Anat & Phys resp system

Question 1

Anatomy of resp system

Answer 1

Nerve supply

• Diaphragm motor innervation is via the L) and R) phrenic nerve. The phrenic nerve roots are C3-C5

Question 2

Physiology of ventilation

Answer 2

Expiration is a totally passive process. It is driven by the elastic recoil of the chest wall and lung tissue. Expiration is 2 thirds of the respiratory cycle.

Ventilation:

• is the act or process of inhaling and exhaling.
• assessed by chest rise, compliance, RR, capnography

Compliance:

• Measurement of delivered tidal volume, peak airway pressure, plateau pressure (during an end-inspiratory occlusion lasting up to 2 s)
• static respiratory compliance = Vt / (plateau pressure - PEEP). Normally 60-100ml/cm H2O. Decreased in pneumonia, edema, atelectasis, pneumothorax, or endobronchial intubation.
• Dynamic resp compliance = Vt / (peak pressure - PEEP). Normally 50-80ml/cmH2O. Decreased by bronchospasm, mucus plugging, kinked tube, or decreased static compliance.

Oxygenation:

• the process of adding oxygen to the body system

Function residual capcity (FRC):

• FRC = ERV + RV
• FRC is the volume of gas in lungs at End of Tidal volume expiration (end of expiration during tidal breathing). It is the point of maximal lung compliance, minimal small airway and pulm vascular resistance
• volume: 30-35ml/kg. 2100-2400mL in normal person
• influenced by lung size (affected by height and gender), lung compliance (affected in emphysema, ARDS, PEEP, intra-abdo pressure, anaesthesia/paralysis), posture (reduced when lying supine)
• PEEP (positive end expiratory pressure) is the most often used means for increasing FRC and improving oxygenation. It improves lung volume and haemodynamics