Cardiac output determined by the CO2 rebreathing method during arm exercise

Summary: Since arm exercise affects the respiratory muscles the CO₂ rebreathing method for determining cardiac output (QR) has to be evaluated during arm exercise. The purpose of this study was (1) to compare three different methods of determining arterial CO₂ tension (PaCO₂) during arm exercise, (2) to verify the linearity of the relationship between QR and oxygen uptake (VO₂) during arm exercise, and (3) to investigate whether the CO₂ rebreathing method according to Collier can determine accurately QR during arm exercise. Sixty male subjects performed arm-cranking exercise at 20%, 40% and 60% of their individual maximal load. Carbon dioxide output (V?O₂) was measured by gas exchange measurement, and mixed venous CO₂ tension (Pv?O₂) was determined from the CO₂ rebreathing plateau at each exercise level. PaCO₂ was estimated in three different ways: (A) by the modified Bohr formula for dead space, (B) by an arterialized blood sample from the hyperaemic ear-lobe, and (C) by the end-expiratory CO₂ tension. A, B, and C were used to calculate QRa, Qb and Qc, respectively. The Pearson's correlation coefficient was high (P < 0–01) among the three different ways of estimating PaCO₂. The QR-VO₂ relationship proved to be linear (P < 0–01). The Q-values showed a good agreement with the direct Fick measurements, and were in the same range compared to other results obtained by dye dilution, electrical impedance cardiography and the exponential CO₂ rebreathing method during arm exercise. In conclusion, the CO₂ rebreathing method appeared to be accurate to determine Q during submaximal arm exercise.,     

Stroke Volume and the Three Phase Cardiac Output Rate Relationship with Ventricular Pacing

Knowledge of how stroke volume (SV), and hence cardiac output (CO), changes with ventricular pacing rate (R) constitutes a key aspect of sensor driven, variable rate pacemakers. It has been established that the relationship between CO and pacing rate exhibits three phases for rest and constant exercise. At low rates (phase 1), CO increases with increasing R; with additional rate increase (phase 2), CO either remains constant or increases slightly; and above some critical rate, CO decreases (phase 3). However, the nature of the relationship between SV and pacing rate has not been as clearly described. Therefore, the objectives of this study were (1) to describe and document the relationship between SV and R, and (2) to demonstrate the consequence of this relationship in terms of the three phase CO versus R relationship. In six anesthetized dogs, right ventricular SV was determined from pulmonary artery blood flow measured using an electromagnetic flow meter, and the right ventricle was paced over a range of rates. In general, SV decreased with increasing R, although the exact nature of the relationship varied from animal to animal. The results demonstrate that it is the manner in which SV decreases with increasing R that determines the three phase relationship between CO and R. The relationships described in this study have important implications for choosing pacing rates for patients receiving sensor driven, variable rate pacemakers.     

Cardiac Resynchronization Therapy:

In patients with heart failure and wide QRS complex, cardiac resynchronization therapy (CRT) is associated with improvement of symptoms and cardiac function. This study examined the effects of a 3-month period of CRT on left ventricular (LV) and right ventricular (RV) ejection fraction (EF) and on LV volumes, both at rest and during exercise. A CRT system was implanted in 15 patients with severe heart failure and wide QRS. Before implant and 3 months later, all patients underwent assessment of cardiac performance with equilibrium Tc⁹⁹ radionuclide angiography with imaging in the best septal left anterior oblique view. Exercise was performed on a bicycle ergometer. At 3 months, a significant improvement in New York Heart Association functional class was observed, and radionuclide angiography showed a significant decrease in LV volumes and a significant increase in LVEF at rest, as well as a significant increase in LVEF during exercise. The remodeling processes associated with CRT did not appear to include RV function, since RVEF did not improve, and changes in RVEF did not correlate with changes in LVEF, neither at rest nor during exercise.     

