Background-Portable peak flow meters are used in clinical practice for measurement of peak expiratory flow (PEF) at many different altitudes throughout the world. Some PEF meters are affected by gas density. This study was undertaken to establish which type of meter is best for use above sea level and to determine changes in spirometric measurements at altitude. Methods-The variable orifice mini-Wright peak flow meter was compared with the fixed orifice Micro Medical Microplus turbine microspirometer at sea level and at Everest Base Camp (5300 m). Fifty one members of the 1994 British Mount Everest Medical Expedition were studied (age range, 19-55). Results-Mean forced vital capacity (FVC) fell by 5% and PEF rose by 25*5%. However , PEF recorded with the mini-Wright peak flow meter underestimated PEF by 31%, giving readings 6-6% below sea level values. FVC was lowest in the mornings and did not improve significantly with ac-climatisation. Lower PEF values were observed on morning readings and were associated with higher acute mountain sickness scores, although the latter may reflect decreased effort in those with acute mountain sickness. There was no change in forced expiratory volume in one second (FEVy) at altitude when measured with the turbine microspirometer. Conclusions-The cause of the fall in FVC at 5300 m is unknown but may be attributed to changes in lung blood volume, interstitial lung oedema, or early airways closure. Variable orifice peak flow meters grossly underestimate PEF at altitude and fixed orifice devices are therefore preferable where accurate PEF measurements are required above sea level. Portable peak flow meters are widely used in clinical practice for measurement of peak ex-piratory flow (PEF) at many different altitudes throughout the world. At altitude the decrease in air density mechanically causes variable orifice meters, such as the mini-Wright, to underestimate flow."l An under-reading of 26% at a simulated altitude of 5455m has been demonstrated in hypobaric chamber experiments .3 However, fixed orifice spirometers such as the Micro Medical Microplus turbine spirometer have recently been evaluated in a hypobaric chamber and are unaffected by barometric pressure.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 al-titude"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. Methods After obtaining informed consent, spirometric data were collected from 51 members of the 1994 British Mount Everest Medic...

1. Both hypoxia and hypocapnia can cause broncho-constriction in humans, and this could have a bearing on performance at high altitude or contribute to altitude sickness. We studied the relationship between spirometry, arterial oxygen saturation and end-tidal carbon dioxide (ETCO2) concentration in a group of healthy lowland adults during a stay at high altitude, and then evaluated the response to supplementary oxygen and administration of a beta 2 agonist. 2. We collected spirometric data from 51 members of the 1994 British Mount Everest Medical Expedition at sea level (barometric pressure 101.2-101.6 kPa) and at Mount Everest Base Camp in Nepal (altitude 5300 m, barometric pressure 53-54.7 kPa) using a pocket turbine spirometer. A total of 205 spirometric measurements were made on the 51 subjects during the first 6 days after arrival at Base Camp. Further measurements were made before and after inhalation of oxygen (n = 47) or a beta 2 agonist (n = 39). ETCO2 tensions were measured on the same day as spirometric measurements in 30 of these subjects. 3. In the first 6 days after arrival at 5300 m, lower oxygen saturations were associated with lower forced expiratory volume in 1 s (FEV1; P < 0.02) and forced vital capacity (FVC; P < 0.01), but not with peak expiratory flow (PEF). Administration of supplementary oxygen for 5 min increased oxygen saturation from a mean of 81%-94%, but there was no significant change in FEV1 or FVC, whilst PEF fell by 2.3% [P < 0.001; 95% confidence intervals (CI) -4 to -0.7%]. After salbutamol administration, there was no significant change in PEF, FEV1 or FVC in 35 non-asthmatic subjects. Mean ETCO2 at Everest Base Camp was 26 mmHg, and a low ETCO2 was weakly associated with a larger drop in FVC at altitude compared with sea level (r = 0.38, P < 0.05). There was no correlation between either ETCO2 or oxygen saturation and changes in FEV1 or PEF compared with sea-level values. 4. In this study, in normal subjects who were acclimatized to hypobaric hypoxia at an altitude of 5300 m, we found no evidence of hypoxic broncho-constriction. Individuals did not have lower PEF when they were more hypoxic, and neither PEF nor FEV1 were increased by either supplementary oxygen or salbutamol. FVC fell at altitude, and there was a greater fall in FVC for subjects with lower oxygen saturations and probably lower ETCO2.

In our cohort, the incidence of repeat anaphylaxis after a comprehensive assessment in the drug-allergy clinic for suspected POA was 4%. Important risk factors include the completeness of referral information provided to the assessor and the role of exacerbating disorders, particularly SM.