QINETIQ PROPRIETARY

QINETIQ PROPRIETARY

QINETIQ PROPRIETARY

QINETIQ PROPRIETARY

Ross Pollock

Alec Stevenson

SAFE Europe 2018

Acceleration Atelectasis:

New risks from an old friend

QINETIQ PROPRIETARY

QINETIQ PROPRIETARY

What is atelectasis?

• Partial collapse of the lung resulting from alveoli (small sack like structures where gas exchange occurs) becoming gasless and collapsing shut

• Difficult to re-open without large change in pressure across the lung – chest wall interface

• Often occurs clinically in anesthetised patients

No Atelectasis

Atelectasis

QINETIQ PROPRIETARY

QINETIQ PROPRIETARY3

• Signs and symptoms associated with the development of acceleration atelectasis:

– Coughing

– Chest Pain

– Breathing difficulty and shortness of breath

– Lowered O2 content of the blood (hypoxaemia)

• Risks associated with acceleration atelectasis:

– Respiratory symptoms can be distracting or, at worst, debilitating

– Lowered O2 content of the blood could increase susceptibility to hypoxia (e.g. altitude, Gz exposure)

– Subsequent increased risk of loss of consciousness

– Atelectasis symptoms could be confused with other hazards (e.g. hypoxia) leading to inappropriate mitigation actions

being taken

Signs, Symptoms and Risks

QINETIQ PROPRIETARY

QINETIQ PROPRIETARY4

• High performance aircraft can pull high G forces that can be sustained for many seconds

– Typhoon aircraft = +9 Gz

– Protection by increasing blood pressure to overcome the hydrostatic forces

– Achieved by compressing the lower body

– Moves blood centrally, reduces volume of vessels (↓volume = ↑ pressure ), diaphragm and chest contents pushed up (reduced distance between heart and head)

• However, G Protection (Anti-G Trousers) compresses the lung

Protection against Head-to-Foot (+Gz ) Acceleration

Normal (+1Gz)Under +Gz without protection Under +Gz with protection

QINETIQ PROPRIETARY

QINETIQ PROPRIETARY5

• To protect against the effects of altitude the O2 concentration of the gas supplied to pilots is increased

• O2 concentrations of >60% are thought to cause atelectasis

Acceleration Atelectasis

Gz and anti-G trouser compresses

the lung

Airways become unstable and close

O2 uptake by blood reduces alveoli

volume and they collapse

Once Gz is offloaded collapsed

alveoli remain shut

QINETIQ PROPRIETARY

QINETIQ PROPRIETARY6

• Approximately 30 % of Typhoon pilots, surveyed in 2011, reported symptoms suggestive of acceleration atelectasis (coughing and chest pain)1

– The majority were reported 5 – 10 mins post +Gz exposure but some remained post sortie

• A survey of Hawk T2 aircrew revealed the majority had experienced coughing and chest tightness post +Gz exposure2

– Symptoms lasted for between 5 mins post exposure and 2-3 hours post sortie

• Symptoms suggestive of acceleration atelectasis (coughing and chest pain) reported by F-22 pilots for up to 4 hours after high Gz sorties performed3

Re-emergence of Acceleration Atelectasis?

1. Wilkinson (2011). Typhoon Pilot Medical Questionnaire (Unpublished); 2. Monberg (2013). Av Spa Enviro Med. 84:247; 3. Flottmann (2013). Av Spa Enviro Med. 84:428

• “Physiological Incidents” have resulted in the grounding of aircraft in military air forces outside of the UK– Encompasses a wide range of causes/effects

– Acceleration atelectasis could be a contributory factor

QINETIQ PROPRIETARY

QINETIQ PROPRIETARY7

• On board oxygen generation systems (OBOGS) designed to adhere to the limits set out in Figure 1

– Do they adhere to these limits?

– Are these limits still valid?

