RV, FRC, TLC

VT tidal volume during normal, quiet breathing ERV expiratory reserve volume FRC functional residual capacity EVC expiratory vital capacity IVC inspiratory vital capacity TLC total lung capacity

RV - residual volume

The volume of the lung after maximal exhalation started from the functional residual capacity.

• In children and adolescents residual volume grows slightly faster than the total lung capacity, mostly on account of changes in chest geometry (references below).
• In healthy adults RV increases with age since a maximal expiration is increasingly impeded by airway closure, preventing dependent alveoli from emptying. In contrast, the total lung capacity does not change with age in adults. As a result the VC decreases with age in healthy subjects.
• Small airway pathology (inflammation, accumulation of secretions, hypertrophy and hyperplasia of glands and smooth muscles) and loss of lung elastic recoil (and therefore diminished elastic stretch of small airways) lead to premature airway closure during a maximal expiration; this causes the RV to increase, and the VC to decrease. Any factors that influence the TLC also affect the VC.

In patients with airway obstruction an FVC maneuver usually ends at a higher lung volume than a maximal expiration started from FRC level; only in the latter instance should end-expiratory volume be called RV.

Recommended procedures:

1. Quanjer PhH, Tammeling GJ, Cotes JE, Pedersen OF, Peslin R, Yernault JC. Lung volumes and forced ventilatory flows. Official Statement of the European Respiratory Society. Eur Respir J 1993; 6 suppl. 16: 5-40. Erratum Eur Respir J 1995; 8: 1629.

FRC - functional residual capacity

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The FRC, the volume of gas contained in the lung after a normal expiration, is mainly determined by the interaction between elastic recoil of the chest and lungs (animation on the left).

In the newborn both the thorax and lung are very compliant, so that the FRC is very small. Particularly in the supine posture, when the diaphragm is pushed up by the abdominal contents, gas transport is hampered by the occurrence of airway closure. Newborns elevate their FRC by glottis closure and by postinspiratory stimulation of inspiratory muscles during expiration.

Increased FRC in airway obstruction
In severe airway obstruction many lung compartments may be incapable of emptying due to airway closure. In addition expiratory flow may be so limited that insufficient time is available to reach the lung volume that would be obtained in the case of elastic equilibrium between lung and chest. This gives rise to a higher endexpiratory volume and a concomitant increase in elastic recoil pressure (pleural pressure falls), slight widening of the airway due to the larger distending pressure and hence some benefit to expiratory flow. The endexpiratory volume increases to the point where a new dynamic equilibrium is reached between inspiratory and expiratory tidal volume. It follows that severe airway obstruction is associated with an increase in FRC (hyperinflation). If FRC is normal in a patient with airway obstruction when at rest, it may increase during exercise; due to flow limitation the time available for lung emptying may not suffice at the increased tidal volume.

Diminished FRC
A low FRC occurs in restrictive ventilatory defects. The FRC also diminishes in the supine posture because the abdominal contents the push the diaphragm upwards; this phenomenon is most pronounced with space occupying intra-abdominal processes (e.g. pregnancy, hepatosplenomegaly, ascites). Unilateral paralysis of the diaphragm is usually not associated with a change in the FRC; bilateral paralysis of the diaphragm is associated with a smaller FRC in both the sitting and supine posture.

Recommended procedures:

Quanjer PhH, Tammeling GJ, Cotes JE, Pedersen OF, Peslin R, Yernault JC. Lung volumes and forced ventilatory flows. Official Statement of the European Respiratory Society. Eur Respir J 1993; 6 suppl. 16: 5-40. Erratum Eur Respir J 1995; 8: 1629.

VT tidal volume during normal, quiet breathing ERV expiratory reserve volume FRC functional residual capacity EVC expiratory vital capacity IVC inspiratory vital capacity TLC total lung capacity

TLC - total lung capacity

The total lung capacity, i.e. the volume of gas contained in the lung after a full inhalation, is determined by a number of factors:

• Normal mental function, so that the subject is capable of performing a full inspiratory maneuver.
• Intact neuromuscular apparatus (think e.g. of poliomyelitis, amyotrophic lateral sclerosis), no inhibition due to pain.
• Normal shape, mobility and elasticity of the thorax (abnormalities due e.g. to Bechterew’s disease, kyphosis, kyphoscoliosis, osteoporosis with collapsed vertebrae, sclerodermia, exceptionally extreme overweight).
• Normal elastic properties of the lung (increased TLC in pulmonary emphysema, decreased TLC in interstitial fibrosis, pleural fibrosis) and normal airway patency (atelectasis e.g. due to an obstructing tumor may lower the TLC);
• Normal thoracic content (disturbances include e.g. pleural effusions, cardiomegaly, pulmonary edema, pneumonectomy or lobectomy).

A restrictive ventilatory defect is associated with a diminished TLC, a very compliant lung with an enlarged TLC. An increased TLC is also observed in children who had asthma from childhood on (ref. 1), or who were born and raised at altitude. In adults the TLC is unaffected by age (ref. 2).

RV, FRC and TLC can't be measured through spirometry. They are measured using a Helium dilution, a Nitrogen wash-out or a bodyplethysmography.

Ref. 1 - Large lungs and childhood asthma

1. Greaves IA, Coleman HJH. Large lungs after childhood asthma: a consequence of enlarged airspaces. Aus NZ J Med 1985; 15: 427-434.
2. Kraemer R, Meister B, Schaad UB, Rossi E. Reversibility of lung function abnormalities in children with perennial asthma. J Pediatr 1983; 102: 347-350.
3. Merkus PJFM, van Essen-Zandvliet EEM, Kouwenberg JM, Duiverman EJ, van Houwelingen JC, Kerrebijn KF, Quanjer PhH. Large lungs during childhood asthma: a case-control study. Am Rev Respir Dis 1993; 148: 1484-1489.
4. Weiss ST, Tosteson TD, Segal MR, Tager IB, Redline S, Speizer FE. Effects of asthma on pulmonary function in children. A longitudinal population-based study. Am Rev Respir Dis 1992; 145: 58-64.

Ref. 2 - Longitudinal behavior of spirometric indices

1. Borsboom GJ, van Pelt W, van Houwelingen HC, van Vianen BG, Schouten JP, Quanjer PhH. Diurnal variation in lung function in subgroups from two Dutch populations: consequences for longitudinal analysis. Am J Respir Crit Care Med 1999; 159: 1163-1171.

Recommended procedures:

1. Quanjer PhH, Tammeling GJ, Cotes JE, Pedersen OF, Peslin R, Yernault JC. Lung volumes and forced ventilatory flows. Official Statement of the European Respiratory Society. Eur Respir J 1993; 6 suppl. 16: 5-40. Erratum Eur Respir J 1995; 8: 1629.