The content herein is provided for informational purposes and does not replace the need to apply This information uses the best available medical evidence and was produced with the support of people living with lung conditions. The uptake of CO can be calculated from the Va and inspired and expired CO concentrations. At the time the article was created Yuranga Weerakkody had no recorded disclosures. (2019) Breathe (Sheffield, England). This site uses Akismet to reduce spam. 0000002029 00000 n While patients had relatively normal spirometry, DLCO was reduced in 50% and DLCO/VA (or KCO, to avoid misinterpretation) reduced in 25%. This is not necessarily true and as an example DLCO is often elevated in obesity and asthma for reasons that are unclear but may include better perfusion of the lung apices and increased perfusion of the airways. Lung Function. 0000046665 00000 n Decreased volume of pulmonary capillary blood or hemoglobin volume, Decreased surface area integrated between capillaries and alveoli, Ventilation/perfusion mismatching or intrapulmonary shunting from atelectasis, The patient needs to hold his or her breath for 10 seconds, then exhale quickly and completely back to RV. 0000001116 00000 n Retrospective study of pulmonary function tests in patients presenting with isolated reductions in single-breath diffusion capacity: Implications for the diagnosis of combined obstructive and restrictive lung diease. Content on HealthUnlocked does not replace the relationship between you and doctors or other healthcare professionals nor the advice you receive from them. endobj Is this slightly below normal or more than that? Asthma, obesity, and less commonly polycythemia, congestive heart failure, pregnancy, atrial septal defect, and hemoptysis or pulmonary hemorrhage can increase Dlco above the normal range. Furthermore, Kco is not a surrogate measurement for Dlco. I appreciate your comments. patients will relax against the valve and the pressure in the alveoli and pulmonary capillaries will actually rise slightly at this time due to the elastic recoil of the lung. Z-iTr)Rrqgvf76__>dJ&x\H7YOpdDK|XYkEiQiKz[X)01aNLCPe.L&>\?0Gf~{LVk&k~7uQ>]%"R0.Lg'7iJ-EYu3Ivx};.e@IbSlu}&kDiqq~6CM=BFRFnre8P+n35f(PVUy4Rq89J%,WNl\Te3. 4 Anemia, COPD with emphysema, ILD, and pulmonary vascular diseases can decrease Dlco below the normal range. So Yet Another Follow Up - Starting I think 2020 - Bizzar, It's love your pet day today and here is himself . Hemoglobin. A normal absolute eosinophil count ranges from 0 to 500 cells per microliter (<0.5 x 10 9 /L). Inspiratory flow however, decreases to zero at TLC and at that time the pressure inside the alveoli and pulmonary capillaries will be equivalent to atmospheric pressure and the capillary blood volume will be constrained by the fact that the pulmonary vasculature is being stretched and narrowed due to the elevated volume of the lung. ichizo, Your email address will not be published. 0000032077 00000 n btw the figures don't look dramatically bad but then again i am only a retired old git with a bit of google related knowledge and a DLCO figure that would scare the pants of you lol . Carbon monoxide transfer coefficient (often abbreviated as KCO) is a parameter often performed as part of pulmonary function tests. Inhaled CO is used because of its very high affinity for hemoglobin. Clinical significance of elevated diffusing capacity. endstream Many (most?) In restrictive lung diseases and disorders. WebKco. uuid:8e0822df-1dd2-11b2-0a00-aa0000000000 It is very frustrating not to get the results for so long. The patient then is asked to perform an unforced, complete exhalation in less than 4 seconds. Lung parenchyma is the portion of the lung involved in gas transfer - the alveoli, alveolar ducts and respiratory bronchioles. Why do we have to keep on ,time and time again asking some professionals about our own test results . Why choose the British Lung Foundation as your charity partner? DLCO is dependent on the adequacy of alveolar ventilation, the alveolar-capillary membrane resistance (its thickness) and the availability of hemoglobin in the blood. WebThe normal adult value is 10% of vital capacity (VC), approximately 300-500ml (68 ml/kg); but can increase up to 50% of VC on exercise Inspiratory Reserve Volume(IRV) It is the amount of air that can be forcibly inhaled after a normal tidal volume.IRV is usually kept in reserve, but is used during deep breathing. COo ADVERTISEMENT: Radiopaedia is free thanks to our supporters and advertisers. Using helium as the inert gas, the concentration of the inhaled helium (Hei) would be known, and