Mechanics of Respiration (Part 2) PDF

Module 07: Cardiovascular and Respiratory Systems Mechanics of Respiration (Part 2) Jonray D. Magallanes, MD, FPCP | December 5, 2023 | Online-Synchronous Composed of the following:...

Module 07: Cardiovascular and Respiratory Systems Mechanics of Respiration (Part 2) Jonray D. Magallanes, MD, FPCP | December 5, 2023 | Online-Synchronous Composed of the following: TABLE OF CONTENTS – Laterally: ribcage Learning Objectives 1 III. Work of Breathing 8 – Anteriorly: sternum I. Chest Wall Mechanics 1 A. Normal 8 – Posteriorly: vertebral column A. Introduction 1 Volume-Pressure Loop – Caudally/inferiorly: diaphragm B. Overview 1 B. Campbell Diagram 8 II. Dynamic Mechanics 2 IV. Summary & Keypoints 9 The diaphragm is the main driver of ventilation. A. Introduction 2 Review Questions 10 − Separates the thorax from the abdomen B. Resistive Work 3 Rationale 10 Zone of Apposition C. Elastic Work 7 References 10 Zone of Apposition: includes the lower part of the rib cage Appendix 11 enclosing the upper part of the abdomen at the functional LEARNING OBJECTIVES residual capacity (FRC) during quiet tidal breathing (at rest) 1. Discuss the different pressures and volumes in the respiratory – Area wherein the diaphragm pushes the rib cage open which system. increases the chest wall volume 2. Describe the concepts and contributory factors of lung – Increase in chest wall volume → pressure drops → movement compliance and resistance. of air into the lung 3. Discuss and differentiate static and dynamic lung and chest wall ▪ Air moves from regions of higher to lower pressure. mechanics. Bucket Handle / Pump Handle Movement I. CHEST WALL MECHANICS Anteroposterior movement of the rib cage A. INTRODUCTION – Spine is fixed while the sternum hugs it Even before, people already knew how to ventilate a patient. – Sternum floats anteriorly 19th century: the proper way of ventilating lungs was discovered. – When a person inhales, the movement produced resembles – Polio epidemic: negative pressure ventilation was used that of a pump handle. People soon found out that such a process was complicated and – Elevation during inspiration does the following: unnecessary. ▪ Elevation of the rib cage A tube can be put into a patient to give positive pressure ▪ Expansion of the lower part of the rib cage due to the zone ventilation. of apposition – More acceptable clinical outcomes and morbidity in Likened to the movement of the ribs in relation to the spine lifting patients suffering from respiratory failure the sternum forward and upward – Positive pressure ventilation can work; the doctors just need Bucket handle movement occurs when the chest wall moves to mimic pressures that govern during a negative pressure outward and laterally in inhalation. ventilation. – Expansion of rib cage causes a pressure drop → sucks in air from atmosphere → negative pressure ventilation B. OVERVIEW Clinical Correlation: Loss of Zone of Apposition → Seen in patients who have been hooked to a ventilator for an extended period of time. a. During ventilation, you do not use your diaphragm since all the work is done by the machine. b. Can be likened to disuse atrophy c. Diaphragm gets thin, causing loss of apposition Figure 2a. Chest X-ray of a patient with COPD; Figure 2b. Chest X-ray with normal lungs (Magallanes, 2023) → Loss of zone of apposition happens in COPD or emphysema causing breathlessness a. Emphysema ○ the lungs become saggy and its elastic properties are Figure 1. Normal movements of the ribcage (Magallanes, 2023) lost → traps air → lungs become hyperinflated → increased volume results in the flattening of the Chest Wall Mechanics: pressure that governs during a negative diaphragm → zone of apposition is lost → downward pressure ventilation; very important during ventilation. sloping of the diaphragm → compresses the abdomen TG5 | Bituin, Calivozo, Castro, Hormigos, Macalalag, Madrigal, Marasigan, Pariñas, Paz, Perez, Reyes, Sarte YL5 07.08b 1 of 12 CG14 | Aala, Agoncillo, Bernardo, Castro, Lapuz, Lim, Navarro, Reyes, Santos, Sayo, Uy  – Based on Equation 5, force in Equation 3 is expressed in + pushes abdomen forward during inspiration (paradoxical breathing) terms of pressure and area, leading to Equation 6. → Even a subtle loss in the zone of apposition can have a – Using Equation 7 as basis, area x distance in Equation 6 is profound effect on the breathlessness of patients simplified to volume to arrive at Equation 8 where work is → Comparing chest X-ray of a patient with COPD (Figure defined as the product of pressure and volume in 2a) vs. normal (Figure 2b) pulmonology. a. Higher amounts of trapped air seen as a more – Equation 8 would repeatedly be used where the pressure radiolucent space inside the ribcage (Figure 2a) b. Flattening of the diaphragm (yellow arrow in Figure 2a) usually only changes depending on location. vs. the dome-shaped diaphragm in Figure 2b ▪ Examples: tubes (resistive forces), lung parenchyma ○ If you see the flattening of the diaphragm or the loss (elastic forces) of apposition in a chest x-ray, expect to see your 𝑊𝑜𝑟𝑘 = 𝐹𝑜𝑟𝑐𝑒 × 𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒 (3) patient to be dyspneic or breathing CO2 after a 6-min 𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒 = 𝐹𝑜𝑟𝑐𝑒/𝐴𝑟𝑒𝑎 (4) walk test. 