CO2 rebreathing model in COPD: Blood-to-gas equilibration

Jack A. Loeppky; Milton V. Icenogle; Arvind Caprihan; Marcos F. Vidal Melo; Stephen A. Altobelli

doi:10.1007/s00421-006-0288-4

CO₂ rebreathing model in COPD: Blood-to-gas equilibration

Jack A. Loeppky, Milton V. Icenogle, Arvind Caprihan, Marcos F. Vidal Melo, Stephen A. Altobelli

Research output: Contribution to journal › Article › peer-review

6 Scopus citations

Abstract

Rebreathing in a closed system can be used to estimate mixed venous P_CO2 (Pv̄_CO2 and cardiac output, but these estimates are affected by V̇_A/Q̇ heterogeneity. The purpose of this study was to validate a mathematical model of CO₂ exchange during CO₂ rebreathing in 29 patients with chronic obstructive pulmonary disease (COPD), with baseline arterial P_CO2 (Pa_CO2ranging from 28 to 60 mmHg. Rebreathing increased end-tidal P_CO2 (PET_CO2by 20 mmHg over 2.2 min. This model employed baseline values for inspired (bag) P_CO2 estimated (Pv̄_CO2, distribution of ventilation and blood flow in one high V̇_A/Q̇ and one low V̇_A/Q̇ compartment, the ventilation increase and conservation of mass equations to simulate time courses of PI_CO2, PET_CO2, Pv̄_CO2 and Pa_CO2. Measured PI_CO2 and PET_CO2during rebreathing differed by an average (SEM) of 1.4 (0.4) mmHg from simulated values. By end of rebreathing, predicted Pv̄_CO2 was lower than measured and predicted Pa_CO2indicating gas to blood CO₂ flux. Estimates of the ventilatory response to CO₂, quantified as the slope (S) of the ventilation increase versus PET_CO2, were inversely related to gas-to-blood P_CO2 disequilibria due to V̇_A/Q̇ heterogeneity and buffer capacity (BC), but not airflow limitation. S may be corrected for these artifacts to restore S as a more valid noninvasive index of central CO₂ responsiveness. We conclude that a rebreathing model incorporating baseline V̇_A/Q̇ heterogeneity and BC can simulate gas and blood P_CO2 in patients with COPD, where V̇_A/Q̇ variations are large and variable.

Original language	English (US)
Pages (from-to)	450-460
Number of pages	11
Journal	European Journal of Applied Physiology
Volume	98
Issue number	5
DOIs	https://doi.org/10.1007/s00421-006-0288-4
State	Published - Nov 2006
Externally published	Yes

Keywords

Body CO stores
Buffering capacity
Gas exchange
Ventilation/perfusion heterogeneity
Ventilatory response to CO

ASJC Scopus subject areas

Orthopedics and Sports Medicine
Public Health, Environmental and Occupational Health
Physiology (medical)

Access to Document

10.1007/s00421-006-0288-4

Cite this

@article{87fc6867a89d4ac3b6dd5cb42824ebdf,

title = "CO2 rebreathing model in COPD: Blood-to-gas equilibration",

abstract = "Rebreathing in a closed system can be used to estimate mixed venous PCO2 (P{\=v}CO2 and cardiac output, but these estimates are affected by {\.V}A/{\.Q} heterogeneity. The purpose of this study was to validate a mathematical model of CO2 exchange during CO2 rebreathing in 29 patients with chronic obstructive pulmonary disease (COPD), with baseline arterial PCO2 (PaCO2ranging from 28 to 60 mmHg. Rebreathing increased end-tidal PCO2 (PETCO2by 20 mmHg over 2.2 min. This model employed baseline values for inspired (bag) PCO2 estimated (P{\=v}CO2, distribution of ventilation and blood flow in one high {\.V}A/{\.Q} and one low {\.V}A/{\.Q} compartment, the ventilation increase and conservation of mass equations to simulate time courses of PICO2, PETCO2, P{\=v}CO2 and PaCO2. Measured PICO2 and PETCO2during rebreathing differed by an average (SEM) of 1.4 (0.4) mmHg from simulated values. By end of rebreathing, predicted P{\=v}CO2 was lower than measured and predicted PaCO2indicating gas to blood CO2 flux. Estimates of the ventilatory response to CO2, quantified as the slope (S) of the ventilation increase versus PETCO2, were inversely related to gas-to-blood PCO2 disequilibria due to {\.V}A/{\.Q} heterogeneity and buffer capacity (BC), but not airflow limitation. S may be corrected for these artifacts to restore S as a more valid noninvasive index of central CO2 responsiveness. We conclude that a rebreathing model incorporating baseline {\.V}A/{\.Q} heterogeneity and BC can simulate gas and blood PCO2 in patients with COPD, where {\.V}A/{\.Q} variations are large and variable.",

