Physiology Flashcards

1
Q

***4 lung volume, 4 lung capacities

A
TLC = VC + RV (Normal: VC = 5L, TV = 500mL)
TLC = IC + FRC
VC = TV + IRV + ERV
FRC = ERV + RV
IC = IRV + TV
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2
Q

Nitrogen wash out test (Determine FRC)

A

Keep Breathing in pure O2 (no nitrogen)
—> wash out all N2 in lungs

[N2] x FRC = [N2 in bag] x volume of expired gas

Other methods of determining FRC:

  • Body plethysmography: Boyle’s law
  • Helium dilution method
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3
Q

Measure uneven ventilation

A
  1. Single breath nitrogen washout
    —> full inspiration of pure oxygen from residual volume to TLC
    —> breathe out slowly and evenly to RV
    —> measure N2 concentration changes

Phase 1:

  • very short
  • 0 N2 concentration (upper airways)
  • pure O2 expired

Phase 2:

  • short
  • rapid increase in N2 concentration
  • N2 washed out from anatomical dead space

Phase 3:

  • alveolar gas
  • flat slope normally
  • slope = % increases in N2 concentration per volume of expired gas
  • measure of UNEVEN ventilation (normal: 0-1.5%)

Phase 4:

  • abruptly increase in N2 concentration
  • when breathing out to RV, only alveoli at the top of lung continue to empty
  • alveolar at the base closed
  • measure closing volume of basal alveoli
  • 10% VC in young adult
  • increase in premature airway closure (emphysema, asthma)
  • basal alveoli 提早 close (during phase 3) —> 拉闊距離 —> increase closing volume
  1. Multiple breaths nitrogen washout test
    - breathe pure oxygen at constant tidal volume for 7 minutes
    - plot N2 concentration against number of breaths
    - exponential curve
    - even ventilation —> uniform washout rate —> straight line on semi-log paper
    - uneven ventilation —> different wash out rate —> no straight line
    - causes:
    —> regional disturbance in expansion (oedema)
    —> regional changes in elasticity/CL (change in time constant: time for filling alveoli)
    —> regional obstruction (bronchoconstriction)
    —> regional check valve (radial traction —> Raw)
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4
Q

Maximal expiratory pressure

A

Relationship between lung volume and maximal expiratory pressure:
—> Volume↑ —> P↑

Length-tension relationship of skeletal muscle
—> tension depends on optimal length of muscle
—> at TLC: expiratory muscle at optimal length —> greatest tension
—> at RV: inspiratory muscle at optimal length —> greatest tension

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5
Q

Maximum flow rate

A

Maximum flow rate = Lung recoil pressure / Raw upstream of EPP

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6
Q

FEV1/FVC

A

FEV1: volume comes out in 1st second
FVC: total volume comes out after forcing

Normal: FEV1: 4L, FVC: 5L —> FEV1/FVC = 80%

Fibrosis: FEV1 no change/↓, FVC ↓↓ —> FEV1/FVC = 90%
Asthma: FEV1 ↓↓, FVC no change/↓ —> FEV1/FVC = 45%

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7
Q

***Maximal expiratory and maximal inspiratory flow-volume curve

A

Ascending limb: effort dependent, Raw dependent
Descending limb: effort independent, Raw dependent

Emphysema:
- TLC ↑ (curve shifts left)
- RV ↑ (curve shifts left)
- VC no change/↓ (curve 無變/窄左)
- Ascending limb
—> gentler slope
—> poor effort (muscle longer than optimal length)
—> Raw ↑
—> lower peak
- Descending limb
—> lower flow rate 
—> scooped out appearance: early closure of airway due to dynamic airway compression
- Inspiration
—> smaller flow
—> easier lung recoil
—> poor effort
—> Raw ↑
***- ↓FEV1 + no change/↓FVC —> FEV1/FVC <80%
Fibrosis:
- TLC↓ (curve shifts right)
- RV↓ (curve shifts right)
- VC↓ (curve 窄左)
- Ascending limb
—> similar slope to normal
—> poor effort (muscle longer than optimal length)
—> but Raw↓ (in favour)
—> lower peak
- Descending limb
—> higher flow rate 
—> bigger lung recoil pressure to force air out
—> Raw↓ (in favour)
- Inspiration
—> smaller flow
—> larger lung recoil
—> poor effort
—> Raw↓ (in favour)
***- no change/↓FEV1 + ↓FVC —> FEV1/FVC>80%
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8
Q

