One second capacity

Synonyms

Tiffeneau's breath test; FEV1; absolute one-second capacity (FEV1); relative one-second capacity (FEV1 / FVC); forced one-second volume;

Initial descriptor

In the mid-1940s, Robert Tiffeneau developed the technology of a pulmonary function test to determine forced expiratory volume of 1st sec (FEV1)(Cockcroft 2019).

The one-second capacity is a breath test within the scope of spirometry that can be used to determine the so-called Tiffeneau index. This index is used to differentiate an obstruction from a restriction (Herold 2022) and to classify the severity of the obstruction (Bösch 2019).

The one-second capacity is differentiated between the

• absolute one-second capacity "FEV 1" (forced expiratory volume in1 sec) and the
• relative one-second capacity "rFEV 1" (forced expiratory volume in1 sec in relation to vital capacity in percent).

(Saloga 2012)

• Indications for performing one-second capacity are:

- Detection of obstruction caused by e.g. bronchial asthma, COPD, bronchiectasis, silicosis, cystic fibrosis, lung parenchymal disease such as sarcoidosis, stenosis in the large airways such as caused by a tumor (Criée 2014).

- screening in smokers

- occupational health control

- Therapy control of bronchopulmonary diseases

- Follow-up of bronchopulmonary diseases (Bösch 2019)

- Assessment of functional operability (Hahn 2010):

- FEV1 > 2 l: no increased respiratory risk.

- FEV1 0.8 - 2 l: increased perioperative risk

- FEV1 > 0.8 l: high surgical risk, independent of arterial blood gases (Larsen 2018).

• Absolute contraindications:

An absolute contraindication is all life-threatening conditions such as:

- acute fulminant pulmonary embolism

- Acute myocardial infarction (in the first 6 weeks [Bösch 2019]).

- tension pneumothorax

- large ascending aortic aneurysm (Criée 2014)

- cerebral aneurysm (Bösch 2019).

• Relative contraindications:

- abdominal / thoracic surgery within the first 1 - 4 weeks (depending on the respective findings)

- extensive pneumothorax within the first weeks

- Brain-, eye-, ear surgery (here you should consult the surgeon, because the period is variable)

- hemoptysis of unclear origin (Criée 2014)

• Disadvantages of one-second capacity:

- negative result despite existing obstruction (in this case, further examinations such as whole-body plethysmography (GKP), diffusion capacity, quantitative CT, etc. are required (Criée 2014)

- the result of the examination is highly dependent on the patient's cooperation (Herold 2022). Should one have the v. a. of decreased VC due to lack of cooperation, body plethysmography to determine TLC is indicated(Bösch 2019).

• Procedure:

Before the examination, the patient should remove or open constricting clothing, determination of body size. The actual examination takes place in a sitting position. After applying a nose clip, the patient receives the mouthpiece of the flow sensor (Criée 2014).

The patient should now inhale and exhale evenly to get used to the apparatus. He is then asked to take a brisk maximum inspiration and then immediately exhale as quickly as possible to the maximum (Herold 2022).

During maximal inspiration, inspiratory vital capacity (VC) can be measured; during forced expiration, forced vital capacity (FVC) can be measured; and within the 1st sec of forced expiration, "forced expiratory volume in the 1st sec" (FEV1 [Herold 2022]) can be measured.

FEV 1 corresponds to the absolute one-second capacity (Saloga 2012).

In addition to the measured absolute value, the relative one-second capacity related to the actual FVC (total exhaled air volume [Kasper 2015]) also plays a role (Hahn 2010).

The relative one-second capacity describes the respiratory volume measured after forced exhalation in the 1st sec in relation to the vital capacity: FEV1 / FVC in % (Bösch 2019).

FEV1 / FVC in % corresponds to the Tiffeneau- Index (Lohr 2002), describes the actual capacity in % (Hahn 2010).

The examination is repeated 3 times. The difference between the individual measurements for FEV1 and FVC should not exceed 5% (Criée 2014).

The FEV1 value is measured:

- before and 15 min after administration of a short-acting beta mimetic such as max. 400 µg salbutamol

- before and 30 min after inhalation with a fast-acting anticholinergic such as 160 µg ipratropium bromide (Criée 2014).

