Altitude Physiology

ALTITUDE PHYSIOLOGY

Q. 1

Which is a feature of high altitude pulmonary edema

 A

Associated with low cardiac output

 B

Associated with pulmonary hypertension

 C

Occurs only in unacclamatized persons

 D

Exercise has no effect

Q. 1

Which is a feature of high altitude pulmonary edema

 A

Associated with low cardiac output

 B

Associated with pulmonary hypertension

 C

Occurs only in unacclamatized persons

 D

Exercise has no effect

Ans. B

Explanation:

associated with pulmonary hypertension [Ref: Harrison 17/e, p 1707 (16/e, p 1617); ACP Medicine (2006); Ganong 22/c, p 685; http://www.emedicine.com/MED/topic1956.htm%5D

High altitude pulmonary edema (HAPE) is a life-threatening form of non-cardiogenic pulmonary edema that occurs in otherwise healthy mountaineers at altitudes above 2,500 meters (8,200 feet).

  • HAPE belongs to a spectrum of High altitude illness. HAPE and High Altitude Cerebral Edema are most ominous forms of High altitude illness. Milder forms are – acute mountain sickness, retinal hemorrhages, and peripheral edema.
  • The initial insult that causes RAPE is excessive hypoxia caused by the lower air pressure at high altitudes. The mechanisms by which this shortage of oxygen causes HAPE are poorly understood, but two processes are believed to be important:
  1. Increased pulmonary arterial and capillary pressures (pulmonary hypertension) secondary to hypoxic pulmonary vasoconstriction
  2. An idiopathic non-inflammatory increase in the permeability of the vascular endothelium.
  • HAPE is seen in unacclamatized yet otherwise healthy persons.
  • Acclamatized high altitude natives may also develop this syndrome upon return to high altitudes after a relatively brief visit at low altitudes.
  • RAPE generally occurs 1-4 days after rapid ascept to altitudes.
  • This syndrome is far more common persons under the age of 25 years. RAPE is rare in infants and small children. Cold weather and physical exertion at high altitude are other predisposing factors.
  • Association with exercise:

Bronchoalveolar lavage fluid (BALF) studies have shown that after heavy exercise, under all conditions, athletes develop a permeability edema with high RALF RBC and protein concentration in the absence of inflammation. Exercise at high altitudes caused significantly greater leakage of RBCs into the alveolar space than that seen with normoxic exercise. These findings suggest that pulmonary capillary disruption occurs with intense exercise in healthy humans and that hypoxia augments the mechanical stress on the pulmonary microcirculation.

  • Autopsy studies performed on patients who died of RAPE have shown a proteinaceous exudate with hyaline membranes. The studies have shown areas of pneumonitis with neutrophil accumulation, although none was noted to contain bacteria. The findings suggest a protein-rich edema with a possibility that clotting abnormalities may be partially responsible for this illness.
  • Mortality/Morbidity – RAPE may be fatal within a few hours if left untreated. Patients who recover from HAPE have rapid clearing of edema fluid and do not develop long-term complications.
  • Prevention and treatment:
  • High-altitude pulmonary edema can often be prevented by use of dexamethasone, calcium channel blocking drugs, or long acting inhaled beta-2 adrenergic agonists.
  • Treatment includes

Descent. from altitude, – Bed rest

– Oxygen

– Inhaled nitric oxide –


Q. 2

“Goitre is prevalent in high altitudes”- is an example of:

 A

Direct association

 B

Temporal association

 C

Indirect association

 D

Spurious association

Q. 2

“Goitre is prevalent in high altitudes”- is an example of:

 A

Direct association

 B

Temporal association

 C

Indirect association

 D

Spurious association

Ans. C

Explanation:

The indirect association is an association between a characteristic (or variable) of interest and a disease due to the presence of another factor, known or unknown that is common to both the characteristic and the disease.

This common factor is also known as the “confounding” variable. In the above example iodine deficiency is the confounding variable.

  • High altitude
  • Iodine deficiency
  • Goitre prevalence
 
Ref: Park 21st edition, page 85.

Q. 3

Which of the following does not cause hyperventilation?