Blood pressure reading

A

Auscultatory (Korotkoff sound) —> Gold standard —> directly measure SBP, DBP
Phase nothing (cuff pressure > systolic pressure)
Phase 1: Regular tapping (cuff pressure = systolic pressure)
Phase 2: tapping + murmur (intermittent / turbulent pulsatile flow)
Phase 3: loud, banging sound
Phase 4: sudden softening (cuff pressure = diastolic pressure —> return to continuous blood flow)
Phase 5: cessation of all sound (slightly below diastolic pressure —> continuous laminar flow)

Electronic / Oscillatory method —> “calculation” of BP
Cuff deflating —> amplitude of pressure wave by pulse detected by monitor —> when amplitude is maximum —> mean arterial pressure —> device estimate systolic and diastolic value from mean arterial pressure

Advantage:

  • can measure BP in critical care patients with muted Korotkoff sounds
  • external noise not a problem

Disadvantage:

  • sensitive to patient movement
  • erroneous determination of mean BP would produce inaccurate value for systolic and diastolic BP
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9
Q

Variation in BP

A
  1. Between-readings:
    - white coat hypertension (SBP may be higher initially, DBP no difference)
  2. Between-events
  3. Difference between left and right arm should be <5mmHg
  4. Inter / intra-observer variation
  5. Different accuracies for different equipment
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10
Q

Effect of posture in change in BP

A
  1. Lying to upright
    - Gravitation pressure act on lower limb blood —> venous return ↓ —> BP ↓ (very short, cannot be detected unless catherterisation
    —> detected by baroreceptors —> cardiovascular centre
    —> ↑ sympathetic activity —> ↑ TPR —> ↑ DBP more —> mean BP after standing up ↑
    —> venomotor tone slowly increase —> ↓ venous compliance —> ↑ venous return
    —> ↑ cardiac output
  2. Arm position (effect of gravitational pressure on weight of blood column above heart)
    Every 1.3 elevation above heart —> 1 mmHg ↓ (affected SBP, DBP equally)
  3. Activity:
    SBP, DBP both ↑ by 10 mmHg
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11
Q

Urine flow and blood pressure

A
  1. Effect of saline infusion —> neural, neurohormonal, hormonal control of BP
2. Effect of carotid artery occlusion
—> ↓ stimulation of baroreceptor
—> ↑ SNS on heart —> ↓ HR, force
—> ↑ SNS on arteriole —> ↑ TPR
—> ↑ SNS on vein —> ↑ venous return —> ↑ SV
  1. Effect of adrenaline
    Low dose: only stimulate beta receptor in heart —> ↑ HR, ↑ force —> ↑ CO —> ↑ BP
    Medium dose: stimulate alpha receptor in vessel —> vasoconstriction —> ↑ TPR —> ↑ BP
    High dose: stimulate renal sympathetic nerve —> ↑ renin release —> ↑ water retention —> ↓ urine output
4. Effect of osmotic diuresis
Filtered concentration > tubular maximum
—> glucose remain in collecting duct
—> ↓ osmotic gradient between collecting duct and interstitial space
—> Diuresis
—> no change in BP
  1. Loop diuretic
    —> inhibit NKCC —> inhibit Na reabsoption
    —> ↓ osmolarity of interstitium
    —> ↓ water reabsorption from collecting duct
    —> Diuresis
6. ADH
—> ↑ permeability of collecting duct to water
—> ↑ water reabsorption
—> ↓ urine output
—> slight ↑ BP
  1. Effect of blood loss / volume depletion
    —> Atrial volume receptor —> neural + neurohormonal control
    —> Baroreceptor —> neural control
    —> Atrial muscle —> hormonal control
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