𝐹𝑜𝑟𝑐𝑒 = 𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒 × 𝐴𝑟𝑒𝑎 (5) II. DYNAMIC MECHANICS 𝑊𝑜𝑟𝑘 = 𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒 × 𝐴𝑟𝑒𝑎 × 𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒 (6) A. OVERVIEW 𝐴𝑟𝑒𝑎 × 𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒 = 𝑉𝑜𝑙𝑢𝑚𝑒 (7) Work of breathing is needed in understanding the movement of 𝑊𝑜𝑟𝑘 = 𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒 × 𝑉𝑜𝑙𝑢𝑚𝑒 (8) air, in and out of our lungs. Resistive work is the work you have to spend to put the air – When a force is applied to an object over a distance, energy through the tube (trachea, segmental bronchus). is required. – Defined as a change in pressure in the tube which is related to – Work is spent on the movement of air into the tubes while the flow and resistance (Equation 2). encountering resistive forces. The flow inside the tube can be subdivided into two, along with – Work is also spent when inflating the balloon or the their characteristics: parenchyma of the lungs while overcoming the elastic – Laminar flow: properties of lungs ▪ More efficient with little frictional disturbances Work of breathing can be subdivided into two: ▪ Dominant in low flow states – Elastic work ▪ Dominant in distal airways (respiratory bronchioles down ▪ Elastic work is the needed work to distend the chest wall to the alveolar sacs and alveoli) and lungs during inspiration. ▪ Has a direct relationship between flow rate and pressure ▪ In normal individuals, 50% of work comes from this while (Figure 4c) the other 50% comes from resistive work. – Turbulent flow: ▪ Formula for elastic work can be seen in Equation 1 where ▪ A chaotic flow (less efficient) ΔP=change in pressure, ΔV=change in volume − The same amount of pressure can move less volume C=compliance. or have slower flow rate of air through a tube for − Reciprocal of compliance is elastance turbulent flow, relative to laminar flow ∆𝑉 ▪ Dominant in branch points and high flow state ∆𝑃𝑇𝑀 = 𝐶 (1) ▪ Dominant in larger, proximal airways (mouth up to – Resistive work terminal bronchioles) ▪ Resistive work comes from the forces needed to overcome inertia of the gas ▪ Resistive work depends on gas properties and airway resistance. ▪ Formula for resistive work can be seen in Equation 2 where ΔP=change in pressure, ⩒=flow and R=resistance. ∆𝑃𝑡𝑢𝑏𝑒 = ⩒𝑅 (2) Figure 4. Comparison of Laminar and Turbulent Flow Nice! → To be more accurate, terminal bronchioles also have laminar flow, aside from turbulent flow Figure 3. Two types of work applied to the lungs (Magallanes, 2023) a. It is from respiratory bronchioles and other more distal Work of breathing is spent only on inhalation. parts (alveolar sacs and alveoli) that the flow of air – Inhalation is voluntary becomes laminar – Exhalation is involuntary. The exhalation part cannot be controlled. Exhalation depends on the elastic forces of the ACTIVE RECALL BOX lung or its ability to go back to its original shape. 1. The reciprocal of compliance is ____ Derivation of work as a function of pressure and volume can be 2. T/F: Turbulent flow shows a direct relationship between flow rate and pressure. seen in Equation 3 to Equation 8. Answers: 1 Elastance, 2F – Equation 4 is rearranged in Equation 5 to isolate force. YL5 07.08b Mechanics of Respiration (Part 2) 2 of 12  B. RESISTIVE WORK Predicts whether the flow will be laminar, turbulent, or both: Types of Flows in Airways – Laminar flow: Reynold’s number is 4000 (high; slower flow Explained by the Poiseuille equation rate) – If Reynold’s number falls within the gray zone (between 2000 as lowest and 4000 as highest), the predominant type of flow cannot be determined. Figure 5. Poiseuille Equation Where: – ⩒ = flow – P = pressure (usually Patmospheric – Palveolar) – r = radius of the tube Figure 7. Equation for Reynold’s Number – ŋ = viscosity – Where: – l = length of tube ▪ r = radius – R = resistance ▪ v = average velocity Flow is directly proportional to pressure and radius to the ▪ d = density of gas fourth power, and inversely proportional to the viscosity of ▪ η = viscosity the fluid and the length of the tube. Turbulent flow (turbulence) Derivation of the original equation will result in a final equation – High Reynold’s number = slower flow rate (T08.07b, 2026) that shows that resistance is equal to eight multiplied by the – Most likely to occur when: viscosity and the length of the tube, and is indirectly ▪ Average velocity of the gas flow is high (fast) proportional to the fourth power of the radius of the tube. ▪ Airway radius is large – There will be more resistance if the fluid is more viscous and if ▪ Gas has high density/low viscosity the length of the tube is longer. – More predominant in the upper airways because the upper – Flow through a tube is dramatically affected by even small airways are large, making gas flow higher changes in tube diameter because resistance increases Laminar flow as the fourth power of the radius. – Low Reynold’s number = faster flow rate (T08.07b, 2026) ▪ The radius of the tube is a very powerful determinant of – Most likely to occur when: resistance. ▪ Average velocity of the gas flow is low ▪ Even a little decrease in the radius of the tube greatly ▪ Airway radius is small increases the resistance. ▪ Gas has low density/high viscosity ▪ Smaller tubes should not be used when aiming to decrease – Laminar flow can be induced if a patient is intubated and the resistive work encountered by the patient. inhales in low flow states Turbulent Flow Clinically: – Airway radius cannot be changed. Change in Pressure or Pressure Drop (∆P) = constant x flow2 – Gas flow can be tweaked, but giving low flow to a dyspneic – ∆P is proportional to the square of the gas flow rate. patient whose flow rate is high will result in dyssynchrony and – ∆P is proportional to the density of the gas and is increased/heightened dyspnea due to the imbalance between independent of its viscosity. what the patient needs and what is being given to support ▪ Density of gas matters more in turbulent flow (T08.07b, that