 A

Anxiety

 B

High altitude

 C

Pulmonary hypertension

 D

Psychotic illness

Q. 3

Which of the following does not cause hyperventilation?

 A

Anxiety

 B

High altitude

 C

Pulmonary hypertension

 D

Psychotic illness

Ans. C

Explanation:

Physiological causes of ventilation are anxiety, altitude, pregnancy, and exercise. Other common pathological causes include hypoxemia, pulmonary conditions like pneumonia, pulmonary embolism, bronchial asthma, cardiac conditions like congestive heart failure and hypotension, acidosis, hepatic failure, psychogenic, salicylates, fever and sepsis.

Ref: Pulmonary Function: A Guide for Clinicians By Gabriel Laszlo, 1994, Page 172 ; Harrison’s 17th ed chapter 258


Q. 4

Which is a feature of high altitude pulmonary edema?

 A

Associated with low cardiac output

 B

Associated with pulmonary hypertension

 C

Occurs only in unacclamatized persons

 D

Exercise has no effect

Q. 4

Which is a feature of high altitude pulmonary edema?

 A

Associated with low cardiac output

 B

Associated with pulmonary hypertension

 C

Occurs only in unacclamatized persons

 D

Exercise has no effect

Ans. B

Explanation:

High altitude pulmonary edema:
High altitude pulmonary edema (HAPE) and High Altitude Cerebral Edema are most ominous forms of High altitude illness. 

Usually develops within the first 2–5 days after acute exposure to altitudes above 2500–3000 metres. It occurs in both unacclamatized and acclamatized inividual who ascends to high altitude from low. An excessive rise in pulmonary artery pressure preceding oedema formation is the crucial pathophysiological factor.

 
Milder forms are;
  • Acute mountain sickness
  • Retinal hemorrhages
  • Peripheral edema
High altitude pulmonary edema (HAPE) is a life-threatening form of non-cardiogenic pulmonary edema that occurs in otherwise healthy mountaineers at altitudes above 2,500 meters (8,200 feet).
 
Predisposing factors:
  • HAPE is seen in unacclamatized healthy persons.
  • Acclamatized high altitude natives may also develop this syndrome upon return to high altitudes after a relatively brief visit at low altitudes.
  • HAPE generally occurs 1-4 days after rapid ascent to altitudes.
  • This is common under the age of 25 years. HAPE is rare in infants and small children. 
  • Cold weather and physical exertion at high altitude are other predisposing factors.
Pathogenesis: HAPE belongs to a spectrum of High altitude illness. The initial insult that causes HAPE is excessive hypoxia caused by the lower air pressure at high altitudes. The mechanisms by which this shortage of oxygen causes HAPE are poorly understood, but two processes are believed to be important:
  • Increased pulmonary arterial and capillary pressures (pulmonary hypertension) secondary to hypoxic pulmonary vasoconstriction.
  • An idiopathic non-inflammatory increase in the permeability of the vascular endothelium.
Clinical features: HAPE presents within 2–5 days of arrival at high altitude Early symptoms of HAPE
include exertional dyspnoea, cough and reduced exercise performance. As pulmonary oedema progresses, cough worsens and breathlessness at rest and sometimes orthopnoea occur. Gurgling in the chest and pink frothy sputum indicate advanced cases. The clinical features are cyanosis, tachypnoea,tachycardia and elevated body temperature.
 
Investigations:
Chest radiographs and computed,tomographic scans of early HAPE show a patchy,peripheral distribution of edema.
 
Prevention and treatment:
Slow ascent is the most effective method of prevention, can often be prevented by use of dexamethasone, calcium channel blocking drugs, or long acting inhaled beta-2 adrenergic agonists.
Treatment includes
  •    Descent from altitude,
  •    Bed rest
  •    Oxygen
  •    Inhaled nitric oxide
  •    Nifidipine.
Ref: Harrison’s Principles of internal medicine, 17th Edition, Page 1707 ; Ganong, Review of medical physiology, 22nd Edition, Page 685

Q. 5

In a person acclimatized for high altitude, O2 saturation is maintained because of:

 A

Hemoconcentration

 B

Decreased CO 2 saturation

 C

Hypoxia

 D

More O2 delivery to tissue

Q. 5

In a person acclimatized for high altitude, O2 saturation is maintained because of:

 A

Hemoconcentration

 B

Decreased CO 2 saturation

 C

Hypoxia

 D

More O2 delivery to tissue

Ans. D

Explanation:

Acclimatization to altitude occur due to a variety of compensatory mechanisms. Secondary to acclimatization there is an increase in red blood cell 2,3 DPG which in turn decrease the oxygen affinity of hemoglobin. This decrease in oxygen affinity increases the availability of oxygen to tissues. 

