Lecture 34: High Altitude Flashcards
Atmospheric pressure progressively ____ as altitude increases
declines
At ______ feet above sea level, the atmospheric pressure is only 380 mmHg, which is ___ its normal sea level value
18,000
halfway
Since the proportion of O2 and N2 in the air remains the same, the PO2 of inspired air at 18,000 ft altitude is ___% of ____ mm Hg, or ____ mm Hg with anatomic dead space taken into account
21%
380
80
At any altitude above 10,000 ft, the arterial PO2 falls into
the steep portion of the O2 Hb dissociation curve below the safety range of the plateau region
As a result, percentage Hb saturation of arterial blood declines with further increases in altitude
Ascent to high altitude causes….
thus….
- hypoxic hypoxia (reduced arterial PO2)
- Adjustments must be made to live at high altitudes where the atmos pressure is drastically reduced
Acclimation
process of adapting to high altitudes
Most common response to high altitude
hyperventilation
In high altitude, the PO2 becomes less than 60 mm Hg, which leads to
stimulation of peripheral chemoreceptors, which leads to stimulation of medullary respiratory center, which leads to an increase in the breathing rate
Polycythemia
- Adaptive response to high altitude
- Increase in rbc concentration/Hb concentration
- Increase in O2 carrying capacity
- Increase in total O2 content of blood, despite decreased arterial PO2
Consequences of polycythemia
An increase in [rbc] leads to an increase in blood viscosity, which leads to an increase in resistance to blood flow, which leads to hypertrophy
Hypertrophy
Hypoxemia -> an increase in synthesis of erythropoietin which acts on bone marrow to stimulate rbc production
Pulmonary vasoconstriction
- Adaptive response to high altitude
- As pulmonary vascular resistance increase, pulmonary arterial pressure must also increase to keep blood flow constant
- Right ventricle must pump against higher pulmonary pressure
- Hypertrophy may result as a response to the increased afterload
Consequence of pulmonary vasoconstriction
-Right sided heart failure
Brisket disease
Right sided heart failure due to pulmonary vasoconstriction in cattle
Fluid accumulates in the brisket
Increase production of 2,3 DPG due to adaptation to high altitude
- Shift to the right of O2-Hb curve
- Increase in P50
Consequence of increased 2,3-DPG due to altitude
Decreased affinity of Hb for O2 in tissues, leading to increased unloading of O2 in tissues
Three increases caused by an adaptive response to high altitude
- Capillary density in tissues - improves gas exchange in blood/tissues
- Mitochondrial density - enables cells to use O2 more efficiently in ATP synthesis
- Muscles myoglobin content - myoglobin stores O2 in the muscle, increases the rate of O2 transfer from blood into muscle fibers
4 causes of hypoxia
- Hypoxemia - Decrease in arterial PO2
- Pulmonary disease
- Inadequate O2 transport to tissues by blood
- Inadequate tissue capability of using O2
Hypoxemia may be due to
O2 deficiency in the atmosphere
Three examples of pulmonary diseases
- Chronic bronchitis - increased airway resistance
- Pulmonary fibrosis - decreased pulmonary compliance
- Pulmonary edema - diminished respiratory membrane diffusion
5 examples of inadequate O2 transport to tissues by blood
- Anemia - not severe at rest. Patients may have difficulty during exercise because limited ability to increase O2 delivery to active tissue
- CO poisoning
- General circulatory deficiency - decrease in cardiac output which decreases blood flow to tissues
- Localized circulatory deficiency (Ischemia) - obstruction of blood flow to tissues
- Tissue edema - reduces gas transfer between the blood and tissues
Inadequate tissue capability of using oxygen
Poisoning of cellular oxidative enzymes
Example of inadequate tissue capability of using oxygen
Cyanide poisoning interferes with O2 utilization of tissues.
One cause of hypoxia that does not involve decreased blood flow or decreased O2 content of the blood
