Vibration Physiology

Question 1

Advise strategies to minimise the impact of vibration on aircrew and passengers

Answer 1

Engineering vibration out with aircraft design, maintenance, lubrication, damping, dynamic vibration absorbers, avoidance.
Administrative and clinical countermeasure with limit exposure, conditioning exercises, back conditioning, supportive management, MECR, lumbar support programme

Question 2

Explain the difference between vibration and resonance

Answer 2

Resonance is the frequency at which the oscillations of vibrations occur with maximum amplitude

Vibration is a form of motion that repeatedly alternates in direction

Question 3

Describe how human anatomy responds to vibration at various frequencies

Answer 3

.Multiple masses connected with complex tissues eg ligaments, tendones
Non - uniform Isolation and damping qualities eg muscles
Shoulder girdle 4-5 Hz
Abdominal organs 4-8 Hz
Head 5-6 Hz
Facial tissues 15-20 Hz
Eyes 60-90 Hz

Question 4

Isolation vs damping

Answer 4

Isolation: spring to isolated something from vibration source but create resonance
Damping reduces resonant but degrade the effects of isolation

Question 5

Identify sources of vibration in aircraft

Answer 5

Fixed wing
Turbulence
Engines/props
High G
Wing flexing
High speed, low level

Rotary wing
Engines/transmissions
Rotors
Blade pass frequency
Blade flap - forward blade moving fast in = more lift = vibration

Weapons

Question 6

Describe the clinically significant effects of vibration exposure.

Answer 6

Symptoms

• Motion sickness at 0.2 - 0.7 Hz
• Abdo, chest and back pain
• fatigue
• performance impairment, distraction
• impaired manual dexterity
• Speech intelligibility
• hyperventilation
• Rubbing injuries

Question 7

Describe how vibration can affect aircrew performance

Answer 7

Function on aircrew
- 2-6 Hz - hand eye coordination, Outstretched hand position poor

• 4-8 Hz - movement of hand on supported arm poor
• 20 Hz - speech intelligibility affected
• 60 Hz - intraocular structures - may affect Va

Study found

• 4-8 Hz less tolerance
• 1–3 Hx breathing difficulty
• 1 min at 8 Hz = tachycardia

Vision

• VA reduced at 20-40 and 60-90 Hz
• Seated subject - spine provides good isolation
• Standing subject - legs rigid, no isolation
• Backrest and headrest - transmit vibration by direct contact

Question 8

Why is low back pain common in aircrew, especially in helicopters

Answer 8

• Hunched posture
• pelvic rotation using rudders
• vibration
• prolonged sitting
• poor ergonomics

Question 9

What is the most operationally important effect for Vibration

Answer 9

Vision effects

Reduced VA with whole body vibration 20-40 and 60-90Hz

Question 10

Explain with visual reflex’s and which one is better at what

Answer 10

Pursuit reflex: Following a moving target with eyes while head is still.

• Slow response eg vibrating instruments become blurry
• effective up to 1Hz

Vestibule-ocular reflex

• Simple and short pathway with rapid response
• effective up to 8 Hz
• useful as can see environment outside even when we are being vibrated around

Question 11

Effects of vibration on cardiovascular system

Answer 11

Increase BMR
Increase HR
Increase BP
Cardiac rhythm changes

Question 12

Effects of vibration on Respiration

Answer 12

Hyperventilation
Hypocapnia
Maximum at 3-4 Hz

Question 13

Effect on Neuromuscular by vibration

Answer 13

Increase muscle activity
Erroneous perception of muscle stretch due vibration at 20-100Hz
Involuntary muscle tensing: mediated through muscle spindles and Golgi tendon organs.

Question 14

Vibration should have little impact on visual cues related to 
A. Printed checklist
B. The horizon
C. Helmet-mounted displays
D. Cockpit instruments

Answer 14

B. The horizon