Aging blunts hyperventilation-induced hypocapnia and reduction in cerebral blood flow velocity during maximal exercise

Cerebral blood flow (CBF) increases from rest to ∼60% of peak oxygen uptake (VO_2peak) and thereafter decreases towards baseline due to hyperventilation-induced hypocapnia and subsequent cerebral vasoconstriction. It is unknown what happens to CBF in older adults (OA), who experience a decline in CBF at rest coupled with a blunted ventilatory response during VO_2peak. In 14 OA (71 ± 10 year) and 21 young controls (YA; 23 ± 4 years), we hypothesized that OA would experience less hyperventilation-induced cerebral vasoconstriction and therefore an attenuated reduction in CBF at VO_2peak. Incremental exercise was performed on a cycle ergometer, whilst bilateral middle cerebral artery blood flow velocity (MCA V_mean; transcranial Doppler ultrasound), heart rate (HR; ECG) and end-tidal PCO₂ (P_ETCO₂) were monitored continuously. Blood pressure (BP) was monitored intermittently. From rest to 50% of VO_2peak, despite greater elevations in BP in OA, the change in MCA V_mean was greater in YA compared to OA (28% vs. 15%, respectively; P < 0.0005). In the YA, at intensities >70% of VO_2peak, the hyperventilation-induced declines in both P_ETCO₂ (14 mmHg (YA) vs. 4 mmHg (OA); P < 0.05) and MCA V_mean (−21% (YA) vs. −7% (OA); P < 0.0005) were greater in YA compared to OA. Our findings show (1), from rest-to-mild intensity exercise (50% VO_2peak), elevations in CBF are reduced in OA and (2) age-related declines in hyperventilation during maximal exercise result in less hypocapnic-induced cerebral vasoconstriction.     

Gas Exchange and Ventilatory Efficiency During Exercise in Pulmonary Vascular Diseases

Background and ObjectiveVentilatory inefficiency (high V′_E/V′CO₂) and resting hypocapnia are common in pulmonary vascular disease and are associated with poor prognosis. Low resting PaCO₂ suggests increased chemosensitivity or an altered PaCO₂ set-point. We aimed to determine the relationships between exercise gas exchange variables reflecting the PaCO₂ set-point, exercise capacity, hemodynamics and V′_E/V′CO₂.MethodsPulmonary arterial hypertension (n = 34), chronic thromboembolic pulmonary hypertension (CTEPH, n = 19) and pulmonary veno-occlusive disease (PVOD, n = 6) patients underwent rest and peak exercise arterial blood gas measurements during cardiopulmonary exercise testing. Patients were grouped according to resting PaCO₂: hypocapnic (PaCO₂ ≤34 mmHg) or normocapnic (PaCO₂ 35–45 mmHg). The PaCO₂ set-point was estimated by the maximal value of end-tidal PCO₂ (maximal P_ETCO₂) between the anaerobic threshold and respiratory compensation point.ResultsThe hypocapnic group (n = 39) had lower resting cardiac index (3.1 ±0.8 vs. 3.7 ±0.7 L/min/m², p < 0.01), lower peak V′O₂ (15.8 ± 3.5 vs. 20.7 ± 4.3 mL/kg/min, p < 0.01), and higher V′_E/V′CO₂ slope (60.6 ± 17.6 vs. 38.2 ± 8.0, p < 0.01). At peak exercise, hypocapic patients had lower PaO₂, higher V_D/V_T and higher P_(a-ET)CO₂. Maximal P_ETCO₂ (r = 0.59) and V_D/V_T (r = −0.59) were more related to cardiac index than PaO₂ or PaCO₂ at rest or peak exercise. Maximal P_ETCO₂ was the strongest correlate of V′_E/V′CO₂ slope (r = −0.86), peak V′O₂ (r = 0.64) and peak work rate (r = 0.49).ConclusionsResting hypocapnia is associated with worse cardiac function, more ventilatory inefficiency and reduced exercise capacity. This could be explained by elevated chemosensitivity and lower PaCO₂ set-point. Maximal P_ETCO₂ may be a useful non-invasive marker of PaCO₂ setpoint and disease severity even with submaximal effort.     