• Interpretation:

A decreased expiratory volume is said to occur when the index is < 70% of the predicted value (Kasper 2015). It should be noted that the target values for FEV1 are age-dependent (Herold 2022).

When the FEV1- value is decreased, it is referred to as a limitation of ventilatory flow reserve (Herold 2022). If this is the case, the quotient FEV1- value / VC should be calculated. If the quotient is normal, this indicates a restriction. If the quotient is decreased, for an obstruction (Jünger 2005).

Obstruction:

In obstruction, early onset closure of the small airways occurs during the forced breathing maneuver, trapping air peripherally (Saloga 2012), also referred to as the "air-trapping phenomenon" (Herold 2022). This creates a difference between inspiratory vital capacity and forced expiratory vital capacity (Saloga 2012).

The Tiffeneau- index is when obstruction is below the 5th percentile (Kasper 2015), i.e., when FEV1 / FVC is < LLN (< 5th percentile) (LLN = below normal limit) (Criée 2014). The severity of obstruction can also be determined:

- mild at an FEV1 ≥ 85% LLN

- moderate at an FEV1 < 85 % LLN and ≥ 55 % LLN

- severe with an FEV1 < 55 % LLN (Criée 2014).

The classification of severity for COPD according to GOLD:

• Severity I (mild):

FEV1 / FVC: < 70 %.

FEV1 (%of target): > 80 %

• Severity II (moderate):

FEV1 / FVC: < 70 %

FEV1 (%of target): 50 - 80 %.

• Severity III (severe):

FEV1 / FVC: < 70 %

FEV1 (%of target): 30 - 50 %.

• Severity IV (very severe):

FEV1 / FVC: < 70 %

FEV1 (%of target): < 30 % (Bösch 2019)

• Combined assessment of COPD according to the guideline:
  • A 1: FEV1 > 80 % of target, few symptoms
  • A 2: FEV1 < 80 % of target, few symptoms
  • B 1: FEV1 > 80 % of set point, many symptoms, 0 - 1 exacerbation or inpatient treatment / year
  • B 2: FEV1 < 80 % of set point, many symptoms, 0 - 1 exacerbation or hospitalization / year
  • C 3: FEV1 30 - 50 % of target value, high risk, few symptoms, > 1 exacerbation or inpatient treatment /year
  • C 4: FEV1 < 30 % of target value, high risk, few symptoms, > 1 exacerbation or inpatient treatment / year
  • D 3: FEV1 30 - 50 % of target value, high risk, many symptoms, > 1 exacerbation or inpatient treatment / year
  • D 4: FEV1 < 30 % of set point, high risk, many symptoms, > 1 exacerbation or inpatient treatment / year(Criée 2014).

Causes of decreased FEV 1 may include:

- Decrease in retraction force in the lungs.

- Weakness of the respiratory muscles

- Endobronchial obstruction

- Exobronchial obstruction (Herold 2022)

- Emphysema:

In this case, the FEV1 value is also reduced, but there is a kink in the early expiratory curve followed by a flatter curve. This is also called the "check valve phenomenon". If the airway is unstable, as is the case with emphysema, expiratory collapse of the small bronchioles occurs (Herold 2022).

If there is a symmetrical decrease in FEV1 and FVC on spirometry, further testing should be performed such as diffusing capacity of the lungs, measurement of lung volume, etc. (Kasper 2015).

- Artifactually normal FEV1- value:

It is possible, for example, that despite the presence of obstruction, the FEV1- value is "normal" and this is when the TLC- value is more than 100% (Kasper 2015).

Restriction:

In a restrictive ventilatory disorder, there is a decrease in vital capacity (VC [Saloga 2012]), total lung capacity (TLC) is normal (Jünger 2013), and FEV1 / FVC is usually above the age norm (Saloga 2012).

In the presence of marked restriction, the FEV1- value may also be decreased, but the Tiffeneau- index is normal (Herold 2022).

One-second capacity provides evidence of any airflow restrictions that may be present, which in turn leads to an increase in airway resistance with hyperinflation of the lungs and increased residual volume (Kasper 2015).

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