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Lecture 6

Lecture 6 (revised).docx

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Kinesiology&Physical Education
EDKP 395
Russell T Hepple

11/1/2012 12:50:00 PM Physiological challenges to respiratory system during exercise Exercise induced increase in VO2 and VCO2 causes blood returning to lungs from exercising muscle to get progressively more o hypoxic Decrease PO2, SaO2 (arterial O2 saturation), CvO2 o Hypercapnic/acidic Increased PCO2, dec. pH this disturbs acid base balance and compromises O2 delivery via hypoxic state Ventilatory requirements 20-30x above resting levels MUST BE MET while minimizing the O2 cost of breathing/mechanical work (i.e. most efficient way possible) o This requires Feed forward & feedback control mechanisms to ensure ventilatory response to exercise is driven in proportion to muscle metabolic requirements (VCO2, VO2) Precise control of dynamic operating lung volumes which act to minimize the mechanical work & O2 cost of breathing o Increased ventilatory requirements are not a problem for healthy individuals, but will affect those w/ respiratory diseases o Control of breathing process by End inspiratory lung volume- breath in End expiratory volume- breath out Note: at rest respiratory system is extremely efficient less energy used than is needed to power a lightbulb The work produced by both locomotor and respiratory muscles increase several fold during exercise o Blood flow/O2 requirements of both sets of muscles must be met Excessive work and O2 cost of breathing will steal blood flow away from exercising muscle located in ideal position to do this Leads to muscle fatigue o Respiratory muscles important skeletal muscle 11/1/2012 12:50:00 PM PAO2= oxygen tension in alveoli PcapO2= pressure O2 in caps Va= alveolar ventilation Determinants Pressure gradient for diffusion (high low) o dependant on PAO2 which is determined by Va if Va is inadequate, PaO2 will be inadequate to ensure that the rate at which O2 diffuses from alveoli into blood is able to fully saturate the RBCs during that time in the pulmonary caps. More of a challenge w/ heavy exercise since both mixed venous PO2 & RBCs transit time DECREASES this decreases amount of time for pulmonary O2 gas exchange to take place Ficks Law of diffusion Rate of diffusive O2 flux from lungs to blood is proportional to SA: lung/blood interface (# alveolar units) Diffusion coefficient of gas (D) o Solubility & size of gas molecule o Constant Driving pressure (P1-P2) o PAO2 PcapO2 gradient o Higher the difference = greater flux Diffusion distance (T) o Thickness of alveolar capillary membrane Decrease distance = increased flux Rate = SA x D x (P1-P2)/T Pulmonary edema (Lung water) o Increases resistance of O2 moving form lungs ot blood by increasing diffusion distance Neg. effect on flux Emphysema o Marked loss of SA for gas exchange Like a bag of tennis balls instead of a beehive due to expansion of alveolar sacs Decreased SA = decreased flux 11/1/2012 12:50:00 PM Gas Equations for O2 and CO2 PACO2- alveolar PCO2 Dictates acidity of blood VCO2- rate of CO2 production Pb- barometric pressure PaCO2- arterial PCO2 PAO2- alveolar PO2 PiO2- inspired PO2 VO2- rate of O2 consumption PaO2- arterial PO2 SaO2- arterial O2 saturation CaO2- arterial O2 content During exercise, respiratory system needs to maintain alveolar gas exchange by protecting both alveolar PO2 (PAO2) and PCO2 (PACO2) via Precise matching of alveolar venilation and muscle metabolism o PACO2 = VCO2/VA x (Pb 47) o PAO2 = PiO2 PaCO2/(VCO2/VO2) If metabolic rate of CO2 production increases we will see more CO2 in arterial blood this will cause Decrease in PAO2 in alveoli (decreased pressure gradient b/w alveoli and blood) Decrease in arterial PaO2 SaO2 and CaO2 Causes fatigue If exercising muscle doesnt get enough O2 fatigue happens quicker and exercise tolerance is compromised o Therefore we must match ventilation to metabolic demands Maintain levels of CO2 in blood/lungs Pulmonary Gas exchange Alveolar ventilation (VA, L/min) different then ventilation at the mouth o Portion of each breath that reaches the alveoli and participates in alveolar gas exchange
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