Bi-level Positive Airway Pressure (BiPAP) with Standard Exhalation Valve Does Not Improve Maximum Exercise Capacity in Patients with COPD

Background: Although BiPAP has been used as an adjunct to exercise, little is know about its effect on exercise in COPD. We aimed to evaluate the acute effect of BiPAP delivered with a standard valve (Vision, Respironics), compared to no assist, on exercise capacity in individuals with COPD. Methods: Peak exercise workload (WL_peak), dyspnea (Borg), end-expiratory lung volume (EELV), tidal volume (V_T), minute ventilation (V_E), O₂ uptake (VO₂), and CO₂ production (VCO₂) were assessed in 10 COPD patients (FEV₁ 53 ± 22% pred) during three symptom-limited bicycle exercise tests while breathing i) without a ventilator (noPS), ii) with a pressure support (PS) of 0 cm H₂O (PS0; IPAP & EPAP 4 cm H₂O) and iii) PS of 10 cm H₂O (PS10; IPAP 14 & EPAP 4 cm H₂O) on separate days using a randomized crossover design. Results: WL_peak was significantly lower with PS10 (33 ± 16) and PS0 (30.5 ± 13) than noPS (43 ± 19) (p < 0.001). Dyspnea at peak exercise was similar with noPS, PS0 and PS10; at isoload it was lower with noPS compared to PS10 and PS0 (p < 0.01). V_T and V_E were highest with PS10 and lowest with noPS both at peak exercise and isoload (p < 0.001). EELV was similar at peak exercise with all three conditions. VO₂ and VCO₂ were greater with PS10 and PS0 than noPS (p < 0.001), both at peak exercise and isoload. Conclusion: Use of BiPAP with a standard exhalation valve during exercise increases V_T and V_E at the expense of augmenting VCO₂ and dyspnea, which in turns reduces WL_peak in COPD patients.     

Feasibility and safety of automated CO2 angiography in peripheral arterial interventions

Carbon dioxide (CO₂) gas is an established alternative to iodine contrast during angiography in patients with risk of postcontrast acute kidney injury and in those with history of iodine contrast allergy. Different CO₂ delivery systems during angiography are reported in literature, with automated delivery system being the latest. The aim of this study is to evaluate the safety, efficacy, and learning curve of an automated CO₂ injection system with controlled pressures in peripheral arterial interventions and also to study the patients’ tolerance to the system.From January 2018 to October 2019 peripheral arterial interventions were performed in 40 patients (median age-78 years, interquartile range: 69–84 years) using an automated CO₂ injection system with customized protocols, with conventional iodine contrast agent used only as a bailout option. The pain and tolerance during the CO₂ angiography were evaluated with a visual analog scale at the end of each procedure. The amount of CO₂, iodine contrast used, and radiation dose area product for the interventions were also systematically recorded for all procedures. These values were statistically compared in 2 groups, viz first 20 patients where a learning curve was expected vs the rest 20 patients.All procedures were successfully completed without complications. All patients tolerated the CO₂ angiography with a median total pain score of 3 (interquartile range: 3–4), with no statistical difference between the groups (P = .529). The 2 groups were statistically comparable in terms of comorbidities and the type of procedures performed (P = .807). The amount of iodine contrast agent used (24.60 ± 6.44 ml vs 32.70 ± 8.70 ml, P = .006) and the radiation dose area product associated were significantly lower in the second group (2160.74 ± 1181.52 μGym² vs 1531.62 ± 536.47 μGym², P = .043).Automated CO₂ angiography is technically feasible and safe for peripheral arterial interventions and is well tolerated by the patients. With the interventionalist becoming familiar with the technique, better diagnostic accuracy could be obtained using lower volumes of conventional iodine contrast agents and reduction of the radiation dose involved.     

