Transcapillary fluid shifts in tissues of the head and neck during and after simulated microgravity

Abstract

To understand the mechanism, magnitude, and time course of facial puffiness that occurs in microgravity, seven male subjects were tilted 6 degrees head-down for 8 h, and all four Starling transcapillary pressures were directly measured before, during, and after tilt. Head-down tilt (HDT) caused facial edema and a significant elevation of microvascular pressures measured in the lower lip: capillary pressures increased from 27.7 +/- 1.5 mmHg (mean +/- SE) pre-HDT to 33.9 +/- 1.7 mmHg by the end of tilt. Subcutaneous and intramuscular interstitial fluid pressures in the neck also increased as a result of HDT, whereas interstitial fluid colloid osmotic pressures remained unchanged. Plasma colloid osmotic pressure dropped significantly by 4 h of HDT (21.5 +/- 1.5 mmHg pre-HDT to 18.2 +/- 1.9 mmHg), suggesting a transition from fluid filtration to absorption in capillary beds between the heart and feet during HDT. After 4 h of seated recovery from HDT, microvascular pressures in the lip (capillary and venule pressures) remained significantly elevated by 5-8 mmHg above baseline values. During HDT, urine output was 126.5 ml/h compared with 46.7 ml/h during the control baseline period. These results suggest that facial edema resulting from HDT is caused primarily by elevated capillary pressures and decreased plasma colloid osmotic pressures. The negativity of interstitial fluid pressures above heart level also has implications for maintenance of tissue fluid balance in upright posture.

Cerebral Circulation during Acute Microgravity Induced by Free Drop in Anesthetized Rats.

“…This is supported by several human studies, i.e. an increase in cross-sectional area of the jugular vein seen during space flight and an increase in microvasculature pressure of the head seen during simulated G by head-down tilt [10,11]. The increase in venous pressure will result in a decrease in venous outflow from the intracranial space.…”

Inhibition of active lymph pump by simulated microgravity in rats

“…The facial edema and increased upper extremity tissue fluid volume associated with microgravity are thought to result in part from elevated capillary blood pressure, reduced capillary colloid osmotic pressure, and a net transvascular fluid filtration (46,58). However, these considerations do not take into account the important influences that lymphatic function has on interstitial volume regulation (55).…”

Introduction to Visual Impairment and Intracranial Pressure

“…During simulated microgravity, transcapillary filtration increases in upper regions of the body because capillary blood pressure increases, causing facial edema (Parazynski et al, 1991). We have assembled a series of chapters to provide a scientific overview of key elements of spaceflight-induced vision impairment.…”