Cardiac output and circulating blood volume analysis by pulse dye-densitometry

Objective. Pulse dye-densitometry (PDD) is a newly developed methodfor monitoring the indocyanine green (ICG) concentration in an artery withwhich cardiac output (CO) and circulating blood volume (CBV) can bedetermined. We evaluated its accuracy for clinical use. Methods. In 7patients under general anesthesia, ICG-sensitive optical probes (805 and 890nm) were attached to a finger. Following injection of ICG, the arterialconcentration of dye was recorded optically by the non-invasive testinstrument and sampled arterial blood ICG concentration was also measuredphotometrically for comparison. In order to validate the PDD analysis, CO wasalso measured by both the dye dilution cuvette method and by thermodilutionin 8 patients scheduled for coronary artery bypass grafting. In 30 otherpatients, CBV assessed by PDD was compared with its value estimated from bodysize. Results. The blood dye concentration correlated well with thevalues obtained by PDD (r = 0.953, p < 0.01). Meanbias for the test PDD CO was +0.15 ± 0.72 minl^–1 (not significant (n.s.)) compared with the cuvette methodwhile the mean bias of the thermodilution method vs thecuvette method was +0.79 ± 0.84 min l^–1 (p < 0.0001.). The average value of CBV obtained by PDD was 3.81± 1.39 L compared with that estimated value, 3.72 ± 0.77 L (n.s.).Conclusions. CO determined by PDD agrees wellwith cuvette densitometry, and somewhat less well with CO by thermodilution.The new method, by not requiring a pulmonary arterial catheter, is lessinvasivethan either older method, and yields in addition a value of CBV.     

Cardiac Pacemakers in Pediatric Heart Transplant Recipients: Incidence, Indications, and Associated Factors

This study was undertaken to assess the incidence, indications, and predisposing factors for pacemaker placement in a pediatric heart transplant population. From November 1985 to May 1994, 246 pediatric patients have undergone cardiac transplantation at Loma Linda University Medical Center. Seven (2.8%) have received pacemaker placement with an 8–50 month follow-up period. Median age at transplant was 462 days (0 days to 2.5 years). The median time to pacemaker placement was 190 days (18–1,672 days) after transplantation. Indications were sick sinus syndrome (SSS) in 5 and heart block in 2 patients (1 during acute rejection). Three patients with SSS underwent electrophysiology studies (EPS); 1 was normal and 2 showed sinus node dysfunction. The mode of pacing was WIR in 6 patients and WI in 1 patient. All 6 survivors are doing well and 5 patients' pacemakers still provide support. These 7 patients were compared with 185 pediatric patients (0 days to 12-years-old) transplanted during 1985 through 1993 who survived at least 6 months after transplantation. There was no correlation between the receipt of a pacemaker and graft cold ischemic time, rejection history, donor age, or recipient age at transplantation. The 5 patients with SSS had significantly lower average heart rates in the first month after transplantation (108 ± 16 vs 130 ± 12; P = 0.0002). The need for permanent pacemakers in this population is uncommon. Pacemakers, however, can be safely performed when necessary with excellent clinical results.     

Role of Sonographic Automatic Volume Calculation in Measuring Fetal Cardiac Ventricular Volumes Using 4‐Dimensional Sonography

Objective. The purpose of this study was to compare the agreement and reliability of virtual organ computer‐aided analysis (VOCAL) and sonographic automatic volume calculation (sonoAVC) for measurements of ventricular volume from fetal heart data sets acquired by 4‐dimensional sonography with spatiotemporal image correlation (STIC). Methods. We studied 45 volumes from fetuses with normal (n = 30) and abnormal (n = 15) hearts. Spatiotemporal image correlation data sets were frozen in end systole and end diastole, and ventricular volumes were measured with VOCAL and sonoAVC. The stroke volume was calculated from these measurements. Reliability and agreement of the two techniques were evaluated with intraclass correlation coefficients (ICCs), and proportionate Bland‐Altman plots were constructed. The time necessary to complete the measurements with either technique was compared. Intraobserver and interobserver agreement of measurements was calculated. Results. All data sets could be measured with both techniques. A high degree of reliability was observed between VOCAL and sonoAVC (left ventricular stroke volume ICC, 0.978; 95% confidence interval [CI], 0.957–0.989; right ventricular stroke volume ICC, 0.985; 95% CI, 0.972–0.992). The time necessary to measure the stroke volume was significantly shorter with sonoAVC (2.8 versus 11.7 minutes; P < .0001) than with VOCAL. Bland‐Altman tests showed no clinically significant mean percent differences between stroke volume measurements obtained from each ventricle by the same observer or by 2 independent observers using either VOCAL or sonoAVC. Conclusions. There was good agreement between cardiac volumes measured with VOCAL and sonoAVC. Sonographic automatic volume calculation represents a rapid technique for estimating fetal stroke volume and promises to become the method of choice.     