Distinguishing exercise intolerance in early‐stage pulmonary hypertension with invasive exercise hemodynamics: Rest V E/VCO2 and ETCO2 identify pulmonary vascular disease

BackgroundAmong subjects with exercise intolerance and suspected early‐stage pulmonary hypertension (PH), early identification of pulmonary vascular disease (PVD) with noninvasive methods is essential for prompt PH management.HypothesisRest gas exchange parameters (minute ventilation to carbon dioxide production ratio: V _E/VCO₂ and end‐tidal carbon dioxide: ETCO₂) can identify PVD in early‐stage PH.MethodsWe conducted a retrospective review of 55 subjects with early‐stage PH (per echocardiogram), undergoing invasive exercise hemodynamics with cardiopulmonary exercise test to distinguish exercise intolerance mechanisms. Based on the rest and exercise hemodynamics, three distinct phenotypes were defined: (1) PVD, (2) pulmonary venous hypertension, and (3) noncardiac dyspnea (no rest or exercise PH). For all tests, *p < .05 was considered statistically significant.ResultsThe mean age was 63.3 ± 13.4 years (53% female). In the overall cohort, higher rest V _E/VCO₂ and lower rest ETCO₂ (mm Hg) correlated with high rest and exercise pulmonary vascular resistance (PVR) (r ~ 0.5–0.6*). On receiver‐operating characteristic analysis to predict PVD (vs. non‐PVD) subjects with noninvasive metrics, area under the curve for pulmonary artery systolic pressure (echocardiogram) = 0.53, rest V _E/VCO₂ = 0.70* and ETCO₂ = 0.73*. Based on this, optimal thresholds of rest V _E/VCO₂ > 40 mm Hg and rest ETCO₂ < 30 mm Hg were applied to the overall cohort. Subjects with both abnormal gas exchange parameters (n = 12, vs. both normal parameters, n = 19) had an exercise PVR 5.2 ± 2.6* (vs. 1.9 ± 1.2), mPAP/CO slope with exercise 10.2 ± 6.0* (vs. 2.9 ± 2.0), and none included subjects from the noncardiac dyspnea group.ConclusionsIn a broad cohort of subjects with suspected early‐stage PH, referred for invasive exercise testing to distinguish mechanisms of exercise intolerance, rest gas exchange parameters (V _E/VCO₂ > 40 mm Hg and ETCO₂ < 30 mm Hg) identify PVD.     

Alveolar Air and O2 Uptake During Exercise in Patients With Heart Failure

Background

Peak exercise pulmonary oxygen uptake (V?O₂) is a primary marker of prognosis in heart failure (HF). The pathophysiology of impaired peak V?O₂ is unclear in patients. To what extent alveolar airway function affects V?O₂ during cardiopulmonary exercise testing (CPET) has not been fully elucidated. This study aimed to describe how changes in alveolar ventilation (V?_A), volume (V_A), and related parameters couple with exercise V?O₂ in HF.

Relationship between cardiorespiratory fitness and preoperative evaluation findings in patients with morbid obesity undergoing sleeve gastrectomy: A cross-sectional study

