Effect of gravity on chest wall mechanics

Abstract

Chest wall mechanics was studied in four subjects on changing gravity in the craniocaudal direction (G(z)) during parabolic flights. The thorax appears very compliant at 0 G(z): its recoil changes only from -2 to 2 cmH(2)O in the volume range of 30-70% vital capacity (VC). Increasing G(z) from 0 to 1 and 1.8 G(z) progressively shifted the volume-pressure curve of the chest wall to the left and also caused a fivefold exponential decrease in compliance. For lung volume<30% VC, gravity has an inspiratory effect, but this effect is much larger going from 0 to 1 G(z) than from 1 to 1.8 G(z). For a volume from 30 to 70% VC, the effect is inspiratory going from 0 to 1 G(z) but expiratory from 1 to 1.8 G(z). For a volume greater than approximately 70% VC, gravity always has an expiratory effect. The data suggest that the chest wall does not behave as a linear system when exposed to changing gravity, as the effect depends on both chest wall volume and magnitude of G(z).

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.…”

Effect of changing the gravity vector on respiratory output and control

“…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. For these same subjects, previous studies (5,6) showed that a change in gravity and posture induced a change in the mechanical properties of both lung and chest wall and, consequently, a displacement of FRC.…”

“…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.…”

“…We explored a possible relationship between total elastic WI and total respiratory compliance (CT). The CT was calculated as CT ϭ (Cw ϩ CL)/(Cw⅐CL), where Cw and CL are the chest wall and lung compliance values, respectively, determined in a previous study on the same set of data (5,6). Values for CT are reported in Table 1.…”

“…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 .…”