Effect of Near-Vacuum Exposures on Pulmonary Circulation in Dogs 1

Abstract

Investigations concerning near-vacuum exposures, in support of current high altitude and space flights, are essential to help evaluate the risk and recovery potentials after encounters to reduced pressures. During and immediately after World War II, studies to pressures equivalent to about 72,000 ft (30 Torr) ascertained that general circulation ceased within less than 16 sec (1–4). More recently, it has been reported that vascular (5–8) and biochemical (9) changes measured at pressures approaching a vacuum are generally of greater magnitude than those measured at 30 Torr, and decompressions to 2 Torr within 1 sec result in circulatory arrest within a few seconds, as evaluated by bloodpressure gradients (5, 7). The present study is designed to investigate the direction and distribution of pulmonary blood flow during such an exposure, where ordinary techniques and methods of measurement are either difficult or unrealiable owing to artifacts associated with pressures that are less than that of water vapor.

Method. Eight adult mongrel dogs, weighing about 20 kg each, were anesthetized with pentobarbital sodium. A catheter, placed in the jugular vein, penetrated the wall of the altitude chamber and connected with a three-way stopcock outside the chamber. The catheter was filled with bubble-free saline at room temperature. The location of the catheter tip in the blood vessel was estimated by monitoring the pulmonary arterial pressure with a previously calibrated P-23 series Statham Pressure Transducer and a Honeywell Visicorder (Model 1108). The catheter tip location was later verified by careful dissection.

Each animal breathed 100% oxygen through a tracheal cannula and a demand oxygen regulator, anad was slowly decompressed to 180 Torr. After 5 min, 0.1 cc of degassed corn oil was injected into the vascular cannula to serve as a visible marker for movement of fluid. One microcurie of ¹²⁵I, contained within 0.1 cc of 5% aqueous albumin solution, was introduced part way into the catheter, followed by 0.5 cc of degassed saline.