Evaluating various parameters, including preoperative cardiorespiratory fitness markers, is critical for patients with morbid obesity. Also, clinicians should prescribe suitable exercise and lifestyle guideline based on the tested parameters. Therefore, we investigated cardiorespiratory fitness and its correlation with preoperative evaluation in patients with morbid obesity scheduled for laparoscopic sleeve gastrectomy.A retrospective cross-sectional study was conducted with 38 patients (13 men and 25 women; mean age, 34.9 ± 10.9 years) scheduled for laparoscopic sleeve gastrectomy. Cardiopulmonary exercise stress tests were also performed. Measured cardiopulmonary responses included peak values of oxygen consumption (VO₂), metabolic equivalents (METs), respiratory exchange ratio, heart rate (HR), and rate pressure product. Body composition variables were analyzed using bioimpedance analysis, laboratory parameters (hemoglobin A1c, lipid profile, inflammatory markers), and comorbidities. In addition, self-reported questionnaires were administered, including the Beck Depression Inventory (BDI), Hamilton Depression Rating Scale (HDRS), Short-Form Health Survey (SF-36), and Moorehead-Ardelt Quality of Life Questionnaire (MAQOL).The average body mass index (BMI) and percent body fat were 39.8 ± 5.7 kg/m⁻² and 46.2 ± 6.1%, respectively. The VO_2peak/kg, METs, RER_peak, HR_peak, RPP_peak, age-predicted HR percentage, and VO_2peak percentage were 18.6 ± 3.8 mL/min⁻¹/kg⁻¹, 5.3 ± 1.1, 1.1 ± 0.1, 158.5 ± 19.8, 32,414.4 ± 6,695.8 mm Hg/min⁻¹, 85.2 ± 8.8%, and 76.1 ± 14.8%, respectively. BMI (P = .026), percent body fat (P = .001), HR_peak (P = .018), erythrocyte sedimentation rate (P = .007), total BDI (P = .043), HDRS (P = .025), SF-36 (P = .006), and MAQOL (P = .007) scores were significantly associated with VO_2peak/kg. Body fat percentage (P < .001) and total SF-36 score (P < .001) remained significant in the multiple linear regression analysis.Various cardiorespiratory fitness markers were investigated in patients with morbid obesity who underwent the sleeve gastrectomy. Peak aerobic exercise capacity was significantly associated with preoperative parameters such as body fat composition and self-reported quality of life in these patients. These results could be utilized for preoperative and/or postoperative exercise strategies in patients with morbid obesity scheduled for laparoscopic sleeve gastrectomy.     

The relationship between resting lung-to-lung circulation time and peak exercise capacity in chronic heart failure patients

BackgroundPeak exercise capacity (VO_2peak) is a measure of the severity of chronic heart failure (CHF); however, few indices of resting cardiopulmonary function have been shown to predict VO_2peak. A prolonged circulation time has been suggested as an index of increased severity of CHF. The aim of this study was to investigate the relationship between resting lung-to-lung circulation time (LLCT) and VO_2peak in CHF.Methods and ResultsThirty CHF patients (59 ± 13 years, New York Heart Association: 1.9 ± 1.0) undertook the study. Each subject completed resting pulmonary and echocardiography measures and an incremental exercise test. LLCT was measured using the reappearance of end-tidal acetylene (P_ET,C₂H₂) after a single inhalation. Univariate and multivariate stepwise linear regression was used to determine the predictors of VO_2peak. Univariate correlates of VO_2peak (group mean 1.53 ± 0.44 L/min⁻¹) included LLCT (r = −0.75), inspiratory capacity (r = 0.41), ejection fraction (r = 0.33), peak early flow velocity (r = −0.39), and the ratio of early to late flow velocity (r = −0.31). LLCT was the only independent predictor where VO_2peak = 3.923–0.045 (LLCT); r² = 54%.ConclusionsThese results suggest that resting LLCT determined using the soluble inert gas technique represents a simple, noninvasive method that provides additional information regarding exercise capacity in CHF.     

Exercise tolerance in obese vs. lean adolescents: a systematic review and meta‐analysis

To prescribe feasible and medically safe exercise interventions for obese adolescents, it remains to be determined whether exercise tolerance is altered and whether anomalous cardiopulmonary responses during maximal exercise testing are present. Studies that examined cardiopulmonary responses to maximal exercise testing in obese adolescents were searched: cardiopulmonary exercise tests with respiratory gas exchange measurements of peak oxygen uptake (VO_2peak) were performed and comparisons between obese and lean adolescents were made. Study quality was assessed using a standardized item list. By meta‐analyses VO_2peak, peak cycling power output (W_peak) and peak heart rate (HR_peak) were compared between groups. Nine articles were selected (333 obese vs. 145 lean adolescents). VO_2peak (L min^?1), HR_peak and W_peak were not different between groups (P ≥ 0.10), while a trend was found for a reduced VO_2peak (mL min^?1 kg^?1 lean tissue mass) (P = 0.07) in obese vs. lean adolescents. It remained uncertain whether anomalous cardiopulmonary responses occur during maximal exercise testing in obese adolescents. In conclusion, a trend was found for lowered VO_2peak (mL min^?1 kg^?1 lean tissue mass) in obese vs. lean adolescents. Whether cardiopulmonary anomalies during maximal exercise testing would occur in obese adolescents remains uncertain. Studies are therefore warranted to examine the cardiopulmonary response during maximal exercise testing in obese adolescents.     