patient. As such, there is little that can be done to change 2026) the average velocity of the gas flow. – Resistance (R) cannot be described using the traditional – Only the density and viscosity properties of the gas can Hagen-Poiseuille equation. be changed (a less dense and highly viscous gas should be Gas velocity is blunted and higher driving pressure is needed chosen). to support a given turbulent flow than to support a similar laminar flow. Clinical Correlation: HeliOx → A gas mixture of Helium and Oxygen used in patients with upper airway obstruction to relieve the difficulty of breathing → Inhaling Helium (from balloons, for example) results in a higher-pitched voice because the gas going into the vocal cords has a more laminar flow (high flow rate) → How does HeliOx make breathing easier? a. Has high viscosity and low density (T08.07b, 2026) b. Reynold’s number is decreased → more laminar flow → higher-pitched chipmunk voice c. Especially used for asthmatic patients or those with upper airway obstruction who have turbulent flow → Not readily available; only available in large medical centers Figure 6. Comparison of Laminar and Turbulent Flow Reynold’s Number Dimensionless number; more useful clinically (T08.07b, 2026) Predicts if the flow being given to a patient is more turbulent or more laminar in order to help the patient overcome resistive work and, as a result, breathe easier YL5 07.08b Mechanics of Respiration (Part 2) 3 of 12  Airway Resistance Clinical Correlation: Fibrosis → When there are problems with expanding lungs (i.e. fibrosis), there are elastic and resistive work-related problems because of the “negligible” resistance not being negligible → You cannot expand the lungs due to less elasticity from having fibrosis. → Patients with pulmonary fibrosis can have both elastic Figure 8. Poiseuille’s Equation for Airway Resistance problem and resistive problems → needs bronchodilation even if the problem is purely parenchymal Conductance – Inverse of resistance – It measures how much flow the airway can let through in – If compliance measures the softness of the lung, conductance measures accommodation of the lungs for the airway that it will let through its tube. – As opposed to resistance, conductance clearly shows the linear effect of volume in airway resistance/conductance. Flow-Related Airway Collapse in a Normal Lung Figure 9. Graphs showing relationship between airway generation and dependent While the lung parenchyma and tubes resist the flow during variables, cross-sectional area and resistance inhalation, flow-related airway collapse is very prominent Much of lung volume is at the smaller airways. during exhalation. Once you get into the respiratory zone, the total cross sectional Resistive work is also encountered during exhalation. area exponentially increases such that the smaller areas – This is normal and does not need much work of breathing. convey the least resistance (inverse funnel graph). Structures (as seen in Figures 10a-10f): The highest resistance is within medium-sized airways – Circular (balloon-like) figure: alveolus (medium-sized bronchi are the first 7-8 generations of airways) – Red-orange figure: intrapleural space – Airways which have muscles are very responsive to ▪ The outline of this figure represents the pleura. beta-agonists (a type of drug that relaxes muscles of – Horizontal figure: airways airways). ▪ With ruler lines: extrathoracic airway (trachea) – Neurologically innervated by sympathetic and − The trachea is surrounded by rings of cartilage, parasympathetic nerves represented by the ruler lines, which keep the trachea – Could either dilate or constrict airways dilated and prevent it from collapsing regardless of – Even if they offer the highest airway resistance, the body or external pressures. brain can control size of airways through medications that ▪ Without ruler lines: intrathoracic/intrapulmonary airway would either dilate or constrict airways (i.e. the beta-agonists). − The distal parts of the airways without cartilaginous ▪ Examples: salbutamol, terbutaline, other medicines used rings may or may not collapse, depending on the for nebulizing asthmatic patients pleural pressures. Terminal airways Prevailing Pressures: – Smaller airways – Pm: mouth pressure – Distal airways have negligible contribution to airway – Palv: alveolar pressure resistance. – Pa: airway pressure ▪ Airway velocity decreases substantially and the flow is – Ppl: pleural pressure laminar in distal airways. – Pel: elastic pressures ▪ The airway branches in each generation exist in parallel – Pa – Ppl: transairway pressure rather than in a series. – Palv – Ppl: transpulmonary pressure ▪ In a parallel circuit, the proportions are added. This applies Normal lung at rest: to distal airways. – Pm = 0; Pa = 0; Palv = 0 Volume-Related Airway Collapse ▪ At functional residual capacity, there is no movement of air; hence, mouth pressure and airway pressure are Offers “negligible” resistance zero. – Tubes consist of extrathoracic, intrathoracic, ▪ The pleural pressure and the elastic pressure of the extraparenchymal tubes (tubes not embedded in lungs) and alveolus are balanced at rest; hence, alveolar pressure is intraparenchymal tubes or intrapulmonary airways (tubes zero. embedded in or tethered to the lung parenchyma). – Ppl = –30 – Therefore when a lung inflates, tethered airways open or ▪ The pleural pressure is always negative. enlarge. – An increase in airway diameter decreases the resistance Nice! such that during inhalation, there is less resistance. → Pleural pressure is always equal to –5. – It is not only the tubes that offer resistance, as the lung → The pleural pressure in this