Respiration under stress

Information about Respiration under stress

Published on August 1, 2014

Author: kalaithemaverick

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Respiration under stress Dr.KALAIKOVAN .B DNB Resident Dept of Pulmonology Yashoda Hospitals : Respiration under stress Dr.KALAIKOVAN .B DNB Resident Dept of Pulmonology Y ashoda Hospitals Respiration under stress: Respiration under stress Exercise High altitude Diving EXERCISE!: EXERCISE! Ventilation Oxygen consumption Arterial blood gases Oxygen diffusion capacity Alveolar-arterial oxygen tension difference Circulation EXERCISE: EXERCISE Neural signals (rate & depth) PCO2 (PO2 and pH) Cardiac Output Maximal Hb saturation Dilate airways PowerPoint Presentation: Alveolar ventilation may increase as much as 20-fold Oxygen diffusion capacity as much as 3-fold C ardiac output as much as 6-fold Blood flow to muscle as much as 25-fold O xygen consumption as much as 20-fold and Heat production as much as 20-fold. Alveolar ventilation may increase as much as 20-fold : Alveolar ventilation may increase as much as 20-fold The cerebral cortex send collateral signals to the medulla oblongata to increase the rate and depth of breathing. 2. Proprioceptors in the moving muscles, tendons, and joints transmit sensory signals via the spinal cord to the respiratory centers of the medulla . 3. The increase in body temperature during exercise also may contribute to increased ventilation PowerPoint Presentation: During normal quiet breathing, an adult exchanges about 6 L of air per minute. During strenuous exercise, this can increase to 120 L/min, a 20-fold increase . The increased alveolar ventilation is produced mainly by an increased depth of ventilation (increased tidal volume ),rather than by an increased rate of ventilation PowerPoint Presentation: During very heavy exercise, both an increased depth and frequency of ventilation are seen. The tidal volume is usually about 50 percent of the vital capacity, and the respiratory rate is usually between 40 and 50 breaths/min. PowerPoint Presentation: The first stage -an increase in alveolar ventilation , within seconds after the onset of exercise . The second stage -a slow, gradual further increase in alveolar ventilation The third stage , alveolar ventilation stabilizes. When an individual stops exercising, alveolar ventilation decreases abruptly OXYGEN CONSUMPTION : OXYGEN CONSUMPTION At rest, normal oxygen consumption (Vo2 ) is about 250 mL /min. The skeletal muscles account for approximately 35 to 40 percent of the total . During exercise,the skeletal muscles may account for more than 95 percent . During heavy exercise,Vo2 of an untrained person may be more than 3500 mL of O2/mm. &of an elite athlete may be over 5000 mLO2/min. Respiratory responses to exercise: Respiratory responses to exercise PowerPoint Presentation: No significant PaO2 ,PaCO2 , or pH changes are seen between rest and approximately 60 to 70 percent of maximal Vo2 . The PaO2 remains constant during mild, moderate, and heavy exercise Respiratory responses to exercise: Respiratory responses to exercise PowerPoint Presentation: Comparison of the increases in blood flow and ventilation Oxygen diffusion capacity as much as 3-fold : Oxygen diffusion capacity as much as 3-fold Results from the increased cardiac output during exercise. The increased cardiac output increases the intravascular pressure in the pulmonary artery and left atrium. (1) distend the pulmonary capillaries that are not fully dilated (2 ) open, or recruit, closed pulmonary capillaries Additional changes with exercise: Additional changes with exercise Pulmonary