Effect of chest physiotherapy on respiratory mechanics.

1. Effect of chest physiotherapy on respiratory mechanics. By Dr Sahar Elkaradawy Assistant Professor in Anaesthesia and Pain Management

2. Objectives Basic mechanism of breathing. Ventilation perfusion (V/P)relationships Ventilation perfusion in awake and paralised patient Role of physiotherapy during mechanical ventilation.

3. Basic mechanism of breathing Expansion of the lungs ( during inspiration) is carried out by skeletal muscle contraction, but there is no direct connection between the respiratory muscles and the lungs

4. Pleural space and pressure Between the lungs and the chest wall, there is a space: the pleural cavity. The mechanical behaviour of this airtight space follows Boyle's law, meaning that its pressure is inversely proportional to its volume. Both the lungs and the chest wall have elastic proparties. The chest wall has tendency to expand, while the lungs tends to collapse.

5. Pleural space and pressure In this way, the movements of either the lungs or chest wall change the volume of the pleural cavity and, creat negative intrapleural pressure.

6. Spontaneous ventilation Trans-pulmonary pressure= intra alveolar p - intrapleural p. Intra-alveolar p in resting position is zero. -1 or +1 in inspiration and expiration Intra- pleural p is always negative. During inspiration, it reaches -6

7. Spontaneous ventilation During inspiration, diaphragm and intercostal muscle activate to expand lung and decrease intrapleural P (-7). As a result, intra- alveolar P decreases and gas flows. At end of inspiration airflow ceases and intra- alveolar P becomes zero. During expiration, diaphragm relaxes, intra pleural P becomes less (-5) and elastic recoil of lung makes lung to collapse and gas flows out

8. Distribution of ventilation through lungs Pleural pressure in apex is more negative than that in base, due to gravity Alveoli at the top of the lung are more fully expanded than those at the bottom( less compliant) Alveoli at the bottom of the lung expand considerably more than those at the top (better ventilated)( more compliant

9. Distribution of perfusion through lungs In healthy individuals at rest with normal cardiac output, pulmonary blood flow is distributed unevenly in the upright lung. Similar to the distribution of ventilation, pulmonary blood flow is preferentially directed to the base of the lungs.

10. Perfusion of normal lungs In healthy individuals at rest with normal cardiac output, pulmonary blood flow is preferentially directed to the base of the lungs Distribution is dependent on three relative pressures alveolar pressure, pulmonary arterial pressure and pulmonary venous pressure.

11. Distribution of ventilation perfusion ratio in upright position zone I, where PA>Pa>Pv, alveolar pressure exceeds vascular pressures resulting in less perfusion.( alveolar dead space) Zone II best V/P matching Zone III more perfusion ( Shunt) In healthy subjects under normal perfusion pressures, zone I is not present because arterial pressures is just sufficient to raise blood to the top of the lung and exceed alveolar pressure. Zone I may be present if pulmonary arterial pressure is reduced (following severe hemorrhage) or if alveolar pressure is raised (during positive pressure ventilation).In healthy subjects under normal perfusion pressures, zone I is not present because arterial pressures is just sufficient to raise blood to the top of the lung and exceed alveolar pressure. Zone I may be present if pulmonary arterial pressure is reduced (following severe hemorrhage) or if alveolar pressure is raised (during positive pressure ventilation).

12. Effect of lateral position on V/Q matching in awake person In the upright lung the greatest ventilation perfusion ratio is at the top of the lungs ( ?V/Q ratio) and the lowest ratio at the base of the lungs ( ? V/Q ratio). In lateral decubitus position in awake patient dependant lung is well ventilated and more perfused due to presence of lower diaphragm in higher position and effect of gravity on perfusion of lung.

13. Effect of lateral position on V/Q matching in awake and anaesthetised person Thus, in the lateral decubitus position in awake person, the dependent lung receives the majority of the tidal ventilation. V, alveolar volume; P, transpulmonary pressure The anesthetised patient, with or without paralysis, in the LDP and with a closed chest has a nondependent lung that is well ventilated but poorly perfused and a dependent lung that is well perfused but poorly ventilated, which results in an increased degree of V/Q mismatching.

14. Effect of anaesthesia and deep sedation in lung mechanics ?function residual capacity( FRC) Lung atelectasis retention of secretion ?degree of V/Q mismatching. So change in patient position in ICU and physiotherapy are of para- amount important to improve lung oxygenation.

15. Distribution of ventilation perfusion ratio in abnormal conditions

16. Change in Distribution of Ventilation with Exercise use more apical alveoli (to match increased blood flow) blood CO2 concentration rises, so chemoreceptors increase respiratory rate and tidal volume so use more apical alveoli intercostal and accessory muscles are progressively recruited so use more apical alveoli during exercise, air more even distribution

17. Pneumonia Is the single most common nosocomial infection among patients undergoing treatment in the intensive care units (ICUs). Despite considerable progress that has been achieved in the recent past in the diagnosis, prevention, and therapy of hospital-acquired infections, ventilator-associated pneumonia (VAP) continues to create complications during the course of treatment in the case of a significant proportion of patients receiving mechanical ventilation.

18. Intubation and mechanical ventilation may impair mucociliary clearance and lead to sputum retention, airway occlusion, atelectasis, and VAP. Mucociliary clearance depends on the complex interaction between ciliated columnar epithelial cells of tracheobronchial tree and the special viscoelastic properties of the bronchial secretions.

19. The mucociliary system represents an important protective mechanism of the upper and lower respiratory tract whereby inhaled particles and microorganisms are removed from the tracheobronchial system.

20. Many risk factors have been associated with VAP: Chronic obstructive pulmonary disease (COPD). Airway intubation . Reduced conscious state. Mechanical ventilation greater than 7 days. Use of positive end expiratory pressure (PEEP) and supine patient positioning.