Bioimpedance-derived differences in cardiac physiology during exercise stress testing in low-risk chest pain patients

BACKGROUND: Little has been written about the utility of thoracic electrical bioimpedance (TEB)-derived cardiac physiologic variables in evaluating patients with low-risk chest pain syndromes. Noninvasive bioimpedance can monitor cardiac physiology while a patient is performing an exercise stress test. In addition, the demographics of patients with chest pain, the incidence of coronary artery disease (CAD), and the methods used for evaluation have well-documented sex differences. OBJECTIVE: The objectives are to show that there are different cardiac physiologic responses to exercise stress test in Chest Pain Evaluation Unit patients with and without true CAD that could be used to stratify patients and that there is a sex difference in TEB results. METHODS: Patients 18 to 65 years of age with low-risk chest pain were eligible. Patients were attached to the TEB throughout the exercise stress test procedure. Heart rate (HR) was monitored. Primary dependent variables were TEB-measured cardiac output (CO, L/min) and stroke volume (SV, ml) at peak exercise. Secondary variables were TEB-measured ejection fraction (%), end-diastolic volume (EDV, ml), ventricular ejection time (ms), and thoracic fluid index (omega) at peak exercise. Outcome variables were either proved CAD or patient sex. CAD was proved by angiography, stress scintigraphy, or stress echocardiogram. Results were compared using a Student's t test assuming equal variances, with significance considered at a P < 0.05, and 95% confidence intervals were calculated for significant results. RESULTS: Nine patients had proved CAD, 82 patients did not. Forty-three women and 48 men were included in the study. At peak exercise, patients with CAD had a significantly smaller increase in EDV than patients without CAD (32.8 +/- 59.5 ml versus 89.3 +/- 101.8 ml) without a significant change in CO, SV, or HR. At peak exercise, women had a significantly smaller increase in CO and SV without a significant change in HR. In addition, women had a significantly smaller increase in EDV. CONCLUSION: When compared with patients without CAD, patients with CAD have a significantly smaller increase in EDV and a trend toward the same effect in CO and SV. Women have significantly smaller increases CO, SV, and EDV compared with men. Because there were no differences in HR, using HR as the sole end point would miss these differences. TEB is a practical means of measuring these variables.     

Estimation of cerebral blood flow during cardiopulmonary resuscitation in humans

Cerebral blood flow (CBF) and cardiac output (CO) were measured during cardiopulmonary resuscitation in patients who were unsuccessfully resuscitated by use of C14-iodoantipyrine injected into the left ventricle. CO varied between 1.3 and 2.2 l/min with mean 1.8 +/- 0.6 l/min (+/- SD) (28 ml/kg/min). The cortical CBF was found between 14 and 211 ml 100 g-1.min-1 with mean 42 ml 100 g-1.min-1 and mean white matter CBF equal to 27 ml 100 g-1.min-1. It is suggested that the external cardiac massage in humans may be of poor efficacy in terms of brain revival. Cortical CBF after long-lasting cardiopulmonary resuscitation showed signs of maldistribution suggestive of a patchy and incomplete perfusion.     

Continuous,non-invasive techniques to determine cardiac output in children after cardiac surgery: evaluation of transesophageal Doppler and electric velocimetry

Background. Continuous and non-invasive measurement of cardiac output (CO) may contribute helpful information to the care and treatment of the critically ill pediatric patient. Different methods are available but their clinical verification is still a major problem. Aim. Comparison of reliability and safety of two continuous non-invasive methods with transthoracic echocardiography (TTE) for CO measurement: electric velocimetry technique (EV, Aesculontrade mark) and transesophageal Doppler (TED, CardioQPtrade mark). Methods/Material. In 26 infants and children who had undergone corrective cardiac surgery at a median age of 3.5 (1-17) years CO and stroke volume (SV) were obtained by EV, TED and TTE. Each patient had five measurements on the first day after surgery, during mechanical ventilation and sedation. Results. Values for CO and SV from TED and EV correlated well with those of TTE (r = 0.85 and r = 0.88), but mean values were significantly lower than the values of TTE for TED (P = 0.02) and EV (P = 0.001). According to Bland-Altman analysis, bias was 0.36 l/min with a precision of 1.67 l/min for TED vs. TTE and 0.87 l/min (bias) with a precision of 3.26 l/min for EV vs. TTE. No severe adverse events were observed and the handling of both systems was easy in the sedated child. Conclusions. In pediatric patients non-invasive measurement of CO and SV with TED and EV is useful for continuous monitoring after heart surgery. Both new methods seem to underestimate cardiac output in terms of absolute values. However, TED shows tolerable bias and precision and may be helpful for continuous CO monitoring in a deeply sedated and ventilated pediatric patient, e.g. in the operating room or intensive care unit.     

