Gravity dependence of phases III, IV, and V in single-breath washout curves

Abstract

The gravity dependence of phases III (IIIa and IIIb), IV, and V of simultaneously performed He-bolus and N2-resident gas single-breath washout curves was studied in different body positions by the technique of 180 degrees body inversion between inspiration and expiration. Phase IIIa was mainly determined by nongravitational factors. Phase IIIb was influenced by gravitational, as well as nongravitational, factors. The former were more important with the bolus method in both lateral decubitus positions and the latter with the N2 method in the prone and supine positions. Phases IV and V were mainly gravity dependent. The difference in gravity dependence between the He and N2 methods appeared to be correlated with the vertical interregional concentration gradients of both gases; indeed the vertical gradient was larger for the 133Xe bolus inhaled at residual volume (which is comparable to the He-bolus distribution) than for the 133Xe residual volume-to-total lung capacity ratio (which is comparable to the N2-resident gas distribution). The greater gravity dependence in the lateral decubitus positions than in the supine or prone postures was related to the larger vertical interregional concentration difference as well as to the more pronounced sequential ventilation in the former positions. Finally the negligible effect of gravity on phase IIIa, its moderate effect on phase IIIb, and its predominant effect on phases IV and V were in agreement with the increased sequential filling and emptying due to gravity near residual volume.

A Novel Interpretation of Closing Volume Based on Single-Breath Nitrogen Washout Curve Simulation

“…This oscillation disappeared without gravity effect (not indicated), because there is no nitrogen concentration difference within the lung. The negative slope of phase IV by postural change reported by Verhamme [17] was also reproduced (Fig. 7D).…”

“…Lung tissue beneath the heart was deformed by the heart mass. Verhamme et al recorded SBNW curves with a rotating bed by which the gravitational direction was reversed just before expiration [17]. To mimic their experiment, we calculated nitrogen concentration at supine posture and volume change at prone posture.…”

Cardiogenic oscillation phase relationships during single-breath tests performed in microgravity

“…GRAVITY IS AN IMPORTANT CONTRIBUTOR to the distribution of ventilation (V A) and to ventilatory inhomogeneity (1,7,8,18,24). The commonly applied gravitational model of V A distribution predicts that, for a vital capacity (VC) maneuver in an upright subject, there will be preferential V A in the dependent zones of the lungs (1,13,16,19).…”

Estudo da influência do esforço e da posição corporal no esvaziamento pulmonar regional em indivíduos saudáveis por meio da tomografia de impedância elétrica

“…Os principais métodos utilizados, principalmente nas décadas de 1950 a 1980, para estudo da distribuição da ventilação pulmonar foram as análises de gases radioisótopos (Xenônio 133 ) 2 , 3 4, 5 gases não-residentes em forma de bolus (Hélio e Argônio) 6,7 e gás residente (Nitrogênio) 8…”

“…60% da CV expirada. Assumindo que o fechamento de vias aéreas ocorra nas regiões dependentes em baixos volumes pulmonares, como já demonstrado 5 e aceito por diversos autores6,7,19,29 como um dos principais responsáveis pelo aparecimento da fase IV no WN2 (motivo pelo qual a transição da fase III para a fase IV é chamada de volume de fechamento) é plausível que esse fenômeno ocorra quando o pulmão dependente chegue ao seu VR. Como a TIE registra apenas a diminuição da variação de volume local, não podemos afirmar diretamente por esta técnica que o fechamento de vias aéreas esteja presente.…”