A STUDY OF FVC, PEFR AND MEP IN DIFFERENT TRIMESTERS OF PREGNANCY

Objective: Pregnancy is characterized by profound changes in the function of virtually every regulatory system in the human body. The events in pregnancy elicit one of the best examples of selective anatomical, physiological & biochemical adaptation that occurs during pregnancy & profound changes in respiratory physiology is a part of the same process. Thus this study was designed to evaluate the pulmonary function tests in 1, 2 and 3 trimesters of pregnancy & compare them with non-pregnant control group. Method: A cross-sectional study was carried in 200 healthy women in the age range of 19-35 years .The subjects were distributed in four groups, i.e control (non-pregnant) group and 1 , 2 &3 trimester pregnant groups. Number of subjects in each group is 50. We recorded respiratory parameters in control and study groups. Statistical analysis done by ‘Z’ test. Result: There was significant decrease in FVC, PEFR & MEP in all trimesters of pregnancy with maximum decrease of FVC in 1 trimester & PEFR, MEP in 2 trimester. Conclusion: The changes in pulmonary function are attributed to major adaptations in the maternal respiratory system & are also be influenced by the mechanical pressure of enlarging gravid uterus, elevating the diaphragm & restricting the movements of lungs thus hampering the forceful expiration & decrease in 1 trimester might be due to decline in alveolar Pco2 caused by hyperventilation which acts as bronchoconstrictor & due to sensitization of respiratory centre due to progesterone.


Introduction
Pregnancy is characterized by profound changes in the function of virtually every regulatory system in the human body. The events in pregnancy elicit one of the best examples of selective anatomical, physiological & biochemical adaptation that occur during pregnancy & profound changes in respiratory physiology is a part of the same process 1 .The changes in the respiratory physiology 2 are due to increasing size of the fetus with advancing gestation which constitutes a mechanical impediment to normal process of ventilation 3 & due to hormone Progesterone which increases ventilation by increasing respiratory centre sensitivity to carbondioxide as a result the tidal volume and minute ventilation is increased [4][5][6] . The physiological adaptation of the pregnant woman involves the circulatory, respiratory, digestive, renal, endocrine & metabolic systems. Their precise knowledge allows the clinician to verify the extent of the adaptation in pregnant women & helps to avoid unnecessary treatment of physiology changes misinterpreted as pathological changes in reference to pre pregnancy standards 7 . The knowledge of the expected or desired changes in pulmonary parameters is fundamental in understanding of how the disease states affect pregnancy & vice versa 8 . Also, information regarding status of pulmonary function is essential for assessment of fitness for anaesthesia 9 . The serial testing initiated early in pregnancy permits valid interpretation of pulmonary function changes with advance in gestation. The respiratory changes are adaptive in nature. In order to evaluate any respiratory ailment during pregnancy, an accurate knowledge of the physiological changes in pulmonary function during normal pregnancy is necessary. The changes in maternal pulmonary function tests during pregnancy have been reported. 10 Aim of this study was to evaluate the changes in the pulmonary functions of women in the age group of 19-

Statistical analysis:
The results were expressed as Mean + SD. Z test was used for comparison between control and study groups in consultation with statistician. A 'p' value of 0.05 or less was considered as statistically significant.

Forced Vital Capacity (FVC) in Litres:
There was statistically very highly significant decrease in FVC in 1 st (p<0.001), 2 nd (p<0.001) & 3 rd (p<0.001) trimesters of pregnancy when compared to control group. However, there was statistically significant increase in FVC of 3 rd trimester (p<0.01) as compared to 2 nd trimester of pregnancy.

Peak Expiratory Flow Rate (PEFR) in
Liters/sec: There was statistically very highly significant decrease in PEFR in 1 st (p<0.001), 2 nd (p<0.001) & 3 rd (p<0.001) trimesters of pregnancy when compared to non pregnant women. Maximum decrease was in 1 st trimester.

Maximum Expiratory Pressure in mmHg:
There was statistically significant decrease in MEP in 1 st (p<0.041), 2 nd (p<0.004) & 3 rd trimesters when compared to control group. Maximum decrease in MEP was seen in 2 nd trimester of pregnancy.
IJBAR (2012) 03(08) www.ssjournals.com    17 . In addition some degree of obstruction to the expiratory flow, especially late in pregnancy also contributes 18 . Some studies suggest, inadequate nutrition due to morning sickness, altered eating habits associated with advancing gestation that resulted in muscular weakness & the lesser force of contraction of main expiratory muscles 19 . A study by Leo R. Brancazio & workers showed that PEFR does not change with pregnancy. Not only are the absolute mean peak expiratory flow rates similar at all four times, but the mean normalized peak expiratory flow rates ( calculated by using formula PEFR (L/min) = 198.07 + 3.07 age -0.0477 age 2 + 3.6 height ) in all groups are close to unity 19 .

MEP:
Our study showed significant decrease in MEP from 1 st trimester to 3 rd trimester as compared to control with maximum decrease in 2 nd trimester.

Conclusion
The significant decrease in FVC & PEFR might be due to the mechanical pressure of enlarging gravid uterus, elevating the diaphragm & restricting the movements of lungs thus hampering the forceful expiration and maximum decrease in 1 st trimester due to decline in alveolar Pco 2 caused by hyperventilation which acts as bronchoconstrictor. The statistical significant decrease in PEFR & MEP in all trimesters might be due to decrease in expiratory muscle power. To establish the cause of decrease in respiratory parameters more in first trimester of pregnancy than in 2 nd & 3 rd , further studies are to be undertaken by hormonal assay in different trimesters to know the relation between hormone and respiratory parameter