Must know:

Changes occurring during Acclimatization:

  • Hyperventillation results in respiratory alkalosis
  • Increase in 2,3 BPG which decreases the affinity of oxygen affinity of hemoglobin. This inturn shift the oxygen dissociation curve to the right.
  • Increase in erythropoetin level
  • Increase in red blood cell count and hemoglobin
Ref: Human Adaptation Rev By A. Roberto Frisancho, page 244-8

Q. 6

High-altitude acclimatization may be facilitated by all except?

 A

Increased production of red blood cells

 B

Increased alveolar ventilation

 C

Growth of new blood vessels

 D

Growth of new skeletal muscle fibers

Q. 6

High-altitude acclimatization may be facilitated by all except?

 A

Increased production of red blood cells

 B

Increased alveolar ventilation

 C

Growth of new blood vessels

 D

Growth of new skeletal muscle fibers

Ans. D

Explanation:

Erythropoietin secretion increases promptly on ascent to high altitude and then falls somewhat over the following 4 days as the ventilatory response increases and the arterial PO2 rises. The increase in circulating red blood cells triggered by the erythropoietin begins in 2–3 days and is sustained as long as the individual remains at high altitude. Compensatory changes also occur in the tissues.

The mitochondria, which are the site of oxidative reactions, increase in number, and myoglobin increases, which facilitates the movement of O2 into the tissues. The tissue content of cytochrome oxidase also increases.The natives who live in high altitudes are barrel-chested and markedly polycythemic. They have low alveolar PO2 values, but in most other ways they are remarkably normal.

 
Ref: Barrett K.E., Barman S.M., Boitano S., Brooks H.L. (2012). Chapter 35. Gas Transport & pH. In K.E. Barrett, S.M. Barman, S. Boitano, H.L. Brooks (Eds), Ganong’s Review of Medical Physiology, 24e.

Q. 7

A 32 year old high altitude rock climber is observed to have a hematocrit of 70 percent. Which of the following represents the MOST likely explanation?

 A

Polycythemia with increased red cell mass

 B

Relative Polycythemia due to dehydration

 C

Polycythemia due to hemoconcentration

 D

Polycythemia with high altitude pulmonary edema

Q. 7

A 32 year old high altitude rock climber is observed to have a hematocrit of 70 percent. Which of the following represents the MOST likely explanation?

 A

Polycythemia with increased red cell mass

 B

Relative Polycythemia due to dehydration

 C

Polycythemia due to hemoconcentration

 D

Polycythemia with high altitude pulmonary edema

Ans. A

Explanation:

Mountaineers at high altitude develop physiological increase in erythropoietin levels due to decreased arterial oxygen saturation. This leads to absolute Polycythemia with increased red cell mass. ‘Red cell mass’ is the investigation of choice to establish the diagnosis. Once ‘red cell mass’ determination confirms absolute erythrocytosis, a diagnosis of high altitude associated secondary Polycythemia can be established by demonstrating elevation in serum erythropoetin levels.

Ref: Review of Medical Physiology by William ganong, 22nd edn/page  686.


Q. 8

During acclimatization to high altitude all of the following take place, EXCEPT:

 A

Increase in erythropoetin

 B

Increase in minute ventilation

 C

Increase in the sensitivity of central chemoreceptors

 D

Shift of oxygen hemoglobin dissociation curve to the left

Q. 8

During acclimatization to high altitude all of the following take place, EXCEPT:

 A

Increase in erythropoetin

 B

Increase in minute ventilation

 C

Increase in the sensitivity of central chemoreceptors

 D

Shift of oxygen hemoglobin dissociation curve to the left

Ans. D

Explanation:

Acclimatization refers to changes in the body tissues in response to long term exposure to hypoxia, such as living at high altitude for a long time. Hypoxia raises the 2, 3 BPG level in the blood. 2,3 BPG binds to beta chain of hemoglobin molecule, leading to stabilization of the deoxy form of hemoglobin, which in turn favor the unloading of oxygen from hemoglobin. This ultimately result in shift of oxygen hemoglobin dissociation curve to the right.