example (Ppl = –30) is only for parenchyma offers resistance as well. the sake of demonstrating the changes in pressure more clearly. – Transairway: Pa – Ppl = 0 – (–30) = 30 – Transpulmonary: Palv – Ppl = 0 – (–30) = 30 YL5 07.08b Mechanics of Respiration (Part 2) 4 of 12  ▪ Transpulmonary pressure, which is the difference or ▪ More proximal airways have lesser transairway pressure, gradient between alveolar pressure and pleural pressure, is until the pleural pressure negates and supersedes the always positive. airway pressure. – Equal pressure point (EEP): the point at which the airway pressure is equal to the governing pleural pressure (Pa = Ppl) ▪ Once pleural pressure overcomes airway pressure (Ppl > Pa), the airway will collapse intraluminally. ▪ In normal individuals, this is already at the trachea. − Since the trachea up until the first few segments of the segmental bronchi are cartilaginous, these parts of the airways will not collapse. − Hence, there is almost no work of breathing during exhalation because air can still leave the lungs freely. Figure 10a. Flow-Related Airway Collapse of a Normal Lung at Rest Normal lung at end-inspiration: – The lungs and alveolar sacs are fully distended, and air enters the alveoli (T08.07b, 2026). – When the lungs are at total lung capacity, the elastic forces of the lungs are coupled with the elastic forces of the rib cage (T08.07b, 2026). ▪ Elastic forces of the rib cage want to push air out of the lungs. ▪ These contribute to the positive alveolar pressure and positive pleural pressure. Figure 10c. Flow-Related Airway Collapse of a Normal Lung at Exhalation – Palv = 90 ▪ Upon inhalation, alveolar pressure increases as there is Flow-Related Airway Collapse in a Diseased Lung now greater volume inside the alveolus. Flow-related airway resistance becomes problematic in patients ▪ Since the alveolus is connected to the outside with chronic obstructive pulmonary disease (COPD). environment, air within this structure has not been diluted and a lot of air has entered, increasing Palv. Nice! – Ppl = –60 → Air-trapping: highly elevated alveolar pressure along with ▪ Pleural pressure becomes more negative because more saggy elastic forces, preventing the lungs from going back air is drawn in, increasing the volume of air in the pleura. to their original place – Transpulmonary: Palv – Ppl = 90 – (–60) = 150 a. Because the air is trapped, there is more alveolar ▪ Transpulmonary pressure is highest at end-inspiration. pressure at end-expiration. − This is the pressure that tends to collapse the lungs. → Steps in simulating the breathing of an emphysematous patient: a. Inhale and exhale fully for two cycles b. On the third inhale, exhale only half c. Repeat Step B 3-4 times → At the end of three to four cycles with insufficient expiration, air is trapped. a. This is how dyspnea works in emphysematous patients. b. It is difficult to inhale when the lungs are already full, because near total lung capacity (TLC), the lungs are not very compliant anymore and can no longer accommodate more air inside. c. When breathing at the top of one’s lungs, the accessory respiratory muscles might already be engaged. Figure 10b. Flow-Related Airway Collapse of a Normal Lung at End-Inspiration Diseased lung at rest: Normal lung at exhalation: – Palv = 70 – Palv = 90; Pa is decreasing ▪ The alveolar pressure is elevated, in comparison to a ▪ In the first moments of expiration, pressure inside the normal lung at rest wherein Palv = 0. alveoli down to the airways drops gradually. ▪ The air trapped in alveoli exerts more pressure (T07.10b, ▪ From an alveolar pressure of 90, Pa decreases until it 2027). reaches zero and equalizes with atmospheric pressure. – Palv = Ppl + Pel − Atmospheric pressure is usually zero. ▪ Elastic forces are lost, resulting in the increase of the – Ppl = 60 alveolar pressure. ▪ The pleural pressure is positive because as the chest – Ppl = –30 wall collapses, the pleural space decreases in volume – Transpulmonary: Palv – Ppl = 70 – (–30) = 100 (T07.10b, 2027). – Transpulmonary: Palv – Ppl = 90 – 60 = 30 – Transairway: range of values YL5 07.08b Mechanics of Respiration (Part 2) 5 of 12  Figure 10d. Flow-Related Airway Collapse of a Diseased Lung at Rest Figure 10f. Flow-Related Airway Collapse of a Diseased Lung at Exhalation Diseased lung at end inspiration: ACTIVE RECALL BOX – Palv = 70 3. T/F. Expansion of the lower part of the rib cage during ▪ Since the elastic pressures that compress the lungs are inspiration is due to the zone of apposition. 4. T/F. Extrapulmonary airways are tethered to the lung non-existent, nothing compresses the lungs to push air out parenchyma. Therefore when a lung inflates, tethered airways (T08.07b, 2026). enlarge or are opened. ▪ The alveolar pressure in a diseased lung at end-inspiration 5. Which among the following pressures is not equal to zero (Palv = 70) is less than the alveolar pressure in a normal when a normal lung is at rest? lung at end-inspiration (Palv = 90) (T08.07b, 2026). a. Mouth pressure – Ppl = 60; Pa is decreasing b. Alveolar pressure c. Pleural pressure ▪ The pleural pressure is more positive, pushing air in and d. Airway pressure compressing the alveolus. 6. In expiration of a normal lung, airway pressure decreases until ▪ This causes the airway pressure to gradually decrease it reaches zero and equalizes with __________. until it equalizes to zero in the mouth. 