Non-invasive stroke volume assessment in patients with pulmonary arterial hypertension: left-sided data mandatory

Background

Cardiovascular Magnetic Resonance (CMR) is an emerging modality in the diagnosis and follow-up of patients with Pulmonary Arterial Hypertension (PAH). Derivation of stroke volume (SV) from the pulmonary flow curves is considered as a standard in this respect. Our aim was to investigate the accuracy of pulmonary artery (PA) flow for measuring SV.

Methods

Thirty-four PAH patients underwent both CMR and right-sided heart catheterisation. CMR-derived SV was measured by PA flow, left (LV) and right ventricular (RV) volumes, and, in a subset of nine patients also by aortic flow. These SV values were compared to the SV obtained by invasive Fick method.

Results

For SV by PA flow versus Fick, r = 0.71, mean difference was -4.2 ml with limits of agreement 26.8 and -18.3 ml. For SV by LV volumes versus Fick, r = 0.95, mean difference was -0.8 ml with limits of agreement of 8.7 and -10.4 ml. For SV by RV volumes versus Fick, r = 0.73, mean difference -0.75 ml with limits of agreement 21.8 and -23.3 ml. In the subset of nine patients, SV by aorta flow versus Fick yielded r = 0.95, while in this subset SV by pulmonary flow versus Fick yielded r = 0.76. For all regression analyses, p < 0.0001.

Conclusion

In conclusion, SV from PA flow has limited accuracy in PAH patients. LV volumes and aorta flow are to be preferred for the measurement of SV.     

Non-invasive Cardiac Output by Transthoracic Electrical Bioimpedence in Post-cardiac Surgery Patients: Comparison with Thermodilution Method

OBJECTIVE: Thoracic electrical bioimpedance (TEB) cardiac output (CO) is being explored increasingly as a non-invasive alternative to the pulmonary artery catheter (PAC). This study compared TEB-CO measured using a new instrument - NICOMON (Larsen & Toubro Ltd. India) with thermodilution (Td) CO in post-cardiac surgery patients. METHODS: Postoperative cardiac surgical patients requiring a PAC for their management were studied. TEB-CO was measured by passing a 4 mA RMS alternating current across the chest and measuring the analog bioimpedence across the thorax. Kubicek equation was used to estimate TEB-CO. Td-CO was measured using a PAC. Bland-Altman analysis was used to compare paired data. RESULTS: One hundred and ninety-seven pairs of CO measurements were made by the two methods among 35 patients. Mean TEB-CO was 5.15 +/- 1.27 l/min and mean Td-CO was 5.22 +/- 1.28 l/min. Pearson correlation coefficient (r) for these measurements was 0.856 (P < 0.01), with bias -0.0651 l and precision: +/-1.37 l/min. The percentage error of measurement of this precision was 26.44%. Cardiac index also correlated among the two methods (r = 0.789; P = 0.01). CONCLUSIONS: Thoracic electrical bioimpedance cardiac output compares favorably with thermodilution method among post-cardiac surgery patients. Further studies are indi- cated with this instrument to validate its efficacy in various clinical situations and utility in monitoring hemodynamic interventions.     