keywords = "Body CO stores, Buffering capacity, Gas exchange, Ventilation/perfusion heterogeneity, Ventilatory response to CO",

author = "Loeppky, {Jack A.} and Icenogle, {Milton V.} and Arvind Caprihan and {Vidal Melo}, {Marcos F.} and Altobelli, {Stephen A.}",

year = "2006",

month = nov,

doi = "10.1007/s00421-006-0288-4",

language = "English (US)",

volume = "98",

pages = "450--460",

journal = "European Journal of Applied Physiology",

issn = "1439-6319",

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TY - JOUR

T1 - CO2 rebreathing model in COPD

T2 - Blood-to-gas equilibration

AU - Loeppky, Jack A.

AU - Icenogle, Milton V.

AU - Caprihan, Arvind

AU - Vidal Melo, Marcos F.

AU - Altobelli, Stephen A.

PY - 2006/11

Y1 - 2006/11

N2 - Rebreathing in a closed system can be used to estimate mixed venous PCO2 (Pv̄CO2 and cardiac output, but these estimates are affected by V̇A/Q̇ heterogeneity. The purpose of this study was to validate a mathematical model of CO2 exchange during CO2 rebreathing in 29 patients with chronic obstructive pulmonary disease (COPD), with baseline arterial PCO2 (PaCO2ranging from 28 to 60 mmHg. Rebreathing increased end-tidal PCO2 (PETCO2by 20 mmHg over 2.2 min. This model employed baseline values for inspired (bag) PCO2 estimated (Pv̄CO2, distribution of ventilation and blood flow in one high V̇A/Q̇ and one low V̇A/Q̇ compartment, the ventilation increase and conservation of mass equations to simulate time courses of PICO2, PETCO2, Pv̄CO2 and PaCO2. Measured PICO2 and PETCO2during rebreathing differed by an average (SEM) of 1.4 (0.4) mmHg from simulated values. By end of rebreathing, predicted Pv̄CO2 was lower than measured and predicted PaCO2indicating gas to blood CO2 flux. Estimates of the ventilatory response to CO2, quantified as the slope (S) of the ventilation increase versus PETCO2, were inversely related to gas-to-blood PCO2 disequilibria due to V̇A/Q̇ heterogeneity and buffer capacity (BC), but not airflow limitation. S may be corrected for these artifacts to restore S as a more valid noninvasive index of central CO2 responsiveness. We conclude that a rebreathing model incorporating baseline V̇A/Q̇ heterogeneity and BC can simulate gas and blood PCO2 in patients with COPD, where V̇A/Q̇ variations are large and variable.

AB - Rebreathing in a closed system can be used to estimate mixed venous PCO2 (Pv̄CO2 and cardiac output, but these estimates are affected by V̇A/Q̇ heterogeneity. The purpose of this study was to validate a mathematical model of CO2 exchange during CO2 rebreathing in 29 patients with chronic obstructive pulmonary disease (COPD), with baseline arterial PCO2 (PaCO2ranging from 28 to 60 mmHg. Rebreathing increased end-tidal PCO2 (PETCO2by 20 mmHg over 2.2 min. This model employed baseline values for inspired (bag) PCO2 estimated (Pv̄CO2, distribution of ventilation and blood flow in one high V̇A/Q̇ and one low V̇A/Q̇ compartment, the ventilation increase and conservation of mass equations to simulate time courses of PICO2, PETCO2, Pv̄CO2 and PaCO2. Measured PICO2 and PETCO2during rebreathing differed by an average (SEM) of 1.4 (0.4) mmHg from simulated values. By end of rebreathing, predicted Pv̄CO2 was lower than measured and predicted PaCO2indicating gas to blood CO2 flux. Estimates of the ventilatory response to CO2, quantified as the slope (S) of the ventilation increase versus PETCO2, were inversely related to gas-to-blood PCO2 disequilibria due to V̇A/Q̇ heterogeneity and buffer capacity (BC), but not airflow limitation. S may be corrected for these artifacts to restore S as a more valid noninvasive index of central CO2 responsiveness. We conclude that a rebreathing model incorporating baseline V̇A/Q̇ heterogeneity and BC can simulate gas and blood PCO2 in patients with COPD, where V̇A/Q̇ variations are large and variable.

KW - Body CO stores

KW - Buffering capacity

KW - Gas exchange

KW - Ventilation/perfusion heterogeneity

KW - Ventilatory response to CO

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