DOI: 10.5061/dryad.d7wm37q86
title: Changes in ventilatory responses at high altitude measured using rebreathing

description: Ventilatory responses to hypoxia and hypercapnia play a vital role in
 maintaining gas exchange homeostasis, and in adaptation to high-altitude
 environments. This study investigates the mechanisms underlying
 sensitization of hypoxic and hypercapnic ventilatory responses (HVR and
 HCVR, respectively) in individuals acclimatized to moderate high altitude
 (3800 m). Thirty-one participants underwent chemoreflex testing using the
 Duffin modified rebreathing technique. Measures were taken at sea level
 and after 2 days of acclimatization to high altitude. Ventilatory
 recruitment thresholds (VRT), HCVR-Hyperoxia, HCVR-Hypoxia, and HVR were
 quantified. Acclimatization to high altitude resulted in increased HVR
 (p&lt;0.001) and HCVR-Hyperoxia (p&lt;0.001), as expected. We also
 observed that the decrease in VRT under hypoxic test conditions
 significantly contributed to the elevated HVR at high altitude since the
 change in VRT across hyperoxic and hypoxic test conditions was greater at
 high altitude compared to baseline sea level tests (p=0.043). Pre-VRT, or
 basal, ventilation also increased at high altitude (p&lt;0.001), but
 the change did not differ between oxygen conditions. Taken together, this
 data suggests that the increase in HVR at high altitude is at least
 partially driven by a larger decrease in the VRT in hypoxia versus
 hyperoxia at high altitude compared to sea level. This study highlights
 the intricacies of respiratory adaptations during acclimatization to
 moderate high altitude, shedding light on the roles of the VRT, baseline
 respiratory drive, and two-slope HCVR in this process. These findings
 contribute to our understanding of how the human respiratory control
 responds to hypoxic and hypercapnic challenges at high altitude.
description: Chemoreflex measures were collected using the Duffin modified
 rebreathing technique at sea level and after 2 days of acclimtization to
 3800 m elevation.
description: # High Altitude Chemoreflex Data
 [https://doi.org/10.5061/dryad.d7wm37q86](https://doi.org/10.5061/dryad.d7wm37q86) This dataset includes supplemental figures and chemoreflex data. Chemoreflex data was collected using the Duffin modified rebreathing technique[1] in participants at sea level and after 2 days of acclimatization to 3800 m elevation. Complete methods detail is provided in the corresponding article. ## Description of the data and file structure This is a csv file including all physiological and chemoreflex data collected in 35 participants. Chemoreflex tests were repeated in 18 participants at high altitude so some data points are paired by subject number within years at high altitude. Ventilatory volume data is raw and not BTPS corrected in this dataset as it was corrected downstream in our data analysis. ##### Variable descriptions: * **year:** The year in which the data was collected. * **subject:** Subject identification number. * **condition:** The oxygen condition under which the data were collected. Each test was run twice: once in a hyperoxic treatment (inspired PO2 = 30% sea-level equivalent (228 mmHg)) and once in a hypoxic treatment (end-tidal PO2 = 50 mmHg). * **Location:** The location at which the tests were performed.          * **SpO2_rest:** Pulse oxygen saturation (SpO2, unit: %) during the first 5 minutes of the test during normal quiet resting breathing. * **TV_rest:** Tidal volume (TV, unit: L) during the first 5 minutes of the test during normal quiet resting breathing. * **f_rest:** Breathing frequency (f, unit: bpm) during the first 5 minutes of the test during normal quiet resting breathing. * **ve_rest:** Minute ventilation (VE, unit: L/min) during the first 5 minutes of the test during normal quiet resting breathing. * **ETPCO2_rest:** End-tidal PCO2 (ETPCO2, unit: mmHg) during the first 5 minutes of the test during normal quiet resting breathing. * **HR_rest:** Heart rate (HR, unit: bpm) during the first 5 minutes of the test during normal quiet resting breathing. * **VRT:** The ventilatory recruitment threshold (VRT, unit: mmHg CO2) * **HCVR:** The hypercapnic ventilatory response (HCVR, unit: L/min/mmHg CO2). * **HVR45:** The hypoxic ventilatory response (HVR, unit: L/min/SpO2) calculated at an end-tidal PCO2 of 45 mmHg. * **HVR50:** The hypoxic ventilatory response (HVR, unit: L/min/SpO2) calculated at an end-tidal PCO2 of 50 mmHg. * **HVRvrt3:** The hypoxic ventilatory response (HVR, unit: L/min/SpO2) calculated at an end-tidal PCO2 of 3 mmHg above the VRT. Missing data is indicated by NA. VRT values are missing for participants in which a clear VRT was not observed in the raw data trace. This can occur when the VRT is below the starting end-tidal PCO2 level. The HVR is calculated at three end-tidal PCO2 levels (45 mmHg, 50 mmHg, and 3 mmHg above the VRT). In the event that high quality ventilation or SpO2 data were not available at one of these PCO2 levels, an HVR could not be calculated. This could occur due to either high ventilatory sensitivity causing early termination of the test when ventilation reached 100 mmHg, a participant ending the test early, or poor quality flow signal. ## **References:** \[1] Duffin J. Measuring the ventilatory response to hypoxia. J Physiol. 2007 Oct 1;584(Pt 1):285-93. doi: 10.1113/jphysiol.2007.138883. Epub 2007 Aug 23. PMID: 17717019; PMCID: PMC2277066.