because the inhaled volume (Vi) is measured, measuring the concentration of exhaled helium (Hee) will give the volume of lungs exposed to helium, or Va, as follows: Vi is the volume of inhaled gas minus the estimated dead space (since dead space will not contain any helium). Because, in both disease entities, pulmonary congestion is present and then DLCO and KCO should be increased. Sivova N, Launay D, Wmeau-Stervinou L, et al. Conversely, obesity, kyphoscoliosis, and neuromuscular disease will reduce Va, but Kco, due to relatively increased Vc for a given Va, will be increased, resulting in a normal range or slightly decreased Dlco. 0000012865 00000 n Carbon monoxide diffusing capacity (Dlco) probably is the least understood pulmonary function test (PFT) in clinical practice worldwide, even among experienced pulmonologists. Neder JA, Marillier M, Bernard AC, O'Donnell DE. A decreasing Dlco is superior to following changes in slow vital capacity (SVC) or TLC in ILDs. The results can be affected by smoking, so if you are a smoker, dont smoke for 24 hours before your test. The specificity and sensitivity of Dlco for specific lung diseases has not been studied extensively until recently, particularly for pulmonary arterial hypertension (PAH) and systemic sclerosis with or without interstitial lung disease (ILD). The normal values for KCO are dependent on age and sex. Top tips for organising a brilliant charity quiz, Incredible support from trusts and foundations, Gwybodaeth yng Nghymraeg / Welsh language health information, The Asthma UK and British Lung Foundation Partnership, Why you'll love working with the British Lung Foundation, Thank you for supporting the British Lung Foundation helpline. 2001; 17: 168-174. Comparing the DLCO and DLCO/VA, the sensitivity of DLCO was greater than that of DLCO/VA for all cut-off values=5070%, and the area under the ROC This demonstrates that Dlco could be lowered by 2 different mechanisms in the same patient. 2011, Jaypee Brothers Medical Publishers, Ltd. Horstman MJM, Health B, Mertens FW, Schotborg D, Hoogsteden HC, Stam H. Comparison of total-breath and single-breath diffusing capacity if health volunteers and COPD patients. It also indicates that 79% to 60% of predicted is a mild reduction, 59% to 40% is a moderate reduction, and that Dlco values less than 40% of predicted are severely reduced.1. Which pulmonary function tests best differentiate between COPD phenotypes? Dlco correction by Va cannot reliably rule out the presence of underlying emphysema or parenchymal lung disease.4, Dlco usually is decreased in COPD when emphysema is present; it typically is normal in chronic bronchitis alone or in asthma, where it even could be increased during acute attacks.5. A fit young adult may have a KCO of approximately 1.75 mmol/min/kPa/litre, an elderly adult may be about 1.25. The technique was first described 100 years ago [ 1-3] and Breathing techniques for moving or lifting, Non-tuberculous mycobacterial infection (NTM), Connective tissue and autoimmune diseases, Pulmonary haemorrhage (bleeding into the lung), Your living with a lung condition stories, Northern Ireland manifesto: Fighting for Northern Ireland's Right to Breathe, Northern Ireland manifesto: live better with it, Stoptober: the 28-day stop smoking challenge, Take action on toxic air in Greater Manchester, How air pollution makes society more unequal, Invisible threat: air pollution in your area. This measures how well the airways are performing. Pattern of diffusion disturbance related to clinical diagnosis: The KCO has no diagnostic value next to the DLCO. It is a common pitfall to correct Dlco for Va and thus misinterpret Dlco/Va that appears in the normal range in patients with obstructive lung diseases such as COPD and asthma-COPD overlap syndrome (ACOS), which can produce spuriously normal results, leading to errors in interpretation and decision-making. However as noted, blood flow of lost alveolar units is diverted to the remaining units, resulting in a slight increase in Kco; as a result, Dlco falls relatively less than Va and not always proportionately. I also have some tachycardia on exertion, for which I am on Bisoprolol 1.25 mg beta blocker. you and provide you with the best service. UB0=('J5">j7K\]}R+7M~Z,/03`}tm] This understanding is particularly useful in clinical situations in which the expected values do not correlate clinically or with other PFTs such as TLC. Standardization of the single-breath determination of carbon monoxide uptake in the lung. This is because the TLC is more or less normal in obstructive lung diseases and it is the DLCO, not