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Free «Respiratory Control» Essay Sample


Respiratory system provides an exchange route for carbon dioxide and oxygen gas between the alveoli and in pulmonary capillary blood. The oxygen inhaled diffuses across alveoli walls into the blood where it mixes with hemoglobin in the blood and transported to the heart. After the blood circulation, the carbon dioxide is transported back to the lungs for elimination inform of bicarbonate ions. Carbon dioxide diffuses from the blood to the lungs through alveoli walls and is exhaled outside through the nose. Pressure of the two gases is monitored by peripheral chemoreceptors found in the carotid bodies and central chemoreceptors found in the medulla. Peripheral nervous system contains autonomic nervous system that affects the heart rate. Autonomic nervous system contains sympathetic nervous system that increases the heart rate while the parasympathetic nervous system decreases the heart rate. The purpose of this exercise is to see the effects of different type of breathing conditions on heart and blood pressure. I hypothesize that the heart rate and blood pressure tends to increase from the normal condition through hyperventilation to re-breathe condition.


Table 1




Blood Pressure

Heart Rate

Blood Pressure

Heart Rate

Blood Pressure

Heart Rate

76 BPM


76 BPM


80 BPM




I measured the heart rate and blood pressure in normal, hyperventilation and re-breathe conditions using a blood pressure cuff. During the first test, I measured the heart rate and blood pressure at rest or normal condition. In the second test, the heart rate and blood pressure was measured during the 30 seconds of hyperventilation. Finally, the heart rate and blood pressure was measured after 1 minute of re-breath.. Equipments used were a Stop Watch and a blood pressure cuff


 At rest, the heart beats about 60 to 80 times a minute. The blood pressure rises with every rise of a heartbeat and relaxes when the heartbeat falls. For a normal and a healthy adult, the blood pressure is around 120/80 mm HG. Blood pressure that stays between 120-139/80-89 is considered pre-hypertension while that above 140/90 mm HG is usually considered as hypertension. In normal conditions during the experiment, the heart rate beats at 110/76 while the blood pressure and blood pressure is at 76 BPM. During the hyperventilation, the act of breathing harder and faster causes the heart faster in order to pump more blood in and out of the lungs to cater for diffusion of gases been driven in and out at a higher speed and intensity. In the re-breath condition, the heart rate and blood pressure are very high because the carbon dioxide builds up in the body forming carbonic acid. This makes the blood less basic and pH lowers. The deep breath after 60 seconds of breathing in a paper expels carbon dioxide making the blood more basic. This leads to the increase of pH. That’s why we see the rise in heart rate and blood pressure. 

Chemoreflex is a physiological reflex that is instigated by a chemical substance. A motor reaction responds to such environments. It is a vital modulator whenever there is a sympathetic activation.  Central chemoreceptors in the brainstem and peripheral chemoreceptors in the carotid bodies respond to hypercapnia and hypoxemia respectively. Their activation brings out sympathetic activation and hyperventilation. Low oxygen concentration leads to an increased chemoreceptor drive through the carotid body. At rest, hypoxic ventilator responsiveness is always at normal conditions and it increases with work rate. With increased work  rates, there is a further production of an enhanced ventilator responsiveness to hypoxia by muscular exercises.

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Hypoxia increases the uptake of carbon dioxide and slows down oxygen uptake. At sea level, hypoxia stimulus controls the drive to breathe at sea level because of the increased central and absent peripheral to carbon dioxide. A normal Breath-hold is a voluntary act. Humans can only suppress their respiratory system to hold a certain volume of breath. During a breath-hold, carbon dioxide is prevented from exiting the alveoli which in turn distorts the pressure gradient that drives carbon dioxide from the blood to the alveoli. In this case, any oxygen that has been extracted fails to be replaced by an equal volume of carbon dioxide. 

A breaking point is caused by a very strong involuntary mechanism that overrides the voluntary breath hold. This generally occurs when the oxygen concentration falls far below the normal levels and when the carbon dioxide concentration rises far above the normal levels. Hyperventilation occurs when there is either a faster breathing, a deeper breathing or both. Before a breath-hold, hyperventilation helps in exhale and inhale of large volumes of carbon dioxide and oxygen respectively. This leads to a faster circulation of gases at the start of a breath hold. The large volume of oxygen inhaled helps in prolonging the breath-hold. Re-breathing occurs when there is inhalation of previously exhaled gases. Before a breath hold, one tends to exhale and then take a deep inhalation. It is this extra volume of inhale that prolongs the duration of a breath-hold.

 Inspiration causes the Intrathoracic pressure to become negative. This is the pressure that occurs during the intake of air into the lungs. Inspiration makes the pressure gradient in the venacava to pull the blood to the right atrium. Inspiration causes the diaphragm to compress the abdominal organs through abdominal pressure. Venous return is the rate at which blood flows back to the heart. Inspiration leads to an increase in Venous return which finally results to an increase in cardiac output. During an inspiration, venous return leads to an increase the stoke volume (SV), pulmonary circulation and the left heart return. A decrease in atrial pressure through inspiration leads to an increase in venous return.

Baroreflex is a body mechanism that maintains blood pressure. An inspiration activates Baroreflex which causes the heart rate to increase. Autonomic outflow is associated with autonomic nervous system. It is changed when the blood pressure in a person having an injury in the spinal cord becomes extremely high when the autonomic nervous system is overactive. The outcome of this factor can lead to a life threatening situation e.g. stroke or death. Expiration is the act of breathing out. It causes the Intrathoracic pressure to become positive, the venous return decreases, the pulmonary blood volume is reduced, the left SV decreases, and the Baroreflex sensitivity decreases. During inspiration, liver is pushed downwards by the diaphragm. In some animals, it’s likely that the liver controls the flow of blood from splanchnic to central circulation. One can then deduce that liver controls venous return. It is also likely that a liver decreases the positive end respiratory pressure. Liver’s role in this response is either the emergence of an increase in venous resistance or through the increase in venous backpressure. 


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