Nichol G M, Michels D B, Guy H J
J Appl Physiol Respir Environ Exerc Physiol. 1982 Jan;52(1):34-43. doi: 10.1152/jappl.1982.52.1.34.
A downward-deflecting phase V is often seen following the phase IV terminal rise in the single-breath N2 washout test (SB N2). This phase V was studied in eight normal nonsmoking subjects aged 27-41, using both the SB N2 test and single-breath washouts of boluses of inert tracer gas slowly inhaled from residual volume (RV). All of the subjects showed a distinct phase V in both tests. Expiratory flow rates between 0.1 and 2.0 1/s were used; at each flow rate phase V appeared shortly after expiration became flow limited. Thus the volume above RV at which phase V began increased with increasing expiratory flow rate. The difference between the exhaled volumes at which flow became limited and phase V appeared was shown to be approximately equal to the anatomic dead space. This behavior is predicted by a model of lung emptying in a gravitational field. As expiration proceeds, flow limitation occurs first in the (tracer-poor) lower lung regions and then progresses toward the (tracer-rich) upper lung regions causing phase IV. When all lung regions have finally become flow limited, the amount of flow from the upper regions decreases relative to that of the lower regions, thereby causing phase V.
在单次呼吸氮气洗脱试验（SB N2）中，IV期终末上升之后常常可见向下偏转的V期。对8名年龄在27至41岁的正常不吸烟受试者进行了研究，采用了SB N2试验以及从残气量（RV）缓慢吸入惰性示踪气体团注后的单次呼吸洗脱法。所有受试者在两项试验中均表现出明显的V期。使用了0.1至2.0升/秒的呼气流量；在每个流量下，V期在呼气变为流量受限后不久出现。因此，V期开始时高于残气量的体积随着呼气流量的增加而增加。流量受限和V期出现时呼出体积之间的差异显示大约等于解剖无效腔。这种行为由重力场中肺排空的模型预测。随着呼气进行，流量受限首先发生在（示踪剂贫乏的）下肺区域，然后向（示踪剂丰富的）上肺区域发展，导致IV期。当所有肺区域最终都变为流量受限时，来自上区域的流量相对于下区域的流量减少，从而导致V期。