the KCO, that is the primary way to differentiate between a primarily airways disease like asthma and one that also involves the lung tissue like emphysema. Typically, a gas transfer test will give 3 results: Low lung efficiency is when your measured results are less than 80% of the normal predicted values. WebK co will be greater than 120% predicted in case 1, 100120% in case 2, and 40120% in case 3, depending on pathology. For the purpose of this study, a raised Kco was diagnosed only if it exceeded the predicted value for Kco (van The exhaled breath from alveolar lung volume is collected after the washout volume (representing anatomic dead space) and is discarded as described in the, A checklist can be helpful in establishing a regular routine for interpreting Dlco, Va and Kco (. Variability in how Dlco is reported is a concern. 0000014758 00000 n (2000) Respiratory medicine. The exhaled breath from alveolar lung volume is collected after the washout volume (representing anatomic dead space) and is discarded as described in the Figure. Because an inert gas is used, it is reasonably assumed that a change in exhaled concentration from the inhaled concentration is purely due to redistribution (dilution) of the gas into a larger volume. DLCO however, is highest at TLC and lowest at FRC and this is because it is primarily a measurement of functional gas exchange surface area (and not the rate at which CO disappears). Other drugs that can cause lung diseases include amphotericin, methotrexate, cyclophosphamide, nitrofurantoin, cocaine, bleomycin, tetracycline, and many of the newer biologics. Dlco is the product of Va and Kco, the rate of diffusion across a membrane that is dependent upon the partial pressure of the gas on each side of the alveolar membrane. During the breath-hold period of the single-breath diffusing capacity maneuver the mouthpiece is usually closed by a shutter or valve. This by itself would be a simple reason for KCO to increase as lung volume decreases but the complete picture is a bit more complicated. You are currently on the The result of the test is called the transfer factor, or sometimes the diffusing capacity. z-score -1.5 to -1.645 or between 75 and 80 percent of predicted), the correlation with the presence or absence of clinical disease is less well-defined. please choose your country or region. weakness) then the TLCO is low but the KCO is normal or increased. At the time the article was last revised Patrick J Rock had no recorded disclosures. In defence of the carbon monoxide transfer coefficient KCO (TL/VA). 0000008215 00000 n 2023-03-04T17:06:19-08:00 How about phoning your consultants secretary in about ten days time? Simultaneously however, the pulmonary capillaries are also stretched and narrowed and the pulmonary capillary blood volume is at its lowest. As one might postulate, a proportional decrease in Dlco would be expected if there were a reduction in lung volume and hence alveolar surface area, as seen in patients after pneumonectomy. A test of the diffusing capacity of the lungs for carbon monoxide (DLCO, also known as transfer factor for carbon monoxide or TLCO), is one of the most clinically valuable tests of lung function. The ATS/ERS standards for DLCO of course contraindicate either Valsalva or Muller maneuvers during the breath-hold period because they do affect the pulmonary capillary blood volume (and therefore the DLCO). H Little use without discussion with your consultant. As an example, if a patient had a pulmonary emboli that blocked blood flow to one lung then DLCO would be about 50% of predicted, but in these circumstances KCO would also be 50% of predicted. Physiology, measurement and application in medicine. In the setting of a normal chest radiograph, early ILD or pulmonary vascular disease or both can be present. A low KCO can be due to decreased perfusion, a thickened alveolar-capillary membrane or an increased volume relative to the surface area. The Fick law of diffusion can explain factors that influence the diffusion of gas across the alveolar-capillary barrier: V is volume of gas diffusing, A is surface area, D is the diffusion coefficient of gas, T is the thickness of the barrier, and P1P2 is the partial pressure difference of gas across the alveolar-capillary barrier. inhalation to a lung volume below TLC), then DLCO may be underestimated. When factored in with a decrease in alveolar volume (which decreases the amount of CO available to be transferred), the rate at which CO decreases during breath-holding (for which KCO is an index) increases. Thank you for your informative PFT Blog! Because CO in the pulmonary capillary compartment is usually close to zero, the partial pressure gradient of CO across the alveolar-capillary integrated interface, or membrane, is estimated to be partial pressure of CO in the alveolar compartment alone (or atmospheric pressurewater vapor pressure at 37C). useGPnotebook. 