Ventilation Mechanics - Human Anatomy & Physiology PDF

Ventilation Mechanics Human Anatomy & Physiology 2024-2025 HTHSCI 1H06 A/B McMaster Mohawk Lecture Outline Today we will discuss: Some definitions (incl. Boyles Law) Mechanics (muscles involved) Lung volumes (spirometry) Impedances to ventilation Breathing cycle (putting...

Ventilation Mechanics Human Anatomy & Physiology 2024-2025 HTHSCI 1H06 A/B McMaster Mohawk Lecture Outline Today we will discuss: Some definitions (incl. Boyles Law) Mechanics (muscles involved) Lung volumes (spirometry) Impedances to ventilation Breathing cycle (putting it all together)  CO2 O2 Some Definitions Ventilation and respiration External respiration: Ventilation CO2 O2 pulmonary gas exchange Movement of air into and out of the lungs Involves anatomy and mechanics Respiration Exchange of gasses (O2 and CO2) Happens at many levels: External – between blood and lungs Internal – between the tissue and blood O2 Definition includes ventilation Internal respiration: (above) systemic gas CO22 exchange Mechanisms of Ventilation Boyles Law Boyles Law Ventilation of the lungs (alveoli) works on this principle PV = k pressure x volume = constant Quick simply: Increase in volume = Decrease in pressure Decrease in volume = Increase in pressure Differences in pressure drive the movement of air into and out of the lungs (ventilation) Mechanisms of Ventilation Muscles Respiration Quiet Breathing Accessory Airflow is passive Sternocleidomastoid Scalenes Active Breathing Principal Internal intercostals External intercostals MUSCLES OF Diaphragm EXHALATION Depress ribs Compress abdomen (elevates the diaphragm) Compress thorax External oblique MUSCLES OF INHALATION Elevate ribs Lower diaphragm Enlarge thorax (AP and SI Internal oblique dimensions) Transversus abdominis Rectus abdominis Mechanisms of Ventilation Pressure changes during pulmonary ventilation Atmospheric pressure = 760 mmHg Atmospheric pressure = 760 mmHg 2 During inhalation, the diaphragm contracts the and external 1 Prior to inspiration, the intercostals contract. diaphragm is relaxed, The chest cavity alveolar pressure PA = 760 PA = 758 expands, and the equals atmospheric alveolar pressure pressure, and there is drops below no air flow. atmospheric Ppl = 754 pressure. Air enters the lungs. Atmospheric pressure = 760 mmHg 3 During exhalation, the diaphragm and During deep external intercostals relax. The chest inhalation (forced and lungs recoil, causing the chest inspiration) the cavity to decrease in size. The alveolar scalene and pressure increased above atmospheric, sternocleidomastoid and air exits the lungs. muscles expand the PA = 762 chest further, causing During forced exhalations, the internal a greater drop in intercostals and abdominal muscles Ppl = 756 alveolar pressure. contract, further reducing the size of the Mechanisms of Ventilation Intercostal VAN Visceral pleura Parietal pleura The intercostal VAN contains an intercostal vein, an Rib Innermost intercostals intercostal artery, and an Costal groove intercostal nerve (mixed spinal thoracic nerve). These Intercostal VAN structures supply the intercostal muscles that support ventilation. The intercostal VAN sits in the Internal intercostals intercostal groove at the External intercostals inferior border of each rib. If a chest tube or thoracentesis Rib needs to be performed, then Posterior we must avoid theExternal VAN…intercostal Internal intercostal Innermost intercostal superficial view Mechanisms of Ventilation Clinical application: thoracentesis Thoracentesis is performed to remove fluids from the pleural space that interfere with the normal lung expansion. Knowledge of the location of the intercostal VAN is necessary to prevent damage to structures supporting the intercostal muscles. Measuring Lung Volumes Spirometry Measuring Lung Volumes Spirographic record Illustrated here 6 are some lung Inspirato Vital volumes ry Capacity measured using Reserve spirometry 4 Volume Lung Tidal You should Total Volum Volume know the Lung definitions of