22.3c Regulation of Respiration

The number of times a person breathes in 1 minute, the ?, is unique in that both voluntary and involuntary nervous system mechanisms control it.

respiratory rate

We do not ordinarily need to make a conscious effort to breathe; our brains automatically ?.

regulate this function

However, we can voluntarily ? our involuntary respirations until physical and chemical mechanisms signal the nervous system’s respiratory centers to provide involuntary impulses and correct any breathing irregularities.

override

The main respiratory center lies in the ? located in the brainstem.

medulla

Various neurons within the medulla initiate impulses that result in ?.

respiration

A rise in the frequency of these impulses ?.

increases the respiratory rate

Conversely, a decrease in their frequency ?.

decreases the respiratory rate

The medulla is connected to the respiratory muscles primarily via the ?.

vagus nerve

The medulla's connection to respiratory muscles is an ?.

involuntary pathway

If the medulla fails to initiate respiration, an additional control center in the pons called the ? assumes respiratory control to ensure the continuation of respirations.

apneustic center

A third center, the ?, also in the pons, controls expiration

pneumotaxic center

During inspiration, the lungs become distended, activating ?.

stretch receptors

As the degree of stretch increases, these receptors fire ?.

more frequently

The impulses they send to the brainstem inhibit the medullary cells, decreasing the ?.

inspiratory stimulus

Thus, the respiratory muscles relax, allowing the elastic lungs to recoil and ?.

expel air from the body

As the stretch decreases, the stretch receptors ?.

stop firing

This process called the ? prevents overexpansion of the lungs.

Hering-Breuer reflex

Other involuntary respiration controls include ?.

central chemical receptors in the medulla
peripheral chemoreceptors in the carotid bodies and in the arch of the aorta

These chemoreceptors are stimulated by ?.

decreased PaO₂, increased PaCO₂, and decreased pH

The pH scale expresses the degree of ?.

acidity or alkalinity

A lower pH indicates greater ?

acidity

A higher pH indicates greater ?

alkalinity

The pH of ? is the primary control of respiratory center stimulation.

cerebral spinal fluid (CSF)

The CSF pH responds very quickly to changes in ?

arterial PCO₂

Any increase in PCO₂ ? CSF pH, which in turn stimulates the central chemoreceptors to increase respiration.

decreases

Conversely, low PaCO₂ levels ? CSF pH, in turn decreasing chemoreceptor stimulation and slowing respiratory activity.

raise

Because PaCO₂ is inversely related to CSF pH, PaCO₂ is seen as the ?.

normal neuroregulatory control of respirations

Additionally, any increase in the arterial PCO₂ stimulates the peripheral chemoreceptors to signal the brainstem to increase respiration, thus speeding ? from the body.

CO₂ elimination

While increasing PaCO₂ levels are the most important driver of ventilation, low oxygen levels (?) are a secondary driver.

hypoxic drive

Traditional teaching is that patients with chronic respiratory diseases such as COPD depend on hypoxic drive rather than elevated blood levels of CO₂ because their CO₂ levels are ?.

chronically elevated

Under this concept, patients with COPD would only breathe when their oxygen level became low and, as a result, administering supplemental oxygen could cause ? (cessation of breathing).

apnea

It is true that some patients with COPD retain CO₂ and giving them oxygen can lead to hypoventilation with ?, but it is not because of a hypoxic drive (and should not be a reason to withhold oxygen therapy to those who need it).

rising CO₂ levels and coma

Patients with COPD, even ones who have chronically elevated CO₂ levels still have PaO₂ levels ?.

above those that would stimulate a hypoxic drive

COPD leads to the ?.

destruction of alveoli and a ventilation/perfusion mismatch

These localized areas of poor ventilation lead to corresponding alveolar capillaries that have ?.

chronically low oxygen levels

This, in turn, leads to localized ? as an effort to shunt blood away from the underventilated alveoli and reverse the shunt that COPD causes.

vasoconstriction

High concentrations of supplemental oxygen administered to the patient reverses this localized vasoconstriction, leading to ?.

increased ventilation perfusion mismatch, increased “dead space,” increased CO₂ levels, and decreased upper O₂ levels

The bottom line is that ? in the COPD patient is a much more complicated physiologic phenomenon than previously suspected.

ventilation

The correct approach to a hypoxic patient with COPD is to ? to maintain a slightly lower SpO2 range than we would for other patients.

titrate supplemental oxygen