The Why of Pulmonary Ventilation

1
The Why of Pulmonary Ventilation

• Four specific purposes
• Exchange of O2
• Exchange of CO2
• Control of blood acidity
• Oral communication

2
Rhythmicity of Ventilation

• Complex neural control mechanism makes normal
  breathing unnoticed, unconscious
• Inhalation Exhalation are regulated in two
  basic ways by frequency and by amount or volume
• Complex conscious breathing patterns can be
  learned and precisely integrated into motor
  performance?automatic and nearly unconscious

3
Environmental Influences on Pulmonary Gas Volumes

• Environmental conditions have significant effect
  on pulmonary gas volumes
• Pulmonary gas volumes can be presented under
  three (3) conditions or standards
• STPD-VO2 in liters . min-1
• BTPS-VE in liters . min-1
• ATPS-VI in liters . min-1

4
Pressure Relationships in Thoracic Cavity

• Atmospheric pressure (Patm) - pressure exerted by
  the air surrounding the body
• Sea level 760 mm Hg
• Intrapulmonary pressure pressure within the
  alveoli, that rises falls with phases of
  breathing (761-759)
• Intrapleural pressure within the pleual cavity
  (usually 4 mm Hg less than alveoli)

5
Pulmonary Pressures
6
Minute Ventilation

• Definition
• Rest
• During Exercise
• Hyperventilation
• Ventilation and the Anaerobic Threshold

7
Lung Volume or Capacity

• Tidal Volume (TV) 500 mL
• Inspiratory reserve volume (IRV) 3100 mL
• Expiratory reserve volume (ERV) 1200 mL
• Residual volume (RV) 1200 mL
• Vital capacity 4800 mL
• Total lung capacity 6000 mL

8
Dynamic Lung Measures

• Maximum Voluntary Ventilation (MVV)
• Forced Vital Capacity (FEV1.0)

9
The How of Ventilation

• Setting up of diffusion or pressure gradients
• Between respiring cells and atmosphere
• Minimize diffusion distances between alveoli
  surrounding capillaries
• Optimization of O2 CO2 transport
• Control of ventilation rate
• Medulla - receives input from the brain (neural
  factors) receptors from lungs and skeletal
  muscle (peripheral) other inputs are bloodborne
  (humoral)

10
Muscles of Respiration

• Inspiration - Diaphragm, external intercostals
  contract, scalenes elevate ribs 1 2,
  sternocleidomastoid elevates the
  sternum---gtintrapulmonary pressure ? momentarily
  atmospheric air moves in
• Expiration - external intercostals relax along
  with diaphragm decreasing volume of thorax
  transiently ? intrapulmonary pressure forcing
  pulmonary air out

11
Control of Ventilation

• Pneumotaxic center - pons - stimulates expiration
  center
• Apneustic center - pons - stimulates inspiratory
  center
• Medullary expiratory center
• Medullary inspiratory center
• Phrenic and intercostal nerves
• Humoral - Any substance that circulates in the
  blood and that has general effects at a site
  removed from location of secretion of substance
  humor.

12
Gas Exchange - Diffusion

• Partial Pressure of Gases
• PO2 and PCO2
• Partial pressure of oxygen in alveoli 105 mm Hg
• Solubility of O2 in body water at 37oC is low
• Rely on erythrocytes containing heme-iron
  compound - hemoglobin - which binds oxygen
  according to its partial pressure
• Hemoglobin usually nearly 100 saturated with O2

13
Changes in Ventilation Rest Exercise -Recovery

• Rapid increase w/in seconds
• Replaced with a slower rise
• Steady state
• Sudden decrease
• Slow gradual decline

14
Pulmonary Limitations in Highly Trained Athletes

• Adequacy of ventilatory system during maximal
  exercise
• They observed decreases in PaO2 (hypoxemia, low
  blood oxygen)
• Ve during exercise approaches a limit imposed by
  ability to generate expiratory and inspiratory
  flows and pressures

15
Ventilatory Threshold The sing talk test
16
Application of the Ventilatory Threshold

• How does the ventilation slope differ in this
  picture from previous slide?
• http//www.usidr.org/Running20University/RULectur
  e1.htm

17
Application of the Ventilatory Threshold

• What do you think?
• Agree?
• Disagree?

18
Respiration

• External respiration movement of oxygen
  carbon dioxide down pressure gradients (pulmonary
  capillary blood and air in alveoli
• Internal respiration capillary blood of
  systemic circulation and cell being perfused with
  blood

19
Gas Partial Pressures

• Atmospheric air
• Alveolar air

20
Diffusion Capacity

• Exercise
• Rest

21
Pulmonary Diffusion
22
Pulmonary Perfusion

• Definition passage of blood or other fluid
  through a vascular bed
• Balance between perfusion and ventilation
• Non-linear increase in ventilation (5-190 l/min)
• Cardiac output - increases from 5 l/min -
  25 to 30 l/min

23
Blood Hemoglobin Concentration, Hematocrit

• Before After Change
• Variable Training Training ()
• Hb (g/dl) 15.3 15.1 -1
• Blood Vol 5.25 6.58 25
• Total Hb (g) 803 994 24
• Arterial O2 20.8 20.5
• (ml/dl)
• Hematocrit 42 41 -2
• ()

24
Solubility and diffusion Characteristics of
Respiratory Gases

• Gas Solubility Diffusing Cap Diffusing Cap
• Rest Exercise
• (ml/min/mmHg) (ml/min/mmHg)
• Oxygen 0.024 20 65
• CO2 0.57 400 1300

