Adaptative mechanism of the equilibrative nucleoside transporter 1 (ENT-1) and blood adenosine levels in elite freedivers.

PURPOSE: Long static or intense dynamic apnoea-like high-altitude exposure is inducing hypoxia. Adenosine is known to participate to the adaptive response to hypoxia leading to the control of heart rate, blood pressure and vasodilation. Extracellular adenosine level is controlled through the equilibrative nucleoside transporter 1 (ENT-1) and the enzyme adenosine deaminase (ADA). The aim of this study was to determine the control of adenosine blood level (ABL) via ENT-1 and ADA during apnoea-induced hypoxia in elite freedivers was similar to high-altitude adaptation. METHODS: Ten freediver champions and ten controls were studied. Biological (e.g. ENT-1, ADA, ABL, PaO2, PaCO2 and pH) and cardiovascular (e.g. heart rate, arterial pressure) parameters were measured at rest and after a submaximal dry static apnoea. RESULTS: In freedivers, ABL was higher than in control participants in basal condition and increased more in response to apnoea. Also, freedivers showed an ADA increased in response to apnoea. Finally, ENT-1 level and function were reduced for the free divers. CONCLUSION: Our results suggest in freedivers the presence of an adaptive mechanism similar to the one observed in human exposed to chronic hypoxia induced by high-altitude environment.

Paradoxical gas embolism after SCUBA diving: hemodynamic changes studied by echocardiography.

Hemodynamic changes induced by self-contained underwater breathing apparatus diving were investigated using Doppler echocardiography. We detected circulating bubbles in both right and left cavities of the heart and in the cerebral circulation in two divers with a large patent foramen ovale. A reduction in the left ventricular preload was suggested by echocardiographic measurements. The decreased cardiac preload was paralleled to a lower stroke volume and cardiac output. These findings were also observed in divers with no evidence of circulating bubbles. In these subjects, pulmonary vascular resistances remained unchanged while an increase was observed in the two divers with arterial bubbles. This increase could promote right-to-left shunting.

Inter-limb changes in arterial function after intense cycling exercise.

We investigated whether muscle exercise, by inducing a subsequent local response, alters local and systemic arterial function differently. Eleven healthy volunteers (31±8 years) performed a 45-min cycling session at a heart rate corresponding to 10% above ventilatory threshold. Measurements were performed before and 45 min after exercise. Central and peripheral blood pressures were assessed by applanation tonometry and automatic sphygmomanometer, respectively. Brachial and popliteal arterial changes in diameter and blood flow were assessed using ultrasonography. The endothelium-dependent function was assessed simultaneously on brachial and popliteal arteries by flow-mediated dilation. Systolic blood pressure decreased significantly in both upper and lower limbs as well as centrally. Ankle-brachial index decreased significantly. Cross-sectional area and blood flow of popliteal and brachial arteries increased significantly. The increase in blood flow was higher in the brachial than in the popliteal artery, whereas diameter increase was of similar magnitude between the two arteries. When normalized with shear rate, brachial flow-mediated dilation was significantly greater, whereas popliteal flow-mediated dilation was similar post- vs. pre-exercise. After an acute bout of intense cycling, blood flow increase and endothelial function were greater in the non-exercised upper limb compared to the exercised lower limb, suggesting that anaerobic exercise blunts the enhancement of systemic endothelium-dependant vasodilation in active muscle beds.

A2A adenosine receptor function in patients with vasovagal syncope.

