Respiratory System Response to Exercise - Control of Ventilation

O2 Requirement Of Breathing

small at rest and during light-to-moderate exercise

• up to 100 L/min

O2 Cost

1.5 mL/L of air breathed each minute

O2 Represents A

small portion of VO2 at rest and low-to-moderate exercise intensities

O2 Can Increase

substantially at max exercise

During Exercise an Increased VO2 Means

more oxygen travels from your lungs to your muscles

During Exercise an Increased VCO2 Means

more CO2 travels from your muscles to lungs to be breathed out

Ventilations Increase Mainly Through

increase in tidal volume

Pulmonary Ventilation is Precisely Regulated At

both rest and during exercise

Clusters of Neurons in the Medulla Oblongota Act As

a “pacemaker”

Change in Ventilation is Determined By

exercise intensity

Control of Ventialtion at Rest

• inspiration is active process (expiration is passive)

• respiratory muscles controlled by somatic MNs and SC

Activity of MNs Is Controlled By

respiratory control centers (in medulla oblongata)

Respiratory Control Center is Located in

brain stem within 2 distinct areas

• medulla oblongota and pons

RCC Controls The

rhythm and rate of beathing

3 Distinct Rhythm Centres

1. PreBotZ - inspiration

2. RTN/pFRG - expiration

3. Pontine respiratory center - rate and pattern

Normal Rhythm is Due to

interaction between clusters of the MNs

• both +ve and -ve feedback to tightly regulate breathing

At Rest preBotzinger Interacts With

other centres to regulate

RCC Receives Input From

higher brain centers and periphery

Neural Input - Higher Brain Centres and Afferent Pathways

• motor cortex can alter breathing in proportion to the amount of exercise

• afferent input from muscle spindles, GTOs, joint pressure receptors

Neural Input is Important to Regulating Breathing During

submaximal, steady-state exercise

Humoral Input

chemoreceptors detecting blood

Chemoreceptors

specialized neurons detecting changes in internal environment

Humoral Input - Central

loacted in the medulla

• PCO2 and H+ concentrations in CSF

Humoral Input - Peripheral

located in aortic arch and carotid artery

• PO2, PCO2, H+ and K+ in blood

At Rest Greatest Respiratory Stimulus Is

PCO2 in arterial pressure

• small ↑ in PCO2 in inspired air trigger large ↑ in VE

• 1 mmHg ↑ in PCO2 ↑ VE in 2 L/min

Blood pH Affects VE

• acidosis reflects CO2 retention

• breathing must ↑ to remove CO2

At Sea Level, Changes in PO2 Have

a small affect on ventilation

Environmental Changes Can

decrease PO2 and stimulate peripheral chemoreceptors

Carotid Bodies Monitor

arterial blood as it perfuses the brain

• protection agaisnt decrease PO2 in inspired air

Plasma PO2 and VE Stimulate Ventilation During Exercise Due to

• increase temperature

• increase acidity

• CO2 and K+

Central Chemoreceptors

• stimulus: PCO2 ↑

• ↑ VE

Peripheral Chemoreceptors - Carotid Body

• stimulus: PCO2 ↑, pH and PO2 ↓

• ↑ VE

Peripheral Chemoreceptors - Aortic Body

• stimulus: PCO2 ↑, pH ↓

• ↑ VE

Muscle Mechanoreceptors

• stimulus: muscle activity

• ↑ VE

Muscle Chemoreceptors

• stimulus: pH ↓, K+ ↑

•  ↑ VE

Regulation of VE During Exercise: Cortical Influence

anticipation of exercise stimulate respiratory neurons in the medulla to initiate the abrupt increase in exercise VE

Regulation of VE During Exercise: Peripheral Influence

sensory input from joints, tendons, and muscles influence bentilatory adjustments during exericse

Ventilatory Control During Submaximal Exercise

• primary drive: higher brain denters

• fine tuned by: humoral chemoreceptors and neural feedback

Ventilatory Control During Heavy Exercise

a linear rise in VE

• increase blood H+ stimulates carotid bodies

• K+, body temp, and catecolamines play a role

Control of Ventilation - How it Works Together

1. you start exercising

2. higher brain centers signal increased breathing, while receptors and chemoreceptors provide feedback

3. respiratory control center (medulla oblongata) receives these signals

4. respiratory muscles increase breathing rate and depth

5. ventilation increase to bring in more O2 and remove more CO2

Phase I of VE in Exercise and Recovery

• neurogenic stimuli from the cerebral cortex and feedback from the active limbs stimulate the medulla to increase VE abruptly

• neural control

Phase II of VE in exercise and recovery

• after a short plateau minute ventilation rises expontentially to achieve a steady level related to metabolic gas exchange demands

• humoral control

Phase III of VE in exercise and recovery

• fine-tuning of the steady-state ventilation through peripheral sensory feedback mechanisms

• sensory control

Effect of Training on Ventilation

• no effect on lung structure and function at rest

• normal lung exceeds demand for gas exchange - adaption no required

Effect of Training on VE - Elite Endurance Athletes

failure of lung to adapt to TR results in hypoxemia

Does the Pulmonary System Limit Exercise Performance - Low-to-Moderate Intensity

pulmonary system not seen as a limitation

Does the Pulmonary System Limit Exercise Performance - Maximal Exercise

• respiratory muscle fatigue does occur during high intensity exercise

• may be limiting in elite endurance athletes (40-50% experience hypoxemia)

Maximum Voluntary Ventilation

evaluates ventilatory capacity

• rapid and deep breathing for 15 seconds

• extrapolated to volume if subject continued for 1 min

25% > VE in Maximal Exercise

• exercise does not maximally stress healthy person

• 140 to 180 L/min in college aged men

• 80 to 120 L/min healthy, college-aged women

Training Ventilatory Muscles Increases

• ST

• endurance

• inspiratory muscle function

• MVV