PubMed · 6364164
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
C S Houston. 1983. D. Bruce Dill.. https://pubmed.ncbi.nlm.nih.gov/6364164/
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
The hypobaric hypoxia of moderate altitude elicits various mechanisms of acute to subacute physiologic adaptations of the healthy lung: First of all it causes a hyperventilation, which increases the diminished arterial pO2. Because of hypoxemia-induced vasoconstriction, pulmonary arterial hypertension develops. The adrenergic stimulation of the cardiac output also increases the pulmonary perfusion. Most likely because of the diminished density of ambient air there is a measurable increase of exspiratory bronchial flow or, respectively, a diminution of the peripheral airway resistance. In higher altitudes, limitation of oxygen-diffusion under physical exertion is observed. The consequences of acute hypobaric hypoxia for diseased lungs depend on preexisting ventilation/perfusion mismatch or diffusion impairment. Arterial hypoxemia and hence also pulmonary arterial hypertension are increased. In the presence of normal chemoreceptor sensitivity (type pink puffer), a hyperventilation, which is often perceived as dyspnea by the patient, is induced. Mostly patients with chronic obstructive pulmonary disease adapt, however, surprisingly well to moderate altitude. Bronchial asthma improves frequently because allergen concentrations are low and air density is diminished. On the other hand, physical exertion in dry and cold ambient air may also elicit acute asthmatic exacerbations. The assessment of moderate altitude tolerance by patients with chronic lung diseases and prophylactic precautions before the ascent are discussed. The only altitude-specific disease of the healthy lung is the so-called high-altitude pulmonary edema. The major pathogenetic factor for its development is an inadequate or overshooting response to hypobaric hypoxia (nonuniform pulmonary arterial vasoconstriction, diminished hypoxic ventilatory drive, retention of fluid, centralization of blood volume and capillary leak). Prophylactic and therapeutic implications are discussed.
A group of rats was born in and spent the first 4 weeks of life at a simulated altitude of 3550 m. Two animals were killed immediately afterwards and the remaining 16 were allowed to recover for various times up to a maximum of 12 weeks at sea-level atmospheric pressure. On ultrastructural examination, the pulmonary arterioles of hypoxic rats showed muscularization, the new layer of mature smooth muscle cells containing abundant organelles and myofilaments. These cells were bounded by prominent elastic laminae. During the recovery period, the medial layer became progressively thinned, but the cells still retained some characteristics of smooth muscle by 12 weeks' recovery. When a similar group of ten hypoxic rats was allowed to recover for 12 weeks before being given monocrotaline, there was early enlargement of the residual smooth muscle cells in the media of pulmonary arterioles and within 5 weeks there was again a thick layer of medial smooth muscle. This was in contrast to the sparse, weakly muscularized arterioles seen in eight similarly treated rats born under normoxic conditions. The relevance is discussed of these findings to the rare occurrence of primary pulmonary hypertension in people who were born at high altitude but returned to sea-level during childhood.
UNLABELLED: STUDY RATIONALE AND OBJECTIVE: Sleep-disordered breathing is commonly treated with nasally applied continuous positive airway pressure (CPAP). Typically, pressures are titrated to pneumatically splint the airway to prevent its collapse in response to negative inspiratory pressure. This investigation was prompted by several patient complaints of sleep-related breathing difficulty associated with travel to high altitudes. CPAP devices create pressure with fan-generated airflow; therefore, CPAP performance should behave according to collective fan laws. MEASUREMENTS AND RESULTS: In the present study, we examined the effect of simulated altitude change on four commercially available CPAP machines. Machines were tested using anatomic airway mannequins in an altitude chamber. We made three simulated ascents to 12,000 feet with machines set at 5, 10, and 12 cm H2O sea level pressure equivalents. We measured pressure using water manometers at 2,000-foot increments during ascent and descent. Mask pressures varied systematically with changing altitude in three machines. One machine, equipped with a pressure regulation feature, maintained pressure within 1 mm H2O at all pressure and altitude combinations. CONCLUSIONS: Altitude significantly alters delivered pressure according to predictions made by the fan laws, unless a unit has pressure-compensating features. Clinicians should consider this factor when CPAP is prescribed for patients who live or travel to places located at significantly higher or lower elevations than the titration site.