W4 - Hyperbaria

Question 1

What are the two forces that produce increased external pressure (hyperbaria) in diving?

Answer 1

Hydrostatic Pressure - weight of water above diver. Weight of atmosphere (ata/ bar) at water’s surface

Question 2

How much force does each 10m of seawater exert?

Answer 2

1 ata, therefore diver experiences 2 ata (1 seawater 1 air at surface)

Question 3

What is Boyle’s Law?

Answer 3

at constant temperature, the volume of a given mass of gas varies inversely with pressure. When pressure doubles, volume halves; conversely, reducing pressure by one half expands any gas volume to twice its previous size, producing a curvilinear relation between lung volume at the surface and depth in seawater

Question 4

What does Boyles Law mean for scuba divers?

Answer 4

If they hold their breath there’s an increased chance of pneumothorax
6-L lung volume at a 10-m depth expands to 12 L at the water’s surface

Question 5

What are the 2 factors the limit snorkel size?

Answer 5

Increased hydro pressure on lungs, even at 1m inspiratory muscles cannot overcome external pressure. Note: Air under pressure from an external source to promote inspiratory action counter- acts the external hydrostatic force. Increased pulmonary dead space ((the volume of air that is inhaled that does not take part in the gas exchange) by enlarging the snorkel’s volume

Question 6

What does the duration of a breath hold dive depend upon?

Answer 6

Breath-hold duration until arterial carbon dioxide pres- sure reaches the breath-hold breakpoint
2. Relationship between a diver’s total lung capacity (TLC) and residual lung volume (RLV)

Question 7

What happens during the breath hold response?

Answer 7

Oxygen is utilised, PO2 drops (60mmHg) PCO2 increases (50mmHg)
Chemoreceptors: breathe!

Question 8

What are the benefits and costs of hyperventialting before a breath hold dive?

Answer 8

A skin diver hyperventi- lates at the surface before a dive to reduce arterial Pco2 to augment breath-hold duration. The diver now takes a full inhalation and descends beneath the water. Alveolar oxy- gen continually moves into the blood for delivery to active muscles. Owing to previous hyperventilation, arterial car- bon dioxide levels remain low, freeing the diver from the urge to breathe. Concurrently, as the diver swims deeper, external water pressure compresses the thorax,increasing gas pressure within this cavity. Increased intrathoracic pres- sure maintains a relatively high alveolar Po2. Even though absolute alveolar oxygen quantity decreases as oxygen moves into the blood during the dive, Po2 continually loads hemo- globin as the dive progresses. When the diver senses the need to breathe from carbon dioxide buildup and begins to ascend,reversalsoccurinintrathoracicpressure.Aswater pressureonthethoraxdecreaseswithascent,lungvolume expands and alveolar Po2 decreases to a level where no gra- dient exists for oxygen diffusion into arterial blood. This places the diver in a hypoxic state. Near the surface, alveo- lar Po2 reaches levels so low that dissolved oxygen diffuses from venous blood returning to the lungs and flows into the alveoli; this causes the diver to suddenly lose consciousness before surfacing.

Question 9

What ratio of divers Total Lung Capacity to Relative Lung Capacity (RLC) generally determins the depth before lung squeeze?

Answer 9

Total maximum lung volume (4-6L). However Lung volume can decrease to residual volume (remaining air after forceful expiration (1-1.2L)). Below this problems can occur. As a result depth limit determined by total lung volume to residual volume ratio: TLC/RV
For example, for a diver with a 6.0-L TLC and a 1.5-L RLV, Boyle’s law pre- dicts that TLC would compress to RLV at 30 m or 4 ata exter- nal pressure (4:1)

Question 10

What are the 4 different responses to the diving reflex (what humans do when immersed in water)?

Answer 10

1. Bradycardia (<hr>

Question 11

Immersion increases venous return - why?

Answer 11

In water body orientation less likely to be upright. Systems used on surface (valves) less useful.

Question 12

Can autonomic conflict occur as a result of cold water immersion?

Answer 12

Simultaneous ANS (cold shock response, attempted breath hold > tachychardia) and PNS (diving reflex > bradychardia) stimulation which can cause arrhythmia

Question 13

What are the CV responses to Head-out water immersion (hydrostatic pressure to lower body):?

Answer 13

Head-out water immersion (hydrostatic pressure to lower body):
• ↓blood pooling in legs (because of venous return)
• ↑venous return
• ↑stroke volume
• ↓heart rate(~10-12beats/min lower than in air, doesn’t need to work as hard)
• ↓cardiac strain
• ↑plasma volume. Part of reason hydrostatic treatments used with CV patients

Question 14

What happens to the spleen during immersion?