AIMS: Adenosine is a possible mediator in vasovagal syncope (VVS) via the activation of its receptors. High expression of adenosine A2A receptors (A2AR) has been reported in VVS. The function of these over-expressed receptors in this population has never been evaluated. METHODS AND RESULTS: We used Adonis, a specific-made antibody with A2AR agonist properties, to evaluate binding parameters (i.e. dissociation constant KD) and cAMP production (i.e. EC50) by peripheral blood mononuclear cells of 16 VVS patients. Eight healthy volunteers served as controls. A2AR expression was higher in patients than controls; mean: 11.5 ± 1.2 vs. 7.7 ± 0.8 AU, P = 0.04. Also, KD values were higher in patients than controls: 2.1 ± 0.02 × 10(-7) vs. 5 ± 1 × 10(-8) M, P < 0.01 In controls, KD values were lower than EC50 (5 ± 1.7 × 10(-8) vs. 2.8 ± 0.4 10(-7) M, P < 0.01), but in patients, KD values did not differ from EC50: 2. ± 0.2 × 10(-7) vs. 2.5 ± 0.4 × 10(-7) M, P > 0.05. However, four patients had lower EC50 (3.5 ± 0.3 × 10(-8) M) than KD (2.9 ± 1.2 × 10(-7) M; KD/EC50 = 9.6), suggesting the presence of spare receptors. CONCLUSION: The function of A2AR of patients with VVS was preserved since their stimulation by Adonis led to cAMP production with an EC50 comparable with those in controls. However, their affinity was lower than those of controls. Our results suggest that A2AR are implicated in the physiopathology of VVS.

Cardiac alterations induced by a fish-catching diving competition.

Cardiac changes induced by repeated breath-hold diving were investigated after a fish-catching diving competition. Eleven healthy subjects carried out repeated breath-hold dives at a mean maximal depth of 20 ± 2.7 msw (66 ± 9 fsw) during 5 h. One hour after the competition, the body mass loss was -1.7 ± 0.5 kg. Most of the breath-hold divers suffered from cold and although the core temperature remained normal, a decrease in cutaneous temperature was recorded in the extremities. Systolic blood pressure was reduced in both upper and lower limbs. Heart rate was unchanged, but left ventricular (LV) stroke volume was reduced leading to a decrease in cardiac output (-20%). Left atrial and LV diameters were significantly decreased. LV filling was assessed on a trans-mitral profile. An increase in the contribution of the atrial contraction to LV filling was observed. Right cavity diameters were increased. The cardiac autonomic alterations were in favor of sympathetic hyperactivity. After a fish-catching diving competition in cold water, alterations suggesting dehydration, contraction in plasma volume and sympathetic hyperactivity were observed. Furthermore, enlargements of right cavities were in favor of right ventricular strains. Repeated apnea and swimming in cold water may account for these alterations.

Ultrasound lung comets induced by repeated breath-hold diving, a study in underwater fishermen.

Pulmonary edema has been reported in breath-hold divers during fish-catching diving activity. The present study was designed to detect possible increases in extravascular lung water (EVLW) in underwater fishermen after a competition. Thirty healthy subjects were studied. They participated in two different 5-h fish-catching diving competitions: one organized in the winter (10 subjects) and one organized in the autumn (20 subjects). A questionnaire was used to record underwater activity and note respiratory problems. An increase in EVLW was investigated from the detection of ultrasound lung comets (ULC) by chest ultrasonography. Complementary investigations included echocardiography and pulmonary function testing. An increase in EVLW was detected in three out of 30 underwater fishermen after the competition. No signs of cardiovascular dysfunction were found in the entire population and in divers with an increase in the ULC score. Two divers with raised ULC presented respiratory disorders such as cough or shortness of breath. Impairment in spirometric parameters was recorded in these subjects. An increase in EVLW could be observed after a fish-catching diving competition in three out of 30 underwater fishermen. In two subjects, it was related to respiratory disorders and impairment in pulmonary flow.

Specific diving training-induced arterial circulation changes.

