Lung Volumes and Capacities PDF

LUNG VOLUMES AND CAPACITIES RESIDUAL VOLUME (RV),about 1,200 mL, is the volume of air still remaining in the lungs LUNG VOLUMES AND CAPACITIES after...

LUNG VOLUMES AND CAPACITIES RESIDUAL VOLUME (RV),about 1,200 mL, is the volume of air still remaining in the lungs LUNG VOLUMES AND CAPACITIES after the expiratory reserve volume is exhaled. LUNG CAPACITIES TOTAL LUNG CAPACITIES (TLC), about 6,000 mL, is the maximum amount of air that can fill the lungs (TLC= TV+IRV+ERV+RV). VITAL CAPACITY (VC), about 4,800 mL, is the total amount of air that can be expired after fully inhaling (VC= TV+IRV+ERV= approximately 80% TLC) INSPIRATORY CAPACITY (IC), about 3,600 mL, is the maximum amount of air that can be inspired (IC= TV+IRV) FUNCTIONAL RESIDUAL CAPACITY (FRC), about 2,400 mL, is the amount of air remaining in the lungs after a normal expiration (FRC= RV+ERV) LUNG VOLUMES TIDAL VOLUME (VT), ABOUT 500 mL, is the amount of air inspired during normal, relaxed breathing. INSPIRATORY RESERVE VOLUME (IRV), about 3,100 mL is the additional air that can be forcibly inhaled after the inspiration of a normal tidal volume. LUNG VOLUME LUNG CAPACITIES EXPIRATORY RESERVE VOLUME (ERV), TIDAL VOLUME INSPIRATORY about 1,200 mL, is the additional air that can CAPACITIES be forcibly exhaled after the expiration of a normal tidal volume. INSPIRATORY FUNCTIONAL RESERVE RESIDUAL VOLUME CAPACITIES  LUNG VOLUMES AND CAPACITIES EXPIRATORY VITAL CAPACITIES RESERVE VOLUME RESIDUAL TOTAL LUNG VOLUME CAPACITIES 3 INDIRECT TECHNIQUES TO MEASURE LUNG VOLUMES Because RV cannot be exhaled, RV, FRC, and TLC cannot be measured by directly spirometry. ​ Helium Dilution ​ Nitrogen Washout ​ Body Plethysmograph The He dilution and N washout techniques measure whatever gas is in the lungs at the beginning of the test, if the gas is in contact with unobstructed airways. The body plethysmographic technique measures all the gas in the thorax at the resting expiratory volume. HELIUM DILUTION In healthy patients and patients with a small FRC, equilibrium occurs in 2-5 minutes. Uses closed, rebreathing circuit Patients with obstructive lung disease may Bases on the assumption that the patient has require 20 minutes to equilibrate because of no He in his or her lungs, and that an slow gas mixing in the lungs. equilibration of He can occur between the spirometer and the lungs. The He dilution time or the duration of the test gives a reasonable indication of the First, volume (V1) and concentration (C1) of distribution of ventilation. He are measured at the beginning of the test. COMPUTATION FOR FRC : Next, the valve is turned to connect the patient to the breathing circuit, usually at the FRC= (Volume 2)V2 - (Volume 1)V1 resting expiratory level of the FRC. The patient is connected to the air mixture, NITROGEN WASHOUT and the concentration of He is diluted slowly by the patient’s lung volume.  LUNG VOLUMES AND CAPACITIES The nitrogen N technique uses a non breathing or open circuit. The technique is based on the assumption that N concentration in the lungs is 78% and in equilibrium with the atmosphere, that the patient inhales 100% 02, and that the 02 replaces all the N in the lungs. Similar to the He dilution techniques, the patient is connected to the system at FRC. The patient’s exhaled gas is monitored, and COMPUTATION FOR FRC its volume and N percentage are measured. FRC= VE X FEN2/ 0.78 - FAN2 Two types of circuits are used to measure lung volumes with this technique VE- Total volume of gas exhaled FEN2- Fractional concentration of exhaled Generally, two types of circuits are used to nitrogen measure volumes with this technique. FAN2- Fractional concentration of nitrogen in the alveoli at the end of the test. In one type of circuit, all of the exhaled gasses 0.78- Constant value (percentage of are collected in a large container, where the atmosphere in the atmosphere) volume and concentration of N are measured. BODY PLETHYSMOGRAPH In the second type of circuit, the volume and concentration of each exhaled breath are measured separately and stored in a Has more advantage than dilution techniques. memory; the sum of the volumes and the weighted average of the N concentration are Thoracic volume and change in pressure calculated by a computer. are measured directly by the body plethysmograph. Nitrogen washout would take 2-5 minutes for a normal patient. Also, the total contained air in the thorax is measured. Thoracic gas volume (VTG). If nitrogen washout takes more than 5 minutes (>5 minutes). The patient has The plethysmography technique applies obstructed lung disease. Boyle’s law and uses measurements of volume and pressure changes to determine lung volume, assuming temperature is constant.  