Dynamic Changes in Lymphocyte GRK2 Levels in Cardiac Transplant Patients: A Biomarker for Left Ventricular Function

G protein‐coupled receptor kinase 2 (GRK2), which is upregulated in the failing human myocardium, appears to have a role in heart failure (HF) pathogenesis. In peripheral lymphocytes, GRK2 expression has been shown to reflect myocardial levels. This study represents an attempt to define the role for GRK2 as a potential biomarker of left ventricular function in HF patients. We obtained blood from 24 HF patients before and after heart transplantation and followed them for up to 1 year, also recording hemodynamic data and histological results from endomyocardial biopsies. We determined blood GRK2 protein by Western blotting and enzyme‐linked immunosorbent assay. GRK2 levels were obtained before transplant and at first posttransplant biopsy. GRK2 levels significantly declined after transplant and remained low over the course of the study period. After transplantation, we found that blood GRK2 signifi cantly dropped and remained low consistent with improved cardiac function in the transplanted heart. Blood GRK2 has potential as a biomarker for myocardial function in end‐stage HF. Clin Trans Sci 2010; Volume #: 1–5     

Cardiac complications in thalassemia: noninvasive detection methods and new directions in the clinical management

The natural history of thalassemia has shown substantial change during these years. This applies for each aspect of the pathology (for example, endocrinological, hepatological and psychological) and also for the pathology that has presented and still presents the main cause of death: myocardial dysfunction. In this review, the pathophysiology of cardiac complications, possible role of myocarditis, new knowledge on pathogenesis, and noninvasive detection methods for iron overload in the heart are pointed out. Prophylaxis of cardiomyopathy and new therapy strategies of myocardial dysfunction, including the impact of the new chelation treatment, are discussed.     

Impedance Cardiography for Cardiac Output Estimation in Pacemaker Patients: Review of the Literature

Impedance curdiogrciphy permits noninvasive beat-to-beat determination of cardiac output, the product of the amplitude of the first derivative of thonicic impedance signal (dZ/dt), the venfricular ejection time, and heart rate corrected by the distance between the measuring electrodes. Its use is based on: (1) the dZ/dt signal that originates from the upper thorax; (2) the ventricular ejection period measured by the dZ/dt curve that occurs between the opening and closing of the aortic vnlve: (3) the dZ/dt curve is similar in morphology and timing to the aortic flow curve measured by an electromagnetic flowmefer with a significant linear correlation (r = 0.9) between dZ/dt and peak aortic flow; (4) similarity of the linear correlation between stroke volume, determined by the flowmeter and the impedance signal; and (5) significant reduction of the dZ/dt signal by 90% follows simultaneous occlusion of the aorta and the pulmonary artery. The rapid systolic portion of the impedance signal occurs only when blood is ejected into the aorta and is independent of right ventricular ejection. Most studies comparing impedance cardiography results with standard cardiac output determination have shown a correlation of 0.7–0.9. While the accuracy of impedance cardiography remains controversial and can be affected by the inherent limitations of the technique and by low cardiac output, intracardiac shunts. and valvular regurgitation. the high reproducibility of the method is established and may be comparable or superior to other commonly used techniques. When accurate determination of cardiac output is crucial, impedance cardiography may be used in conjunction with a standard technique to establish a baseline reference, thereby permitting further analysis. If only the trend need be followed, the high reproducibility of impedance cardiography measurements allows small changes in cardiac output to be detected on a frequent and ongoing basis. The ease and precision of this technique warrants its more widespread use in the assessment of pacemaker patients. Further use of this promising technique will allow a better definition of its role in the assessment of a wide range of cardiac patients.     