Noninvasive Cardiac Output Measurement by Transthoracic Electrical Bioimpedence: Influence of Age and Gender

Background  Thoracic electrical bioimpedance (TEB) as a method of measuring cardiac output (CO) is being explored increasingly over the last two decades, as a non-invasive alternative to the pulmonary artery catheter. The objective of this study was to establish normative data for measurement of CO by TEB and define the effect of age and gender on CO. Method  Stroke volume (SV) of 397 normal individuals (203 men, 194 women) in the age range of 10–77 years was determined using Kubisek and Bernstein formulae by TEB method. Derived cardiac parameters including CO, cardiac index (CI), systemic vascular resistance and resistance index were calculated and analyzed. Results  We found significant difference in CO among age groups and between gender. CO between Kubicek formula and Bernstein formula correlated well, but their means differed significantly. Cardiac indices peak in the third and seventh decade and were comparable between genders. Conclusion  A comprehensive data set of normalized values expressed as 95% confidence interval and mean ± SD in different age groups and different gender was possible for cardiac parameters using TEB. Sathyaprabha TN, Pradhan C, Rashmi G, Thennarasu K, Raju TR. Noninvasive cardiac output measurement by transthoracic electrical bioimpedence: influence of age and gender.     

Modelling lung and tissue diffusion using a membrane oxygenator circuit

A simple model lung has been designed using a membrane oxygenator circuit comprising two membrane oxygenators primed with one to two litres of equine blood, giving reproducible results over several hours. Normoxia and normocapnia were achieved consistently over the duration of the test with a blood flow of 2.5 l/min, oxygenator ventilation gas flow of 5 l/min air with 0.3 l/min O2 and deoxygenator ventilation gas flow of 5 l/min 5% CO2 in N2 with 0.2 l/min CO2. The measured PaO2 was 81.3 (SD 3.35 mmHg), PvO2 38.3 (SD 1.38 mmHg), PvCO2 60.6 (SD 1.13 mmHg) and PaCO2 36.1 (SD 0.69mmHg). MO2 and MCO2 were 116 ml/min and 169 ml/min, respectively. An increasing linear relationship was observed for FiO2 and the corresponding PaO2 and, similarly, with FiCO2 and PvCO2, providing reference ranges for this model.     

胸阻抗无创血流动力学监测在危重患者的应用研究

目的评价胸阻抗（TEB）无创血流动力学监测在危重患者的应用价值。方法选取2006年10月至2007年8月入住本院综合ICU住院时间超过24h的危重患者48例,所有病例在常规监护基础上进行TEB监测,并在此期间行超声心动图检查,对两种方法同时测得的心输出量（CO）、心脏指数（CI）、每搏播出量（SV）、每搏指数（SI）等结果进行相关性分析。结果TEB法与超声心动图法所测得的CO、CI、SV和SI均具有很好的相关性。结论 TEB法与超声心动图法监测结果有很好的相关性;TEB法可用于危重患者的血流动力学监测。     

A Novel Approach to Measure Cardiac Output Noninvasively: A Comparison with the Thermodilution Method on Critical Care Patients

OBJECTIVE: To compare the accuracy and reliability of cardiac output (CO) measurement by a Noninvasive Hemodynamic Analyzer (NHA) to the thermodilution cardiac output (COTD) technique in ICU patients of cardiac condition. METHOD: ICU retrospective data collected in a 700-bed university-affiliated regional medical center. The data results from 203 patients who required invasive hemodynamic monitoring for clinical and/or surgical management. RESULTS: The ranges of the two CO measurements were: CO(TD) = 2.06 to 8.8 l/min and CO(NHA) = 2.06 to 8.46 l/min, respectively. The Mean and SD of CO(NHA) = 4.819 l/min +/- 1.053 was near to CO(TD) = 4.902 l/min +/- 1.421. Variance was better for CO(NHA) = 1.110 l/min compared to CO(TD) = 1.421 l/min. Median of CO(NHA) showed 4.813 l/min and CO(TD) = 4.660 l/min. Bias was 0.083 l/min with 95% Confidence Interval (Precision): -0.26 to 0.040, and 95% Limits of Agreement was between -1.661 to 1.827 l/min. CONCLUSIONS: The results of this retrospective study indicate that the CO(NHA) technique may be a promising screening method. Additional studies are needed to explore its diagnostic trending capability. This noninvasive CO technique has been proven to be clinically accurate and may be applicable for telemedicine applications.     