Comparison of ventilatory expired gas parameters used to predict hospitalization in patients with heart failure

Background Several ventilatory expired gas measures obtained during exercise testing demonstrate prognostic value in the heart failure (HF) population. Comparison of prognostic efficacy between pertinent measures is sparse. Methods The ability of various expressions of peak oxygen consumption (VO₂), the relationship between minute ventilation (VE) and carbon dioxide production (VCO₂), and the partial pressure of end-tidal carbon dioxide (P_ETCO₂) were assessed to determine which measure(s) best predicted cardiac-related hospitalization over a 1-year period in subjects diagnosed with HF. Results Univariate Cox regression analysis found that several expressions of peak VO₂, VE-VCO₂ relationship, and P_ETCO₂ were significant predictors of hospitalization. Multivariate Cox regression analysis revealed that the VE/VCO₂ slope significantly predicted hospitalization (χ² = 29.1, P < .00001). Peak VO₂ and P_ETCO₂ did not provide additional predictive value. Conclusions The prognostic superiority of the VE/VCO₂ slope over peak VO₂ may be a result of the latter measure's partial dependence on subject effort and skeletal muscle function. (Am Heart J 2002;143:427-32.)     

Effect of Acute β-blocker Withholding on Ventilatory Efficiency in Patients With Advanced Chronic Heart Failure

BackgroundThis is the first study to examine the effect of acute (24-hour) β-blocker withholding on ventilatory efficiency in patients with advanced chronic heart failure (CHF) during maximal incremental treadmill cardiopulmonary exercise test.Methods and ResultsSeventeen CHF patients were studied either 3 hours after administration of β-blocker (BB_ON) or 27 hours after the last β-blocker ingestion (BB_OFF). The ventilatory efficiency was measured via the slope of the linear relationship between ventilation (V′_E) and carbon dioxide production (V′CO₂) (ie, V′_E/V′CO₂ slope). Measurements were also made at rest, anaerobic threshold (AT), maximal end-tidal pressure for carbon dioxide (P_ETCO_2max), respiratory compensation point (RC), and peak exercise. Compared with BB_ON, the V′_E/V′CO₂ slope was significantly increased during BB_OFF (30.8 ± 7.4 vs. 29.1 ± 5.4, P = .04). At peak exercise, oxygen uptake (V′O₂, 16.0 ± 2.7 vs. 15.6 ± 2.8 mL·kg·min) and V′CO₂ (1458 ± 459 vs. 1414 ± 429 mL/min) were not different between the 2 conditions, whereas V′_E was higher during BB_OFF (49.5 ± 10.7 vs. 46.1 ± 9.6 L/min, P = .04). No differences were noted at AT and RC in V′O₂, V′CO₂, V′_E, V′_E/V′O₂, and V′_E/V′CO₂ ratios during the 2 conditions. At P_ETCO_2max, used to noninvasively estimate the CO₂ set point, V′_E was higher (33.9 ± 7.6 vs. 31.7 ± 7.3 L/min, P = .002) and P_ETCO₂ was lower (37.4 ± 4.8 vs. 38.5 ± 4.0 mm Hg, P = .03), whereas V′CO₂ was unchanged (1079 ± 340 vs. 1050 ± 322 mL/min) during BB_OFF.ConclusionAcute β-blocker withholding resulted in decreased ventilatory efficiency mostly from an increase of V′CO₂-independent regulation of V′_E and less likely from a change in ventilation/perfusion mismatching.     

