Monthly Archives: July 2017

Hypoxia and Aviation

A passel of recent headlines (here, here and here, for instance) have highlighted a persistent hypoxia problem facing pilots of jet aircraft in both the Air Force and the Navy. These or similar episodes, designated “physiological episodes”, are blamed for the deaths of four Naval aviators over the past several years.

“Mountain sickness”, that is, the effects of altitude, were first written about in western literature in the 16th century, most particularly in a description of the syndrome by Father Jose de Acosta, who, in 1590, published his observations on the effects of altitude on men and animals in the Andes mountains of Peru. The British scientist Robert Boyle was the first to identify a vital factor in air that was lacking at altitude. Joseph Priestly identified that vital factor in 1774, and Antoine Lavoissier named it “oxygen” in 1777.

There the matter lay until men started going up in balloons, although apparently the first recorded “altitude-related” hypoxic deaths resulted when three men (two of whom died) were subjected to a simulated altitude of 28,000 feet in a pressure chamber developed by French physiologist Paul Bert, in 1875. As a result of these and other experiments, Bert was able to show that the breathing of supplemental oxygen could prevent the physiological ill effects of altitude.

With the advent of fixed wing aviation, and in particular, military aviation in World War I, the main thrusts of aviation medical research involved the physical safety of pilots (restraining apparatus and the like), and dealing with the cold of altitude. The use of supplemental oxygen apparently was a given, and both gaseous and liquid O2 were used.

Aviation medicine research between the wars depended on a few unsung stalwarts who responded to queries concerning the physiological effects – now including loss of consciousness while pulling gs – from the aviators and engineers who designed ever more capable aircraft. That said, developing oxygen delivery systems for aircraft expected to operate at high altitudes for hours at a time – bombers – was a critical matter. The advent of high performance jet aircraft in the late 1940s led to significant improvements in aircraft oxygen systems.

Physiologists now break the effects of hypoxia out in “stages”, viz.,

STAGES OF HYPOXIA

  1. INDIFFERENT STAGE – The only adverse effect is on dark adaptation.
  2. COMPENSATORY STAGE – Physiological compensations provide some defense against hypoxia so that the effects are reduced unless the exposure is prolonged or unless exercise is undertaken. Respiration may increase in depth or slightly in rate, and the pulse rate, the systolic blood pressure, the rate of circulation, and the cardiac output increases.
  3. DISTURBANCE STAGE – In this stage the physiological compensations do not provide adequate oxygen for the tissues.
    Subjective symptoms may include fatigue, lassitude (state of exhaustion), somnolence (drowsiness, sleepiness), dizziness, headache, breathlessness, and euphoria.
    Objective symptoms include:
        Special Senses – Both the peripheral and central vision are impaired and visual acuity is diminished. 
        Extraocular muscles are weak and incoordinate
     – Touch and pain are diminished or lost. Hearing is one of the last senses to be impaired or lost.
        Mental Processes – Intellectual impairment is an early sign and makes it improbable for the individual to comprehend his own disability. Thinking is slow. Calculations are unreliable.
    Memory is faulty. Judgment is poor. Reaction time is delayed.
        Personality Traits – There may be a release of basic personality traits and emotions as with alcoholic intoxication (euphoria, elation, pugnaciousness, overconfidence, or moroseness).
    Hyperventilation Syndrome
     – Over-breathing due to excitement or stress. Cyanosis – Blue discoloration of the skin.
  4. Critical Stage – In the critical stage consciousness is lost. Death follows shortly.

Source: http://www.mountainflying.com/pages/mountain-flying/hypoxia.html, accessed 31 July 2017

Which brings us to today. Modern jet combat aircraft – including the T-45 trainer, Navy F/A-18s and E/A-18s, and all F-35s – have very sophisticated on-board oxygen generation systems. Engineers’ attention is now being directed to this commonality, the “OBOGS”, among the aircraft where the “hypoxia-like” episodes have happened. Another factor seems to be altitude: all reported episodes appear to be have occurred above 25,000 feet, and engineers now suspect a malfunction in the oxygen metering device in these systems at these altitudes.

Until the engineers find a solution to the problem, the services are limiting operations in OBOGS-bearing aircraft to below 25,000 feet, introducing oxygen monitoring devices and beefed up supplemental oxygen supplies, and giving aviators additional training in how to recognize symptoms of hypoxia before they reach the “disturbance” stage.

(c)2017 Thomas L Snyder

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Navy Medicine in Araby (Episode 2)

This is part 2 of a 7 part presentation contrasting 19th century navy medicine with the care the navy medical team gives our sailors, Marines and soldiers now:

In the early 19th century the most widely accepted general theory of disease is that it represented an imbalance of the system, either in direction of “excitement” or its opposite, “enfeeblement”. Treatments were therefore aimed at reversing these imbalances. For example, most fevers were interpreted as manifestations of too much excitement, and a common treatment was to tip the balance toward enfeeblement by bleeding the patient, often at a pint or more at a go. Other enfeebling regimens included aggressive catharsis using calomel, a mercury containing compound and inducing vomiting by use of medications like tartar emetic.[1] Very few “targeted” treatments were available, among which was calomel used with success against syphilis, Peruvian bark (which contains quinine, then effective in treating malaria, a disease manifested by cyclical fevers) for treatment of any fever, and after many fits and starts, the juice of citrus for prevention and treatment of scurvy. Interestingly, although lime juice had been part of the recipe for grog in the Royal Navy since 1747 because of its proven antiscorbutic effects, the eminent American Naval surgeon Edward Cutbush, in his 1808 treatise Observations on the Preservation of the Health of Soldiers and Sailors, seems not to have entirely bought into the idea, as he does allow that “[w]hen in countries where limes or lemons and sugar can be purchased cheap, it would be well to … issue sugar and lime …to make punch, which would counteract any tendency to scurvy that may be among the crew.[2]

