Carbon Dioxide Regulation by Normal Respiration

Going back to the carbon dioxide regulation, the Medulla Oblongata, a sector of the brain that controls autonomous reactions in the body, is responsible for monitoring the carbon dioxide levels and pressure. Once the medulla oblongata sees retention of carbon dioxide past normal pressures, the medulla oblongata activates respiratory reflex loops. This will in turn lead to inspiration to restore the balance or homeostatic conditions of the arterial blood gasses. The chemoreceptors that are controlled by the Medulla oblongata are indeed Carbon dioxide chemoreceptors. It is generally stated that since the medulla oblongata is bathed in carbon dioxide, it is able to use the carbon dioxide chemoreceptors within that specific area to easily monitor the transitory carbon dioxide levels. The medulla oblongata tracks the gas levels in order to make sure that acidity will be controlled. Acidity in the body is important because of the sole reason that the acids and bases in the body retain the ability to control all metabolic activities in the body. (A.C.F.A.S.P. 2009, p 2)

Note that the information here pertains to the normal Carbon Dioxide regulation and not through Chemoreception of peripheral chemoreceptors. There is a big difference as there is a Medulla Oblongata for normal CO2 regulation

Here is a picture of the Human upper body. The Medulla Oblongata is just under the brain and is where the regulation occurs with our primary carbon dioxide regulatory system( respiratory system).

Carotid Body Function and Unique Characteristics

Once the chemoreceptors pick up the trace of O₂ deprivation, they release neurotransmitters. These neurotransmitters in turn set off a chain of reactions that cause the body to release stored ATP and AMPK that will allow for the body to restore functions. (Wyatt, Mustard, and others, p 282) In essence, ATP and AMPK are the compounds in our body that are essential to body functions and processes that occur throughout every microcell of our body. (Khakh and Burnstock) The carotid body sensing is significantly different from normally used Carbon dioxide chemoreceptors. Carbon dioxide chemoreceptors are located in brain stem, coronary arteries and in carotid bodies as well. However, the major difference between the carbon dioxide chemoreceptors and the oxygen chemoreceptors is that the carbon dioxide chemoreceptors react to changes on a far more optimized level in the sense that they induce major alveolar ventilation with sensation of extraneous levels of carbon dioxide within the body. (Dean and Nattie 2010) The point in the making is that oxygen chemoreceptors can pick up the slightest drops; however, they do not introduce or rather initialize or catalyze a reaction until the oxygen pressure drops below an approximated 60 torr. The problem with an oxygen pressure below 60 torr is that the pressure is dubbed as Hypercapnic respiratory failure which is detrimental to the cellular functions of the body and the brain itself.




Above is a picture of AMPK and its uses within the body. The main elemental nature of AMPK is that it provides the power for protein synthesis which esentially drives the cellular functions of the body.

Carotid Bodies - The functioning units of the Hypoxic Drive

As mentioned before, the Hypoxic Drive is regulated by the peripheral chemoreceptors located in Carotid bodies. In fact, the carotid bodies are integral in the sensing of systemic hypoxia and then activating the reflex of Hypoxic Driven ventilation. Carotid bodies are unique in that they respond instantaneously to even a moderate drop in peripheral oxygen (PO₂) levels. (Prabhakar , p 17) The carotid bodies are released bilaterally in the body and mainly in the carotid arteries where they are allowed to sense Hypoxic before it becomes a stimulus for the central nervous system. One of the fine functions of carotid bodies is that it can sense a stimulus in a very small range. For example, a change of between 100 and 180 torr in oxygen pressure will activate the nerves within carotid bodies. This is on a far smaller scale than other chemoreceptors. 

The diagram above shows the carotid body locations above the myo-cardial area. The carotid bodies are what contain the Peripheral chemo-receptors in a certain concentration that is regulated by the brain. There are peripheral chemo-receptors elsewhere in the body as well.

Graphical Representations of Hypoxic Drive

There are several diagrams or rather artifacts which can be used to explain and aid the Hypoxic Drive.

1. This picture below is a capnography which is used to chart electrical activity within the body and also levels of gasses. The graph shows that there are intemittent spikes that represent where the Hypoxic Drive actively engages in regulation.

2. This next pixture is a side by side set of four diagrams which can be used to clarify the effect of the Hypoxic Drive kicking in. The charts of A,B, and D can be used to see that the Hypoxic Drive is able to engage in increaseing the regulation in the body after there is an extended period of Hypoxia. Hypoxia, if not explained before is the condition under which the body does not receive an adequate oxygen supply.  Graph C shows that there is a higher response over time as the Hypoxic Drive kicks in. The response refers to metabolic responses.