artery, venous and capillary pressures rise Recruitment and distension of capillaries Pulmonary vascular resistance falls Pulmonary diffusing capacity increases Shifts of the O 2 dissociation curve Capillaries open up in exercising muscle Systemic vascular resistance falls PowerPoint Presentation: Altitude Physiology The environment changes that occur with altitude are is:: The environment changes that occur with altitude are is: a decreased barometric pressure a decreased temperature a decreased relative humidity hypoxia, i.e., a relatively lower level of ambient oxygen PowerPoint Presentation: SIGNIFICANT ATMOSPHERIC PRESSURE VARIATION WITH ALTITUDE: ALTITUDE PRESSURE (FEET) ( mm of Hg) (ATMOSPHERIC UNIT) 0 760 1 18,000 380 1/2 34,000 190 1/4 48,000 95 1/8 63,000 47 1/16 BASIC CONCEPT:: BASIC CONCEPT : Human body is specifically designed in such a way that it delivers adequate O2 to the tissues only when oxygen is supplied at a pressure close to the sea-level (P = 760 mm Hg  PO2 =159 mm Hg) So, at high altitude there is hypoxic hypoxia  tissue oxygenation suffers physiological derangements. “ connecting a 24 volt motor to a 6 volt battery ”—perfect comparison by J.S.Milledge . PHYSIOLOGICALY CRITICAL ALTITUDES:: PHYSIOLOGICALY CRITICAL ALTITUDES : Upto 10,000 ft (3,000 m) ”safe zone of rapid ascent”classically defines ‘high altitude’ At 18,000 ft (5,500 m)  upper limit of permanent human inhabitation Above 20,000 ft (6,000 m)  life is endangered without supplemental oxygen From 40,000 ft(12,000 m)  Ozone layer starts PowerPoint Presentation: Mount Everest 29,028 ft (8848mt) Atmospheric Pr=255mmHg PO2= 53mmHg Inspired PO2=21%x(255-47) =44mmHg Unacclimatized person Unconscious in 45 seconds Dead in 4 to 6 minutes WARNING!: When hemoglobin saturation falls below serious cellular dysfunction occurs; and if prolonged, can cause death 60% WARNING! At higher altitudes, there is an adverse affect on one’s ability to provide sufficient oxygen: At higher altitudes, there is an adverse affect on one’s ability to provide sufficient oxygen Dalton’s law states that the partial pressure of a gas = the % concentration of the gas x total pressure of gas mixture e.g., at sea level: barometric pressure = ~ 760 mmHg % O 2 in the air = 20.93% partial pressure of O 2 = 0.2093 x 760 mmHg = 159 mmHg PowerPoint Presentation: Inspired O 2 Content Sea-level 2000 m 760 x 0.2093 = 159 mmHg 596 x 0.2093 = 125 mmHg 462 x 0.2093 = 97 mmHg 354 x 0.2093 = 74 mmHg 267 x 0.2093 = 56 mmHg Barometric Pressure P I O 2 4000 m 6000 m 8000 m PowerPoint Presentation: vs. say the summit of Mt. Everest (8848 m) BP = ~252 mmHg %O 2 = 20.93% PO 2 = 0.2093 x 252 mmHg = ~ 53 mmHg PAO2=0.2093 x (252-47) =0.21 x205 =43 PowerPoint Presentation: Climber on the Everest Summit PHYSIOLOGICAL RESPONSES TO HIGH ALTITUDE HYPOXIA:: PHYSIOLOGICAL RESPONSES TO HIGH ALTITUDE HYPOXIA: Arbitrarily Divided into following two--- Acute responses (aka accommodation) Long term responses ( aka acclimatization) Accomodation Refers to immediate reflex adjustments of respiratory and cardiovascular system to hypoxia Acclimatization Refers to changes in body tissues in response to long term exposure to hypoxia ACCOMMODATION AT HIGH ALTITUDE:: ACCOMMODATION AT HIGH ALTITUDE: I mmediate reflex responses of the body to acute hypoxic exposure. Hyperventilation: arterial PO2  stimulation of peripheral chemoreceptors  increased rate & depth of breathing B) Tachycardia: Also d/t peripheral chemo. Response  CO  oxygen delivery to the tissues Contd…..: Contd….. Increased 2,3-DPG conc. in RBC : within hours, ↑ deoxy-Hb conc.  locally ↑pH  ↑2,3-DPG  ↓oxygen affinity of Hb  tissue O2 