Both gravity and non‐gravity dependent factors determine regional blood flow within the goat lung

Abstract

Distribution of pulmonary blood flow has traditionally been regarded as determined by gravity. This view has been challenged recently by reports describing marked gravity-independent distribution of flow. These reports were based on experiments in which local blood flow was measured by methods that have not been thoroughly evaluated. In the present study, we showed that in the goat lung regional trapping of i.v. infused microspheres (O = 15 microns) correlated to endothelial uptake of a simultaneously i.v. infused diamine (r = 0.99, region size approximately 1.5 cm3, dry weight approximately 40 mg). This indicates that the deposition of microspheres reflects true regional pulmonary blood flow. Using the microsphere method, we found a marked gravity-independent heterogeneity in blood flow (coefficient of variation approximately 40%) in the awake goat. We could find no pattern related to anatomy that could account for this variability. We re-examined the influence of gravity by analysing the distribution of pulmonary blood flow in anaesthetized goats both in prone and supine positions. The dorsal to sternal distribution of flow appeared to be inverted when the animals were turned from prone to supine recumbency, indicating that gravity influenced the distribution of pulmonary blood flow along this axis. However, along the gravitational axis, distribution of blood flow varied considerably from lung to lung. It appears that in awake goats the distribution of pulmonary blood flow is the result of several different determinants.

Physiological imaging of the lung: single-photon-emission computed tomography (SPECT)

“…The size of these particles (10 -150 m) causes them to become trapped in the pulmonary microcirculation in proportion to regional blood flow, which has been confirmed with other measurement methods (52). A maximum dose of MAA corresponds to ϳ700,000 particles, which occludes Ͻ1 ϫ 10 Ϫ4 % of the pulmonary capillaries (Mallinckrodt Medical, Petten, The Netherlands); according to one manufacturer the particles have a biological half-life of 11 h (Mallinckrodt Medical).…”

Pulmonary Hemodynamics

“…Additionally, if the body position changes appreciably, this gradient reorients in the appropriate direction relative to the forces of gravity (Chaliki et al, 2002;Romand et al, 1994;Takeda et al, 1987). However, it is important to note that in quadrupeds such as horses (Hlastala et al, 1996), goats (Melsom et al, 1995), dogs (Parker et al, 1995), sheep (Walther et al, 1997), pigs , and ponies (Jarvis et al, 1992), gravity may not be as important a determinant of pulmonary blood flow distribution because the posture of quadrupeds produces a relatively shorter vertical gradient compared with those of humans (Hughes, 1996). In contrast, baboons, like humans, spend most of their time in the upright posture and have remarkably similar pulmonary structures and physiology to humans, where gravity plays a significant role in pulmonary blood flow (Glenny et al, 1999).…”

Time Course and Pattern of Pulmonary Flow Distribution following Unilateral Airway Occlusion in Sheep

“…It has been shown that the number of trapped microsopheres in a piece of lung correlates closely to the pulmonary flow through that piece [9], and that the recovery of infused fluorescent-labelled microspheres is similar to that of radioactively labelled ones [ 101.…”