Lecture Notes on Respiratory Physiology and Pneumothorax

Flashcards on Pneumothorax, Mechanism of Breathing, Transmural Pressures, Boyle's Law, Lung Volumes, and Related Concepts

What is Boyle's Law and how does it relate to breathing?

Boyle's Law states that gas travels from an area of high pressure to low pressure (P1V1 = P2V2). Decreasing volume increases pressure, and this principle governs air movement during breathing.

What is the Intrapulmonary pressure?

Pressure in the lung (alveoli)

What is the Intrapleural pressure?

Pressure in the pleural cavity

What is the Atmospheric Pressure?

Pressure outside the system

What is the role of serous/pleural fluid?

Prevents friction between the epithelial layers during inspiration and expiration.

What is Transpulmonary pressure? How is it calculated?

Pressure exerted across the visceral pleura. Calculated as Intrapulmonary pressure - intrapleural pressure.

What does a positive transpulmonary pressure indicate?

Lungs are inflated.

Why is intrapleural pressure normally negative?

Elasticity of the lung parenchyma wants to collapse inwards, and the elasticity of the chest wall wants to expand outwards, both increasing pleural cavity volume.

What is Transthoracic pressure? How is it calculated?

Pressure exerted across the chest wall. Calculated as intrapleural pressure - Atmospheric pressure.

What does negative Transthoracic pressure mean?

Chest wall is being deflated.

What is Transrespiratory pressure? How is it calculated?

Pressure exerted from lung to atmosphere. Calculated as intrapulmonary pressure - Atmospheric pressure.

What does a neutral Transrespiratory pressure mean?

No gas flow anywhere.

What muscles are involved in quiet inspiration?

External intercostals and diaphragm.

What is the role of the apneustic center, DRG, and pneumotaxic center in quiet inspiration?

Apneustic center stimulates DRG; DRG triggers inspiratory signals; pneumotaxic center inhibits apneustic center, controlling inspiration duration.

Which nerves are stimulated by the DRG to cause diaphragm contraction?

Nerves in C3,4,5, activating motor neurones and innervating the diaphragm via the phrenic nerve.

What is bucket-handle movement?

Outward movement of the external intercostals during inspiration.

What muscles involved in forced inspiration, in addition to the quiet inspiration muscles?

SCM, A/P/M scalenei, pectoralis minor, serratus anterior.

Which respiratory group is also active in forced inspiration?

Ventral respiratory group (VRG).

What muscles are involved in quiet expiration?

None - it's a passive process, relying on elastic recoil.

What factors prevent the lungs from collapsing during quiet respiration?

Surfactant, produced by type II alveolar cells.

What muscles are involved in forced expiration?

Quadratus lumborum, external/internal oblique, transverse/rectus abdominis, internal intercostals.

Where are central and peripheral chemoreceptors found, and to what are they sensitive?

Central chemoreceptors are found in the medulla and detect changes in pH of CSF. Peripheral chemoreceptors are found in the bifurcation of the common carotid artery and are sensitive to partial pressure of CO2 and O2 in blood.

Where are baroreceptors located and to what are they sensitive?

Located in the carotid and aortic bodies (glossopharyngeal and vagus nerves, respectively), sensitive to changes in blood pressure.

What is the Hering-Breuer reflex?

When lungs become overstretched, signals transmitted through the vagus nerve into DRG prevent further inspiration.

What is the definition of tidal volume (TV)?

Volume of air exchanged during normal inspiration & expiration.

What is the definition of Inspiratory Reserve Volume (IRV)?

Maximal volume that can be inspired in addition to a tidal inspiration

What is the definition of Expiratory Reserve Volume (ERV)?

Maximal volume that can be expired in addition to a tidal expiration

What is Residual Volume (RV)?

Volume remaining in the lungs at the end of a maximal expiration

How is minute volume calculated?

Minute volume = tidal volume × Respiratory frequency

What is Inspiratory Capacity?

Maximal volume that can be inspired following a normal expiration

What is Functional Residual Capacity?

Volume remaining in the lung at the end of a normal expiration.

What is Total Lung Capacity?

Volume in lungs at the end of a maximal inspiration

Define Pneumothorax

Collection of air in the pleural cavity causing a real instead of potential pleural space.

What happens when intrapleural pressure > intrapulmonary pressure

The lungs cannot inflate

What is the size range of a small pneumothorax?

1-2cm between lung margin and chest wall

What is the size of a large pneumothorax, and what does this entail?

2cm, which means lung function is down by 50%

What are the differences between primary and secondary spontaneous pneumothorax?

Primary: no lung disease and occurs without external trauma; secondary: patient has underlying lung disease

Who is typically affected by Primary spontaneous pneumothorax

Typically affects tall, thin, male, smokers and younger individuals

Under what conditions is open and closed traumatic pneumothorax most likely to occur?

Closed occurs after blunt or penetrating chest trauma; open occurs after penetrating chest injury.

How does hypoxemia develop from Air accumulating in the pleural cavity?

Intrapleural pressure> intrapulmonary. Lung collapses -> alveoli collapse -> less oxygen gets to it. Gradient between alveoli and capillary is affected alongside approaching ischemia - less oxygenated blood

What are common clinical features of tension pneumothorax?

Sudden onset chest pain, dyspnea, reduced breath sounds on affected side and reduced chest wall movement.

What are treatment options for pneumothorax?

Restore the negative intrapleural pressure, Chest drain (5th intercostal space mid-axillary), Needle decompression (2nd intercostal space mid clavicular line).

Name the Autonomic Nervous System neurotransmitters?

Sympathetic: Norepinephrine (Adrenergic); Parasympathetic: Acetylcholine (Cholinergic)

What are the different receptors for Acetylcholine, and Norepinephrine?

Acetylcholine Receptors – Nicotinic and Muscarinic. Norepinephrine Receptors: Alpha 1, Alpha 2, Beta 1, Beta 2, Beta 3

What are the functions of the different Norepinephrine (Adrenergic) receptors?

Alpha 1 – Smooth Muscle Contraction. Alpha 2 – Inhibits Adenylate Cyclase, decreases cAMP. Beta 1 – Located mainly in heart, increases cardiac output. Beta 2 – Located mainly in lungs, bronchodilation. Beta 3 – Located in fat cells, lipolysis

What is Lidocaine used for?

Lidocaine hydrochloride (local anaesthetic) blocks nerve conductance, preventing pain signals from reaching the brain

What are the 3 ways the respiratory epithelium signals that it is intact so that macrophages do not inflame?

1) epithelium produced IL-10 2) CD200 receptor on cell surface which sends a negative signal to not inflame 3) surfactant is produced in excess, interacts with the surface of the macrophage to alert it not to inflame