tension maintained at higher than normal level ACCLIMATIZATION AT HIGH ALTITUDE:: ACCLIMATIZATION AT HIGH ALTITUDE: Delivery of atmospheric O2 to the tissues normally involve 3 stages---with a drop in PO2 at each stage . When the starting PO2 is lower than normal, body undergoes acclimatization so as to — .. A)Sustained Hyperventilation:: A)Sustained Hyperventilation: Prolonged hyperventilation  CO2 wash-out  respiratory alkalosis renal compensation alkaline urine normalization of pH of blood & CSF withdrawal of central chemo- mediated respiratory depression  net result is ↑resting pulmonary ventilation (by ~5 folds ),primarily d/t ↑ in TV ( upto 50% of VC) Such powerful ventilatory drive is also possible as- ↑sensitivity of chemo receptor to PO2 & PCO2 Somewhat ↓ in work of breathing  make hyperventilation easy & less tiring B) Other Respiratory Changes:: B) Other Respiratory Changes: ↑ TLC : esp in high- landers (natives for generations)  evidenced by relatively enlarged (barrel-shaped) chest l/t ↑ ventilatory capacity in relation to body mass. ↑ Diffusing capacity of lungs : d/t hypoxic pulmonary vasoconstriction  Pul . Hypertension  ↑ no. of pulmonary capillaries C)↑Vascularity of the Tissues:: C)↑ Vascularity of the Tissues: More capillaries open up in tissues than at sea-level (normal ~25 % open & rest—remaining as‘reserve ’). This combined with systemic vasodilatation(also a hypoxic response)  more O2 delivery to tissues. D) Cellular level changes: ↑ intracellular mitochondrial density ↑ conc. of cellular oxidative enzyme E) Physiological Polycythemia:: E) Physiological Polycythemia : Polycythemia at 4600 m altitude: Polycythemia at 4600 m altitude Hemoglobin concentration 19.8 g/dl Arterial PO 2 45 mm Hg O 2 saturation 81% O 2 concentration 22.4 ml/dl F) CVS Changes:: F) CVS Changes: Adequate restoration of tissue O2 supply  gradual reversal of the hyperdynamic activity (occurred during initial accommodative period)  ↑performance & ↓discomfort. PowerPoint Presentation: Uneven hypoxic pulmonary vasconstriction exposes some capillaries to high pressure PowerPoint Presentation: Inspired O 2 , arterial blood O 2 , and O 2 saturation all decrease with increasing altitude PowerPoint Presentation: PO 2 cascade at sea level and high altitude PowerPoint Presentation: Exercise Performance At moderate altitudes, the reduced air density and wind resistance, and the reduced availability of oxygen tends to : (a) decrease aerobic exercise performance; (b) increase anaerobic exercise performance PowerPoint Presentation: Toronto ~ 75 m PowerPoint Presentation: Mexico City, 1968 Summer Olympics Altitude = 2800 m (~9200 ft) World records: all of the men’s races <400m (including relays) 400m hurdles Triple jump Long jump (Bob Beman broke the record by 55 cm!) PowerPoint Presentation: Endurance events: -all exhibited poor performances Rule of thumb- 11% decrease in Vo2 Max for every 1000m increase above 2500m Diving: Diving PowerPoint Presentation: Physiological Stresses with Diving Mechanism of decompression sickness Treatment and prevention of decompression sickness Use of helium-oxygen for breathing Saturation diving Inert gas narcosis CNS toxicity caused by high-pressure oxygen Pulmonary oxygen toxicity Hyperbaric oxygen therapy Concentration of dissolved O2 in the blood with hyperbaric therapy: Concentration of dissolved O 2 in the blood with hyperbaric therapy Barometric pressure = 3 x 760 mm Hg Alveolar and arterial PO 2 exceed 2000 Solubility of O 2 is 0.003 ml/dl/mm Hg Dissolved O 2 = 6 ml/dl This exceeds the normal arterial-venous difference for O 2

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