Evaluation of wall motion abnormality by comparing values of cardiac output obtained by M-mode and Doppler echocardiography: Parameter revealing wall motion abnormality in stress echocardiography

Dobutamine and dipyridamole stress echocardiographies are both well able to detect myocardial ischemia resulting from coronary diseases by recognizing the regional wall motion abnormality (WMA). Here we report a method for describing WMA in detail. In pharmacological stress echocardiography, because of difficulties in recognizing the two-dimensional pattern, accuracy sometimes depends upon the skill of the operator. Two stroke volumes obtained using the M-mode and Doppler methods were examined to detect abnormal regional cardiac function by the dipyridamole stress test. Stroke volume obtained by the M-modereflects regional cardiac function and that estimated from the outflow using the Doppler methodreflects total cardiac function. These two stroke volumes were compared in normal subjects and patients with coronary-diseases. The results indicated consistent discrepancies between these two stroke volume in the ischemic hearts as a results of coronary stenosis, whereas changes in stroke volumes in the normal subjects showed the same tendency. This method of combining information about the regional and total functions is thus useful in examining the WMA and regional cardiac function, although it can not be applied to subjects whose stroke volume does not increase under stress.     

超声心动图测量E/e'比值的临床应用

E/e'是超声心动图多普勒组织成像(DTI)技术的衍生指标,源于传统二尖瓣血流图与多普勒组织运动速度曲线图(DT-PW).该指标因无创、简便、高敏感度,越来越受到国内外学者广泛关注.其临床应用范围广泛,包括心肌收缩、舒张功能及左室充盈压的评估等,此外还提供了重要的预后信息.本综述阐述了该指标的基本概念及测量方法,并讨论其主要临床应用以及存在的局限性和发展前景.     

Crosstalk of the Heart and Periphery: Skeletal and Cardiac Muscle as Therapeutic Targets in Heart Failure

Heart failure syndrome is initiated as the body's metabolic needs temporarily exceed the pumping capacity of the heart. In most cases, this phenomenon tends to occur during physical exercise. Although not always subjectively recognized, limited exercise capacity remains the clinical hallmark of congestive heart failure. It can be measured objectively as reduced skeletal muscle performance and maximal whole-body oxygen uptake, which are not necessarily explained by central haemodynamic abnormalities. In fact, the initial cardiac condition sets forth a series of peripheral adaptations that are potentially life-saving during acute decompensation but become disadvantageous and symptom-generating in stable heart failure. Inodilator drugs were theoretically ideal to revert the adverse haemodynamic crosstalk between the heart and periphery. However, these drugs failed to improve prognosis in congestive heart failure, whereas drugs that did so showed typically unimpressive haemodynamic effects. Exercise therapy has recently emerged as a safe and effective way to enhance physical performance and subjective well-being in congestive heart failure. A dual therapeutic approach is suggested, consisting of exercise training to improve the periphery and the use of cardioprotective drugs to limit cardiac cellular damage from neurohormonal activation.     

悬吊训练治疗脑卒中患者平衡功能障碍的临床研究

目的: 观察悬吊训练（SET）对脑卒中患者平衡功能恢复的影响。方法: 脑卒中平衡功能障碍患者40例,随机分为对照组和观察组各20例,2组均接受常规康复训练,在此基础上,观察组加以悬吊训练。治疗前和治疗4周后采用Berg平衡量表（BBS）、Barthel指数（BI）以及采集竖脊肌表面肌电平均肌电值（AEMG）和中位频率值（MF）对2组患者进行评定。结果: 治疗4周后,2组BBS、BI评分均明显高于治疗前（均P<0.01）,且观察组以上评分均明显高于对照组（均P<0.05）。治疗前,2组患者AEMG、MF值组内比较健侧均明显高于患侧（均P<0.05）;治疗４周后,2组患者健患侧竖脊肌AEMG、MF值均较治疗前明显提高（均P<0.05）,观察组健患侧AEMG、MF值均较对照组明显提高（均P<0.05）,但观察组健患侧AEMG、MF值之间无统计学差异。结论: SET能够改善脑卒中患者的竖脊肌AEMG、MF值及BBS和BI评分,提高脑卒中患者躯干肌肉运动功能,从而提高平衡功能以及日常生活活动能力,值得在临床推广应用。     

