Respiratory Physiology of Pregnancy and Functional Diagnosis in Asthma

The transport of oxygen through the placenta is a complex process and the greatest danger to the fetus of a pregnant woman with asthma is insufficient therapy and control of asthma. Most diagnostic procedures for evaluating the function of the respiratory system during pregnancy are not harmful to the fetus. Except for the forced expiratory volume in the first second, the other pulmonary function tests are reduced and decrease with the progress of pregnancy. Hyperventilation and dyspnea are normal phenomena, and pregnancy is not a contraindication for stopping exercise. However, in case of severe dyspnea, additional diagnostic tests should be performed. Bronchoprovocation tests, ventilation-perfusion scintigraphic scans and cardio-pulmonary stress tests should be avoided, and forced expiratory tests should also be avoided in the later stages of pregnancy. Daily measurement of peak expiratory flow is simple, safe, inexpensive, and very informative in determining the control and therapy of pregnant women’s asthma.

Keywords: Asthma; Pregnancy; Respiratory physiology; Functional diagnostics

Abbreviations: FRC-Functional residual capacity; ERV-Expiratory reserve volume; TLC-Total lung capacity; FVC-Forced vital capacity; FEV1%- Forced expiratory volume in 1 second; PEF-Peak expiratory flow; V′E-Minute ventilation; VT-Tidal volume; Pga-gastric pressure; Poes-oesophageal pressure; TLCO-transfer capacity of the lung for the uptake of carbon monoxide; DLCO-diffusing capacity of the lungs for carbon monoxide; PaO2- partial pressure of oxygen in arterial blood FEF25-75%-forced expiratory flow over the middle one-half of the forced vital capacity; PaCO2-partial pressure of carbon dioxide in arterial blood; DO2-oxygen delivery; sO2-oxygen saturation; Hgb-hemoglobin; SV-specific ventilation; VO2-oxygen consumption; C(a-v)O2-arterial-venous oxygen content difference; CO-carbon monoxide; SVO2-mixed venous oxygen saturation; 2,3 DPG-2,3 diphosphoglyceric acid; FeNO-fractioned exhaled nitric oxide; ppb-parts per billion