Question

List the factors that influence respiration rate and discuss reflex respiratory activity and the brain centers involved in the control of respiration.

Answer 1

Factors that influence respiration rate:

The respiratory system includes structures such as the mouth, nose, trachea, lungs and the muscular diaphragm. The main purpose of the respiratory system is to draw air into the lungs, where oxygen can be harvested and incorporated into the blood for delivery to the rest of the body. It also functions to remove waste products, such as carbon dioxide, that collect from metabolism. The system is essentially a series of tubes that divides further and further, ending in small membranous sacs called alveoli. It is here that the gas exchange occurs. Breathing is usually an unconscious function, and there are several factors that affect how we breathe.

Heart Function

The heart's job is to pump blood throughout the body to deliver oxygen and other nutrients. The medulla is a portion of the brain that controls breathing. It measures the oxygen needs of the body and paces respiration to match. If the heart is unable to function properly due to disease, the blood it delivers will need to be extra-rich in oxygen in order to meet the body's needs, causing the rate of respiration to speed up.
>Drugs
Many prescription medications, as well as illegal drugs, will affect the breathing rate. Stimulants such as caffeine, nicotine, amphetamines and cocaine will speed up respiration, and some have the potential to cause hyperventilation. Sedatives such as sleeping pills and alcohol will decrease the breathing rate. Anesthesia medications can slow or even stop breathing altogether, making it necessary to put surgical patients on an artificial ventilator. Opiate pain medications can also alter breathing.
>Posture
The way we sit, particularly in a car or at a desk, can cause compression of portions of the rib cage and lungs, making effective breathing more difficult. In order to breathe deeply and ventilate fully, good, upright posture is required.
>Activity
Activity level can affect breathing. As we increase our activity level the oxygen needs of the body increase, so our rate and depth of breathing is increased. It is possible to overexert ourselves to the point where we cannot inhale enough oxygen fast enough to meet the metabolic needs of the body, such that we are forced to stop and rest. On the other hand, when we are asleep, our bodies require less oxygen and our breathing becomes slow and shallow.
>Disease
Many diseases affect our breathing, such as emphysema, which is a disease that makes gas exchange within the lungs very difficult and breathing to become labored. Bronchitis causes inflammation and mucous production, inducing fits of coughing. Asthma is an inflammatory condition that causes the airways to be constricted, making ventilation difficult. According to the American Lung Association, if you have a chronic cough, have shortness of breath, are coughing up blood or are wheezing, these may be warning signs of a lung disease.

Reflex Respiratory Activity

>The Hering-Breuer Inflation Reflex
Receptors located in the visceral pleura, walls of the bronchi and bronchioles.
Lung distention causes stretch receptors to send inhibitory signals to DRG, stopping further inspiration.
In adults active only on large VT (>800 ml)
Regulates rate and depth of breathing during moderate to strenuous exercise
Viewed as a protective mechanism.
>Deflation reflex
Sudden lung collapse results in hyperpnea as seen in pneumothoraces.
>Head's paradoxic reflex
May maintain large VT during exercise and deep sighs
May be responsible for babies first breaths at birth
>Irritant receptors
Subepithelial mechanoreceptors in the trachea bronchi and bronchioles
Stimulated by inhaled irritants or mechanical factors
Cause bronchospasm, cough, sneeze, tachypnea, and narrowing of glottis
These are vasovagal reflexes.
In hospital triggered by Suctioning, bronchoscopy, endotracheal intubation
Irritation reponse can be anesthetized by instilling lidocaine into the airway through the endotracheal (breathing) tube.
J-receptors
C-fibers - located in the small airways, blood vessels, interstitial tissues between the pulmonary capillaries and alveolar walls
J-fibers - Located in lung parenchyma juxtacapillary
Stimulated by pneumonia, CHF, pulmonary edema
Cause rapid, shallow breathing and dyspnea
Peripheral proprioceptors
Found in muscles, tendons, joints, and pain receptors
Movement stimulates hyperpnea.
Moving limbs, pain, cold water all stimulate breathing in patients with respiratory depression