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Ch.12 Pulmonary Structure And Function/Ch.13 Gas Exchange and Transport/Ch…

- - - - Cellular respiration defines metabolic processes that occur within the cell that generate energy via oxygen utilization and carbon dioxide production.
      - Pulmonary respiration defines lung ventilation with a resulting uptake of oxygen and elimination of carbon dioxide to maintain blood-gas homeostasis
  - - - The lungs contain 600+ million alveoli, the final branching of the respiratory tree. These membranous sacs provide the vital surface for gas exchange between lung tissue and blood.
      - The pressure differential between the air in the lungs and the lung-chest wall interface causes them to adhere to the chest wall and literally follow its every movement. Any change in thoracic cavity volume correspondingly alters lung volume.
      - Lung volumes and capacities
        
        Static Lung Volumes
        
        Inspiratory reserve volume (IRV) is the maximum amount of air inspired above inspired tidal air.
        
        Expiratory reserve volume (ERV) is the maximum amount of air expired above the expired tidal air.
        
        Forced vital capacity (FVC) is the maximum volume expired after maximum inspiration. FVC = TV + IRV + ERV
        
        Residual lung volume (RLV) is the volume in lungs after maximum expiration.
        
        RLV increases with age, whereas IRV and ERV decrease proportionally with age. A decline in lunge tissue elasticity components with aging probably decreases breathing reserve and concomitantly increases residual lung volume.
        
        The RLV allows uninterrupted exchange of gas between the blood and alveoli to prevent fluctuations in blood gases during phases of the breathing cycle including deep breathing.
        
        The RLV temporarily increases from an acute bout of either short-term or prolonged activity. Two possible factors that increase RLV with physical activity are:
        
        1) Close of small peripheral airways
        
        2) Increase in thoracic blood volume
        
        The added blood volume does not alter the lungs' mechanical properties, but it does displace air, thus preventing complete exhalation (reduced FVC).
        
        Total lung capacity (TLC) is volume in lungs after maximum inspiration. TLC = RLV + FVC
        
        Exercise training does not appreciably change static lung volumes. Those with larger lung volumes generally reflect genetic influences and body size characteristics.
        
        Tidal volume (TV) describes air volume moved during either the inspiratory or expiratory phase of each breathing cycle. Under resting conditions TV is between .4 and 1.0L.
        
        Dynamic Lung Volumes
        
        Adequacy of pulmonary ventilation depends on how well an individual sustains high airflow levels rather than on air movement in a single breath.
        
        Dynamic ventilation depends on two factors; 1) Maximum "stroke volume" of the lungs (FVC), 2) Speed of moving a volume of air (breathing rate)
        
        Air flow velocity depends on the resistance of the respiratory passages to the smooth flow of air and the "stiffness" imposed by the mechanical properties of the chest and lung tissue to a change in shape during breathing, termed lung compliance.
        
        Forced expiratory volume (FEV) is a dynamic measurement over a time of 1s. It reflects pulmonary expiratory power and overall resistance to air movement upstream in the lungs.
        
        Some individuals with sever lung disease achieve near-normal FVC values if measured with no time limit. For this reason clinicians prefer the FEV for measurement.
        
        Maximal voluntary ventilation (MVV) evaluates ventilatory capacity with rapid and deep breathing for 15s. MVV also averages 25% higher than the ventilation during maximal exercise because exercise does not maximally stress how a healthy person breathes.
        
        Training of the ventilatory muscles improves their strength and endurance and increases both inspiratory muscle function and MVV.
        
        Ventilatory training in patients with chronic pulmonary disease enhances exercise capacity and reduces physiologic strain.
- - - - The external intercostal muscles become active and the internal intercostal muscles relax during inhalation.
        
        The diaphragm, external intercostals, sternocleidomastoids, scapular elevators, anterior serrati scleni and spinal erector muscles compose the inspiratory muscles that elevate and enlarge the thorax.
        
        The diaphragm is a dome shaped sheet of striated musculofibrous tissue. Primary ventilatory muscle. Creates airtight separation of abdominal and thoracic cavities. Its mitochondrial volume density, oxidative capacity of muscle fibers, and aerobic capacity exceed by up to fourfold that of most other skeletal muscles.
        