Correlation of the oxygen cost of breathing and length of weaning from mechanical ventilation

We studied 20 patients (ages 43 to 84 yr), whose forced vital capacity, peak negative inspiratory pressure and alveolar-arterial gradient indicated that they were unlikely to be withdrawn rapidly from mechanical ventilation. Their mean oxygen consumption (VO2) during controlled ventilation (CV) was 292 +/- 21 (SEM) ml/min. During spontaneous ventilation (SV) through endotracheal tube and ventilator circuit, the VO2 rose significantly (p less than .001) to 323 +/- 20 ml/min. The oxygen cost of breathing (OCB) (the difference in VO2 between CV and SV) and the OCB as a fraction of the oxygen consumed during SV (OCB/VO2 SV) both correlated significantly by linear regression analysis with the total time to wean in days (-11.6 + 0.93 for OCB, r = .79; and -12.6 + 293.1 for OCB/VO2 SV, r = .84, p less than .001 for both). As the OCB was correlated with the total wean time, this variable may be a useful index of the effect of many influences on the weaning process.     

Bioimpedance versus thermodilution cardiac output measurement: The bomed NCCOM3 after coronary bypass surgery

Values obtained for cardiac output (CO) were compared using thermodilution (TD) with those obtained using bioimpedance (Bi) as measured using the Bomed NCCOM3 (Revision 6) in 28 consecutive patients in the first 24h after coronary artery bypass surgery (CABS). In 46 paired measurements made in the first 12 h after CABS Bi values for CO were significantly lower than TD values, the limits of agreement between the two methods were also unacceptably large (mean Bi 4.38 (SD 1.40) l/min, mean TD 5.46 (SD 1.19) l/min, limits of agreement–3.05 to +0.89). In 55 paired measurements made after 12h (all in spontaneously breathing patients) there was no significant difference between the two methods and acceptable limits of agreement, mean Bi 5.69 (SD 1.2) l/min mean TD 5.6 (SD 1.2) l/min, limits of agreement–0.99 to +1.17). The significantly lower BiCO values obtained in the first 12h after CABS show that BiCO measurement is not consistently reliable in the intensive care setting.     

Cardiovascular response to rapid infusion of lactated Ringer's

Cardiovascular response to rapid infusion of lactated Ringer's was investigated in 5 adult dogs (average body weight = 21.1 kg) under 1% halothane anesthesia. Following implantation of aortic flow probe and left atrial line, the chest was closed and splenectomy was performed prior to the experiment. Warmed lactated Ringer's was administered at five different infusion rates (2.5, 5, 10, 15 and 20 ml/kg/min in random sequence) to each dog until left atrial pressure (LAP) reached 20 mmHg or a maximum of 50 ml/kg had been infused. Subsequent infusions were done after stroke volume (SV) spontaneously returned to the control level. Cardiac output (CO), SV, heart rate (HR), mean arterial pressure (MAP), LAP and central venous pressure (CVP) were monitored simultaneously during infusions. HR was stable during infusions, whereas MAP increased by 39% of control. Response of LAP to volume infused was nearly linear at fast infusion rates (10, 15 and 20 ml/kg/min). Response of LAP to slow infusion rates (2.5 and 5 ml/kg/min) was curvilinear (decelerating curve). The relationship between CVP and volume infused was similar to LAP vs. volume infused. Ventricular function curves (SV, CO and stroke work vs. LAP) were also influenced by the rate of infusion with steeper curves at slow infusion rates than curves derived from fast infusion rates. However, initial changes in SV and CO curves were not significantly affected by the rate of infusion. We conclude that the cardiovascular response to rapid infusion of lactated Ringer's is rate dependent but initial changes in SV and CO curves are not significantly affected at infusion rates of 2.5, 5, 10, 15 or 20 ml/kg/min.     

Lithium dilution cardiac output measurement: a clinical assessment of central venous and peripheral venous indicator injection

