Effect of gravity and posture on lung mechanics

Abstract

The volume-pressure relationship of the lung was studied in six subjects on changing the gravity vector during parabolic flights and body posture. Lung recoil pressure decreased by approximately 2.7 cmH(2)O going from 1 to 0 vertical acceleration (G(z)), whereas it increased by approximately 3.5 cmH(2)O in 30 degrees tilted head-up and supine postures. No substantial change was found going from 1 to 1.8 G(z). Matching the changes in volume-pressure relationships of the lung and chest wall (previous data), results in a decrease in functional respiratory capacity of approximately 580 ml at 0 G(z) relative to 1 G(z) and of approximately 1,200 ml going to supine posture. Microgravity causes a decrease in lung and chest wall recoil pressures as it removes most of the distortion of lung parenchyma and thorax induced by changing gravity field and/or posture. Hypergravity does not greatly affect respiratory mechanics, suggesting that mechanical distortion is close to maximum already at 1 G(z). The end-expiratory volume during quiet breathing corresponds to the mechanical functional residual capacity in each condition.

Microgravity and the respiratory system

“…The relatively small effect on the rib cage is also consistent with the relatively small changes in in oesophageal pressure seen in seated subjects in parabolic flight [26]. The studies in parabolic flight had the advantage of measurements both in micro-and hypergravity, and these showed significant nonlinearity in chest wall behaviour [27,28], emphasising the inability to adequately predict the situation in microgravity by extrapolation from hypergravity.…”

Influência da variação dos decúbitos laterais na deposição pulmonar de aerossol

“…These findings are supported by basic pulmonary physiology, which demonstrates that differences in regional ventilation are the result of variation in vertical pleural pressure, and that these differences are influenced by gravity [17][18][19][20][21][22][23] .…”

Effect of changing the gravity vector on respiratory output and control

“…The subjects had previous parabolic flight experience, were trained to perform the respiratory maneuvers, and were well accustomed to abrupt changes in G z, which could occur several times during each flight. This same subject set had previously performed studies on how changes in G z affect chest wall and lung mechanics (5,6). Subjects gave their informed consent, and the protocol was approved by a review board.…”

“…Figure 2 presents the average volume-pressure relationships (obtained as described in Ref. 5) of the lungs and chest wall and the average volume pressure loops at 1, 1.8, and 0 G z , and in the supine posture for all the subjects. During quiet breathing, the loops begin at the intersection between the lung and chest wall volume-pressure curves, namely FRC, which corresponds to the mechanical resting point of the respiratory system.…”

“…OUR LABORATORY HAS PREVIOUSLY SHOWN that microgravity represents a condition of minimum distortion of the respiratory system and, furthermore, that increasing the gravity vector in the craniocaudal direction (G z ) during parabolic flights or changing its orientation in the dorsoventral direction (shifting from head-up to supine) causes marked changes in the configuration and in the elastic properties of the lung and chest wall, as well as in their mechanical coupling (5,6). This paper reports the first computation of respiratory work when the distortion of the respiratory system is minimal (i.e., during microgravity) and provides a comparison with conditions in which the system is loaded by varying G z .…”