L8 Compliance and Work of Breathing PDF

# Compliance & Work of Breathing ## Prepared by staff members of Physiology department - Prof. Dr. Maha Dief - Prof. Dr./ Amel Elsawaf **01/12/2024** **Faculty of Dentistry** **Pharos University** **General Physiology (PHY211)** # Compliance ## (definition, value and factors affecting it) -...

# Compliance & Work of Breathing ## Prepared by staff members of Physiology department - Prof. Dr. Maha Dief - Prof. Dr./ Amel Elsawaf **01/12/2024** **Faculty of Dentistry** **Pharos University** **General Physiology (PHY211)** # Compliance ## (definition, value and factors affecting it) - Definition: It is expressed as the change in lung volume per unit change in distending (transpulmonary) pressure. - Equation: $C = \frac{\Delta V}{\Delta P} = \frac{change\ in\ lung\ volume}{change\ in\ distending\ pressure}\ ml/cm\ H_2O$ ## Compliance of the lung (CL): - 200 ml/cm H2O ## Pulmonary system compliance: - It is the compliance of the lungs and thoracic cage together. - It is about 130 ml/cm H2O. # Causes of decreased pulmonary compliance - ## Rigidity of the lungs - Pulmonary fibrosis, increase of fibrous tissue in the lung - Pulmonary edema, which prevents the inflation of some alveoli. - Atelectasis (collapse) of some alveoli. - Pulmonary congestion venous pressure is increased and the lung becomes engorged with blood. - ## Rigidity of the thoracic cage - Deformities of vertebral column e.g. kyphosis (antro-posterior bending) scoliosis (lateral bending). - Poliomyelitis of respiratory muscles. - Arthritis of the joints of the thoracic cage or vertebral column. # Causes of increased pulmonary compliance - ## COPD: - Pulmonary emphysema. in emphysema, where many alveolar walls are lost, the lungs become so loose and floppy that only a small pressure difference is necessary to maintain a large volume. - Thus, the lungs in emphysema would be considered highly compliant. - ## Old age - In both instances, an alteration in the elastic tissue in the lung is probably responsible. # Work of breathing - ## Compliance work (Elastic resistance) 65% - It is the work required to stretch the elastic tissue of the lung and chest wall. - It increases in all conditions associated with decreased lung compliance. - ## Tissue resistance work (7%) - It is the work required to overcome the viscosity of the lung and chest wall structures (Non elastic tissues). - It increases in diseases: - affecting thoracic cage e.g. kyphosis - respiratory muscle disease as poliomyelitis. - ## Airway resistance work (28%) - It is the work required to overcome airway resistance - The major factor of the airway resistance is the diameter of the passage ways (major site of resistance is medium sized bronchi). - It increases in obstructive lung diseases as: - emphysema - chronic bronchitis - bronchial asthma # Control of Ventilation - The respiratory center is composed of several groups of neurons located bilaterally in the medulla oblongata and pons of the brain stem - 1) a **dorsal respiratory group**, located in the dorsal portion of the medulla, which mainly causes inspiration. - 2) a **ventral respiratory group**, located in the ventrolateral part of the medulla, which mainly causes expiration. - 3) **Pneumotaxic center**, located dorsally in the superior portion of the pons, which mainly controls rate and depth of breathing - 4) **Apneustic center:** it is located in the caudal part of the pons. These neurons send continuous excitatory nerve impulses to dorsal respiratory group producing deep and prolonged inspiration and decrease respiratory rate. - A diagram of the respiratory center is shown next. - # Central Chemoreceptors - Located on the ventral surface of the medulla. - Sensitive to CO2 in the blood. - Not affected by H+ in the blood as H+ ions do not cross the BBB (Blood-Brain barrier) - # Peripheral Chemoreceptors - Located in the carotid bodies - Detect changes in oxygen in the blood, although they also respond to a lesser extent to changes in carbon dioxide and hydrogen ion concentrations. # Chemical Control of Respiration - ## Effect of CO2 and H⁺: - Excess carbon dioxide or excess hydrogen ions in the blood cause greatly increased strength of both the inspiratory and the expiratory motor signals to the respiratory muscles. - ## **Effect of O2:** - In contrast, it does not have a significant direct effect on the respiratory center of the brain in controlling respiration. - Instead, it acts almost entirely on peripheral chemoreceptors located in the carotid and aortic bodies, and these in turn transmit nervous signals to the respiratory center for control of respiration. # Thank you