OBJECTIVE: The lithium indicator dilution technique has been shown to measure cardiac output (CO) accurately by using central venous injection of lithium chloride (Li-CCO). This study aimed to compare the measurement of CO by using peripheral venous administration of lithium chloride (Li-PCO) with Li-CCO. DESIGN: Prospective, observational human study. SETTING: Surgical intensive care unit. PATIENTS: Thirty-one patients were studied after major surgery. All patients had arterial, central, and peripheral venous catheters. A total of 24 patients had pulmonary artery catheters. MEASUREMENTS: Serial measurements of Li-CCO and Li-PCO were made during hemodynamically stable conditions. CO was also measured using thermodilution (TDCO) when a pulmonary artery catheter was present. Data were analyzed by linear regression, the generalized estimating equation, and the comparison method described by Bland and Altman. MAIN RESULTS: There were 93 Li-CCOs, 93 Li-PCOs, and 216 TDCOs recorded. The ranges of COs were similar: Li-CCO, 2.36-11.52 L/min (mean, 5.22 L/min; n = 31); Li-PCO, 1.63-9.99 L/min (mean, 5.22 L/min; n = 31), and TDCO, 3.28-10.4 L/min (mean, 5.75 L/min; n = 24). There was good linear correlation between Li-CCO and Li-PCO (R2 =.845). The mean difference for Li-CCO-Li-PCO was very small and insignificant (p =.97), and the limits of agreement were acceptable (mean difference +/- sd, 0.0005 +/- 0.64 L/min). The mean difference for Li-CCO-Li-PCO was smaller if the peripheral injection site was proximal rather than distal to the wrist (p =.053). Li-PCO and Li-CCO values were lower than simultaneously obtained TDCO measurements (Li-PCO-TDCO, -0.538 +/- 0.95 L/min, p =.003; Li-CCO-TDCO, -0.526 +/- 0.67 L/min, p =.0001). CONCLUSIONS: Li-PCO gives a measurement that agrees well with Li-CCO. Accuracy of Li-PCO is probably improved if a proximal arm vein is used. Li-PCO provides accurate measurements of CO without the risks of pulmonary artery or central venous catheterization.     

RETRACTED ARTICLE: Noninvasive assessment of cardiac output using thoracic electrical bioimpedance in hemodynamically stable and unstable patients after cardiac surgery: a comparison with pulmonary artery thermodilution

Objective To compare noninvasive cardiac output (CO)measurement obtained with a new thoracic electrical bioimpedance (TEB) device, using a proprietary modification of the impedance equation, with invasive measurement obtained via pulmonary artery thermodilution.Design Prospective, observational study.Setting Surgical intensive care unit (ICU) of a university-affiliated community hospital.Patients and participants Seventy-four adult patients undergoing elective cardiac surgery with routine pulmonary artery catheter placement.Interventions None.Measurements and results Simultaneous paired CO and cardiac index (CI) measurements by TEB and thermodilution were obtained in mechanically ventilated patients upon admission to the ICU. For analysis of CI data the patients were subdivided into a hemodynamically stable group and a hemodynamically unstable group. The groups were analyzed using linear regression and tests of bias and precision. We found a significant correlation between thermodilution and TEB (r = 0.83; n< 0.001), accompanied by a bias of –0.01 l/min/m² and a precision of ±0.57 l/min/m² for all CI data pairs. Correlation, bias, and precision were not influenced by stratification of the data. The correlation coefficient, bias, and precision for CI were 0.86 (n< 0.001), 0.03 l/min/m², and ±0.47 l/min/m² in hemodynamically stable patients and 0.79 (n< 0.001), 0.06 l/min/m², and ±0.68 l/min/m² in hemodynamically unstable patients.Conclusions Our results demonstrate a close correlation and clinically acceptable agreement and precision between CO measurements obtained with impedance cardiography using a new algorithm to calculate CO from variations in TEB, and those obtained with the clinical standard of care, pulmonary artery thermodilution, in hemodynamically stable and unstable patients after cardiac surgery.     

Regional cerebral blood flow (rCBF) in migraine during the interictal period: different rCBF patterns in patients with and without aura

The aim of this study was to evaluate the rCBF (¹³³Xe clearance method) in migrainous patients free from attack. Fifty patients suffering from migraine without aura (group M) and 20 suffering from migraine with aura (group MA) (age range 20-50 years) were submitted to 32 channel rCBF mapping during the interictal period. The rCBF data of patients were compared with those obtained from 60 healthy control subjects (group C) and 21 patients suffering from tension-type headache (group TH). The mean (average of all channels) rCBF values were: group M=70.5 ± 13.7ml/100g/min; group MA=56.6 ± 11.4ml/100g/min; group C=62.3 ± 8.3ml/100g/min; group TH=62.1 ± 8.4ml/100g/min (F=11.93; p <0.001). As expected, patients belonging to group TH had a normal rCBF. The mean rCBF of group M was significantly higher than that of groups C and TH, while in group MA it was significantly lower than in groups C and TH. Group M showed a diffuse hyperemia, while group MA showed rCBF values significantly lower than normal in posterior regions, according to aura. Our results suggest that: (a) the rCBF pattern in migrainous patients is different from that in both controls and TH patients, even during the interictal period; (b) patients suffering from migraine with and without aura are two distinct subpopulations with opposite rCBF deviations.     

