Lung Volume In Normal Subjects Research Articles

A study of postural variation in peak expiratory flow rates in healthy adult female subjects in South India

Background: Peak expiratory flow rate (PEFR) reflects the strength and condition of respiratory muscles and the degree of airflow limitation in large airways. PEFR shows postural variation that follows a specific pattern in asthmatics and healthy individuals has been identified. Adequate data are not available for the postural variation in normal individuals, who are students in professional courses, and had a sedentary lifestyle. Lung volumes in normal subjects were significantly higher in a standing position. Others have reported that in healthy subjects spirometric indices were higher in the standing in comparison with the sitting position whereas other studies have reported no differences between spirometric values obtained in lying, sitting, and standing positions. Hence, this study is undertaken to study the postural variation in PEFR in healthy adult female subjects in South India. Methods: PEFR was recorded in 50 adult healthy female students aged 18-23 years and studying in professional courses (MBBS, BDS, Nursing, and MSc). Mini wright's peak flow meter was used to measure the PEFR. Three readings were taken PEFR in standing and lying posture. Best of three recordings is taken as the final value. Results: PEFR is decreased in lying posture compared to standing posture in subjects studied, and the quantum of difference was noted. Conclusion: In postural changes, PEFR measurements significantly differ based on whether the measurements are taken in the standing or in the lying posture in healthy participants. The effect of posture may be of importance in recording PEFR and changing to a better posture may be especially useful for those patients with weak expiration.

CPAP Reduces Inspiratory Work More Than Dyspnea During Hyperinflation With Intrinsic PEEP

Hyperinflation with intrinsic positive end-expiratory pressure (PEEPi) loads the respiratory muscles and causes dyspnea in obstructive lung disease. Continuous positive airway pressure (CPAP) has shown some efficacy in reducing inspiratory work and dyspnea. However, in obstructive lung disease, inspiratory work and dyspnea may be increased by additional factors that may not be affected by CPAP. Therefore, to study the effects of hyperinflation with intrinsic PEEP and CPAP in isolation, we used a mechanical analog of airway closure to increase end-expiratory lung volume in normal subjects. In five subjects in whom inspiratory work was measured, increasing end-expiratory lung volume by 1 and 2 L increased inspiratory work per breath from 0.42 +/- 0.04 J to 1.17 +/- 0.15 J (p < 0.05 compared with baseline) and 1.58 +/- 0.22 J (p < 0.05 compared with baseline and to the lesser level of hyperinflation). Although CPAP reduced work per breath and per minute to levels not significantly different from baseline, it had little effect on dyspnea. In ten subjects hyperinflated to 2.4 +/- 0.12 L above FRC, breathing could be sustained 19.5 +/- 4.5 min before quitting the load. This was increased to 26.7 +/- 5.2 min by 10 cm H2O CPAP (p = 0.052). Inspiratory dyspnea was modestly reduced by CPAP during these endurance trials. We conclude that CPAP can substantially ameliorate the respiratory work load induced by hyperinflation with intrinsic PEEP. However, the effects of CPAP on dyspnea and endurance are more limited. This suggests that the limits to breathing at high lung volumes are related to factors in addition to respiratory muscle work, and that CPAP may be of more value in reducing the work than in relieving the distress of obstructive lung disease.

Effect of volume history on changes in DLcoSB-3EQ with lung volume in normal subjects.

The purpose of this study was to determine the relationship between the three-equation diffusing capacity for carbon monoxide (DLcoSB-3EQ) and lung volume and to determine how this relationship was altered when maneuvers were immediately preceded by a deep breath. DLcoSB-3EQ maneuvers were performed in nine healthy subjects either immediately after a deep breath or after tidal breathing for 10 min. The maneuvers consisted of slow inhalation of test gas from functional residual capacity to 25, 50, 75, or 100% of the inspiratory capacity and, without breath holding, slow exhalation to residual volume. After either a deep breath or tidal breathing, we found that DLcoSB-3EQ decreased nonlinearly with decreasing lung volume. At all lung volumes, DLcoSB-3EQ was significantly greater when measured after a deep breath than after tidal breathing. This effect increased as lung volume decreased, so that the greatest difference between DLcoSB-3EQ after a deep breath and that after tidal breathing occurred at the lowest lung volume. We conclude that a deep breath or spontaneous sigh has a role in reestablishing the pathway for gas exchange during tidal breathing.

The Effects of Posture on Lung Volumes in Normal Subjects and in Patients Pre- and Post-coronary Artery Surgery

Summary The effects of posture on lung volumes, including functional residual capacity (FRC), were investigated in 20 normal subjects and in 10 male patients prior to, and a mean of 78 hours (range 61–94 hours) following, coronary artery surgery. Post-operatively, FRC was reduced to a mean (± SEM) of 70% ± 3.9% of the pre-operative value (p

MEASUREMENT OF LUNG VOLUME BY MULTIPLE INDICATOR DILUTION: Testing a Modelled Hypothesis with On-line Computation

Respiratory mass spectrometry and on-line computation were used to estimate lung volume in normal subjects by a rebreathing technique, using oxygen, nitrogen and argon as indicators. The computation had previously been tested in a numerical model. In real normal lungs, it performed well enough for practical purposes, despite recognizable oversimplifications in the modelling assumptions. The differences in estimate to be expected from different composition changes between control and rebreathing were less than 100 ml, and those from different indicators within a composition change were less than 50 ml. The use of two indicators in lung volume measurement allows a correction for volume changes attributable to carbon dioxide and nitrous oxide, and a third indicator provides a degree of quality control.

Effect of ventilation and diffusion nonuniformity on DLCO (exhaled) in a lung model.

Recent studies have shown that diffusing capacities measured at multiple intervals during a single exhalation [DLCO(exhaled)] remained constant with lung volume in normal subjects, but decreased with decreasing lung volume in patients who may have had diffusion nonuniformity. We have examined the theoretical basis of these results by determining what factors affected DLCO(exhaled) in a computerized lung model in which diffusion in each compartment remained constant with lung volume. DLCO(exhaled) decreased with decreasing lung volume when a small lung region lacked diffusion. However, the change in DLCO(exhaled) with lung volume was also affected by nonuniform ventilation and these effects could not be eliminated by correcting the carbon monoxide decay and the simultaneous decay of helium. DLCO(exhaled) values were also influenced by the exhaled flow rate in the presence of nonuniform ventilation and/or nonuniform diffusion. However, prolonging the period of breath holding prior to exhalation reduced DLCO(exhaled) values at all lung volumes when non-uniform diffusion was simulated, but did not affect DLCO(exhaled) when only nonuniform ventilation was simulated.

The uncertain relationship between airway conductance and lung volume.

The concept that airway conductance is proportional to lung volume was tested in normal subjects and by an analysis of data on normal subjects from five published studies. No useful correlation could be found in the six studies between airway conductance and lung volume. If airway conductance were proportional to lung volume in normal subjects, this ratio should vary less among subjects than airway conductance itself. This did not prove to be the case. In 12 normal subjects, conductance was measured at voluntarily varied lung volumes. In most instances, conductance did not correlate with lung gas volume. Although the concept that airway conductance is proportional to lung volume is a useful one, and although there may be a general tendency for conductance to increase with increasing lung volume, the relationship is too variable to be of any practical value.