Pulmonary ventilation and pulmonary arterial pressure both rise progressively during the first few hours of human acclimatization to hypoxia. These responses are highly variable between individuals, but the origin of this variability is unknown. Here, we sought to determine whether the variabilities between different measures of response to sustained hypoxiawere related, which would suggest a common source of variability. Eighty volunteers individually underwent an 8-h isocapnic exposure to hypoxia (end-tidal PO2=55 Torr) in a purpose-built chamber. Measurements of ventilation and pulmonary artery systolic pressure (PASP) assessed by Doppler echocardiography were made during the exposure. Before and after the exposure, measurements were made of the ventilatory sensitivities to acute isocapnic hypoxia (GpO2 ) and hyperoxic hypercapnia, the latter divided into peripheral (GpCO2 ) and central (GcCO2 ) components. Substantial acclimatization was observed in both ventilation and PASP, the latter being 40% greater in women than men. No correlation was found between the magnitudes of pulmonary ventilatory and pulmonary vascular responses. For GpO2 , GpCO2 and GcCO2 , but not the sensitivity of PASP to acute hypoxia, the magnitude of the increase during acclimatization was proportional to the pre-acclimatization value. Additionally, the change in GpO2 during acclimatization to hypoxia correlated well with most other measures of ventilatory acclimatization. Of the initial measurements prior to sustained hypoxia, only GpCO2 predicted the subsequent rise in ventilation and change in GpO2 during acclimatization. We conclude that the magnitudes of the ventilatory and pulmonary vascular responses to sustained hypoxia are predominantly determined by different factors and that the initial GpCO2 is a modest predictor of ventilatory acclimatization.
Fatemian, MHerigstad, MCroft, QFormenti, FCardenas, RWheeler, CSmith, TFriedmannova, MDorrington, KRobbins, P
Faculty of Health and Life Sciences\Department of Nursing
Year of publication: 2015Date of RADAR deposit: 2016-03-17