Ref: Variations in Human Physiology  By D. E. Evan, Page 92 ; Physiology: Prep Manual For Undergraduates 3rd Edition, By Josh Page 245-246.

Q. 9

Acclimatization to a high altitude is associated with which of the following changes?

 A

Hyperventilation

 B

Polycythemia

 C

O2 dissociation curve shifts to right

 D

Decreased concentration of systemic capillaries

Q. 9

Acclimatization to a high altitude is associated with which of the following changes?

 A

Hyperventilation

 B

Polycythemia

 C

O2 dissociation curve shifts to right

 D

Decreased concentration of systemic capillaries

Ans. C

Explanation:

Oxygen hemoglobin dissociation curve, is the curve relating percentage saturation of the oxygen carrying power of hemoglobin to the PO2. It has a characteristic sigmoid shape due to the T-R interconversion. In deoxyhemoglobin, globin units are tightly bound in a tense (T) configuration which reduces the affinity of the molecule for oxygen.

When the first oxygen is bound, the bonds holding the globin units are released, producing a relaxed (R) configuration which exposes more oxygen binding sites. Thus, binding of one oxygen molecule increases the affinity of hemoglobin to bind other O2 molecules.

Ascent to high altitude triggers a substantial rise in 2,3 DPG concentration in red blood cells.
Factors causing shift of the curve to right includes:
  • Fall in pH
  • Rise in temperature
  • Increase in 2, 3 BPG
  • pH of the blood falls as its CO2 content increases, so that when PCO2 rises the curve shifts to right.
Ref: Textbook of Medical Physiology By Guyton, 10th Edition, Page 466 ; Ganong’s Review of Medical Physiology, 23rd Edition, Page 667-9

 


Q. 10

Under physiological conditions heat acclimatization is accomplished WE.

 A

Decreased Renal Blood Flow

 B

Increased urine sodium

 C

Increased aldosterone secreti on

 D

Excessive sweating

Q. 10

Under physiological conditions heat acclimatization is accomplished WE.

 A

Decreased Renal Blood Flow

 B

Increased urine sodium

 C

Increased aldosterone secreti on

 D

Excessive sweating

Ans. B

Explanation:

B i.e. Increased urine sodium


Q. 11

Which of the following adaptations will be apt to increase the work capacity at high altitude:

 A

Increasing workload, decreasing duration of exercise

 B

Increasing workload, increasing duration of exercise

 C

Decreasing workload, increasing duration of exercise

 D

Decreasing workload, decreasing duration of exercise

Q. 11

Which of the following adaptations will be apt to increase the work capacity at high altitude:

 A

Increasing workload, decreasing duration of exercise

 B

Increasing workload, increasing duration of exercise

 C

Decreasing workload, increasing duration of exercise

 D

Decreasing workload, decreasing duration of exercise

Ans. A

Explanation:

Increasing workload, decreasing duration of exercise

At high altitudes, work capacity is increased by acclimatization, increased rate of 02 upake the body can achieve, decreased respiratory work load and decreased duration of exerciseQ.

Work load of breathing

  • It includes work done by respiratory muscles for – Stretching the elastic tissues of chest wall & lung (Elastic work, 65%) and

Moving inelastic tissues (Viscous resistance, 7%) and moving air through respiratory passage (Airway resistance, 28%) known as non elastic work (35%).

  • Work of breathing can be calculated from relaxation pressure curve (by pressure X volume = g/cm2 x cm3 = g xcm).