Pediatric cardiac output measurement using surface integration of velocity vectors: an in vivo validation study

OBJECTIVE: To test the accuracy and reproducibility of systemic cardiac output (CO) measurements using surface integration of velocity vectors (SIVV) in a pediatric animal model with hemodynamic instability and to compare SIVV with traditional pulsed-wave Doppler measurements. DESIGN: Prospective, comparative study. SETTING: Animal research laboratory at a university medical center. SUBJECTS: Eight piglets weighing 10-15 kg. INTERVENTIONS: Hemodynamic instability was induced by using inhalation of isoflurane and infusions of colloid and dobutamine. MEASUREMENTS: SIVV CO was measured at the left ventricular outflow tract, the aortic valve, and ascending aorta. Transit time CO was used as the reference standard. RESULTS: There was good agreement between SIVV and transit time CO. At high frame rates, the mean difference +/- 2 SD between the two methods was 0.01+/-0.27 L/min for measurements at the left ventricular outflow tract, 0.08+/-0.26 L/min for the ascending aorta, and 0.06+/-0.25 L/min for the aortic valve. At low frame rates, measurements were 0.06+/-0.25, 0.19+/-0.32, and 0.14+/-0.30 L/min for the left ventricular outflow tract, ascending aorta, and aortic valve, respectively. There were no differences between the three sites at high frame rates. Agreement between pulsed-wave Doppler and transit time CO was poorer, with a mean difference +/- 2 SD of 0.09+/-0.93 L/min. Repeated SIVV measurements taken at a period of relative hemodynamic stability differed by a mean difference +/-2 SD of 0.01+/-0.22 L/min, with a coefficient of variation = 7.6%. Intraobserver coefficients of variation were 5.7%, 4.9%, and 4.1% at the left ventricular outflow tract, ascending aorta, and aortic valve, respectively. Interobserver variability was also small, with a coefficient of variation = 8.5%. CONCLUSIONS: SIVV is an accurate and reproducible flow measurement technique. It is a considerable improvement over currently used methods and is applicable to pediatric critical care.     

Comparison of different flow-reducing bag-valve ventilation devices regarding respiratory mechanics and gastric inflation in an unprotected airway model

OBJECTIVE: Gastric inflation (GI) is a significant issue when ventilation is performed on unprotected airways. DESIGN: Experimental analysis on the respiratory effects of hose extended bag-valve ventilation devices designed to reduce inspiratory pressure and flow. SETTING: Laboratory with lung/oesophageal sphincter simulator and pressure-flow-volume analyser. Lung compliance: 300ml/kPa, airway resistance: 0.5kPa/l/s. Lower oesophageal sphincter pressure (LOSP): 0.5kPa. INTERVENTIONS: Bag-valve ventilation of lung simulator. Twelve academic dental staff members used four devices: Ambu Mark III attached to either a reservoir bag (R) or a pressure relief valve (SV), SMART BAG (SB), and Easy Grip (EG) as control. RESULTS: After Bonferroni correction (p-level of significance 0.0083) for multiple comparisons, no evidence of difference between inspiratory tidal volumes (TVIN) administered by use of R (median 137ml) and SB (149ml) was found. Differences in TVIN were only detected between R and SV (188ml) (p=0.002). Only a trend towards TVIN differences between SB and R in comparison to EG (195ml) was found (p=0.009). Distributions of peak pressures differed when R (median 0.7kPa) and SV (1.0kPa) (p=0.006) or SB (0.7kPa) and SV (p=0.002) were compared. Peak inspiratory flow rates differed between EG (median 59l/min) and R (32l/min) as well as SB (42l/min) and between SB and SV (50l/min) (all with p=0.001). GI was lowest by use of R (median 103ml) compared to all other devices (EG: 518ml, SV: 394ml, SB: 271ml) (p=0.001). The areas under the pressure/flow over time curves were larger during SB compared to R ventilation. Mean airway pressures were significantly lower by use of R (0.1kPa) compared to SB (0.3kPa) (p<0.008). CONCLUSION: Lowering GI by pressure-flow reduction may result in lower TV depending on the device used. Lowest GI resulted from R ventilation. This may be explained by the specific pressure/time or flow/time patterns achieved by use of this device.     

