Exam 2- Lecture 8 Flashcards
When are respiratory centers in the brain stain active?
they are spontaneously active
Central Chemoreceptors
Very sensitive to H+
pH surrounding chemosensitive cells; the H+ level is related to CO2 levels
Peripheral Chemoreceptors
Sensitive to O2 (and CO2 and H+, but to a lesser extent)
what is the primary controller of ventilation at rest?
PaCO2 sensed at the central chemoreceptor
At rest, when does ventilation increase?
as PaCO2 increases
What neural mechanisms are involved in the regulation of ventilation at the onset of exercise?
central command and feedback from exercising muscle
what is central command?
neural projections from the rostral brain (activated as part of the voluntary decision to move) that result in simultaneous activation of locomotion and the initial ventilatory and cardiovascular responses to exercise
what is the evidence of central command in humans?
partial curarization of exercising muscles results in addition increase in ventilation
Curare decreases muscle strength
brain increases “effort” in an attempt to maintain exercise goal
Increased central command results in greater minute ventilation
What do mechanically sensitive group III/IV afferents in skeletal muscle do?
they project to reparatory and CV brainstem sites and can also initiate hypernea
what are group III/IV afferents associated with?
collagen structures in the muscle- they are sensitive to mechanical events during contractions
low level dynamic exercise stimulates group III/IV muscle afferents
in human, when does minute ventilation abruptly increase?
at onset of passive exercise
passive exercise activates muscle mechanoreceptors (group III/IV)
Chemical feedback during phase II and III of exercise ventilation
becomes more important as exercise continues in duration and intensity
what do peripheral chemoreceptors do?
fine tune the ventilatory response
explain increased neural feedback from chemosenstive muscle receptors during heavy exercise
contribute to higher minute ventilation
they are sensitive to products of cellular metabolism
involved in CV regulation during exercise
discuss the relationship between metabolite driver afferent activity and the respiratory system regulation during heavy exercise
metabolite driver afferent activity during heavy exercise is more important for CV regulation than reparatory system regulation during heavy exercise
3 words used interchangeably
ventilatory threshold
lactate threshold
anaerobic threshold
Ventilatory equivalent for oxygen
Ratio of minute ventilation to volume of O2
what is the ventilatory equivalent for oxygen in adults during stead state exercise
about 25/1 (up to 55% of VO2max)
ventilatory threshold
as intensity increases >60% VO2max, there is a short increase in minute ventilation without a corresponding increase in VO2
minute ventilation increases from 25 up to 35-40
“excess ventilation” represented by the elevated ventilatory equivalent for O2 is a response to an number of inputs including:
- arterial metabolic acidosis
- a response to increases in interstitial potassium, catecholamines, and increased neural feedback from exercising muscles
- increased central command
want does ventilatory threshold correspond in time to?
lactate threshold
what is lactate threshold?
- the exercise VO2 above which there is a sustained rise in blood lactate
- the point where lactate increases more than 1 mM over pre-exercise values