Reproducibility of hypercapnic ventilatory response measurements with steady-state and rebreathing methods

Abstract

In this study, the hypercapnic ventilatory response (HCVR) was measured, defined as the ventilation response to carbon dioxide tension (PCO2). We investigated which method, rebreathing or steady-state, is most suitable for measurement of the HCVR in healthy subjects, primarily based on reproducibility. Secondary outcome parameters were subject experience and duration.20 healthy adults performed a rebreathing and steady-state HCVR measurement on two separate days. Subject experience was assessed using numeric rating scales (NRS). The intraclass correlation coefficient (ICCs) of the sensitivity to carbon dioxide above the ventilatory recruitment threshold and the projected apnoea threshold were calculated to determine the reproducibility of both methods.The ICCs of sensitivity were 0.89 (rebreathing) and 0.56 (steady-state). The ICCs of the projected apnoea threshold were 0.84 (rebreathing) and 0.25 (steady-state). The steady-state measurement was preferred by 16 out of 20 subjects; the differences in NRS scores were small.The hypercapnic ventilatory response measured using the rebreathing setup provided reproducible results, while the steady-state method did not. This may be explained by high variability in end-tidal PCO2. Differences in subject experience between the methods are small.

Ventilatory response to CO2 with Read's rebreathing method in normal infants

“…The ICC of the VRCO 2 in our study was 0.79. The number of cases was smaller than that of Mannee, however the ICC was high and close to that of Mannee 12 …”

“…Mannee et al 12 performed the VRCO 2 with the steady‐state and rebreathing method multiple times in 20 normal adults and evaluated the ICC of the VRCO 2 . While the ICC of the rebreathing method was as high as 0.89, the ICC of the steady‐state method was 0.56.…”

Ventilatory response to CO2 with Read's rebreathing method in normal infants

“…In this examination, MV was measured when breathing 0%, 2%, and 4% CO 2 gas, and the VRCO 2 was evaluated by the relationship between MV and F I CO 2 rather than EtCO 2 . The VRCO 2 using F I CO 2 could be underestimated because the error tended to be larger between F I CO 2 and blood CO 2 of the respiratory center than the error between EtCO 2 and blood CO 2 , as in the study by Mannee et al 10) . In fact, the values of VRCO 2 (mL/min/mmHg/kg) in normal infants were a median of 34.6 in our study and an average of 48.7 in the study by Wingkun et al 4) compared to a low average of 10.9 in the study by Ali et al 5) This study has some limitations.…”

“…After focusing on the difference between methods, we focused on the difference in results of the same rebreathing method. The value of VRCO 2 (ΔMV/ΔEtCO 2 ) in three studies with the rebreathing method in normal adults were 1.2, 4.6, 1.7 L/min/mmHg, respectively 7,8,10) . In addition, Akiyama reported the value of VRCO 2 in 2 studies, 2.2 for 28 patients 11) and 1.9 for 17 patients 12) , respectively with the rebreathing method in normal adults.…”

“…Some studies of normal adults studied the average measuring the VRCO 2 multiple times 7), 11) . We designed to measure the VRCO 2 once in this study, because this physiologic test is difficult to perform in infants and the reproducibility of the rebreathing method is high 10) . We plan on evaluating the respiratory center of infants in more detail by performing the VRCO 2 to preterm infants, infants with apneic attacks and infants treated with caffeine, using the data of normal infants obtained from this study.…”