UNDERSTANDING THE PRINCIPLES OF

Transcription

1 AVIATION MEDICINE IN ACTION: UNDERSTANDING THE PRINCIPLES OF AVIATION MEDICINE IN FLYING OPERATIONS MAJ(DR) Dominic TAN Air Force Medical Service Republic of Singapore Air Force

2 2 WHAT IS AVIATION MEDICINE Aviation medicine is a medical specialty... preventive, occupational, environmental and clinical medicine with the physiology and psychology of man in flight health and safety of those who fly... selection and performance of those who hold aviation licenses. - International Civil Aviation Organisation

3 3 INTRODUCTION Specialised Branch of Occupational Medicine Aspects of the Flight Environment Altitude physiology and the air we breathe Sustained acceleration and its effects Orientation in a 3-dimensional space Flying at night Clinical Aviation Medicine Aeromedical risk assessment

4 4 OVERVIEW OF RSAF DETACHMENTS & EXERCISES

5 22/11/201 8 Public Health and Occupational Medicine Conference ALTITUDE PHYSIOLOGY

6 6 THE ATMOSPHERE Gas Composition (% by Volume) Nitrogen: Oxygen: Argon: 0.93 Carbon dioxide: 0.03 Temperature 1.98 C drop per 1,000 feet Pressure Halved at 18,000 feet

7 22/11/201 8 Public Health and Occupational Medicine Conference HYPOXIA How bad can it get? Helios Airways 522 The Ghost Flight

8 10 TIME OF USEFUL CONSCIOUSNESS (TUC) Time interval between a reduction in oxygen tension of inspired gas and the point at which there is a specified degree of impairment of performance

9 11 PREVENTION OF HYPOXIA Cabin Pressurisation Supplementary Oxygen Systems

10 12 TRAINING FOR HYPOXIA Early Recognition of Symptoms Allows corrective actions to be taken Hypoxic Signature Hypobaric hypoxia training Current training pedagogy Conducted at 25,000 feet Risks include Decompression sickness Barotrauma Pre- and post-run restrictions

11 13 NEWER HYPOXIA TRAINING PEDAGOGIES

12 22/11/2018 Public Health and Occupational Medicine Conference NEWER HYPOXIA TRAINING PEDAGOGIES Breathing Quality Air / Reduced Oxygen Breathing Device Combined Altitude Depleted Oxygen BQA Mask-on hypoxia at 25,000 feet Simulate regulator failure ROBD Use of O 2 and N 2 mixture to produce atmospheric oxygen content at altitude Integration with flight simulator Cost reduction Altitude of 10,000 feet Oxygen depleted gas mixture resulting in a physiological altitude of 25,000 feet Greater fidelity of training Mask-on hypoxia

13 22/11/201 8 Public Health and Occupational Medicine Conference ACCELERATION PHYSIOLOGY

14 22/11/201 8 Public Health and Occupational Medicine Conference TYPES OF ACCELERATION Linear Acceleration Change in speed with no change in direction Radial Acceleration Change in direction with no change in speed Angular Acceleration Change in speed and direction

15 17 EFFECTS OF +G Z ACCELERATION Musculoskeletal Effects Increased weight of soft tissues, head and limbs Cardiovascular Effects Hydrostatic pressure P = ρgh Blood volume re-distribution Changes in intravascular pressure increase in transmural pressure reduce peripheral resistance pooling of blood in the peripheries Baroreceptor reflex Increase heart rate and heart contractility Benign cardiac dysrhythmias

16 18 EFFECTS OF +G Z ACCELERATION Visual Effects Grey-out or blackout Effect on Skin Capillaries Petechiae Hormonal Effects Release of cortisol, adrenaline and vasopressin

17 19 PREVENTING G-LOC Resting G-Tolerance Anti-G Straining Manoeuvre (AGSM) Muscle tensing + Valsalva manoeuvre Anti-G Suit Positive-Pressure Breathing (PPB) Akin to automation of Valsalva manoeuvre

18 22/11/2018 Public Health and Occupational Medicine Conference 2018 TRAINING TO PREVENT G-LOC Awareness of Unwanted Effects of Acceleration Human Training Centrifuge (HTC) Periodic assessment Close monitoring Refinement of AGSM technique Dynamic Flight Simulator (DFS) Combination of flight simulator and centrifuge Greater training fidelity 20

19 21 SPATIAL (DIS)ORIENTATION

20 22 HOW BIG IS THE PROBLEM? United States Military US Navy 1980 to some 112 major aircraft accidents involved SD... US Air Force same period... SD led to 270 major aircraft mishaps.... recent US Air Force study examined SD across 15 years of accident data SD accounted for 11 percent of US Air Force accidents and 69 percent of accident fatalities during the period 1990 to United Kingdom Military UK Army percent of their accidents were attributable to SD. General Aviation US study examining disorientation in general aviation percent of major accidents and 2.5 percent of fatal accidents to SD.

21 23 HOW BIG IS THE PROBLEM? In general SD accounts for some 6 to 32 percent of major accidents to 69 percent of fatal accidents.... for a given pilot, the career incidence of SD is in the order of 90 to 100 percent no chance that he/she will escape experiencing at least one episode of SD.