28 0 obj Respiratory tract symptoms and abnormalities on chest radiographs and/or chest computed tomography (CT) scans are essential to properly interpret any PFT, including Dlco. endobj DLCO is the volume of CO that is absorbed during breath-holding. Am Rev Respir Dis 1981; 123:185. The diffusing capacity for nitric oxide (D lNO ), and the D lNO /D lCO ratio, provide additional insights. You then hold your breath for a minimum of 8 seconds, then breathe out steadily into the machine.You will need to do this a few times, with a pause of a few minutes in between. Reference Source: Gender: Optional Observed Values Below Enter to calculate Percent Predicted FEV1 (L): FEF25-75% (L/s): FEV1/FVC%: Hence, seeing a low Kco would be a clue that the patient with neuromuscular disease has a concomitant disease or disorder that impairs gas exchange (ie, pulmonary fibrosis or pulmonary vascular disease) on top of the lower alveolar volume. A more complex answer is that because vascular resistance increases, cardiac output will be diverted to the pulmonary circulation with the lowest resistance. xokOpcHL# Ja3E'}F>vVXq\qbR@r[DUL#!1>K!-^L(_qG@'t^WDb&R!4Ka7|EtpfUP3rDKN"D]vBYG2dQ@@xVk*T=3%P0oml J l, 2023-03-04T17:06:19-08:00 monitor lung nodules). A low VA/TLC ratio (less than 0.85) indicates that a significant ventilation inhomogeneity is likely present. 0000126565 00000 n If the patients VC is less than 2.0 L, it is recommended that the washout volume be reduced to 0.5 L. The averages of the 2 Dlco measurements must be within 10% of each other. Authors: For example, if the patient has a disease that causes a decrease in lung surface area, or has had a lung removed, then there is a decrease in transfer factor but there is a normal KCO. The American Thoracic Society/European Respiratory Society statement on PFT interpretation advocates the use of a Dlco percent predicted of 80% as the normal cutoff. Do you find that outpatient rehabilitation is effective for your patients with multiple sclerosis? Find out how we produce our information. I have had many arguments about KCO over the years and have tried my hardest to stop physicians using the phrase TLCO is normal when corrected for lung volume yuk. Reference article, Radiopaedia.org (Accessed on 05 Mar 2023) https://doi.org/10.53347/rID-80732. KCO is only a measurement of the rate at which CO disappears during breath-holding (i.e. Subgroups of patients with asthma, emphysema, extrapulmonary lung disease, interstitial lung disease and lung resection were identified. During inspiration the amount of negative pressure inside the lung will be the product of inspiratory flow and airway resistance. This has had the unintended consequence of many clinicians considering Dlco/Va to be the Dlco corrected for the Va, when it is actually Kcoa rate constant for CO uptake in the lung. Accessed April 11, 2016. The term DL/VA is misleading since the presence of VA implies that DL/VA is related to a lung volume when in fact there is no volume involved. Eur Respir J. 71 0 obj <>stream Respir Med 1997; 91: 263-273. Whenever Dlco is reduced, the predominant reason for this reduction (eg, whether it is predominantly a reduced Va, or reduced Kco, or both) has critical diagnostic and pathophysiologic implications. [43 0 R] Va is calculated by a change in the concentration of an inhaled inert gas (such as helium or methane) after that gas has had an opportunity to mix throughout the lungs. 0000002152 00000 n Kiakouama L, Cottin V, Glerant JC, Bayle JY, Mornex JF, Cordier JF. eE?_2/e8a(j(D*\ NsPqBelaxd klC-7mBs8@ipryr[#OvAkfq]PzCT.B`0IMCruaCN{;-QDjZ.X=;j 3uP jW8Ip#nB&a"b^jMy0]2@,oB?nQ{>P-h;d1z &5U(m NZf-`K8@(B"t6p1~SsHi)E When the heart squeezes, it's called a contraction. practitioner should be consulted for diagnosis and treatment of any and all medical conditions. Hughes JMB, Pride NB. When significant obstructive airways disease is present however, VA is often reduced because of ventilation inhomogeneity. The test is performed as described for the transfer factor; in addition the inhaled gas contains 10% helium. The answer is maybe, but probably not by much. To one degree or another a reduced VA/TLC ratio is an artifact of the DLCO measurement requirements. PFT Blog by Richard Johnston is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License. Despite this, Va typically approximates TLC within a few percentage points (Va/TLC>95%) in the normal lung. CO has a 200 to 250 times greater affinity for hemoglobin than does oxygen. Check for errors and try again. A gas transfer test measures how your lungs take up oxygen from the air you breathe. At this time the alveolar membrane is stretched and at its thinnest which reduces the resistance to the transport of gases across the membrane. 