LUNG VOLUMES AND CAPACITIES The patient holds his or her cheeks and performs gentle panting as 1 Hz or one pant per second. Decrease in cabinet volume= Increase in thoracic volume During the panting, changes in airway pressure and changes in chamber volumes are measured. Boyle’s law formula Because the panting maneuver occurs with small pressure changes around barometric P1 V1= P2 V2 pressure, the simplified equation used to calculate TCV is: The amount of air pressure and the volume change during the breathing is measured. TGV= PB X V/P The Plethysmography technique applies Body plet steps: Boyle’s law The plethysmography technique measures the volume of all: ​ Compressible gas in the thorax including gas trapped behind airway instructions or in the pleural space. INTERPRETATION OF LUNG VOLUMES When measurement of TGV is being done, AND CAPACITIES the patient sits in the chamber. Initially breathes normal tidal volume through the mouthpiece. When the patient is near FRC, the shutter is closed at an expiration for 2 to 3 seconds.  LUNG VOLUMES AND CAPACITIES CO and O2 have similar molecular weights and solubility coefficients. Lung Degree Impairment Volum e and Similar to 02, CO also chemically combines Capaci with hemoglobin (Hb) ty CO has a very high affinity for Hb and 1. TLC Increased Obstructive lung diffuses rapidly into the pulmonary blood. 2. FRC disease 3. RV Decrease Restrictive lung DIFFUSING CAPACITY disease TLC Decrease Restrive lung ​ Single-Breath Technique disease ​ Steady-State Technique ​ Rebreathing techniques IC Decreased Restrictive lung disease Diffusion of Gases Factors: IC Normal Mild obstructive lung disease 1. Gas volume- amount of gas transferred into the lungs Moderate-severe 2. P1- Partial pressure of gas in the alveolus Decrease Obstructive lung diseases 3. P2- Partial pressure of gas in the capillary IRV Normal Obstructive lung FORMULA FOR DLCO: diseases and Restrictive lung DLCO= VCO/ PACO disease ERV Normal / Obstructive lung SINGLE BREATH TECHNIQUE (DLCO-SB) Decrease diseases and Restrictive lung disease Also known as the modified krogh method. FRC Increase Acute and The patient exhales completely to RV. and RV chronic lung disease Rapidly inspires to TLC a volume of air containing small concentration of CO and He DIFFUSING CAPACITY OF THE LUNG Maintains breath holding for 10 seconds, and FOR CARBON MONOXIDE then exhales at least 1 L rapidly. DLCO is expressed in ml/min/mm Hg under STPD. Reliability and Acceptability Test Of DLCO: CO is used as the transfer gas because CO is ❖​ RELIABILITY similar to 02 in important ways. -Based on the repeatability of the -At least 4 minutes should be allowed between the tests.  LUNG VOLUMES AND CAPACITIES -In patients with obstructive lung Begin rebreathing from the reservoir as this diseases, longer period more than 10 level minutes ​ During rebreathing, the subject should maintain a rebreathing rate as close to ❖​ ACCEPTABLE TEST 30 bpm (breaths per minutes) -​ One that is reproducible to within 10% ​ The reservoir must be emptied or 3ml CO ml/min/mmHg, whichever completely with each inspiration. is greater. 2 REBREATHING METHOD TECHNIQUES STEADY-STATE TECHNIQUE 1. RESERVOIR-SAMPLING TECHNIQUE Allows for measurement to be made with subject performing relatively normal VT The subject rebreathes the gas mixture for a time period, approximately 30-45 seconds. A A gas mixture containing 0.1% CO with the sample of rebreathe gas is taken from the remaining balanced air is inhaled by subject reserve gas. with each other. The concentration of Carbon monoxide and During the last two minutes of breathing, the Helium, as well as oxygen is measured. subject’s exhaled air is collected in Douglas bag, sample volume is taken from the exhaled 2. WASHOUT-SAMPLING TECHNIQUE air. Rebreathing continues until a gas FORMULA FOR DLCO: concentration equilibrium is reached between the reservoir and the subjects lungs. DLCO-SS= VCO (STPD)/ PACO Next, the subject is switched in inhaling air. RE-BREATHING TECHNIQUE The exhalation washes the mixture from the subject’s lungs and allow for concentration of Like DLCO-SS, allow for measurement to be carbon monoxide and Helium to be analyzed. made during tidal breathing of the subject 2 REBREATHING METHOD TECHNIQUES INTERPRETATION OF DLCO ​ Reservoir-sampling technique ​ Washout-sampling technique Normal values for DLCO using SB technique are based primarily on the patient’s height, Both technique involved having subject age, and gender. rebreathe gas mixture from a bag or balloon-like reservoir. Normal value 40 mL/min/mm HG The gas mixture contains: 0.3% CO & 10% Factors known to affect test result: He ​ Patient should be tested is a seated position Exhales down to RV level ​ Should not breathe supplemental 02 for 10 mins before the test  LUNG VOLUMES AND CAPACITIES ​ Patients who recently smoke Degree Impairment DLCO Decreased Obstructive lung disease and Restrictive lung disease and Pulmonary embolism Destruction of the alveoli in Less than pulmonary Normal emphysema, small lung volume and w/ fibrosis of the alveoli is asbestosis. DLCO Increase Polycythemia, Congestive heart failure (left side), Increase in pulmonary vascular blood volume. PFT INTERPRETATION