External Respiratory System, Volume and Pressure Change PDF

External Respiratory System, Volume and Pressure Change Dr. Duygu TARHAN Department of Biophysics School of Medicine Bahcesehir University [email protected] Lecture Overview • At the end of this lecture, you will be able to: Ø Define the lung volumes and capacity Ø Describe the changes obser...

External Respiratory System, Volume and Pressure Change Dr. Duygu TARHAN Department of Biophysics School of Medicine Bahcesehir University [email protected] Lecture Overview • At the end of this lecture, you will be able to: Ø Define the lung volumes and capacity Ø Describe the changes observed in volume and pressure during respiration Ø Describe the work of breathing Ø Discuss the work performed during the respiration process based on the pressure-volume differences Ø Discuss the relationship between respiratory frequency and work required for breathing Lung volumes and capacities • The total volume of the lung is divided into smaller units of volume • These units are created based on the total lung capacity, the resting endexpiratory volume of the lung, and several breathing maneuvers • Measuring and differentiating the volumes of the lungs this way is helpful, because different respiratory diseases will affect different volumes and capacities • The changes in different volumes and/or capacities can be measured through pulmonary function testing to help diagnose and treat different illnesses • Knowing how respiratory conditions affect volumes and capacities of the lung aid in ventilating the patient more effectively and safely • There are four different volumes, and four different capacities • Note: a capacity is a combination of two or more volumes of lung Lung volumes and capacities • Tidal volume (VT) : Volume of air during normal, quiet breathing - 500 ml • Inspiratory reserve volume (IRV): Volume of air that can be inspired above tidal volume – 2500 ml • Expiratory reserve volume (ERV): Volume of air that can be expired following tidal expiration – 1500 ml • Residual volume (RV): Volume of air in the lungs following a maximal expiration – 1500 ml Lung volumes and capacities • Inspiratory Capacity (IC): The maximum volume of air inhaled from normal resting endexpiratory level – 3000 ml • Functional Residual Capacity (FRC): Volume of air remaining in the lungs at resting - 3000ml • Vital Capacity (VC): The maximum volume of air exhaled following a maximum inspiration or vice versa – 4500 ml • Total Lung Capacity (TLC): The volume of air contained in the lungs following a maximum inspiration – 6000 ml Pulmonary function test-Spirometer https://www.youtube.com/watch?v=hQzNG89pESQ IC = VT + IRV FRC = RV + ERV VC = ERV + VT + IRV TLC = RV + ERV + VT + IRV Pressure Differences During Breathing • Changes in lung volume occur in response to pressure gradients created by thoracic expansion and contraction • There are four different thoracic pressures involved in breathing and three key pressure gradients involved in the mechanics of breathing • Pulmonary pressures are referred to in relative terms to atmospheric pressure (0 = 760 mm Hg, or 1 atmosphere) • Mouth pressure (Pm) is always 0 unless positive pressure is applied to the airway • Pressure at the body surface (Pbs) is also always 0, unless the patient is being ventilated with a negative pressure ventilator • Alveolar pressure (Palv) and pleural pressure (Ppl) will vary throughout the respiratory cycle Pressure Differences During Breathing • The three key pressure gradients involved in the mechanics of breathing are described as below • The transrespiratory pressure gradient is the difference between the atmosphere (Pm) and the alveoli, and is responsible for the actual flow of gas into and out of the alveoli during breathing • The transpulmonary pressure gradient is the difference between the pressure in the alveoli and the pleural space, and is responsible for maintaining alveolar inflation • The transthoracic pressure gradient is the difference between the pressure in the pleural space and the pressure at the body surface, and represents the total pressure required to expand or contract the lungs and chest wall Respiratory Cycle Volume and Pressure Changes Work of Breathing • Work of breathing is the energy used by the muscles for respiration 𝑊𝑜𝑟𝑘 = 𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒 𝑥 𝑉𝑜𝑙𝑢𝑚𝑒 • Elastic work: Energy required to overcome elastic forces. About 65% of total work, and is stored as elastic potential energy • Resistive work: Energy required to overcome frictional forces. About 25% of total energy is used to overcome airway resistance while 5% is used to overcome tissue resistance Work of Breathing Resistive expiratory work is typically done by elastic recoil of lungs and stored potential energy of inspiration is used during quiet breathing However, additional active work of expiration may occur in case of obstructive lung disease or when minute ventilation is high (forced breathing) Work of Breathing Comparison • Restrictive lung diseases limit lung expansion resulting in a decreased lung volume, an increased work of breathing, and inadequate ventilation and/or oxygenation • In restrictive lung diseases, the area of the volume-pressure curve is greater because the slope of the static component (compliance) is less than normal • Restrictive lung disease most often results from a condition causing stiffness in the lungs themselves • Some conditions causing restrictive lung disease are: idiopathic pulmonary fibrosis, sarcoidosis, obesity, scoliosis, muscular dystrophy or amyotrophic lateral sclerosis Work of Breathing Comparison • Obstructive lung diseases cause shortness of breath because of damage to the lungs or narrowing of the airways and lead difficulties exhaling all the air from the lungs • In obstructive lung diseases, the area of the volume-pressure curve is increased because the portion associated with resistance is markedly widened • The most common causes of obstructive lung disease are: Chronic obstructive pulmonary disease (COPD) such as emphysema and chronic bronchitis, asthma, bronchiectasis, cystic fibrosis • Obstructive lung disease makes it harder to breathe, as the rate of breathing increases, there is less time to breathe all the air out before the next inhalation Work of Breathing Comparison • In healthy individuals, the mechanical work of breathing depends on the pattern of ventilation • Large VT (tidal volume) increases the elastic component of work • High breathing rates and high flows increase frictional work Breaths per minute • When changing from quiet breathing to exercise ventilation, a healthy person adjusts VT and breathing frequency to minimize the work of breathing • In normal lungs, total work of breathing is minimal at approximately 15 breaths/min Work of Breathing Comparison • Adjustments occur in individuals who have lung disease • To achieve the same minute volume with stiff lungs (restrictive lung disease), minimum work is performed at higher frequencies • With increased airflow resistance (obstructive lung disease), minimum work requires lower rates of breathing Work of Breathing Comparison • Patients with “stiff lungs” (i.e., increased elastic work of breathing), such as in pulmonary fibrosis, often assume a rapid, shallow breathing pattern – minimizing the mechanical work of inflating the lungs but at the expense of more energy to increase breathing rate • Patients who have airway obstruction may assume a ventilatory pattern that reduces the frictional work of breathing – breathing slowly and using pursed-lip breathing during exhalation minimize airway resistance Gas laws of respiration