7. Which among the choices is true in the end-inhalation of a – Transpulmonary: Palv – Ppl = 70 – 60 = 10 diseased lung? a. Pleural pressure becomes more positive. b. Air is pushed outward from the alveolus. c. EEP moves distally towards the alveolus. d. Alveolar pressure is elevated. Answers: 3T, 4F, 5C, 6 Atmospheric pressure, 7A FEV1 Volumes and flows are measured through spirometry. FEV1 (Forced Exhaled Volume at 1 Second) – Volume of air exhaled at first second of exhalation – Most used lung function measure to gauge ability of lung – Normal FEV1 = 80% of FVC – In spirometry, when you blow up to six seconds, this is equivalent to the amount of air blown out in the first second. Figure 10e. Flow-Related Airway Collapse of a Diseased Lung at End-Inspiration FVC (Forced Vital Capacity) – Total volume of air exhaled during a forced expiration Diseased lung at expiration: maneuver – The equal pressure point moves distally towards the alveoli. – This includes all of the tidal volumes, inspiratory reserve ▪ This means that it moves to the intrapulmonary airways volume, and expiratory reserve volumes. with no cartilage. ▪ Only the residual volume is left in the lungs. – Palv = 70; Ppl = 60; Pa is decreasing – In spirometry, this is the amount of air blown out for the entire ▪ The alveolar pressure in a diseased lung at exhalation (Palv duration. = 70) is less than the alveolar pressure in a normal lung at FEV1/FVC (ratio of FEV1 and FVC) exhalation (Palv = 90) (T07.10b, 2027). – Can be a measurement of obstruction ▪ The pleural pressure overcomes the airway pressure and – Absolute cut-off in the Philippines = 70% causes the intrapulmonary airway to collapse, preventing – In spirometry, this is the amount of air blown out in the first extra air from being expired. second divided by the amount of air blown out for the entire − This leads to a vicious cycle of air trapping. duration. − The more trapping occurs, the more dyspneic the ▪ This proportion should be more than 80%. person becomes. − There is leeway to determine if a patient is obstructed – Transpulmonary: Palv – Ppl = 70 – 60 = 10 or not at 80%. − Normally, 80% is used to determine asthma. Obstructive pathologies – When you have an obstruction (asthma, COPD, or any obstruction in the upper airway), FEV1 is very low or decreased. ▪ This can lead to or may manifest as dyspnea. – The patient has prolonged exhalation. YL5 07.08b Mechanics of Respiration (Part 2) 6 of 12  ▪ For a certain volume inhaled, it will take a prolonged length There is surface tension involved but is negated by surfactants. of time for this amount to be exhaled, as compared to Remember, △V/ △P = compliance normal exhalation. – Refers to how soft your lung is ▪ There is a very small amount exhaled in the first second Dynamic compliance is always lower than static compliance (FEV1) in contrast with restrictive pathologies. because it accounts for the amount of energy or work spent on Restrictive pathologies airflow resistance (high flow rate required → higher resistance → – Even though there is little lung movement, the patient can lower dynamic compliance) have a normal or elevated FEV1 or FVC. – Resulting in a small volume-pressure loop when actively – However, you can still have dyspnea because the total breathing amount inhaled is very low. Dynamic compliance decreases with a faster breathing cycle ▪ Breaths are short and shallow and increases with deeper and slower breaths. ▪ Small amounts of air are inhaled and exhalation is shallow – When panting, dynamic compliance is low Both pathologies, obstructive and restrictive, can lead to ▪ It is not accommodating much volume and there is no dyspnea. change in pressure. – When doing deep breathing, dynamic compliance is increased. ▪ You move into your TLC, and down to ERV while RV remains. ▪ It is said that in doing yoga, deep breathing exercises are done to use much of the unused space in the lungs to breathe so that the exchange of gasses would be more efficient. − To some extent, there is a truth to this. In Figure 12: Figure 11a. FEV1/FVC Graphs – Red: static plot ▪ Lungs are in vitro, instilled or insufflated with air. – Blue: dynamic plot ▪ When breathing normally and encountering resistance with airways and mouth intact, a dynamic compliance or a dynamic volume-pressure curve is in the middle and within the static curve. − This is because normal breathing does not always constitute breathing in deeply. Figure 11b. Flow Rate vs. Lung Volume Graph from Spirometry Dynamic Compliance and Increase in Respiratory Rate In Figure 11b: Dynamic compliance is measured in real-time. – Graph is flow against volume Not all alveoli are created equal, there are slow and fast alveoli, – A shows normal breathing from spirometry therefore some fill up fast with air, and some do not. – B shows obstructive and restrictive pathologies – Alveoli have different rates of filling up the air. ▪ There is prolonged exhalation in obstructive pathologies ▪ This depends on the resistance that will be encountered ▪ There are short and shallow breaths in restrictive At the end of inspiration, the inspiratory flow stops so not all the pathologies alveoli are distended. C. ELASTIC WORK – Resulting in less △V per unit △P in dynamic compliance Dynamic Compliance ▪ Due to actively breathing in and out and the Pendelluft phenomenon ▪ Analogy used: Ejection fraction in left ventricular filling and tachycardia − When tachycardic, there is less time to fill the left ventricle and there is less volume to accommodate in the left ventricle. o Same with lungs; breathing fast drops the dynamic compliance because the volume it can only accommodate is low against the pressure drop. No breath-holding → no pendelluft phenomenon In static compliance, at each incremental pressure, there will be a breath-hold allowing pendelluft – Pendelluft: movement of air from alveoli to alveoli equalizing Figure 12. TLC Volume versus Translung Pressure the pressure At