The elastic work required to inflate the whole respiratory system (ABCA) < the amount of elastic work required to inflate (increase volume of) lungs (ABCDEA) because part of work comes from elastic energy stored in thorax. The elastic energy (work) lost from thorax (AFGBA) is equal to gained by lungs (AEDCA)

  • The pressure volume curves that the lung follows during inflation & deflation are different. This behaviour is k/a hysteresis. The lung volume at any given pressure during deflation is larger than during inflation. Pressure volume curve of lung is nonlinear, with the lung becoming stiffer at high volumes.
  • In quiet breathing, when pressure is plotted against volume, it forms a hysteresis loop rather than a straight line because intrapuleural pressure changes lit lung volume changes during inspiration & expiration. Area AXBYA represents non elastic work done required to over come lung viscosity & airway resistance
  • Resistance to air movement is relatively small during quiet breathingQ. When air flow becomes turbulent during rapid breathing the energy required to move air is greater than when the flow is laminar. Total work of

quiet breathing is 0.3 – 0.8 kg- m /min, which rises markedly during exerciseQ, and in diseases such as emphysema, asthma, & CHF.

When over stretched, respiratory muscles contract with less strength, become fatigue & fail (d/t length- tension relationship) leading to in adequate ventilation  at sea level, but even well acclimatized low lander can almost never achieve this.

Work capacity

  • Capacity to do work (work capacity of all muscles skeletal & cardiac is greatly decreased in hypoxia & at high altitudes.
  • Work capacity is reduced in direct proportion to the decrease in maximum rate of 02 uptake that the body can achieveQ.
  • Acclimatization increases work cavacitu

Person

Work capacity

(% of normal)

Unacclimatized

50

Low lander acclimatized

for 2 months

68

Naturally acclimatized

native living at 1300 feet

but working at 1700 feet

87

  • Naturally acclimatized native person can achieve a daily work output even at high altitude almost equal to that of low lander

Q. 12

Compensating mechanisms involved in acclimatization to altitude :

 A

Hyperventilation

 B

Hypoventilation

 C

Respiratory depression

 D

Respiratory depression

Q. 12

Compensating mechanisms involved in acclimatization to altitude :

 A

Hyperventilation

 B

Hypoventilation

 C

Respiratory depression

 D

Respiratory depression

Ans. A

Explanation:

A i.e. Hyperventilation

Acclimatization to altitude occurs through respiratory alkalosis produced by the hyperventilationQ, which shifts the O2– Hb dissociation curve to left.

Ventilatory Response

– The initial ventilatory response is small as alkalosis tends to counteract effect of hypoxia. However ventilation increases over next 4days (d/t CSF PH). After 4 days, ventilatory response begins to decline slowly but it takes years of residence at higher altitudes for it to decline to the initial levels.

–    The respiratory alkalosis produced by hyper ventilation shifts O2­Hb dissociation curve to the leftQ, but a concomitant increase in RBC 2, 3, BPG tends to decrease the O2 affinity of hemoglobinQ

The net effect is a small increase in P5o. The decrease in O2 affinity makes more O2 available to tissue. However the value of increase in

P50 is limited because when the arterial PO2 is markedly reduced, the decreased O2 affinity also interferes with O2 uptake by Hb in lung.

Hyperventilation cause respiratory alkalosis d/t CO2 washout.


Q. 13

All of the following are the causes of relative polycythemia except:

 A

Dehydration.

 B

Dengue haemorrhagic fever

 C

Gaisbock syndrome

 D

High altitude.

Q. 13

All of the following are the causes of relative polycythemia except:

 A

Dehydration.

 B

Dengue haemorrhagic fever

 C

Gaisbock syndrome

 D

High altitude.

Ans. D

Explanation:

Answer is D (High altitude)

High altitude is associated with physiological increase in erythropoetin levels and leads to absolute polycythemia and not relative polycythemia.

Relative erythrocytosis due to reduction in plasma volume alone is also known as stress or spurious erythrocytosis or `Geisbock’s syndrome’


Q. 14

Correct statement regarding high altitude:

September 2006

 A

Po2 is less

 B

Pco2 is more

 C

In the air, percentage of oxygen is less

 D

Decrease in number of RBC’s

Q. 14

Correct statement regarding high altitude:

September 2006

 A

Po2 is less

 B

Pco2 is more

 C

In the air, percentage of oxygen is less

 D

Decrease in number of RBC’s

Ans. A

Explanation:

Ans. A: P02 is less

The immediate effect of decreased pressure causes decreased partial pressure of oxygen. Resulting hypoxemia, sensed by the carotid bodies, causes hyperventilation. However, hyperventilation also causes the adverse effect of respiratory alkalosis, inhibiting the respiratory center from enhancing the respiratory rate as a result of fall in Pco2.

