Central cardiovascular system limits to aerobic capacity.

NEW FINDINGS: What is the topic of this review? The limits to maximal aerobic capacity. What advances does it highlight? A synthesis of data and ideas about what limits maximal aerobic capacity demonstrates the central roles of cardiac output, stroke volume and red blood cell mass in the complex physiological responses to maximal exercise. In healthy humans these factors, along with skeletal muscle blood flow, dominate systemic delivery of oxygen to the contracting muscles and set the upper limit of aerobic energy production by skeletal muscles. In elite athletes and patients with pulmonary disease the lungs can also limit oxygen uptake and delivery. ABSTRACT: In this paper we review the physiological determinants of V̇O2max and discuss the role this variable plays as a determinant of endurance exercise performance. Because the ability to sustain a given pace during a competitive athletic event requires competitors to 'manage' fatigue and go as fast as possible without fatiguing prematurely, V̇O2max is one of the variables that sets the physiological upper limit for sustained energy production by the contracting skeletal muscles.

Cardiac output monitoring with thermodilution pulse-contour analysis vs. non-invasive pulse-contour analysis.

Intravenous fluid boluses guided by changes in stroke volume improve some outcomes after major surgery, but invasive measurments may limit use. From October 2016 to May 2018, we compared the agreement and trending ability of a photoplethysmographic device (Clearsight) with a PiCCO, calibrated by thermodilution, for haemodynamic variables in 20 adults undergoing major elective surgery. We analysed 4519 measurement pairs, including before and after 68 boluses of 250 ml crystalloid. The bias and precision of stroke volume measurement by Clearsight were -0.89 ± 4.78 ml compared with the invasive pulse-contour cardiac output device. The coefficient of agreement for stroke volume variation after fluid boluses between the two devices was 0.79 ('strong'). Fluid boluses that increased stroke volume by ≥ 10% increased mean absolute volume (SD) and mean percentage (SD) stroke volume measurements similarly for the invasive pulse-contour cardiac output and Clearsight devices: 9 (4) ml vs. 8 (4) ml and 16% (8%) vs. 15% (10%), respectively, p > 0.05. The non-invasive Clearsight pulse-contour analysis was similar to an invasive pulse-contour device in measuring absolute and changing stroke volumes during major surgery.

Bioimpedância transtorácica comparada à ressonância magnética na avaliação do débito cardíaco / Transthoracic impedance compared to magnetic resonance imaging in the assessment of cardiac output

FUNDAMENTO: A ressonância magnética cardíaca é considerada o método padrão-ouro para o cálculo de volumes cardíacos. A bioimpedância transtorácica cardíaca avalia o débito cardíaco. Não há trabalhos que validem essa medida comparada à ressonância. OBJETIVO: Avaliar o desempenho da bioimpedância transtorácica cardíaca no cálculo do débito cardíaco, índice cardíaco e volume sistólico, utilizando a ressonância como padrão-ouro. MÉTODOS: Avaliados 31 pacientes, com média de idade de 56,7 ± 18 anos, sendo 18 (58%) do sexo masculino. Foram excluídos os pacientes cuja indicação para a ressonância magnética cardíaca incluía avaliação sob estresse farmacológico. A correlação entre os métodos foi avaliada pelo coeficiente de Pearson, e a dispersão das diferenças absolutas em relação à média foi demonstrada pelo método de Bland-Altman. A concordância entre os métodos foi realizada pelo coeficiente de correlação intraclasses. RESULTADOS: A média do débito cardíaco pela bioimpedância transtorácica cardíaca e pela ressonância foi, respectivamente, 5,16 ± 0,9 e 5,13 ± 0,9 L/min. Observou-se boa correlação entre os métodos para o débito cardíaco (r = 0,79; p = 0,0001), índice cardíaco (r = 0,74; p = 0,0001) e volume sistólico (r = 0,88; p = 0,0001). A avaliação pelo gráfico de Bland-Altman mostrou pequena dispersão das diferenças em relação à média, com baixa amplitude dos intervalos de concordância. Houve boa concordância entre os dois métodos quando avaliados pelo coeficiente de correlação intraclasses, com coeficientes para débito cardíaco, índice cardíaco e volume sistólico de 0,78, 0,73 e 0,88, respectivamente (p < 0,0001 para todas as comparações). CONCLUSÃO: A bioimpedância transtorácica cardíaca mostrou-se acurada no cálculo do débito cardíaco quando comparada à ressonância magnética cardíaca.