e (L) Expirato Functional Capaci these 2 ry Residual ty volumes… Reserve Capacity Volume *Residu ** al 0 Volume 0 30 60 Time (s) Rates of Ventilation Minute ventilation and alveolar ventilation Minute ventilation VE = rate that air moves in and out of the mouth VE = breathing frequency (fb) x tidal volume (VT) At rest = 12 breaths/min x 500 ml/breath = 6 l/min 30x increase! Max exercise = 60 breaths/min x 3000 ml/breath = 180 l/min Alveolar ventilation VA = rate that fresh air moves in and out of alveoli VD Less than VE due to dead space volume of lungs (VD) (VD) = 150 ml Dead space is the volume of air occupying the non- respiratory segments of the airways (e.g. nose, pharynx, larynx, trachea, bronchi, bronchioles, terminal bronchioles) and does not participate in gas exchange. At rest = fb x (VT - VD) = 12 x (500-150) = 4.2 l/min If VT is decreased (e.g. chest pain, fractured rib) then a higher f b is necessary to maintain VA Impedances to Ventilation Factors affecting pulmonary ventilation Two factors determine the ease of pulmonary ventilation: compliance/elastance & airway resistance Elastance A measure of the ‘stiffness’ of the lungs Related to the forces needed to blow up a balloon V V = volume in (L) ∆P P = P = pressure (mmHg) P ∆V Elastanc e Lungs with low elastance are compliant (e.g., emphysema) V Lungs with high elastance are stiff (e.g., fibrosis, low surfactant) Compliance = 1 / Elastance Impedances to Ventilation Factors affecting pulmonary ventilation Two factors determine the ease of pulmonary ventilation: compliance/elastance & airway resistance Effect of lung Surfactant on lung Compliance Elastic tissues of the lung are highly compliant (low elastance) Surface tension of water has low compliance compared to lung elastic tissue Water lining alveoli decreases lung compliance (increases lung elastance) Elastic recoil of lungs = 1/3 elastic tissue + 2/3 surface tension Surfactant is a phospholipid released by type II pneumocytes and reduces the surface tension of water. Reduces the effort needed to breathe Impedances to Ventilation Factors affecting pulmonary ventilation Two factors determine the ease of pulmonary ventilation: compliance/elastance & airway resistance Resistance Related to the pressure needed to generate air flow Can be likened to ‘drag’ which opposes air flow ∆P ∆P.= Resistance = flow (L/s) V P = pressure. P1 V P2. V Lungs with high resistance are obstructed (e.g., asthma, COPD) The factor with the biggest influence on resistance is airway diameter (caliber) Resistance ∝ 1 / r4 Ventilation Mechanics Changes in pleural pressure The lung is inside the thoracic cage (chest wall) and separated from it by the pleural space (containing a thin layer of serous Airway fluid) Changes in lung Alveoli volume occur when the PIP Pleural Space muscles of ventilation move the chest wall Ppl Chest wall and produce changes in plural pressure. PIP = intrapulmonary pressure The lungs come along Ppl = pleural pressure for the ride!  Ventilation Mechanics Positive pressure ventilation The lungs are inflated by increasing the pressure inside the alveoli (intrapulmonary pressure) This is like mechanical ventilation of a patient or providing mouth-to-mouth resuscitation V P PIP PIP P =Increase pressurethe pressure applied and you get an increase in lung volume to mouth PIP = intrapulmonary pressure  Ventilation Mechanics Normal ventilation The lungs are expanded by reducing the pressure surrounding the lungs to sub-atmospheric pressures Sub-atmospheric pressures are sometimes called negative pressures V Ppl Ppl PIP = intrapulmonary pressure Ventilation Mechanics Breathing cycle (quiet breathing) Key points: Intrapulmonary pressure fluctuates (+/-) Intrapleural pressure fluctuates but is almost always negative (subatmospheric) Summary Today we discussed: Some definitions (incl. Boyles Law) Mechanics (muscles involved) Lung volumes (spirometry) Impedances to ventilation Breathing cycle (putting it all together) Next time We will discuss gas exchange, transport, and control of breathing.