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Archived Comments for: Effects of simulated altitude (normobaric hypoxia) on cardiorespiratory parameters and circulating endothelial precursors in healthy subjects

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  1. Re: Effects of normobaric hypoxia on cardiorespiratory parameters and endothelial progenitor cells in peripheral blood in healthy subjects

    E Sankaranarayanan Prakash, School of Medicine, Asian Institute of Medicine, Science & Technology, Bedong, 08100 Kedah Darul Aman, Malaysia

    14 November 2007

    Ciulla et al are complemented for their investigation of an important research question.

    From data in Table 1, it is seen that oxygen saturation of hemoglobin is as high as 86.8% (mean value) when alveolar PO2 is as low as 30 mm Hg. Typically, the oxygen saturation of Hb A is expected to be as low as 50% when the arterial PO2 is 30 mm Hg [1]. Were the PAO2 values directly estimated by sampling end tidal alveolar gas? Or were they calculated from the alveolar gas equation? Anyway PaCO2 has not been estimated.

    In Table 1 (on page 17 of the PDF version), it is mentioned that the concentration of endothelial precursor cells has increased from 0.38 +/- 0.56; [mean (SD)] to 0.65 +/-0.72 cells per microliter. The P value for this difference is noted as 0.016. From calculating a P value with just the mean and SD, for a sample size of 8, I got a P value of 0.42.

    The increase in minute ventilation in response to hypoxemia is insignificant although this may be attributable to the fall in PaCO2 and rise in pH of blood. In this context, it would have been useful to have a sample of arterial blood sampled at the end of 1 hour of normobaric hypoxia.


    [1] Ciulla MM et al. Effects of simulated altitude (normobaric hypoxia) on cardiorespiratory

    parameters and circulating endothelial precursors in healthy subjects. Respiratory Research 2007, 8:58; doi:10.1186/1465-9921-8-58

    [2] Ganong WF. Review of Medical Physiology, International Edition, 2005, Mc Graw Hill Co., figure 35-2 in p. 667.

    Competing interests


  2. Circulating endothelial precursors and the hypoxia machinery. Reply to comments

    Michele Ciulla, Istituto di Medicina Cardiovascolare, Centro Interuniversitario di Fisiologia Clinica e Ipertensione, University of Milan

    4 March 2008

    Respiratory Research

    Reply to comments December 24, 2007

    Dear Dr Prakash,

    Thank you for you interest in our paper that we believe that is the first linking in healthy subjects a simulated altitude [1] with the circulating endothelial precursors and the hypoxia machinery.Your comments give us the opportunity to clarify some aspects.

    1. In our study we measured the SpotOxygen Saturation of haemoglobin(SpO2)by using a pulseoximeter. Pulseoximetry is the most convenient non-invasive method of monitoring arterial saturation continuously. Although there are many advantages of using pulse oximetry as a tool for monitoring oxygen saturation in arterial blood, there are also potential pitfalls.The pulsatile component of the signal represents the arterial absorption and forms only a small proportion of the total, the signal is thus very susceptible to noise, for example in association to movements and during fluctuations in ambient light that can produce false pulsatile signals; also carboxyhaemoglobin causes misreadings the pulsatile oximeter to overread. Furthermore, no absolute method for calibrating pulseoximeters yet exists, and manufacturers make use of specific equations obtained by comparing wavelength measurement with arterial blood samples from volunteers [2]. Nonetheless the measurement of the peripheral oxygen saturation of haemoglobin is considered a standard, therefore the SpO2 measurements we reported are affordable. The Alveolar Oxygen Partial Pressure(PAO2) values were measured by using a gasanalyzer, estimated indirectly by using the following equation:


    where: - FiO2 is the inhaled Fraction of oxygen- BP is the barometric pressure - PaCO2 is the arterial pressure of CO2 (derived from another formula) - R is the respiratory exchange rate. As you can see 47 is the pH2O that is considered as a constant in the formula, while both the hypoxicator and the gasanalyzer dried the air out during the test, so the volunteers breathed a low pH2O air. If you consider this and correct the formula with the pH2O value of 36, you obtain the data shown in table 1. Since hypoxia was applied to all subjects in the same experimental conditions of pH2O, in the table reported in the paper we preferred to show the data as calculated by the gasanalyzer, without changing the original equation. Therefore the PAO2 values accounting for a different pH2O could be derived simply by introducing a correction factor in the original equation.

    2. The t-test is a useful tool for comparing the means of two groups; in our study we used the ANOVA test that is indicated when comparing 3 or more groups; furthermore, our samples are PAIRED, this fact means that individual values (same subjects) obtained before and after the test are compared; comparison of the means is not allowed in this model but only for UNPAIRED samples.

    3. We agree that an arterial blood sample would have been useful but this procedure was not justified in healthy volunteers (students). Finally, many thanks to BMCO penAccess model that allows all researchers to discuss on-line their results.


    1.Ciulla MM, et al.: Effects of simulated altitude (normobarichypoxia) on cardiorespiratory parameters and circulating endothelial precursors in healthy subjects. Respir Res 2007; 8:58.

    2. Hutton P, Clutton-Brock T: The benefits and pitfalls of pulse oximetry. BMJ 1993, 307:457-458.

    atmospheric air (baseline)

    gas - P(mmHg) - Dry-fraction

    O2 - 160 - 0,21

    CO2 - 0 - 0

    N2 - 588 - 0,79

    H2O - 12 - 0

    atmospheric air (hypoxia)

    gas - P(mmHg) - Dry-fraction

    O2 - 80 - 0,12

    CO2 - 0 - 0

    N2 - 672 - 0,88

    H2O - 8 - 0

    t0 alveolar air

    gas - P(mmHg)

    O2 - 100

    CO2 - 40

    N2 - 573

    H2O - 47

    Tot 760

    t0-t1 alveolar air

    gas - P(mmHg)

    O2 - 52

    CO2 - 40

    N2 - 632

    H2O - 36

    Tot 760

    Competing interests