Question

1. A recent news story (not really!) highlighted the near-drowning of a Navy Seal recruit that deliberately hyperventilated before diving into the water. The recruit was practicing an exercise that required them to hold their breath underwater for an extended period of time. The recruit reasoned that hyperventilation prior to the exercise would alter their physiology in a way that would increase the length of time they could hold their breath. Explain the physiological basis of this belief (use the terms hypocapnia and hypercapnia in your answer)

2. The digestive system and respiratory system share some structures, yet others must be kept separate to prevent choking. Describe how substances that are intended to be swallowed may get “misdirected” and lead to choking. Be sure to include all structures involved.

Answer 1

Alterations in physiology:

HYPERCAPNIA:

Carbon dioxide (CO₂) retention, or hypercapnia, is a known risk of diving that can cause mental and physical impairments leading to life-threatening accidents. Often, such accidents occur due to elevated inspired carbon dioxide. For instance, in cases of CO₂ elimination system failures during rebreather dives, elevated inspired partial pressure of carbon dioxide (PCO₂) can rapidly lead to dangerous levels of hypercapnia. Elevations in PaCO₂ (arterial pressure of PCO₂) can also occur in divers without a change in inspired PCO₂. In such cases, hypercapnia occurs due to alveolar hypoventilation. Several factors of the dive environment contribute to this effect through changes in minute ventilation and dead space. Predominantly, minute ventilation is reduced in diving due to changes in respiratory load and associated changes in respiratory control. Minute ventilation is further reduced by hyperoxic attenuation of chemosensitivity. Physiologic dead space is also increased due to elevated breathing gas density and to hyperoxia. The Haldane effect, a reduction in CO₂ solubility in blood due to hyperoxia, may contribute indirectly to hypercapnia through an increase in mixed venous PCO₂. In some individuals, low ventilatory response to hypercapnia may also contribute to carbon dioxide retention. This review outlines what is currently known about hypercapnia in diving, including its measurement, cause, mental and physical effects, and areas for future study.

Hypocapnia:

We are using diagram for better understanding.

2. There are three main divisions of the pharynx: the oral pharynx, the nasal pharynx, and the laryngeal pharynx. The latter two are airways, whereas the oral pharynx is shared by both the respiratory and digestive tracts.

The funnel-shaped pharynx connects the nasal cavity and mouth superiorly to the larynx and esophagus inferiorly. Commonly called the throat, the pharynx is the site where our respiratory pathway, from nose to larynx, crosses the digestive pathway, from mouth to esophagus.

The other is the trachea, which is the opening air must pass through to get to the lungs. When swallowing occurs, the trachea is covered by a flap called the epiglottis, which prevents food from entering the lungs.

Misdirected: Structural dysphagia occurs when there is any swallowing difficulties caused by a problem in the structure of the muscles and nerves used to swallow. Structural abnormalities can occur in the oral cavity (mouth), the pharynx (throat) and the oesophagus (food pipe).