Transcutaneous PCO(2) -based dead space ventilation at submaximal exercise accurately discriminates healthy controls from patients with chronic obstructive pulmonary disease.

Increased physiological dead space ventilation (VD /VT ) at exercise reflects pulmonary gas exchange impairment and is a sensitive marker of cardio-respiratory disease. VD /VT is typically not measured during routine cardiopulmonary exercise testing (CPET) because its calculation requires arterial blood gas analysis for determination of PaCO2 . Instead, dead space ventilation is indirectly evaluated as a determinant of the ventilation (VE)/VCO2 relationship, which also depends on the PaCO2 set point. We hypothesized that VD /VT calculations based on non-invasive transcutaneous PCO2 (PtcCO2 ) measurement had better diagnostic characteristics than the VE/VCO2 slope for the discrimination of healthy subjects from patients with COPD, a common disease associated with impaired pulmonary gas exchange. Retrospective study of 19 healthy controls and 24 COPD patients who underwent CPET with continuous PtcCO2 monitoring. Areas under receiver operating characteristics curves (AUC) were calculated to assess diagnostic accuracy of CPET measurement for the discrimination of COPD and Controls. The AUC for PtcCO2 -based VD /VT at VT1 (0.977) was significantly higher than for the VE/VCO2 slope (0.660), SpO2 at peak exercise (0.913), decrease in inspiratory capacity (0.719), and ventilatory reserve (0.708). At a threshold of 0.24, the sensitivity and specificity of PtcCO2 -based VD /VT for the discrimination of COPD patients and healthy Controls were 100% and 84%, respectively. All Control subjects had PtcCO2 -based VD /VT  ≤ 0.25. PtcCO2 -based VD /VT was the most accurate measurement to discriminate healthy controls from subjects with COPD, a chronic lung disease associated with altered pulmonary gas exchange. Non-invasive monitoring of PtcCO2 may be useful for routine CPET.

Leprat T ，Ivanes F ，Bernard A ，Marchand-Adam S ，Plantier L ... -  《-》

Physiological dead space and arterial carbon dioxide contributions to exercise ventilatory inefficiency in patients with reduced or preserved ejection fraction heart failure.

Patients with heart failure (HF) with reduced (HFrEF) or preserved (HFpEF) ejection fraction demonstrate an increased ventilatory equivalent for carbon dioxide (V̇E /V̇CO2 ) slope. The physiological correlates of the V̇E /V̇CO2 slope remain unclear in the two HF phenotypes. We hypothesized that changes in the physiological dead space to tidal volume ratio (VD /VT ) and arterial CO2 tension (PaCO2 ) differentially contribute to the V̇E /V̇CO2 slope in HFrEF vs. HFpEF. Adults with HFrEF (n = 32) and HFpEF (n = 27) [mean ± standard deviation (SD) left ventricular ejection fraction: 22 ± 7% and 61 ± 9%, respectively; mean ± SD body mass index: 28 ± 4 kg/m2 and 33 ± 6 kg/m2 , respectively; P < 0.01] performed cardiopulmonary exercise testing with breath-by-breath ventilation and gas exchange measurements. PaCO2 was measured via radial arterial catheterization. We calculated the V̇E /V̇CO2 slope via linear regression, and VD /VT  = 1 - [(863 × V̇CO2 )/(V̇E  × PaCO2 )]. Resting VD /VT (0.48 ± 0.08 vs. 0.41 ± 0.11; P = 0.04), but not PaCO2 (38 ± 5 mmHg vs. 40 ± 3 mmHg; P = 0.21) differed between HFrEF and HFpEF. Peak exercise VD /VT (0.39 ± 0.08 vs. 0.32 ± 0.12; P = 0.02) and PaCO2 (33 ± 6 mmHg vs. 38 ± 4 mmHg; P < 0.01) differed between HFrEF and HFpEF. The V̇E /V̇CO2 slope was higher in HFrEF compared with HFpEF (44 ± 11 vs. 35 ± 8; P < 0.01). Variance associated with the V̇E /V̇CO2 slope in HFrEF and HFpEF was explained by peak exercise VD /VT (R2  = 0.30 and R2  = 0.50, respectively) and PaCO2 (R2  = 0.64 and R2  = 0.28, respectively), but the relative contributions of each differed (all P < 0.01). Relationships between the V̇E /V̇CO2 slope and both VD /VT and PaCO2 are robust, but differ between HFpEF and HFrEF. Increasing V̇E /V̇CO2 slope appears to be strongly explained by mechanisms influential in regulating PaCO2 in HFrEF, which contrasts with the strong role of increased VD /VT in HFpEF.

Van Iterson EH ，Johnson BD ，Borlaug BA ，Olson TP ... -  《-》

Transcutaneous PCO(2) for Exercise Gas Exchange Efficiency in Chronic Obstructive Pulmonary Disease.