In the short term, the human body undergoes hyperventilation, fluid loss (due to a decreased thirst drive and decrease in ADH), an increase in heart rate, and slightly lowered stroke volume. In the longer term, the body has lower lactate production (because reduced glucose breakdown decreases the amount of lactate formed), compensatory alkali loss in urine, decreased plasma volume, increased Hematocrit (polycythemia), increased RBC mass, a higher concentration of capillaries in skeletal muscle tissue, increased myoglobin, increased mitochondria, increased aerobic enzyme concentration, increase in 2, 3-BPG, hypoxic pulmonary vasoconstriction, and right ventricular hypertrophy.


Q. 15

Which of the following is seen at high altitude:

September 2011

 A

Low PaO2

 B

High PaO2

 C

Normal PaO2

 D

High PaCO2, Low PaO2

Q. 15

Which of the following is seen at high altitude:

September 2011

 A

Low PaO2

 B

High PaO2

 C

Normal PaO2

 D

High PaCO2, Low PaO2

Ans. A

Explanation:

Ans. A: Low PaO2

With increasing altitude, barometric pressure decreases, so the total pressure of the air decreases and pH2O and pCO2 remains constant So p02 and pN2 decreases progressively with height

High-altitude illness

  • Usually occurs at altitudes of over 1,500 m (4,921 ft)
  • Caused primarily by hypoxia but is compounded by cold and exposure.
  • Hypoxia is the main contributor to high-altitude illness.
  • Atmospheric pressure and the partial pressure of oxygen decrease rapidly at increasing levels above the earth’s surface
  • pCO2 and pH2O remain constant, pN2 also decreases
  • It presents as one of three forms: acute mountain sickness (AMS), high-altitude pulmonary edema (HAPE) and high-altitude cerebral edema (HACE).
  • Cardinal symptoms include dyspnea on exertion and at rest, cough, nausea, difficulty sleeping, headache and mental status changes.
  • Treatment requires descent, and gradual acclimatization provides the most effective prevention.
  • Acetazolamide is an effective preventive aid and can be used in certain conditions as treatment.

Q. 16

Ascent to high altitude may cause all of the following except:     

March 2012

 A

Cerebral edema

 B

Pulmonary edema

 C

Cerebral palsy

 D

Venous thrombosis

Q. 16

Ascent to high altitude may cause all of the following except:     

March 2012

 A

Cerebral edema

 B

Pulmonary edema

 C

Cerebral palsy

 D

Venous thrombosis

Ans. C

Explanation:

Ans: C i.e. Cerebral palsy

Complications of ascent to high altitude

  • HACE/ high altitude cerebral edema is rare, life threatening and usually preceded by AMS/ acute mountain sickness
  • HAPE/ high altitude pulmonary edema is a life threatening condition which usually occurs in the first 4 days after scent above 2500 m.
  • Venous thrombosis has been reported at altitudes over 6000 m.

Q. 17

Most severe and persistent symptom for acute mountain sickness is:     

 A

Headche

 B

Dizziness

 C

Drowsiness

 D

Cyanosis

Q. 17

Most severe and persistent symptom for acute mountain sickness is:     

 A

Headche

 B

Dizziness

 C

Drowsiness

 D

Cyanosis

Ans. A

Explanation:

Ans. A: Headche

Headaches are the primary symptom used to diagnose altitude sickness, although a headache is also a symptom of dehydration.

A headache occurring at an altitude above 2,400 metres (8000 feet = 76 kPa), combined with any one or more of the following symptoms, may indicate altitude sickness:

  • Lack of appetite, nausea, or vomiting
  • Fatigue or weakness
  • Dizziness or light-headedness
  • Insomnia
  • Pins and needles
  • Shortness of breath upon exertion


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