        During inspiration the scaleni and external intercostal muscles between the ribs contract, causing the ribs to rotate and lift up and away form the body. This action corresponds to a handle on a bucket.
      - During inspiration, the sternum thrusts outward to increase the lateral and anterior-posterior diameter of the thorax.
  - - - During strenuous activity, internal intercostal and abdominal muscles act powerfully on the ribs and abdominal cavity to reduce thoracic dimensions.
- - - - No difference emerges when comparing the average FVC of prepubescent and Olympic wrestlers, middle-distance athletes and untrained healthy subjects.
      - Similar values emerged for static and dynamic lung function of accomplished endurance athletes compared with untrained subjects of similar body size.
      - For healthy untrained individuals, no relationship exists between maximal oxygen consumption and FVC or MVV (adjusted for body size). Fatigue from strenuous physical activity frequently relates to feeling "out of breath" or "winded", yet normal capacity for pulmonary ventilation for most individuals does not limit maximal aerobic performance.
  - - - Airway warming of inspired air greatly increases the air's capacity to hold moisture, which produces considerable water loss form the respiratory passages. In cold weather, the respiratory tract loses considerable water and heat, most notably during strenuous exercise with large ventilatory volumes.
        
        Fluid loss from the airways often contributes to overall dehydration, dry mouth, burning sensation in the throat, and generalized irritation of the respiratory passages.
        
        Wearing a scarf or cellulose mask-type "balaclava" that covers the nose and mouth traps the water in exhaled air and subsequently warms and moistens the next incoming breath of air.
- - - - Minute ventilation (Ve) is the volume of air breathed each minute. The normal breathing rate during quiet breathing at rest in a thermoneutral environment averages 12 breathes per minute and TV averages .5L of air per breath. The minute ventilation equals 6L.
        
        An increase in either the rate or depth of breathing or both increases minute ventilation
      - During strenuous activity healthy young adults readily increase their breathing rate to 35-45 breaths per minute. Elite endurance athletes breathe as rapidly as 60-70 times per minute during maximal effort. TVs of 2.0L and higher commonly occur in most adults during physical activity.
        
        Even with large minute ventilations (200L among athletes), TVs for trained and untrained individuals rarely exceed 60% of vital capacity.
    - - A portion of the air in each breath does not enter the alveoli and participate in gaseous exchange with the blood. The term anatomic dead space describes this air that fills the upper airway structures (mouth, nasal passages, nasopharynx, larynx, trachea and other nondiffusible conducting portions of the respiratory tract.)
        
        The anatomic dead space generally ranges about 30% of the resting TV in healthy persons.
        
        The composition of dead-space air remains almost identical to ambient air except for its full saturation with water vapor.
        
        Shallow breathing, when compared to deeper breathing, reduces the amount of each breath to enter into and mix with alveolar air. The shallow breathing can reduce TV (example 150mL) yet still maintain 6L a minute by increasing breathing rate to 40 breaths a minute. The same 6L minute volume results from decreasing breathing rate to 12 breaths per minute and increasing TV too 500mL.
        
        Alveolar ventilation determines the gaseous concentrations at the alveolar-capillary membrane.
        
        In the example of shallow breathing, dead-space air represents the only air volume moved without any alveolar ventilation.
        
        The preceding example is an oversimplification because it assumes a constant dead space. Anatomic dead space increases as TV becomes larger; it often doubles during deep breathing from some stretching of the respiratory passages with a fuller inspiration.
        
        Importantly, any increase in dead space still represents proportionately less volume than the accompanying increase in TV. Consequently, deeper breathing provides more effective alveolar ventilation than similar minute ventilation achieved through increased breathing rate.
      - Ventilation-Perfusion Ratio
        
        Adequate gas exchange between alveoli and blood requires effective matching of alveolar ventilation to the blood perfusing the pulmonary capillaries.
        
        Approximately 4.2L of air normally ventilates the alveoli each minute at rest, and an average of 5.0L of blood flows through the pulmonary capillaries. In this case, the ratio of alveolar ventilation to pulmonary blood flow, termed the ventilation-perfusion ratio, equals .84 (4.2 divided by 5.0)..
        
        In light activity the ventilation-perfusion ratio remains approximately 0.8. During intense activity, a disproportionate increase in alveolar ventilation is produced (may exceed 5.0 in healthy persons).
        
        Sometimes the alveoli may not function adequately in gas exchange because of two factors; 1) underperfusion of blood, 2) inadequate ventilation relative to alveolar surface
        
        The term physiologic dead space describes the portion of the alveolar volume with a ventilation-perfusion ratio that approaches zero. (Portion of air distributed to either poorly ventilated or poorly perfused alveoli).
        
