Respiratory Measurements I LUNG FUNCTION TESTS PY3002

2. LECTURE OUTLINE How to detect respiratory dysfunctions? methods available specificities / limits differential diagnosis Measures of lung volumes ? transport of O2 to the alveoli spirometry body plethysmography / helium dilution Gas exchanges ? diffusion of O2 into the bloodstream blood gases diffusing capacity Place of exercise tests in Respiratory Dept?

3. Obstructive lung disorders ? ? airway resistance Asthma COPD (Chronic Obstructive Pulmonary Disease) Chronic bronchitis Inflammation of the bronchi Emphysema Destruction of the alveoli Prevalence: 80 million people worldwide moderate to severe COPD In the UK: 1%, ? with age: 10% in men older than 75 (probably under-diagnosed!) COMMON CHRONIC RESPIRATORY DISEASES

4. Loss of airway compliance lung stiffness incomplete lung expansion Fibrosis: formation or development of excess fibrous connective tissue Cystic fibrosis (CF) Mutation of a gene ? thick and sticky mucus frequent lung infections Prevalence UK birth prevalence: about 0.4 per 1,000 (300 new cases each year) RESTRICTIVE RESPIRATORY DISEASES

16. In body plethysmography, the patient sits inside an airtight box, inhales or exhales to a particular volume (usually FRC), and then a shutter drops across their breathing tube. The subject makes respiratory efforts against the closed shutter (this looks, and feels, like panting), causing their chest volume to expand and decompressing the air in their lungs. The increase in their chest volume slightly reduces the box volume (the non-person volume of the box)and thus slightly increases the pressure in the box. Using the data from the plethysmography requires use of Boyles Law. To compute the original volume of air in the lungs, we first compute the change in volume of the chest.Using Boyle's Law (P1V1=P2V2, at constant temperature), we set the initial pressure in the box times the initial volume of the box(both of which we know), equal to the pressure times volume of the box at the end of a chest expansion (of which we know only the pressure). We solve for the volume of the box during the respiratory effort. The difference between this volume and the initial volume of the box, is the change in volume of the box, which is the same as the change in volume of the chest. Armed with this piece of information, we use Boyle's Lawagain, this time on the fixed amount of gas in the chest before and at the end of a respiratory effort. We set the initial volume of the chest (unknown) times the initial pressure at the mouth(known), equal to the inspiratory volume of the chest (the same unknown volume plus the change in the volume of the chest, which we have just computed) times the pressure at the mouth during the inspiratory effort (known). Now we solve for the unknown volume, which will be the original volume of gas present in the lungs when the shutter was closed. As mentioned before, the shutter is usually closed at the end of a normal exhalation, or at FRC. Body plethysmography is particularly appropriate for patients who have air spaces within the lung that do not communicate with the bronchial tree. In these people, gas dilution methods of measurement would give an erroneously low volume reading. In body plethysmography, the patient sits inside an airtight box, inhales or exhales to a particular volume (usually FRC), and then a shutter drops across their breathing tube. The subject makes respiratory efforts against the closed shutter (this looks, and feels, like panting), causing their chest volume to expand and decompressing the air in their lungs. The increase in their chest volume slightly reduces the box volume (the non-person volume of the box)and thus slightly increases the pressure in the box. Using the data from the plethysmography requires use of Boyles Law. To compute the original volume of air in the lungs, we first compute the change in volume of the chest.Using Boyle's Law (P1V1=P2V2, at constant temperature), we set the initial pressure in the box times the initial volume of the box(both of which we know), equal to the pressure times volume of the box at the end of a chest expansion (of which we know only the pressure). We solve for the volume of the box during the respiratory effort. The difference between this volume and the initial volume of the box, is the change in volume of the box, which is the same as the change in volume of the chest. Armed with this piece of information, we use Boyle's Lawagain, this time on the fixed amount of gas in the chest before and at the end of a respiratory effort. We set the initial volume of the chest (unknown) times the initial pressure at the mouth(known), equal to the inspiratory volume of the chest (the same unknown volume plus the change in the volume of the chest, which we have just computed) times the pressure at the mouth during the inspiratory effort (known). Now we solve for the unknown volume, which will be the original volume of gas present in the lungs when the shutter was closed. As mentioned before, the shutter is usually closed at the end of a normal exhalation, or at FRC. Body plethysmography is particularly appropriate for patients who have air spaces within the lung that do not communicate with the bronchial tree. In these people, gas dilution methods of measurement would give an erroneously low volume reading.

17. After several minutes of breathing, the helium concentrations in the spirometer and lung become the same. From the law of conservation of matter, we know that the total amount of helium beforehand after is the same. Therefore we can set the fractional concentration times the volume before equal to the fractional concentration times the volume, because of the conservation law of matter. We solve for the volume after (the volume of the lung and spirometer), subtract out the volume of the spirometer, and we get the volume of the lung. Helium poorly soluble in water and thus diffuses very poorly across the alveolar wall. Subjects breath a gas that cannot escape from the lungsAfter several minutes of breathing, the helium concentrations in the spirometer and lung become the same. From the law of conservation of matter, we know that the total amount of helium beforehand after is the same. Therefore we can set the fractional concentration times the volume before equal to the fractional concentration times the volume, because of the conservation law of matter. We solve for the volume after (the volume of the lung and spirometer), subtract out the volume of the spirometer, and we get the volume of the lung. Helium poorly soluble in water and thus diffuses very poorly across the alveolar wall. Subjects breath a gas that cannot escape from the lungs

21. Diffusion impairment equilibration does not occur between the PO2 in the pulmonary capillary blood and alveolar gas Shunt some bloods reaches the arterial system without passing through ventilated regions of the lungs Diffusion impairment equilibration does not occur between the PO2 in the pulmonary capillary blood and alveolar gas Shunt some bloods reaches the arterial system without passing through ventilated regions of the lungs

22. respiratory acidosis: caused by CO2 retention metabolic acidosis: caused primary by a fall in HCO3- respiratory alkalosis: in severe hyperventilation metabolic alkalosis: in severe prolonged vomiting respiratory acidosis: caused by CO2 retention metabolic acidosis: caused primary by a fall in HCO3- respiratory alkalosis: in severe hyperventilation metabolic alkalosis: in severe prolonged vomiting

38. MANNITOL TEST Principle: change the osmolarity of the ASL fluid by inhalation of a dry powder ? if inflammation: cells activated and mediators released (histamine, PG, LT) Inhaled agent: Dry powder Mannitol (Sugar) Progressive Protocol: 0, 5, 10, 20, 40, 80, 160, 160 mg Measurements : FEV1 Pre and at 1 min post dose Positive Response: Fall in FEV1?15% or ?10% for EIB Expression of result: PD15 or PD20 for EIB Anderson et al., AJRCCM 1997;156:758-65 Brannan et al., AJRCCM 1998; 158:1120-6

39. MANNITOL IN ASTHMATICS