Ventilatory Expired Gas at Constant-Rate Low-Intensity Exercise Predicts Adverse Events and is Related to Neurohormonal Markers in Patients With Heart Failure

BackgroundVentilatory efficiency (VE/VCO₂ ratio) and the partial pressure of end-tidal carbon dioxide (P_ETCO₂), obtained during moderate to high levels of physical exertion demonstrate prognostic value in heart failure (HF). The present investigation assesses the clinical utility of these variables during low-intensity exercise.Methods and ResultsOne hundred and thirty subjects diagnosed with HF underwent a 2-minute, constant-rate treadmill session at 2 miles per hour. Both the VE/VCO₂ ratio and P_ETCO₂ were recorded during exercise (30-second average) and their change (Δ) from rest. B-type and atrial natriuretic peptide (BNP and ANP) were also determined. Only P_ETCO₂ and ΔP_ETCO₂ emerged from the multivariate Cox regression. Receiver operating characteristic curve analysis revealed the prognostic classification schemes were significant with thresholds of </≥34 mm Hg (hazard ratio: 4.2, 95% CI: 2.2–8.0, P < .001) and </≥1 mm Hg (hazard ratio: 3.5, 95% CI: 1.9–6.6, P < .001) being optimal for P_ETCO₂ and ΔP_ETCO₂, respectively. Moreover, subjects with a P_ETCO₂≥34 mm Hg had a significantly lower BNP (214.1 ± 431.9 vs. 1110.5 ± 1854.0 pg/mL, P=.005) and ANP (108.2 ± 103.6 vs. 246.2 ± 200.4 pg/mL, P < .001).ConclusionsThe results of this pilot study indicate ventilatory expired gas analysis during a short bout of low-intensity exercise may provide insight into prognosis and cardiac stability.     

Exercise Ventilatory Efficiency in Older and Younger Heart Failure Patients With Preserved Ejection Fraction

Background

Patients with heart failure with preserved ejection fraction (HFpEF) exhibit pulmonary abnormalities, but the studies to date have reported wide variability in the ventilatory equivalent for carbon dioxide (V?_E/V?CO₂) slope. It is possible that aging may contribute to that variability. We sought to compare ventilatory efficiency and its components in older and younger HFpEF patients during exercise.

Synthesis of Dense MgB2 Superconductor via In Situ and Ex Situ Spark Plasma Sintering Method

In this study, high-density magnesium diboride (MgB₂) bulk superconductors were synthesized by spark plasma sintering (SPS) under pressure to improve the field dependence of the critical current density (J_c-B) in MgB₂ bulk superconductors. We investigated the relationship between sintering conditions (temperature and time) and J_c-B using two methods, ex situ (sintering MgB₂ synthesized powder) and in situ (reaction sintering of Mg and B powder), respectively. As a result, we found that higher density with suppressed particle growth and suppression of the formation of coarse particles of MgB₄ and MgO were found to be effective in improving the J_c-B characteristics. In the ex situ method, the degradation of MgB₂ due to pyrolysis was more severe at temperatures higher than 850 °C. The sample that underwent SPS treatment for a short time at 850 °C showed higher density and less impurity phase in the bulk, which improved the J_c-B properties. In addition, the in situ method showed very minimal impurity with a corresponding improvement in density and J_c-B characteristics for the sample optimized at 750 °C. Microstructural characterization and flux pinning (f_P) analysis revealed the possibility of refined MgO inclusions and MgB₄ phase as new pinning centers, which greatly contributed to the J_c-B properties. The contributions of the sintering conditions on f_P for both synthesis methods were analyzed.     