        In certain pathologic situations, physiologic dead space increases to 50% of the TV (emphysema, asthma, pulmonary fibrosis etc.)
        
        Increasing the rate and depth of breathing increases alveolar ventilation in physical activity.
        
        As breathing becomes deeper during activity, alveolar ventilation increases from 70% of the total minute ventilation at rest to more than 85% of the exercise ventilation.
        
        Each person develops a "style" of breathing where breathing rate and TV blend to provide efficient alveolar ventilation. Attempts to modify breathing during running or other general physical activities offer no benefit to exercise performance
        
        During rest and all levels of exertion, a healthy person should breathe in the manner that seems most natural.
- - - - An accompanying decrease in hydrogen ion concentration [H+] increases plasma pH.
  - - - Both conditions excite the inspiratory center to increase breathing rate and depth. Failure to adequately regulate arterial carbon dioxide and [H+] most likely relates to low aerobic fitness levels and a poorly conditioned ventilatory musculature.
  - - - During the valsalva inthrathoracic pressure increases to more than 150 mm Hg. Pressures increase to higher levels within the abdominal cavity during a maximal exhalation against a closed glottis.
        
        The valsalva does not cause the large increases in blood pressure during heavy resistance exercises. A prolonged valsalva dramatically reduces blood pressure. Lifting weights greatly increases systolic blood pressure whether with or without a valsalva maneuver.
    - - The valsalva stabilizes the abdominal and thoracic cavities to enhance muscle action.
- - - - The molecules of each specific gas in a mixture of gases exert their individual partial pressure. The mixture's total pressure weals the sum of the partial pressures of the individual gases in the mixture.
  - - - Two factors govern the rate of gas diffusion into a fluid; 1) the pressure differential between the gas above the fluid and the gas dissolved in the fluid, 2) the solubility of the gas in the fluid
    - - During physical activity, oxygen and carbon dioxide diffuse rapidly as their pressure gradients widen.
  - - - Oxygen leaves the blood and diffuses toward cells, while carbon dioxide flows from cells into the blood. Blood then passes into the venous circuit (venues and veins) for return to the heart and delivery to the lungs.
        
        The body does not attempt to rid itself completely of carbon dioxide. To the contrary, each liter of blood leaving the lungs with a Pco2 of 40 mm Hg contains about 50mL of carbon dioxide.
        
        This small "background level" of carbon dioxide provides the chemical basis for ventilatory control though its stimulating effect on the neurons of the pons and medullary centers of the brainstem.
        
        The term respiratory center describes this collection of neural tissue that controls ventilation.
  - - - In males, each dL of blood contains about 15g of hemoglobin. The value decreases 5-10% for females and averages nearly 14g per dL of blood.
        
        This gender difference partly explains the lower aerobic capacity of women relative to men, even when considering differences in body mass and body fat.
        
        The reason for higher hemoglobin concentrations in men relates to the stimulating effects on red blood cell production of the "male" hormone testosterone.
      - An active muscle's uncompromising capacity to use available oxygen in its large blood flow supports the position that oxygen supply (blood flow), not muscle oxygen use, limits aerobic capacity
      - The lungs/tissues are oxygenated by the loading of hemoglobin, and they are deoxygenated by the unloading of hemoglobin.
    - - A significant decrease in the iron content of red blood cells reduces the blood's oxygen-carrying capacity. Such iron-deficiency anemia diminishes a person's capacity to sustain even mild-intensity aerobic activity.
        
        One study of iron-deficiency anemic men and women with low hemoglobin levels. The results show that the anemic group given iron supplements improved in exercise response compared with their nonsupplemented counterparts. Peak heart rate during 5min of stepping decreased from 155 to 113 beats per minute for me and from 152 to 123 for women. This translates into an average of 15% more oxygen delivered per heartbeat.
    - - Oxyhemoglobin dissociation curve illustrates the saturation of hemoglobin with oxygen at various Po2 values including alveolar-capillary gas at sea level (Po2 100 mm HG).
        
