Immediate effect of expiratory loading on left ventricular stroke volume

A method of detecting and quantifying severity of myocardial perfusion defects with intravenous ultrasound contrast and breath holding during stress echocardiography

Although breath holding is commonly used to improve and maintain image quality during stress echocardiography, its effects on the qualitative and quantitative analysis of myocardial contrast enhancement (MCE) following intravenously injected microbubbles is unknown. The purpose of this study was to determine how breath holding affects MCE following either an intravenous bolus or continuous infusion of perfluorocarbon containing microbubbles. In 48 patients, intravenous Optison was given at peak dobutamine stress to assess myocardial perfusion. The degree of myocardial opacification was assessed immediately following a breath hold in inspiration (BH(ini)), at the end of a breath hold (BH(term)), and following expiration and a subsequent second breath hold (BH(reinsp)). Pulmonary venous time velocity integrals were recorded during these different phases as well. Eleven patients had quantitative coronary angiography. Mean duration of the breath hold was 7 +/- 1 seconds. Pulmonary venous return fell by 29% +/- 18% at BH(term) (P < 0.001). There was complete disappearance of MCE at BH(term) in 27 of 35 bolus injection patients at peak stress, and no return of MCE following flash destruction during breath holding in 11 of 13 patients receiving continuous infusions. BH(reinsp) resulted in a boluslike return of contrast, with a transient, bright MCE in 44 of 48 patients, and a time intensity plot that resembled a gamma variate function. Perfusion defects were visualized in 25 patients during BH(ini) and 28 patients during BH(reinsp). Coronary artery territory agreement between perfusion assessed during BH(ini) and BH(reinsp) and quantitative coronary angiography was 76% and 81%, respectively.

Noninvasive quantification of respiratory modulation on left ventricular size and stroke volume

To noninvasively explore the complex interactions between heart rate, left ventricular (LV) stroke volume (SV) and respiration, different techniques were proposed and applied to the beat-to-beat measurements of end-diastolic (ED), end-systolic (ES) volumes and SV, obtained from echocardiographic acoustic quantification LV volume signal. Data were obtained from eight patients with dilated cardiomyopathy (DCM, age 60 +/- 2, mean +/- SE), and from 11 age-matched healthy volunteers (N, age 63 +/- 2). Spectral analysis showed an increase in HF power in DCM, both in ED (in ml2, 58 +/- 18 versus 19 +/- 5 in N) and in SV (in ml2, 55 +/- 12 versus 17 +/- 5 in N), together with an increase in total power (in ml2, ED: 119 +/- 31 in DCM versus 48 +/- 9 in N; SV: 88 +/- 17 in DCM versus 31 +/- 8 in N). Folded scattergrams evidenced higher amplitude oscillations in DCM (in ml, ES: 7.93 +/- 1.29; ED: 7.94 +/- 1.59; SV: 7.27 +/- 0.91) compared to N (in ml, ES: 4.08 +/- 0.64; ED: 3.56 +/- 0.65; SV: 3.63 +/- 0.43). Moreover, the prevalent effect of increased afterload generating SV reduction during inspiration was pointed out in N, while an intersubject dispersion in the relation between respiratory phase and LV dimension changes was found in DCM. Black-box model identification summarized these mechanisms by means of a few quantitative parameters.

The effect of graded hemorrhage and intravascular volume replacement on systolic pressure variation in humans during mechanical and spontaneous ventilation

In dogs and humans, the magnitude of the variation in systolic pressure (SPV) over the respiratory cycle during mechanical ventilation appears to be inversely related to intravascular volume. Also reported to correlate with changes in volume status is delta down, the difference between systolic pressure at end-expiration and the lowest value during the respiratory cycle. These variables were examined during graded hemorrhage in eight anesthetized, mechanically ventilated subjects, and seven awake, spontaneously breathing subjects. SPV and delta down were measured in sequence at baseline, after 500 mL blood removal, after 1000 mL (total) blood removal, after 500 mL hetastarch replacement, after 1000 mL (total) hetastarch replacement, and after 500 mL normal saline (NS). Repeated-measures analysis of variance was used to test the significance of the change in SPV and delta down among the interventions. During mechanical ventilation, each 500-mL hemorrhage significantly increased SPV and delta down, and each 500-mL hetastarch infusion significantly decreased SPV and delta down. After hetastarch, both SPV and delta down were smaller than at baseline and may explain why the infusion of NS caused nonsignificant reductions in SPV and delta down. A SPV of 5 mm Hg or less, or a delta down of 2 mm Hg or less appeared to indicate minimal intravascular volume depletion. During spontaneous ventilation, delta down could not be determined accurately in several subjects, and SPV did not change in the appropriate direction in all cases of hemorrhage and volume infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Within-breath modulation of left ventricular function during normal breathing and positive-pressure ventilation in man

