#(it’s almost like the decompression sickness that deep sea divers experience when they swim back to the surface too quickly)

[hearthtales]

The effects of what happens should one eat human food after-the-fact. Bran’s face flushed with embarrassment. He nodded, his focus fixed on the bread again, and fiddled with the ring on his finger. Mixing the jam with warm water. Bran glanced up at Sow'in, curious where he’d learned such a detail and why he’d chosen to share it with the boy.

But the ghoul seemed ready to leave. “Thank you for the food,” Bran hurried to say, manners kicking in at the last moment. He meant it, his tone sincere, though his voice had grown quieter as well, his face troubled. If he could only eat fae food now… how would he get more after their day was up?

He took a slow bite of bread, still cautious. It tasted… good. Not like mud or decay in the slightest. And the taste stayed good even as he chewed and swallowed. The rest of the bread slice went down faster, the boy’s hunger catching up with him at last.

Nettie had found courage in speaking to the ghoul aloud without consequences, even if it was only a single syllable. Summoning this bravery again, she took a breath, clutched her dress with both hands simply for something to hold, and blurted another syllable before he could leave. “Um!” She looked up at him, jittery with nerves, and managed to continue. “Wh- what do the words on the stone mean?”

Sow'in acknowledged Bran's answer with a nod. "Correct. An' we've all seen the effects of what happens should one eat human food after-the-fact," added the ghoul, referring to Bran's reaction to breakfast earlier that morning.

"I trust this supply will agree with you, favorably, an' that it shall suffice for the day." He first pointed out the basket, and then continued as if begrudgingly relaying a message from someone else. "..Ah was told that one can mix the jam with warm water to make a sweet drink. Do with that information what you will."

"Now, if you'll excuse me." Seeing that his job was done, seeing to his half of the bargain and providing the bare necessities, Sow'in took his leave. Surely the children would have no need of him until tomorrow morning.

[marinememoirs-blog]

Physiological effects of scuba diving and high atmospheric pressure.

Scuba diving

SCUBA diving is possible by the use of a self contained breathing apparatus using air consisting of 21% oxygen and 78% nitrogen. The use of scuba enables divers to swim at great depths and for long periods of time, which is not possible through aquatic activities such as normal swimming or snorkeling.

At sea level the barometric pressure of 760mmg is the equivalent of 1atm (atmospheric pressure). Scuba diving exposes the body to higher atmospheric pressure than usual and at a depth of 10 meters' of sea water the pressure is already 2atm, double that of sea level. The recreational limit for scuba diving is 40m where the pressure is already four times that of the surface however, many tech divers dive to much deeper depths.

Despite being an extremely enjoyable activity such pressures can cause physiological effects on the body with the two systems most affected by high atmospheric pressure being the cardiac and respiratory systems of the body. 

Air is inspired down into the trachea into the two bronchi which divide more so into the five lobes of the lung (three on the right, two on the left) until it passes into the bronchioles which have small air filled sacs called alveoli. These alveoli have an incredibly large surface area to enable for fast diffusion of O2 into the capillaries (which are one cell thick) from deoxygenated blood from the body and the fast diffusion of CO2 back into the alveolar sacs. The tidal volume of air breathed is approximately 500 mL, with ventilation into the lungs being made possible by pressure differences.

During inspiration contractions of the intercostal muscles and diaphragm enlarges the chest cavity resulting in an increase of alveolar volume leading to a decrease in alveolar pressure. This decrease in pressure gives way to air movement into the lungs which equalizes the pressure. Air leaves and is pushed out the lungs due to the relaxation of the prior contracted muscles. This is the elastic recoil.

The cardiovascular or circulatory systems carry blood from the heart round the body and back to the heart. This transport of blood round the body allows for the exchange of gasses, nutrients and waste products (e.g CO2) in the body blood and blood vessels.  Pulmonary circulation oxygenates the blood in the lungs before it is transported back to the heart to be pumped round the body. It is important for the cardiovascular to to regulate blood pressure regulation and blood levels to tissue to maintain homeostasis.  To help understand the effects of diving and high atmospheric pressure on the body it is important to understand the gas laws.