Answer 14

Importantorgan
• Storage of oxygen-rich red blood cells
• Diving/Hyperbaria/Facial immersion/ Peripheral vasoconstriction triggers release:
> Contractionofthespleen
• Ejects oxygen-rich red blood cells into the blood supply. Bajau bigger spleen

Question 15

What are the two basic scuba designs?

Answer 15

1. Common open-circuit system
2. closed-circuit system

Question 16

What is Henry’s Law?

Answer 16

quan- tity of gas dissolved in a liquid at a given temperature varies directly with two factors:
1. Pressure differential between the gas and the liquid 2. Gas solubility in the liquid. Underwater breathing systems must supply air, oxygen, or other gas mixtures at sufficient pressure to overcome the force of water against the diver’s thorax. For example, at 3 ata (20-m depth) the respired gas requires delivery at approximately 2280 mm Hg (3 × 760 mm Hg), whereas gas delivery at 60 m requires a pressure of 5320 mm Hg.

Question 17

Name 3 hazards associated with improper equalisation in scuba diving?

Answer 17

Face mask squeeze; bloackge of eustachian tube; blockage of sinus

Question 18

What’s the difference bwteen air embolism and pneumothorax?

Answer 18

If expansion of air in the respiratory tract causes lung tissue to rupture during ascent from underwater—air bubbles enter the pulmonary venous system. and then flow to the heart and enter the systemic circulation (Air Embolism). Continued expansion of trapped air during ascent collapses the ruptured lung, a condition called pneumothorax.

Question 19

Breathing gas with a PO2 above how many atmospheres increase susceptibility to O2 poisoning?

Answer 19

Inspiring a gas with a Po2 above 2 ata (1520 mm Hg) greatly increases a diver’s susceptibility to oxygen poison- ing, particularly at elevated metabolic rates during physical activity. Less O2 unloading at tissue → hemoglobin remains saturated with O2 → impairs CO2 elimination

Question 20

What is Nitrogen Narcosis?

Answer 20

• Effect is similar to alcohol/intoxication, related to partial pressur worsen w depth, hence why nitrox only used at shallow depth. Limited acclimation.

Question 21

Apart from rate of ascent, what can influence bubble formation ref decompression sickness?

Answer 21

Bubbles formation can be influenced by:
• Hydration, thermal tolerance, exercise, sex, body fat, and previous experience

Question 22

At what depth requires inhalation of compressed mixed gases?

Answer 22

at depths greater than 60 fsw (about 20m), diving with compressed air and saturation diving increase risk of oxygen toxicity. Div- ing lower than this depth requires breathing compressed mixed gases (nonair) with a lower Po2

Question 23

What are the benefits of heliox diving?

Answer 23

Breathing mixtures of helium and oxygen (heliox) allows dives to depths of 2000 fsw. Heliox diving eliminates nitrogen narcosis risk and minimizes risk of oxygen poisoning. “
Nitrox
• Nitrogen and oxygen
• Used for relatively shallow dives (29-34m)
Trimix
• Helium, nitrogen, and oxygen
• Used for any dives where the nervous system can be impaired (Helium can cause neurological symptoms (>60m)”

Question 24

What are the symptoms and cause of High Pressure Nervous Syndrome, and how do they relate to Heliox diving?

Answer 24

During rapid descent to depths in excess of 300 fsw up to 2280 fsw, divers breathing helium–oxygen mixtures can experience potentially incapacitating nausea, muscle tremors, and other central nervous effects

Question 25

What depths is saturation diving required?

Answer 25

Thus, dives below 300 fsw (approx 90m)
generally take place with saturation diving in a deep-diving system using a helium–oxygen–nitrogen (trimix) breathing mixture

Question 26

What is technical diving?

Answer 26

technical diving defines untethered dives beyond the traditional compressed air range for military operations, science, salvage, and recre- ational pursuits. Technical diving requires special equip- ment, expertise, and vigilant management of gas mixtures. Technical divers routinely use various mixtures of trimix com- pressed gas to dive below 300 fsw.

Question 27

Whats the impact of exercise while diving?

Answer 27

Exercise induces increased gas exchange - Exercise increases HR/CO, diving increases SV - Can increase narcosis and O2 toxicity > O2 gas loading. Note: exercise Before Diving Can reduce bubble formation in SCUBA divers

Question 28

Whats the impact of exercise after diving?

Answer 28

Even with submaximal exercise, it can exacerbate bubble formation AND intrapulmonary shunting (Poor gas diffusion from lung to blood)