Effects and biological limitations of +Gz acceleration on the autonomic functions-related circulation in rats

Abstract

The effects of gravitational loading (G load) on humans have been studied ever since the early 20th century. After the dangers of G load in the vertical head-to-leg direction (+Gz load) became evident, many animal experiments were performed between 1920 and 1945 in an effort to identify the origins of high G-force-induced loss of consciousness (G-LOC), which led to development of the anti-G suit. The establishment of norms and training for G-LOC prevention resulted in a gradual decline in reports of animal experiments on G load, a decline that steepened with the establishment of anti-G techniques in humans, such as special breathing methods and skeletal muscle contraction, called an anti-G straining maneuver, which are voluntary physiological functions. Because the issue involves humans during flight, the effects on humans themselves are clearly of great importance, but ethical considerations largely preclude any research on the human body that probes to any depth the endogenous physiological states and functions. The decline in reports on animal experiments may therefore signify a general decline in research into the changes seen in the various involuntary, autonomic functions. The declining number of related reports on investigations of physiological autonomic systems other than the circulatory system seems to bear this out. In this review, we therefore describe our findings on the effects of G load on the autonomic nervous system, cardiac function, cerebral blood flow, tissue oxygen level, and other physiological autonomic functions as measured in animal experiments, including denervation or pharmacological blocking, in an effort to present the limits and the mechanisms of G-load response extending physiologically. We demonstrate previously unrecognized risks due to G load, and also describe fundamental research aimed at countering these effects and development of a scientific training measure devised for actively enhancing +Gz tolerance in involuntary, autonomic system functions. The research described here is rough and incomplete, but it is offered as a beginning, in the hope that researchers may find it of reference and carry the effort toward completion. The advances described here include (1) a finding that cerebral arterial perfusion pressure decreases to nearly zero under +5.0 Gz loads, (2) indications that G load may cause myocardial microinjuries, (3) detection of differences between cerebral regions in tissue-oxygen level under +3.0 Gz load, (4) discovery that hypotension is deeper under decreasing +Gz loads than increasing +Gz loads with use of an anti-G system, due in part to suppression of baroreceptor reflex, and (5) revelations and efforts investigating new measures to reduce cerebral hypotension, namely the “teeth-clenching pressor response” and preconditioning with slight but repeated G loads.

Gravitational Influence on Human Living Systems and the Evolution of Species on Earth

“…Therefore, we can assume that its influence was also constant throughout the emergence and evolution of life upon Earth. Today there is evidence that our musculoskeletal [ 73 , 74 , 75 ], cardiovascular [ 76 , 77 , 78 ] and immune systems [ 79 , 80 , 81 ] function under the tight control of gravity.…”

Unreactive N2 (Nitrogen gas) or the Reactive Toxic but Potent Anesthetic H2S (Hydrogen Sulfide gas) for More Humane Prisoner Executions and Animal Euthanasia? More Lessons, and Questions, from Anesthesia

“…17 During the performance of high-speed maneuvers, jet fighter pilots can experience rapid (5-6 seconds 18 ) +Gz-induced LOC. 19,20,21 Here blood flow to the brain, and consequently O2 supplied to the brain, is suddenly severely reduced due to downward increased gravitational/centrifugal forces. Since the PaO2 in the CB does not drop as quickly because it is situated lower in the body than the brain, the HVR doesn't necessarily occur.…”

Volatile Anesthetics and O2 Activate TASK-1/3 by Weak H-Bonding with X-Gate Uncharged Arg-245: The Major Molecular Mechanism for Carotid Body Hypoxic Sensitivity and Further Insights into Fighter Pilot +Gz-Induced LOC

“…This topic is related to the serious +Gz-induced LOC (in as little as 5 -6 seconds 195 ) experienced by jet fighter pilots during tight high-speed maneuvers. 196,197,198 (Gravitational forces act in the "z" direction with + signifying a gravitational/centripetal force acting from head to foot pulling down.) After years of intense research the molecular pathways are still poorly understood but it is considered to result from a sudden drop in brain O 2 levels, decreasing rSO 2 as a result of an increase in the downward gravitational force (or centripetal force).…”