        On television, you will see athletes on sidelines breathing gas mixture of concentrated oxygen following strenuous activity. This makes no sense from an oxygen-transport perspective. The oxyhemoglobin dissociation curve shows little or no potential for increased hemoglobin loading from additional pressure of supplemental oxygen inhaled at sea level or at relatively low altitude.
    - - Reddish muscle fibers have a high concentration of this respiratory pigment, whereas myoglobin-deficient fibers appear pale or white.
      - Myoglobin resembles hemoglobin because it also combines reversibly with oxygen but each molecule contains one iron atom while hemoglobin contains four.
      - During intense activity, myoglobin facilitates oxygen transfer to the mitochondria when intracellular Po2 in active skeletal muscle decreases dramatically.
- - - - Inherent activity of neurons in the medulla regulates the normal respiratory cycle.
      - Input from higher brain centers, the lungs, and other sensors throughout the body interacts with medullary neural output to regulate ventilation.
      - At rest the chemical state of the blood exerts the greatest control of pulmonary ventilation.
        
        Variations in arterial Po2, Pco2, pH and temperature activate sensitive neural units in the medulla and arterial system to adjust ventilation and maintain arterial blood chemistry within narrow limits.
      - Three nonchemical regulatory factors augment ventilatory adjustments to exercise:
        
        1) cortical activation in anticipation of activity and outflow from the motor cortex when movement begins
        
        2) peripheral sensory input from chemoreceptors and mechanoreceptors in joints and muscles
        
        3) increased body temperature.
      - The ventilatory response to physical activity occurs in three phases:
        
        Phase I; cortical stimulus plus feedback from active limbs causes the abrupt increase in ventilation as activity begins.
        
        Phase II; ventilation then rises exponentially to reach a steady level related to the activity demands.
        
        Phase III; ventilation involves fine-tuning of steady-state ventilation through peripheral sensory feedback mechanisms.
      - During recovery
        
        the abrupt decline in ventilation when physical when physical activity ceases reflects removal of the central command drive and the sensory input from previously active muscles. More than likely, the slower recovery phase recovery phase results from two factors:
        
        1) gradual diminution of the short-term potentiation of the respiratory center
        
        2) reestablishment of the body's normal metabolic, thermal, and chemical milieu
    - - The stimulus to breathe comes primarily from increased arterial Pco2 and H+ concentration, not decreased Po2 in the breath-holding condition.
        
        If one intentionally hyperventilates, alveolar air becomes more like ambient air. A larger than normal quantity of carbon dioxide leaves the blood and arterial Pco2 decreases.
        
        Hyperventilation extends breath-holding duration until arterial Pco2 and/or H+ concentration rises to levels that again stimulate the urge to breathe.
- - - - With exercise, oxygen diffuses from the alveoli into the venous blood as it returns to the lungs, while about the same quantity of carbon dioxide moves from the blood into the alveoli.
    - - During light activity ventilation increases linearly with oxygen consumption. With higher levels of intense effort, minute ventilation increases disproportionately in relation to oxygen consumption.
        
        This point at which pulmonary ventilation increases disproportionately with oxygen consumption is termed the ventilatory threshold.
        
        At this point pulmonary ventilation no longer links tightly to oxygen demand at the cellular level. The excess ventilation comes directly from carbon dioxide's release from the buffering of lactic acid that begins to accumulate from increased glycolysis.
    - - The onset of blood lactate accumulation (OBLA) signifies when blood lactate concentration systematically increases to 4.0mM
        
        Some researchers often use the terms lactate threshold and OBLA interchangeably, although each represents an operationally different precise point for intensity of effort and blood lactate level.
        
        A word of caution: research using radioactive-labeled carbohydrate indicates that lactate's appearance in venous blood is more indicative of an imbalance between lactate production and lactate clearance within the muscle than the onset of anaerobic conditions.
        
        The fast-twitch fibers within active muscle that produce lactate "shuttle" this lactate to the muscle's slow-twitch oxidative fibers for use as aerobic energy substrate.
        
        The active muscles take up any lactate released into venous blood; other lactate-using organs like the heart and brain also catabolize lactate as an aerobic energy substrate.
        
        A threshold of lactate appearance could result from four factors:
        
        1) Imbalance between the rate of glycolysis and mitochondrial respiration
        
        2) Decreased redox potential (increased NADH relative to NAD+)
        
        3) Lower blood oxygen content
        
        4) Lower blood flow to skeletal muscle
        
        OBLA follows task specificity
        
        Different activity modes cannot interchangeably define the point of OBLA during graded exercise testing. Each must be determined in its own exercise mode.
        
        Variations in muscle mass activated in each activity form help to explain these differences.
        
        At a particular intensity or sub maximal oxygen consumption, a higher metabolic rate per unit of active muscle mass exists for arm-crank and bicycle exercise than treadmill walking or running.
        
        OBLA therefore occurs at a lower level (oxygen consumption) during bicycling and arm-crank exercise.
        
