the respiratory system under stress zhj. 2 objectives use the knowledge to predict the response of...

THE RESPIRATORY

SYSTEMUNDER STRESS

ZHJ

2

OBJECTIVES Use the knowledge to predict the response

of the respiratory system to three physiologic stresses

—Exercise

—Ascent to altitude

—Diving

3

Identifies the physiologic stresses involved in exercise

Predicts the responses of the respiratory system to acute exercise

Describes the effects of long-term exercise programs (training) on the respiratory system

4

Identifies the physiologic stresses involved in the ascent to altitude

Predicts the initial responses of the respiratory system to the ascent to altitude

Describes the acclimatization of the cardiovascular and respiratory systems to residence at high altitude

5

Identifies the physiologic stresses involved in diving

Predicts the responses of the respiratory system to various type of diving

6

EXERCISE AND THE RESPIRATORY SYSTEM

Exerciseincrease

Metabolism

(the working muscles)

the demand for oxygen

the productionof carbon dioxide

lactic acid production

the respiratory system

the cardiovascular system

7


Acute Effects

－ the effects of exercise in an untrained person are mainly a function of an increase in the cardiac output coupled with an increase in alveolar ventilation

8


Mechanics of breathing Alveolar ventilation Pulmonary blood flow Ventilation-perfusion relationships Diffusion through the alveolar-capillary barrier Oxygen and carbon dioxide transport by the blood Acid-base balance

9


Mechanics of breathing

Elastic work of breathing

Resistance work of breathing

Moderateexercise

Severeexercise

10


Alveolar ventilation

Tidal volume

Frequency

Anatomic dead space

Alveolar dead space (if present)

VD/VT

Moderateexercise

Severeexercise

11


Pulmonary blood flow

Perfusion of upper lung

Pulmonary vascular resistance

Linear velocity of blood flow

Moderateexercise

Severeexercise

12


Ventilation-perfusion relationships

Ventilation-perfusion matching

Ventilation-perfusion ratio

Moderateexercise

Severeexercise

13



Distance up the lungtopbottom

rest

exercise

1

2

3

VA

/Q．

．

14


Diffusion through the alveolar-capillary barrier

Surface area Perfusion limitation Partial pressure gradients

Moderateexercise

Severeexercise

15


At the tissues

Oxygen unloading

Carbon dioxide loading

Moderateexercise

Severeexercise

16


PAo2

Pao2

Paco2

pHa

Arteriovenous O2 difference

Moderateexercise

Severeexercise

or、

17

Training Effects

The ability to perform physical exercise increases with training

Alterations in the cardiovascular system and in muscle metabolism rather than changes in the respiratory system

The increase of maximal oxygen uptake is mainly a result of an increased maximal cardiac output

18

Training Effects Physical training lowers the resting heart

rate and increases the resting stroke volume

--inducing mitochondrial proliferation

--increasing the concentration of oxidative enzymes

-- increasing the synthesis of glycogen and triglyceride

19

ALTITUDE AND ACCLIMATIZATION

PAo2 =PIo2-PAco2 /R+[F]

PIo2 =0.21×(PB-47torr) altitude (ft ) PB (torr) PIo2 PA co2 PAo2

15000 429 80.2 32 45

18000 380

20000 349

50000 87

63000 47 (the fluid in blood “boils”)

20

ALTITUDE AND ACCLIMATIZATION Acute Effects

The symptoms are mainly due to hypoxiaand may include: sleepiness decreased visual acuity laziness clumsiness a false sense of well-being tremors impaired judgment loss of consciousness blunted pain perception death

increasing errors on simple tasks

21

ALTITUDE AND ACCLIMATIZATION Acute Effects Acute mountain sickness － a group of symptom

s include headache dizziness breathlessness at rest weakness malaise nausea anorexia sweating palpitations dimness of vision partial deafness sleeplessness fluid retention dyspnea on exertion

These symptoms are a result of hypoxia and hypocapnia,

and alkalosis or cerebral edema, or both.

22

ALTITUDE AND ACCLIMATIZATION Control of breathing

The decreased PAo2 and Pao2 result in stimulation of the arterial chemoreceptors rather than the central chemoreceptors

Pao2 =45torr, minute ventilation is doubled

Paco2 fall , causing respiratory alkalosis The pH of the cerebrospinal fluid increasing the central chemoreceptors is depressed by

hypocapnia alkalosis

23


Mechanics of breathing Rate and depth of breathing ↑ Interstitial fluid volume of the lung ↑ (vc↓ in the fi

rst 24h) More turbulent airflow, resistance work of breath

ing ↑ Maximal airflow rates ↑, due to decreased gas d

ensity

24


Alveolar ventilation The anatomic dead space ↓, the reflex bronchoconstriction↑, the opposing effect of increased VT