0000019293 00000 n K co will be greater than 120% predicted in case 1, 100120% in case 2, and 40120% in case 3, depending on pathology. 31 0 obj <> endobj 22 (1): 186. I):;kY+Y[Y71uS!>T:ALVPv]@1 tl6 Rearranging this equation gives us a way to determine Va from carefully measured values of Vi, He, As Marie Krogh first modeled in 1915, CO leaves the alveolar space at an exponential rate related to the gradient of CO between the alveolar compartment and the pulmonary capillary compartment. %%EOF Citation: Immune, Lipid Biomarkers May Predict Onset of Atopic Dermatitis in Infants, Treatment for Type 2 Diabetes Reduces Major CV Events in Men, Inflammation Reduction Medications May Lower Dementia Risk in Patients With Rheumatoid Arthritis, Sepsis Increases Risk of Post-Discharge Cardiovascular Events, Death, AHA Releases Statement on Hypertension Induced by Anticancer Therapy, Consultant360's Practical Updates in Primary Care. In the first 0000005039 00000 n However, at the same time despite the fact that KCO rises at lower lung volumes (i.e. Carbon monoxide transfer coefficient (transfer factor/alveolar volume) in females versus males. Overlooking a reduced Dlco can delay early diagnosis and treatment of a disease. K co and V a values should be available to clinicians, as Using and Interpreting Carbon Monoxide Diffusing Capacity (Dlco) Correctly. For DLCO values that are close to the lower limit of the normal range (eg. Chest 2004; 125: 446-452. van der Lee I, Zanen P, van den Bosch JMM, Lammers JWJ. xb```c`` b`e` @16Y1 vLE=>wPTPt ivf@Z5" A fit young adult may have a KCO of approximately 1.75 mmol/min/kPa/litre, an elderly adult may be about 1.25. When Dlco is below the predicted reference range (75% to 140% of predicted) it becomes a clue to the presence of a physiologic problem that ultimately may impair exercise, and even affect long-term survival from common lung diseases and disorders. I dont know if this is the case for pulmonary veno-occlusive disease and pulmonary capillary hemangiomatosis since they are both rare and under-diagnosed. You will be asked to take in a big breath through a mouthpiece while wearing a nose clip. Registered charity in England and Wales (326730), Scotland (SC038415) and the Isle of Man (1177). White blood cells, also called leukocytes, are a key part of your immune system. This observation underscores the need for chest CT for confirming the diagnosis of ILD. Additionally, Dlco may predict mortality in a variety of lung diseases (including cancer), various ILDs (including idiopathic pulmonary fibrosis), and severe PAH. <>stream Hughes JMB, Pride NB. Using DL/VA (no, no, no, its really KCO!) Scarring and a loss of elasticity causes the lung to become stiffer and harder to expand which decreases TLC. Webdicted normal values, that is, those recommended by Cotes (1975). x. Best, In addition, there is an implicit assumption is that DLCO was normal to begin with. Because it is not possible to determine the reason for either a low or a high KCO this places a significant limitation on its usefulness. This ensures that Dlco remains relatively constant at various volumes from tidal breathing to TLC. This estimates the lung surface area available for gas exchange. (I am the senior scientist in he pulmonary lab). Hi Richard. Kaminsky DA, Whitman T, Callas PW. 0000016132 00000 n Routine reporting of Dlco corrected to normal with Va without fully understanding the implications is misleading and can cause clinicians to lose their clinical index of suspicion and underdiagnose diseases when in fact Dlco still is abnormal. This parameter is useful in the interpretation of a reduced transfer factor. After elimination of estimated dead-space exhaled breath, a volume of exhaled breath is sampled to measure test gas concentrations (, Va is calculated by a change in the concentration of an inhaled inert gas (such as helium or methane) after that gas has had an opportunity to mix throughout the lungs. You suggest that both low V/high Q and high V/low Q areas are residing in these patients lungs. 