        Some independence between OBLA and VO2max
        
        Endurance training often improves the exercise intensity at OBLA without concomitant increases in VO2max. This suggests that different factors influence OBLA and VO2max
        
        Muscle fiber type, capillary density, mitochondrial size and number, and enzyme concentrations play major roles in establishing the accumulation.
        
        In contrast, the functional capacity of the cardiovascular system for oxygen transport and the total muscle mass activated in exercise determine the VO2max.
        
        African and South African endurance runners consistently show greater resistance to fatigue at the same percentage of peak treadmill running velocity than Caucasian counterparts despite similar values for VO2max and peak treadmill velocity.
        
        Two important factors influence endurance performance in a specific activity mode; 1) maximum capacity to consume oxygen (VO2max), 2) maximum level for steady-rate exercise (OBLA)
        
        Most exercise physiologists apply VO2max as a yardstick to gauge capacity for endurance activity.
        
        This measure generally relates to performance, but it does not fully explain success because one does not perform endurance activities at VO2max.
        
        The exercise intensity at the point of OBLA consistently and powerfully predicts endurance performance of men and women.
  - - - For ventilations up to about 100L per minute the oxygen cost equals about 3-5% of the total oxygen consumption in moderate activity and 8-11% for minute ventilations at VO2max values.
        
        Among highly trained endurance athletes with maximum minute ventilations of 150L per minute and higher, the cost of exercise hypernea can exceed 15% of total oxygen consumption.
        
        At this level, the inspiratory muscles operate at 40-60% of maximum capacity to generate force.
        
        Up to 15% of the total blood flow sustains the metabolic demands of respiratory muscles during maximal effort.
        
        Evidence from healthy, fit individuals indicates a "competition" for blood flow and oxygen between respiratory and locomotor muscles during intense activity.
    - - Unfortunately, exercise training produces only small improvements in pulmonary function parameters or disease status.
      - Despite their poorer performance in maximal testing (ie, shorter time to fatigue), the smokers spent more time to reach a heart rate of 130 beats per minute during a graded exercise test.
        
        This indicates a relatively higher fitness level (ie more exercise accomplished before reaching the sub maximal heart rate value).
        
        An altered sensitivity in autonomic neural control from cigarette smoking may inhibit the heart rate response of smokers to sub maximal effort.
  - - - Even during maximal activity, a considerable breathing reserve exists because minute ventilation at VO2max equals only 60-85% of a healthy person's maximum voluntary ventilation (MVV). Most individuals have a 20-40% MVV reserve during intense physical activity.
        
        Pulmonary function does not form a "weak link" in the oxygen transport system of healthy individuals with average to moderately large aerobic capacities.
        
        For endurance athletes, the pulmonary system lags behind their exceptional cardiovascular and aerobic muscular adaptations to training.
        
        The potential for inequality in alveolar ventilation relative to pulmonary capillary blood flow (ie impaired ventilation-perfusion ratio) during intense activity may compromise arterial saturation and oxygen transport capacity; a condition termed exercise-induced arterial hypoxemia (EIH).
- - - - The symbol pH designates a quantitative measure of acidity or alkalinity (basicity) of a liquid solution. Specifically, pH refers to the concentration of protons or H+.
        
        Acid solutions have more H+ than OH- at a pH below 7.0, and vice versa for basic solutions whose pH exceeds 7.0.
        
        Three mechanisms regulate the pH of the internal environment; 1) Chemical buffers, 2) Pulmonary ventilation, 3) Renal function
        
        An increase in plasma carbon dioxide or H+ concentration immediately stimulates ventilation to eliminate "excess" carbon dioxide.
        
        Conversely, a decrease in plasma H+ concentration inhibits the ventilatory drive and retains carbon dioxide that then combines with water to increase acidity (carbonic acid) and normalize pH.
        
        Reducing normal alveolar ventilation (hypoventilation) by one-half increases blood acidity by approximately .23 pH units.
        
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        Doubling alveolar ventilation by hyperventilation at rest increases blood alkalinity and pH by .23 units, from 7.40 to 7.63.
        
        There is an inverse linear relationship between blood lactate concentration and blood pH.
        
        Values for blood pH rarely fall below pH of 6.9, even during the most strenuous activity, although values at the active muscle are lower.
        
        A plasma pH below 7.00 does not occur without consequences; this level of acidosis produces nausea, headache, and dizziness, in addition to discomfort and pain that ranges from mild to severe within active muscles.