23.8 Breathing Rate and Homeostasis

Hyperventilation

A breathing rate or depth that is increased above the body’s demand.

Hyperventilation may be caused by….

• Anxiety

• Panic

• Ascending to a high altitude

Hyperventilation may also be performed voluntarily when…

you consciously inspire and expire at an accelerated rate.

What happens to PO2 and PCO2 during hyperventilation?

PO2 levels increase

PCO2 levels decrease (in the alveoli)

What is a significant result of hyperventilation?

Additional carbon dioxide leaves the blood to enter the alveoli due to a steeper PCO2 gradient leading to arterial blood PCO2 decreasing below the reference range (35 mm Hg)

Hypercapnia

Decrease in blood carbon dioxide below typical levels.

Low arterial blood PCO2/Hypercapnia can cause?

Vasoconstriction of systemic blood vessels.

The blood vessels within the brain are especially vulnerable to these changes.

Decrease in blood H+(and increase in blood pH)

One result of hyperventilation that is related to the vasoconstriction of systemic blood vessels?

Decreased oxygen delivery to the brain due to the generalized vasoconstriction.

Symptoms that accompany hyperventilation

• Feeling faint or dizzy

• Numbness

• Tingling of the mouth and fingertips

• Muscular cramps

• Tetany

Symptoms from prolonged hyperventilation:

• Disorientation

• Loss of consciousness

• Coma

• death

Hypoventilation

Breathing that is either too slow or too shallow.

Bradypnea

Breathing rate that is too slow to adequately meet metabolic needs.

Hypopnea

Breathing rate that is too shallow to adequately meet metabolic needs.

Causes of hypoventilation

• Airway obstruction

• pneumonia

• brainstem injury

• Obesity

• Any condition that interferes with pulmonary ventilation or pulmonary gas exchange.

What happens to O2 and CO2 during hypoventilation?

Oxygen levels decrease and carbon dioxide levels increase in the alveoli

This leads to smaller partial pressure gradients between the alveoli and blood for both O2 and CO2.

The smaller partial pressure gradients between the alveoli and blood for both O2 and CO2 leads to the diffusion of the respiratory gases to be altered during pulmonary gas exchange as follows:

• Lower amounts of oxygen diffuse from the alveoli into the blood, and blood PO2 decreases. This is a condition called hypoxemia (hi-pok'se me-ă), which may lead to low oxygen in the tissue called hypoxia (hi-pok'sē-ă).

• Lower amounts of carbon dioxide diffuse from the blood into the alveoli. This causes blood Pco2, to increase, a condition called hypercapnia (hi'pěr-kap'nē-ă).

Hypoxemia

Decrease in blood oxygen below typical levels.

Hypoxia

Decreased oxygen level in body tissues.

Low blood oxygen levels may result in

insufficient oxygen delivery to systemic cells, with a subsequent decrease in aerobic cellular respiration.

Symptoms resulting from insufficient blood Po2, increased blood Pco2 or BOTH:

• Lethargy

• sleepiness

• headache

• polycythemia(low oxygen triggers release of erythropoietin)

• cyanotic tissues

Prolonged hypoventilation can cause:

• Convulsions

• Unconsciousness

• Death

Hypoventilation can be performed voluntarily and cause:

The accumulation of CO2 in the blood to stimulate chemoreceptors to relay signals to the respiratory center to initiate inspiration before of after loss of concsciousness but always before the brain suffers damage from lack of oxygen.

Stimulation of breathing:

• Sensory input relayed to the respiratory center from proprioceptors in muscles, tendons, and joints in response to movement.

• Motor output originating in the cerebral cortex that initiates muscular movement during exercise, simultaneously relaying signals to the respiratory center

• the conscious anticipation of participating in exercise.