Physiology of Gases in Respiration

Exercise at High Altitude

• High altitude is defined as 10,000 feet (3048 meters) or higher
• Moderate altitude is defined as 4,921 feet (1,500 meters) or above 5,000
• Atmospheric pressure decreases with higher altitude
• Partial pressure of gases (O2, CO2, and N2) in the air remain the same, but the partial pressure of each gas decreases at higher altitudes
• This results in lower partial pressures of oxygen, carbon dioxide, and nitrogen at higher altitudes.

Gas Exchange at Sea Level

• At sea level, air has weight, and this weight is related to barometric pressure
• At higher altitudes, the air is thinner, leading to lower barometric pressure and thus lower weight than at sea level
• The ideal gas law (PV=nRT) demonstrates the relationship between pressure, volume, temperature and the number of moles of gas present.

The Ideal Gas Law

• The ideal gas law (PV=nRT) describes the relationship between pressure (P), volume (V), number of moles (n), ideal gas constant (R), and temperature (T) of a gas
• The constant R is equal to 8.31 kPa • L / K • mol
• Knowing three of the variables allows calculation of the fourth.

Boyle's Law

• Boyle's Law links volume and pressure at constant temperature. Volume varies inversely with pressure.

Charles' Law

• Charles' law states that volume and temperature are directly related at a constant pressure. Volume changes proportionally to temperature change

Dalton's Law

• Dalton's Law states that the total pressure of a mixture of gases equals the sum of partial pressures of all gases. For a mixture of gases in a closed container, the total pressure equals the sum of partial pressures of individual gases

Partial Pressures of Air at Sea Level

• Standard atmospheric pressure at sea level is 760 mmHg
• Nitrogen (N2) comprises 79.04% of air and has a partial pressure of 600.7 mmHg
• Oxygen (O2) comprises 20.93% of air and has a partial pressure of 159.1 mmHg
• Carbon dioxide (CO2) comprises 0.03 % and has a partial pressure of 0.2 mmHg

Partial Pressures of Air (Inspired/Expired)

• Inspired air has higher partial pressure of O2 and lower partial pressure of CO2, compared to expired air.
• The partial pressure of O2 in the alveoli is 104 mmHg
• The partial pressure of CO2 in the alveoli is 40 mmHg
• Partial pressure of O2 in venous blood is 40 mmHg
• Partial pressure of CO2 in venous blood is 46 mmHg

PO2 and PCO2 in Blood

• Partial pressure of oxygen (PO2) and partial pressure of carbon dioxide (PCO2) are critical for gas exchange in the lungs and tissues.
• PO2 in arterial blood is 100 mmHg and in venous blood is 40 mmHg.
• The opposite is true for PCO2 (low in arterial and high in venous blood).

External/Internal Respiration

• External respiration is the exchange of gases between the alveoli in the lungs and the blood
• Internal respiration is the exchange of gases between the blood and the body tissues.
• Oxygen and carbon dioxide move based on their respective partial pressures in these exchanges.

Partial Pressures of Air (Table 10.1)

Numerical data of the partial pressure of various gases at sea level in a table format.

Oxygen-Hemoglobin Dissociation Curve

• The Oxygen-Hemoglobin Dissociation curve shows the relationship between the partial pressure of oxygen (PO2) and the percentage of hemoglobin saturated with oxygen (sO2)
• In the resting state, arterial blood has a higher PO2 and S02 compared to venous blood.

Henry's Law

• Henry's Law describes the solubility of gases in liquids, stating that the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid.

Henry's Law & Soft Drinks

• Carbonated drinks contain dissolved carbon dioxide under pressure to keep the carbon dioxide in solution
• Once the pressure on the container is reduced, gaseous CO2 escapes, resulting in the formation of bubbles

Altitude

• Atmospheric pressure decreases as altitude increases
• The percentages of O2, CO2, and N2 remain the same in the air, but their partial pressures decrease
• Hypoxia occurs at low PO2.
• Normoxia has normal PO2
• Hyperoxia is high PO2

Conditions at Altitude

• Reduced PO2
• Reduced air temperature
• Low humidity
• Increased solar radiation

Changes in Barometric Pressure (PB) and Partial Pressure of Oxygen (PO2)

• A table lists barometric and PO2 at different altitudes.

Altitude-Related Conditions

• Acute Mountain Sickness (AMS)
• High-Altitude Pulmonary Edema (HAPE)
• High-Altitude Cerebral Edema (HACE)
• High-Altitude Retinal Hemorrhage (HARH)

Acute Mountain Sickness (AMS)

• Headache, nausea, vomiting, dyspnea, insomnia
• Usually appears 6–96 hours after arriving at altitude
• Often caused by carbon dioxide accumulation

High-Altitude Pulmonary Edema (HAPE)

• Shortness of breath, excessive fatigue, blue lips and fingernails, mental confusion, dry cough, "rales"
• Occurs at altitudes above 10,000 ft (3,048 m).
• Results from fluid accumulation in the lungs.

High-Altitude Cerebral Edema (HACE)

• Mental confusion, progressing to coma and death.
• Occurs above 4,300 m (14,108 ft)
• Results from accumulation of fluid in the cranial cavity

High-Altitude Retinal Hemorrhage (HARH)

• Climbers experience blood pressure surges during exercise
• Increases lead to retinal capillary ruptures

Acclimatization to Altitude

• Individuals who live at high altitudes may adapt over time in preparation for extended high-altitude stays or activities
• Improvements and acclimatization takes place over weeks.

