead space) x Respiratory Frequency

This is more useful way of measuring total ventilation in terms of gas exchange. This can be affected by changes in physiological dead space + breathing pattern.

Increases alveolar ventilation by decreasing the proportion of breath that is contained within the anatomical dead space

• COPD patients who may have increased alveolar dead space taught to breath via pursed lip breathing.

• Slow deep breathing increases tidal volume (vol of air breathed in/out in one min) = more air reaches alveoli, reducing dead space)

• Reduces RR > more time for gas exchange

• This can help improve movement of air in and out of the lungs, open airways and move trapped air, control RR, reduce anxiety and promote relaxation

Anterior body of T1 vertebra, medial borders of rib 1 (L+R) and superior border of manubrium

Trachea, oesophagus, major blood vessels and nerves

Descending oesophagus, descending aorta and ascending inferior vena cava

Anterior body of T12 vertebra, floating ribs 11/12, costal margin, Xiphoid process superiorly and anteriorly.

Sternal angle = angle of loui, its where the manubrium meets the body of sternum.

Horizontally it is at the level of T4,T5, it marks the area of beginning and end of arch of the aorta and bifurcation of bronchus to left and right

Ribs can be classified as typical and atypical (ribs 1, 11, 12)

They can also be classified as true, false and floating

• Ribs 1-7 - True ribs

  • Directly articulates with sternum via costal cartilage

• Ribs 8-10 - False ribs

  • Indirectly articulates with sternum via costal cartilage to rib 7. This forms costal margin

• Ribs 11-12 - Floating ribs

  • Do not articulate with sternum

1. Pump handle movement - increases volume of thorax, there is a superior and anterior movement of the ribs and sternum

2. Bucket handle movement - Elevates the rib and also increase thoracic volume. Occurs medially to laterally

Left lung

• has 2 lobes - superior and inferior lobe, separated by oblique fissure

Right lung

• Has 3 lobes - superior, middle and inferior lobe, seperated by horizontal fissure superiorly and oblique fissure inferiorly

Trachea is the conducting airway inferior to the larynx which ends inferiorly at lower border of cricoid cartilage (C6) an enters the thoracic cavity through thoracic inlet.

Carina is the bifurcation of the trachea at the level T4-T5.

Same as sternal angle.

(it is also the same level where arc of the aorta start and ends

Trachea bifurcates into right and left main bronchus

• R is steeper than left and slightly wider = high likely to get lodging of aspirated materials.

• The main bronchi then split into lobar bronchi

• 1st rib

• Left brachiocephalic vein

• Arc of aorta

• oesophagus

• descending aorta

Also has large indentation where heart would be

Hilum of the lung is the triangular depression located on the medial aspect of each lung. Structures (superior to inferior):

• Pulmonary artery

• Bronchus

• pulmonary vein

The pleura is a membrane around the lungs and the inside of the thoracic wall. It is a continuous layer but divided into:

• The parietal pleura, which lines the inside of the thoracic wall

• The visceral pleura, which lines the outside of the lungs.

It extends into fissures and continuous at the hilum.

Between the layers of parietal and visceral pleura, there is a small vol of serous fluid known as parietal fluid.

Function - prevents friction between the layers and lubricate them. Aslo helps to keep the layers against one another.

Rib # can be anterior or posterior

• Pneumothorax:

  • rib # can damage the surface of the lung > air entry into the pleural cavity. will affect the adhesive effect that couples the lung and thoracic wall > lung collapse

• Haemothorax:

  • if the # is severe, the sharp edges of the rib can damage the neurovascular bundle in the costal groove > blood building in the pleural cavity.

• Frail chest

  • this is where isolated section of the chest wall moves opposite direction to the chest wall - moves in during inspiration and out during expiration

• Tension pneumothorax

  • Air is drawn into the thorax but cant escape > increased pressure on the mediastinal structures

A pressure difference between alveolar pressure (PA) and barometric pressure (PB) (atmospheric).

• PB cant be changed so alveolar pressure is changed for pressure gradient

Boyle’s Law

• Pressure of a gas varies inversely with vol of the container of the gas - so if the vol is halved, pressure is doubled.

Alveolar pressure decreases below atmospheric pressure.

• This causes air to move into lung via inspiration.

Alveolar pressure increases above atmospheric pressure

• Decrease in lung vol > increase alveolar pressure > air moves out via expiration

Diaphragm

• Thoracic vol is altered primarily by movement of diaphragm.

• If larger changes in vol are needed, accessory muscles of inspiration and expiration is used.

External intercostals, scalenes, sternocleidomastoid muslces

• Contraction of these muscles causes changes in lateral, vertical and antero-posterior dimensions of thorax.

Internal intercostals and abdominal muscles

Visceral pleura - lines surface of the lungs

parietal pleura - lines inner surface of the thorax

> Work of breathing is done by respiratory muslces of thoracic cage and the pleural membrane couple these. Each lung has its own pleural membrane.

Pleural fluid (lubricating)

• Pleural space is the space between visceral and parietal pleira

The lung volume at the end of normal expiration when respiratory muscles are relaxed

Inwards

Outwards

Opposing elastic recoil of lung and chest wall creates sub-atmospheric pressure

When alveolar pressure equals barometric pressure

The change in volume per unit change in pressure

Pressure inside the lung minus pressure outside the lung

Around FRC

Compliance divided by FRC

It is lower (the system is stiffer than either component alone)

FRC increases

Air in the pleural space causing loss of negative intrapleural pressure

The lung collapses and the chest wall expands

A pneumothorax with a one-way valve mechanism causing progressive air trapping

It causes mediastinal shift, compresses the heart and great veins, and leads to shock