BPK 305 - Lecture 24

how does air move in the body?

- convection in the upper airways

- diffusion in the alveoli

what is convection?

air moves from high to low pressure areas

what is the driving force for inhalation and exhalation?

difference between atmospheric (PB) and alveoli pressure (PA)

what is Boyles law?

P = 1/V

what causes the pressure changes required for ventilation?

changes in the volume of the lungs

muscles of inhalation

- external intercostals

- diaphragm

- scalenes

- sternocleidomastoid

- upper respiratory tract muscles

what are the muscles in exhalation?

- internal intercostals

- rectus abdominus

- external obliques

spinal cord injury above C5

inspiration dependent on accessory muscles

spinal cord injury above C3

requires artificial

ventilation

quiet inspiration muscles

diaphragm and external intercostals

forced inspiration muscles

- scalenes

- sternocleidomastoid

- neck and back muscles

- upper respiratory tract muscles

quiet exhalation muscles

none, it is a passive process

forced expiration muscles

- abdominal muscles

- internal intercostals

- neck and back muscles

what is the pleural cavity filled with?

pleural fluid

what doe pleural fluid do?

- allows lungs to slide over chest wall

- "sticks" lungs to chest wall (5-35 µm separation)

What are the two pleural membranes?

visceral and parietal

what is the pressure in the pleural cavity?

negative

what does the negative intrapleural pressure do?

counters elastic recoil of the alveoli and keeps alveoli open

pneumothorax

- puncture of pleural space

- lung collapse; alveoli collapse = atelectasis

lung compliance

highly distensible

what is the compliance of the lungs?

ease with which lungs can expand under pressure

compliance equation

change in volume/change in pressure

what is lung compliance determined by?

elastin and collagen fibres in lung parenchyma

what happens during lung inflation?

elongates fibres, exerting more elastic force causing elastic recoil so lungs revert to initial size following distension

what causes lungs to collapse during pneumothorax?

elastic recoil

what does decreased lung compliance do?

increases resistance to distention

what is hysteresis?

More pressure is needed to open an

airway than for it to collapse

what does lung inflation have to overcome?

- elastic recoil

- surface tension

what alveoli have high ST?

collapsed

adult lung compliance

200ml of air per cm of H2O change in pleural pressure

emphysema

- increased compliance

- difficult to exhale

what causes emphysema?

- smoking causes macrophages to release schematic factors for neutrophils

- neutrophil accumulate

- neutrophil elastase activation

- decreased elastin

fibrosis

- decreased compliance

- difficult to inhale

what causes fibrosis?

- particulate matter triggers monocytes to differentiate to macrophages

- macrophages secrete pro fibrotic factors causing proliferation of fibroblasts

- fibroblasts increase collagen deposition

what does surface tension do to bubbles?

acts to decrease radius and increase pressure inside

LaPlaces Law

P=2T/r

what happens in smaller alveoli?

It will take twice the inspiratory pressure to keep a small alveolus open compared to one twice as large

what prevents alveolar collapse?

- Principle of interdependence

- Alveoli contain surfactant

principal of interdependence

alveoli are mechanically tethered together to remain open

surfactant composition

- 90% lipids

- 10% proteins

surfactant lipids

- dipalmitoylphosphatidylcholine (DPPC)

- phosphatidylcholine

(hydrophobic)

surfactant proteins

- albumin

- IgA

- apoproteins SP-A, SP-B, SP-C, SP-D

(hydrophilic)

- SP-A & -D also have immune functions

how is surfactant secreted?

lamellar bodies

what happens after surfactant is secreted?

forms tubular myelin rich in surfactant apoproteins

what does surfactant do?

- decreases surface tension

- minimizes the tendency for small alveoli to collapse

- increases compliance and decreases elastic recoil so the

lungs are easier to inflate

- keeps alveoli moist

- minimizes fluid accumulation

- maintains alveolar size

- Marangoni effect

how does surfactant prevent different alveoli expanding at different rates?

- In rapidly expanding alveoli

surfactant becomes more dispersed

- This increases the surface tension

- Counteracts the rapid expansion

- Equalizes alveolar expansion

cause of infant respiratory distress syndrome

- most common for births <28 weeks gestation

- reduced/absent surfactant

IRDS symptoms

- shortness of breath and grunting sounds

- lungs are stiff and hard to inflate (alveoli collapse in exhalation)

- unusual breathing movement

IRDS treatment

- high oxygen and humidity

- artificial ventilation

- synthetic/animal-derived lung surfactant