Human Physiology (Bio2424) Lab
RESPIRATORY MOVEMENTS – EXPECTED RESULTS
1.
Normal Respiratory Pattern: Expiration more or less equal to inspiration in depth (amplitude); expiration longer than
inspiration; rate (frequency) about 10-20 breaths/min. (Normal ranges listed vary from 13-18 breaths/min. to 5-22
breaths/min.)
2.
Hyperventilation: Lowers the PCO2 in blood, which increases the blood pH. This decreases the stimulation of the
medullary respiratory centers by CO2 until the PCO2 increases to normal again. This results in a period of apnea (temporary
cessation of breathing) or shallow breathing with a decreased depth and rate following hyperventilation. As the PCO2
increases toward normal, the stimulation of the respiratory centers returns and rate and depth return to normal.
3.
Hyperventilation in a closed system: Although hyperventilation is occurring, the PCO2 is increasing due to the rebreathing
of exhaled air. Thus, there occurs a slow increase in the PCO 2, which decreases the blood pH and, thus increases the
stimulation of the respiratory centers. The exact effect(s) seen will depend on the PCO2 produced, as follows:
- Blood PCO2 = 0.04%-3.07%  increased depth only with no increase in rate
- Blood PCO2 = 3-5%  increased rate and depth
- Thus, initially the depth should increase only; later both the rate and depth may increase
4.
Rebreathing: Same as above (#3) except that the effects should occur more rapidly. Thus, the increasing stimulation of the
medullary respiratory centers by the increasing PCO2 will initially produce an increase in the respiratory depth only; later
both the rate and depth may increase.
5.
Effect of Mental Concentration: The activity in the higher centers of the brain (i.e. the cortex) during mental concentration
has an inhibitory or dampening effect on the medullary respiratory centers. Thus, the rate and depth of respiratory
movements should decrease or even short periods of apnea may be produced, if the concentration is deep. If this is
continued, the PCO2 in the blood will gradually increase, eventually producing stimulation of the medullary respiratory
centers. The result will be a deep inspiration and a deep expiration, which is commonly called a sigh. During mental
depression (such as during sleepiness), inhibition or dampening of the respiratory centers occurs, respiratory rate and depth
decreases, and PCO2 increases. The increased PCO2 eventually stimulates the respiratory centers, producing a deep
inspiration and deep expiration, also known as a yawn.
6.
Effects of speech on respiration: To produce audible speech, one inspires, holds their breath, then talks during the
expiration. When needed, another inspiration occurs and talking continues. Thus inspiration occurs before talking. In silent
reading the respiratory rate and depth decrease (but the rhythm remains normal) due to increased cortical activity (as in
experimental procedure #5)
7.
Breath Holding: Voluntary cortical activity results in the inhibition of the respiratory centers for a time and a dramatic and
rapid increase in the blood PCO2. Eventually, the PCO2 becomes so elevated (and the blood pH so low) that their stimulation
of the respiratory centers “breaks through” the voluntary cortical inhibition (the PCO2 reaches the “breaking point”) and
respiration begins involuntarily. A deep expiration and inspiration followed by a period of increased rate and depth
(stimulated by the effect of the increased PCO2 on the respiratory centers), which gradually decrease the blood PCO2,
decrease the respiratory center stimulation, and return the rate and depth to normal.
8.
Obstruction of Respiratory Passageways: Any obstruction of the respiratory passageways will result in the retention of
CO2 by the lungs. This results in an increase in PCO2, increased stimulation of the respiratory centers, and finally increased
rate and depth of respiration. Examples of conditions producing such obstructions are foreign objects (mechanical blockage),
tumors n the bronchi, asthma, and anaphylactic shock.
9.
Effect of Exercise: During exercise, increased concentrations of CO2 are produced by body cells (especially muscle) due to
increased cellular respiration (remember: C6H12O6 + O2  CO2 + H2O + ATP + Heat). As CO2 accumulates, the blood
PCO2 rises. This stimulates the medullary respiratory centers and the respiratory depth increases first. With further exercise
and increased PCO2 both rate and depth increase.
MORE RESPIRATORY TERMS (respiratory terms from L.M. (Tharp pg. 186) can be found below & in your textbook)
Polypnea – very rapid breathing
Anoxia – a pathological deficiency of oxygen in the body
Asphyxia – unconsciousness or death caused by lack of oxygen; the condition in which one struggles to breathe against some
obstruction in the respiratory passageways (e.g. smothering, strangling, etc.)
Hypercapnia – abnormally high concentrations of CO2 in the body
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