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Respiratory Muscle Fatigue and Ventilatory Failure

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Abdominal paradox. Respiratory alternans. Pathophysiology of Respiratory Muscle Fatigue ... of fatigue--level of exercise which cannot be sustained indefinitely, ... – PowerPoint PPT presentation

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Title: Respiratory Muscle Fatigue and Ventilatory Failure


1
Respiratory Muscle Fatigue and Ventilatory Failure
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2

Respiratory Failure
Lung Failure
Pump Failure
Gas exchange failure
Ventilatory failure
manifested by
Hypoxemia
manifested by
Hypercapnia
Central
Fatigue
Mechanical
depression
defect
3
Physical Signs of Respiratory Muscle Fatigue
  • Tachypnea
  • Abdominal paradox
  • Respiratory alternans

4
Pathophysiology of Respiratory Muscle Fatigue
  • Muscle contractile failure
  • Neuromuscular transmission failure
  • Fatigue of central nervous system

5
Muscle Contractile Failure
  • Slow muscle, a high oxidative potential, is less
    susceptible to developing fatigue than fast
    muscle
  • MgATP H2O ? MgADP Pi H
  • Glycogen depletion, lactic acid accumulation,
    inability to utilize blood-borne substances, and
    decrease in the rate of ATP hydrolysis are merged
    to explain loss of force.

6
Neuromuscular Transmission Failure
  • Action potential fatigue minimized when
    contraction was inhibited by hypertonic solution
    and abolished completely in noncontracting fibers
    poisoned with cyanide or iodoacetate
  • Neuromuscular transmission failure in man during
    diaphragmatic fatigue not clearly understood

7
Determinants of Critical Task (Pressure, Work)
  • The threshold of fatigue--level of exercise which
    cannot be sustained indefinitely, expressed as a
    percentage of the maximum performance
  • Diaphragm--40 of maximum, all the inspiratory
    muscle--50 to 70 of the maximum, mean
    inspiratory flow--0.6-0.9 L/s, the ratio of
    inspiratory time--0.3-0.5
  • Largely affected by other factors (pressure-time
    index, velocity of contraction, operational
    length, energy supply, efficiency of the muscle)

8
Fatigue of The Central Nervous System
  • Fatigue characterized not only by loss of force
    but also by slowing of the muscle contractile
    speed
  • Afferent information via large (types I and II)
    and small (types III and IV) fibers affects the
    central respiratory controllers discharge in
    terms of firing rate, firing time, and frequency
    of breathing

9
Respiratory Muscle Fatigue and Ventilatory
Failure in Clinical
  • Fatigue during loaded breathing
  • Fatigue during weaning
  • Fatigue as a cause of respiratory failure

10
Fatigue Druing Loaded Breathing
  • Stage of infinite possibilities (task of limited
    duration)
  • Stage of alternative strategies (partial resting
    of one group of muscles)
  • Stage of exhaustion (no longer sustain the
    breathing task, and gives up)

11
Fatigue During Weaning
  • Tachypnea
  • Bradypnea
  • Central apnea

12
Fatigue as Cause of Respiratoy Failure
  • CO2 retainers in chronic state of fatigue or that
    the CNS sets a pattern of breathing in an attemp
    to avoid exhaustion
  • VT ?, VD/VT ?, PaCO2?

13
THE END
  • THANKS FOR YOUR ATTENTION!
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