0000020808 00000 n It is important to remember that the VA is measured from an expiratory sample that is optimized for measuring DLCO, not VA. The normal values for KCO are dependent on age and sex. 16 0 obj A reduced Dlco (primarily from reduction in Kco) is a useful tool for detecting early ILD before lung volumes become decreased, for detecting pulmonary vascular diseases from venous thromboembolism or PAH, and for monitoring response to therapy and disease progression. These individuals have an elevated KCO to begin with and this may skew any changes that occur due to the progression of restrictive or obstructive lung disease. A fit young adult may have a KCO of approximately 1.75 mmol/min/kPa/litre, an elderly Hemangiomatosis is accompanied with a proliferation of pulmonary capillaries and fibrosis while veno-occlusive disease isnt. decreased DMCO). Given the fact that these disorders affect the pulmonary circulation I wouldnt be surprised to see a wide degree of Q heterogeneity but Im not certain I see a cause for a high degree of V heterogeneity. I am 49, never smoked, had immunosuppressant treatment for MS last year but otherwise healthy I had thought. Your email address will not be published. Similarly, disease states that result in loss of alveolar units, such as pneumonectomy, lobectomy, or lobar collapse as reflected by a low Va can reduce Dlco. Every clinician knows that Dlco measures the quantity of carbon monoxide (CO) transferred per minute from alveolar gas to red blood cells (specifically hemoglobin) in pulmonary capillaries, and that this value, expressed as mL/min/mm Hg, represents mL of CO transferred per minute for each mm Hg of pressure difference across the total available functioning lung gas exchange surface.1 But has anyone stopped to ask why Dlco measurement is ordered, how it is determined, and what it means when it is reduced or not? Johnson DC. Saydain G, Beck KC, Decker PA, Cowl CT, Scanlon PD. WebEnter Age, Height, Gender and Race. Standardized single breath normal values for carbon monoxide diffusing capacity. For a given gas, the rate of diffusion for this gas, Dl, is dependent upon the thickness of the diffusing membrane (DM, the alveolar-capillary membrane), the rate of uptake of a gas by red blood cells, , and the pulmonary capillary blood volume, Vc. Unable to process the form. It also indicates that 79% to 60% of predicted is a mild reduction, 59% to 40% is a moderate reduction, and that Dlco values less than 40% of predicted are severely reduced. KCO has an extremely limited clinical utility and frankly if it wasnt reported at all there would be little to no difference in how DLCO results would be interpreted. As lung volume decreases towards FRC, the alveolar membrane thickens which increases the resistance to gas transport but this is more than counterbalanced by an increase in pulmonary capillary blood volume. 0000002120 00000 n Could you please make a quick table to compare between DLCO and KCO to make it easier for us to understand the difference between both of them ( i.e definition, factors they depend on, condition which make them high / low , etc ). Rearranging this equation gives us a way to determine Va from carefully measured values of Vi, Hei, and Hee: Unlike TLC, Va is calculated from a single breath. In the normal lung KCO tends to increase at lung volumes below TLC because of a decrease in alveolar volume (less CO to transfer per unit of volume) and an increase in capillary blood volume per unit of alveolar volume. At TLC alveolar volume is at its greatest but pulmonary capillary blood volume is at least somewhat constrained. Spirometer parameters were normal. At least 1 Kco measurement <40% of predicted values; 2. Low Dlco less than or equal to 50% predicted can predict hypoxemia with exercise. But a cornucopia of lung disorders that disturb oxygen uptake by hemoglobin in the lungs (and increase the work of breathing, perceived as dyspnea) can be detected by a reduction in Dlco. Therefore, Dlco is defined as follows: Pb is atmospheric pressurewater vapor pressure at 37C, and Kco is kco/Pb. In my labs software predicted KCO is derived from [predicted DLCO]/[Predicted TLC-deadspace] but the DLCO and TLC come from entirely different studies and different populations. Therefore, the rate of CO uptake is calculated from the difference between the initial and final alveolar CO concentrations over the period of a single breath-hold (10 seconds). 24 0 obj What is DLCO normal range? Amer J Respir Crit Care Med 2012; 186(2): 132-139. pbM%:"b]./j\iqg93o7?mHAd _42F*?6o>U8yl>omGxT%}Lj0 The Va/TLC ratio does not depend on age, sex, height, or weight but decreases when there is intrapulmonary airflow obstruction and/or uneven distribution of ventilation.