1. To investigate how intrathoracic pressure affects left ventricular function during normal breathing and positive-pressure ventilation, beat-by-beat measurements of left ventricular stroke volume (LVSV; pulsed Doppler ultrasound), heart rate and blood pressure were made in five normal subjects breathing actively and then undergoing passive positive-pressure ventilation. 2. To assess the within-breath effects of positive-pressure ventilation on left ventricular function in the clinical setting, further measurements were made in six patients sedated, paralysed and ventilated because of brain injuries, who had no disease of the heart or lungs. 3. In the normal subjects, there were minimal phasic variation in LVSV during positive-pressure ventilation with the subject passive. Heart rate and blood pressure also stayed relatively constant throughout the ventilator cycle. During active breathing at the same depth and rate, there were large phasic respiratory variations in LVSV, with the lowest values occurring during inspiration. 4. In the paralysed and unconscious patients, an increase in LVSV was associated with the increase in airway pressure which occurred during lung inflation; however, the phase lag between the rise in airway pressure and the rise in LVSV varied widely between patients. These changes occurred whether or not sinus arrhythmia was present. 5. Addition of 4.6 +/- 1 cmH2O of positive end-expiratory pressure (PEEP) did not increase the within-breath LVSV variations, but resulted in a mean depression of LVSV of 5.4% (paired t test, P = 0.035). 6. The smaller variations in LVSV during positive-pressure ventilation compared to normal breathing in the conscious subjects may reflect (a) the smaller magnitude of positive, compared to negative, pleural pressure excursions which accompany a given tidal volume, and (b) an asymmetry between the effects of positive and negative pleural pressure on the heart. 7. The prominent effects of positive-pressure ventilation on LVSV in unconscious patients, compared to the minimal effects seen in ventilated normal subjects, may result from reduced lung compliance and a degree of pulmonary vascular congestion in the patients which was undetectable clinically or radiologically.

Calcium-channel blockers and anaesthesia

Verapamil was the first calcium-channel blocker (CCB). It has been used since 1962 in Europe then in Japan for its antiarrhythmic and coronary vasodilator effects. The CCB have become prominent cardiovascular drugs during the last 15 years. Many experimental and clinical studies have defined their mechanism of action, the effects of new drugs in this therapeutic class, and their indications and interactions with other drugs. Due to the large number of patients treated with CCB it is important for the anaesthetist to know the general and specific problems involved during the perioperative period, the interactions with anaesthetics and the practical use of these drugs.

Calcium-channel blockers in acute myocardial infarction

The calcium-channel blockers are useful in treating a variety of cardiovascular disorders. Due to their antiischemic and spasmolytic properties, these agents have been studied in the prophylaxis and treatment of acute myocardial infarction. This article reviews this application with respect to reduction of mortality, infarct size, and reinfarction rate. Of the agents currently available for clinical use, nifedipine has been studied most extensively. This agent shows no beneficial effects in this setting and its use may in fact be harmful. Of the few trials that have been conducted with verapamil, none have shown decreased mortality. Verapamil may reduce infarct size although further confirmation is required. Diltiazem is the only agent that has been shown to have short- and long-term benefits in the patient with acute myocardial infarction. Proper patient selection is of utmost importance in ensuring successful therapy. In particular, those patients with non-Q-wave infarctions and/or normal left ventricular function can be expected to derive the most benefit in terms of reducing mortality and reinfarction rate associated with the acute event.