Physiological Changes of Respiratory System in Pregnancy

Pulmonary diseases are one of the major indirect causes of maternal deaths. Pregnancy is a unique physiological state during which changes occur in all systems of the body to meet metabolic needs of both the mother and growing foetus. Enlarging uterus and increasing hormonal levels cause changes in volumes and mechanics of lungs. Understanding the basic physiology of the cardiovascular and respiratory changes during pregnancy along with the pathology of disease processes are vital in making therapeutic decisions. Pre-existing conditions like asthma, tuberculosis, and acute illnesses like pneumonia, acute respiratory distress syndrome (ARDS), pneumothorax can have calamitous effect on mother and child health. Continual foetal monitoring throughout pregnancy is very important in early recognition of foetal jeopardy. Key words; Pregnancy, Pulmonary Diseases, Lung Mechanics, Asthma, Tuberculosis Raghu S, Surya Kiran P. Respiratory diseases in pregnancy. J Clin Sci Res 2015;4:149-58. DOI: http:// dx.doi.org/ 10.15380/2277-5706.JCSR.14.048. Corresponding author: Dr S. Raghu, Associate Professor, Department of TB and Chest diseases, Guntur Medical College, Chest Physician, Government Fever Hospital, Guntur, India. e-mail: [email protected] Online access http://svimstpt.ap.nic.in/jcsr/apr-jun15_files/ra215.pdf DOI: http://dx.doi.org/10.15380/2277-5706.JCSR.14.048 Received: August 21, 2014; Revised manuscript received: March 18, 2015; Accepted: March 29, 2015. INTRODUCTION In 2013 Globally, there were 289000 maternal deaths. Of these, (n=50,000;17%) India and Nigeria (n=40,000;14%) accounted for onethird of maternal deaths. Pulmonary diseases are one of the major indirect causes of maternal death. Significant physiological changes occur in pregnancy to meet metabolic needs of both mother and foetus in-situ. Getting an insight of such changes is important in making therapeutic decisions. PHYSIOLOGICAL CHANGES OF RESPIRATORY SYSTEM IN PREGNANCY First trimester changes Nasal congestion occurs at an early stage of first trimester (first 12 weeks) due to hyperaemia and glandular hyperplasia, but reaches peak at late stage in pregnancy and often disappears within 48 hours of delivery. Nasal congestion and resultant mouth breathing reduces concentrations of inhaled nitric oxide (NO), a potent mediator of pulmonary vascular tone, produced primarily in the maxillary sinuses; contributing to complications associated with snoring. Increased progesterone level is the primary cause for hyperventilation, augmented by an increased metabolic rate and carbon dioxide production in response to enlarging uterus and increasing weight. Early in the first trimester there is an increase in the subcostal angle of the rib cage and the circumference of the lower chest causing diaphragm to move up. In first trimester, there is a 20% 30% decrease in mean functional residual capacity (FRC), 3.7% decrease in mean expiratory reserve volume (ERV) and increase of nearly 9.7% mean tidal volume. Whereas residual volume (RV) shows a decrease of 21.4%, minute volume (MV) and vital capacity (VC) show an increase of 1.9% and 3.5% respectively. Closing volume and closing capacity change minimally during pregnancy. Diffusing capacity Respiratory disease in pregnancy Raghu et al