The first meaningful U. S. naval force arrived in the Mediterranean, ship by ship, throughout 1802. The frigate Chesapeake was the flagship of this squadron. In her sickbay – below decks and generally devoid of natural light and fresh air – the ship’s surgeon and his assistants (an assistant surgeon or surgeon’s mate, and a loblolly boy) would care for sailors who were too ill to work, or who were convalescing from debilitating injuries. In an era when men did not have the benefit of modern scientific knowledge, deaths from disease greatly outnumbered those from combat. Yet common sense and an emerging experience led Cutbush to recommend attention to “the following leading particulars: 1st. In keeping the ship dry and properly ventilated. 2ndly. In attending to the cleanliness of the crew in their persons and clothing. 3rdly. In their avoiding cold, fatigue and intoxication. 4thly. In keeping them warm by fires in the winter season. 5thly. In preserving an exact and regular discipline, and in furnishing the crew with sound, wholesome provisions and water.

“If a contagious disease appear on board: 1st. Separate the sick from the well and prevent all unnecessary communication with the sick berth. 2ndly. Keep the ship clean, dry, and properly ventilated. 3rdly. Let the men avoid cold, fatigue and intoxication. 4thly. Dissipate moisture betwixt decks by means of fires. 5thly. Avoid depressing the spirits of the people by unnecessary severity. 6thly. Let the berth deck be frequently whitewashed with lime.”[3] Based on the principles laid down by Cutbush, we may conclude that he placed much emphasis on the prevention of disease by encouraging cleanliness of both ships and men and by providing a more healthful environment and decent food. Although medicos in the early 19th century had no idea of bacteria or viruses as the cause of disease, or of the mechanisms of contagion, they did get the public health principle of isolating the sick quite right. The beneficial effects of whitewashing appear to be limited to making a dark space like the berth deck seem brighter; that whitewash – essentially lime paint – traps dirt and insect parts, in effect promoting cleanliness, and may have mild antibacterial effects is discussed mainly in modern treatises on buildings.[4],[5],[6]

The ship’s cockpit is where the surgeon and his assistants would care for battle casualties. Such care was pretty much limited to stopping hemorrhage with tourniquets or ligature – tying off bleeding vessels – dressing wounds and amputating limbs. The commonest combat injury to sailors in this era was from flying wood splinters, and these produced terrible, shredding-type wounds. In these cases, the surgeon’s task was to remove as many of the splinters as possible, because, it was thought, these splinters were the direct cause of lockjaw[7]. The surgeon would also cleanse the wounds with water and vinegar and apply ointments and dressings. Part of the surgeon’s cockpit kit was a pail of sand that could be spread on the deck so the surgeon and his assistants might keep their footing when it became slippery from spilled blood. According to Professor Langley, American forces lost at least 181 men during the Barbary period, of whom perhaps 45 were combat-related. Three men, including two medical men and one Marine Corps lieutenant, died as a result of duals.[8]

[1] Warner, John Harley, “From Specificity to Universalism in Medical Therapeutics – Transformation in the United States in the 19th Century”, In Leavitt, Judith Walzer, and Ronald L Number, eds., “Sickness and Health in America: Readings in the History of Medicine and Public Health, Madison, University of Wisconsin Press, 3rd Edition (Revised), 1997, pp 88, 89.

[2] Cutbush, Edward, Observations on the Means of Preserving the Health of Soldiers and Sailors; and on the Duties of the Medical Department of the Army and Navy, with Remarks on Hospitals and Their Internal Arrangement, Philadelphia, Thomas Dobson, 1808, pp 119. Obtained on line at https://archive.org/details/2548038R.nlm.nih.gov, downloaded as a pdf file on 24 August 2016.

[3] Cutbush, op. cit. p 131, 132.

[4] Resilience.org, “Use Whitewash Instead of Paint for Traditional Look and No Toxins”, http://www.resilience.org/stories/2014-04-29/use-whitewash-instead-of-paint-for-traditional-look-and-no-toxins, accessed 13 September 2016.

[5] GSA, “Properties and Uses of Whitewash Paints”, http://www.gsa.gov/portal/content/112558, accessed 13 September 2016.

[6] 5 Acres & A Dream, The Blog, “Amish Whitewash”, http://www.5acresandadream.com/2014/05/amish-whitewash.html, accessed 13 September 2016. This article in particular cites two sources, from 2005 and 1919, which describe the “mild antimicrobial” effect of whitewash.

[7] Which we now know is caused by the bacterium clostridium tetani, carried into the tissues by the splinters.

[8] Langley, op. cit., p 106

(c)2017 Thomas L Snyder

Your Correspondent on Streaming Radio

Occasionally, a surprise opportunity falls into our laps. This radio interview, broadcast on a streaming service called ReachMD, has me discussing my interest in the history of naval / maritime medicine, the society I co-founded (The Society for the History of Navy Medicine), the history of the Navy’s first hospital on the west coast (at Mare Island in the San Francisco Bay), and the contrast between Navy medicine in the 19th century and the 21st century. The audio clip is 11min29sec long. Learn and Enjoy!

https://www.reachmd.com/programs/clinicians-roundtable/the-history-american-naval-medicine-a-military-doctors-society-mission/9658/

(c)2017 Thomas L Snyder

Navy Medicine in Araby – Then and Now (Episode 1)

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