CHA2DS2-VASc score predicts the slow flow/no-reflow phenomenon in ST-segment elevation myocardial infarction patients with multivessel disease undergoing primary percutaneous coronary intervention

ST-segment elevation myocardial infarction (STEMI) patients with multivessel disease (MVD) have a higher incidence of slow-flow/no-reflow (SF-NR) phenomenon during primary percutaneous coronary intervention (PPCI) than those with single vessel disease. Currently, no effective tools exist to predict the risk of SF-NR in this population. The present study aimed to evaluate whether CHA₂DS₂-VASc score can be used as a simple tool to predict this risk.This study consecutively included STEMI patients hospitalized in Beijing Anzhen Hospital from January 2005 to January 2015. Among these patients, 1032 patients with MVD were finally enrolled. Patients were divided into SF-NR (+) group and SF-NR (–) group according to whether SF-NR occurred during PPCI. SF-NR was defined as the thrombolysis in myocardial infarction (TIMI) grade ≤2.There were 134 patients (13%) in the SF-NR (+) group. Compared with the SF-NR (–) group, patients in the SF-NR (+) group are elder, with lower left ventricular ejection fraction and higher CHA₂DS₂-VASc score. Multiple logistic regression analysis indicated that CHA₂DS₂-VASc score ≥3 (odds ratio [OR], 2.148; 95% confidence interval [CI], 1.389–3.320; P = .001), current smoking (OR, 1.814; 95% CI, 1.19–2.764; P = .006), atrial fibrillation (OR, 2.892; 95% CI, 1.138–7.350; P = .03), complete revascularization (OR, 2.307; 95% CI, 1.202–4.429; P = .01), and total length of stents ≥40 mm (OR, 1.482; 95% CI, 1.011–2.172; P = .04) were independent risk factors of SF-NR. The incidence of SF-NR in patients with CHA₂DS₂-VASc score ≥3 was 1.7 times higher than that in patients with CHA₂DS₂-VASc score <3. Additionally, patients with CHA₂DS₂-VASc score ≥3 plus ≥2 risk factors have 3 times higher incidence of SF-NR than those with CHA₂DS₂-VASc score ≥3 plus 0 to 1 risk factor.CHA₂DS₂-VASc score ≥3 can be used as a simple and sensitive indicator to predict SF-NR phenomenon and guide the PPCI strategy in STEMI patients with MVD.     

The Influence of Sex Differences on Cardiopulmonary Exercise Metrics Following Heart Transplant

BackgroundPrevious work has shown sex-related differences in cardiopulmonary responses in patients with heart failure (HF); however, sex differences following heart transplant (HTx) have not been examined. Thus, we hypothesized women would demonstrate lower peak oxygen uptake (VO_2peak) but similar ventilatory efficiency (V_E/VCO₂ slope) compared with men prior to HTx. Furthermore, we hypothesized that, following HTx, women would exhibit greater improvements in VO_2peak and V_E/VCO₂ slope compared with men.MethodsHTx patients with cardiopulmonary exercise testing (CPET) between 2007 and 2016 were included. Pre-HTx CPET occurred within 24 months pre-HTx with post-HTx CPET within 12 months following HTx. VO_2peak was measured via standard protocol. V_E/VCO₂ slope was calculated using rest-peak ventilation (V_E) and carbon dioxide production (VCO₂).ResultsEighty-eight patients (Men [M]: n = 63, age: 55 ± 12 years; Women [W]: n = 25, age: 47 ± 11 years) were assessed. Pre-HTx VO_2peak (M: 13.9 ± 5.0 vs W: 11.6 ± 3.9 mL/kg/min, P = 0.17) and V_E/VCO₂ slope (M: 42 ± 12 vs W: 46 ± 18, P = 0.53) were not different between sexes. Overall, VO_2peak (Pre: 13.3 ± 4.8 vs Post: 18.4 ± 4.8 mL/kg/min, P < 0.01) and V_E/VCO₂ slope (Pre: 43 ± 14 vs Post: 37 ± 6, P = 0.02) improved following HTx. Post-VO_2peak (M: 19.0 ± 4.8 vs W: 16.8 ± 4.5 mL/kg/min, P = 0.24) and V_E/VCO₂ slope (M: 37 ± 6 vs W: 37 ± 7, P = 0.99) and delta VO_2peak (M: 5.0 ± 4.8 vs W: 5.3 ± 4.9 mL/kg/min, P = 0.85) and V_E/VCO₂ slope (M: –5 ± 11 vs W: –9 ± 17, P = 0.29) were not different between sexes.ConclusionsThese data demonstrate that cardiopulmonary improvements following HTx patients occur for both sexes. Importantly, women show similar significant functional improvements following HTx compared with men.     