Pascal’s principle equates that any change in pressure in an enclosed fluid is equally is transmitted equally throughout that fluid, thus enabling our bodies to withstand the ambient pressure of the surrounding media. Most space in the body is made from water and therefore incompressible. It is only air filled spaces that are effected by pressure changes. Boyles law states that pressure and volume are inversely proportional at a given temperature, as pressure increases volume decreases, at 30m the volume of gas is 1/3 that at sea level.  Linking to Daltons law by which as the pressure increases as does the partial pressure of the constituent gas and as the partial pressure increases as does the amount dissolved into the tissues of the body accounted for by Henry’s law.

Hyperbaric conditions

Scuba diving exposes divers to hyperbaric conditions, in such condition there are many variable changes to that of sea level or 1atm.  When submerged there is a higher ambient pressure, divers as a result are exposed to and increase respired gas density, increased partial pressures and experience increased work while breathing. Notably there is also increased dead space (when using a breathing apparatus this refers to the space in the breathing apparatus by which the gasses must flow through as ventilation occurs) due to the regulator and hose. Even immersion in water up to the neck can begin to cause physiological changes activating the sympathetic nervous system and the parasympathetic nervous system through the diving reflex – a cardiovascular-respiratory response to immersion by the cardiovascular and pulmonary system.

This increase redistribution of blood helps to maintain blood pressure minimizing the effects of a lower heart rate. Heart rate variability (HRV) is the cyclic variations of heart rate created by the autonomic nervous system. It has been found that HRV increases during scuba diving and it is likely that this change in HRV is due to the haemodynamic changes involved in submersion. 

Exchange of oxygen by the lung is not impaired significantly by scuba diving especially up to the recreational limit. In many cases most of the pulmonary related effects of diving are related to to the immersion related increase of pulmonary blood volume, increase of dissolved gas and higher levels of inspired PO2 altering gas exchange functionality. Divers may experience and increase of dead space as the regulator hose decreases alveolar ventilation. The use of a demand valve regulator or a full face rebreathe mask reduces dead space as the diver does not have to breath in and out of the same hose pipe reducing the amount of CO2 in the chamber, such is the case with snorkeling. If ventilation is insufficient it can lead to hypercapnia due to elevated levels of CO2. To compensate for this respiratory rate or tidal volume must be increased. Compliance measures the ease by which the lungs and thorax expand. At depths there is an increase resistive and elastic loads, meaning greater effort is required for inhalation and exhalation due to the increased density of breathable gas. This decrease in lung compliance increases the amount energy necessary for breathing to occur.  Much of this is related to the increase in the gas density of air from scuba tanks largely because dense air has increased flow resistance with this resistance increasing with depth.

Expiratory reserve volume (ERV) relates to the amount of air that can be expired forcefully after expiration of tidal volume. Diving causes a decrease in ERV at shallower depths however with increasing depth there is an increase of ERV likely attributed to a bodily attempt to increase airway diameter and counteract increased airway resistance of dense breathable air.

Decompression sickness is attributed to ascent in diving. When at depth nitrogen is absorbed into tissues at the same pressure of the surroundings, problems occur when the dissolved inert gas nitrogen increases in size and moved out of the dissolved state and into the tissues forming bubbles which especially effect cavities in the body and can stretch or block blood vessels causing oxygen depravation. This condition can be avoided however if divers make necessary safety stops upon ascent. It is also important to breathe to enable an equilibrium of volume and ambient pressure of the surroundings. If divers ascend with a closed glottis it may cause lungs to burst. Arterial gas embolisms (AGE) may occur if gas bubbles block the transport of blood to the heart. AGE’s are likely to occur due to the pressure decrease of assent as the gas bubbles increase in size. If these bubbles are in the circulatory system, then can travel through he body and lead to brain embolisms.

The respiratory and cardiac systems have great abilities to withstand the increased pressures involved with diving as long as necessary precautions are taken place. The cardiorespiratory systems functions at almost normal capacity with the aid of SCUBA with most of the diver’s physiological effects in this system resulting from the increased work of having to breathe gas at a higher density than usual and increased air way resistance. At great depths > 40m it is commonplace to use alternative gas mix’s which make it easier for respiration during diving and also avoid negative effects of breathing ‘normal air’ at depth such as oxygen narcosis. Such deep dives would not be possible without alternate air mix’s and much greater physiological problems would occur. With a combination of natural body mechanisms and technological equipment it is possible to keep the physiological effects of hyperbaric conditions to a minimum.