Lung Aeration During Sleep

doi:10.1378/chest.06-0359

Chest

Volume 131, Issue 1, January 2007, Pages 122-129

https://doi.org/10.1378/chest.06-0359 Get rights and content

Abstract

Background:During sleep, ventilation and functional residual capacity (FRC) decrease slightly. This study addresses regional lung aeration during wakefulness and sleep.

Methods:Ten healthy subjects underwent spirometry awake and with polysomnography, including pulse oximetry, and also CT when awake and during sleep. Lung aeration in different lung regions was analyzed. Another three subjects were studied awake to develop a protocol for dynamic CT scanning during breathing.

Results:Aeration in the dorsal, dependent lung region decreased from a mean of 1.14 ± 0.34 mL (± SD) of gas per gram of lung tissue during wakefulness to 1.04 ± 0.29 mL/g during non-rapid eye movement (NREM) sleep (− 9%) [p = 0.034]. In contrast, aeration increased in the most ventral, nondependent lung region, from 3.52 ± 0.77 to 3.73 ± 0.83 mL/g (+ 6%) [p = 0.007]. In one subject studied during rapid eye movement (REM) sleep, aeration decreased from 0.84 to 0.65 mL/g (− 23%). The fall in dorsal lung aeration during sleep correlated to awake FRC (R²= 0.60; p = 0.008). Airway closure, measured awake, occurred near and sometimes above the FRC level. Ventilation tended to be larger in dependent, dorsal lung regions, both awake and during sleep (upper region vs lower region, 3.8% vs 4.9% awake, p = 0.16, and 4.5% vs 5.5% asleep, p = 0.09, respectively).

Conclusions:Aeration is reduced in dependent lung regions and increased in ventral regions during NREM and REM sleep. Ventilation was more uniformly distributed between upper and lower lung regions than has previously been reported in awake, upright subjects. Reduced respiratory muscle tone and airway closure are likely causative factors.

Section snippets

Subjects

Ten healthy, nonsmoking subjects (7 men and 3 women; mean age, 34 ± 10 years [± SD]) were investigated awake and during sleep. Three additional men (mean age, 38 ± 16 years) were studied awake in order to develop the CT scan protocol. Informed consent was obtained from all subjects, and the regional ethics committee approved the study protocol in advance.

Spirometry and Airway Closure

Pulmonary function tests were performed in the afternoon with the subjects awake (Vmax 229; SensorMedics; Yorba Linda, CA). Spirometry was

Spirometry and Airway Closure

Characteristics of the subjects and spirometric data are given inTable 1. The spirometric findings (vital capacity and FEV₁) and CV (supine position) were normal. However, as expected the FRC and ERV measured in the supine position were lower than reference values acquired in the upright position. CV-ERV was close to zero, indicating airway closure near to, and in some subjects above, the FRC level.

Awake

No significant change regarding gas/tissue ratio was seen in any of the four ROIs over the 4-cm

Discussion

In the present study, using a novel approach of CT, new data have been obtained regarding aeration of the lung during sleep. The results indicate the occurrence of what has previously been anticipated but not shown, namely an increased lung density and loss of air in the dependent lung region during sleep.

Acknowledgments

The authors are grateful for the assistance of Maj Olofsson and Lena Nilsson, radiograph technicians, Anders Persson, MD, PhD, and Pia Franberg, physicist.

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The authors have no conflicts of interest to disclose.

This study was supported by grants from the Swedish Medical Research Council (No. 5315), the Swedish Heart and Lung Foundation, the Uppsala County Association Against Heart and Lung Diseases, and the Mid Sweden's Research and Development Centre.

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Chest

Original ResearchLung Aeration During Sleep

Abstract

Section snippets

Subjects

Spirometry and Airway Closure

Spirometry and Airway Closure

Awake

Discussion

Acknowledgments

Respiration during sleep in normal man

Thorax

Decrease in functional residual capacity during sleep in normal humans

J Appl Physiol

Influence of sleep on lung volume in asthmatic patients and normal subjects

J Appl Physiol

Lung mechanics and gas exchange during sleep

Sleep

Sleep apnea, hypopnea and oxygen desaturation in normal subjects

N Engl J Med

Mechanism of hemoglobin desaturation during rapid-eye-movement sleep in normal subjects and in patients with cystic fibrosis

Am Rev Respir Dis

Standardized lung function testing: report Working Party Standardization of Lung Function Tests; European Community for Coal and Steel

Bull Eur Physiopathol Respir

Predicted values for closing volumes using a modified single breath nitrogen test

Am Rev Respir Dis

Clinical evaluation of a new finger oximeter

Crit Care Med

A manual of standardized terminology, techniques and scoring system for sleep stages of human subjects

UCLA Brain Information Service/Brain Research Institute

Analysis of lung density by computed tomography before and during general anaesthesia

Acta Anaesth Scand

Density pattern in normal lungs as determined by computed tomography

Radiology

Effect of body orientation on regional lung expansion: a computed tomographic approach

J Appl Physiol

Vertical gradient of regional lung inflation in adult respiratory distress syndrome

Am J Respir Crit Care Med

Tomography of regional ventilation and perfusion using krypton 81m in normal subjects and asthmatic patients

Thorax

Regional intrapulmonary gas distribution in awake and anesthetized-paralyzed man

J Appl Physiol

Influence of diaphragmatic contraction on ventilation distribution in horizontal man

J Appl Physiol

Influence of non-REM sleep on inspiratory activity and lung volume in asthmatic subjects

Am Rev Respir Dis

Mechanics of the rib cage and diaphragm during sleep

J Appl Physiol

Original Research
Lung Aeration During Sleep