this point, air has entered through the tubes into the terminal Take Note! bronchioles. – It has overcome the resistive forces → At this point, we have discussed: Elastic forces which try to prevent the lungs from inflating are a. Resistive forces in the airway encountered b. Elastic forces that are needed in the lungs for inflation When measured in the presence of airflow (breathing in and out c. Flow-related airway collapse, which is a resistive work actively), it is called dynamic compliance that is encountered during exhalation – Dynamic compliance is during tidal breathing YL5 07.08b Mechanics of Respiration (Part 2) 7 of 12  III. WORK OF BREATHING A. NORMAL VOLUME-PRESSURE LOOP Figure 12a. Small part of the Campbell Diagram which depicts Normal Volume-Pressure Loop We encounter many forces that we work against during inspiration and expiration which are plotted in the Campbell Figure 12b. Campbell Diagram: Elastic Properties of the Lung Diagram. In Figure 12a: Elastic Properties of the Chest Wall – Inspiration (on the right): more negative pressure – Expiration (on the left): more positive pressure ▪ Causes a “looping back” to a more positive pressure – Area under the curve: work of breathing ▪ Increases in the diagram Total Work: Area under curve, below pressure across the volume – Elastic Work: Area under 0ABCD – Non-Elastic Work: Area under AECF ▪ Looks like a football ▪ Further subdivided into nonelastic expiration and inspiration work − ABCF (expiratory part) is shouldered by the Elastic Work o Inspiration part: only part where work is voluntarily exerted o Expiration part: work is not exerted = Inherent elastic work of the lungs shoulders the ABCF work during exhalation − AECB is the only one expending work during inspiration Figure 12c. Campbell Diagram: Elastic Properties of the Chest Wall Take Note! Red-shaded area: elastic work required to reduce the → Figure 12a is an example of how the Campbell Diagram is intrathoracic volume down to the FRC by chest wall depicted in textbooks such as Guyton and Hall or Berne and – Work done to overcome elastic properties of the chest wall Levy. However, this is just a small part of the complete – As you inhale, pleural pressure goes down (becomes more Campbell Diagram, which will be shown in the following negative) (T07.10b, 2027) sections. Elastic Work of both the Lungs and Chest Wall → The complete Campbell Diagram also shows the relaxation curve of pressure and volume. Elastic properties of the lungs and the chest wall can be plotted simultaneously B. CAMPBELL DIAGRAM There is a significant overlap with the work done as the area Assumes that work can be derived in an area when volume is bounded by the elastic work (blue-shaded area) produced by the plotted versus pressure natural tendency of the chest wall to “pop-out” would shoulder Can show how the overlap or contribution of the work required to some of the elastic work performed to inflate the lungs inflate the “collapsing” lung and the work required to deflate – This explains why when you exhale, you do not really feel the the always “popping out” chest wall work of breathing. Elastic Properties of the Lung Relaxation curve of pressure and volume – Y-axis: volume – X-axis: pleural pressure – Blue curved line: elastic properties of the lung ▪ Tends to collapse the lungs at baseline Elastic work to inflate the lung (blue-shaded area) – Work spended when breathing through tidal volume – Equivalent to 0ACD in Normal Volume-Pressure Loop YL5 07.08b Mechanics of Respiration (Part 2) 8 of 12  Breathing to Total Lung Capacity (TLC) Figure 12f. Campbell Diagram: Breathing During TLC Figure 12d. Campbell Diagram: Lungs and Chest Wall During forced inspiratory maneuvers: (Figures 12b and 12c superimposed) – Much of the elastic work is done to overcome the elastic Quiet Tidal Breathing properties of the lung that tends to collapse Work done is greatly increased (teal-shaded area) Take Note! → For the exam: Doc might ask for the interpretation of the Campbell Diagram in certain clinical scenarios a. Example: What part of the Campbell Diagram (i.e., elastic work, inspiratory elastic, inspiratory non-elastic) can increase if the patient is intubated or there is a decrease in diaphragmatic excursion? → Need to know how to interpret the Campbell diagram to predict the work of breathing of the patient Table 1. Elastic vs. Resistive Work Elastic Work Resistive Work For tissue resistance For elastic recoil of the lungs For chest wall resistance For lung resistance For airway resistance Natural airway resistance (i.e. Surplus elastic recoil of chest trachea, segmental bronchi) wall If the patient is intubated, add resistive work (device resistance) Figure 12e. Campbell Diagram: Inspiration and Expiration during Quiet Tidal Breathing ACTIVE RECALL BOX During quiet tidal breathing: 8. T/F: Non-elastic work in the Normal Volume-Pressure Loop is – Much of the elastic work is done passively by the inward the area within 0ABCD 9. What happens to resistance and inspiratory work when a recoil of the lungs patient is intubated? ▪ The lungs need little to no help during tidal exhalation a. Resistance increases, work decreases – During inspiration: b. Resistance increases, work increases ▪ Work against airway resistance (dark violet-shaded area c. Resistance decreases, work decreases under the curve) is being expended d. Resistance decreases, work increases − Parenchymal flow resistive forces Answers: 8F, 9B o Examples: resistive forces in the trachea, air pipe, II. SUMMARY & KEY POINTS segmental bronchi, etc. Work of breathing can be subdivided into elastic work and – Example: intubating a patient resistive work. ▪ Length of tube is directly proportional to resistance Inhalation is voluntary while exhalation is involuntary. (T07.10b, 2027) Laminar flow is more efficient, found mostly in low-flow, distal ▪ Introduce more work of breathing to the patient airways. − This is because the patient needs to overcome Turbulent flow is chaotic and found in high-flow, large, breathing through a narrow and long tube → inspiratory proximal airways. work of breathing will increase ▪ In cases like these, the work of breathing through the apparatus is increased YL5 07.08b Mechanics of Respiration (Part 2) 9 of 12  REVIEW QUESTIONS 4. [B] – Refer to Figure 7. Equation for Reynold’s Number. 