VD/VT ↓(in any event) Previously collapsed or poorly ventilated alveoli will be better

ventilated Regional distribution of alveolar ventilation more uniform

25

ALTITUDE AND ACCLIMATIZATION Pulmonary blood flow

Lung inflation

Arterial chemoreceptor

Sympathetic stimulation

of the cardiovascular

system

Cardiac output

Heart rate

Systemic blood

pressure

Hypoxic pulmonary

vasoconstriction

Cardiac output

Sympathetic stimulation

of larger pulmonary vessels

Pulmonary artery

pressure

Right ventricular work load

26



regional VA/Q more uniform

27


Diffusion through the alveolar-capillary barrier

PAo2↓ ↓

PVo2↓Partial pressure gradients ↓

The thickness of the barrier

Pulmonary vascular distention

Higher lung volumes

28


Oxygen and carbon dioxide transport by the blood PAo2 to be below the flat part of the oxyhemoglo

bin dissociation curve , causing a low arterial oxygen content

Hypocapnia aid in oxygen loading in the lung and interfere with oxygen unloading at the tissues

the hemoglobin concentration ↑ (the first 2d)

29


Cerebral circulation Hypocapnia is a strong cerebral

vasoconstrictor Hypoxia cause cerebral vasodilation and can

cause hyperperfusion The hyperperfusion and cerebral edema

elevate intracranial pressureLead to increase in sympathetic activity in the

body increasing the possibility of pulmonary edema and

promoting renal salt and water retention

30


Acid-base balance

hypocapnia

respiratory alkalosis

31


Acclimatization

see the following four lists

32

Immediate Early adaptive

(72H)

Late adaptive

(2 to 6 weeks)

Spontaneous ventilation

Minute ventilation ↑ ↑ ↑ Respiratory rate variable variable variable

Tidal volume ↑ ↑ ↑ Arterial Po2 ↓ ↓ ↓ Arterial Pco2 ↓ ↓ ↓ Arterial pH ↑ ↑ ↑ Arterial HCO-

3 ↓ ↓

table1

33


(72H)

Late adaptive

(2 to 6 weeks)

Evaluation of lung function

Vital capacity ↓ Maximum airflow rates ↑ ↑ ↑

Functional residual

capacity

Ventilatory response to inhaled CO2

↑ ↑

Ventilatory response to hypoxia

Pulmonary vascular resistance

↑ ↑ ↑

table2

34


(72H)

Late adaptive

(2 to 6 weeks)

Oxygen transport

Hemoglobin ↑ ↑ Erythropoietin ↑ P50 ↓ ↑ ↑ 2,3-BPG ↑ ↑ Cardiac output ↑ ↓

table3

35


(72H)

Late adaptive

(2 to 6 weeks)

Central nervous system

Headaches, nausea, insomnia

↑

Perception, judgment ↓ Spinal fluid pH ↑ Spinal fluid HCO-

3 ↓ ↓

Cerebral edema ↑

table4

36

DIVING AND THE RESPIRATORY SYSTEM

The major physiologic stresses involved in diving include Elevated ambient pressure Decreased effects of gravity Altered respiration Hypothermia Sensory impairment

37


The severity of the stress involved depends on

The depth attained The length of the dive Whether the breath is held or a breathing

apparatus is used

38


Physical principles At a depth of 33 ft of seawater (or 34 ft of fresh

water) , total ambient pressure is equal to 1520 torr

Follow Boyle’s law, at 33 ft of depth (2atm) lung volume is cut in half

According to Dalton’s law, the partial pressures of the constituent gases also increase

According to Henry’s law, the amounts dissolved in tissues of the body increase

39


Effects of immersion up to the neck (Mechanics of breathing)

Averaging about 20 cm H2O Decrease FRC by about 50 percent ERV decreased by as much as 70 percent IRV is increased RV is slightly decreased VC and TLC are only slightly decreased The work of breathing increases by about 60

percent

40


Effects of immersion up to the neck (Pulmonary blood flow)

Augmenting venous return, by approximately 500ml

Right atrial pressure increases from about -2 to +16 mmHg

The cardiac output and stroke volume increase by about 30 percent

Pulmonary blood flow and PAP increase Immersion diuresis (a few minutes,4~5folds)

41


Breath-hold diving (Mechanics of breathing)

The total pressure of gases within the lungs is equal to ambient pressure

The volume within the thorax must decrease proportionately

Partial pressures of gases increase

42


Breath-hold diving

The diving reflex Demonstrate a profound bradycardia and increa

sed systemic vascular resistance with face immersion (especially into cold water)

43


Breath-hold diving

Gas exchange in the lungs

Before a dive, PAo2 =120torr

PAco2 =30torr During a breath-hold dive to a depth of 33 ft

The transfer of oxygen from alveolus to blood is undisturbed

vice versa, retention of carbon dioxide in the blood

44


The use of underwater breathing apparatus

During a dive with scuba gear, gas pressure within the lungs remains close to the ambient pressure at any particular depth

45



(Mechanics of breathing) At very great depths , increased gas density

becomes a problem because it elevates the airways resistance work of breathing during turbulent flow

this is one reason for replacing nitrogen with helium for deep dives (helium is only about one-seventh as dense as nitrogen)

46



Control of breathing The respiratory system’s sensitivity to carbon

dioxide is decreased at great depths because of increased gas densities and high Pao2

47


Other hazards at depth Barotrauma Decompression illness Nitrogen narcosis Oxygen toxicity High-pressure nervous syndrome

48

Thank you for constructive criticism and help !

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