• Aircraft capabilities and anti-G systems have improved since limits were set

– Longer durations of +Gz can be sustained at higher altitudes

– Higher Gz levels can be experienced without the need to perform the anti-G straining manoeuvre

Possible causes of increased incidence

Figure 1. Typical OBOGS O2 delivery schedule limits

QINETIQ PROPRIETARY

QINETIQ PROPRIETARY8

Aim and Protocol

• Overarching aim to improve our understanding of acceleration atelectasis when wearing modern anti-G trousers and breathing gas mixtures containing high levels of O2

1

3

5

Accele

ration (

Gz)

0

20

40

60

80

100

FiO

2 (%

)

1

3

5A

ccele

ration (

Gz)

0

20

40

60

80

100

FiO

2 (%

)

1

3

5

Accele

ration (

Gz)

0

20

40

6080

100

FiO

2 (%

)

• Phase 1: To investigate the effects of +Gz duration on acceleration atelectasis

• Phase 2: To investigate the effects of inspired O2 concentration on acceleration atelectasis

• Phase 3: To investigate the effects of cumulative exposure to +Gz and different O2 concentrations on acceleration atelectasis

QINETIQ PROPRIETARY

QINETIQ PROPRIETARY9

Experimental Protocol

• 14 subjects completed all phases of testing (2 to 3 females in each phase)

• All runs to 5 Gz (at 1.0 G.s-1) with subjects wearing Typhoon AEA

– Positive pressure breathing for Gz protection was not utilised

• During all Gz exposures subjects maintained clear vision using muscle tension only

– i.e. the breathing component of the anti-G straining manoeuvre (AGSM) was not performed

Measurements MadePredicted Effect

on Atelectasis

Forced Inspiratory Vital

Capacity (FIVC)↓

Regional FIVC ↓

Symptomology ↑

QINETIQ PROPRIETARY

QINETIQ PROPRIETARY10

Example FIVC and Symptoms

Post +5Gz breathing air (21% O2) Post +5Gz breathing 94% O2

QINETIQ PROPRIETARY

QINETIQ PROPRIETARY11

Results: Effect of Gz duration on lung volume

***

**

Data are mean ± SE

* Significantly Different from baseline

QINETIQ PROPRIETARY

QINETIQ PROPRIETARY12

Results: Effect of O2 concentration on lung volume

12

Phase 1Phase 2

Data are mean ± SE

QINETIQ PROPRIETARY

QINETIQ PROPRIETARY13

Symptomology: Effect of +Gz Duration and Inspired O2 Concentration

94% O2

QINETIQ PROPRIETARY

QINETIQ PROPRIETARY14

Phase 3 Results – Symptoms and FIVC

Mean ± SE

* Significantly different from 60 %†Significantly different from 95 % baseline

‡ Significantly different from 60 % baseline

QINETIQ PROPRIETARY

QINETIQ PROPRIETARY15

Operational Significance of Findings

• The majority of individuals will develop acceleration atelectasis when exposed to >90 s of moderate +Gz breathing high oxygen concentrations– Reducing the length of exposure moderates this but less than 30 s required to prevent it

– Reducing the % of oxygen inspired markedly reduces the extent of atelectasis

– 60% still produces atelectasis in susceptible individuals

– <45% required to prevent it

• Cumulative exposure can lead to atelectasis– Exposures that would otherwise not be expected to result in atelectasis (e.g. 30 s breathing 60%) can do if they are

repeated a number of times

• On average the performance of two deep breaths can reverse acceleration atelectasis– A greater number may be required for those individuals more prone to developing atelectasis

QINETIQ PROPRIETARY

QINETIQ PROPRIETARY16

Where do we go from here?

• We have found evidence of atelectasis during cumulative exposure to +Gz acceleration despite breathing O2

concentrations that are thought to reverse it

– Are operational flight profiles causing atelectasis in fast jet aircrew?

– Could we minimise the effect of cumulative exposure by having aircrew taking deep breaths after exposure to high Gz?

Typical air combat manoeuvre Gz profile in the F-18 taken from: Newman DG & Callister R (1999); Av Spa Enviro Med. 70(4); 310

• Flight trials to investigate the incidence of atelectasis when breathing high O2

concentrations

– Limited ability to control O2 concentration

• Operational relevant profiles could be investigated on centrifuges with simulator capabilities (e.g. the new RAF centrifuge being built at RAF College Cranwell)

– Would allow safe study of techniques to

reverse atelectasis or prevent

QINETIQ PROPRIETARY

QINETIQ PROPRIETARY