|Year : 2002 | Volume
| Issue : 12 | Page : 607-12
Effect of body posture on dynamic lung functions in young non-obese Indian subjects.
A Talwar, S Sood, J Sethi
Department of Physiology, Pt B. D. Sharma Post Graduate Institute of Medical Sciences, Rohtak-124001,
|Date of Acceptance||15-Apr-2002|
Department of Physiology, Pt B. D. Sharma Post Graduate Institute of Medical Sciences, Rohtak-124001
Flow volume loop and its various indices can be used to diagnose UAO. Change in posture from sitting to horizontal position per se causes a decrease in effort dependent inspiratory and expiratory flow rates but no significant change in upper airway obstruction indices. Thus, measurement of FVL in supine posture may be used to detect UAO as it may be missed if spirometry is performed in sitting posture.
Keywords: Adult, Body Weight, physiology,Comparative Study, Forced Expiratory Volume, physiology,Human, Male, Maximal Expiratory Flow-Volume Curves, physiology,Posture, physiology,Respiratory Mechanics, physiology,
|How to cite this article:|
Talwar A, Sood S, Sethi J. Effect of body posture on dynamic lung functions in young non-obese Indian subjects. Indian J Med Sci 2002;56:607
Maximal expiratory flow volume curves have become an essential tool to assess various dynamic lung function parameters in humans. Although highly reproducible details in flow volume loop (FVL) configuration are reported but they have been demonstrated to be highly individualistic to an extent so as to constitute a near finger print like specificity of airway mechanics in an individual subject.
Upper airway obstruction (UAO) is relatively in frequent cause of obstruction to airflow as compared to obstruction of lower airways but, is important since upper airway obstruction may produce respiratory failure. There has been a need for a simple, inexpensive and noninvasive diagnostic test to evaluate functional and an atomic narrowing of upper airways as most of these obstructing lesions require sophisticated endoscopic technique or highly advanced imaging procedures. Conventional lung function tests mostly don't disclose the extent or the severity of upper airway pathology. The role of FVL is emerging in defining anatomical upper airway obstruction by using simple dry spirometer in routine pulmonary function laboratory. However, role of FVL in predicting functional upper airway narrowing e.g. in sleep apnea syndrome is still controversial. Studies have confirmed that in normal awake subjects oropharyngeal passage of airways have a smaller diameter in lying than in sitting posture with no further change in supine as compared to lateral lying position.
Sunderam et aI stressed on the importance of FVL measurement in supine posture in diagnosing UAO which may be missed if spirometry is performed in sitting posture, but the effect of horizontal posture on FVL derived parameters has not been reported in non-obese Indian subjects.
This study is aimed to determine the effect of horizontal body positions on FVL and various derived parameters from it and upper airway indices in normal young non-obese Indian subjects.
| ¤ MATERIALS and METHODS|| |
Twenty four normal healthy, nonsmoking males were selected for study with the mean age 21.08±3.5 years, mean body weight 63.1±9.63kg, height 170.2±6.2 cm and BMI 21.57±2.43. None of the subjects had any history of cardio-respiratory disease, an upper airway disorder, disease of the spine or respiratory tract infection in the recent past.
In all the subjects, flow volume curves were measured in the morning using vitalograph-compact having Fleisch type pneumotachograph in four different postures i.e. Sitting, supine, right lateral and left lateral recumbent positions in a random sequence. A ten minutes rest was given between recording in any two postures to avoid any fatigue. In each body posture the subjects performed three maximum forced expiratory and inspiratory maneuvers. It was made sure that subjects understood the instructions and performed the test with maximum inspiration followed by a forced and smooth exhalation followed again by inhalation using quick maximal effort. All the subjects were familiarized with the technique of the test The subjects performed the test repeatedly until the sum of FEV1 and FVC for at least three maneuvers was with in 5% of best sum. The following parameters were included in the study: FEV1, FEV0.5, FVC, FEF50, FEF0.2-1.2,, FEF25-75, FEF75-85, PEF, PIF, FIF50, MVV. The upper airway obstruction indices calculated were: FEV1/FEV0.5 ratio (unit less), FEV1/PEF ratio (mL/L/min), PEF/ PIF ratio (unit less) and FEF50/FIF50 ratio (unitless).
