Category Archives: Cardiac Surgery

Hemodynamic Changes Induced by Recreational Scuba Diving: Recommendation

Hemodynamic Changes Induced by Recreational Scuba Diving: RecommendationIn our study, ultrasonographic investigations were performed 1 h after diving; consequently, the probability of an hyperoxia-induced cardiac relaxation impairment was low. Physiologically, the RV and LV are two distinct chambers that are anatomically and functionally bound: both share the interventricular septum and both are enclosed in the pericardium. As a consequence, alterations in RV size and function influence LV filling. In the present study, RV diameters were unchanged after the dive and no LV septal shift was observed. Consequently, the decrease of the cardiac preload demonstrated by cardiac diameters and SV decrease seemed to be the principal factor of the LV filling modification.
IVRT measurement confirms our hypothesis. The decreased LV preload, as seen previously, by reducing the pressure gradient from the LA to the LV may explain the increase in IVRT observed after diving (Table 4). An increase in maximal velocity of tricuspid regurgitation flow, suggesting an increase in the RV/RA gradient, was also observed.

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Hemodynamic Changes Induced by Recreational Scuba Diving: Conclusion

Water immersion promotes a redistribution of blood volume with a relative increase in central blood volume. The relative hypervolemia lead to the release of atrial natriuretic peptide and the lowering of noradrenaline, arginine vasopressin, aldosterone, and plasma rennin activity. The changes in neuroendocrine activities produce a marked diuresis. Body fluid loss is increased by exercise (swimming) during scuba diving. Consequently, dehydration is frequently observed after cessation of immersion.
Furthermore, experimental studies have demonstrated that during the decompression, circulating bubbles activate leukocytes and platelets, adversely affect blood rheology, and induce an activation of the complement system and a release of kinines. Endothelial transformations seem to be due to the mechanical effects of the circulating bubbles as well as the activation of leukocytes.
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Hemodynamic Changes Induced by Recreational Scuba Diving: Discussion

Hemodynamic Changes Induced by Recreational Scuba Diving: DiscussionWe emphasize that our study was conducted in actual diving conditions because more bubbling has been reported when the dives were performed in the open sea rather than when they were performed in hyperbaric chambers. Furthermore, during water immersion several modifications including hemodynamic, neuroendocrine, and autonomic activities changes have been demonstrated. Consequently, hemodynamic modifications should be very different after scuba diving when compared with dry hyperbaric exposures.
The diving profile studied is commonly performed by recreational divers but generates a rather important bubble grade in all volunteers. Indeed, a grade 3 was found in 7 of 10 divers 1 h after surfacing.
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Hemodynamic Changes Induced by Recreational Scuba Diving: Baseline Echocardiographic Variables

Baseline echocardiographic examinations were normal in all volunteers. Mean indexed LVM was 101 ± 21 g/m2. Mean aortic cross-section surface was 4.2 ± 0.54 cm2. A tricuspid regurgitant flow was identified in 7 of 10 divers, and instantaneous systolic pressure gradient from the RV to RA could be assessed in these subjects.
None of the divers presented any disorders suggesting a diving accident.
Circulating Bubbles Detection: Circulating bubbles were detected in all divers. Bubbles were observed in right cavities of the heart using 2D echocardiography in seven divers. Pulsed Doppler confirmed the existence of venous gas emboli in these cases and detected circulating bubbles that were not seen in 2D echography in three other divers. Discrepancies were observed in subjects with poor image quality. Circulating bubbles were graded according to the 2D echocardiographic and pulsed Doppler grade. A grade 3 was observed in seven divers, grade 2 in one diver, and grade 1 in two divers. No circulating bubbles were detected in left heart cavities.

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Hemodynamic Changes Induced by Recreational Scuba Diving: Statistical Analysis

Hemodynamic Changes Induced by Recreational Scuba Diving: Statistical AnalysisLV Filling: LV filling was studied using transmitral blood velocities recorded by pulsed Doppler. Doppler measurements were averaged from at least three consecutive beats. Transmitral blood velocities were obtained from the apical four-chamber view, positioning the sample volume at the mitral valve leaflet tips. Doppler velocity curves were recorded at 100mm/s. Peak velocity and VTI of the initial flow (E wave), representing the early filling phase, and of the late flow (A wave), representing the atrial contraction, were measured. The peak velocities ratio (E/A) and the ratio of the A wave VTI to the total VTI (relative contribution of atrial contraction to the total LV filling) were calculated. Other following variables were measured: the deceleration pressure half time of early diastolic transmitral flow (pressure half-time) and isovolumetric relaxation time (IVRT). The IVRT was the interval from the aortic valve closure signal to the mitral valve opening signal.

