Distribution of ventilation in young and elderly adults determined by electrical impedance tomography

https://doi.org/10.1016/j.resp.2004.07.014Get rights and content

Abstract

To determine the effect of age and posture on regional lung ventilation, eight young (26 ± 1 years, mean ± S.D.) and eight old (73 ± 5 years) healthy men were studied by electrical impedance tomography in four body positions (sitting, supine, right and left lateral). The distribution of gas into the right and left lung regions was determined in the chest cross-section during tidal breathing at the resting lung volume, near residual volume and total lung capacity, as well as forced and slow vital capacity maneuvers. In the young, significant posture-dependent changes in gas distribution occurred during resting tidal breathing whereas they were absent in the elderly. In the older subjects, the contribution of the right lung to global ventilation fell with the transition from sitting to supine posture during both full expiration maneuvers. During forced vital capacity, the high flow rate and early airway closure in the dependent lung, occurring at higher volumes in the elderly, minimized the posture-dependency in gas distribution which was present during the slow maneuver. Our study revealed the significant effect of age on posture-dependent changes in ventilation distribution.

Introduction

The mechanical properties of the chest–lung system influence the distribution of gas within the lung. Stiffening of the chest wall, reduction of lung elastic recoil and diminished respiratory muscle strength are known to affect respiratory mechanics in the elderly (Gibson et al., 1976, Rossi et al., 1996, Babb and Rodarte, 2000). The effect of aging on global static and dynamic ventilatory parameters is well established (Campbell and Lefrak, 1978, Rossi et al., 1996, Zeleznik, 2003), however, regional lung ventilation in the elderly has only seldom been studied. The few studies performed to date have used radioactive tracer gases to follow the topographical distribution of ventilation along the vertical axis only during slow, quasi-static maneuvers (Holland et al., 1968, Kronenberg et al., 1973). These techniques do not permit continuous assessment of regional lung ventilation during undisturbed spontaneous breathing.

Recently, a radiation-free imaging technique, electrical impedance tomography (EIT), has become available, allowing non-invasive study of regional lung ventilation in a cross-section of the chest. Various validation studies using established techniques (e.g., computed tomography and ventilation scintigraphy) have proved the capacity of EIT to trace local air volume changes in lungs (Frerichs et al., 2002, Serrano et al., 2002, Hinz et al., 2003a, Hinz et al., 2003b). On this basis EIT has been proposed as a possible future tool for monitoring regional lung ventilation in a clinical setting (Frerichs et al., 2001b, Rimensberger, 2002, Caples and Hubmayr, 2003, Stenqvist, 2003).

The majority of patients, including those who may benefit from the possible clinical use of EIT in the future, are of older age. However, the specific changes in regional lung function associated with aging are not known in detail. Therefore, the aim of our study was to use modern EIT technology to study the distribution of ventilation in a group of elderly subjects, and to establish how the distribution of gas in the lungs is modified by the change in body position during several ventilatory maneuvers. Additionally, a comparison was made with a group of young subjects studied using the same protocol.

Section snippets

Subjects

Eight young (26 ± 1 years, mean age ± S.D.) and eight old (73 ± 5 years) healthy men were studied. The study was approved by the local ethical committee and written informed consent was obtained from all participants. All subjects were nonsmokers with no clinical evidence of cardiorespiratory disease. Basic physical characteristics and results of lung function testing are given in Table 1. Lung function was assessed by spirometry and body plethysmography (Masterlab, Jaeger, Wuerzburg, FRG) and

Resting tidal breathing

The regional tidal volumes in the left and right lungs determined in all postures and both groups of subjects during resting tidal breathing revealed a small difference between the young and elderly: The regional tidal volume in the left lung in the right lateral posture was significantly lower in the young subjects. The corresponding EIT data, i.e. the sums of end-inspiratory-to-end-expiratory relative impedance changes in the left and right lung regions, are given in Fig. 2. (The four

Discussion

In our study, two groups of healthy young and old subjects were studied to determine the effect of age on the distribution of gas in lungs during various ventilatory maneuvers. The subjects were followed in four postures whereby the effect of the changing orientation of chest in the gravity field on regional ventilation distribution could be assessed. The findings of the present study are in keeping with the current state of knowledge of the physiological effects of age and gravity on

Conclusion

The present study revealed several differences between regional ventilation distribution in healthy young and old subjects in various breathing conditions. The results manifest how changes in respiratory mechanics associated with the physiological aging process affect the distribution of gas in the lungs. We expect that our results obtained in healthy subjects will serve as a basis for future EIT studies on older patients suffering from pulmonary diseases and undergoing ventilator therapy.

Acknowledgement

This study was supported by the German Aerospace Center (DLR) and the German Ministry for Education and Research (BMBF) grant no. 50 TK 9804.

References (30)

  • J. Hinz et al.

    Regional ventilation by electrical impedance tomography: a comparison with ventilation scintigraphy in pigs

    Chest

    (2003)
  • O. Stenqvist

    Practical assessment of respiratory mechanics

    Brit. J. Anaesth.

    (2003)
  • J. Zeleznik

    Normative aging of the respiratory system

    Clin. Geriatr. Med.

    (2003)
  • A. Adler et al.

    Monitoring changes in lung air and liquid volumes with electrical impedance tomography

    J. Appl. Physiol.

    (1997)
  • T.G. Babb et al.

    Mechanism of reduced maximal expiratory flow with aging

    J. Appl. Physiol.

    (2000)
  • D.C. Barber

    A review of image reconstruction techniques for electrical impedance tomography

    Med. Phys.

    (1989)
  • E.J. Campbell et al.

    How aging affects the structure and function of the respiratory system

    Geriatrics

    (1978)
  • S.M. Caples et al.

    Respiratory monitoring tools in the intensive care unit

    Curr. Opin. Crit. Care

    (2003)
  • N.H. Edelman et al.

    Effects of respiratory pattern on age differences in ventilation uniformity

    J. Appl. Physiol.

    (1968)
  • I. Frerichs et al.

    Gravity effects on regional lung ventilation determined by functional EIT during parabolic flights

    J. Appl. Physiol.

    (2001)
  • I. Frerichs et al.

    Non-invasive radiation-free monitoring of regional lung ventilation in critically ill infants

    Intensive Care Med.

    (2001)
  • I. Frerichs et al.

    Detection of local lung air content by electrical impedance tomography compared with electron beam CT

    J. Appl. Physiol.

    (2002)
  • L.A. Geddes et al.

    The specific resistance of biological materials—a compendium of data for the biomedical engineer and physiologist

    Med. Biol. Eng.

    (1967)
  • G.J. Gibson et al.

    Sex and age differences in pulmonary mechanics in normal nonsmoking subjects

    J. Appl. Physiol.

    (1976)
  • G. Hahn et al.

    Elektrische Impedanztomographie (EIT) als Methode zur regionalen Beurteilung der Lungenventilation

    (1996)
  • Cited by (0)

    View full text