Statistical methods: Parameters were expressed as mean values±standard deviation (S.D.) Analysis of variance for repeated measures was used to determine the effect of body postures on various parameters and upper airway indices. IF ANOVA revealed statistical significance, Duncan's multiple range test was used to compare the difference between body postures to determine the level of statistical significance. A difference when p was <0.05 was considered significant.
| ¤ Results|| |
The decrease in mean FVC(p<0.01), FEV1(p<0.01), FEV0.5(p<0.001), PEF (p<0.01), FEF50(p<0.001), FEF0.2-1.2 (p<0.001), PIF(p<0.01), FIF50(p<0.01) was statistically significant in all the three horizontal postures compared with the sitting posture, but, there was no stastistically significant difference among the three horizontal postures. FEV./FVC, FEF25-75 and FEF75-85 showed no significant difference in any of the four body positions [Table - 1]. No significant difference in mean FEV1/FEV0.5, PEF/PIF, FEF50/FIF50 and FEV1/PEF were observed among any of the four body postures. [Table - 2]
| ¤ Discussion|| |
Flow volume loop has been recognised as available test for detection and assessment of upper airway obstruction by Miller and Hyatt. Forced inspiratory and forced expiratory maneuvers produce changes in transmural pressures which bring about changes in calibre of collapsible part of upper airways and effort dependent inspiratory and expiratory flows which are exaggerated in the presence of upper airway lesion. Changes in these flow rates on assuming any of the three horizontal positions was studied in the present study.
The results show that in normal subjects each of the measured maximum inspiratory and expiratory flow rates decreased when they assumed any of the horizontal postures compared to sitting posture except FEF25-75 and FEF75-85 [Table - 1], but the upper airway obstruction indices did not change significantly with recumbency [Table - 2]. None of the subjects developed a flow plateau on the maximal inspiratory and expiratory flow volume curves.
Shephard and Burger reported that a change in body position from upright to supine in patients with obstructive sleep apnea syndrome was associated with decrease in FVC, FEV1 but no change in FEV1/FVC ratio. There was no inspiratory flows (FIF25, FIF50, FIF75), but there was a small reduction in expiratory flow rates in supine posture in obstructive sleep apnea syndrome (OSAS) patients suggesting the possibility that expiratory airflow resistance increased in these patients. Data on effect of recumbency in control subjects was however, not available.
Masumi et al measured FIF25_75 (forced inspiratory flow between 25% and 75% of vital capacity) and documented significant reduction in airflow in supine posture. The presumed mechanism was gravity causing an approximation of tongue and soft palate relative to the posterior unmovable pharyngeal wall. This parameter was not recorded in the present study.
In the present study the decrease in flow rates in the three recumbent positions could not be attributed to fatigue as the order in which the test was performed in different body positions was kept at random. Also a ten minutes rest was given between the test done in any two body positions.
Position of the neck was kept constant with regards to both the neck flexion-extension and head rotation as neck position may alter the longitudinal tension on the trachea and thus tracheal stiffness which may affect expiratory flow rates.
Change in effort dependent maximum inspiratory and expiratory flow rates could be due to increase in the resistance of upper airways on assuming horizontal postures as the pharyngeal size decreased significantly in supine posture as compared to upright posture in norma1, and in OSAS patients. This decrease is attributed to gravitational forces acting on the tongue and soft palates and is not related to posture related decrease in functional residual capacity.
This extrathoracic mechanism could contribute to decrease in forced inspiratory flow rates, but not the forced expiratory flow rates especially the less effort dependent FEV and FEF50.
Addition of supine FVLs increased the sensitivity of the FVL for detecting upper airway obstruction in patients with OSAS. Nahmias and Karetzy reported that increased proportion of patients of OSAS showed flattening of maximum inspiratory flow volume curves in supine position but no change in FVC or FEV1. Shore and Millman suggested that position alters the configuration of the upper airways and sensitivity and specificity of FVL for diagnosing of OSAS were higher when loops were recorded in supine than in sitting position. Sunderam et al reported the importance of supine FVL measurement in a case of Hashimoto's thyroiditis.
Most probable explanation for recumbency induced change in flow rates is a decrease in lung volume. Recumbency produces a decrease in Total lung capacity, Residual volume and vital capacity, these changes are small and are related mainly to increase in intrathoracic blood volume so the flow rates also decrease with decreasing lung volume. A reduction in forced vital capacity and PEF and FEF50 in the supine posture was correlated by Elliot et al in the astronauts. In our study also, FVC decrease by 6.76 to 10.04% was associated with a reduction in PEF by 8.32 to 9.50% and FEF50 by 8.17 to 9.76% depending on different horizontal positions.
There was no change in FEF25-75 and FEF75-85 on assuming any of the three horizontal positions as compared to sitting position. At smaller lung volumes, intrathoracic airways are compressed and flow then depends on elastic recoil of lungs alone and is dependent of effort.
Although all the measured inspiratory and expiratory flow rates decreased with recumbency the upper airway indices derived from these flow rates did not change significantly in any of the horizontal postures as compared to sitting posture. The mean values of the derived UAO indices compare well to those reported earlier,, As there was no change in the value of UAO indices with recumbency this indicates that the flow rates which constituted these ratios decreased proportionately with horizontal postures. These indices can thus be used to indicate the presence or absence of UAO in recumbent postures. Measurement of FVL in supine posture may increase their sensitivity to detect upper airway obstruction.
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[Table - 1], [Table - 2]