1 1 #1: T/F: Elevation of the chest wall during inspiration causes 𝑅𝑒 = 𝑘 η =𝑘 (2η) the lung volume to increase, which then decreases the 5. [D] — Against the highest airway resistance, the body or brain pressure inside the lungs. This process, called positive pressure ventilation, sucks air into lungs. can still control the size of the airways. The size can also be controlled by medications called beta-agonists that are capable True or false? of dilating or constricting airways. #2: T/F: Work of breathing is spent only on exhalation. 6. [B] — Pleural pressure of a normal lung at end-inhalation True or false? becomes more negative (relative to the pleural pressure of a #3: What would happen to flow if the radius of the tube was normal lung at rest) because more air is drawn in, increasing the halved? volume of air in the pleura. A. Increase by a factor of 2 7. [False] — The absolute cut-off for FEV1/FVC in the Philippines is B. Decrease by a factor of 4 70%. C. Decrease by a factor of 8 8. [C] — The residual volume is left after a forced expiration D. Decrease by a factor of 16 maneuver, which leads to the value FVC. 9. [D] — ABCF is part of the Non-Elastic Work, but since there is an #4: What would happen to the Reynold’s number if viscosity overlap, it is being shouldered by the elastic work of the lungs. is doubled? REFERENCES A. The Reynold’s number would have a two-fold increase B. The Reynold’s number would decrease by half REQUIRED RESOURCES C. The Reynold’s number would have a two-fold decrease Koeppen, B.M., Stanton, B.A., Levy, M.N., & Berne, R.M. D. The Reynold’s number would have a four-fold decrease (2018). Berne and Levy Physiology (Sixth Edition). Elsevier. Hall, A.E. (2015). Guyton and Hall Textbook of Medical #5: Against the highest airway resistance, the body or brain Physiology (Thirteenth Edition). Elsevier. cannot control the size of the airways. The size can be Magallanes, J.R. (2023). Mechanics of Ventilation Part 2 controlled by medications that would either dilate or [Lecture Slides]. constrict airways (i.e. the alpha-agonists). SUPPLEMENTARY RESOURCES A. Statement 1 is true. Statement 2 is false. ASMPH 2026. (2022). [08.07b] Mechanics of Respiration Part B. Statement 2 is true. Statement 1 is false. 2. C. Both statements are true. ASMPH 2027. (2022). [07.10b] Mechanics of Respiration Part D. Both statements are false. 2. Hurley, J. J., & Hensley, J. L. (2022). Physiology, Airway #6: In end-inhalation of a normal lung, pleural pressure Resistance. In StatPearls [Internet]. StatPearls Publishing. becomes more positive due to the increased volume of air in http://www.ncbi.nlm.nih.gov/books/NBK542183/ the pleura. Meanwhile, a normal lung at rest always has a Piqueras, M. G., & Cosio, M. G. (2001). Disease of the negative pleural pressure. airways in chronic obstructive pulmonary disease. The A. Statement 1 is true. Statement 2 is false. European Respiratory Journal, 18(1), 41–49. B. Statement 2 is true. Statement 1 is false. https://doi.org/10.1183/09031936.01.00234601 C. Both statements are true. Solomon, N. (2023). How to read a normal chest x ray: A step D. Both statements are false. by step approach. Kenhub. https://www.kenhub.com/en/library/anatomy/normal-chest-x #7: The absolute cut-off for FEV1/FVC is 80%. -ray True or False? Evaluate us! #8: The lung volume left after FVC is called: A. Expiratory Reserve Volume ✔ Feedback Form: bit.ly/2028EvalsYearRoundForm B. Vital Capacity ✔ Errata Tracker: https://tinyurl.com/CRErrataTracker28 C. Residual Volume FREEDOM SPACE D. Inspiratory Reserve Volume #9: In a Normal Volume-Pressure Loop, what area is being shouldered by the natural elastic properties of the lung? A. 0ABCD B. ABCD C. AECF D. ABCF Answer Key 1F, 2F, 3D, 4B, 5D, 6B, 7F, 8C, 9D RATIONALE TO ANSWERS OF REVIEW QUESTIONS 1. [False] — The process described is called negative pressure ventilation instead of positive pressure ventilation. Positive pressure ventilation involves the delivery of oxygen mixed with other gasses directly into the lungs. 2. [False] — Work of breathing is spent only on inhalation. Exhalation is involuntary and depends on the elastic forces. 3. [D] — Refer to Figure 5. Poiseuille equation. We can look at flow (⩒) only in terms of r and treat all the other terms as constant. 