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Hemodynamic Changes Induced by Recreational Scuba Diving: Cardiac Function Assessment

Examinations were made using 2D and M-mode echocardiography associated with pulsed and continuous-wave Doppler. Echocardiography allows the measurements of cardiac diameters and LV systolic function; Doppler permits the measurements of CO as well as an assessment of LV filling pattern.
Images were obtained via a transthoracic approach from the parasternal views (long axis and short axis) and from an apical four-chamber view. The subjects were placed in a left lateral position for the parasternal views and in a supine position for the apical four-chamber view. Second harmonic imaging was used to improve the image quality. Doppler recordings were performed at the end of normal expiration in order to eliminate the effects of respiration on the parameters studied. Measurements were averaged from at least three consecutive beats. Tape recordings were obtained at a paper speed of 100 mm/s with simultaneous tracing of the ECG. Examinations were recorded on standard videotape for later review.

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Hemodynamic Changes Induced by Recreational Scuba Diving: Doppler Echographic Study

Hemodynamic Changes Induced by Recreational Scuba Diving: Doppler Echographic StudyDivers underwent two Doppler echographic examinations with a 1-week interval: the first examination in basal conditions, and the second examination 1 h after the investigational scuba dive. The ultrasonographic examinations were carried out by an experienced investigator (A.B.) using a commercially available Doppler echocardiograph (Diasonics Vingmed CFM 750 A; GE Medical Systems; Milwaukee, WI) connected to a transducer array of 2.5 to 3.5 MHz. Investigations were performed in a quiet room with a stable environmental temperature (25°C). Subjects stayed at rest for 10 min before the ultrasonographic examination. HR was recorded by echocardiogram, and the rate was averaged over 60 s. Sphygmomanometric BP measurements on the right arm were obtained after each echographic examination. Two-dimensional (2D) echography and Doppler studies were used to detect circulating bubbles after diving and to assess cardiac function. so

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Hemodynamic Changes Induced by Recreational Scuba Diving: Divers

The subjects included in the study were 10 medically fit, male, recreational divers (mean age, 44 ± 7 years; range, 33 to 54 years; mean weight, 79 ± 11 kg; range, 58 to 96 kg; mean height, 177 ± 5 cm; range, 170 to 186 cm; mean body mass index, 25 ± 3; range, 19.8 to 31.7). In accordance with French law concerning biomedical research, the divers gave informed consent and protocol was approved by the institutional ethical committee. Each subject passed a screening examination, including physical examination and medical history. All volunteers denied taking any medication at the time of the study. Diving was the only physical activity performed by eight of the subjects. Diving took place in sea water at a mean depth of 34.3 ± 2.7 m of sea water (113 ± 9 feet) and a mean duration of 25 ± 4 min.
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Hemodynamic Changes Induced by Recreational Scuba Diving

Hemodynamic Changes Induced by Recreational Scuba DivingDuring a scuba dive, subjects undergo environmental constraints such as immersion, exposure to cold, and increased ambient pressure. All of these constraints may be responsible for hemodynamic modifications, which have been well studied in healthy volunteers. Immersion in water induces a cephalad shift of peripheral venous blood that augments central blood volume. Atrial natriuretic peptid and diuresis are markedly increased. Ventilation against resistance induces modifications of intrathoracic pressure and consequently modifications of cardiac preload and afterload.During the scuba dive, increased ambient pressure generates an increase in Po2 and nitrogen partial pressure. A decrease in cardiac output (CO) related to the simultaneous decrease of the heart rate (HR) and the stroke volume (SV) is found at high Po2. Beginning from the partial pressure of 1 atmosphere absolute, an increase in systemic vascular resistance is also observed. add comment

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Closing Capacity and Gas Exchange in Chronic Heart Failure: Dyspnea

A possible explanation for the finding of increased central drive without a decrease in the VT would be the difference in operational length compensation of the diaphragm. Patients with CHF have smaller lungs and longer resting length of their diaphragms, which results in greater force generation for the same output during quiet breathing. This implies greater inspiratory effort with weaker inspiratory muscles, leading to an increased Borg dyspnea score at rest.
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