Ventilatory capacity during prolonged exposure to simulated altitude without hypoxia

Abstract

Studies have been conducted in a sealed environment altitude chamber to study the chronic effect of reduced barometric pressure without reduced oxygen tension on human respiratory function and other physiological processes. Experiments were conducted at ground level, at 18,000 ft equivalent altitude (pO2 150 mm Hg), at 27,000 ft equivalent altitude (pO2 243 mm Hg), and at 33,500 ft equivalent altitude (pO2 174 mm Hg). Results were as follows: 1) Tests of pulmonary functions which are dependent on high volume flow rates are increased at altitude. These tests include maximum breathing capacity (increased 37% at 33,500 ft) and per cent of forced vital capacity during the first second of effort. 2) Expiratory minute volume was unchanged at altitude when oxygen partial pressure was maintained. 3) Forced vital capacity was reduced 3.1% at 18,000 ft, 2.9% at 27,000 ft, and 7.6% at 33,500 ft. This result was not due to hypoxia or abdominal distention and confirms the earlier findings of Rahn and Hammond. The cause of this change remains obscure but may be related to decreased lung volume. 4) The magnitude of changes observed appears to be somewhat proportional to altitude. Evidence is presented to relate increases in the flow-dependent tests to reduced density and reduced turbulent flow in the respiratory passages. respiratory physiology; sealed environment; spacecraft; atmosphere selection; space medicine Submitted on October 22, 1963

Effect of altitude on spirometric parameters and the performance of peak flow meters.

“…4 In the same way that decreased air density causes variable orifice meters to under-read, by decreasing resistance to respiratory gas flow5 it causes true PEF to rise at altitude.36 Forced vital capacity (FVC) falls with ascent to altitude"9 and a decrease of 3% at 5500 m simulated altitude has been recorded. 6 We compared the mini-Wright peak flow meter with the a hand held turbine spirometer to assess the performance of the two meters in a field study at altitude. FVC, PEF, and forced expiratory volume in one second (FEV1) were documented using a turbine spirometer, and PEF using the mini-Wright peak flow meter, in a large study of members of the 1994 British Mount Everest Medical Expedition.…”

Cambios espirométricos y en la saturación arterial de oxígeno durante la ascensión a una montaña de más de 3.000 metros

“…Algunos de ellos aprecian un retorno a la normalidad 1,9,11 o bien una tendencia a mejorar que no alcanza significación 3 . Otros no detectan esta normalización de la FVC con la aclimatación y sólo observan la recuperación de los volúmenes pulmonares al descender 2,8,13 o al cabo de dos 3 o siete 6 días tras el descenso. En el presente estudio hallamos que en el primer día de permanencia en las proximidades de la cumbre se produjo una notable recuperación de los flujos y volúmenes pulmonares, y que la leve limitación que aún persistía al tercer día desapareció completamente con el descenso.…”

Blutgaswerte und Atemwegswiderstand bei Gesunden und Patienten mit obstruktiven Atemwegserkrankungen vor und nach Höhenadaptation

“…Die Ursache der von Bu r c k h a r d t [7] bereits 1932 beschriebenen plötzlichen Besserung bei Eintreffen in mittleren Höhen ist nicht sicher bekannt; bisher wurden folgende Gründe angeführt: 1. Verringerung des Atemwiderstandes durch verminderte Luftdichte [8,14,30,40,45]; 2. Lufttrockenheit [34,35]; 3.…”