Cao M ，Stringer WW ，Corey S ，Orogian A ，Cao R ，Calmelat R ，Lin F ，Casaburi R ，Rossiter HB ，Porszasz J ... -  《-》

Use of 'ideal' alveolar air equations and corrected end-tidal PCO(2) to estimate arterial PCO(2) and physiological dead space during exercise in patients with heart failure.

Arterial CO2 tension (PaCO2) and physiological dead space (VD) are not routinely measured during clinical cardiopulmonary exercise testing (CPET). Abnormal changes in PaCO2 accompanied by increased VD directly contribute to impaired exercise ventilatory function in heart failure (HF). Because arterial catheterization is not standard practice during CPET, this study tested the construct validity of PaCO2 and VD prediction models using 'ideal' alveolar air equations and basic ventilation and gas-exchangegas exchange measurements during CPET in HF. Forty-seven NYHA class II/III HF (LVEF=21±7%; age=55±9years; male=89%; BMI=28±5kg/m2) performed step-wise cycle ergometry CPET to volitional fatigue. Breath-by-breath ventilation and gas exchange were measured continuously. Steady-state PaCO2 was measured at rest and peak exercise via radial arterial catheterization. Criterion VD was calculated via 'ideal' alveolar equations, whereas PaCO2 or VD models were based on end-tidal CO2 tension (PETCO2), tidal volume (VT), and/or weight. Criterion measurements of PaCO2 (38±5 vs. 33±5mmHg, P<0.01) and VD (0.26±0.07 vs. 0.41±0.15L, P<0.01) differed at rest vs. peak exercise, respectively. The equation, 5.5+0.90×PETCO2-0.0021×VT, was the strongest predictor of PaCO2 at rest and peak exercise (bias±95%LOA=-3.24±6.63 and -0.98±5.76mmHg; R2=0.57 and 0.75, P<0.001, respectively). This equation closely predicted VD at rest and peak exercise (bias±95%LOA=-0.03±0.06 and -0.02±0.13L; R2=0.86 and 0.83, P<0.001, respectively). These data suggest predicted PaCO2 and VD based on breath-by-breath gas exchange and ventilatory responses demonstrate acceptable agreement with criterion measurements at peak exercise in HF patients. Routine assessment of PaCO2 and VD can be used to improve interpretability of exercise ventilatory responses in HF.

Van Iterson EH ，Olson TP 《-》

Dead-space ventilation is linked to exercise capacity and survival in distal chronic thromboembolic pulmonary hypertension.

Cardiopulmonary exercise testing (CPET) is frequently used for the evaluation of patients with pulmonary hypertension (PH). Non-operable distal chronic thromboembolic pulmonary hypertension (CTEPH) represents a unique subgroup of PH where microvascular disease resembling pulmonary arterial hypertension (PAH) may predominate and efficacious medical therapy is now available. However, little is known regarding the detailed CPET profile of patients with distal CTEPH, and whether ventilation and gas exchange responses are different from PAH. Forty-nine consecutive patients with non-operable distal CTEPH according to multidisciplinary team assessment and 45 PAH patients underwent CPET and right heart catheterization. Patients were followed up for a median of 3.2 years (interquartile range: 1.8 to 4.4). Pulmonary hemodynamics were similar in distal CTEPH and PAH groups, but patients with distal CTEPH achieved a lower percent predicted peak oxygen consumption (59 ± 13% vs 66 ± 14%, p < 0.05). At peak exercise, higher physiologic dead-space fraction (VD/VT) (0.45 ± 0.07 vs 0.35 ± 0.07, p < 0.0001) and higher arterial-to-end-tidal carbon dioxide gradient (9 ± 3 vs 5 ± 3 mm Hg, p < 0.0001) were observed in distal CTEPH compared with PAH. Ventilatory efficiency, expressed as VE/VCO2 slope, was also more impaired in distal CTEPH (52.2 ± 10.1 vs 43.8 ± 8.4 liters/min, p < 0.0001). In the distal CTEPH group only, higher VD/VT was associated with lower peak oxygen consumption (r = -0.46, p = 0.003) and worse survival. Compared with PAH, a distinct pattern of response to exercise was observed in distal CTEPH, characterized by increased dead-space ventilation that resulted in worse ventilatory efficiency and greater impairment of exercise capacity. In distal CTEPH, dead-space ventilation correlated with exercise capacity and was associated with survival.

Godinas L ，Sattler C ，Lau EM ，Jaïs X ，Taniguchi Y ，Jevnikar M ，Weatherald J ，Sitbon O ，Savale L ，Montani D ，Simonneau G ，Humbert M ，Laveneziana P ，Garcia G ... -  《-》