Cardiovascular changes induced by cold water immersion during hyperbaric hyperoxic exposure.

The present study was designed to assess the cardiac changes induced by cold water immersion compared with dry conditions during a prolonged hyperbaric and hyperoxic exposure (ambient pressure between 1.6 and 3 ATA and PiO(2) between 1.2 and 2.8 ATA). Ten healthy volunteers were studied during a 6 h compression in a hyperbaric chamber with immersion up to the neck in cold water while wearing wet suits. Results were compared with measurements obtained in dry conditions. Echocardiography and Doppler examinations were performed after 15 min and 5 h. Stroke volume, left atrial and left ventricular (LV) diameters remained unchanged during immersion, whereas they significantly fell during the dry session. As an index of LV contractility, percentage fractional shortening remained unchanged, in contrast to a decrease during dry experiment. Heart rate (HR) significantly decreased after 5 h, although it had not changed during the dry session. The changes in the total arterial compliance were similar during the immersed and dry sessions, with a significant decrease after 5 h. In immersed and dry conditions, cardiac output was unchanged after 15 min but decreased by almost 20% after 5 h. This decrease was related to a decrease in HR during immersion and to a decrease in stroke volume in dry conditions. The hydrostatic pressure exerted by water immersion on the systemic vessels could explain these differences. Indeed, the redistribution of blood volume towards the compliant thoracic bed may conceal a part of hypovolaemia that developed in the course of the session.

Operation Everest III (Comex'97): altitude-induced decompression sickness during a hypobaric chamber experiment: necessity for circulating venous gas emboli monitoring for the investigators.

INTRODUCTION: Acute exposure to altitude changes increases the risk of decompression sickness (DCS). Altitude-induced DCS incidence is from 15 to 20% and > 30% above 8,000 m. A particular risk occurs for scientific investigators during hypobaric chamber experiments. OBJECTIVE: In the present study, we assess whether the detection of nitrogen venous gas emboli (VGE) could help to screen the investigators at risk for altitude-induced DCS. MATERIAL AND METHODS: During a 32-day hypobaric chamber experiment, we collected clinical episodes of DCS symptoms in the investigators, and performed detection of VGE using two-dimensional (2D) echocardiography and pulsed Doppler ultrasonography guided by 2D images, graded from 0 to 5. RESULTS: Eight investigators made a total of 32 flights, including 8 flights above 8,000 m, with a 15.6% overall incidence of DCS symptoms and a 50% incidence above 8,000 m. VGE detections were systematically performed at or above 8,000 m (eight detections), and some detections were performed at 5,000 m, 6,000 m, and 7,000 m. VGE grades 3 and 4 were present in all but one subject with DCS symptoms and preceded the "bends" in all cases. VGE detection thus confirmed, in a more sensitive way compared to clinical examination, that our precautionary measures for DCS were not optimized. CONCLUSION: VGE monitoring for investigators during hypobaric chamber experiments increased the sensitivity for the detection of subjects at risk for DCS.

Evaluation of left ventricular filling pressure by transthoracic Doppler echocardiography in the intensive care unit.

OBJECTIVE: To determine whether Doppler transmitral and pulmonary venous flow pattern is related to left ventricular filling pressures in critically ill patients. DESIGN: Prospective clinical investigation. SETTING: Medical intensive care unit of a university hospital. PATIENTS: Fifty-four mechanically ventilated patients (age, 63 +/- 16 yrs) were investigated via transthoracic echocardiography and Doppler. Main diagnoses were pneumonia (31%), acute exacerbation of chronic obstructive pulmonary disease (24%), congestive heart failure (11%), and poisoning (11%). INTERVENTIONS: Doppler examinations were performed simultaneously with measurements of pulmonary artery occlusion pressure via a right heart catheter. MEASUREMENTS AND MAIN RESULTS: Pulmonary artery occlusion pressure correlated with transmitral peak E-wave velocity (r =.46) and E/A ratio (r =.55). Pulmonary artery occlusion pressure inversely correlated with deceleration time of the transmitral E-wave (r = -.52), pulmonary venous peak S-wave velocity (r = -.37), and systolic fraction of the pulmonary forward flow (r = -.56). An E/A ratio >2 predicted a pulmonary artery occlusion pressure >18 mm Hg with a positive predictive value of 100%. A duration of pulmonary venous A-wave reversal flow exceeding the duration of the transmitral A-wave forward flow predicted a pulmonary artery occlusion pressure >15 mm Hg with a positive predictive value of 83%. A systolic fraction of the pulmonary venous forward flow <0.4 predicted a pulmonary artery occlusion pressure >12 mm Hg with a positive predictive value of 100%. CONCLUSION: Transmitral and pulmonary venous flow patterns measured by transthoracic Doppler echocardiography can be used to estimate the left ventricular filling pressure in critically ill patients.

Haemodynamic effects of hyperbaric hyperoxia in healthy volunteers: an echocardiographic and Doppler study.

In the present study, we observed the haemodynamic changes, using echocardiography and Doppler, in ten healthy volunteers during 6 h of compression in a hyperbaric chamber with a protocol designed to reproduce the conditions as near as possible to a real dive. Ambient pressure varied from 1.6 to 3 atm (1 atm=101.325 kPa) and partial pressure of inspired O2 from 1.2 to 2.8 atm. Subjects performed periods of exercise with breathing through a closed-circuit self-contained underwater breathing apparatus (SCUBA). Subjects did not eat or drink during the study. Examinations were performed after 15 min and 5 h. After 15 min, stroke volume (SV), left atrial (LA) diameter and left ventricular (LV) end-diastolic diameter (LVEDD) decreased. Heart rate (HR) and cardiac output (CO) did not vary, but indices of the LV systolic performance decreased by 10% and the LV meridional wall stress increased by 17%. After 5 h, although weight decreased, the serum protein concentration increased. Compared with values obtained after 15 min, SV and CO decreased, but LV systolic performance, LA diameter, LVEDD and LV meridional wall stress remained unchanged. Compared with the reference values obtained at sea level, total arterial compliance decreased, HR remained unchanged and CO decreased. In conclusion, hyperbaric hyperoxia results in significant haemodynamic changes. Initially, hyperoxia and the SCUBA system are responsible for reducing LV preload, increasing LV afterload and decreasing LV systolic performance, although CO did not change. Prolonged exposure resulted in a further decrease in LV preload, because of dehydration, and in a further increase in LV afterload, due to systemic vasoconstriction, with the consequence of decreasing CO.