Key result
End-tidal CO2 measurements were highly correlated with the partial pressure of arterial CO2, blood pH, and arterial O2 in conscious rats.
Microcapnometry provides a sensitive and reliable noninvasive method for monitoring changes in arterial CO2 tension in conscious rats.
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May refine respiratory monitoring in conscious rodent models; leaves open human clinical validation.
Characterizing disorders in the control of pulmonary ventilation requires measuring changes in both ventilatory parameters and the partial pressure of arterial CO2. Although the conscious rat has been used as a model for evaluating the effects of drugs, environmental agents, and disease on the control of pulmonary ventilation, obtaining samples of arterial blood for CO2 analysis by needle puncture or arterial catheterization during ventilatory measurements is not practical in the conscious rat and has limited the use of this model. The objective of this study was to develop a noninvasive method for monitoring arterial CO2 tension in conscious rats during ventilatory measurements using end-tidal CO2 measurements. Progressive increases in end-tidal CO2 (125–400% of baseline) caused by progressive decreases in pulmonary ventilation (75–25% of baseline) following intravenous doses of the opioid analgesic morphine were measured in conscious rats using this noninvasive method. Changes in end-tidal CO2 were compared with changes in arterial blood gases and pH. Increases in end-tidal CO2 (expressed as partial pressures) were linearly related to increases in the partial pressure of arterial CO2 (y = 0.1 × + 14.6) and decreases in arterial blood pH (y = -0.006x + 7.5) and the partial pressure of arterial O2 (y = –-0.9x + 116.3). These relationships were highly correlated with correlation coefficient (r) values of +0.94, –-0.93, and -0.90 for arterial CO2, blood pH, and O2, respectively. The results of this study demonstrated that measuring end-tidal CO2 is a sensitive and reliable method for noninvasively monitoring changes in the partial pressure of arterial CO2 in conscious rats and, together with ventilatory measurements, offers a model system for characterizing the effects of drugs, environmental agents, or disease on the control of breathing.
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Murphy et al. (1994) studied Conscious rats (animal model). End-tidal CO2 measurement (microcapnometry) vs. Arterial blood gases and pH was evaluated on Correlation between end-tidal CO2 and partial pressure of arterial CO2 (r = +0.94). End-tidal CO2 measurements were highly correlated with the partial pressure of arterial CO2, blood pH, and arterial O2 in conscious rats.
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