BACKGROUND: Cardiac magnetic resonance imaging is considered the gold-standard method for the calculation of cardiac volumes. Transthoracic impedance cardiography assesses the cardiac output. No studies validating this measurement, in comparison to that obtained by magnetic resonance imaging, are available. OBJECTIVE: To evaluate the performance of transthoracic impedance cardiography in the calculation of the cardiac output, cardiac index and stroke volume using magnetic resonance imaging as the gold-standard. METHODS: 31 patients with a mean age of 56.7 ± 18 years were assessed; of these, 18 (58%) were males. Patients whose indication for magnetic resonance imaging required pharmacologic stress test were excluded. Correlation between methods was assessed using the Pearson's coefficient, and dispersion of absolute differences in relation to the mean was demonstrated using the Bland-Altman's method. Agreement between methods was analyzed using the intraclass correlation coefficient. RESULTS: The mean cardiac output by transthoracic impedance cardiography and by magnetic resonance imaging was 5.16 ± 0.9 and 5.13 ± 0.9 L/min, respectively. Good agreement between methods was observed for cardiac output (r = 0.79; p = 0.0001), cardiac index (r = 0.74; p = 0.0001) and stroke volume (r = 0.88; p = 0.0001). The analysis by the Bland-Altman plot showed low dispersion of differences in relation to the mean, with a low amplitude of agreement intervals. Good agreement between the two methods was observed when analyzed by the intraclass correlation coefficient, with coefficients for cardiac output, cardiac index and stroke volume of 0.78, 0.73 and 0.88, respectively (p < 0.0001 for all comparisons). CONCLUSION: Transthoracic impedance cardiography proved accurate in the calculation of the cardiac output in comparison to cardiac magnetic resonance imaging.

Hemodynamic Changes and Transesopahgeal Echocardiographic Findings of Intravenous Amiodarone Loading in Patients Undergoing CABG / 대한마취과학회지

BACKGROUND: Determining the precise magnitude, duration, and mechanism of hypotension caused by intravenous amiodarone could potentially increase the safety of drug administration to critically ill patients. The objective of this study was to characterize the immediate cardiovascular actions of an intravenous loading dose of amiodarone administered using echocardiographic and hemodynamic measurements. METHODS: In a prospective double-blind trial, 20 patients undergoing off-pump coronary artery bypass graft surgery were randomly assigned to receive intravenous amiodarone (n = 10) or placebo (n = 10). Heart rate (HR), arterial blood pressure (systolic, diastolic, mean; SAP, DAP, MAP), pulmonary artery pressure (systolic, diastolic, mean; PSAP, PDAP, PMAP), cardiac output (CO), central venous pressure (CVP), left ventricular ejection fraction (LVEF) were measured. RESULTS: HR, SAP, DAP, MAP, PSAP, PDAP, PMAP, CO by thermodilution method, CVP, LVEF by echocardiographic measurements was not significantly different in both group. Hypotension requiring intervention occurred in 2 of 10 patients after amiodarone administration and in none of 10 patients after placebo. CONCLUSIONS: Hypotension requiring intervention occurred 20% after amiodarone administration, the cause of these hypotension were thought to be arterial dilatation but was not associated with decreased cardiac output or left ventricular ejection fraction and corrected successfully by intravenous administration of phenylephrine.