Noninvasive Rejection Monitoring of Cardiac Transplants Using High Resolution Intramyocardial Electrograms: Initial US Multicenter Experience

Endomyocardial biopsy (EMB) remains the mainstay for the diagnosis of acute cellular rejection in cardiac transplant patients. A noninvasive alternative that would supplant or reduce the number of EMBs would be a highly desirable and cost-effective tool. To evaluate one potential alternative, a pacemaker with high resolution telemetry capabilities and two fractally coated epimyocardial leads were implanted in 30 patients at five transplant centers during the heart transplant procedure. Ventricular electrograms were recorded during intrinsic and paced activity and digitized to a laptop-based data acquisition device. Electrograms were recorded at frequent intervals and systematically on days when EMBs were performed. The electrogram data were then transferred via the Internet to a central data processing site. Clinical patient management was blinded to the electrogram results and varied considerably among the five centers. Using EMB together with clinical assessment of the transplant revealed 18 cases of clinically significant rejection beyond postoperative day 27 that required antirejection therapy. The normalized parameter values extracted from the electrogram recordings during pacing (the ventricular evoked response) that were associated with significant rejection were statistically lower (86%± 16% versus 96%± 22%, P < 0.005). The application of a single-threshold diagnosis model to the parameter values allowed detection of significant rejection with a negative predictive value of 98%. This analysis also showed that as many as 55% of the routine surveillance EMBs could have been eliminated had the pacemaker monitoring technique been used as a screening tool prior to EMB. A prospective study should further define the role of this technique in the detection and management of cardiac transplant patients.     

Cardiac resynchronization therapy: effects on left and right ventricular ejection fraction during exercise

In patients with heart failure and wide QRS complex, cardiac resynchronization therapy (CRT) is associated with improvement of symptoms and cardiac function. This study examined the effects of a 3-month period of CRT on left ventricular (LV) and right ventricular (RV) ejection fraction (EF) and on LV volumes, both at rest and during exercise. A CRT system was implanted in 15 patients with severe heart failure and wide QRS. Before implant and 3 months later, all patients underwent assessment of cardiac performance with equilibrium Tc(99) radionuclide angiography with imaging in the best septal left anterior oblique view. Exercise was performed on a bicycle ergometer. At 3 months, a significant improvement in New York Heart Association functional class was observed, and radionuclide angiography showed a significant decrease in LV volumes and a significant increase in LVEF at rest, as well as a significant increase in LVEF during exercise. The remodeling processes associated with CRT did not appear to include RV function, since RVEF did not improve, and changes in RVEF did not correlate with changes in LVEF, neither at rest nor during exercise.     

Hemodynamic Effects of Atrial Synchronization in Acute and Long-Term Ventricular Pacing

The acute and long-term hemodynamic benefit from atrial synchronization in ventricular (VAT) pacing has been investigated at rest and during exercise in 10 patients undergoing pacemaker implantation for complete A-V block. The results were compared to conventional (VOO) ventricular stimulation at rates of 70 BPM and 96 BPM. Cardiac index (CI) in VAT-pacing increased at rest by 8% and during exercise by 15% more than with VOO pacing (p < 0.01). No significant change between the two different rates of asynchronous pacing was observed. CI at rest and during exercise was unchanged after 10 weeks of VAT-pacing. CI is regulated by change of stroke volume in VOO-pacing and by heart rate only with VAT-pacing. In contrast to earlier results with asynchronous ventricular pacing, the hemodynamic benefit of pacing in an atrial synchronized mode is long-lasting. Physiologic mechanisms regulate hemodynamics during exercise and in heart failure. (PACE, Vol. 5, September-October, 1982)