Below are two more pictures which help identify the activity of the Hypoxic Drive. The first is a graph which represents a marginal change in regulation of gasses after a solid depression in the chemical regulation levels. The second picture shows a cell  which is deprived of oxygen. The cell has shriveled up areas and the white area is created by loss of oxygen. The cell is under the state of Hypoxia which is a strong initiator of Hypoxic Ventilation in the body.

Hypoxic Cellular condition (pic. 2)

Inner Workings of the Hypoxic Drive and Intro to Disadvantages of Hypoxic Ventilation

The hypoxic ventilatory response is initiated and regulated by the peripheral chemoreceptors that are located in carotid bodies. Hypoxia is defined as the lack of oxygen in tissues of organisms, and in more depth, it is the reduction of oxygen supply to tissues below physiological levels despite adequate perfusion of tissue by blood.[1]  David J Pierson states that the mechanism of Hypoxic Ventilation has been adapted to maintain cellular activity at a minimum acceptable level. [2] This is important because this contributes to the reasoning as to why the Hypoxic Drive is not the primary respiratory drive in human beings.  Pierson states that the Hypoxic drive maintains only 10% of ventilation in average humans with no troubling medical conditions.

There are some disadvantages of the Hypoxic Drive that remain in the shadows at times though. In patients with COPD (Chronic obstructive pulmonary disease), the patients have a low saturation of oxygen at all times, thus their bodies have adapted to such an environment. However, with an increase in the oxygen saturation due to Hypoxic drive, the patients have an added stimulus which often does not help the patient and can be at times harmful.[3]  COPD patients. Long term Hypoxic ventilation however has shown to be effective in increasing the survival of such patients because of adaptation over a lengthy period of time.

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[1] KK Jain Textbook of Hyperbaric Medicine Chapter 5 (p.g. 38)

[2] David K Pierson (p.g. 44)

[3] Emerg Med J. 2006 February; 23(2): 144–146.

Order of Respiratory Processes and Function of Hypoxic Drive

To better understand the Hypoxic drive, its components and purposes should be understood on a deeper level. The body compensates for an acute drop in the oxygen levels of the body through the Hypoxic ventilatory response. The response involves the pulmonary ventilation increasing the uptake of oxygen with each breath. It is noticed in neonatal human beings as well that a small drop in oxygen levels will cause a difference in ventilation rates. [1]The ventilation is complementary to a drop in metabolism levels which also lead to a smaller use of oxygen to metabolize within the human body. Metabolism is a tangential topic as well, but not a point of emphasis in the paper. The Hypoxic drive is also activated by an extended period of Hypoxia in the body.  It is the main response to hypoxia and is a response to primarily the drop in Peripheral oxygen levels.[2]  The second response that comes after the hypoxic drive is worked is hypoxic vasodilation which increases perfusion of O₂ rich blood to the tissues of the body, but is less common than the regulation by Hypoxic ventilatory control.[3]

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[1] Tepemma 2010

[2] David K Pierson Pathophysiology and Clinical Effects of Chronic Hypoxia (p.g. 44)

[3] Am J Pathol. 2004 June; 164(6): 1875–1882

Investigation Focus and Research

The hypoxic drive, a secondary respiratory drive in humans is an effective respiratory drive. It serves to regulate the oxygen levels within humans based on oxygen chemoreceptors located in the arteries and peripheral parts of the human body. The normal respiratory drive that is the primary form of respiration in humans integrates several major parts of the body to regulate the level of carbon dioxide within the body. Doctors contest that there is a great extent up to which the Hypoxic drive is used as a primary drive in humans as well, but in the light of certain conditions that affect humans. Although it is known that the Hypoxic Drive serves as a backup drive, it begs the question of why the Hypoxic drive is not the primary respiratory drive in humans. The investigation focuses on the point at which the human species severed the primacy of the Hypoxic drive and naturally shifted into the utilization of the respiratory system that regulates carbon dioxide levels. The investigation traverses a biological field that could open up many medical possibilities such as the possible transfer of human reliance on the respiratory system to the Hypoxic drive in the event that the respiratory system fails to sufficiently regulate gas respiration processes. The investigation will be ensconced in evolutionary biology developments regarding human respiration.