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taken from the available literature including the production rate of NO in the tissue layer.
Using these equations they could then explain the pattern of NO seen in single exhalations
under different conditions including with and without breath holds and at different expiratory
flows. Overall, the model worked well and appeared to mirror actual results from the human
studies, although the predictions of the initial peaks seen with single exhalations were of
variable accuracy. Generally the model underestimated the peak in single exhalations and
overestimated the peak after breath-holds. The researchers stated in their paper that "Initial
reports have suggested that ambient levels of NO do not affect the exhalation profile." I also
could not ascertain if they took into account any upper airway contamination or whether, like
a later group (Silkoff, Sylvester et al. 2000), they assumed closed vellum. These could be
potential sources of error.
Figure 9.1: A two-compartment model of NO exchange
x
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(J
E
o
nr.v(t)
Car,v(r)
o''f*
:I
v;,c;
Dead space
ALVeoli
Ftg. l. Schematlc of Z-compartment model for nltric oxtde (NO)
pulmonary exchange. Flrst comPartment rePresents relatively nonexpanslle
conducting airways; second compartment represents exPansile
alveoli. Each compartment ls adJacent to a layer of tissue that is
capable of producing and consumlng NO. Exterior to tissue is a layer
of-blood that represents bronchlal or.pulmonarv clrculation and
seryes as an infinlte slnk for NO. Ve and V1, exPlratory and
Insplratory flow, respectively; Ce and Cr, exPiratory and inspiratory
concentration, respectlvely; Ca1 and C61v, airway and alveolar concentratlon,
respectivCly; Var and Vap, airway and alveolar volume,
respectively; Jrrg,ar, and Jr:g,atv, total flux of NO from tlssue to alr and
from alveolar tlssue, respectively; t, time; V volume.
A two-compartment model of NO exchange dynamics using equations to derive the measurement of
NO from different lung compartments depending on the expiratory flow.
Taken from Tsoukias NM, George SC. A fwo-compartment model of pulmonary nitric oxide exchange
dynamics. Joumalof Applied Physiology 1998;85(2): 653-666 (Tsoukias and George 1998).
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