THE RESPIRATORY SYSTEM UNDER 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 Exercise increase Metabolism (the working muscles) the demand for oxygen the production of carbon dioxide lactic acid production the respiratory system the cardiovascular system

7 EXERCISE AND THE RESPIRATORY SYSTEM 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 EXERCISE AND THE RESPIRATORY SYSTEM  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 EXERCISE AND THE RESPIRATORY SYSTEM  Mechanics of breathing Elastic work of breathing Resistance work of breathing Moderate exercise Severe exercise

10 EXERCISE AND THE RESPIRATORY SYSTEM  Alveolar ventilation Tidal volume Frequency Anatomic dead space Alveolar dead space (if present) V D /V T Moderate exercise Severe exercise

11 EXERCISE AND THE RESPIRATORY SYSTEM  Pulmonary blood flow Perfusion of upper lung Pulmonary vascular resistance Linear velocity of blood flow Moderate exercise Severe exercise

12 EXERCISE AND THE RESPIRATORY SYSTEM  Ventilation-perfusion relationships Ventilation-perfusion matching Ventilation-perfusion ratio Moderate exercise Severe exercise

13 EXERCISE AND THE RESPIRATORY SYSTEM  Ventilation-perfusion relationships Distance up the lung topbottom rest exercise V A /Q ． ．

14 EXERCISE AND THE RESPIRATORY SYSTEM  Diffusion through the alveolar-capillary barrier  Surface area  Perfusion limitation  Partial pressure gradients Moderate exercise Severe exercise

15 EXERCISE AND THE RESPIRATORY SYSTEM  At the tissues Oxygen unloading Carbon dioxide loading Moderate exercise Severe exercise

16 EXERCISE AND THE RESPIRATORY SYSTEM P A o 2 Pa o 2 Pa co 2 pHa A rteriovenous O 2 difference Moderate exercise Severe exercise 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 P A o 2 =P I o 2 -P A co 2 /R+[F] P I o 2 =0.21 ×( P B -47torr) altitude (ft ) P B (torr) P I o 2 P A co 2 P A o (the fluid in blood “boils”)

20 ALTITUDE AND ACCLIMATIZATION  Acute Effects The symptoms are mainly due to hypoxia and 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 symptoms 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 P A o 2 and Pa o 2 result in stimulation of the arterial chemoreceptors rather than the central chemoreceptors  Pa o 2 =45torr, minute ventilation is doubled  Pa co 2 fall, causing respiratory alkalosis  The pH of the cerebrospinal fluid increasing  the central chemoreceptors is depressed by hypocapnia alkalosis

23 ALTITUDE AND ACCLIMATIZATION  Mechanics of breathing  Rate and depth of breathing ↑  Interstitial fluid volume of the lung ↑ (vc↓ in the first 24h)  More turbulent airflow, resistance work of breathing ↑  Maximal airflow rates ↑, due to decreased gas density

24 ALTITUDE AND ACCLIMATIZATION  Alveolar ventilation  The anatomic dead space ↓, the reflex bronchoconstriction ↑, the opposing effect of increased V T  V D /V T ↓(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 ALTITUDE AND ACCLIMATIZATION  Ventilation-perfusion relationships regional V A /Q more uniform

27 ALTITUDE AND ACCLIMATIZATION  Diffusion through the alveolar-capillary barrier P A o 2 ↓ ↓ P V o 2 ↓ Partial pressure gradients ↓ The thickness of the barrier Pulmonary vascular distention Higher lung volumes

28 ALTITUDE AND ACCLIMATIZATION  Oxygen and carbon dioxide transport by the blood  P A o 2 to be below the flat part of the oxyhemoglobin 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 ALTITUDE AND ACCLIMATIZATION  Cerebral circulation  Hypocapnia is a strong cerebral vasoconstrictor  Hypoxia cause cerebral vasodilation and can cause hyperperfusion  The hyperperfusion and cerebral edema elevate intracranial pressure  Lead to increase in sympathetic activity in the body  increasing the possibility of pulmonary edema and promoting renal salt and water retention

30 ALTITUDE AND ACCLIMATIZATION  Acid-base balance hypocapnia respiratory alkalosis

31 ALTITUDE AND ACCLIMATIZATION  Acclimatization see the following four lists

32 ImmediateEarly adaptive (72H) Late adaptive (2 to 6 weeks) Spontaneous ventilation Minute ventilation ↑↑↑ Respiratory rate variable Tidal volume ↑↑↑ Arterial Po 2 ↓↓↓ Arterial Pco 2 ↓↓↓ Arterial pH ↑↑↑ Arterial HCO - 3 ↓↓ table1

33 ImmediateEarly adaptive (72H) Late adaptive (2 to 6 weeks) Evaluation of lung function Vital capacity ↓ Maximum airflow rates ↑↑↑ Functional residual capacity Ventilatory response to inhaled CO 2 ↑↑ Ventilatory response to hypoxia Pulmonary vascular resistance ↑↑↑ table2

34 ImmediateEarly adaptive (72H) Late adaptive (2 to 6 weeks) Oxygen transport Hemoglobin ↑↑ Erythropoietin ↑ P 50 ↓↑↑ 2,3-BPG ↑↑ Cardiac output ↑ ↓ table3

35 ImmediateEarly adaptive (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 DIVING AND THE RESPIRATORY SYSTEM  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 DIVING AND THE RESPIRATORY SYSTEM  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 DIVING AND THE RESPIRATORY SYSTEM  Effects of immersion up to the neck (Mechanics of breathing)  Averaging about 20 cm H 2 O  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 DIVING AND THE RESPIRATORY SYSTEM  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 DIVING AND THE RESPIRATORY SYSTEM  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 DIVING AND THE RESPIRATORY SYSTEM  Breath-hold diving The diving reflex  Demonstrate a profound bradycardia and increased systemic vascular resistance with face immersion (especially into cold water)

43 DIVING AND THE RESPIRATORY SYSTEM  Breath-hold diving Gas exchange in the lungs  Before a dive, P A o 2 =120torr P A co 2 =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 DIVING AND THE RESPIRATORY SYSTEM  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 DIVING AND THE RESPIRATORY SYSTEM  The use of underwater breathing apparatus (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 DIVING AND THE RESPIRATORY SYSTEM  The use of underwater breathing apparatus Control of breathing  The respiratory system’s sensitivity to carbon dioxide is decreased at great depths because of increased gas densities and high P a o 2

47 DIVING AND THE RESPIRATORY SYSTEM  Other hazards at depth  Barotrauma  Decompression illness  Nitrogen narcosis  Oxygen toxicity  High-pressure nervous syndrome

48 Thank you for constructive criticism and help !