22 24 SPATIAL ORIENTATION Perception Orientation in space Orientation relative to own aircraft and/or other aircraft Orientation of aircraft in space Brain Integration and interpretation of signals based on inputs, experience and expectancy Sensors Visual Vestibular Proprioception

23 25 SPATIAL DISORIENTATION Type I Unrecognised Inappropriate control Accounts for majority of accidents Type II Recognised May lead to Type I due to disorientation stress

24 22/11/201 8 Public Health and Occupational Medicine Conference SPATIAL ORIENTATION

25 27 SPATIAL DISORIENTATION - PREVENTION Aircrew Factors Health Both physical and mental Drugs Impairment of cognitive function Alcohol, sedative anti-histamines Training Spatial Disorientation Trainer Aircraft Factors Instrumentation Instrument reliability and clarity Cockpit Ergonomics Positioning of instruments and controls Operational Factors Pilot s training and experience

26 28 FLYING AT NIGHT

27 29 HAZARDS OF NIGHT FLYING Night Vision Lack of visual cues Affected by hypoxia, smoking and carbon monoxide Lack of colour vision Reduced acuity and night myopia Susceptibility to Illusions and Spatial Disorientation Autokinesis Relative motion illusion Featureless terrain illusion False references and aircraft Somatogravic illusion Fatigue

28 31 NIGHT VISION GOGGLES Reduced Visual Acuity 6/9 at best Narrower Field of Vision 40 circular field of vision Depth Perception Loss of visual cues Degradation of stereopsis Erroneous estimation of clearance distances Magenta-Coloured After Effects

29 32 INTEGRATED NIGHT VISION TRAINING Air Force Night Vision Integrated Laboratory Physical terrain board Urban and rural settings Ability to control amount of illumination and other environmental settings

30 33 CROSSING TIME ZONES Disruption of Inner Circadian Clock Results in sleep disturbances Worse with Eastward Travel Inner circadian rhythm tends to be slightly >24 hours Jet-Lag Management Environmental modification Pharmacological

31 22/11/201 8 Public Health and Occupational Medicine Conference PILOT FATIGUE Long Duty Hours Unpredictable Work Hours Demand for Aviation Services Workforce Reductions Circadian Disruptions Sleep Deprivation

32 35 FATIGUE MANAGEMENT Non-Pharmacological Education On-Board Sleep/Cockpit Naps Controlled Rest Breaks Proper Crew Work-Rest Scheduling Melatonin Bright Light Exposure Pharmacological Sleep Promoting Compounds Optimise quality of crew rest in circumstances where sleep is possible but difficult to obtain Examples include Temazepam and Zolpidem Alertness Enhancing Compounds Adequate sleep opportunities are nonexistent Examples include Caffeine and Modafinil

33 36 MEASURING FATIGUE Absence of Blood Investigation Conditions for Fatigue Time of day <8 hours of sleep in last 24 hours Long periods of continuous wake hours Time on task/workload SAFTE Model Development of Fatigue Avoidance Scheduling Tool (FAST) Estimate level of performance degradation Estimate schedule induced fatigue risk

34 37 CONTINUOUS IMPROVEMENT PROCESS Feedback to process Schedule evaluation Actigraph recordings Monitor Measure Operating practices Individual lifestyle Modify & Mitigate Model & Analyse Collaborate for solutions Commitment to solve problem Manage Model the fatigue problem Analyse fatigue factors

35 22/11/201 8 Public Health and Occupational Medicine Conference AEROMEDICAL RISK ASSESSMENT

36 39 OBJECTIVE RISK ASSESSMENT Purpose of Aeromedical Examinations Causes of Incapacitation Disease-related Adverse effect of treatment

37 40 1% RULE 1 in in in 10 9 Aircraft System System 1 System 1 System 1 System 1 System 1 System 1 System 1 System 1 System 1 Systems System 1 System 1 System 1 System 1 System 1 System 1 System 1 System 1 System 1 Sub- Systems

38 41 1% RULE Medical Incapacitation as a Proportion of All-Cause Fatal Accident Risk Risk of pilot failure = 1 in 10 8 hours Risk of pilot incapacitation = 1 in 10 9 hours Overall risk of fatal accident = 1 in 10 7 hours

39 42 1% RULE Two-Pilot Operations Successful take over on 99/100 occasions 1 in 10 2 Critical Portions of Flight Take-off and landing 10% of total flight 1 in 10 In two-pilot operations, only one in 1,000 in-flight incapacitations is anticipated to result in a fatal accident, so the acceptable risk for a pilot can be increased by a factor of 1000 from one incapacitation in 10 9 hours to one in 10 6 hours

40 43 1% RULE 10,000 (10 4 ) Hours/Year Incapacitation rate of 1 in 10 6 hours is approximately equivalent to a rate of 1% per year 1 in 10 6 hours = 0.01 in 10 4 hours = 1/100 in 10 4 hours = 1% in 10 4 hours = 1% per annum

41 44 LIMITATIONS OF 1% RULE Critical Flight Period Too long or too short? Incapacitation During Non-Critical Flight Periods Inconsequential? Flight Duration Advancements in Aircraft Technology

42 45 OTHER CONSIDERATIONS Statistical Uncertainties Psychiatric illnesses Human performance and medical illness are often not easy to analyse statistically Errors in aeromedical assessment Polymorphic Risk Sum of separate, lesser, single risks More critical in single-pilot operations

43 46 THANK YOU Questions