25
Gas Exchange

• Entry of O2 into blood
• We ventilate to keep the partial pressure of O2
  at 105 mmHg
• Diffusion distance for O2 into erythrocytes is
  short
• Short distance is necessary - low solubility of
  O2 in body water
• Erythrocytes contain the heme-iron compound
  hemoglobin which binds O2 based on partial
  pressure

26
Oxygen Transport

• 1.34 ml of O2 per g of Hb (15 g Hb/100 ml)
• 1.34 x 15 20 ml O2 / 100 ml blood
• Partial pressure effect
• Temperature, H, and 2,3-diphosphoglycerate
  (2,3-DPG) 2,3 DPG levels are higher at altitude
  
• Helps tissues obtain more O2

27
Oxyhemoglobin Dissociation Curve
28
Oxyhemoglobin Dissociation Curve
29
pH, PCO2, Temperature on Hemoglobin Saturation

• Influence hemoglobin saturation by modifying Hbs
  3-dimensional structure
• Increases in PCO2, H content of blood,
  temperature decrease Hbs affinity for O2
• Curve shifts to the right - enhancing oxygen
  unloading from the blood
• These factors (2,3 biphosphoglycerate) are at
  their highest levels in systemic capillaries
  where oxygen unloading is the goal
• Declining pH weakens the Hb-O2 bond - this is
  called the Bohr effect

30
Hemoglobin - Nitric Oxide

• Nitric oxide (NO) - secreted by cells of lungs
  and vascular endothelial cells
• Vasodilator - plays role in BP regulation
• Hemoglobins heme (iron group) detroys NO -
  therefore, reputation as a vasoconstrictor
• Yet, local vessels dilate where gases are being
  unloaded and loaded
• Recent research a second (non-respiratory)
  hemoglobin cycle involving NO
• NO latches onto Hb following oxygen loading in
  lungs (chemically protected from heme)

31
Carbon Dioxide Transport

• Carbon dioxide transported in following forms
• Dissolved in plasma (least amount - 7-10)
• Chemically bound to hemoglobin in red blood cells
  (20-30) - called carbaminohemoglobin HbCO2
• Bicarbonate ion in plasma (highest amount -
  60-70) (HCO3-)
• Carbaminohemoglobin
• CO2 binds to amino acids of globin (not heme)
  therefore, does not compete with oxygen or NO
• CO2 rapidly dissociates from Hb in lungs where
  PCO2 is lower than in blood

32
Bicarbonate (HCO3-) Ion in Plasma

• CO2 diffuses into RBCs combines with water (CO2
  H2O ----gt H2CO3 (carbonic acid)
• Carbonic acid is unstable and quickly dissociates
  into H HCO3-
• H ions bind to Hb triggering Bohr effect - thus
  oxygen release is enhanced by carbon dioxide
  loading in tissues
• HCO3- ion diffuse rapidly into plasma (after
  exchanging with chloride ion (Cl-) and carried to
  lungs (Cl- - HCO3- exchange protein transporter)
• In lungs HCO3- diffuses back into RBC and binds
  with H to form carbonic acid CO2 H2O --? H2CO3

33
Bicarbonate (HCO3-) Ion in Plasma (contd)

• H formed from carbonic acid dissociation reacts
  rapidly with reduced Hb (hemoglobin that has
  dissociated its O2)
• Reduced Hb is a strong buffer taking up much of
  H formed as a result of CO2 transport

34
The Red Blood Cell and Hb inCO2 Transport

• 5-7 CO2 transported in dissolved form
• RBC contains carbonic anhydrase in addition to
  hemoglobin
• CO2 H2O ---gt H2 CO2 (formed very quickly in
  RBC)
• H2 CO2 ----gt HCO3- H

35
Anatomy Physiology of the Heart

• Atrium (R L) - thin-walled, low-pressure
  chambers that serve as resevoirs for ventricles
• Ventricles (R L) - smaller rt ventricle pumps
  blood into pulmonary artery to lungs larger more
  muscular left ventricle pumps blood to aorta
  general circulation
• Valves - Tricuspid valve (rt) mitral valve (lt)
  pulmonary and aortic valves
• Myocardium - cardiac muscle striated
  involuntary has inherent rhythmicity - contracts
  at regular intervals

36
Specialized Conduction System

• Sequence of Activation Conduction Vel Time
  Rate
• (M/sec)
  (Sec) (B/min)
• SA Node .15
  60-100
• AV Node 0.02-0.05
  
• AV Bundle 1.2-2.0
  0.08 40-45
• Bundle Branches 2.0-4.0
  25-40
• Purkinje Network
  

37
Cardiac Cycle

• Diastole Systole
• Atria act as reservoirs for the ventricles and
  during exercise as primer pumps
• Walls of left ventricle are thicker than those of
  the right due to peripheral resistance
• Amount of blood ejected from each ventricle
  stroke volume (SV)
• SV difference between peak ventricular filling
  (end-diastolic volume) - ventricular emptying
  (end-systolic volume)
• Percentage of end-diastolic volume pumped from
  ventricles ejection fraction

38
Training and the ECG

• Appearance of the sinus bradycardia - as low as
  28 beats/min
• Probable cause reduction from sympathetic n. s.
  increased stimulation of parasympathetic n. s.
• Possibly a lower intrinsic rate

39
Ventilatory Threshold

• With training the ventilatory threshold shifts to
  the right
• With over-training, the curve would shift back
  towards the left