Lung volume & capacity during pregnancy

Lung volume & capacity during pregnancy


Acceptable spirograms demonstrate good test initiation (eg, a quick and forceful onset of exhalation), no coughing, smooth curves, and absence of early termination of expiration FRC is measured using gas dilution techniques or body-box plethysmography. Gas dilution techniques include nitrogen washout and helium equilibration. With nitrogen washout, the patient exhales to FRC and then breathes from a spirometer containing 100% O2. The test ends when the exhaled nitrogen concentration is zero.

The collected volume of exhaled nitrogen is equal to 81% of the initial FRC. With helium equilibration, the patient exhales to FRC and then connects to a closed system containing known volumes of helium and O2. Helium concentration is measured until it is the same on inhalation and exhalation, indicating it has equilibrated with the volume of gas in the lung, which is estimated by helium dilution

the patient inhales as deeply as possible, seals his lips around a mouthpiece, and exhales as forcefully and completely as possible into an apparatus that records the exhaled volume Flow rate and lung volume measurements can be used to differentiate obstructive from restrictive pulmonary disorders, to characterize disease severity, and to measure responses to therapy.

Pregnancy similarly has minor effects on spirometric indices. The total lung capacity and the VC remain unchanged, but the FRC decreases by 10-25 %. This similarly may lead to airway closure in the normal tidal breathing range. Measurements are typically reported as absolute flows and volumes and as percentages of predicted values derived from large populations of people presumed to have normal lung function.

changes to the mucosal vasculature of the respiratory tract lead to capillary engorgement and swelling of the lining in the nose, oropharynx, larynx, and trachea. Symptoms of nasal congestion, voice change and upper respiratory tract infection may prevail throughout gestation. Forced expiratory volume measures how much air a person can exhale during a forced breath. The amount of air exhaled may be measured during the first (Forced expiratory volume 1), second (Forced expiratory volume 2), and/or third seconds (Forced expiratory volume 3) of the forced breath.