Abstract
Introduction: The ptcCO2 delay has been estimated to 16 sec (healty subjects) [1] and <60 sec (hypercapnic patients) [2]. We simultaneously record polysomnography (PSG) and ptcCO2 from COPD patients and needed the response time in our setup.
Material: 9 stable COPD patients (6 male) with mean FEV1 41% of pred. (SD 20).
Method: Patient in supine position wearing face mask connected to a stopcock, inlet selecting either room air or a bag with 4% CO2 in air. PtcCO2 measured by Radiometer TOSCA 500, probe on the earlobe. Arterial samples from arterial catheter analyzed by Radiometer ABL 500.
3 test-phases, each 200 sec: 1) stable phase breathing room air, 2) increasing phase after switching to 4% CO2, 3) decreasing phase after switching back to room air.
TOSCA ptcCO2 was read every 5. sec for 120 sec, then every 10. sec. Arterial samples were drawn 3 times during phase 1), every 5. sec the first 30 sec of phase 2) and 3), then every 30. sec for a total of 150 sec.
Results: First response time (Tfr) meaning time from change in alveolar pCO2 to ptcCO2 >2SD off stable phase.
Mean Tfr (SD) in increasing phase: 54 (5,6) sec.
Mean Tfr (SD) in decreasing phase: 57 (15) sec.
For arterial pCO2: 13,3 (5,6) sec and 11,7 (2,5) sec, accordingly.
Conclusion: Scoring PSG from COPD patients, the transcutane pCO2 signal should be left-shifted 2 epochs (1 minute) as a respiratory event changing alveolar pCO2 will show a first ptcCO2 response after 54-57 sec.
References:
1. Kesten S. et al Chest 1991;99:1211-15.
2. Janssens J.P. et al Chest 1998; 113:768–773.
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