Alveolar-arterial PCO2 differences and diffusion limitation

The alveolar-arterial PCO₂ differences in man due to a decrease of the lung membrane diffusing capacity (D _L) and of the lung capillary transit time (t _c) are computed using a mathematical model which takes into account the finite speed of the blood CO₂ reactions and the O₂-CO₂ interactions. The results of the computer simulations suggest that large PCO₂ differences could be observed only whenD _L ort _c are below 10% normal. The magnitude of the PCO₂ differences is influenced significantly by the finite speed of the blood reactions when t_c is reduced, but not whenD _L is decreased. The Bohr and Haldane effects have a small influence on the PCO₂ differences.     

Causes of breathing inefficiency during exercise in heart failure

BackgroundPatients with heart failure (HF) develop abnormal pulmonary gas exchange; specifically, they have abnormal ventilation relative to metabolic demand (ventilatory efficiency/minute ventilation in relation to carbon dioxide production [V_E/VCO₂]) during exercise. The purpose of this investigation was to examine the factors that underlie the abnormal breathing efficiency in this population.Methods and ResultsFourteen controls and 33 moderate-severe HF patients, ages 52 ± 12 and 54 ± 8 years, respectively, performed submaximal exercise (～65% of maximum) on a cycle ergometer. Gas exchange and blood gas measurements were made at rest and during exercise. Submaximal exercise data were used to quantify the influence of hyperventilation (PaCO₂) and dead space ventilation (V_D) on V_E/VCO₂. The V_E/VCO₂ relationship was lower in controls (30 ± 4) than HF (45 ± 9, P < .01). This was the result of hyperventilation (lower PaCO₂) and higher V_D/V_T that contributed 40% and 47%, respectively, to the increased V_E/VCO₂ (P < .01). The elevated V_D/V_T in the HF patients was the result of a tachypneic breathing pattern (lower V_T, 1086 ± 366 versus 2003 ± 504 mL, P < .01) in the presence of a normal V_D (11.5 ± 4.0 versus 11.9 ± 5.7 L/min, P = .095).ConclusionsThe abnormal ventilation in relation to metabolic demand in HF patients during exercise was due primarily to alterations in breathing pattern (reduced V_T) and excessive hyperventilation.     

Cardiopulmonary Exercise Testing as a Diagnostic Tool for the Detection of Left-sided Pulmonary Hypertension in Heart Failure

BackgroundRecently, it has become increasingly recognized that pulmonary hypertension (PH) is a particularly ominous consequence of left-sided heart failure (HF). The primary aim of this investigation was to assess the ability of key cardiopulmonary exercise testing (CPX) variables to detect elevated pulmonary pressures in a HF cohort.MethodsThis was a retrospective analysis of a prospectively collected database. Two hundred ninety-three subjects with HF (63 ± 10 years old, 79% male) underwent Doppler echocardiography to estimate resting pulmonary artery systolic pressure (PASP). Peak oxygen consumption (VO₂), the minute ventilation/carbon dioxide production (VE/VCO₂) slope, peak partial pressure of end-tidal CO₂ (P_ETCO₂) and exercise oscillatory ventilation (EOV) were determined.ResultsForty-six percent (n = 134) of the subjects presented with a PASP ≥40 mm Hg. A VE/VCO₂ slope </≥36.0 was the best predictor of a PASP ≥40 mm Hg (odds ratio [OR] 12.1, 95% confidence interval [CI] 6.8–21.4; P < .001). Peak P_ETCO₂ ≤34 mm Hg (OR 3.8, 95% CI 1.3–11.2; P < .001) and the presence of EOV (OR 3.2, 95% CI 1.8–5.8; P < .001) added significant diagnostic value.ConclusionsAlthough CPX is an established prognostic assessment in the HF population, the results of the present investigation indicate that it may also have important diagnostic utility for PH.