Hematologic Changes

• Increased red blood cell mass on return to sea level
• Not proven that altitude training improves sea-level performance
• Difficult to study due to reduced intensity and volume at altitude
• Residents live at a high altitude and train at lower altitudes.
• Adjustments include decreased plasma volume and elevated hematocrit and RBC concentration

Cellular Changes

• Increased capillarization
• Increased myoglobin
• Increased mitochondria
• Increase 2, 3-diphosphoglycerate (2, 3-DPG)

Performance

• VO2max decreases 3% per 1000 ft increase in altitude
• Threshold for decrements occurs at 5,000 ft and higher altitudes
• Endurance athletes are most affected because they rely on aerobic energy and oxygen transport

Cardiovascular Responses

• Norepinephrine levels increase
• Blood pressure and heart rates increase with altitude changes
• Blood volume usually decreases at higher altitudes

Cardiorespiratory and Metabolic Changes

• Numerical data on VO2, VE, HR (Heart Rate), SV (Stroke Volume), and A-V O2 diff at different altitudes.

Oxygen Transport

• Ventilation, diffusion, hemoglobin (O2 affinity), cardiac output, peripheral circulation, and metabolism (aerobic energy production) all play vital roles in oxygen transport.

Fluid Loss

• Dehydration is common at altitude
• Increased respiration, perspiration, and urinating all contribute to fluid loss

Fluid Recommendations

• Additional fluid intake is recommended for moderate and high altitude
• Urine should be light.

Optimal Nutrition

• Adequate calorie and nutrient intake is essential for acclimatization in high-altitude areas
• A high-carbohydrate diet is recommended

General Nutrition Hints

• Increase caloric intake as activity increases
• Plan meals that cook in 15 minutes
• Drink 3-5 liters of water daily
• Frequent water consumption is important
• Know the time to melt or boil water at high elevations
• Increase carbohydrate intake is preferred
• Alcohol should be avoided at high altitudes

Safety Recommendations

• Ascend slowly and in stages
• Conduct climbs with guides or teams when possible
• Avoid dehydration and overexertion
• High carbohydrate diets help reduce acute mountain sickness (AMS) symptoms
• Medication can be helpful to prevent AMS symptoms.

Altitude Training for Sea-Level Performance

• Increased red blood cell mass upon return to sea level
• Not scientifically proven that altitude training will improve low-altitude sea-level performance
• Altitude training can be difficult to measure objectively because intensity, and volume may vary
• Living at high altitudes and training at lower altitudes may improve aerobic performance

Training for Optimal Altitude Performance

• Compete after a 24-hour arrival at altitude
• Train in moderate and high elevations for at least two weeks before competition
• Increase VO2max at sea level to allow for competition at lower relative intensities

Effect of Altitude on Performance

• Short-term anaerobic activity is not affected by altitude
• Lower air resistance may improve performance
• Long-term aerobic performance is negatively impacted

Effect of Altitude on VO2max

• Decreased VO2max at higher altitudes
• Reductions in rate and maximum cardiac output may correlate

Changes in VO2max With Increasing Altitude

• Numerical data displayed in a graph with different studies demonstrating VO2max decline at higher altitudes

Effect of Altitude on Submaximal Exercise

• Higher heart rate

Effect of Altitude on Submaximal Heart Rate Response

• Numerical data in a graph of heart rate versus oxygen consumption at sea level and 3,100 m

Effect of Altitude on Submaximal Ventilation Response

• Numerical data in a graph of pulmonary ventilation versus oxygen consumption at the indicated altitudes

Adaptation to High Altitude

• Acclimatization to altitude results in production of more red blood cells
• Adaptation for an individual raised at altitude is different compared to a person just arriving in those conditions

Training for Competition at Altitude

• Training outcomes related to VO2max are variable between athletes
• Ability to undergo high intensity training at altitude may vary

The Quest for Everest

• Mount Everest was climbed without supplemental oxygen in 1978
• Previously, VO2max was miscalculated and underestimated

Challenges of High Altitude Climbing

• Successful climbers have a high capacity for hyperventilation
• Reduced PCO2 and H+ in blood
• Allows for more O2 binding to hemoglobin without impacting PO2
• Weight loss as a result of reduced appetite
• Reduction in muscle fiber diameter

Altitude Acclimatisation

• Living at high altitudes results in sufficient tissue anoxia to stimulate EPO release and red blood cell productions
• Changes are observed

Altitude Acclimatization

• Adjustments related to the circulation, hyperventilation and a reduced buffering power of the blood occur
• Reduced blood volume and shifts in Hb dissociation curve are also observed

Live High, Train Low

• Technique involves living in high altitude locations for training but exercising at lower altitudes for competitions
• Preliminary data suggest this approach may enhance performance

Performance

• VO2max decreases 3% with each 1000-foot elevation increase above 5,000 feet
• Aerobic performance can be reduced in the long term as a result of living at high altitudes

This quiz covers key concepts related to the partial pressures of gases like oxygen and carbon dioxide in the respiratory system, as well as the effects of altitude on hydration and solubility according to Henry's Law. Test your understanding of how these factors influence respiratory physiology and performance at high altitudes.