Breathing Compliance Overview

Study Notes

Compliance is the change in lung volume per unit change in distending (transpulmonary) pressure.
The formula for compliance is: C = ΔV/ΔP, where C is compliance, ΔV is the change in lung volume, and ΔP is the change in distending pressure.
The unit for compliance is ml/cm H2O.
Lung compliance (CL) is 200 ml/cm H2O.
Pulmonary system compliance (the lungs and thoracic cage together) is about 130 ml/cm H2O.

Rigidity of the lungs:
- Pulmonary fibrosis (increased fibrous tissue in the lung)
- Pulmonary edema (prevents the inflation of some alveoli)
- Atelectasis (collapse of some alveoli)
- Pulmonary congestion (increased venous pressure, lung engorged with blood)
Rigidity of the thoracic cage:
- Deformities of the vertebral column (e.g., kyphosis, scoliosis)
- Poliomyelitis (respiratory muscle disease)
- Arthritis (joints of the thoracic cage or vertebral column)

COPD (Chronic Obstructive Pulmonary Disease), specifically emphysema: Loss of alveolar walls makes the lungs loose and floppy, needing less pressure difference to maintain a large volume.
Old age: Alterations to lung elastic tissue.

Compliance work (elastic resistance): 65%
- The work needed to stretch the elastic tissue of the lung and chest wall.
- Increases in conditions associated with decreased lung compliance.
Tissue resistance work: 7%
- Work to overcome the viscosity of lung and chest wall structures (non-elastic tissues).
- Increases in diseases affecting the thoracic cage (e.g., kyphosis) or respiratory muscle diseases (e.g., poliomyelitis).
Airway resistance work: 28%
- Work to overcome airway resistance.
- The major factor is the airway diameter (medium-sized bronchi).
- Increases in obstructive lung diseases: emphysema, chronic bronchitis, bronchial asthma.

The respiratory center is composed of groups of neurons in the medulla oblongata and pons of the brain stem.
Dorsal respiratory group: Located in the dorsal portion of the medulla; mainly responsible for inspiration.
Ventral respiratory group: Located in the ventrolateral part of the medulla; mainly responsible for expiration.
Pneumotaxic center: Located in the superior portion of the pons; controls breathing rate and depth.
Apneustic center: Located in the caudal part of the pons; sends continuous excitatory impulses to the dorsal respiratory group, causing prolonged inspiration and decreasing respiratory rate.

Central chemoreceptors: Located on the medulla's ventral surface, sensitive to CO2 in the blood. Not affected by H+ ions (blood-brain barrier).
Peripheral chemoreceptors: Located in the carotid bodies; detect oxygen changes in the blood. Also respond to carbon dioxide and hydrogen ion changes.
Effect of CO2 and H+: Excess CO2 or hydrogen ions increase the strength of both inspiratory and expiratory motor signals to the respiratory muscles.

Oxygen does not directly affect the respiratory center in controlling respiration.
It acts on peripheral chemoreceptors in the carotid and aortic bodies, which then send signals to the respiratory center.