OBJECTIVE: Several stressors such as cold water immersion, hyperoxic exposure and decompression-induced circulating bubbles can alter arterial circulation after a dive. The aim of this study was to investigate the arterial modifications induced by a specific diving training including repeated hyperbaric exposures and physical training. METHOD: Arterial pressure measurement and pulse wave velocity (PWV) recordings were performed in 12 student military divers before and after 15 weeks' training. The results were compared with the same investigations performed in 12 non-diver healthy subjects. RESULTS: A decrease in systolic blood pressure and pulse pressure was observed at both upper and lower limbs in student military divers after the training. Non-significant decreases in both carotido-femoral PWV and carotido-pedal PWV were found after the training. When the pulse time transit was divided by the cardiac cycle length between two R peaks ((RR) interval), a significant increase was observed between the carotid and femoral sensors. On the other hand, some differences were noticed between military divers and controls. Controls and divers were matched appropriately according to age and height, although the divers had a higher aerobic capacity as well as lower resting heart rate and lower pulse wave velocity. CONCLUSION: In trained military subjects, a training which includes repeated diving exposures and endurance exercises leads to vascular modifications suggesting an increase in central arterial compliance. There was no sign of arterial alteration induced by repeated diving exposures.

Military diving training improved arterial compliance.

This study was aimed at investigating whether repeated SCUBA diving might induce long term cardiovascular and autonomic modifications. In 11 military mine clearance diving students, arterial compliance (ultrasound scan study of brachial artery and ratio of stroke volume to pulse pressure: SV/PP), resting spectral analyses of heart rate and blood pressure variability, and a cold pressor test were performed before and after a 15-week military diving training course. After the diving training, arterial compliance was improved, as indicated by the significant increase in brachial arterial compliance (from 24+/-10 to 37+/-14 ml.mmHg (-1)) and SV/PP (from 1.7+/-0.2 to 1.9+/-0.2 ml.mmHg (-1)), and by the significant decrease in systolic, diastolic and pulse pressures (from 130+/-8 to 120+/-7; from 71+/-4 to 67+/-4; and from 58+/-8 to 53+/-5 mmHg, respectively). The peak oxygen uptake increased significantly from 54.3+/-2.0 to 56.8+/-4.0 mL.kg (-1).min (-1). Finally, the vasoconstrictive response during the cold pressor test increased (p<0.05). These findings point to a positive effect of a 15-week military diving training course on vascular function, and for a concomitant development of some peripheral vascular acclimatization to cold.

Fin swimming improves respiratory gas exchange.

Data in the literature suggest that compared to dry-land exercise fin swimming might delay the activation of the anaerobic metabolism. To verify this hypothesis, we explored indirect indices such as the oxygen pulse (VO(2)/HR), carbon dioxide production (VCO(2)), and ventilatory threshold, comparing fin swimming exercise to dry-land cycling. Thirteen participants, experienced or inexperienced in fin swimming, completed an incremental fin swimming exercise and a maximal exercise on a cycloergometer with breath-by-breath measurements of heart rate (HR), ventilation (VE), tidal volume (VT), VO(2), VCO(2), and VO(2)/HR and determination of the ventilatory threshold and maximal oxygen uptake (VO(2)max). Compared to dry-land cycling exercise, fin swimming resulted in elevated or absent ventilatory threshold. Although VO(2)max did not differ in either condition, in fin swimming the maximal HR value was lower (-18%, p=0.0072), maximal VO(2)/HR higher (+20%, p=0.0325), and maximal VCO(2) lower (-17%, p=0.0071). We also measured significant reduction of VE, VT, and HR variations for the same VO(2) increase. This study suggests that the anaerobic muscle metabolism might be delayed in fin swimming. An attenuated chemoreflex drive to the heart and respiratory centres exerted by muscle metabolites might explain the depressed cardiopulmonary response to fin swimming.

Is impairment similar between arm and leg cranking exercise in COPD patients?

