Respiratory Physiology 2

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Eugenia Nash
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1 Respiratory Physiology 2 Session Objectives. What you will cover Gaseous Exchange Control of Breathing Rate Your objectives are State the function of support structures and epithelia of the bronchial tree Describe the role of surfactant in terms of airway patency State the function of the diaphragm and accessory muscles involved in breathing movements Describe the physical events involved in inhalation and exhalation Explain how transpulmonary pressures facilitate breathing Explain the role of pleural membranes in breathing Define compliance and airway resistance and explain how they contribute to work of breathing. Define and identify lung volumes, capacities and flow rates. Name the centres in the brain stem that regulate normal breathing Explain how these centres control breathing rate Describe how carbon dioxide regulates breathing rate Suggested reading: Tortora, Ch 23 Marieb Ch 23 50

2 Respiratory Physiology Lung Volumes and Capacities. The volume of air that moves in or out of the lungs is called pulmonary ventilation. It is the product of the amount of air inspired in each breath and the number of breaths per minute. Respiratory volumes are measured with a spirometer. The subject breathes through a tube that is connected to a set of bellows. These move down or up with the breathing movement. This displacement is recorded onto graph paper. The diagram below shows a typical spirograph recording. The changes in air volumes at different stages of breathing are shown. Note that some of the measures are volumes, while others are capacities. Knowledge of these volumes and capacities can assist in the diagnosis and monitoring of disease. 51

3 . List the volumes and capacities separately. Volume Capacity Complete the definitions of the lung volumes and capacities in the table. Use the diagram to help you find the volumes for males and females. Volume/Capacity Definition Typical Male Volume [ml] Typical Female Volume [ml] Tidal Volume Inspiratory Reserve Volume Expiratory Reserve Volume Residual Volume Total Lung Capacity Vital Capacity Functional Residual Capacity 52

Use the words provided to complete the blanks. Intrapulmonary pressure is the air pressure found in the alveoli. At rest intrapulmonary pressure is about mm Hg.

4 Transpulmonary Air Pressures The images below show what happens to air pressure in the lungs during inhalation and exhalation. Essentially it is the differences between the pressures inside the lungs and the pleural membranes that drive the movement of air. Complete the missing words. Use the words provided to complete the blanks. Intrapulmonary pressure is the air pressure found in the alveoli. At rest intrapulmonary pressure is about mm Hg. On this pressure drops by about 1mm Hg to. This difference allows approximately 500 ml of air to enter the lungs. This is roughly the volume. When you breathe heavily the size of the pressure gradient so that air enters the lungs. There is also a pressure exerted between the pleural membranes. This is approximately 756mm Hg That is mm Hg less than intrapulmonary pressure. This is because the natural elastic recoil of lungs pulls on the pleural membranes, then lowers pressure. In fact, intrapleural pressure is lower than intrapulmonary pressure at all times. If the pleural membranes are damaged or burst in any way, this causes the intrapleural pressure to equalise with intrapulmonary pressure. The result of this is that the lungs, a condition known as. To treat this, as much air as possible is removed from the space, which causes the air pressure to be less than that of the lungs. 760 mm Hg increases four collapse 759 mm Hg pressure more atelectasis tidal intrapleural Controlling Breathing Rate 53

5 Respiratory Rate This is used clinically as a baseline measure or general observation of patient health. What is a normal breathing rate for an adult in breaths per minute? State meaning of the following terms tachypnoea bradypnoea? Dyspnoea Control of Respiratory Rate We do have some limited control over our breathing rate this control allows us to sing and speak or play wind instruments. This control is exerted by the cerebral cortex. There is also very tightly regulated involuntary control of our breathing rate. Contrary to popular belief, it is not driven by a need for oxygen. If we think in terms of homeostasis, most systems work by using negative feedback controls. It is therefore sensible for the body to regulate itself by being driven by levels of potential toxins. Carbon dioxide and the hydrogen ions produced by the body s attempts to balance blood ph are what drive our breathing rate. 54

6 Where is the respiratory centre located? Where are the apneustic and pneumotaxic areas and what is their function? Apneustic location Function Pneumotaxic location Function Name the two regulatory areas of the medullary rhythmicity centre and give their functions 55

7 Work of Breathing The amount of energy expended on breathing depends on The rate and depth of ventilation The ease with which the lungs and thorax can be expanded [compliance] The resistance to airflow from the airways Compliance This is the stretchability of the lung tissue and the chest wall. What is meant by high compliance? Give an example to illustrate your answer. The following four factors decrease lung compliance. Give an explanation of how these cause reduced compliance. Lung fibrosis Loss of flexibility of thoracic cage Reduced surfactant production Small airway blockage. Airway Resistance In which airways are you most likely to experience resistance to airflow? Why is there greater resistance in these airways? Suggest two other factors that affect airway resistance. 56

8 What is the Hering- Breuer reflex and what is thought to be it s function? Where are the chemoreceptors for carbon dioxide located? What is the term for high blood carbon dioxide levels? Give definitions for the following Histotoxic Hypoxia Ischemic Hypoxia Hypoxemic Hypoxia 57

Respiratory Physiology Gaseous Exchange

Respiratory Physiology Gaseous Exchange Session Objectives. What you will cover Basic anatomy of the lung including airways Breathing movements Lung volumes and capacities Compliance and Resistance in