This invention relates to the field of non-intrusive, non-invasive physiological monitoring of a human test subject and particularly to the monitoring of cranial region physiological conditions in the aircrew members of high performance aircraft.
G-force induced loss of consciousness (GLOC), an extreme example of physiological deterioration, has been found to be second only to the phenomenon of spatial disorientation in the priority of human factors threats facing aircrew members of a modern tactical aircraft. GLOC, in fact, is believed to be one of the primary causes of present-day tactical aircrew fatalities notwithstanding the use of anti-G suits and a number of other human factor improvements in the modern fighter aircraft. Each increment of aircraft performance improvement since the early 1900's has, in fact, been accompanied by an increased measure of danger from this source to aircrew members with the threshold of GLOC having been crossed at least in the early 1920's or some 65 years ago. The U.S. military, particularly the U.S. Air Force and U.S. Navy, have been active in advancing the loss of consciousness prevention art as is exemplified, for example, by numerous issued patents relating to anti-G-force suits and other G-force threat minimizing apparatus. The major concern with which GLOC and other human stress problems are regarded in modern tactical aircraft is also exemplified by the reclined seat, advanced anti-G suit servo valves, G limiting flight control computer, and other human factors considerations that are standard equipment in the F-16 and other present-day tactical aircraft.
Notwithstanding these efforts, however, there has heretofore been a notable absence of satisfactory operational loss of consciousness monitoring arrangements for aircrew members. Principally, this absence arises because such monitoring has been considered to necessarily involve the use of either anatomically invasive instrumentation devices or at best, the use of dermal sensing electrodes. Such arrangements are, of course, highly disfavored or even considered to be physiologically and psychologically threatening by aircrew members.
To be acceptable in an aircraft operational environment, it is necessary that the physiological condition monitoring arrangement be totally invisible o unobtrusive to an aircrew member. In addition to this non-interfering nature of practical GLOC monitoring equipment, the meaningful use of such equipment is, for example, to actuate an alarm system or activate an automatic pilot system and assume control of the aircraft. This demands that an employed GLOC system be both highly reliable and impeccably accurate. Accuracy of this degree, for example, goes well beyond the bounds of sensing the G-force loading incurred by the aircraft and its crew members. Such accuracy requires that real time individual responses of crew members, notwithstanding person to person variations and variations in the physiological resilience of a given person from time to time be considered.
One of the more promising approaches to such improvement in the GLOC and physiological monitoring of an aircrew member involves extension of the oximeter instrumentation commonly used in patient monitoring systems in a modern hospital into the arena of aircrew physiological monitoring. A first-blush consideration of this extension, however, incurs difficulty with a need for intimately placed and often, subjectively located anatomical sensors in the case of monitored hospital patients. This necessity of intimate sensors for the hospital oximeter has, in fact, prompted the principal usage of such instrumentation to be with unconscious or severely movement restrained patients in the hospital setting. In one frequently used oximeter system, for example, the presence of patient movement and the resulting spurious signals received at the oximeter has prompted the use of EKG related signals, (signals derived from chest electrodes) as a timing trigger source to increase oximeter reliability. Clearly, arrangements of this type are unsuitable for use in an operational aircraft environment.
The usefulness of the oximeter instrument in a hospital setting is illustrated by a number of U.S. patents which relate to the oximeter instrument. Included in these patents are several relating to the probe or transducer device used in collecting oximeter or physiological condition signals from a person--e.g. the following patents: U.S. Pat. Nos. 4,770,179; 4,700,708; 4,685,464; 4,621,643; 4,167,331; 3,998,550; 3,847,483; 3,704,706; 3,638,640.
In addition to these probe related patents, many of which are concerned with the need for a low-cost disposable and sterile probe in the hospital environment, the patent art includes a number of documents relating to various aspects of the oximeter monitoring system in general. Several of these patents describe the operating theory and other aspects of designing a practical oximeter instrument. Included in these overall system documents are the following U.S. patents:
U.S. Pat. No. 4,714,341--"Multi-Wavelength Oximeter Having a Means for Disregarding a Poor Signal" issued to K. Hamaguri et al. PA0 U.S. Pat. No. 4,653,498--"Pulse Oximeter Monitor" issued to W. New, Jr. et al. PA0 U.S. Pat. No. 4,603,700--"Probe Monitoring System for Oximeter" issued to R. A. Nichols et al. PA0 U.S. Pat. No. 4,266,554--"Digital Oximeter" issued to K. S. Hamaguri et al. PA0 U.S. Pat. No. 4,407,290--"Blood Constituent Measuring Device and Method" issued to S. A. Wilber. PA0 U.S. Pat. No. 3,704,706--"Heart Rate and Respiratory Monitor" issued to P. R. Herczfeld et al. PA0 U.S. Pat. No. 3,998,550--"Photoelectric Oximeter" issued to M. Koniski et al. PA0 U.S. Pat. No. 2,706,927--"Apparatus for Determining Percentage Oxygen--Saturation of Blood" issued to E. H. Wood et al.
The disclosure of this group of overall oximeter system patents is hereby incorporated by reference into the present specification.
Notwithstanding these examples of inventive attention to oximeter related instruments, the patent art has failed to provide a satisfactory operational physiological monitoring system for the pilot or other aircrew member of a high-performance aircraft.