UNLABELLED: Impaired skeletal muscle function has been reported in patients with chronic obstructive disease (COPD), but such impairment is not homogenous and its distribution between the upper and the lower limbs is still unclear. The present study was designed to assess and compare upper and lower limb capacities in patients with moderate to severe COPD during incremental and constant-load exercises. Thirteen COPD patients of similar age with moderate to severe air flow limitation (FEV(1): 35%+/-5% predicted) and 19 healthy subjects were studied. Four sessions were organized: two incremental and two constant-load cycling exercises with arm or leg in randomized order. As observed in a previous study involving incremental and constant tests, power, VO(2), RER, VE, and HR were all significantly lower in the upper and lower limbs of patients with COPD than in healthy controls. In the healthy population, aerobic capacity and mechanical efficiency (ME) were lower in the course of arm exercises than in leg exercises. For the same relative workload, dyspnea and blood lactate production were higher during arm exercise. In contrast, no significant difference was observed between arm and leg capacities for any of these parameters in COPD patients. CONCLUSION: Although aerobic capacity is impaired in COPD patients, arm aerobic capacity is relatively preserved. Given the lack of significant difference between arm and leg capacities in COPD, we hypothesize that upper limb muscles are less compromised than lower limb muscles in this patient population.

Observational study of potential risk factors of immersion pulmonary edema in healthy divers: exercise intensity is the main contributor.

BACKGROUND: The risk factors of pulmonary edema induced by diving in healthy subjects are not well known. The aim of the present study was to assess the parameters contributing to the increase in extravascular lung water after diving. METHODS: This study was carried out in a professional diving institute. All divers participating in the teaching program from June 2012 to June 2014 were included in the study. Extravascular lung water was assessed using the detection of ultrasound lung comets (ULC) by chest ultrasonography. Clinical parameters and dive profiles were recorded using a questionnaire and a dive computer. RESULTS: One-hundred six divers were investigated after 263 dives. They used an open-circuit umbilical supplying compressed gas diving apparatus in 202 cases and a self-contained underwater breathing apparatus in 61 cases. A generalized linear mixed model analysis was performed which demonstrated that the dive induced a significant increase in ULC score (incidence rate ratio: 3.16). It also identified that the predictive variable of increased extravascular lung water after the dive was the exercise intensity at depth (z = 3.99, p < 0.0001). The other parameters studied such as the water temperature, dive profile, hyperoxic exposure, or anthropometric data were not associated with the increase in extravascular lung water after the dive. CONCLUSIONS: In this study, the exercise intensity was the main contributor to the increase in extravascular lung water in healthy divers. To improve the prevention of immersion pulmonary edema, the exercise intensity experienced during the dive should thus be adapted to the aerobic fitness level of the divers.

Hyperoxia and hypergravity are independent risk factors of atelectasis in healthy sitting humans: a pulmonary ultrasound and SPECT/CT study.

Aeroatelectasis has developed in aircrew flying routine peacetime flights on the latest generation high-performance aircraft, when undergoing excessive oxygen supply. To single out the effects of hyperoxia and hypergravity on lung tissue compression, and on ventilation and perfusion, eight subjects were studied before and after 1 h 15 min exposure to +1 to +3.5 Gz in a human centrifuge. They performed the protocol three times, breathing air, 44.5% O2, or 100% O2 and underwent functional and topographical imaging of the whole lung by ultrasound and single-photon emission computed tomography combined with computed tomography (SPECT/CT). Ultrasound lung comets (ULC) and atelectasis both increased after exposure. The number of ULC was <1 pre protocol (i.e., normal lung) and larger post 100% O2 (22 ± 3, mean ± SD) than in all other conditions (P < 0.001). Post 44.5% O2 differed from air (P < 0.05). Seven subjects showed low- to medium-grade atelectasis post 100% O2 There was an effect on grade of gas mixture and hypergravity, with interaction (P < 0.001, respectively); 100% O2, 44.5% O2, and air differed from each other (P < 0.05). SPECT ventilation and perfusion were always normal. Ultrasound concurred with CT in showing normal lung in the upper third and ULC/atelectasis in posterior and inferior areas, not for other localizations. In conclusion, hyperoxia and hypergravity are independent risk factors of reversible atelectasis formation. Ultrasound is a useful screening tool. Together with electrical impedance tomography measurements (reported separately), these findings show that zones with decreased ventilation prone to transient airway closure are present above atelectatic areas.

Iatrogenic cerebral air embolism: importance of an early hyperbaric oxygenation.