𝑟 4 4 4 𝑘𝑟 ⩒ = 𝑘𝑟 = 𝑘( 2 ) = 16 YL5 07.08b Mechanics of Respiration (Part 2) 10 of 12  APPENDIX SUMMARY OF TERMS COPD Chronic Obstructive Pulmonary Disease Table A1. Homework on Flow-Related Airway Collapse Question Answer Figure A1. Flow-Related Airway Collapse of a Diseased Lung at Exhalation A decrease in airway caliber can be observed in bronchiolitis, a pathological hallmark of COPD. In exhalation of a diseased lung (examples: asthma, COPD), This constricts the airway and limits airflow. Moreover, since the airway radius is decreased and what happens if you have decreased caliber in your airways? airflow is limited, this results in a lower FEV1 value (Piqueras & Cosio, 2001). The relationship between radius and flow is explained by Poiseuille’s Law or the Hagen-Poiseuille equation: Figure A2. Poiseuille Equation This law shows that flow is directly proportional to the fourth power of radius. This means that What is the effect of radius on flow? (i.e. Will resistive work any change in the radius of the tube (in this case, the airway) is proportionately magnified in gas increase or decrease?) flow. For example, if r is replaced by 2r, ⩒ will increase by 16 times. Inversely, if r is replaced by ⅓r, then ⩒ will decrease by 81 times. The derived equation explains the relationship of airway resistance with flow and radius. Airway resistance is inversely proportional to gas flow and to the fourth power of radius. This means that any decrease in radius or flow rate causes an increase in airway resistance, and vice versa. Notably, minor changes in the radius of the tube will lead to dramatic effects on resistance. For instance, if r is cut by half, airway resistance would increase 16-fold. This makes the radius of the tube the most important factor in both flow rate and airway resistance. This diagram simulates obstructive lung diseases like asthma. Asthma is characterized by the chronic inflammation of the conducting portion of the respiratory tract, which causes airway Can you think of a situation that is simulated in this diagram? narrowing and prevents the expiration of air inside the lungs. As a result, dyspnea and air trapping can occur (Hurley & Hensley, 2022). Table A2. Q&A with Dr. Magallanes Question Dr. Magallanes’ Responses Q1: Clarification with the Campbell Diagram “When you were talking about the football diagram, you were talking about how the elastic work is what helps with exhalation because the inherent elastic Differentiating elastic work of the lung and the elastic work of the chest wall work does the involuntary work for Elastic work of the lung tends to collapse the lungs. exhalation because normally, the Very different from the elastic work of the chest wall inhalation is what’s voluntary. So all of – Tends to work the opposite way - pops out the lungs the elastic work would be normally – Defined as the “elastic work required to reduce the intrathoracic volume down to the FRC” what’s used for the involuntary ▪ Very small and negated by the elastic properties of the lung (which tends to collapse) exhalation. But then when we moved on to the Campbell diagram, that’s when you started talking about how the elastic work was used for inspiration.” YL5 07.08b Mechanics of Respiration (Part 2) 11 of 12  Figure A3. Campbell Diagram: Lungs and Chest Wall (Figures 12b and 12c superimposed) Diagram: [in Blue] Area of the elastic properties done by the lung vs. [in Red] Area of the elastic work done by the chest wall – Doc says that the elastic properties of the lung is much higher than the one exerted by the chest wall – During expiration, the inherent elastic properties of the lung (which collapses it), totally negates the work done by the chest wall when it comes to expanding the lung – No work of breathing is exerted due to this phenomenon – Referring to the “football” diagram: ▪ Areas in 0, A, C, & D indicate that there is no work spent there during the phenomenon ▪ Areas A, E, C, B indicates the work spent only during inspiration Figure A4. Campbell Diagram: Inspiration and Expiration during Quiet Tidal Breathing Diaphragmatic breathing: Voluntary, “paradoxical” breathing wherein you spend much energy in your diagram to Q2: Diaphragmatic Breathing move your diaphragm lower so that when you expire, there is a spring-back action “Na-mention niyo po kanina nang – Results in a louder, more modulated, and controlled voice (controlled expiratory arm) nag-bbreathing, dapat kitang Response to Follow-up Question: You will not visibly notice if a person uses normal or diaphragmatic breathing. gumagalaw yung inspiratory muscles. – Diaphragmatic breathing is not normal as it contracts the diaphragm beyond its limit Paano po, halimbawa, kapag sanay na sa Diaphragmatic breathing for long periods of time will be more tiresome since you spend more effort and there is diaphragmatic breathing, mas yung belly increased voluntary energy exerted in the inspiratory arm yung nag-ddistend o nag-eeffort. Diba – Tiring out activates the accessory muscles (sternocleidomastoid, scalenes, etc.) po may be the difference between chest and diaphragmatic breathing.” – Problematic if the diaphragm is not trained for diaphragmatic breathing, you are prone to tiring out and can lead to evident dyspnea. “Follow-up Q: Does diaphragmatic – Ultrasound of opera singers and song professionals show thicker diaphragm breathing impact normal breathing ▪ Significantly much more force can be exerted in the same contraction of the diaphragm and accommodate capacity?” more volume capacity in the lung. Q3: Use of formulas in the exam No use of calculus and integrals. – Berne and Levy use it, but will not be covered in the exam. “We used a lot of formulas in the lecture. In the physiology questions, no math Will we only be using the algebraic – More centered on the relationships equations?” – Examples: Double length/ radius, what will happen to A, B, C, etc. Q4: Recommended book reference Guyton and Hall Q5: Medical usage of Endotracheal Tube (ET) Overall, it is a “necessary evil” – The production of positive pressure so that patients can breathe “Why do we put ET tubes on patients Doc said that as pulmonologists, they compensate for the added work of breathing when they ventilate their who have a hard time breathing when the patients. ET tube increases the work of – They calculate the right tidal volumes and pressures to supply the patient with breathing?” YL5 07.08b Mechanics of Respiration (Part 2) 12 of 12