DOI: 10.5061/dryad.d7wm37qfg
title: Skin CO<sub>2</sub> sniffing for wearable metabolic monitoring

description: CO2 is a key physiological parameter used to assess hypoventilation and to
 estimate metabolic rates. However, current CO2 monitoring relies on bulky
 breath-analysis systems that are impractical for continuous use in daily
 life. Here, we present a wearable on-skin gas-sniffing system that
 quantifies skin-emitted CO2 and establishes its physiological relevance
 through direct correlation with exhaled CO2 and metabolic rate.
 Participant studies demonstrate strong correlations between CO2 flow rates
 from the skin and breath during both rest and exercise, with skin-emitted
 CO2 approximately four orders of magnitude lower than exhaled CO2.
 Skin-emitted CO2 also correlates with metabolic rate, suggesting its
 potential as a surrogate for breath-based indirect calorimetry. With its
 wearable form factor and physiological relevance, this skin gas sniffing
 system enables continuous, non-invasive metabolic monitoring and opens new
 opportunities for studying skin gas exchange.
description: # Skin CO~2~ sniffing for wearable metabolic monitoring Dataset DOI:
 [10.5061/dryad.d7wm37qfg](https://doi.org/10.5061/dryad.d7wm37qfg) ##
 Description of the data and file structure This repository contains raw
 data supporting the figures in the manuscript “Skin CO2 sniffing for
 wearable metabolic monitoring”. Data are organized by figure number
 corresponding to the main figures in the manuscript (Fig. 2–5). Each
 figure folder contains raw data used to generate the corresponding
 results. Additional supporting raw data are provided in the “Supporting
 information” folder. ### Files and variables #### File: Fig._2.zip
 **Description** Raw data used to generate Fig. 2, showing representative
 Skin CO2 time-series measured during stationary cycling using the wearable
 Skin CO2 sniffer. **Subfolder(s)** * D/: Raw time-series data recorded
 during stationary cycling at different power outputs (75 W, 100 W, 125 W,
 150 W), used for Fig. 2D. **File naming convention**
 YYYY-MM-DD-hh-mm-ss-C-00-VP-UNIX S4 W.csv, where
 W indicates the cycling power condition. **Variables** *
 Timestamp [s]: Unix timestamp in seconds. * Temperature x0.1 [oC]:
 Temperature recorded by the logging application. Actual temperature in oC
 is obtained by multiplying the stored values by 10. * Relative humidity
 x0.1 [%]: Relative humidity recorded by the logging application. Actual
 relative humidity in % is obtained by multiplying the stored values by 10.
 * Concentration x0.001 [ppm]: Raw Skin CO2 concentration. Actual CO2
 concentration in ppm is obtained by multiplying the stored values by 1000.
 #### File: Fig._3.zip **Description** Raw data used to generate Fig. 3,
 characterizing Skin CO2 accumulation and calibration using FEM simulations
 and chamber measurements. **Subfolder(s)** * A/: Cross-sectional images
 generated from FEM simulations (Fig. 3A). * B/: Raw experimental data and
 FEM-derived results comparing Skin CO2 transients between sealed and
 semi-open housing configurations (Fig. 3B). * C/: FEM-derived flux sweep
 data used to establish the relationship between imposed Skin CO2 flux and
 steady-state ΔSkin CO2 (Fig. 3C). **File naming convention** File names
 indicate the measurement date, housing configuration (sealed or
 semi-open), and experimental condition. Text files contain FEM-derived
 results corresponding to the indicated Skin CO2 flux condition.
 **Variables** CSV files: * Timestamp [s] * Temperature x0.1 [oC] *
 Relative humidity x0.1 [%] * Concentration x0.001 [ppm] TXT files (time
 response): * Time (min) * Skin CO2 (mol) * ΔSkin CO2 (mol/m3) * ΔSkin CO2
 (ppm) TXT file (flux sweep): * J_input: Imposed Skin CO2 flux. * ΔSkin CO2
 amount [mol] * ΔSkin CO2 [mol/m3] * ΔSkin CO2 [ppm] #### File: Fig._4.zip
 **Description** Raw data used to generate Fig. 4, comparing wearable Skin
 CO2 measurements with physiological measurements obtained from a metabolic
 cart during rest and constant-power exercise. **Subfolder(s)** * B/: Raw
 time-series data, including wearable Skin CO2 measurements, heart rate,
 and metabolic cart outputs used for Fig. 4B. **File naming convention**
 Wearable sensor files include the measurement date and sensor identifier.
 Metabolic cart files are named according to the participant identifier and
 recording time. **Variables** Heart rate file: * Time: Time of measurement
 (hh:mm:ss). * Heart Rate: Heart rate in beats per minute (bpm). Wearable
 Skin CO2 files: * Timestamp [s] * Temperature x0.1 [oC] * Relative
 humidity x0.1 [%] * Concentration x0.001 [ppm] Metabolic cart files
 contain multiple respiratory and metabolic parameters. Variables used in
 this study: * VO2: Oxygen consumption rate. * VCO2: Carbon dioxide
 production rate. * WorkR: External work rate during cycling. Other columns
 originate from the standard metabolic cart output and were not used in the
 analysis. #### File: Fig._5.zip **Description** Raw data used to generate
 Fig. 5, demonstrating quantitative correlations between Skin CO2 emission
 and whole-body metabolic parameters across participants. **Subfolder(s)**
 * B/: Raw time-series data used to correlate Skin CO2 with Breath CO2. *
 C/: Raw time-series data used to correlate Skin CO2 with metabolic rate.
 **File naming convention** Wearable sensor files include the participant
 and session identifiers. Metabolic cart files are named according to the
 participant identifier and recording time. **Variables** Wearable Skin CO2
 files (both subfolders): * Timestamp [s] * Temperature x0.1 [oC] *
 Relative humidity x0.1 [%] * Concentration x0.001 [ppm] Metabolic cart
 files, Subfolder B: * VCO2: Carbon dioxide production rate (L min-1).
 Metabolic cart files, Subfolder C: * VO2: Oxygen consumption rate (L
 min-1). * VCO2: Carbon dioxide production rate (L min-1). #### File:
 Supporting_information.zip **Description** Raw data used to generate Fig.
 S1, evaluating the effects of environmental temperature and humidity on
 Skin CO2 measurements. **File naming convention** File names indicate the
 measurement date and environmental condition. **Variables** * Skin CO2
 concentration (ppm) * Temperature (oC) * Relative humidity (%) ##
 Code/software Not applicable