OBJECTIVES: To assess the relationship between the time period before hyperbaric oxygenation therapy (HBO) and clinical outcome in patients with iatrogenic cerebral air embolism. DESIGN AND SETTING: Retrospective study in a hyperbaric chamber and medical intensive care unit of a university hospital. PATIENTS: All patients with air embolism from 1980 to 1999. INTERVENTIONS: We retrieved the cases of 86 patients who benefited from an identical HBO and analyzed the relationship between the time period before HBO and clinical outcome. RESULTS: Patients treated with HBO less than 6 h had a better outcome than those treated later. In patients treated within this delay the cause was venous air embolism in 84% and arterial air embolism in only 16% of cases. After this delay the cause was venous air embolism (53%) and arterial air embolism (47%). Patients with venous air embolism and recovery had a shorter delay than patients with sequelae or death (2 h 15 min vs. 4 h). Patients with venous air embolism treated less than 6 h had a better outcome than those treated later. In patients with arterial air embolism the time period before HBO was longer than in venous air embolism (8 h vs. 3 h) and the outcome worse (recovery in 35% vs. 67%). In patients with arterial air embolism no difference in the time period was found between patients with recovery and sequelae or death. CONCLUSIONS: We stress the beneficial effect of an early HBO in air embolism, the importance of an increased awareness of physicians concerned with this severe complication, and the need to develop techniques to detect air emboli in the cerebral circulation.

Left-sided superior vena cava: diagnosis by magnetic resonance imaging.

We describe a case of left-sided superior vena cava. The diagnosis was suggested by chest radiograph after central venous catheter placement. This was subsequently confirmed by magnetic resonance imaging.

Gallbladder abnormalities in medical ICU patients: an ultrasonographic study.

Patients in the intensive care unit (ICU) have many risks factors for gallbladder stasis or acute acalculous cholecystitis (ACC), including fasting, total parenteral nutrition, sedation, mechanical ventilation, infection and shock. We have performed a prospective study to estimate the prevalence of ultrasonographic gallbladder abnormalities in 30 consecutive medical ICU patients during the first 2 days of their stay in the ICU. Two patients had previously undergone cholecystectomy and were excluded from the study. Seventeen (61%) of the remaining 28 patients presented with gallbladder abnormalities. Considering three major criteria of ACC, 14 patients (50%) presented with either sludge (25%), wall thickening (22%) or hydrops (11%). However, none of the patients needed a surgical procedure during the study because of gallbladder disease. We conclude that an important proportion of ICU patients presented with gallbladder abnormalities shown by ultrasonography and that this may have implications for establishing a diagnosis of ACC using ultrasonographic criteria.

Echocardiography on HIV patients admitted to the ICU.

A prospective echocardiographic study was conducted in 68 patients with the human immunodeficiency virus (HIV) admitted to the intensive care unit (ICU) (C3 stage 78%, i.v. drug abuse 71%) in order, firstly to, assess the prevalence of cardiac abnormalities, and, secondly, to make an early therapeutic decision. Only five patients presented clinical evidence of cardiac disease. Echocardiographic abnormalities were identified in 35 patients (51%): pericardial effusion: 20 cases (29%), with tamponade in 2 cases that led to an immediate pericardiocentesis. Left ventricular dysfunction: 15 cases (22%) requiring treatment of cardiac failure. Mitral bioprosthesis rupture in 1 patient that led to a surgical procedure. Vegetations of the tricuspid value in 3 drug addicts (4%) requiring early antibiotic treatment. Echocardiography proved to be very helpful in detecting hidden cardiac dysfunctions. It is immensely valuable in ICU management of HIV patients, since prompt initiation of appropriate treatment is essential.

Economic impact of a rational use of antibiotics in intensive care.