Plasma and renal clearance of iohexol--a study on the reproducibility of a method for the glomerular filtration rate

The reproducibility of iohexol clearance as a determination of the glomerular filtration rate was assessed in 12 healthy subjects during triplicate constant-rate infusions. Renal and plasma clearance of iohexol demonstrated a total within-subject variation (CV) ranging between 0% and 16%. The inter-individual variation in renal clearance was about 10%, the clearance values being (mean +/- SD) 116 +/- 10, 117 +/- 9 and 110 +/- 12 ml/min 1.73 m2 in the three experiments and corresponding figures for the plasma clearance were 120 +/- 17, 118 +/- 12 and 112 +/- 14 ml/min 1.73 m2. The renal clearance (CLR) and the plasma clearance (CL) showed good correlation (regression equation CL = 11.80 + 0.93 CLR, rs = 0.67). The method is simple and reproducible; thus, it is suitable for both clinical examinations and research.     

Carbon monoxide diffusing capacity of the lungs determined by single-breath and steady-state exercise methods

We measured carbon monoxide diffusing capacity of the lungs (DL,CO) by both the resting single-breath (SB) and steady-state (SS) exercise methods in 95 patients referred for pulmonary function testing. A 10-second breath-holding method was used for the SB test. DL,CO (SS) was measured during the last minute of a 3-minute exercise test on a 9-inch step. Results of the two methods showed good agreement, the SB-SS difference averaging -0.70 (SD, 3.39) ml/min per mm Hg. The difference between the two methods was not correlated with other measurements of pulmonary function except minute ventilation during the exercise performed in the DL,CO (SS) procedure. In a separate study of laboratory personnel, the day-to-day variabilities of the two tests were similar (SD, 1.4 ml/min per mm Hg). Alveolar volume obtained by helium dilution during the SB test was comparable to total lung capacity (TLC) estimated by multiple-breath nitrogen washout in patients without severe airway obstruction. In severe airway obstruction, the mean SB alveolar volume was 13.8% less than the TLC by nitrogen washout, a difference that may be useful as an indicator of inefficiency of gas mixing in the lungs. We conclude that the SB and SS exercise methods provide similar estimates of DL,CO in patients referred to a pulmonary function laboratory.     

Changes in cardiac output and stroke volume as measured by non-invasive CO monitoring in infants with RSV bronchiolitis

Objectives: The primary aim of the study was to determine the changes, if any, in cardiac output (CO) and stroke volume (SV) in normal infants with RSV bronchiolitis. The secondary aim was to determine whether changes in CO (??CO) and SV (??SV) are associated with changes in respiratory rate (??RR). Methods: Non-invasive CO recordings were obtained within 24?h of admission and discharge. Changes in CO, SV, and HR measurements were compared using paired t-tests. The effect of fluid boluses during the first 24?h (<60 or ??60?cc/kg) on CO was assessed by 2 way ANOVA with time and group as main effect. The relationship between ??RR and ??CO or ??SV was assessed by linear regression. Data is presented as Mean?±?SEM and mean differences with 95?% confidence interval (p?Results: 15 infants with RSV bronchiolitis were studied. CO (1.31?±?0.13 to 1.11?±?0.11?l/min (0.21 [0.04?C0.37]) and SV (9.42?±?1.10 to 7.75?±?0.83?ml/beat (1.67 [0.21?C3.12]) decreased significantly while HR (142.1?±?4.0 to 145.2?±?3.1 beats/min 3.0 [?5.3 to 11.3]) was unchanged. SV (p?=?0.02) and CO (p?=?0.04) significantly decreased only in the 7 infants that received ??60?cc/kg. ??RR correlated significantly with ??CO (r ²?=?0.28, p?=?0.04); but not with ??SV (r ²?=?0.20, p?=?0.09). Conclusions: ?CO was related to ??SV and not ?? HR. The ?CO and ??SV were affected by fluid boluses. ??RR correlated with ??CO. Non-invasive CO monitoring can trend CO and SV in infants with bronchiolitis during hospitalization.