OBJECTIVE: To evaluate the economic impact of a rational policy in antibiotic treatment. DESIGN: Comparative study with a retrospective and a prospective part. SETTING: An 11-bed intensive care unit (ICU) in a general hospital. PATIENTS: All patients admitted to the unit in 1994, 1995 and 1996. INTERVENTIONS: In 1995, a program of cost control was started and a contract of agreed objectives signed with the director of the hospital. This contract included a commitment to refund the eventual savings in order to improve the quality of care. Prescribing protocols were established by consensus as guidelines for a rational policy in antibiotic therapy. MEASUREMENTS AND RESULTS: The cost of antibiotic therapy, the patients' characteristics and the incidence of nosocomial infection were compared prior to and during the program. The expenses for antibiotic drugs decreased by 19% in 1995 and by 22% in 1996. Most of the savings were refunded to the ICU and contributed to the employment of an additional nurse and the purchase of new material. In number of patients, type of disease, mean age, Simplified Acute Physiology Score, occupancy rate, length of stay, omega score, artificial ventilation, readmission within 7 days, mortality and incidence of nosocomial infection, no significant difference was found. CONCLUSIONS: We proved a positive economic impact of a rational policy in antibiotic therapy realized with a contract of agreed objectives. The savings made while applying our program of cost control were used to improve the quality of care.

Ascent rate, age, maximal oxygen uptake, adiposity, and circulating venous bubbles after diving.

Decompression sickness in diving is recognized as a multifactorial phenomenon, depending on several factors, such as decompression rate and individual susceptibility. The Doppler ultrasonic detection of circulating venous bubbles after diving is considered a useful index for the safety of decompression because of the relationship between bubbles and decompression sickness risk. The aim of this study was to assess the effects of ascent rate, age, maximal oxygen uptake (VO(2 max)), and percent body fat on the production of bubbles after diving. Fifty male recreational divers performed two dives at 35 m during 25 min and then ascended in one case at 9 m/min and in the other case at 17 m/min. They performed the same decompression stops in the two cases. Twenty-eight divers were Doppler monitored at 10-min intervals, until 60 min after surfacing, and the data were analyzed by Wilcoxon signed-rank test to compare the effect of ascent rate on the kinetics of bubbles. Twenty-two divers were monitored 60 min after surfacing. The effect on bubble production 60 min after surfacing of the four variables was studied in 47 divers. The data were analyzed by multinomial log-linear model. The analysis showed that the 17 m/min ascent produced more elevated grades of bubbles than the 9 m/min ascent (P < 0.05), except at the 40-min interval, and showed relationships between grades of bubbles and ascent rate and age and interaction terms between VO(2 max) and age, as well as VO(2 max) and percent body fat. Younger, slimmer, or aerobically fitter divers produced fewer bubbles compared with older, fatter, or poorly physically fit divers. These findings and the conclusions of previous studies performed on animals and humans led us to support that ascent rate, age, aerobic fitness, and adiposity are factors of susceptibility for bubble formation after diving.

[Prognosis in iatrogenic gas embolism]. / La prognosi delle embolie gassose iatrogene.

Prognosis of iatrogenic air embolism is various according to previous studies. The purpose of this study was to determine the risks factors associated with the prognosis of iatrogenic air embolism. We conducted a retrospective analysis of 113 patients treated with HBO therapy in our hyperbaric center from 1979 to 1993. Initial symptomatology consisted in neurological disorders (71% of cases), respiratory disorders (43% of cases) and hemodynamic disorders (33% of cases). When neurological disorders were observed, HBO therapy included immediate compression to 6 atm abs for 10 to 15 mn with air followed by decompression to 2 atm abs where the patients received 100% oxygen during 1 hour. When no neurological disorders was observed, HBO therapy consisted in an oxygenation for 1 h, 2 atm abs, FiO2 = 1. Overall outcome was: recovery: 69 per cent of cases, sequelae: 26 per cent of cases, death: 5 per cent of cases. Prognosis was very different according to etiologies and existence of neurological disorders. Venous emboli had a better improvement than arterial emboli. In conclusion, patterns of air embolism can be divided clinically into two major categories, cerebral and pulmonary air embolism, which should be individualised in clinical studies. The studies must also individualised etiologies.